This document discusses the effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes. It summarizes that:
1) Different deposition methods including electroreduction, anodization, thermal oxidation, and chemical oxidation were used to deposit planar and 1D nanostructured Cu2O thin films on copper foil with varying morphologies.
2) Mesoscopic and planar Cu2O morphologies exhibited large differences in carrier density and charge transfer resistance, but these differences did not strongly influence their photoelectrochemical performance.
3) Planar Cu2O deposited via electroreduction provided the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE,
Device simulation of perovskite solar cells with molybdenum disulfide as acti...journalBEEI
Organo-halide Perovskite Solar Cells (PSC) have been reported to achieve remarkably high power conversion efficiency (PCE). A thorough understanding of the role of each component in solar cells and their effect as a whole is still required for further improvement in PCE. In this paper, the effect of Molybdenum Disulfide (MoS2) in PSC with mesoporous structure configuration was analyzed using Solar Cell Capacitance Simulator (SCAPS). With the MoS2 layer which having two-fold function, acting as a protective layer, by preventing the formation of shunt contacts between perovskite and Au electrode, and as a hole transport material (HTM) from the perovskite to the Spiro-OMETAD. As simulated, PSC demonstrates a PCE, ŋ of 13.1%, along with stability compared to typical structure of PSC without MoS2 (Δ ŋ/ŋ=-9% vs. Δ ŋ/ŋ=-6%). The results pave the way towards the implementation of MoS2 as a material able to boost shelf life which very useful for new material choice and optimization of HTMs
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Device simulation of perovskite solar cells with molybdenum disulfide as acti...journalBEEI
Organo-halide Perovskite Solar Cells (PSC) have been reported to achieve remarkably high power conversion efficiency (PCE). A thorough understanding of the role of each component in solar cells and their effect as a whole is still required for further improvement in PCE. In this paper, the effect of Molybdenum Disulfide (MoS2) in PSC with mesoporous structure configuration was analyzed using Solar Cell Capacitance Simulator (SCAPS). With the MoS2 layer which having two-fold function, acting as a protective layer, by preventing the formation of shunt contacts between perovskite and Au electrode, and as a hole transport material (HTM) from the perovskite to the Spiro-OMETAD. As simulated, PSC demonstrates a PCE, ŋ of 13.1%, along with stability compared to typical structure of PSC without MoS2 (Δ ŋ/ŋ=-9% vs. Δ ŋ/ŋ=-6%). The results pave the way towards the implementation of MoS2 as a material able to boost shelf life which very useful for new material choice and optimization of HTMs
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.
Remarkable self-organization and unusual conductivity behavior in cellulose n...Pawan Kumar
Aqueous suspensions of cellulose nanocrystals were blended with Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [PEDOT:PSS], and cast into thin films. The morphology, structure and electrical properties of the resulting nanocomposite thin films were thoroughly characterized. We found that the CNC–PEDOT:PSS blends self-organize into a layered vertical stack with a pitch of 100–200 nm while retaining a continuous percolation network for PEDOT. Atomic force microscopy, dynamic light scattering and multi-angle light scattering measurements confirmed the wrapping of polymer chains around the rod-like CNCs. The blended films exhibited improved molecular ordering of the PEDOT chains with concomitant improvement in the carrier mobility. The remarkable self-organization and enhanced structural order enabled the CNC–PEDOT:PSS blends to exhibit a high conductivity typical of PEDOT:PSS even when the content of the insulating CNCs in the nanocomposite was as high as 50 wt%.
Use of conventional sources of energy to generate electricity is
increasing rapidly due to growing energy demands in every sector which is the major cause for pollution as well and also is an environmental concern for future. Considering this, there is lot of R&D going on in the field of alternate energy sources with recent advancements in technology. One of the recent advancement is the perovskite solar technology in the photovoltaics industry. The power conversion efficiency of perovskite solar cells has been improved from 9.7 to 20.1% within 4 years which is the fastest advancement ever in the photovoltaic industry. Such a high photovoltaic performance can be attributed to optically high absorption characteristics of the hybrid lead perovskite materials.
In this review, different perovskite materials are discussed along with the fundamental details of the hybrid lead halide perovskite materials. The fabrication techniques, stability, device structure and the chemistry of the perovskite structure are also described aiming for a better understanding of these materials and thus highly efficient perovskite solar cell devices. In addition some advantages and drawbacks are also discussed here to outline the prospects and challenges of using the perovskites in commercial PV devices.
An introduction of perovskite solar cellsalfachemistry
This article introduces the development, structure and work mechanism of perovskite solar cells. Visit https://www.alfa-chemistry.com/products/perovskite-solar-cells-139.htm for more information.
Perovskite: introduction, classification, structure of perovskite, method to synthesis, characterization by XRD and UV- vis spectroscopy , lambert beer's law, material properties and advantage and application.
Advantages and problems of perovskite solar cellalfachemistry
This article mainly introduces the advantages and problems of perovskite solar cell. Visit https://www.alfa-chemistry.com/products/perovskite-solar-cells-139.htm for more information.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Quantum dots for optoelectronic devices - phdassistancePhD Assistance
Nanometre-scale semiconductor chips have been imagined as next-generation technology with high functionality and convergence. Quantum dots, also known as artificial atoms, have special properties owing to their quantum confinement in all three dimensions. Quantum dots have a lot of interest in optoelectronic systems because of their special properties.
For decades, self-assembled nanostructures have been a topic of considerable concern and significance.
Learn More:https://bit.ly/3xJJAiZ
Contact Us:
Website: https://www.phdassistance.com/
UK: +44 7537144372
India No:+91-9176966446
Email: info@phdassistance.com
Progress in all inorganic perovskite solar cellMd Ataul Mamun
Since their first introduction in the research arena, the hybrid organic-inorganic perovskite photovoltaic cells have been showing frequent record breaking power conversion efficiencies (PCEs). Despite the rapid increase in PCE by engaging new perovskite materials as active layers as well as new fabrication techniques, their stability remains too poor to go for a mass production. Mainly the organic materials in the hybrid PSCs are responsible for this instability. Consequently, very recently, different approaches are taken to replace these organic components by inorganic ones to fabricate all-inorganic PSCs. Though these first-generation all-inorganic PSCs are yet to produce competitive PCEs like their counterparts, they have already demonstrated superb stability to be a propitious bidder for solar cell energy yielding. The state-of-the-art quantum dots based cells shown efficiency as high as 10.77% and intact stability for months.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar Eg and Efb values of 1.93±0.04 eV and 0.48±0.06 eV respectively. Eonset of 0.48±0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for the bare Cu2O photocathodes. Although different deposition methods show a similar average photocurrent density 2.8±0.3 mA/cm2 at 0 V vs RHE, large variations in the photocurrent density are observed for samples prepared under nominally identical deposition methods.
Remarkable self-organization and unusual conductivity behavior in cellulose n...Pawan Kumar
Aqueous suspensions of cellulose nanocrystals were blended with Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) [PEDOT:PSS], and cast into thin films. The morphology, structure and electrical properties of the resulting nanocomposite thin films were thoroughly characterized. We found that the CNC–PEDOT:PSS blends self-organize into a layered vertical stack with a pitch of 100–200 nm while retaining a continuous percolation network for PEDOT. Atomic force microscopy, dynamic light scattering and multi-angle light scattering measurements confirmed the wrapping of polymer chains around the rod-like CNCs. The blended films exhibited improved molecular ordering of the PEDOT chains with concomitant improvement in the carrier mobility. The remarkable self-organization and enhanced structural order enabled the CNC–PEDOT:PSS blends to exhibit a high conductivity typical of PEDOT:PSS even when the content of the insulating CNCs in the nanocomposite was as high as 50 wt%.
Use of conventional sources of energy to generate electricity is
increasing rapidly due to growing energy demands in every sector which is the major cause for pollution as well and also is an environmental concern for future. Considering this, there is lot of R&D going on in the field of alternate energy sources with recent advancements in technology. One of the recent advancement is the perovskite solar technology in the photovoltaics industry. The power conversion efficiency of perovskite solar cells has been improved from 9.7 to 20.1% within 4 years which is the fastest advancement ever in the photovoltaic industry. Such a high photovoltaic performance can be attributed to optically high absorption characteristics of the hybrid lead perovskite materials.
In this review, different perovskite materials are discussed along with the fundamental details of the hybrid lead halide perovskite materials. The fabrication techniques, stability, device structure and the chemistry of the perovskite structure are also described aiming for a better understanding of these materials and thus highly efficient perovskite solar cell devices. In addition some advantages and drawbacks are also discussed here to outline the prospects and challenges of using the perovskites in commercial PV devices.
An introduction of perovskite solar cellsalfachemistry
This article introduces the development, structure and work mechanism of perovskite solar cells. Visit https://www.alfa-chemistry.com/products/perovskite-solar-cells-139.htm for more information.
Perovskite: introduction, classification, structure of perovskite, method to synthesis, characterization by XRD and UV- vis spectroscopy , lambert beer's law, material properties and advantage and application.
Advantages and problems of perovskite solar cellalfachemistry
This article mainly introduces the advantages and problems of perovskite solar cell. Visit https://www.alfa-chemistry.com/products/perovskite-solar-cells-139.htm for more information.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Quantum dots for optoelectronic devices - phdassistancePhD Assistance
Nanometre-scale semiconductor chips have been imagined as next-generation technology with high functionality and convergence. Quantum dots, also known as artificial atoms, have special properties owing to their quantum confinement in all three dimensions. Quantum dots have a lot of interest in optoelectronic systems because of their special properties.
For decades, self-assembled nanostructures have been a topic of considerable concern and significance.
