The document describes a study where V2C MXene nanosheets were synergistically coupled with hypophosphite-intercalated FeNi layered double hydroxide (LDH) nanosheets to create an electrocatalyst for the oxygen evolution reaction (OER). The hybrid material, denoted H2PO-2/FeNi-LDH-V2C, was synthesized via a hydrothermal method. Electrochemical tests showed the material had excellent OER performance in 1.0 M KOH electrolyte, with an overpotential of 250 mV at 10 mA/cm2 and a small Tafel slope of 46.5 mV/dec. The strong interaction and electronic coupling between the
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
This document summarizes research on using graphene nanosheets as electrode materials for supercapacitors. The researchers investigated the effect of ion size and properties on the pseudocapacitance and double layer capacitance of graphene electrodes in different electrolytes. They found that the electrode showed better double layer characteristics in NaOH electrolyte compared to LiBr electrolyte. This was attributed to the smaller size and higher mobility of ions in NaOH, allowing more ions to be stored on the graphene surface. Electrochemical tests showed the electrode exhibited both double layer capacitance and pseudocapacitance, with pseudocapacitance contributing more in LiBr electrolyte. The morphology of the graphene nanosheets formed a continuous porous network suitable for
This document summarizes research investigating graphene/cerium oxide nanoparticles as an electrode material for supercapacitors. Scanning electron microscopy images showed the layered structure of graphene with cerium oxide nanoparticles dispersed across the surface. Electrochemical testing found the electrode achieved a maximum specific capacitance of 11.09 F g−1 in 3 M NaCl electrolyte. Charge/discharge cycling showed good reversibility and 37% increase in capacitance after 500 cycles. The graphene/cerium oxide composite performed better than cerium oxide alone due to graphene's conductivity and the formation of an electrical double layer at the electrode interface.
This document summarizes a study that developed a new hybrid electrocatalyst for oxygen evolution reaction (OER) by anchoring cobalt oxide (Co3O4) nanoparticles onto titanium carbide (Ti3C2) MXene nanosheets. The Co3O4/MXene hybrid (denoted CM) was synthesized using a solvothermal method. Characterization showed uniform distribution of small Co3O4 nanoparticles on MXene nanosheets. Electrochemical tests found the CM catalyst achieved overpotential of 300 mV at 10 mA/cm2 for OER, which was lower than Co3O4 or MXene alone. The enhanced performance was attributed to strong interactions and charge transfer between
MXene supported CoxAy (A ¼ OH, P, Se), first OER-converted.docxJamimtiaz3
This document describes a study investigating MXene-supported cobalt phosphide (CoP) and cobalt selenide (Co7Se8) electrocatalysts for overall water splitting. Large, exfoliated MXene sheets provide a conductive support for CoP and Co7Se8, enhancing electrocatalytic performance. CoP/MXene shows high oxygen evolution reaction activity with low overpotential. A CoP/MXene//CoP/MXene bifunctional electrode demonstrates highly stable and efficient overall water splitting, outperforming an IrO2/C//Pt/C benchmark. The role of anion oxidation in catalyst activity and stability is explored, finding surface oxidation of CoP/MX
1) The document investigates the effect of cation and anion sizes on the charge storage capabilities of graphite nanosheets as electrode materials for electrochemical double layer capacitors.
2) Scanning electron microscope images confirm the layered structure of the graphite nanosheets used, which are 12nm thick with 3.36 Angstrom spacing between layers.
3) Electrochemical measurements using cyclic voltammetry and impedance spectroscopy indicate that the graphite electrodes exhibited better charge storage and delivery in 3M NaCl electrolyte compared to NaOH and KOH electrolytes, due to the smaller ion sizes matching better with the graphite structure.
This document describes research on fabricating a novel graphene electrode embedded with zirconium dioxide nanoparticles for electrochemical capacitors. The electrode showed a maximum specific capacitance of 11.84 F g−1. SEM images showed ions redepositing as agglomerates on the electrode surface after one charge/discharge cycle, accompanied by a decrease in surface area. Electrochemical tests confirmed pseudocapacitive behavior and low resistance. The research aims to investigate how electrolyte ion and active material redeposition affects the electrode's charge distribution ability.
The document describes a method for synthesizing NiFe2O4 nanoparticles fully anchored within a carbon network using a facile pyrolysis technique. Key points:
- NiFe2O4 nanoparticles were synthesized within a carbon network using a polyol-assisted pyrolysis method without an external carbon source.
- Characterization with SEM and TEM showed the NiFe2O4 nanoparticles were uniformly distributed and fully embedded within the carbon network.
- Electrochemical testing showed the NiFe2O4/C anode delivered a reversible capacity of 381.8 mAh/g after 100 cycles at 1C rates and 263.7 mAh/g at a high rate of 5C, demonstrating enhanced performance over bare
Few-layered MoSe2 nanosheets an an advanced...suresh kannan
This document summarizes the synthesis and characterization of few-layered molybdenum diselenide (MoSe2) nanosheets as an electrode material for supercapacitors. The MoSe2 nanosheets were synthesized using a facile hydrothermal method. Characterization with Raman spectroscopy, TEM, and XRD confirmed the formation of few-layered nanosheets. Electrochemical testing of the MoSe2 electrode in a symmetric cell configuration showed a maximum specific capacitance of 198.9 F g−1 and capacitance retention of approximately 75% after 10,000 cycles, indicating potential for supercapacitor applications.
10.1016-j.mssp.2014.10.034-Graphene nanosheets as electrode materials for sup...Mahdi Robat Sarpoushi
This document summarizes research on using graphene nanosheets as electrode materials for supercapacitors. The researchers investigated the effect of ion size and properties on the pseudocapacitance and double layer capacitance of graphene electrodes in different electrolytes. They found that the electrode showed better double layer characteristics in NaOH electrolyte compared to LiBr electrolyte. This was attributed to the smaller size and higher mobility of ions in NaOH, allowing more ions to be stored on the graphene surface. Electrochemical tests showed the electrode exhibited both double layer capacitance and pseudocapacitance, with pseudocapacitance contributing more in LiBr electrolyte. The morphology of the graphene nanosheets formed a continuous porous network suitable for
This document summarizes research investigating graphene/cerium oxide nanoparticles as an electrode material for supercapacitors. Scanning electron microscopy images showed the layered structure of graphene with cerium oxide nanoparticles dispersed across the surface. Electrochemical testing found the electrode achieved a maximum specific capacitance of 11.09 F g−1 in 3 M NaCl electrolyte. Charge/discharge cycling showed good reversibility and 37% increase in capacitance after 500 cycles. The graphene/cerium oxide composite performed better than cerium oxide alone due to graphene's conductivity and the formation of an electrical double layer at the electrode interface.
This document summarizes a study that developed a new hybrid electrocatalyst for oxygen evolution reaction (OER) by anchoring cobalt oxide (Co3O4) nanoparticles onto titanium carbide (Ti3C2) MXene nanosheets. The Co3O4/MXene hybrid (denoted CM) was synthesized using a solvothermal method. Characterization showed uniform distribution of small Co3O4 nanoparticles on MXene nanosheets. Electrochemical tests found the CM catalyst achieved overpotential of 300 mV at 10 mA/cm2 for OER, which was lower than Co3O4 or MXene alone. The enhanced performance was attributed to strong interactions and charge transfer between
MXene supported CoxAy (A ¼ OH, P, Se), first OER-converted.docxJamimtiaz3
This document describes a study investigating MXene-supported cobalt phosphide (CoP) and cobalt selenide (Co7Se8) electrocatalysts for overall water splitting. Large, exfoliated MXene sheets provide a conductive support for CoP and Co7Se8, enhancing electrocatalytic performance. CoP/MXene shows high oxygen evolution reaction activity with low overpotential. A CoP/MXene//CoP/MXene bifunctional electrode demonstrates highly stable and efficient overall water splitting, outperforming an IrO2/C//Pt/C benchmark. The role of anion oxidation in catalyst activity and stability is explored, finding surface oxidation of CoP/MX
1) The document investigates the effect of cation and anion sizes on the charge storage capabilities of graphite nanosheets as electrode materials for electrochemical double layer capacitors.
2) Scanning electron microscope images confirm the layered structure of the graphite nanosheets used, which are 12nm thick with 3.36 Angstrom spacing between layers.
3) Electrochemical measurements using cyclic voltammetry and impedance spectroscopy indicate that the graphite electrodes exhibited better charge storage and delivery in 3M NaCl electrolyte compared to NaOH and KOH electrolytes, due to the smaller ion sizes matching better with the graphite structure.
This document describes research on fabricating a novel graphene electrode embedded with zirconium dioxide nanoparticles for electrochemical capacitors. The electrode showed a maximum specific capacitance of 11.84 F g−1. SEM images showed ions redepositing as agglomerates on the electrode surface after one charge/discharge cycle, accompanied by a decrease in surface area. Electrochemical tests confirmed pseudocapacitive behavior and low resistance. The research aims to investigate how electrolyte ion and active material redeposition affects the electrode's charge distribution ability.
The document describes a method for synthesizing NiFe2O4 nanoparticles fully anchored within a carbon network using a facile pyrolysis technique. Key points:
- NiFe2O4 nanoparticles were synthesized within a carbon network using a polyol-assisted pyrolysis method without an external carbon source.
- Characterization with SEM and TEM showed the NiFe2O4 nanoparticles were uniformly distributed and fully embedded within the carbon network.
- Electrochemical testing showed the NiFe2O4/C anode delivered a reversible capacity of 381.8 mAh/g after 100 cycles at 1C rates and 263.7 mAh/g at a high rate of 5C, demonstrating enhanced performance over bare
Few-layered MoSe2 nanosheets an an advanced...suresh kannan
This document summarizes the synthesis and characterization of few-layered molybdenum diselenide (MoSe2) nanosheets as an electrode material for supercapacitors. The MoSe2 nanosheets were synthesized using a facile hydrothermal method. Characterization with Raman spectroscopy, TEM, and XRD confirmed the formation of few-layered nanosheets. Electrochemical testing of the MoSe2 electrode in a symmetric cell configuration showed a maximum specific capacitance of 198.9 F g−1 and capacitance retention of approximately 75% after 10,000 cycles, indicating potential for supercapacitor applications.