Learn More:https://bit.ly/3xJJAiZ
Contact Us:
Website: https://www.phdassistance.com/
UK: +44 7537144372
India No:+91-9176966446
Email: info@phdassistance.com
Progress in all inorganic perovskite solar cellMd Ataul Mamun
Since their first introduction in the research arena, the hybrid organic-inorganic perovskite photovoltaic cells have been showing frequent record breaking power conversion efficiencies (PCEs). Despite the rapid increase in PCE by engaging new perovskite materials as active layers as well as new fabrication techniques, their stability remains too poor to go for a mass production. Mainly the organic materials in the hybrid PSCs are responsible for this instability. Consequently, very recently, different approaches are taken to replace these organic components by inorganic ones to fabricate all-inorganic PSCs. Though these first-generation all-inorganic PSCs are yet to produce competitive PCEs like their counterparts, they have already demonstrated superb stability to be a propitious bidder for solar cell energy yielding. The state-of-the-art quantum dots based cells shown efficiency as high as 10.77% and intact stability for months.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
Cu2O is a promising earth-abundant semiconductor photocathode for sunlight-driven water splitting. Characterization results are presented to show how the photocurrent density (Jph), onset potential (Eonset), band edges, carrier density (NA), and interfacial charge transfer resistance (Rct) are affected by the morphology and method used to deposit Cu2O on a copper foil. Mesoscopic and planar morphologies exhibit large differences in the values of NA and Rct. However, these differences are not observed to translate to other photocatalytic properties of Cu2O. Mesoscopic and planar morphologies exhibit similar Eg and Efb values of 1.93±0.04 eV and 0.48±0.06 eV respectively. Eonset of 0.48±0.04 eV obtained for these systems is close to the Efb indicating negligible water reduction overpotential. Electrochemically deposited planar Cu2O provides the highest photocurrent density of 5.0 mA cm−2 at 0 V vs RHE of all the morphologies studied. The photocurrent densities observed in this study are among the highest reported values for the bare Cu2O photocathodes. Although different deposition methods show a similar average photocurrent density 2.8±0.3 mA/cm2 at 0 V vs RHE, large variations in the photocurrent density are observed for samples prepared under nominally identical deposition methods.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward
exploiting alternative energy resources such as solar energy. Here, we
report the successful low-cost and easily accessible synthesis of hybrid
semiconductor@TiO2 nanotube photocatalysts. In order to realize its
maximum potential in harvesting photons in the visible-light range, TiO2
nanotubes have been loaded with earth-abundant, low-band-gap fibrous
red and black phosphorus (P). Scanning electron microscopy− and
scanning transmission electron microscopy−energy-dispersive X-ray
spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV−vis measurements have been performed,
substantiating the deposition of fibrous red and black P on top and
inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular morphology of titania and a vapor-transport technique are utilized to form heterojunctions of P and
TiO2. Compared to pristine anatase 3.2 eV TiO2 nanotubes, the creation of heterojunctions in the hybrid material resulted in
1.5−2.1 eV photoelectrocatalysts. An enhanced photoelectrochemical water-splitting performance under visible light compared
with the individual components resulted for the P@TiO2 hybrids. This feature is due to synergistically improved charge
separation in the heterojunction and more effective visible-light absorption. The electronic band structure and charge-carrier
dynamics are investigated in detail using ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy to elucidate
the charge-separation mechanism. A Fermi-level alignment in P@TiO2 heterojunctions leads to a more reductive flat-band
potential and a deeper valence band compared to pristine P and thus facilitates a better water-splitting performance. Our results
demonstrate effective conversion efficiencies for the nanostructured hybrids, which may enable future applications in
optoelectronic applications such as photodetectors, photovoltaics, photoelectrochemical catalysts, and sensors.
Vapor Deposition of Semiconducting Phosphorus Allotropes into TiO2 Nanotube A...Pawan Kumar
Recent evidence of exponential environmental degradation will demand a drastic shift in research and development toward exploiting alternative energy resources such as solar energy. Here, we report the successful low-cost and easily accessible synthesis of hybrid semiconductor@TiO2 nanotube photocatalysts. In order to realize its maximum potential in harvesting photons in the visible-light range, TiO2 nanotubes have been loaded with earth-abundant, low-band-gap fibrous red and black phosphorus (P). Scanning electron microscopy– and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron microscopy, and UV–vis measurements have been performed, substantiating the deposition of fibrous red and black P on top and inside the cavities of 100-μm-long electrochemically fabricated nanotubes. The nanotubular …
The improvement of the color rendering index using convex-dual-layer remote p...TELKOMNIKA JOURNAL
White-light emitting diodes (WLEDs) are semiconductor light sources whose construction design is usually made up of a single pumping chip and a single light-conversion film of phosphor compound. The outstanding problem of this traditional setting is the inadequate chroma rendering index (CRI). Introducing a cluster of multiple blue chips with more than one phosphor layer is demonstrated to address that flaw of W-LEDs. This package is called the dual-film remote-phosphor multi-chip WLED. As a consequence, both the light brightness and the CRI are improved. However, for the maximum results, the test on the second layer of phosphor has been performed to continually alter the proportions and densities of phosphor within the silicone. The researchers employed a unique hue design to control the white-light light emitting diode (LED) module. When comparing the actual result to the simulated color coordinates under the hue standard of international commission on illumination (CIE) 1931, the highest difference is found to be around 0.0063 for correlated color temperatures (CCT) of 6600 K and 7700 K. Experiments indicate that the setting of multi-chip and dual-phosphorus is the optimal design for supporting CRI quality and luminous intensity.
Air- and water-stable halide perovskite nanocrystals protected with nearly-mo...Pawan Kumar
Halide perovskites are exciting candidates for broad-spectrum photocatalysts but have the problem of ambient stability. Protective shells of oxides and polymers around halide perovskite nano- and micro-crystals provide a measure of chemical and photochemical resilience but the photocatalytic performance of perovskites is compromised due to low electron mobility in amorphous oxide or polymer shells and rapid charge carrier recombination on the surface. Herein an in situ surface passivation and stabilization of CsPbBr3 nanocrystals was achieved using monolayered graphenic carbon nitride (CNM). Extensive characterization of carbon nitride protected CsPbBr3 nanocrystals (CNMBr) indicated spherical CsPbBr3 nanoparticles encased in a few nm thick g-C3N4 sheets facilitating better charge separation via percolation/tunneling of charges on conductive 2D nanosheets. The CNMBr core-shell nanocrystals demonstrated enhanced photoelectrochemical water splitting performance and photocurrent reaching up to 1.55 mA cm−2. The CNMBr catalyst was successfully deployed for CO2 photoreduction giving carbon monoxide and methane as the reaction products.
Impact of CuS counter electrode calcination temperature on quantum dot sensit...TELKOMNIKA JOURNAL
In place of the commercial Pt electrode used in quantum sensitized solar cells, the low-cost CuS cathode is created using electrophoresis. High resolution scanning electron microscopy and X-ray diffraction were used to analyze the structure and morphology of structural cubic samples with diameters ranging from 40 nm to 200 nm. The conversion efficiency of solar cells is significantly impacted by the calcination temperatures of cathodes at 100 °C, 120 °C, 150 °C, and 180 °C under vacuum. The fluorine doped tin oxide (FTO)/CuS cathode electrode reached a maximum efficiency of 3.89% when it was calcined at 120 °C. Compared to other temperature combinations, CuS nanoparticles crystallize at 120 °C, which lowers resistance while increasing electron lifetime.
In place of the commercial Pt electrode used in quantum sensitized solar cells, the low-cost CuS cathode is created using electrophoresis. High resolution scanning electron microscopy and X-ray diffraction were used to analyze the structure and morphology of structural cubic samples with diameters ranging from 40 nm to 200 nm. The conversion efficiency of solar cells is significantly impacted by the calcination temperatures of cathodes at 100 °C, 120 °C, 150 °C, and 180 °C under vacuum. The fluorine doped tin oxide (FTO)/CuS cathode electrode reached a maximum efficiency of 3.89% when it was calcined at 120 °C. Compared to other temperature combinations, CuS nanoparticles crystallize at 120 °C, which lowers resistance while increasing electron lifetime.
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Devika Laishram
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−xFexO6−δ
(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2
reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar
energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo),
exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse
up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo
and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using
dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by
wrapping on perovskite established an effective heterojunction between the materials for charge
separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased
photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed
optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven
water-splitting with a Faradaic efficiency as high as ∼88%.
Ultra-optical characterization of thin film solar cells materials using core...IJECEIAES
This paper investigates on new design of heterojunction quantum dot (HJQD) photovoltaics solar cells CdS/PbS that is based on quantum dot metallics PbS core/shell absorber layer and quantum dot window layer. It has been enhanced the performance of traditional HJQD thin film solar cells model based on quantum dot absorber layer and bulk window layer. The new design has been used sub-micro absorber layer thickness to achieve high efficiency with material reduction, low cost, and time. Metallicssemiconductor core/shell absorber layer has been succeeded for improving the optical characteristics such energy band gap and the absorption of absorber layer materials, also enhancing the performance of HJQD ITO/CdS/QDPbS/Au, sub micro thin film solar cells. Finally, it has been formulating the quantum dot (QD) metallic cores concentration effect on the absorption, energy band gap and electron-hole generation rate in absorber layers, external quantum efficiency, energy conversion efficiency, fill factor of the innovative design of HJQD cells.
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and …
Arrays of TiO2 nanorods embedded with fluorine doped carbon nitride quantum d...Pawan Kumar
Graphenic semiconductors such as carbon nitride are attracting increasing attention as photocatalysts due to their chemical stability, visible light absorption and excellent electronic properties. The photocatalytic activity of nanostructured TiO2 catalysts is constrained by the wide bandgap and concomitant low visible light responsivity of TiO2. In this context we present the formation of new fluorine doped carbon nitride quantum dots (CNFQDs) by solid state reaction and the subsequent examination of their heterojunctions with TiO2 for photoelectrochemical water splitting. Arrays of rutile phase TiO2 nanorods embedded with CNFQDs were synthesized by a simple in situ hydrothermal approach and the resulting nanomaterials were found to exhibit strong visible light absorption. The energetics at the heterojunction were favorable for efficient electron transfer from CNFQDs to TiO2 under visible light irradiation and transfer of holes to the aqueous electrolyte. CNFQD-sensitized TiO2 nanorods exhibited a strong photoelectrochemical response up to 500 nm. Reuse experiments confirmed robustness and long term stability of the sample without exhausting the catalytic performance. The present work demonstrates a new pathway to sensitize TiO2 to visible photons by the in situ formation of embedded heterojunctions with fluorine doped carbon nitride quantum dots
Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
Optical Control of Selectivity of High Rate CO2 Photoreduction Via Interband-...Pawan Kumar
Photonic crystals consisting of TiO2 nanotube arrays (PMTiNTs) with periodically modulated diameters were fabricated using a precise charge-controlled pulsed anodization technique. The PMTiNTs were decorated with gold nanoparticles (Au NPs) to form plasmonic photonic crystal photocatalysts (Au-PMTiNTs). A systematic study of CO2 photoreduction performance on as-prepared samples was conducted using different wavelengths and illumination sequences. A remarkable selectivity of the mechanism of CO2 photoreduction could be engineered by merely varying the spectral composition of the illumination sequence. Under AM1.5 G simulated sunlight (pathway#1), the Au-PMTiNTs produced methane (302 µmol h-1) from CO2 with high selectivity (89.3%). When also illuminated by a UV-poor white lamp (pathway#2), the Au-PMTiNTs produced formaldehyde (420 µmol h-1) and carbon monoxide (323 µmol h-1) with almost no methane evolved. We confirmed the photoreduction results by 13C isotope labeling experiments using GC-MS. These results point to optical control of the selectivity of high-rate CO2 photoreduction through selection of one of two different mechanistic pathways. Pathway#1 implicates electron-hole pairs generated through interband transitions in TiO2 and Au as the primary active species responsible for reducing CO2 to methane. Pathway#2 involves excitation of both TiO2 and surface plasmons in Au. Hot electrons produced by plasmon damping and photogenerated holes in TiO2 proceed to reduce CO2 to HCHO and CO through a plasmonic Z-scheme.