Depositacion electroforetica dentro de campos electricos moduladosMario ML
This document reviews electrophoretic deposition (EPD) under modulated electric fields such as pulsed direct current (PDC) and alternating current (AC). Classical EPD uses continuous direct current which can lead to issues depositing from aqueous suspensions due to water electrolysis. Modulated electric fields can reduce electrolysis and produce more uniform coatings. PDC and AC offer advantages over continuous DC like reducing bubble formation and particle aggregation. While deposition rates may decrease under modulated fields, they allow for depositing biochemical and biological materials in more active states. The document discusses EPD mechanisms and modulated field types, and their applications including in biotechnology.
The project will focus on synthesis of hexagonal structured pure phases of compositions: BaM1/3Ti2/3O3-δ and BaM1/6Ti5/6O3-δ, where M= Sc, In and Fe via different methods such as Solid state sintering and wet chemical route. The ultimate goal is to finding structure – functionality relationships within these proton and mixed conducting systems. A substantial effort will focus on search for and fabrication of new materials although the main part of the work will concentrate on detailed structural characterisation (rietveld refinement), impedance spectroscopy, infrared spectroscopy and thermogravimetric analysis.
Oxidized multi walled carbon nanotubes for improving the electrocatalytic act...Iranian Chemical Society
In the present paper, the use of a novel carbon paste electrode modified by 7,8-dihydroxy-3,3,6-trimethyl-3,4-dihydrodibenzo[b,d]furan-1(2H)-one (DTD) and oxidized multi-walled carbon nanotubes (OCNTs) is described for determination of levodopa (LD), acetaminophen (AC) and tryptophan (Trp) by a simple and rapid method. At first, the electrochemical behavior of DTD is studied, then, the mediated oxidation of LD at the modified electrode is investigated. At the optimum pH of 7.4, the oxidation of LD occurs at a potential about 330 mV less positive than that of an unmodified carbon paste electrode. Based on differential pulse voltammetry (DPV), the oxidation current of LD exhibits a linear range between 1.0 and 2000.0 μM of LD with a detection limit (3σ) of 0.36 μM. DPV was also used for simultaneous determination of LD, AC and Trp at the modified electrode. Finally, the proposed electrochemical sensor was used for determinations of these substances in human serum sample.
This document provides background on electrodialytic water splitting technology. The process uses bipolar ion exchange membranes along with cation and anion exchange membranes to convert water soluble salts into their corresponding acids and bases when a direct current is applied. The process is energy efficient as it does not involve electrochemical transformations. The key components and operating principles are described, including the role of the bipolar membrane in splitting water and generating hydrogen and hydroxide ions. Design considerations for optimizing the process such as current density, membrane area, and energy requirements are also discussed.
10.1016-j.mssp.2015.01.037-Electrochemical investigation of graphene_nanoporo...Mahdi Robat Sarpoushi
This study investigated the effect of mixing graphene nanosheets and nanoporous carbon black on the surface morphology and electrochemical performance of electrodes prepared for supercapacitors. Electrodes containing 80% nanoporous carbon black, 10% graphene nanosheets, and 10% PTFE binder showed the highest specific capacitance of 10.22 F/g. The addition of nanoporous carbon black increased the proportion of outer charge stored on the electrode relative to the total charge stored, indicating higher current response and voltage reversal at the end potentials. Scanning electron microscopy images showed that adding nanoporous carbon black particles arranged the graphene nanosheets in different directions, increasing the specific surface area and changing diffusion characteristics to improve capacitance and reversibility
This document summarizes a study investigating the effects of morphology and pore size distribution on the physicochemical properties of graphite nanosheets/nanoporous carbon black/cerium oxide nanoparticle electrodes for electrochemical capacitors. Electrodes with different compositions of these materials were fabricated and their surfaces and pores were characterized using SEM. Electrochemical testing showed that electrodes with a mixture of materials exhibited the highest capacitance due to having macro, micro, and nano pores that increased the accessible surface area. Introducing cerium oxide nanoparticles created micro pores, while carbon black particles created macro pores and rearranged the graphite nanosheets. This nanoporous structure resulted in an electrode with the highest capacitance of 16.2 F/
This document discusses the structural, vibrational, and microwave dielectric properties of double perovskite ceramics with the formula Ba2Zn1-xCaxWO6 (x = 0-0.4). The samples were sintered at temperatures between 1300-1400°C and characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The analysis showed that the tolerance factor and temperature coefficient of resonant frequency decreased with increasing calcium content. Microwave dielectric properties such as relative permittivity and quality factor were measured and found to vary with sintering temperature and calcium concentration.
1) The study investigated the effect of adding zirconium oxide nanoparticles to carbon black electrode materials on surface morphology and electrochemical performance.
2) Scanning electron microscopy showed that adding nanoparticles partially filled gaps between carbon black particles, increasing the specific surface area available for charge storage.
3) Electrochemical analysis found that increasing nanoparticle content initially increased total charge storage due to higher surface area and pseudocapacitive charge storage, but further increases reduced performance due to higher electrode resistance.
Here's an abstract for the presentation titled "Integration of Mxene Supercapacitor and Li-ion Battery"
---
**Abstract**
The integration of Mxene supercapacitors and Li-ion batteries represents a promising advancement in energy storage technology, combining the high power density of supercapacitors with the high energy density of Li-ion batteries. This presentation explores the working principles, challenges, and potential solutions for enhancing the performance of these hybrid systems.
Mxenes, a class of two-dimensional materials comprising transition metal carbides, nitrides, and carbonitrides, exhibit unique properties such as high electrical conductivity, large specific surface area, and tunable surface chemistry, making them suitable for supercapacitor applications. However, issues such as aggregation, hydrophilicity, and synthesis challenges must be addressed to fully leverage their potential.
The presentation delves into various approaches to overcome the energy density limitations of traditional supercapacitors, including the use of asymmetric supercapacitors, graphene hybrids, and nanostructured materials. It also highlights the synthesis processes for Mxenes, comparing methods like hydrofluoric acid etching, fluoride salt etching, molten salt etching, ionic liquid etching, and electrochemical etching, along with their respective advantages and disadvantages.
A detailed comparison of Mxene supercapacitors, Li-ion batteries, and hybrid systems is provided, focusing on parameters such as capacitance, energy density, power density, cycle life, conductivity, and structural stability. The integration challenges, including electrolyte compatibility, electrode balancing, and safety concerns, are discussed, emphasizing the need for efficient and scalable synthesis techniques and a deeper understanding of charge storage mechanisms.
Finally, the future potential of Mxene-carbon hybrids for supercapacitors is explored, outlining prospective directions for research and development in this field. The findings presented underscore the significant role of Mxene-based hybrid systems in advancing energy storage solutions for applications requiring high power and energy density, such as portable electronics and electric vehicles.
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.
This document summarizes the theoretical and practical considerations for designing a copper electrowinning plant. Theoretically, the process is governed by Faraday's law, the Nernst equation, and the Butler-Volmer equation. These equations relate current, potential, and concentration to the rate of the copper electrodeposition reaction. Practically, design considerations include plant layout, cell dimensions, materials of construction, operating cycles, and ancillary equipment. Both theoretical fundamentals and practical requirements must be understood to optimize the design for cost, schedule and product quality.
Computational screening of two dimensional materials for hydrogen evolution reactions
This presentation discusses screening 2D materials computationally for hydrogen evolution reactions. The document outlines the research methodology which involves searching potential 2D materials, assessing their dynamical stability, electronic properties, band edge diagrams, Gibbs free energy calculations, and optical properties. Several potential 2D materials are listed along with their bandgaps and charge mobilities. The goals are to reduce the bandgap of photoelectrodes, increase charge carrier mobility for photocatalysis, optimize Gibbs free energy values, and increase hydrogen adsorption efficiency.
Electrolyte Solutions for Rechargeable Li-Ion Batteries Based on Fluorinated ...AMAL THOMAS
High voltage lithium ion batteries have been a focus in the current energy storage research due to their
potential application as high energy density batteries for electric vehicles. With more energy stored in
a system with the same weight and volume, the impact of battery fabrication and its utilization on the
environment will be minimized .Electrolyte solutions based on fluorinated solvents were studied in
high-voltage Li-ion cells using lithium as the anode has a great enhancement over conventional
electrolyte and Li1.2Mn0.56Co0.08Ni0.16O2 as the cathode provides excellent voltage stability on the 5.0
V at both ambient and elevated temperatures. Performance can be reach peak by replacing convectional
alky carbonate solvents in electrolyte solution by fluorinated cosolvents. Fluorinated electrolyte
solution act as a buffering surface film which is highly reactive electrophilic alkyl carbonates, from
continuous detrimental reactions with solution species. Excellent cyclic performance was recorded in
solution containing fluorinated solvents. The extraordinary electrochemical stability of this electrolyte
solution makes it a suitable candidate for other high-voltage cathode materials.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
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,
So far only a limited number of publications have been
concerned with the study of the mixed alkali effect in
glasses with the former TeO2. To our knowledge all were
focused on Li2O–Na2O–TeO2 glasses. The importance
of studying such a phenomenon in TeO2 glasses is due to
many industrial and technological applications concerning
this type. In the present work five different glass samples
of the system (20-x)K2O.xNa2O.80TeO2 were
selected for the present study, here x=0, 5, 10, 15 and 20
mol%. Bulk density and infrared absorption spectroscopy
were measured at room temperature. Quantitative
evaluation of the infrared absorption spectra showed that
the molecular groups were affected by changing the type
of the nearest neighbour alkali species. AC and dc isothermal
electrical conductivity were measured in the temperature
range 300–600 K and in the frequency range
0–100 kHz. Electrical parameters such as dielectric constant,
loss factor and conductivity were extracted from
these experiments and show mixed alkali effect. The glass
transition temperature was obtained from DTA as well
as from the dc electrical conductivity with a minimum
at Tg=485 K for x=10 mol%. The present results were
discussed in the light of ionic diffusion and interchange
transport mechanism of conduction along with structure
in TeO2 based glasses.