Using triple-layer remote phosphor structures LaVO4:Eu3+ and ZnS:Cu,Sn to imp...TELKOMNIKA JOURNAL
This research paper investigates the novel triple remote phosphor layer for improving the remote phosphor’s angular chroma uniformity (ACU) of down-light lamps by using remote micro-patterned phosphor layers (RMPP). In addition, introducing the triple-layer (TL) RMPP is introduced to offer the potential approach to this objective. This analysis also measures the optical efficiency of the layers and the angle distribution of angular correlated color temperature (ACCT). Drawing a comparison between the traditional
dual-layer (DL) RMPP and the proposed TL is furthermore critical to this study. According to the findings, the triple-layer phosphor configuration can achieve greater hue consistency while having a correlating colour temperature (CCT) variance merely measured at 441 K. Results in the single RMPP layer are 1390 K of the remote phosphor (RP) sheet setting and
556 K for the ACCT deviation. The recreation employing finite-difference
time-domain (FDTD) as well as the approach of ray-tracing ensures an increase in angular color uniformity (ACU). The structure of DL and TL RMPPs results in a 6.68 % and 4.69 % gain in luminous efficiency, respectively, with the standard RMPP layer at a currently driving of 350 mA. The micro-patterned layer’s scattering characteristic and mixing effect may account for the increased ACU and luminous efficiency.
Asymmetric Multipole Plasmon-Mediated Catalysis Shifts the Product Selectivit...Pawan Kumar
Cu/TiO2 is a well-known photocatalyst for the photocatalytic transformation of CO2 into methane. The formation of C2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C–C bonds is currently a major challenge in CO2 photoreduction. In this context, we report the dominant formation of a C2 product, namely, ethane, from the gas-phase photoreduction of CO2 using TiO2 nanotube arrays (TNTAs) decorated with large-sized (80–200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total CxH2x+2 rate of 23.88 μmol g–1 h–1. Under identical conditions, the CxH2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g–1 h–1, respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag–Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate–adsorbate repulsion and facilitates C–C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.
Similar to Effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes (20)
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Isolated Iridium Sites on Potassium-Doped Carbon-nitride wrapped Tellurium Na...Pawan Kumar
Many industrial processes such transesterification of fatty acid for biodiesel production, soap manufacturing and biosynthesis of ethanol generate glycerol as a major by-product that can be used to produce commodity chemicals. Photocatalytic transformation of glycerol is an enticing approach that can exclude the need of harsh oxidants and extraneous thermal energy. However, the product yield and selectivity remain poor due to low absorption and unsymmetrical site distribution on the catalyst surface. Herein, tellurium (Te) nanorods/nanosheets (TeNRs/NSs) wrapped potassium-doped carbon nitride (KCN) van der Waal (vdW) heterojunction (TeKCN) is designed to enhance charge separation and visible-NIR absorption. The iridium (Ir) single atom sites decoration on the TeKCN core-shell structure (TeKCNIr) promotes selective oxidation of glycerol to glyceraldehyde with a conversion of 45.6% and selectivity of 61.6% under AM1.5G irradiation. The catalytic selectivity can reach up to 88% under 450 nm monochromatic light. X-ray absorption spectroscopy (XAS) demonstrates the presence of undercoordinated IrN2O2 sites which improved catalytic selectivity for glycol oxidation. Band energies and computational calculations reveal faile charge transfer in the TeKCNIr heterostructure. EPR and scavenger tests discern that superoxide (O2•−) and hydroxyl (•OH) radicals are prime components driving glycerol oxidation.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Solar-Driven Cellulose Photorefining into Arabinose over Oxygen-Doped Carbon ...Pawan Kumar
Biomass photorefining is a promising strategy to address the energy crisis and transition toward carbon carbon-neutral society. Here, we demonstrate the feasibility of direct cellulose photorefining into arabinose by a rationally designed oxygen-doped polymeric carbon nitride, which generates favorable oxidative species (e.g., O2–, •OH) for selective oxidative reactions at neutral conditions. In addition, we also illustrate the mechanism of the photocatalytic cellulose to arabinose conversion by density functional theory calculations. The oxygen insertion derived from oxidative radicals at the C1 position of glucose within cellulose leads to oxidative cleavage of β-1,4 glycosidic linkages, resulting in the subsequent gluconic acid formation. The following decarboxylation process of gluconic acid via C1–C2 α-scissions, triggered by surface oxygen-doped active sites, generates arabinose and formic acid, respectively. This work not only offers a mechanistic understanding of cellulose photorefining to arabinose but also sets up an example for illuminating the path toward direct cellulose photorefining into value-added bioproducts under mild conditions.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Selective Cellobiose Photoreforming for Simultaneous Gluconic Acid and Syngas...Pawan Kumar
Here, we demonstrate the selective cellobiose (building block of cellulose) photoreforming for gluconic acid and syngas co-production in acidic conditions by rationally designing a bifunctional polymeric carbon nitride (CN) with potassium/sulfur co-dopant. This heteroatomic doped CN photocatalyst possesses enhanced visible light absorption, higher charge separation efficiency than pristine CN. Under acidic conditions, cellobiose is not only more efficiently hydrolyzed into glucose but also promotes the syngas and gluconic acid production. Density functional theory (DFT) calculations reveal the favorable generation of •O2− during the photocatalytic reaction, which is essential for gluconic acid production. Consequently, the fine-designed photocatalyst presents excellent cellobiose conversion (>80%) and gluconic acid selectivity (>70%) together with the co-production of syngas (~56 μmol g-1 h-1) under light illumination. The current work demonstrates the feasibility of biomass photoreforming with value-added chemicals and syngas co-production under mild condition.
Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single...Pawan Kumar
Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer–Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.
Recent advancements in tuning the electronic structures of transitional metal...Pawan Kumar
The smooth transition from finite non-renewables to renewable energy conversion technologies will require efficient electrocatalysts which can harness intermittent energies to store in the form of chemical bonds. The oxygen evolution reaction (OER) impedes the widespread usage of water electrolyzers to convert H2O into H2 and persists as a bottleneck, including other energy conversion devices with sluggish four H+/e− kinetics. In this context, designing highly active and stable catalysts capable of driving a lower overpotential in the OER to produce continuous hydrogen (H2) is a primary demanded. This chapter discussed the mechanism of the OER in conventional adsorbate oxygen and lattice oxygen participation in transition metal oxides (TMOs). Further, the influences of surface engineering, doping, and defects in the TMOs and understanding the electronic structure to screen electrodes towards the structure–activity relationship are highlighted. Specifically, the adsorption strength of O 2p is understood in detail as its binding ability over the surface of TMOs can be correlated directly to the OER activity. The iterative development of TMOs in terms of understanding electronic structural attributes is essential for the commercial deployment of energy conversion technologies. The comprehensive outlook of this chapter investigates thoroughly how TMOs can be used as significant materials for the OER in the near future.
Hole transport materials (HTMs) have a significant impact on the effectiveness of organic electronic devices; therefore, we present a molecular architecture of pyrazino[2,3-g]quinoxaline (PQ10)-based room-temperature organic liquid crystalline semiconductor (OLCS) as an alternative HTM. The PQ10 compound exhibits three different rectangular columnar (Colr) phases offering an impressive hole mobility of 8.8 × 10−3 cm2V−1s−1 which is found to be dexterous than most of existing polymeric hole transport materials. The charge transport mechanism is governed by the hole polarons hopping through H-aggregates of the PQ10 molecules and the hole mobility remains nearly constant throughout the mesophase range, but it decreases with increasing applied electric field. The current-voltage characteristics of the PQ10 have also been investigated in all three Colr phases and explained via the Poole-Frenkel conduction mechanism. The dielectric spectroscopy has been eventually carried out to understand the nature of dielectric permittivity and conductivity as a function of temperature and a correlation is established between the molecular architecture of the Colr phases and aforementioned physical properties. Solar cell simulation has been additionally performed to demonstrate that the PQ10 material can be a better choice as HTM for organic electronics and photovoltaic applications.
Multifunctional carbon nitride nanoarchitectures for catalysisPawan Kumar
Catalysis is at the heart of modern-day chemical and pharmaceutical industries, and there is an urgent demand to develop metal-free, high surface area, and efficient catalysts in a scalable, reproducible and economic manner. Amongst the ever-expanding two-dimensional materials family, carbon nitride (CN) has emerged as the most researched material for catalytic applications due to its unique molecular structure with tunable visible range band gap, surface defects, basic sites, and nitrogen functionalities. These properties also endow it with anchoring capability with a large number of catalytically active sites and provide opportunities for doping, hybridization, sensitization, etc. To make considerable progress in the use of CN as a highly effective catalyst for various applications, it is critical to have an in-depth understanding of its synthesis, structure and surface sites. The present review provides an overview of the recent advances in synthetic approaches of CN, its physicochemical properties, and band gap engineering, with a focus on its exclusive usage in a variety of catalytic reactions, including hydrogen evolution reactions, overall water splitting, water oxidation, CO2 reduction, nitrogen reduction reactions, pollutant degradation, and organocatalysis. While the structural design and band gap engineering of catalysts are elaborated, the surface chemistry is dealt with in detail to demonstrate efficient catalytic performances. Burning challenges in catalytic design and future outlook are elucidated.
Production of Renewable Fuels by the Photocatalytic Reduction of CO2 using Ma...Pawan Kumar
The photo-reductive performance of natural ilmenite was boosted and the production of renewable fuels from the reduction of CO2 was enhanced by doping the natural mineral with magnesium. The doping was achieved by high energy ball milling in the presence of MgO and Mg(NO3)2. The photo-reduction of CO2 in aqueous solution led to the evolution of H2, CH4, C2H4, and C2H6, and the insertion of Mg in the structure of ilmenite enabled increases of up to 1245% in the fuel production yield, reaching total production of 210.9 µmol h-1 gcat-1. Displacements of the conduction band to more negative potentials were evidenced for the samples doped with magnesium. Indirect effects such as increases in the valence band maximum, and the introduction of intermediate energy levels were also evidenced through the measurement of the crystallite size and the determination of the band structure of the materials. Mott-Schottky analyses of the samples showed the n-type nature of the semiconductor materials and enabled the estimation of the density of charge carriers, which strongly influenced the photocatalytic performance. The strong potential of the application of natural ilmenite in gas phase artificial photosynthesis was proved by the evaluation of CO2 reduction in gas conditions, which allowed the enhancement in the selectivity and significantly increased the production of CH4 as compared to aqueous solution, reaching an important yield of CH4 of 16.1 µmol h-1 gcat-1.
Nanoengineered Au-Carbon Nitride Interfaces Enhance PhotoCatalytic Pure Water...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Nanoengineered Au-Carbon Nitride Interfaces Enhance Photo-Catalytic Pure Wate...Pawan Kumar
Photocatalytic pure water splitting using solar energy is one of the promising routes to produce sustainable green hydrogen (H2). Tuning the interfacial active site density at catalytic heterojunctions and better light management are imperative to steer the structure-activity correlations to enhance the photo-efficiency of nanocomposite photocatalysts. Herein, we report the decoration of nitrogen defects-rich carbon nitride CN(T) with metallic Au nanostructures of different morphologies and sizes to investigate their influence on the photocatalytic hydrogen evolution reactions (HER). The CN(T)-7-NP nano-heterostructure comprises Au nanoparticles (NPs) of ~7 nm and thiourea-derived defective CN exhibits an excellent H2 production rate of 76.8 µmol g–1 h–1 from pure water under simulated AM 1.5 solar irradiation. In contrast to large-size Au nanorods, the high activity of CN(T)-7-NP was attributed to their strong localized surface plasmon resonance (LSPR) mediated visible absorption and interfacial charge separation. The surface ligands used to control Au nanostructures morphology were found to play a major role in the stabilization of NPs and improve interfacial charge transport between Au NPs and CN(T). First-principles calculations revealed that defects in CN and Au-CN interfacial sites in these nanocomposites facilitate the separation of e-/h+ pairs after light excitation and provide lower energy barrier pathways for H2 production by photocatalytic water splitting.
Cooperative Copper Single Atom Catalyst in Two-dimensional Carbon Nitride for...Pawan Kumar
Renewable electricity powered carbon dioxide (CO2) reduction (eCO2R) to high-value fuels like methane (CH4) holds the potential to close the carbon cycle at meaningful scales. However, this kinetically staggered 8-electron multistep reduction still suffers from inadequate catalytic efficiency and current density. Atomic Cu-structures can boost eCO2R-to-CH4 selectivity due to enhanced intermediate binding energies (BEs) resulting from favorably shifted d-band centers. Herein, we exploit two-dimensional carbon nitride (CN) matrices, viz. Na-polyheptazine (PHI) and Li-polytriazine imides (PTI), to host Cu-N2 type single atom sites with high density (∼1.5 at%), via a facile metal ion exchange process. Optimized Cu loading in nanocrystalline Cu-PTI maximizes eCO2R-to-CH4 performance with Faradaic efficiency (FECH4) of ≈68% and a high partial current density of 348 mA cm−2 at a low potential of -0.84 V versus RHE, surpassing the state-of-the-art catalysts. Multi-Cu substituted N-appended nanopores in the CN frameworks yield thermodynamically stable quasi-dual/triple sites with large interatomic distances dictated by the pore dimensions. First-principles calculations elucidate the relative Cu-CN cooperative effects between the two matrices and how the Cu-Cu distance and local environment dictate the adsorbate BEs, density of states, and CO2-to-CH4 energy profile landscape. The 9N pores in Cu-PTI yield cooperative Cu-Cu sites that synergistically enhance the kinetics of the rate-limiting steps in the eCO2R-to-CH4 pathway.
Bioinspired multimetal electrocatalyst for selective methane oxidationPawan Kumar
Selective partial electrooxidation of methane (CH4) to liquid oxygenates has been a long-sought goal. However, the high activation energy of C–H bonds and competing oxygen evolution reaction limit product selectivity and reaction rates. Inspired by iron (IV)-oxo containing metalloenzymes’ functionality to activate the C–H bond, here we report on the design of a copper-iron-nickel catalyst for selective oxidation of CH4 to formate via a peroxide-assisted pathway. Each catalyst serves a specific role which is confirmed via electrochemical, in situ, and theoretical studies. A combination of electrochemical and in situ spectroelectrochemical studies revealed that H2O2 oxidation on nickel led to the formation of active oxygen species which trigger the formation of iron (IV) at low voltages. Density functional theory analysis helped reveal the role of iron (IV)-oxo species in reducing the activation energy barrier for CH4 deprotonation and the critical role of copper to suppress overoxidation. Our multimetal catalyst exhibits a formate faradaic efficiency of 42% at an applied potential of 0.9 V versus a reversible hydrogen electrode.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
ANAMOLOUS SECONDARY GROWTH IN DICOT ROOTS.pptxRASHMI M G
Abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Effect of morphology on the photoelectrochemical performance of nanostructured Cu2O photocathodes
1. Nanotechnology
PAPER
Effect of morphology on the photoelectrochemical performance of
nanostructured Cu2O photocathodes
To cite this article: Lian C T Shoute et al 2021 Nanotechnology 32 374001
View the article online for updates and enhancements.
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3. Nanotechnology 32 (2021) 374001 L C T Shoute et al
compatible with low-cost fabrication in addition to meeting the
stringent requirements as a semiconductor photocatalyst viz.
suitable bandgap to absorb a large fraction of the solar spec-
trum, appropriate positions of the conduction and valence band
energy levels with respect to the water reduction and/or oxida-
tion, depletion layer for efficient charge separation, good elec-
trical conductivity for efficient charge transport, facile interfa-
cial charge transfer kinetics, and good photochemical stability
in aqueous electrolytes [18, 19].
The most extensively investigated earth-abundant semicon-
ductor photocatalysts for PEC water splitting are either n-type
TiO2 [20–24], WO3 [25–27]„ ZnO [28–30], BiVO4 [31–34],
and Fe2O3 [14, 35–37] as the photoanode or p-type Cu2O
[38–44] as the photocathode. Among these, Cu2O is the most
promising material whose PEC performance in the water split-
ting reaction is the highest among all oxides in terms of pho-
tocurrent and photovoltage. Cu2O, a direct band gap semi-
conductor with a band gap of 1.9–2.2 eV, has a high absorp-
tion coefficient in the visible region [45, 46], a conduction
band located well above the reduction potential of water, and
valence band edge close to (slightly positive) the water oxida-
tion potential. It has a theoretical maximum solar-to-hydrogen
(STH) conversion efficiency of 18.1% with a corresponding
photocurrent density of ~14.7 mA cm−2
based on the air mass
1.5 global (AM1.5 G) spectrum, making Cu2O the most prom-
ising semiconductor for hydrogen production. However, two
main challenges in the deployment of Cu2O are the photocor-
rosion [43, 47, 48] of Cu2O in aqueous solution and the short
diffusion length (10–100 nm)[43, 49] of minority charge car-
riers in Cu2O.
Photocorrosion of Cu2O occurs because its redox potentials
for reduction and oxidation lie within the band gap of Cu2O
and as a result, the photogenerated electrons and holes react
with Cu2O to form Cu metal and CuO respectively [43, 47, 48].
A simple approach to prevent photo-corrosion is to conform-
ally coat Cu2O with a thin protective layer that is dense enough
to block direct contact with the aqueous solution, transparent
to visible light, and highly conductive to the minority charge
carrier.
The short diffusion length of the minority charge carrier
has an adverse effect on the Cu2O photocatalytic perform-
ance, and its mitigation demands exquisite morphological
and orientation control to satisfy the requirements of long
optical path length for optimal absorption of sunlight and the
short distances needed for efficient collection of the minority
charge carriers [50–53]. These demanding conditions cannot
be met by zero-dimension (0D) nanoparticle films because of
the enhanced electron–hole recombination and electron trap-
ping/scattering at grain boundaries of the nanostructured film
and the random walk-type transport of majority carriers [8, 37,
54, 55]. One-dimensional (1D) nanostructures (e.g. nanowire,
nanotube, nanoribbon) have ideal morphologies that ortho-
gonalize the competing processes of charge generation and
charge separation because light absorption can occur along
the length of the nanostructure while simultaneously providing
short radial distances for efficient charge separation [50–56].
Electrodeposition has been used as a convenient method
to deposit 1D metal oxides, particularly Cu2O, on different
substrates [57–63]. Unprotected electrodeposited Cu2O nor-
mally exhibits a low photocurrent of <1 mA cm−2
similar
to the photocurrent reported for porous Cu2O prepared from
a dispersion of Cu2O powder [64–68]. Improvements in the
electrodeposition process yielded a higher photocurrent [64]
of 2.4 mA cm−2
, and controlling the crystal facets and porosity
led to an even higher photocurrent of 4.07 mA cm−2
[69, 70].
Protective coating and cocatalyst incorporation including car-
bon and graphene have been demonstrated to provide pho-
tocurrents as high as 4.8 mA cm−2
[41, 71–77]. Recently,
Gratzel et al [38, 39, 42, 43, 64]. employed ultrathin protect-
ive layers of n-type oxides conformally deposited on the sur-
face of Cu2O thin films by atomic layer deposition (ALD) and
observed a dramatic improvement in photocurrent and stabil-
ity against corrosion. A protective layer of 21 nm ZnO/11 nm
TiO2 on electrodeposited planar Cu2O and an overlayer of
electrodeposited hydrogen evolution catalyst (HEC) Pt nan-
oparticles to catalyze water reduction enabled them to achieve
a photocurrent of 7.6 mA cm−2
[43]. Further improvement
was achieved using nanowire instead of planar Cu2O [42]. The
Cu2O NW photocathode based on Cu2O/Ga2O3/TiO2/NiMo,
has been demonstrated to exhibit photocurrent densities of
10 mA cm−2
and stable operation of > 100 h [38].