This document summarizes an experiment studying the origins of large voltage hysteresis in metal fluoride lithium-ion battery conversion electrodes. Specifically, it examines iron fluoride (FeF3) as a model system using in situ X-ray absorption spectroscopy, transmission electron microscopy, density functional theory calculations, and galvanostatic intermittent titration technique. The results reveal that the phase evolution during charging and discharging is actually symmetrical, with the same intermediate phases forming. However, the spatial distribution of the electrochemically active phases differs due to kinetic effects. This leads to differences in ohmic voltage drop, reaction overpotential, and compositional inhomogeneity, causing the large observed voltage hysteresis which is kinetic rather than thermodynamic in nature
This document summarizes research on using electrodeposited manganese dioxide (MnO2) coatings on porous carbon substrates for capacitive deionization (CDI) applications. Two carbon substrates with different surface areas and morphologies were coated with MnO2 using galvanostatic and cyclic voltammetric deposition. Characterization of the coated electrodes found mixed MnO2 phases present. Testing in half-cell configurations showed that maximum ion uptake per mass was not necessarily optimal for practical CDI applications, where performance per electrode area is more important. The results suggest the structure and deposition method can impact how effectively the electrode volume participates in ion removal reactions.
Double layer energy storage in graphene a studytshankar20134
This document summarizes research on using graphene for energy storage in electrochemical double layer capacitors (EDLCs). Graphene has potential as an EDLC electrode material due to its high surface area and electrical conductivity. Studies have found specific capacitances of graphene electrodes ranging from tens of F/g to over 1000 F/g depending on preparation methods and electrolytes. However, graphene sheets tend to restack reducing surface area availability. Methods to prevent restacking like adding metal oxides or curving graphene sheets have improved capacitance. Research is optimizing graphene properties and composites to enhance energy and power densities for applications requiring high power such as filtering alternating current.
6th International Conference on Machine Learning & Applications (CMLA 2024)ClaraZara1
6th International Conference on Machine Learning & Applications (CMLA 2024) will provide an excellent international forum for sharing knowledge and results in theory, methodology and applications of on Machine Learning & Applications.
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Depositacion electroforetica dentro de campos electricos moduladosMario ML
This document reviews electrophoretic deposition (EPD) under modulated electric fields such as pulsed direct current (PDC) and alternating current (AC). Classical EPD uses continuous direct current which can lead to issues depositing from aqueous suspensions due to water electrolysis. Modulated electric fields can reduce electrolysis and produce more uniform coatings. PDC and AC offer advantages over continuous DC like reducing bubble formation and particle aggregation. While deposition rates may decrease under modulated fields, they allow for depositing biochemical and biological materials in more active states. The document discusses EPD mechanisms and modulated field types, and their applications including in biotechnology.
The project will focus on synthesis of hexagonal structured pure phases of compositions: BaM1/3Ti2/3O3-δ and BaM1/6Ti5/6O3-δ, where M= Sc, In and Fe via different methods such as Solid state sintering and wet chemical route. The ultimate goal is to finding structure – functionality relationships within these proton and mixed conducting systems. A substantial effort will focus on search for and fabrication of new materials although the main part of the work will concentrate on detailed structural characterisation (rietveld refinement), impedance spectroscopy, infrared spectroscopy and thermogravimetric analysis.
Oxidized multi walled carbon nanotubes for improving the electrocatalytic act...Iranian Chemical Society
In the present paper, the use of a novel carbon paste electrode modified by 7,8-dihydroxy-3,3,6-trimethyl-3,4-dihydrodibenzo[b,d]furan-1(2H)-one (DTD) and oxidized multi-walled carbon nanotubes (OCNTs) is described for determination of levodopa (LD), acetaminophen (AC) and tryptophan (Trp) by a simple and rapid method. At first, the electrochemical behavior of DTD is studied, then, the mediated oxidation of LD at the modified electrode is investigated. At the optimum pH of 7.4, the oxidation of LD occurs at a potential about 330 mV less positive than that of an unmodified carbon paste electrode. Based on differential pulse voltammetry (DPV), the oxidation current of LD exhibits a linear range between 1.0 and 2000.0 μM of LD with a detection limit (3σ) of 0.36 μM. DPV was also used for simultaneous determination of LD, AC and Trp at the modified electrode. Finally, the proposed electrochemical sensor was used for determinations of these substances in human serum sample.
This document provides background on electrodialytic water splitting technology. The process uses bipolar ion exchange membranes along with cation and anion exchange membranes to convert water soluble salts into their corresponding acids and bases when a direct current is applied. The process is energy efficient as it does not involve electrochemical transformations. The key components and operating principles are described, including the role of the bipolar membrane in splitting water and generating hydrogen and hydroxide ions. Design considerations for optimizing the process such as current density, membrane area, and energy requirements are also discussed.
10.1016-j.mssp.2015.01.037-Electrochemical investigation of graphene_nanoporo...Mahdi Robat Sarpoushi
This study investigated the effect of mixing graphene nanosheets and nanoporous carbon black on the surface morphology and electrochemical performance of electrodes prepared for supercapacitors. Electrodes containing 80% nanoporous carbon black, 10% graphene nanosheets, and 10% PTFE binder showed the highest specific capacitance of 10.22 F/g. The addition of nanoporous carbon black increased the proportion of outer charge stored on the electrode relative to the total charge stored, indicating higher current response and voltage reversal at the end potentials. Scanning electron microscopy images showed that adding nanoporous carbon black particles arranged the graphene nanosheets in different directions, increasing the specific surface area and changing diffusion characteristics to improve capacitance and reversibility
This document summarizes a study investigating the effects of morphology and pore size distribution on the physicochemical properties of graphite nanosheets/nanoporous carbon black/cerium oxide nanoparticle electrodes for electrochemical capacitors. Electrodes with different compositions of these materials were fabricated and their surfaces and pores were characterized using SEM. Electrochemical testing showed that electrodes with a mixture of materials exhibited the highest capacitance due to having macro, micro, and nano pores that increased the accessible surface area. Introducing cerium oxide nanoparticles created micro pores, while carbon black particles created macro pores and rearranged the graphite nanosheets. This nanoporous structure resulted in an electrode with the highest capacitance of 16.2 F/
This document discusses the structural, vibrational, and microwave dielectric properties of double perovskite ceramics with the formula Ba2Zn1-xCaxWO6 (x = 0-0.4). The samples were sintered at temperatures between 1300-1400°C and characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The analysis showed that the tolerance factor and temperature coefficient of resonant frequency decreased with increasing calcium content. Microwave dielectric properties such as relative permittivity and quality factor were measured and found to vary with sintering temperature and calcium concentration.
1) The study investigated the effect of adding zirconium oxide nanoparticles to carbon black electrode materials on surface morphology and electrochemical performance.
2) Scanning electron microscopy showed that adding nanoparticles partially filled gaps between carbon black particles, increasing the specific surface area available for charge storage.
3) Electrochemical analysis found that increasing nanoparticle content initially increased total charge storage due to higher surface area and pseudocapacitive charge storage, but further increases reduced performance due to higher electrode resistance.
Here's an abstract for the presentation titled "Integration of Mxene Supercapacitor and Li-ion Battery"
---
**Abstract**
The integration of Mxene supercapacitors and Li-ion batteries represents a promising advancement in energy storage technology, combining the high power density of supercapacitors with the high energy density of Li-ion batteries. This presentation explores the working principles, challenges, and potential solutions for enhancing the performance of these hybrid systems.
Mxenes, a class of two-dimensional materials comprising transition metal carbides, nitrides, and carbonitrides, exhibit unique properties such as high electrical conductivity, large specific surface area, and tunable surface chemistry, making them suitable for supercapacitor applications. However, issues such as aggregation, hydrophilicity, and synthesis challenges must be addressed to fully leverage their potential.
The presentation delves into various approaches to overcome the energy density limitations of traditional supercapacitors, including the use of asymmetric supercapacitors, graphene hybrids, and nanostructured materials. It also highlights the synthesis processes for Mxenes, comparing methods like hydrofluoric acid etching, fluoride salt etching, molten salt etching, ionic liquid etching, and electrochemical etching, along with their respective advantages and disadvantages.
A detailed comparison of Mxene supercapacitors, Li-ion batteries, and hybrid systems is provided, focusing on parameters such as capacitance, energy density, power density, cycle life, conductivity, and structural stability. The integration challenges, including electrolyte compatibility, electrode balancing, and safety concerns, are discussed, emphasizing the need for efficient and scalable synthesis techniques and a deeper understanding of charge storage mechanisms.
Finally, the future potential of Mxene-carbon hybrids for supercapacitors is explored, outlining prospective directions for research and development in this field. The findings presented underscore the significant role of Mxene-based hybrid systems in advancing energy storage solutions for applications requiring high power and energy density, such as portable electronics and electric vehicles.
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.
This document summarizes the theoretical and practical considerations for designing a copper electrowinning plant. Theoretically, the process is governed by Faraday's law, the Nernst equation, and the Butler-Volmer equation. These equations relate current, potential, and concentration to the rate of the copper electrodeposition reaction. Practically, design considerations include plant layout, cell dimensions, materials of construction, operating cycles, and ancillary equipment. Both theoretical fundamentals and practical requirements must be understood to optimize the design for cost, schedule and product quality.
Computational screening of two dimensional materials for hydrogen evolution reactions
This presentation discusses screening 2D materials computationally for hydrogen evolution reactions. The document outlines the research methodology which involves searching potential 2D materials, assessing their dynamical stability, electronic properties, band edge diagrams, Gibbs free energy calculations, and optical properties. Several potential 2D materials are listed along with their bandgaps and charge mobilities. The goals are to reduce the bandgap of photoelectrodes, increase charge carrier mobility for photocatalysis, optimize Gibbs free energy values, and increase hydrogen adsorption efficiency.
Electrolyte Solutions for Rechargeable Li-Ion Batteries Based on Fluorinated ...AMAL THOMAS
High voltage lithium ion batteries have been a focus in the current energy storage research due to their
potential application as high energy density batteries for electric vehicles. With more energy stored in
a system with the same weight and volume, the impact of battery fabrication and its utilization on the
environment will be minimized .Electrolyte solutions based on fluorinated solvents were studied in
high-voltage Li-ion cells using lithium as the anode has a great enhancement over conventional
electrolyte and Li1.2Mn0.56Co0.08Ni0.16O2 as the cathode provides excellent voltage stability on the 5.0
V at both ambient and elevated temperatures. Performance can be reach peak by replacing convectional
alky carbonate solvents in electrolyte solution by fluorinated cosolvents. Fluorinated electrolyte
solution act as a buffering surface film which is highly reactive electrophilic alkyl carbonates, from
continuous detrimental reactions with solution species. Excellent cyclic performance was recorded in
solution containing fluorinated solvents. The extraordinary electrochemical stability of this electrolyte
solution makes it a suitable candidate for other high-voltage cathode materials.
Effect of morphology on the photoelectrochemical performance of nanostructure...Pawan Kumar
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.
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So far only a limited number of publications have been
concerned with the study of the mixed alkali effect in
glasses with the former TeO2. To our knowledge all were
focused on Li2O–Na2O–TeO2 glasses. The importance
of studying such a phenomenon in TeO2 glasses is due to
many industrial and technological applications concerning
this type. In the present work five different glass samples
of the system (20-x)K2O.xNa2O.80TeO2 were
selected for the present study, here x=0, 5, 10, 15 and 20
mol%. Bulk density and infrared absorption spectroscopy
were measured at room temperature. Quantitative
evaluation of the infrared absorption spectra showed that
the molecular groups were affected by changing the type
of the nearest neighbour alkali species. AC and dc isothermal
electrical conductivity were measured in the temperature
range 300–600 K and in the frequency range
0–100 kHz. Electrical parameters such as dielectric constant,
loss factor and conductivity were extracted from
these experiments and show mixed alkali effect. The glass
transition temperature was obtained from DTA as well
as from the dc electrical conductivity with a minimum
at Tg=485 K for x=10 mol%. The present results were
discussed in the light of ionic diffusion and interchange
transport mechanism of conduction along with structure
in TeO2 based glasses.
This document summarizes an experiment studying the origins of large voltage hysteresis in metal fluoride lithium-ion battery conversion electrodes. Specifically, it examines iron fluoride (FeF3) as a model system using in situ X-ray absorption spectroscopy, transmission electron microscopy, density functional theory calculations, and galvanostatic intermittent titration technique. The results reveal that the phase evolution during charging and discharging is actually symmetrical, with the same intermediate phases forming. However, the spatial distribution of the electrochemically active phases differs due to kinetic effects. This leads to differences in ohmic voltage drop, reaction overpotential, and compositional inhomogeneity, causing the large observed voltage hysteresis which is kinetic rather than thermodynamic in nature
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Car accident rates have increased in recent years, resulting in losses in human lives, properties, and other financial costs. An embedded machine learning-based system is developed to address this critical issue. The system can monitor road conditions, detect driving patterns, and identify aggressive driving behaviors. The system is based on neural networks trained on a comprehensive dataset of driving events, driving styles, and road conditions. The system effectively detects potential risks and helps mitigate the frequency and impact of accidents. The primary goal is to ensure the safety of drivers and vehicles. Collecting data involved gathering information on three key road events: normal street and normal drive, speed bumps, circular yellow speed bumps, and three aggressive driving actions: sudden start, sudden stop, and sudden entry. The gathered data is processed and analyzed using a machine learning system designed for limited power and memory devices. The developed system resulted in 91.9% accuracy, 93.6% precision, and 92% recall. The achieved inference time on an Arduino Nano 33 BLE Sense with a 32-bit CPU running at 64 MHz is 34 ms and requires 2.6 kB peak RAM and 139.9 kB program flash memory, making it suitable for resource-constrained embedded systems.
International Conference on NLP, Artificial Intelligence, Machine Learning an...gerogepatton
International Conference on NLP, Artificial Intelligence, Machine Learning and Applications (NLAIM 2024) offers a premier global platform for exchanging insights and findings in the theory, methodology, and applications of NLP, Artificial Intelligence, Machine Learning, and their applications. The conference seeks substantial contributions across all key domains of NLP, Artificial Intelligence, Machine Learning, and their practical applications, aiming to foster both theoretical advancements and real-world implementations. With a focus on facilitating collaboration between researchers and practitioners from academia and industry, the conference serves as a nexus for sharing the latest developments in the field.
Presentation of IEEE Slovenia CIS (Computational Intelligence Society) Chapte...University of Maribor
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Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
A review on techniques and modelling methodologies used for checking electrom...nooriasukmaningtyas
The proper function of the integrated circuit (IC) in an inhibiting electromagnetic environment has always been a serious concern throughout the decades of revolution in the world of electronics, from disjunct devices to today’s integrated circuit technology, where billions of transistors are combined on a single chip. The automotive industry and smart vehicles in particular, are confronting design issues such as being prone to electromagnetic interference (EMI). Electronic control devices calculate incorrect outputs because of EMI and sensors give misleading values which can prove fatal in case of automotives. In this paper, the authors have non exhaustively tried to review research work concerned with the investigation of EMI in ICs and prediction of this EMI using various modelling methodologies and measurement setups.
2. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
2
=
+
=
+
applications due to its high electrical conductivity, hydrophilicity, and
reducibility [31–33]. The MXene can be obtained by selectively etching
of A from the ternary carbides/carbonitrideswiththe general formulaof
Mn+1AXn, where M is an early transition metal, A isa group IIIA or ⅣA
element, X is C and/or N element and n 1 , 2, or 3 [34,35].The
resultantMXene with many surface functional groups ownwell com-
bination of hydrophilic surface, high metallic conductivity associated
with high electron density of states near the Fermi level, and rich surface
chemistries, whichcan fulfill the demand of optimal electronic proper-
ties and interfacial junction for electrochemical reactions [18,36,37].
Among the large family of MXene, V 2C is the lightest one and has
received broad attention because of itshigh electrical conductivity,
excellent mechanical properties and ample reactivity. In addition, the
V 2C MXene is also of great practical interest due to its synthesizability
and applicability for batteries [38]. Comparingto the Ti3C2 MXene, with
m ultiple oXidation states of V ion, the vanadium surface layers of V2C
cou ld potentially enable pseudocapacitive behavior [39], whichcan
promote charge transfer between the adsorbate and V2C support.
Nevertheless, the development of V2C-based synergistic hybrid system is
still need more attentions tomeetthe applicationsin electrochemistry.
In this present work, the exfoliated few-layer V2C nanosheets and
FeNi-LDH nanosheetsare coupled by in-situ assembling through a sim-
ple hydrothermal method (denoted as H2PO—
2 /FeNi-LDH-V2 C), in which
the hypophosphite groups (H2PO—
2 ) w as introduced as intercalated an-
ions in the LDHs laminates in order to alter the surface electronic
structure and thus further enhance the OER activity of the composites
[19,40]. The strong interfacial interaction and electronic coupling be-
tw eenLDHs and V2C nanosheetsguarantee the fast charge transfer ki-
netics and stable structure of the hybrid material, leading to the
enhancement of OER. As a result, the H2PO—
2 /FeNi-LDH-V2 C catalyst
shows superior electrocatalytic activity and stability toward OER, witha
low overpotential of ~ 250mV at the current density of 10mA cm—2
and
a small Tafel slope of 46.5 mV dec—1
in 1.0 M KOH electrolyte. More-
over, the H2PO—
2 /FeNi-LDH-V2 C in rechargeable Zn-air battery reveals
su perior opencircuit potential (1.42 eV), power density (137mWcm—2
)
and durability to conventional Pt/C RuO2 air-cathode. This work
demonstrates the great promise of MXene-based nanohybrids in the
electrocatalytic application.
2. Experimental section
2.1. Materials
The V2AlC (MAX phase) powders were purchased from Shandong
Xiyan new material technology Co., Ltd. (99 wt%, 400 mesh). Hydro-
fluoric acid (~40 wt%), Iron nitrate nonahydrate (Fe(NO3 )3 9•
H2O, 98.5
wt%) and Nickel nitrate hexahydrate (Ni(NO3 )2 6
•
H2 O, 98.0 wt%) were
purchased from Sinopharm Group Chemical Reagent Co., Ltd. Sodium
hypophosphite (NaH2PO2, 99.0 %) and Ammonium fluoride (NH4F, 98
%) were purchased from Aladdin. Sodium hydroXide (NaOH, 90 %),
Tetrapropylammonium hydroXide (TPAOH, 40 wt%) were purchased
from Shanghai Titan Scientific Co., Ltd. Isopropanol were purchased
from Shanghai Lingfeng. Nafion D-520 dispersion (5 wt%) was pur-
chased from Dupont China Holding Co., Ltd. Commercial 20 wt% Pt/C
and the carbon black (XC-72) were purchased from Shanghai HEPHAS
Energy Equipment Co., Ltd. Allmaterialswere used asreceived without
fu rther purification.
2.2. Sample synthesis
2.2.1. Synthesis of V2C MXene nanosheets
First, 1.0 g V2AlC powderswere added gradually into 20 mL of HF
(~40 %) solution ina100mLTeflon-lined with stirring. The suspension
w as constantly stirred for 48 hat 40◦
C. Thenthe black suspension was
washed by Ar de-aerated distilled water for several timesuntil the pH of
the solution reached 6~7. After that, the precipitate was collected by
centrifugation and re-dispersed into 20 mL TPAOH aqueous solution for
24 h under stirring at room temperature. Subsequently, the as-
synthesized multilayer V2C nanosheets was collected and washed for
two times with oXygen-free water to remove the residual TPAOH, fol-
lowed by ultrasonic treatment in oXygen-free water for 2 h. Finally, the
dark green supernatant (few-layer V2C nanosheets) was collected after
the centrifugation for 1 h at 3500rpm, whichwasrestored at4 ◦
C in the
refrigerator before use.