Many top-down and bottom-up techniques [78–81] includ-
ing template-guided growth [82, 83], epitaxial electrode-
position [84], template assisted electrochemical deposition
[85, 86], chemical vapor deposition [87, 88], thermal depos-
ition [89, 90] and reactive sputtering deposition [91–93], have
been developed to deposit Cu2O thin films. Among these,
electrodeposition is the technique of choice to deposit homo-
geneous thin films with controlled thickness and microstruc-
ture since the morphology and orientation can be tuned by
judiciously controlling deposition process parameters such
as pH, electrolyte bath temperature, and applied potential
[38–55, 57–62, 64]. However, the size and morphology con-
trol of 1D nanomaterials is still a challenging issue, because
the control of nucleation and growth processes of nanostruc-
tures is non-trivial. Moreover, the orientation and shape of the
Cu2O crystals composing the polycrystalline Cu2O electrodes
have been demonstrated to affect their photoelectrochemical
properties and photostability [64, 66, 94]. Further, different
facets of Cu2O crystal have been demonstrated to have differ-
ent resistivity, carrier density, and stability; and crystals with
different facet orientations on a substrate can be prepared by
adjusting the pH of the solutions [64, 66, 69, 70, 95–97]. In
addition, there are still intriguing questions on how solar cells
based on planar structures have higher efficiencies over nano-
structures [98–100].
In this work, we have used a number of different tech-
niques to deposit planar and 1D nanostructured Cu2O thin
films on Cu foil as the substrate such as electroreduction, anod-
ization, thermal oxidation, and chemical oxidation at room
temperature and demonstrated the conditions required for pre-
paring Cu2O with different morphologies and photocatalytic
properties. These samples were used as the photocathode in
a PEC cell to characterize their photocatalytic properties and
performance by measuring the photocurrent density, onset
potential, flat band potential, band edges, and interfacial
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4. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Table 1. Solution composition, applied potential, annealing condition, and morphology of Cu2O thin film produce by different deposition
methods.
Sample Deposition Substrate Solution Bias Time Anneal Air Anneal N2 Morphology
code method composition V min 230 ◦
C, h 550 ◦
C, h
NB1 Anodization Cu 1 M KOH 1.3 20 NA 4 1D
NB2 Anodization Cu 2 M KOH 1.3 20 NA 4 1D
NIN1 Anodization Cu 3 M KOH 1.8 3 NA 4 1D
NIN2 Chemical oxidation Cu (NH4)2S2O8 NA 40 NA 4 1D
P1 Electroreduction Cu CuSO4 1.3 40 NA 4 Planar
P2 Anodization Cu 4 M KOH 1.3 20 NA 4 Planar
P3 Anodization Cu 3 M KOH 1.3 20 NA 4 Planar
P4 Anodization Cu 3 M KOH 0.4 60 NA 4 Planar
P5 Air oxidation Cu NA NA NA 3 4 Planar
Note: Abbreviations NB, NIN, and P refer to nanobead, nanoinukshuk, and planar. All sample preparations used an aqueous solution, for chemical oxidation
the solution contains 72 mM (NH4)2S2O8, 52 mM NH4OH, and 1.5 M NaOH. Anodization at 1.3 and 1.8 V correspond to a current density of ~1 mA cm−2
and ~10 mA cm−2
respectively.
charge transfer resistance. Planar and 1D nanostructured Cu2O
samples possessed significantly different carrier densities and
charge-transfer resistances but these differences do not appear
to have a strong influence on the photoelectrochemical per-
formance. The results presented in this work will provide bet-
ter insights into the factors controlling photocatalytic water
splitting by Cu2O photocathode, the effect of deposition meth-
ods and Cu2O morphology on the photocatalytic properties of
Cu2O based PEC.
2. Experimental
2.1. Materials
Potassium hydroxide (88.5%), sodium hydroxide (99.4%),
ammonium persulfate (98 +%), copper sulfate (98.1%), lactic
acid (85%), sodium sulfate (99.3%) and ammonium hydrox-
ide (29.4%) were procured from Fisher Scientific, and used
as received. Deionized (DI) water was used for sample pre-
paration. All solvents used were of HPLC grade. Copper foil
(99.9%) was purchased from McMaster-Carr Inc. A program-
mable tube furnace from Opti-Tech Scientific Inc. was used for
thermal annealing. The power supply for anodization and the
electrochemical reduction was a direct current power supply
(9312-PS MPJA Inc).
2.2. Sample preparation
Cu foil substrates (1 cm x 3 cm) were sonicated in soap water,
deionized water, acetone, 2-propanol and methanol for 5 mins
each and dipped into 1 M HCl before use. Thermal oxida-
tion of Cu foil to copper oxide was achieved by annealing
at 230 ◦
C for 4 h in air. Chemical oxidation of Cu foil to
Cu(OH)2 was carried out by dipping the Cu foil in an aqueous
solution containing 72 mM (NH4)2S2O8, 52 mM NH4OH,
and 1.5 M NaOH for 40 min. Electrochemical reduction of
CuSO4 to Cu2O was carried out in a solution containing 0.3 M
CuSO4 and 3 M lactic acid at pH 12. A two-electrode config-
uration with Cu foil as the cathode and Ti foil as the anode was
used for electrochemical reduction. Anodization of Cu foil to
Cu(OH)2 was performed in a two-electrode configuration at
room temperature with Cu foil as the anode and Ti foil as the
cathode. The morphologies of the Cu(OH)2 deposited on the
Cu foil were controlled by varying the applied potential and
concentration of KOH in the aqueous solution. The applied
potentials, experimental conditions of anodization, and the
morphologies of the copper oxides obtained in this study are
listed in table 1. The transformation of Cu(OH)2 to Cu2O was
achieved by annealing in a tube furnace at 550 ◦
C for 4 h in a
N2 ambient.
2.3. Characterization
Glancing angle x-ray diffraction (XRD) using a Bruker D8
Discover instrument with a sealed Cu Kα x-ray source (incid-
ent angle = 0.5◦
, λ = 1.541 Å, step size = 0.02◦
, dwelling
time = 2 s), was used to probe the phase composition of Cu2O
deposited on the Cu foil as substrate. A Perkin Elmer Lambda-
1050 UV–Vis-NIR spectrophotometer equipped with an integ-
rating sphere accessory was used to collect the optical spec-
tra through diffuse reflectance spectroscopic (DRS) measure-
ments. The surface topographical images of composite films
were obtained using a field emission scanning electron micro-
scopy (FESEM) on a Zeiss Sigma FESEM equipped with
GEMINI in-lens detector at an acceleration voltage of 5 keV.
2.4. Photoelectrochemical and electrochemical impedance
measurements
The photoelectrochemical performance of the Cu2O thin film
deposited on Cu foil was evaluated in a borosilicate glass
beaker with a typical three-electrode photoelectrochemical
cell (PEC) configuration under front-side illumination by AM
1.5 G simulated sunlight from a calibrated Newport-Oriel
Class A solar simulator using a CHI660E potentiostat (CH
Instruments Inc). The PEC consisted of a Cu2O thin film or
nanostructured thin film photocathode, platinum thin film on
fluorine-doped tin oxide (FTO) counter electrode, and satur-
ated Ag/AgCl as the reference electrode immersed in an elec-
trolyte solution containing 0.1 M Na2SO4 aqueous solution at
pH 7. The scan rate for the linear sweep voltammetry (LSV)
was 20 mV s−1
, and chronoamperometry was performed at a
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5. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 1. Anodic, chemical, and thermal oxidation deposition of Cu2O on Cu foil is a two-step process. In the first step, Cu is oxidized to
Cu(OH)2 and or−1
copper oxides, and subsequent annealing at 550 ◦
C under N2 atmosphere produce Cu2O thin film. Top and bottom
panels display photos of typical Cu(OH)2/Cu and Cu2O/Cu samples, and their FESEM images.
potential of −0.6 V vs saturated Ag/AgCl for 3 s with both
measurements performed under chopped irradiation from an
AM 1.5 simulated sunlight. The electrochemical impedance
measurements for Mott-Schottky analysis were carried out in
the dark using a CHI660E potentiostat. The electrolyte was
0.1 M Na2SO4 aqueous solution at pH 7. The potential was
swept in the range of +0.6 V to −0.6 V vs saturated Ag/AgCl
modulated by an AC signal of 10 mV amplitude at a frequency
of 1 kHz. Electrochemical impedance spectroscopy (EIS) was
performed in the dark as well as under AM1.5 G illumin-
ation using a three-electrode configuration by scanning the
frequency of an applied voltage sinusoidal AC amplitude of
10 mV from 0.1 Hz to 1 MHz superimposed on a DC potential
of—0.1 V vs saturated Ag/AgCl in 0.1 M Na2SO4 solution
at pH 7. The potentials vs the saturated Ag/AgCl reference
electrode were converted to the reversible hydrogen electrode
(RHE) scale using Nernst’s equation ERHE = EAg/AgCl (sat) + E0
(Ag/AgCl) + 0.059 pH, where EAg/AgCl (sat) is the measured
potential against the reference electrode saturated Ag/AgCl
and E0 (Ag/AgCl) = 0.197 V at 25 ◦
C.
3. Results and discussion
3.1. Deposition of Cu2O thin films
Thin films of Cu2O on Cu foil with different morphologies
were deposited by anodic, chemical, and thermal oxidation
of copper, and by electrochemical reduction of CuSO4. The
morphology of the deposited Cu2O obtained could be broadly
classified as either planar or 1D nanostructure type. Thermal
oxidation of Cu in air and electrochemical reduction of CuSO4
in aqueous alkaline solution yielded copper oxide with a planar
morphology. On the other hand, chemical oxidation of Cu
with ammonium persulfate in alkaline aqueous solution resul-
ted in 1D nanostructured Cu(OH)2. Interestingly, an attractive
method to deposit a thin film of oxidized copper with different
morphologies on a Cu foil is anodic oxidation. Anodization
of Cu foil in alkaline aqueous solutions can lead to the depos-
ition of either a planar or 1D nanostructured oxidized copper
depending on the concentration of KOH and/or the potential
applied (current density) in the anodization [101].
A schematic illustration of the processes used to deposit
Cu2O on Cu foil is presented in figure 1. As depicted in figure
1, deposition of Cu2O on Cu foil occurs in two steps for every
deposition technique used except in the case of the electro-
chemical reduction of CuSO4 where Cu2O was deposited in a
single step. A simple method to deposit Cu2O thin film on Cu
foil is by annealing Cu foil in the air at 230 ◦
C to form com-
posite CuO/Cu2O thin film. The Cu2O thin film thus formed
has a planar morphology as presented in the Supplementary
figure S1e.
Anodic oxidation of Cu is a versatile technique for depos-
ition of a homogeneous film of copper oxide with controlled
thickness and morphology. The film morphology and thick-
ness can be controlled by varying the alkaline concentra-
tion, applied potential, and duration of anodization. Anodic
oxidation of Cu foil in 2 M KOH at 1.3 V potential applied
(~1 mA cm−2
) for 20 min yields cyan-colored Cu(OH)2. The
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6. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 2. FESEM images of anodically formed 1D nanostructures of (a, c) Cu(OH)2 and (b, d) Cu2O. Conditions for anodic oxidation of
Cu foil are (a) 2 M KOH, 1.3 V potential applied for 20 mins (c) 3 M KOH 1.8 V potential applied for 3 mins; (c, d) Annealing (a) and (c) at
550 ◦
C for 4 h in N2 atmosphere converts Cu(OH)2 to Cu2O.
FESEM image of the Cu(OH)2 displayed in figure 2(a) has the
appearance of grass (nanograss) on a lawn. Subsequent anneal-
ing of the Cu(OH)2 nanograss in an oven at 550 ◦
C for 4 h
under N2 atmosphere transforms Cu(OH)2 to Cu2O following
the reduction of Cu(II) to Cu(I) by Cu resulting from grain
boundary and lattice diffusion in the film. The FESEM image
of the Cu2O formed as shown in figure 2(b) resembled a string
of beads (nanobeads). When the anodization of Cu foil was
carried out at a higher potential of 1.8 V and consequently at
a higher current density of ~10 mA cm−2
applied for 3 min,
the Cu(OH)2 formed has a morphology similar to nanograss.
Upon subsequent annealing in an oven at 550 ◦
C for 4 h
under N2 atmosphere, the Cu2O formed has a morphology
which has some resemblance to a stone pile (nanoinukshuk).
Interestingly, chemical oxidation of Cu by ammonium per-
sulfate in alkaline aqueous solution also led to the depos-
ition of cyan colored Cu(OH)2 with nanograss morphology.
Subsequent annealing in an oven at 550 ◦
C for 4 h under
N2 atmosphere yielded Cu2O with nanoinukshuk morphology
as shown in Supplementary figures S1(a) and (d) (available
at stacks.iop.org/NANO/32/374001/mmedia). Clearly, minor
variations in the anodization conditions have been observed
to lead to profound changes in the morphology of the depos-
ited Cu2O film. As the shape, size, orientation, and facets of
polycrystalline Cu2O are known to have a strong effect on the
resistivity, carrier density, and photocorrosion of the Cu2O
photocathode, anodization is an ideal deposition method to
study the morphology dependent Cu2O cathode photocata-
lytic properties. Furthermore, when the anodization conditions
were slightly varied by increasing the KOH concertation to
4 M while maintaining the applied voltage and duration at
1.3 V (~1 mA cm−2
) and 20 mins respectively, oxides of cop-
per (presumably a composite mixture of Cu(OH)2, CuO and
Cu2O) with dramatically different morphology consisting of
rough facets is obtained as displayed in figure 3(a). Subsequent
annealing in an oven at 550 ◦
C for 4 h under N2 atmosphere
yields Cu2O with planar morphology as shown in figure 3(b).
Electrochemical reduction of CuSO4 in a lactate electro-
lyte at pH 12 at an applied potential of 1.1 V (< 1 mA cm−2
)
led to the deposition of Cu2O with a rough faceted morpho-
logy as shown in figure 3(c). The morphology obtained upon
subsequent annealing in an oven at 550 ◦
C for 4 h under N2
atmosphere is shown in figure 3(d). The FESEM images of
all the Cu2O photocathodes prepared by different deposition
methods such as anodic, chemical, and thermal oxidation of
copper are presented in Supplementary figure S1. The meth-
ods of deposition, experimental conditions, and morphologies
Cu2O thin films used in this study on the photocatalytic prop-
erties of Cu2O as the photocathode in PEC cell are listed in
table 1.
3.2. Spectroscopic characterization
There are two stable forms of copper oxides viz. Cu2O and
CuO. Anodic, chemical, and thermal oxidation of copper pro-
duces composite material composed of Cu(OH)2, CuO and
Cu2O. Cu2O is produced from these composite materials by
thermal annealing at 550 ◦
C under N2 atmosphere where
Cu(II) is reduced to Cu(I) by Cu via grain boundary and
lattice diffusion. To probe the composition of the fabricated
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7. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 3. FESEM images of (a) Anodized Cu foil in 4 M KOH with 1.3 V bias applied for 20 mins, and (c) copper oxide produced by
electrochemical reduction of CuSO4 in lactic acid at pH 12 on Cu foil. Subsequent annealing (a) and (c) at 550 ◦
C for 4 h in N2 atmosphere
yielded Cu2O with planar morphology (b) and a faceted rough morphology (d) respectively.
photocathodes, x-ray diffraction (XRD) patterns were recor-
ded as displayed in figure 4. The XRD spectrum of Cu2O has
peaks at 2θ values of 29.6, 36.4, 42.2, 61.3, 73.4 and 77.4◦
corresponding to reflections from (110), (111), (200), (220),
(311), and (222) crystal planes respectively [102]. The XRD
pattern of the fabricated Cu2O photocathodes has a predomin-
ant peak at 36.4◦
for the (111) planes and less intense peaks
for the (110), (200), (220) and (311) reflections. In addition,
the XRD spectra have peaks due to the Cu metal which is used
as the substrate. However, no peaks attributable to CuO pat-
tern are observed indicating that its concentration is below the
detection limit (< 1%) of the XRD.
Diffuse UV–Vis reflectance spectra of representative planar
(P1) and a 1D nanostructured (NB2) Cu2O photocathodes is
presented in figure 5. The absorption spectra of the samples
displayed significant absorbance at wavelengths > 600 nm
indicating the presence of CuO in the samples. The absorp-
tion and x-ray diffractograms indicated that CuO is present as
a dopant in Cu2O photocathode with concentration < 1%. We
also observe that the NB2 photocathode (red curve in figure
5) has a weaker absorption (i.e. a stronger diffuse reflect-
ance) than the planar P1 photocathode (black curve in figure
5). Figure 2(d) informs us that the NB2 photocathode con-
sists of nanorods approximately 250 nm in width. This is a
size range that corresponds well with strong Mie scattering.
Therefore, the stronger reflectance of the 1D nanostructured
NB2 photocathode is tentatively attributed to higher Mie
scattering.
The optical absorption spectrum provides important
information about the band gap of a semiconductor via the
Tauc relation [103]:
(αhν)n
= A(hν - Eg) (1)
where α is the absorption coefficient, hv is the energy of incid-
ent photon, A is a constant, e.g. is the optical band gap energy,
and the value of n depends on the nature of the transition
[45, 46, 104]. For direct transitions, n is 2 and for indirect
transitions, n is 0.5. Linear fit in the (αhv)2
versus photon
energy (hv) plot indicates allowed transition for Cu2O and the
intercepts on the abscissa yielded band gap energies of 2.00
and 1.91 eV for the Cu2O samples P1 and NB2 respectively.
Tauc plots for other Cu2O morphologies can be found in Sup-
plementary figure S2. Table 2 lists the band gap energies of
all the Cu2O photocathodes prepared by different deposition
methods.
3.3. Photoelectrochemical performance
The photocatalytic properties of the fabricated Cu2O thin
film were determined in a photoelectrochemical cell (PEC)
as presented in figure 6. The PEC consisted of a photocath-
ode (Cu2O thin film), a Pt counter electrode (Pt thin film on
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8. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 4. x-ray diffractograms of Cu2O photocathodes and pure Cu foil. Polycrystalline Cu2O on Cu foil with different morphologies were
prepared by anodic, chemical, and thermal oxidation of copper, and by electrochemical reduction of CuSO4 as described in the text and
listed in .table 1
Figure 5. UV–Vis diffuse reflectance spectra (a) and Tauc plot (b) of planar P1 (black curve) and a 1D nanostructured NB2 (red curve) of
Cu2O photocathodes. Straight lines (b) are linear fit to the spectra.
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9. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Table 2. Experimentally determined photoelectrochemical properties of Cu2O photocathodes with different morphologies and methods of
deposition.
Sample Jmax Jave Eg Vfb NA Ev Ec Vonset Rct (1 sun) Rct (dark)
code (mAcm−2
) (mAcm−2
) (eV) (V) (cm−3
) (eV) (eV) (V) (ohm) (ohm)
NB1 4.9 3.0 ± 1.2 (7) 1.93 0.46 1.3 × 1021
0.33 −1.60 0.50 833 2827
NB2 3.9 2.6 ± 0.7 (8) 2.00 0.48 9.3 × 1020
0.37 −1.63 0.55 651 1706
NIN1 3.8 2.9 ± 0.8 (6) 1.94 0.43 5.2 × 1019
0.39 −1.55 0.49 540 1739
NIN2 3.6 2.8 ± 0.7 (8) 1.98 0.53 3.6 × 1020
0.44 −1.54 0.48 456 664
P1 5.0 3.4 ± 1.1 (7) 1.91 0.58 1.3 × 1019
0.58 −1.33 0.42 1948 9002
P2 3.8 2.6 ± 1.0 (8) 1.90 0.54 5.4 × 1017
0.62 −1.28 0.48 1292 6465
P3 4.4 2.9 ± 1.0 (8) 1.90 0.41 1.0 × 1018
0.47 −1.43 0.52 1045 5967
P4 3.6 2.9 ± 0.6 (4) 1.91 0.39 2.2 × 1018
0.43 −1.48 0.46 971 6108
P5 4.2 2.1 ± 0.9 (20) 1.91 0.50 9.1 × 1018
0.50 −1.40 0.47 1479 8773
Note: Jmax is the highest observed plateau photocurrent density for each morphology prepared using different deposition methods, Jave is the average plateau
photocurrent density from different numbers (in the parenthesis) of independently prepared samples, e.g. is the band gap obtained from Tauc plot, Vfb and NA
are the flat band potential and carrier density from Mott-Schottky analysis, Ev and Ec are valence and conduction band edges, Vonset is the onset potential
obtained from J-V curve, and Rct (1 sun) and Rct (dark) are interfacial charge transfer resistances under AM 1.5 G light illumination and in the dark
respectively, extracted from EIS analysis. All potentials are relative to RHE.
FTO), and a reference electrode (saturated Ag/AgCl). Cu2O
is a p-type semiconductor. Absorption of bandgap and supra-
bandgap photons by the Cu2O photocathode (e.g. = 1.9–
2.0 eV) generates electron-hole pairs in the semiconductor.
Minority carriers (electrons) reach the electrolyte interface
through drift and diffusion. The holes are collected at the
back contact, transported to the counter electrode and become
available for oxidation of water to oxygen (with the applic-
ation of external potential). The electrons upon reaching
the semiconductor-electrolyte interface participate in interfa-
cial electron transfer reactions to reduce water to hydrogen.