2.2.2. Synthesis of H2PO—
2 /FeNi-LDH-V2C
Typically,thehypophosphite-intercalated FeNi-LDH combinedwith
few-layer V2C nanosheets were prepared via a hydrothermal method.
First, 0.6 mM Ni(NO3)2 6•
H2O and 0.2 mM Fe(NO3)3 9•
H2 O w ere dis-
solved in 10 mL DI water to form a homogeneous solution A (Ni: Fe = 3:
1). Meanwhile, 1.25 mmol NaOH and 0.4 mmol NaH2PO2 were dis-
solved in 10 mL DI water to form solution B (the DI water was boiled
ahead for 30min to remove the dissolved carbon dioXide and kept at40
◦
C for u se). Second, the solution A and B w ere drop wise added simul-
taneously into20mLV2C colloidal solution, followed with the pH ofthe
miXed solution adjusted to 14 by 0.2 M NaOH. And then4 mmol NH4F
w as added into the miXture to adjust the morphology of LDHs. After
stirring for 60min, the final solutionwasthen transferred intoa 50mL
Teflon-lined autoclave and hydrothermally heated at 120 ◦
C for 10 h.
After cooling to room temperature, the precipitates were harvested by
several centrifugation -rinsing cycles with deionized water followed by
freeze-drying.
2.2.3. Synthesis of CO2
3
—
/FeNi-LDH-V2C and H2PO—
2 /FeNi-LDH
According to the report of Feng et al. [41], the dissolved CO2
3
—
anions
in w ater have a high affinity to the LDH layers, thus the CO2
3
—
are
commonly acted asthe charge compensating anions in the LDH layers.
For comparison, the traditional CO2
3
—
/FeNi-LDH combined with
few-layer V2 C nanosheet (CO2
3
—
intercalated, denoted as
CO2
3
—
/FeNi-LDH-V2C) was also prepared with the same procedure as
H2PO—
2 /FeNi-LDH-V2 C without the addition of NaH2PO2 and using
common DI w ater. H2PO—
2 /FeNi-LDH and CO2
3
—
/FeNi-LDH w ere pre-
pared without the addition of V2C nanosheets. FeNi-LDH-V2C was pre-
paredwithout the addition of NaH2PO2 andusing DIwater boiled ahead
for 30 min.
2.3. Materials characterization
The powder X-ray diffraction (XRD) patterns were recorded on a
Rigaku D/Max-2550 V X-raydiffractometer witha Cu Kαradiation (λ
0.154 nm, 40 kV, 40 mA) at a scan rate of 4◦
min—1
. SEM character-
ization was performed on a field scanning electron microscope (FEI
Magellan-400) with an accelerating voltage of 5 kV. Transmission
electron microscopy (TEM), high-resolution transmission electron mi-
croscopy (HRTEM), electron energy -loss spectroscopy (EELS), energy
dispersive X-ray spectrometer (EDS) and corresponding EDS-mapping
were performed using a JEM-2100F field emission transmission elec-
tron microscopy (200 kV). Atomic force microscopy (AFM) measure-
mentwasperformed by Veeco DI Nanoscope Multi Mode V system. X-
ray photoelectron spectroscopy (XPS) signals were measured on Thermo
Scientific K-Alpha with a monochromatic Al Kα source (15 kV, 15 mA)
and a charging correction with reference to C 1s at 284.8 eV.
2.4. Electrochemical measurements
The electrocatalytic performance ofthe catalystswasmeasured on a
CHI 760E (CH instruments, Inc., Shanghai) electrochemical workstation
with a standard three-electrode system in 1.0 M KOH solution. During
OER test, a glassy carbon (GC) electrode (Pine Instruments, 5 mm in
diameter) modified by the catalysts were served as the working elec-
trode. Ag/AgCl electrode saturated with KCl solution and graphite rod
w ere employed as reference electrode and counter electrode,
3. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
3
=
—
= +
+
=
× ×
×
—
respectively. The catalyst ink was prepared by ultrasonically dispersing
7 mg of as-prepared samples and 3 mg carbon black in the miXture of
isopropanol (900μL), deionized water (70μL) and Nafion (30 μL, 5 wt
%) toform ahomogeneous suspension. Apart ofthe catalyst ink (10μL)
w as then pipetted onto the surface of glassy carbon electrode (an
average mass loading of around 0.35 mg cm —2
) and dried under ambient
conditions before tests. All the potentialsmeasured against an Ag/AgCl
electrode in this work were converted to potential versus reversible
hydrogen electrode (RHE) according to the Nernst Equation (ERHE =
EAg/AgCl + 0.059 pH + 0.1989 V). The 1.0 M KOH electrolytes were
saturated with high-purity N2 for 30 min before test. A gas flow was
maintained over the electrolyte during the measurement to ensure
continuous gas saturation. Before the electrochemical data w ere ac-
quired, the working electrodes were electrochemically activated with
1 0–20 cyclic voltammetry (CV) cycle with a sweep rate of 50mV s—1
at
1600rpm. The linear sweepvoltammetry (LSV) curveswere obtained at
a scan rate of 5 mV s—1
with 100 % iR compensations. The Tafel slope
was obtained by fitting the linear part ofthe Tafel plots according tothe
Tafel equation (η a b log(j)) to evaluate the kinetic performance of as-
prepared catalysts. The electrochemical impedance spectroscopy (EIS)
measurements were carried out in the frequency range of 106
Hz to
1 0—2
Hz at 1.49 V vs. RHE with 5 mV amplitude. The double layer
capacitance (Cdl) of the electrodes were calculated from CV curves at
different scan rates of 5 30 mV s—1
in a non-Faraday area. The elec-
trochemically active surface areas (ECSAs) canbe calculated asECSA
Cdl / CS, where CS isthe specific capacitancevalue (60 μFcm—2
) for aflat
standard with1 cm—2
of real surface area. In addition, the LSV curves of
ORR were measured in 1.0 M O2-saturated KOH solution at a scan rate of
5 mV s—1
at a rotating speed of 1600 rpm.
2.5. Zinc-Air battery measurements
A homemade liquid Zn-air battery was assembled to estimate po-
tentiality of the prepared catalysts in the practical application. Typi-
cally, 8 mg catalyst and 2 mg carbon black were dispersed in 900 μL
isopropanol, 70 μL deionized water and 30 μL Nafion by ultrasonic to
form a uniform suspension. The as-prepared ink waspipetted onto the
composite substrate (porous carbon paper or nickel foam) as the air
—2
elementary steps:
OH—
+ * → *OH + e—
(1 )
*OH + OH—
→ *O + H2O + e—
(2 )
*O + OH—
→ *OOH + e—
(3 )
*OOH + OH—
→ * + O2 + H2O + e—
(4 )
where * denotes the active sites on the catalyst surface. Based on the
abovemechanism,the free energy ofthreeintermediatestates, *OH,*O,
and *OOH, are important to identify a given material ’s OER activity. The
computational hydrogen electrode (CHE) model [50] was used to
calculate the free energies ofOER, based onwhich the free energy ofan
adsorbed speciesis defined as:
ΔGads = ΔEads + ΔEZPE - TΔSads (5 )
where ΔEads is the electronic adsorption energy, ΔEZPE is the zero point
energy difference between adsorbed and gaseous species, and TΔSads is
the corresponding entropy difference between these two states. The
electronic binding energy is referenced as ½ H2 for each H atom, and
(H2O – H2) for each O atom, plus the energy of the clean slab. The
corrections of zero point energy and entropy of the OERintermediates
can be found inthe supportinginformation (Table S1).
3. Results and discussion
3.1. Catalyst synthesis and characterization
The synthesis of H2PO—
2 /FeNi-LDH-V2 C nanohybrids is achieved by
co-precipitation of Ni2+
and Fe3+
onto the few-layer V2C nanosheets
u nderhydrothermal conditions, as illustrated in Fig.1a. Firstly, multi-
layered V2C wasmade by selectively etching away the Al layers of bulk
V2AlC powders with 40 wt% HF. After intercalation by TPAOH and
exfoliation underultrasonic, few-layered V2C nanosheetswere obtained
with abundant surface functional groups (–OH, –F), which can facili-
tate the anchoring and nucleation of FeNi-LDH nanosheets on V2C sur-
face. In the following hydrothermal process, the hypophosphite-
intercalated FeNi-LDH nanosheets were grown on the flat surface of
cathode, witha loading of2 mg cm . A polished Zn foil was used as the V2C nanosheets to form H2PO—
2 /FeNi-LDH-V2C nanohybrids. The XRD
anode and 6.0 M KOH with 0.2 M Zn(Ac)2 miXed solution was applied as
the electrolyte. The polarization curves of Zn -air battery were recorded
using linear sweep voltammetry (LSV) and charge/discharge cycling
tests were performed on the LAND CT2001 instrument. The Pt/C RuO2
catalystwith themass ratio is1:1 asthe air cathode wasalso assembled
and tested underthe same conditions for comparison.
2.6. DFT calculation details
All the density functional theory (DFT) calculationswere performed
by Vienna Ab-initio Simulation Package (VASP) [42,43], employing the
Projected Augmented Wave (PAW) method [44]. The revised
Perdew-Burke-Ernzerhof (RPBE) functional was used to describe the
exchange and correlation effects [45–47]. The GGA + U calculations are
performed using the model proposed by Dudarev et al. [48] withthe Ueff
(Ueff Coulomb U – exchange J) valuesof 6.4 eV and 4 eV for Ni and Fe,
respectively. The LDH/MXene nanohybrid structure wasmodeled by a
Fe-doped NiOOH monolayer (Fe: Ni = 1: 3) with exposed (001) surface
adsorbed on O-terminatedV2C MXene surface. The supercell consistsof
4 4 unit cells. For all the surface optimizations, the cutoff energy was
set to be 400 eV. The Monkhorst-Pack grids [49] were set to be 1 3 1
to carry out the surface calculations on all the models. At least 20 Å
vacuum layer wasapplied in z-direction of the slab models, preventing
the vertical interactions between slabs. The model structures were
optimized by ionic and electronic degrees of freedom using thresholds
for the total energy of10—4
eV and force of0.08 eV/Å.