Since Cu2O does not have enough overpotential to drive the
water oxidation reaction (OER), application of external bias is
required to drive the reaction.
An important parameter used for comparative evaluation of
the performance of a photoelectrode in PEC is the value of
the plateau photocurrent density (Jmax) obtained at an applied
voltage (Vapp) determined from the photocurrent density-
voltage (J − V) curve. The photoconversion efficiency (η)
[6–17] of a photocathode is related to the plateau photocurrent
density (Jmax), redox potential for water reduction (Vredox), and
the intensity of the illumination (Pin).
η =
Jmax (Vapp − Vredox)
Pin
=
JmaxVapp
Pin
(at pH = 0) (2)
The plateau photocurrent density (Jmax) of the Cu2O pho-
tocathode can be determined at an applied potential (Vapp)
of 0 V vs RHE using chronoamperometry under chopped
AM 1.5 G illumination. Figure 7(a) shows the J-V curve of
Cu2O photocathode measured in 0.1 M Na2SO4 solution under
chopped AM 1.5 G light illumination. The Jmax reaches a plat-
eau value at about 0 V vs RHE. The plateau current density
(Jmax) versus time curve recorded at 0 V vs RHE is shown in
figure 7(b). Since Cu2O photocathodes are susceptible to pho-
tocorrosion, the J-t curve measurements at 0 V vs RHE under
chopped AM 1.5 light illumination with short exposure time
(3 s) were used to determine the plateau photocurrent densities
(Jmax) for the comparative evaluation of the performance of the
photoelectrodes. Figure 7 shows the J-V and the J-t curves for
the Cu2O photocathode (with planar morphology and referred
as P1) deposited by electrochemical reduction of CuSO4. The
Jmax of 5.0 mA cm−2
obtained is the highest photocurrent
density recorded for a Cu2O photocathode prepared by electro-
chemical reduction of CuSO4 and is significantly higher than
the average value determined from several samples as listed
in table 2. It is interesting to note that Jmax of 5.0 mA cm−2
is
higher than the highest photocurrent density reported in the lit-
erature (to the best of our knowledge) for an unprotected Cu2O
photocathode.
Table 2 lists the highest and average plateau (Jmax and
Jave) current densities determined for morphologically differ-
ent Cu2O photocathodes prepared via anodic, chemical, and
thermal oxidation of copper, and electrochemical reduction of
CuSO4. Jave was determined from several independently pre-
pared samples and the number of samples averaged are lis-
ted (table 2) in the parenthesis. In all cases, the champion
Jmax is significantly higher than the average value. In addition,
samples prepared by using a nominally identical deposition
method yielded large variation in the Jmax value as reflected
in the standard deviations. It is interesting to note that both
Jmax and Jave (5.0 and 3.4 mA cm−2
) from Cu2O photocath-
ode with planar morphology are slightly higher than the best
performing Cu2O photocathode with 1D morphology (4.9 and
3.0 mA cm−2
) i.e. sample NB1. This draws us to the famil-
iar question of why solar cells based on planar structures have
higher efficiencies over 1D nanostructures [98–100]. The main
reasons for the unexpectedly low performance of 1D nano-
structured solar cells are believed to arise from enhanced trap-
mediated carrier recombination and slower transport due to
increased surface area and defect density [105–107]. For semi-
conducting Cu2O which has a short minority diffusion length
(10–100 nm) [43, 49], the ideal morphology which ensures
optimal light absorption and efficient harvesting of the elec-
trons for HER is 1D nanostructure. This follows from the fact
that for a vertically oriented Cu2O nanowire (NW) with good
8
10. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 6. Photoelectrochemical cell depicting Cu2O photocathode and an FTO coated platinum thin film as counter-electrode. A third
electrode Ag/AgCl (saturated) is used the reference electrode (not shown).
Figure 7. (a) J-V curve and (b) J-t curve at an applied bias of 0 V vs RHE in 0.1 M Na2SO4 solution of Cu2O photocathode recorded under
chopped AM 1.5 G simulated sunlight. Cu2O photocathode which exhibits planar (P1) morphology was prepared by electrochemical
reduction of CuSO4 solution and annealed at 550 ◦
C in N2 for 4 h.
electrical contact with the Cu foil, the length of the NW should
be of the order of 3α−1
, where α the absorption coefficient,
and its radius on the order of sum of the diffusion distance (Lp)
and space charge layer thickness (W) to ensure that all the pho-
togenerated electrons reach the surface. Since α−1
at 550 nm
is ca. 1.0 µm for Cu2O [64], majority of the electrons will
recombine before reaching the semiconductor/liquid junction
(SCLJ) for a planar structure with enough thickness to ensure
optimal light absorption. On the other hand, for the Cu2O NW
most of the electrons will reach the semiconductor liquid junc-
tion (SCLJ) provided the radius (r) of the NW ⩽ Lp + W. The
FESEM images show that the diameter of the NB1 nanobeads
and other 1D nanostructures such as NB2, NIN1 and NIN2
are in the 200–400 nm range. Their radii are not commensur-
ate with the length of Lp + W required for optimal collection
of the electrons. In the next section, we present the determin-
ation and analysis of key parameters contributing to the per-
formance of Cu2O photocathode using different electrochem-
ical techniques to gain insight into the mechanistic aspects of
the photocatalytic water splitting.
3.4. Capacitance-voltage profiling
Band bending due to the formation of a in the Schottky junc-
tion formed at the semiconductor-electrolyte interface plays a
key role in determining the photoelectrochemical performance
of a semiconducting film. The photogenerated electron-hole
pairs formed in the space-charge layer are efficiently separated
by the electric field determined by the total extent of band-
bending (i.e. flat band potential Vfb). The flat band potential
can be determined from the capacitance of the space-charge
layer using the Mott-Schottky equation [108]:
1
C2
SC
=
2
eεϵε0NA
(V − Vfb −
kBT
e
) (3)
Where NA is the majority hole carrier density in p-type
semiconducting Cu2O, ε0 is the permittivity of the vacuum,
ε is the dielectric constant of the semiconductor (for Cu2O is
10.26), V is the applied potential, e is the electron charge, kB is
the Boltzmann’s constant, and T is the absolute temperature.
The width (WSC)[109] of the space-charge layer depends on
the applied potential as
WSC =
√
2εϵε0 (V − Vfb)
eNA
(4)
The values of the CSC were calculated from the imaginary
component (Z′′
= 1/2πfCsc) of the impedance, experiment-
ally measured as a function of applied DC potential (V) mod-
ulated by a sinusoidal perturbation potential (±10 mV) at a
frequency (f) of 1 kHz. Figure 8 shows the Mott-Schottky
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11. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 8. Mott-Schottky plots for Cu2O photocathodes of different morphologies (a) 1D nanostructure NB2, and (b) planar P1. Straight
lines are linear fit to the data.
plots for representative Cu2O photocathodes with 1D nano-
structured and planar morphologies. Mott-Schottky plots for
other morphologies fabricated by different deposition meth-
ods are presented in Supplementary figure S3. Negative slopes
of the plots obtained for all the morphologies are character-
istic of p-type semiconductors. The slope of the linear part of
the Mott-Schottky plot was used to calculate NA, the majority
hole carrier density in p-type semiconductors Cu2O. The hole
carrier density values obtained for all the morphologies fabric-
ated by different deposition methods are listed in table 2. Fur-
ther, the flat band potential (Vfb) of the Cu2O photocathodes
was obtained from the intercept to the abscissa of the Mott-
Schottky plots. The Vfb values determined are listed in table 2
and exhibit no significant differences between 1D nanostruc-
tured and planar morphologies. This indicates that band bend-
ing and driving force for the photo-induced electron-hole pairs
to separate in the space charge region are not significantly
affected by nanostructuring.
On the other hand, large variations are observed for NA val-
ues for different morphologies and even among samples with
similar morphology (planar or 1D nanostructure). One reason
for this could be that the Mott-Schottky relation is derived for
a planar electrode and the absolute values of acceptor dens-
ity derived from the use of Eqn (3) may not be strictly accur-
ate [110]. The nanostructured electrodes have higher surface
areas leading to a lower specific capacitance and a larger car-
rier density. Nevertheless, the capacitance-voltage data using
Mott-Schottky equation provide carrier densities under sim-
ilar experimental conditions unadjusted for surface area, and
the carrier density values of the different Cu2O morpholo-
gies obtained in the experiments are identically affected. Other
vital information on the Cu2O photocathode properties such as
the valence and conduction band edge positions can be calcu-
lated from Efb and NA from the equation as follows [101]:
EV = EF + kBTln
NV
NA
(5)
Where EF is the Fermi level which is equal to Efb
(Efb = eVfb), and NV is the effective density of states in the
valence band can be obtained from the equation [111]:
NV =
2(2πm∗
kBT)
3/2
h3
(6)
where the effective mass m∗
of the holes in Cu2O semicon-
ductor is 0.58m0 and m0 is the rest mass of an electron [112].
NV equals 1.11 × 1019
cm−3
for Cu2O. Based on the values
of NV, Efb and e.g. listed in table 2, the valence (Ev) and con-
duction (Ecb) band edge positions of Cu2O photocathodes with
different morphologies prepared by different deposition meth-
ods were calculated and listed in table 2. Normally, for a p-
type semiconductor, the Ev is expected to lie 0.1–0.2 V below
Efb. But for the photocathodes reported here, the Ev ~ Efb for
Cu2O with planar morphology, and further for 1D nanostruc-
tured Cu2O the Ev lie 0.04–0.12 V above the Efb. This anomaly
arises from the high values of the acceptor hole carrier densit-
ies (NA) that cause degeneracy, particularly for the 1D nano-
structured Cu2O photocathodes. The reason for the high NA
may be due to doping of Cu2O by CuO and doping is known
to lead to a relatively thin space-charge layer. Doping of Cu2O
by CuO in these samples is indicated in the optical spectra dis-
played in figure 5.
3.5. Onset potentials
The J − V curves recorded for 1D nanostructured (NB2) and
planar (P2) Cu2O photocathodes under chopped AM 1.5 illu-
mination are shown in figure 9. The J − V curve for P1 is
shown in figure 5(a). The J − V curves for other morpho-
logies fabricated by different deposition methods are presen-
ted in Supplementary figure S4. The onset potentials (Vonset)
reported here were determined from the intersection of the tan-
gents to the rising J − V curve and the baseline corresponding
to the chopped dark current. The values of the Vonset determ-
ined for all the morphologies fabricated by different depos-
ition methods are listed in table 2. The Vonset values (table 2),
determined for all the Cu2O photocathodes of different mor-
phologies, vary within a small voltage range (0.48 V ± 0.04 V)
and exhibit no distinct differences between 1D nanostructured
and planar morphologies.