In alkaline conditions, OER cou ld occur in the following four
patterns of bulk V2
AlC and few-layer V2C nanosheets are shown in
Fig. 1b. The sharp peaksat 13.5 and 41.3◦
agree well with the (002) and
(103) crystal planes of V2AlC (PDF#29—0101), respectively. For the
exfoliated few-layer V2C nanosheets, the peaks at 13.5◦
sand 41.3◦
are
complete disappeared, and the characteristic (002) peak is broadened
significantly and downshifted to 5.68◦
, confirming the completely
removal of Al atoms and an increase of c-lattice parameter of few-layer
V2C [33,51]. Moreover, the multilayered V2C exhibitsan accordion-like
morphology from theSEMimagein Fig.1c.Afterfurtherintercalation of
TPAOH,ultrasonic exfoliation and centrifugalization, the Tyndall effect
(right-down inset in Fig. 1d) can be observed in the supernatant meaning
the homogeneously dispersed few-layer V2C nanosheets. The TEM image
in Fig. 1d reveals the ultrathin flakes of few-layer V2C nanosheetswith
many defects edge, and the corresponding thickness is about 6 nm
(right-up inset in Fig. 1d)matching with the dimension of two or three
layers V2C nanosheets in thickness.
The prepared LDHs/MXenes exhibits the similar phase structure
(PDF#40 0215) shown in Fig. S1. The (002) peaks at 5.68◦
of MXene
are disappeared because of the suppressed restacking of MXene sheets
by the surface LDHs nanostructure and the high signals from LDHs.
H2PO—
2 /FeNi-LDH nanoplates w ith a polygon morphology w ere suc-
cessfully synthesized with the thickness of ~6 nm, and the highly ho-
m ogeneous dispersion of O, Fe, Ni, and P elementsverify the successful
insertion of hypophosphite (Fig. S2). For the H2PO—
2 /FeNi-LDH-V2 C
nanohybrids, the SEM and TEM (Fig. 1e and f) indicate the growth of
loosely flaky texture of FeNi-LDH nanosheets on the few-layer V2C
4. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
4
Fig. 1. (a) Sy nthesis of H2P O2
—
/Fe Ni- LDH - V 2C nanohybrids (b) XRD patter ns of bulk V2Al C and few -lay er V2C. SE M images of mul tilayered V2C (c) and H 2P O2
—
/Fe Ni-
LDH - V 2C nanohy brids (e). TE M images of few -l ayer V2C (d) w ith the corresponding Ty ndall effect (right-down inset) and A FM image (right-up inset) and H 2PO—
2 /
FeNi- L DH - V 2C nanohy brids (f), HRTEM images of H2PO—
2 /FeNi- LD H - V 2C nanohy brids (g) w ith the corresponding SAED pattern i n the inset, and the HAADF-ST E M
images i n (h).
surface. Moreover, such flaky morphology is highly desirable to promote
the mass diffusion and charge transfer during the electrochemical re-
actions [37]. High-resolution TEM (HRTEM) observation (Fig. 1g)
showstheinterplanar spacing of0.25 nm and 0.20nm correspondingto
the (100) plane of V2C and (018) plane of H2PO—
2 /FeNi-LDH, respec-
tively, confirming the formation of LDHs on the V2C surface. In addition,
the selected area electron diffraction (SAED) pattern inset in Fig. 1g
presents several diffraction ringsassignable to(110)and (100) planes of
V2 C and (018) plane of H2P O—
2 /FeNi-LDH, respectively, furtherverifying
the formation of H2PO—
2 /FeNi-LDH-V2 C nanohybrids. The uniform
distributions of O, Fe, Ni, V and P elements in H2PO—
2 /FeNi-LDH-V2 C
nanohybrids are shown by elemental mapping analysis in Fig. 1h.
Additionally, from the FTIR measurement (Fig. S3), the bands around
1180and 2358cm—1
canbe attributed to the P–O symmetric stretching
and P–H stretching v ibrational peak, respectively [40], indicating the
presence of the hypophosphite anions in the interlamellar space of the
as-prepared FeNi-LDH m aterials. For comparison, the TEM and
HAADF-STEM images of CO2
3
—
/FeNi-LDH-V2C (carbonate intercalated)
nanohybridsare shown in Fig. S4, with a similarflaky morphology and
u niform distribution of O, Fe, Ni and V elements.
5. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
5
3
3
X-ray photoelectron spectroscopy (XPS) wasmeasurement toinves- corresponding to M–O in oXide, M–OH bond in hydroXide and
tigate the surface compositions and binding structures of obtained cat-
alysts (Fig. 2 and Fig. S5). The XPS survey scan confirms the co-existence
of Fe, Ni, O, V , P and C elements in H2PO—
2 /FeNi-LDH-V2 C (Fig. S5a).In
the P 2p spectra (Fig. S5b), the peak at around 133.4 eV can be ascribed
to hypophosphite [40], consolidating the intercalation of hypophosphite
in the LDHs. The O 1s XPS (Fig. 2a) spectra were deconvoluted into three
component peaks at about 529.6 eV, 531.3 eV and 532.7 eV,
H–O–H in adsorbed w ater, respectively. Fig. 2 b shows the
high-resolution V 2p spectra,with twopeaks of V 2p3/2 at 516.8eV and
V 2 p1/2 at 524.3 eV, corresponding to the V4+
of V2C [52]. Thehigh-
resolution Ni 2p spectra (Fig. 2c) show two characteristic peaks
located at 855.9 eV and 873.5 eV for 2p3/2 and 2p1/2 doublet of Ni2+
,
and two shakeup satellites(defined asSat.), respectively [37]. The Fe 2p
spectra(Fig. 2d) also feature withtwo prominent peaks at 712.6 eV and
Fig. 2. High-resolution XPS spectra of (a) O 1s, (b) V 2p, (c) Ni 2p and (d) Fe 2p i n obtained H2PO—
2 /FeNi- LD H -V 2C, CO2—
/FeNi- LD H -V 2C and H2PO—
2 /FeNi- LD H . Ni
L23 edges (e) and Fe L23 edges (f) el ectron energy-loss spectroscopy (EELS) spectra of H2PO2
—
/F eN i- LD H - V 2C, CO2—
/FeNi- LD H- V 2C and H2PO—
2 /FeNi- LD H .
6. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
6
725.8 eV, corresponding to 2p3/2 and 2p1/2 orbits of Fe3+
, and two
satellite peaks, respectively. Comparing to H2PO—
2 /FeNi-LDH and
CO2
3
—
/FeNi-LDH (Fig. S6), the Ni 2p and Fe 2p peaks of
H2P O—
2 /FeNi-LDH-V2 C and CO2
3
—
/FeNi-LDH-V2C are positively shift
about 0.3—0.4 eV, respectively, the higher binding energies meaning the
higher oXidation states of Ni and Fe irons after combination of V2C.
Obviously, the charge transfer from LDHs to V2C resultsin thevalence
states increase of Ni and Fe irons, indicating the strong chemical inter-
action between the FeNi-LDH and the V2C matriX, which is known
beneficial to accelerate the redoX activity during the OER process [18,
53]. Additionally, according to the slightly higher binding energies of
H2P O—
2 /FeNi-LDH-V2 C than those of CO2
3
—
/FeNi-LDH-V2 C (Fig. 2c and
d), the intercalation of hypophosphite in the LDHs instead ofcarbonate
alsocan facilitate the charge transfer from LDHstoV2C MXene, leading
to the surface electronic reconstruction and higher catalytic activity of
the former. The chemical states of the Ni and Fe species were further
characterized by EELS (Fig. 2e and f), where the L3 and L2 white line
represent the electron excitations from 2p3/2 and 2p1/2 to 3d orbits,
respectively.As shown in Fig.2e and f, the positions ofNi L3,2 edgesand
Fe L3,2 edges shift to higher energy losses, indicating that both the
combination of V2C and the intercalation ofhypophosphite promote the
oXidation of Ni and Fe atoms [54]. Additionally, the total integral in-
tensity ratios (L3/L2) are correlated to the oXidation states of Fe. Ac-
cording to the calculation results, H2PO—
2 /FeNi-LDH-V2C has the highest
Fe L3 /L2 ratio (5.27) than those of CO2
3
—
/FeNi-LDH-V2 C (5.04) and
H2PO2
—
/FeNi-LDH (4 .72), manifesting its highest Fe valance [55,56].
Generally, the EELS analysisprovides evidence that with the combina-
tion of V2C, the charge will transfer from LDHs to V2C, leaving high
oXidation states of Ni and Fe ions.
3.2. Electrocatalytic OER performance
The OER electrocatalytic activity of the obtained catalysts was
evaluated in N2-saturated 1.0 M KOH electrolyte using athree-electrode
system. Fig. 3 a shows the activation process of H2PO—
2 /FeNi-LDH-V2 C
catalyst, demonstrating that after10 cycles ofcyclicvoltammetry scans,
the phase transformed from hydroXides to oXyhydroXides. The peak pair
in the potential range of1.25–1.55 V (vs. RHE) corresponds tothe redoX
cou ple of Ni(II)/Ni(III) [57]. The iR-correction linear sweep voltam-
metry (LSV) curves of all synthesized catalysts and references were
measured at a scan rate of 5 mV s—1
tominimize the capacitive current,
as shown in Fig. 3 b. The H2PO—
2 /FeNi-LDH-V2 C catalyst shows the
strongest redoX peaks at a potential of 1.46 V, indicating the signifi-
cantly accelerated Ni(II)/Ni(III) redo X process. Accordingly, it shows the
highest OERactivity, withalowest overpotential of250mV to achieve a
current density of 1 0 mA cm—2
(η10 = 250 mV) than that of
H2PO—
2 /FeNi-LDH (η10 = 2 70mV), CO2
3
—
/FeNi-LDH-V2 C (η10 = 286 mV)
and commercial RuO2 (η10 = 322 mV). In addition, the OER perfor-
mance of FeNi-LDH-V2 C also has been tested (Fig. S7). Comparing to the
OER performance of H2PO—
2 /FeNi-LDH-V2 C, the inferior catalytic ac-
tivity of FeNi-LDH-V2C (η10 =304 mV) indicated that the intercalated
H2PO—
2 anions in the LDH laminates play a significant role in enhancing
its OERperformance. It isworth noting that the V2C nanosheetsshows
negligible activity, confirming that the LDHs are the active phase for
OER. The combination of V2C nanosheetscan effectively accelerate the
electron transferfrom LDHs to V2C matriX subsequently enhancing the
Fig. 3. OER performance of synthesized catalysts i n 1.0 M KOH. (a) CV curv es of H2PO2
—
/ FeN i- LD H - V 2C at a scan rate of 50 mV s—1
. (b) LSV curves w ith iR-
correction. (c) The corresponding Tafel plots. (d) EIS and its fitting patterns. (e) doubl e-layer capacitance Cdl of sampl es. (f) Comparison of current densities
based on geometric areas and mass activities at 1.53 V v ersus RHE. (g) Faradaic efficiency of the H2PO—
2 /FeNi- LD H- V 2C catal yst i n 1 M KOH at 1600 rpm under N2
saturation. (h) Stability measure m en ts of H2PO—
2 /FeNi- L DH - V 2C and RuO2 at the constant ov erpotential of 0.25 V. (i) Comparison of η10 and Tafel sl ope between
H2PO—
2 /FeNi- LD H -V 2C i n this w ork and v arious Ni/Fe- b ase d and MXen e- base d catal ysts recently reported.
7. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
7
=
+
+
+
OER activity (Fig. 2c and 2d). Hence, it can be concluded that the high
activity of LDHs is associatingwith the hypophosphite-intercalated and
the higheroXidation statesof Ni and Fe ironscaused by the synergistic
electronic effects between LDHs and MXene. As shown in Fig. 3c, the
H2P O—
2 /FeNi-LDH-V2 C catalyst exhibits the lowest Tafel slope of 46.5
mV dec—1
with respect to H2 PO—
2 /FeNi-LDH (53.8 mV dec—1
),
CO2
3
—
/FeNi-LDH-V2C (72.9 mV dec—1
), FeNi-LDH-V2C (7 3.1 mV dec—1
,
Fig. S7b), commercial RuO2 (67.9 mV dec—1
) and V2C (161 mV dec—1
),
m anifestingthe superior OERkinetics.
The electrochemical impedance spectroscopy (EIS) was performed to
evaluated the electrochemical resistances on differentcatalystsat 1.498
V (vs. RHE) in the frequency range from 10—2
to 106
Hz. Fig. 3d dem-
onstrates elliptical semicircles of EIS plots, which is caused by the
roughened surface structure. Therefore, the constant phase element (Q)
is introduced to simulate the double-layered capacitor (inset in Fig. 3d)
[58], where Rs represent the solution resistance, Q1Rct1 and Q2Rct2
represent two charge-transfer processes corresponding to the trans-
formation ofthe active intermediatesand the OER process, respectively
[2 0]. According to the EIS plots in Fig. 3d and the fitting parameters
(Table S2), the H2PO—
2 /FeNi-LDH-V2 C catalyst exhibits the low est Rct
among the prepared catalysts, indicating a faster charge-transfer pro-
cess. The low er electrochemical resistance on H2PO—
2 /FeNi-LDH-V2 C
can be ascribed to the combination of V2C which can accelerate the
electron transfer consequently improving the electrical conductivity.
The electrochemically active surface areas(ECSAs) were also estimated
based on the electrochemical double-layer capacitance (Cdl) of the cat-
alystsrecorded inthe non-Faradaicregion (1.02–1.14 V vs.RHE) since it
had a linear relationship with ECSA in 1.0 M KOH (Fig. S8). As seen from
Fig. 3 e, the measured Cdl v alue of H2PO—
2 /FeNi-LDH-V2 C (6 .52 m F
cm—2
) is larger than those of H2PO—
2 /FeNi-LDH (5.99 m F cm—2
),
CO2
3
—
/FeNi-LDH-V2C (5 .59 m F cm—2
) and V2C (6.28 m F cm—2
).
Accordingly, the ECSA of H2PO—
2 /FeNi-LDH-V2 C is calculated to be
108.67 cm2
(Fig. S9a), which is the highest among the prepared cata-
lysts. Also, when the LSV curves are normalized against ECSA (Fig. S9b),
H2P O—
2 /FeNi-LDH-V2 C catalyst still exhibits much higher OER activity,
fu rtherindicatingthat the synergistic effects betweenLDHs and MXene
significantly improves its intrinsic activity. Additionally, the geometric
current densities and specific mass activities of as-prepared catalystsat
an overpotential of300mV are summarized in Fig.3fandTable S3.And
H2PO—
2 /FeNi-LDH-V2 C displays the highest geometric current density
(89.01 mA cm—2
) as well as relatively high mass activity (249.57 mA
m g—1
).
The turn over frequency (TOF) was calculated to estimate the
intrinsic catalytic activity of per active site (see SupportingInformation
for TOF calculation) [59], which is shown in Fig. S10 and S11. The
H2P O—
2 /FeNi-LDH-V2 C exhibits the highest TOF value of 0.82 s—1
at an
overpotential of 300 mV (Fig. S11), higher than that of H2PO—
2 /FeNi-LDH (0.091 s—1
) and CO2
3
—
/FeNi-LDH-V2 C (0.048 s—1
).
Furthermore, the Faradaic efficiency of H2PO—
2 /FeNi-LDH-V2C was
calculated by rotating ring-disk electrode (RRDE) method (Fig. S12),
where oXygen generated at the disk electrode was swept and reduced at
the Pt ring electrode (see the Supporting Information for the detail of
Faradaic efficiency calculation) [60,61]. Asshown in Fig. 3g, the highest
Faradaic efficiency can be obtained about 99.2 % at 1.48 V (vs RHE),
and then decreased to 67.3 % at 1.52 V (vs RHE). Thisdecrease may be
attributed to the large amounts of undissolved oXygen bubbles gener-
ated by the disk electrode. Thusan average Faradaic efficiency value of
9 6 % (three corresponding Faradaic efficiency values from 1.48to 1.50
V (vs RHE)) has been presented as the OER efficiency of the H2PO—
2 /FeNi-LDH-V2 C catalyst.
Moreover, the H2PO—
2 /FeNi-LDH-V2 C displays an outstanding sta-
bility without any obviousdecrement of the current density after30000
s (Fig. 3h) and even 50000 s (Fig. S13) OER tests, comparing to nearly 50
% decline for the commercial RuO2 catalyst. It’s worth noting that the
current density of H2PO—
2 /FeNi-LDH-V2C have a slight increase during
the OER at the beginning, which can be ascribed to the activation
process of H2PO—
2 /FeNi-LDH-V2C catalyst according to Fig. 3 a. Surpris-
ingly, the OER activity of H2PO—
2 /FeNi-LDH-V2C including the over-
potential and Tafel slope values is comparable and even su perior to
those of themost reported state-of-the-art OER electrocatalysts(Fig.3i
and Table S4). Also, aftera 50000 s OERtest, the XRD and TEM mea-
surements of H2PO—
2 /FeNi-LDH-V2 C w ere performed to further investi-
gate its stability. The XRD patterns in Fig. S14 shows the similar
diffraction peaks of H2PO—
2 /FeNi-LDH-V2C catalyst before and after re-
action. In addition, a hardly unchanged flaky morphology and elements
distribution have been reserved even after 50000 s OER test (Fig. S15),
indicating the excellent structural stability of H2PO—
2 /FeNi-LDH-V2 C
catalyst. Furthermore, the XPS of H2PO—
2 /FeNi-LDH-V2 C after 50000 s
reaction was measured (Fig. S16). It can be seen that the V 2p spectra
(Fig. S16a) still remain at 516.8 eV (V 2p3/2) and 524.3 eV (V 2p1/2),
corresponding to the V4+
state, revealing its favorable stability during
OER. The high-resolution Ni 2p spectra show new characteristic peaks
located at 857.6 eV and 875.5 eV corresponding to 2p3/2 and 2p1/2 or-
bits of Ni3 +
, which can be attributed to the oXidation of Ni2 +
during OER
(Fig. 3a). Also, a slightly positive shift of Fe 2p spectra (Fig. S16c) in-
dicates a slight rise in thevalance state of Fe after reaction. The partial
oXidation of the Ni and Fe species in H2PO—
2 /FeNi-LDH-V2 C after 50000
s reaction suggests its beneficial trend to accelerate the redoX activity
du ring the OER processagreeing withthe document reported [15,20].
3.3. Zinc–air battery performance
To further evaluate the electrocatalytic performance, the ORR
measurement was also performed in O2 saturated 1.0 M KOH solution by
using a standard three-electrode working system. The synthesized
H2PO—
2 /FeNi-LDH-V2 C shows considerable ORR catalytic properties
with an onset potential of0.89 V and a highhalf-wave potential of0.8V
vs. RHE (Fig. S17). The overall oXygen electrocatalysis property of the
catalyst was further evaluated through the potential gap (ΔE) between
the potential of OER at η10 and the half-wave potential (E1/2) of ORR.
And a smaller value of ΔE indicates a superior catalytic activity and
reversibility [62,63]. As illustrated in Fig. S18, the
H2PO—
2 /FeNi-LDH-V2 C electrode reveals a much lower ΔE v alue (0.673
V) than those of H2PO—
2 /FeNi-LDH (0.702 V), CO2
3
—
/FeNi-LDH-V2C
(0.714 V) and V2C (0.936 V), even a little smaller than that of a miXed
Pt/C + RuO2 commercial catalyst (0.682 V).Moreover, the sample
H2PO—
2 /FeNi-LDH-V2 C shows the electron transfer number of ~3 .8 ac-
cording to Fig. S19, illustrating the effective ORR catalytic activity.