Ideally, it is desirable to have a photocathode which has a
high anodic Vfb with Vonset close to Vfb with the photocurrent
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12. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 9. J-V curves recorded under chopped AM 1.5 illumination for Cu2O photocathode with different morphologies: (a) 1D
nanostructure NB2, and (b) planar P2. Vonset for NB2 and P2 are 0.55 V and 0.52 V vs RHE respectively.
rising rapidly with applied potential (Vapp) for Vapp > Vfb to
a plateau (Jmax) value. Such a PEC cell would require little
or no external applied potential for water splitting reaction.
The J − V curves shown in figure 9 have photocurrents rising
slowly with the applied potential displaying properties charac-
teristic for a non-ideal and un-optimized photocathode. Con-
trary to the non-ideal behavior of the J − V curves, the Vonset
values listed in table 2 anomalously are close to the Vfb, appar-
ently exhibiting little or no overpotentials. Although the Vonset
values (0.4–0.5 V vs RHE) obtained here are comparable to
the literature values reported for the bare Cu2O photocath-
odes, it is important to emphasize here that the state-of-the-art
Cu2O photocathode fabricated with a conformally coated pro-
tective layer and decorated with cocatalyst has been reported
with Vonset > 1.0 V vs RHE [38].
3.6. Interfacial charge transfer
Electrochemical impedance (EIS) spectra were measured in
the dark and under AM 1.5 G illumination by scanning the
excitation frequency with a sinusoidal perturbation of ±10 mV
potential superimposed on an applied potential of 0.51 V
vs RHE. The procedure used to analyze the EIS spectra is
described in prior work [113, 114]. Figure 10 shows the
Nyquist and Bode plots for 1D nanostructured (NB2) and
planar (P1) photocathodes. The EIS spectra of Cu2O pho-
tocathodes of other morphologies are presented in Supple-
mentary figure S5. Both plots indicate that two processes dom-
inate the impedance spectra and can be reasonably fitted by
equivalent circuit [115, 116] presented at the top panel of
figure 10. The process occurring in the high frequency region
shown in the insets of figure 10 corresponds to interfacial
charge transfer arising from water oxidation in the counter
electrode (Pt film on FTO) of the PEC cell represented by the
parallel combination of charge-transfer resistance (RCE) and
capacitance (CCE) of the circuit elements. The RCE and CCE
values of 19.1 ± 2.6 Ω and (1.1 ± 0.1) × 10−7
F respectively
were not observed to vary, as expected, with the Cu2O pho-
tocathode morphologies used in the PEC measurements and in
addition, they were observed to be unaffected by the dark and
AM 1.5 illumination measurements. The other circuit element
that was also found to be unaffected by the Cu2O photocath-
ode morphologies and experimental conditions (dark and AM
1.5 illumination) is the circuit element, Rs. It has a value of
6.3 ± 0.3 Ω independent of the Cu2O photocathode morpho-
logies used and accounts for the series resistance including the
resistance of the aqueous solution in the PEC cell.
On the other hand, the processes occurring in the inter-
mediate and low frequency region of the EIS spectrum are a
complex combination of charge transport, charge trapping, and
interfacial charge transfer in the semiconductor liquid (SCLJ)
interface which are key to the performance of the device. The
semicircles representing these processes in the Nyquist plot
were analyzed and represented as Rct, the interfacial charge-
transfer in the SCLJ, and listed in table 2 for all morphologies
fabricated by different deposition methods. In the equivalent
circuit, Rct is in parallel combination with capacitance (CSC)
which has contributions from the space charge layer in the
semiconductor and the Helmholtz layer in the electrolyte. The
semicircle representing Rct dominates the Nyquist plot and is
strongly affected by visible light illumination. Rct is much lar-
ger in the dark than under illumination which is suggestive of a
pinned Fermi level in the dark that is unpinned under illumin-
ation. Under illumination, the electron-hole pair generated in
the photoexcitation are separated by the space-charge layer,
and the holes in Cu2O photocathode can flow to the external
circuit. Interestingly, the morphology of the Cu2O photocath-
ode is observed to have a significant effect on the Rct values.
The Rct values under illumination for 1D nanostructured Cu2O
are greater than 2 fold larger than Cu2O with planar morpho-
logy, which implicates the larger density of surface traps in
the nanostructured electrode potentially causing Fermi level
pinning.
The EIS results provide rich information about the pro-
cesses occurring in the system on different time scales. In the
Bode plot, the region above 10 kHz corresponds to charge
transfer reactions at the counter electrode, the mid-frequency
region between 1 Hz and 10 kHz accounts for electron trans-
port in the Cu2O photocathode and interfacial charge trans-
fer reactions, and the low frequency regions corresponding
to frequencies below 1 Hz are related to the diffusion of the
electrolyte. In the low frequency region, the Bode phase plot
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13. Nanotechnology 32 (2021) 374001 L C T Shoute et al
Figure 10. Nyquist (a, b) and Bode (c, d) plots of the EIS spectra for 1D nanostructured NB2 (a, c) and planar P1 (b, d) Cu2O
photocathodes. The red and black lines correspond to EIS spectra measured under AM 1.5 illumination and in the dark respectively.
Equivalent circuit and circuit elements (top panel) used to fit the EIS spectra. Insets: Nyquist plots showing the low Z′
region.
exhibits a prominent peak for both the dark and illuminated
planar P1 Cu2O photocathode, and on the other hand the
dark and illuminated nanostructured NB2 Cu2O photocath-
ode exhibits a weak hump and a prominent peak. The peak in
the Bode phase plot occurs at a frequency close to the charac-
teristic frequency (ω = 1/RctCSC) or characteristic time con-
stant (ζ = 1/ω = RctCSC and ω = 2πf) of the system. For
the dark and illuminated planar P1 photocathode, the charac-
teristic frequencies are 24 Hz and 63 Hz respectively, and the
shift to higher frequencies upon illumination is as expected for
a decrease in the Rct. Interestingly, for the nanostructured NB2
Cu2O photocathode the peak in the Bode phase plot occurs
at a characteristic frequency (ω) of 2.4 Hz, and is unaffected
by illumination. A closer inspection indicates that the peak
lies below 1 Hz and hence can be attributed to the diffusion
processes in the electrolyte and dominates the electron trans-
port in the Cu2O photocathode and interfacial charge trans-
fer reactions which in turn appear as a weak hump at a fre-
quency of ~1 Hz in the Bode phase plot. In the high frequency
region, the Bode phase plot has a single peak with character-
istic frequency of 1.25 MHz which is unaffected by the dark
and light illumination as well as the morphology of the Cu2O
photocathode because it represents the processes occurring in
the Pt counter electrode, i.e. water oxidation.
Cu2O exhibits very different transport and interfa-
cial recombination parameters depending on the syn-
thesis technique. For instance, hole mobilities higher than
100 cm2
V−1
s−1
have been measured for Cu2O films
formed by thermal oxidation while electrochemically depos-
ited Cu2O films have been reported to have mobilities of
~5 × 10–3
cm2
V−1
s−1
[117, 118]. Such large differences
in transport parameters and the large differences in acceptor
density and interfacial charge transfer resistance found here
(see table 2) would normally be expected to result in extremely
strong morphology-dependent photoelectrochemical perform-
ance where certain morphologies optimized transport and
recombination processes better than others. The absence of
a strong correlation between morphology and photoelec-
trochemical performance, and the observation of a cluster-
ing of photocurrent density and onset potential values in a
tight range, merits some discussion. The likely possibility
is that a dominant bulk phenomenon that is morphology-
independent is the rate-limiting step in the photoelectrochem-
ical performance. This bulk phenomenon could be the intrinsic
12
14. Nanotechnology 32 (2021) 374001 L C T Shoute et al
defect structure of Cu2O. Herein, we note that Cu2O is a com-
pensated material with an acceptor-type deep level situated
0.54 eV above the valence band that is compensated with a
donor-type level situated 0.92 eV below the conduction band
[119]. The compensation ratio NA/ND, is typically close to
1 and almost never higher than 10 [120, 121]. Two direct
consequences of such an intrinsic defect structure are high
minority carrier injection from the electrolyte into Cu2O and
Shockley-Read-Hall (SRH) recombination in the bulk medi-
ated by deep level traps. Both of these aforementioned pro-
cesses would place upper limits on the achievable photocurrent
density.
4. Conclusions
The availability of a simple and low-cost method to deposit
Cu2O thin films of any desired morphology on a substrate
could immensely help in accelerating the development of
a stable and effective Cu2O photocatalyst for solar-to-fuel
conversion. Here, we have presented anodic, chemical, and
thermal oxidation of copper, and electrochemical reduction of
CuSO4 to deposit a wide variety of morphologically differ-
ent Cu2O thin films on Cu foils. Of these methods, anodiza-
tion is the most versatile and has distinct advantages over oth-
ers because it provides the ability to control the morphology
and thickness of the deposited Cu2O thin film by simply vary-
ing the experimental conditions such as alkali concentration,
applied potential, time, and temperature either independently
or in combinations. The photocatalytic properties of 1D nano-
structures and planar Cu2O thin films used as photocathodes
without protective coating and cocatalyst have been determ-
ined and compared. They have similar values of e.g., Ev, Ec,
Vfb, Vonset, and Jmax. The Vonset values are close to the Vfb
values and are very cathodic compared to the state-of-the-
art Cu2O photocathodes. Distinct differences were observed
between the two morphologies (1D vs planar) in the values of
NA (acceptor density) and Rct (interfacial charge transfer res-
istance). The concentration of holes in 1D nanostructures is
10–1000-fold larger and the interfacial charge transfer resist-
ance is 2-fold larger compared to the planar structures. These
differences intriguingly have no apparent effect on the max-
imum photocurrent density (Jmax) values. The photocurrent
densities reported here are among the highest values repor-
ted in the literature for bare Cu2O photocathodes. The path
to stable and efficient Cu2O based photoelectrochemical cells
for solar-to-fuel conversion lies in finding improved methods
for surface passivation, incorporation of cocatalyst, deposition
with controlled morphologies, size and thickness of Cu2O mit-
igating the competing requirements of light absorption, charge
recombination, and charge separation.
Acknowledgments
The authors thank NSERC, CMC Microsystems, Future
Energy Systems, and CFI for financial support, and
NRC-NINT and the University of Alberta nanoFAB for access
to characterization facilities.
ORCID iDs
Pawan Kumar https://orcid.org/0000-0003-2804-9298
Karthik Shankar https://orcid.org/0000-0001-7347-3333
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