Based on the excellent oXygen electrocatalysis properties, a liquid
rechargeable Zn-air battery (ZAB) employing H2PO—
2 /FeNi-LDH-V2C as
the air cathode was assembled to evaluate its feasibility in practical
energy devices. For comparison, the liquid ZAB using Pt/C RuO2
commercial catalyst (mass ratio 1: 1) as the air cathode was also
assembled. The schematic configuration ofa Zn-air battery assembly is
displayed in Fig. 4a. The liquid ZAB driven by the H2 PO—
2 /FeNi-LDH-V2 C
obtains a high open-circuit potential (OCV) of 1 .42 V (Fig. 4b),
exceeding that of driven by the Pt/C RuO2 (1.41 V). The discharge/
charge polarization curves and the corresponding power density curves
of the liquid ZABs are provided in Fig. 4c. The H2PO—
2 /FeNi-LDH-V2 C-
based ZAB exhibits a lower voltage gap between charge and discharge,
together with a maximum power density of 137 mW cm —2
, which is
higher than that of the Pt/C RuO2-based ZAB (43 mW cm—2
), indi-
cating a better rechargeability [64]. The cycle stability of ZABs were
performed under continuous galvanostatic discharge and charge at 5 mA
cm—2
with each cycle being 10 min. As observed in Fig. 4d, the H2PO—
2 /FeNi-LDH-V2 C-based ZAB shows relatively stable operation for 100
h, which is longer than the Pt/C + RuO2-based ZAB (~60 h). Moreover,
the v oltage gap of H2PO—
2 /FeNi-LDH-V2 C-based ZAB only
increased by 0.1 V aftercontinuous 60h (the voltage gap changes from
initial 0.73 V to0.83 V at the 360 th cycle), corresponding toonly 4.3 %
decrease of round-trip efficiency (discharging end voltage divided by
charging end voltage [65,66]) (Fig. 4 e). For a conventional Pt/C +
8. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
8
Fig. 4. Zn-air batteries w ith H2PO—
2 /FeNi- L D H- V 2C and Pt/C + RuO2 catal ysts as air cathodes. (a) Schematics of the primary configuration of a Zn–air battery. (b)
Open circuit potential curves. (c) The discharge/charge polarization curves and the corresponding pow er density curves. (d) Gal vanostatic charging/discharging
cy cling curves at a current density of 5 mA cm—2
. Long- term cy cling performance w ith H2PO2
—
/Fe Ni- L DH - V 2C (e) and Pt/C + RuO2 (f) catalysts as air cathodes. (g)
Photographs of different l ight-emitting diode w ith H2PO—
2 /FeNi- LD H - V 2C as air cathodes.
RuO2-based ZAB, itsvoltage gap increases from 0.77 V to 0.97 V, with
the round-trip efficiency decreases of 9.1 % from 61.3 % at the opening
stage to 52.2 % after 60 h (Fig. 4f). As an exemplification for practical
applications, the LED display (1.5 V) and different light-emittingdiode
(2 –2.2 V) were powered by two series of ZABs with theH2PO—
2 /FeNi-LDH-V2 C as air cathode (Fig. 4g), and the light-emitting
Fig. 5. (a) Side v iew of model structure of H2PO2
—
/F eNi- LD H -V 2C hy brid sy stem. (b) DOS of H2PO2
—
/ FeN i- LD H - V 2C and H2PO—
2 /FeNi- LD H . (c) PDOS of the Ni and Fe
3d orbitals from H2PO—
2 /FeNi- LD H- V 2C and H2PO2
—
/Fe Ni- L DH . The dashed l ines indicate the d-band center for each system. (d) The reaction pathway of OER in
al kaline sol ution. The free energy diagrams at an equilibrium potential of 0 V (e) and 1.23 V (f) for ov erall OER pathway.
9. Y. Chen et al. Applied Catalysis B: Environmental 297 (2021) 120474
9
diode can be powered for 36 h without brightness decay. The results
corroborate the usability of H2PO—
2 /FeNi-LDH-V2 C in actual recharge-
able Zn-airbatteries, which demonstrates itspromisingapplication for
advanced energystorage and conversion technologies.
3.4. DFT calculation
To gain fundamental insight into the origin of oXygen electro-
catalytic activity for H2PO—
2 /FeNi-LDH-V2C, spin-polarized density
fu nctional theory (DFT) calculations with focus on the interaction be-
tw een FeNi-LDH and MXene and the catalytic pathways of oXygen
electrocatalytic reactionswere performed,as shown in Fig.5.According
to the activation process of H2P O—
2 /FeNi-LDH-V2 C in Fig. 3a and some
previous studies [15,20,67], the FeNi-LDHs usually undergo a phase
transformation from hydroXides to oXyhydroXides during the OERpro-
cess in alkaline solution, where the oXyhydroXidesare generally recog-
nized asthe active phase for OER. Therefore, the computation structure
of LDH/MXene is modeled as Fe-doped NiOOH monolayer (Ni: Fe = 3: 1)
su pported by O-terminated V 2C considering the alkaline conditions.
(Fig. 5a).
The Mulliken charge analysis indicates that an electron transfer of
0.42 e—
per unit cell from FeNi-LDH to V2C, leaving more positively
charged of Fe and Ni atoms than those in FeNi -LDH nanosheets, which is
well agreement with the XPS results (Fig. 2c and d). The density of states
(DOS) and partial density of states (PDOS) for H2PO—
2 /FeNi-LDH-V2C
and H2PO2
—
/FeNi-LDH are first calculated and exhibited in Fig. 5 b and
5c, respectively. As shown in Fig. 5b, the electron density around the
Fermi level of H2PO—
2 /FeNi-LDH-V2C exhibits enhanced DOS comparing
to that of H2PO—
2 /FeNi-LDH, w hich can promote the charge transfer and
facilitate the adsorption/desorption properties of reaction in-
termediates, thus increasing the conductivity of catalyst and reducing
the energy barriers for OER[53,68]. Fig.5c indicates thatthe PDOS (Fe
and Ni 3d orbital band) of H2PO—
2 /FeNi-LDH-V2 C are more down-shifted
than that of H2PO2
—
/FeNi-LDH, where the d-band center is calculated to
be —3.04 and —2.44 eV for H2PO—
2 /FeNi-LDH-V2 C and
H2P O—
2 /FeNi-LDH, respectively. The downshift of d-band center for
H2PO—
2 /FeNi-LDH-V2 C means the appropriate adsorption strength to-
w ard mediates, which canaccelerate the OERprocess according tothe
d-band center theory [50,69–71]. Thus, a balance between the d-band
center and intrinsic activity should be taken into consideration.
Fig. 5d shows the reaction pathway of OER. Accordingly, the free
energy diagrams at an equilibriumpotential of 0 V and1.23 V for overall
OER pathway are depicted in Fig.5e and 5f, respectively. Asillustrated
in Fig. 5e, for the H2P O—
2 /FeNi-LDH and H2PO—
2 /FeNi-LDH-V2 C, the OER
rate-determining step (RDS) is the formation of *OOH from *OHwith
the free energy barrier of 1.69 eV and 1.56 eV, respectively. The lower
free energy barrier of H2 PO—
2 /FeNi-LDH-V2 C, indicates that the forma-
tion energy of O–O band canbe reduced by the combination FeNi-LDH
withV2C. After1.23 V potentialhasbeen applied to the system (Fig.5e),
the ΔG*OH of H2PO—
2 /FeNi-LDH reveals a negative value, demonstrating
the strong adsorption with *HO, leading to a marked uphill formation
for the subsequent *O and *OOH intermediates. In contrast, relatively
low values of ΔG between intermediates are shown on H PO—
/FeNi-
alkaline electrolyte. The obtained H2 PO—
2 /FeNi-LDH-V2 C electrocatalyst
exhibits the remarkable OER performance with a low η10 of 250 mV, a
small Tafel slope of 46.5 mV dec—1
, and a long-time durability in1.0 M
KOH solution. Additionally, the H2PO—
2 /FeNi-LDH-V2 C in rechargeable
Zn-air battery reveals superior open circuit potential (1.42 eV), power
density (137 mW cm—2
) and well durability to conventional Pt/C +
RuO2 air-cathode. The remarkable oXygen electrocatalytic performance
can be attributed to the synergy and interplay of H2PO—
2 /FeNi-LDH and
conductive V 2C MXene. Strong electronic interaction between FeNi-
LDHs and V2C MXene guarantees the prominent charge transfer and
enhances the reaction kinetics for OER on the one hand, and on the other
hand, combination FeNi-LDHs to V2C MXene can reduce the O adsorp-
tion capacity by shifting down the d-band center of Fe/Ni atomsleading
to an appropriate balance between the adsorption of OH speciesand the
desorption of O2 and theneventually promoting the intrinsic activity.
CRediT authorship contribution statement
Yafeng Chen: Conceptualization, Methodology, Validation, Formal
analysis, Investigation, Visualization, Writing - original draft. Heliang
Yao: Investigation, Resources. Fantao Kong: Conceptualization,
Investigation, Resources. Han Tian: Investigation, Resources. Ge Meng:
Resources. Shuize Wang: Resources. Xinping Mao: Conceptualization,
Methodology. Xiangzhi Cui: Conceptualization, Methodology, Super-
vision, Investigation, Writing - review & editing. Xinmei Hou:
Conceptualization, Methodology, Supervision, Investigation, Writing -
review & editing. Jianlin Shi: Conceptualization, Methodology.
Declaration of Competing Interest
The authors report no declarationsof interest.
Acknowledgments
This work was supported by the National Science Fund for Distin-
guished Young Scholars (No. 52025041), the National Natural Science
Foundation of China (No.51974021), the Natural Science Foundation of
Shanghai (19ZR1479400), and the State Key Laboratory of Advanced
Technology for Materials Synthesis and Processing (Wuhan University of
Technology).
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcatb.2021.120474.
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