Acs.energyfuels.1c03300

Polyoxomolybdate−Polypyrrole−Graphene Oxide Nanohybrid
Electrode for High-Power Symmetric Supercapacitors
Sukanya Maity, Madhusree JE, Bhimaraya R. Biradar, Pranay R. Chandewar, Debaprasad Shee,
Partha Pratim Das,* and Sib Sankar Mal*
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sı Supporting Information
ABSTRACT: Supercapacitors have emerged as one of the most
promising candidates for high-performance, safe, clean, and
economical routes to store and release of nonfossil energy.
Designing hybrid materials by integrating double-layer and
pseudocapacitive materials is crucial to achieving high-power and
high-energy storage devices simultaneously. Herein, we synthesized
a polyoxomolybdate−polypyrrole−graphene oxide nanohybrid via
a one-pot reaction. The inclusion of polypyrrole enables a uniform
distribution of the polyoxomolybdate clusters; it also confines the
restacking of graphene oxide nanosheets. The structural and
morphological analysis to unveil the nanohybrid architecture implies excellent interfacial contact, enabling fast redox reaction of
polyanions, and a quick transfer of charge to the interfaces. Electrochemical characteristics tested under a two-electrode system
exhibit the highest capacitance of 354 F g−1
with significantly high specific energy and power of 49.16 Wh kg−1
and 999.86 W kg−1
,
respectively. In addition, the cell possesses a high-rate capability and long cycle life by maintaining 96% of its capacitance over 5000
sweeping cycles. The highest specific power of ∼10 000 W kg−1
was computed with Coulombic efficiency of 92.30% at 5 A g−1
current density. Electrochemical impedance spectroscopy additionally reveals enhanced redox charge transfer due to double
hybridization. Furthermore, it also demonstrates the impedance and capacitive behavior of supercapacitor cells over a definite
frequency regime.
1. INTRODUCTION
Energy storage has become a paramount concern owing to the
intermittency of renewable energy sources. Supercapacitors
(SCs) have garnered considerable attention in energy
technology by achieving high specific energy alongside high
power with a satisfactory lifespan.1,2
Over the past decades,
extensive research has been carried out to develop SCs to
achieve high specific energy as batteries without compromising
their high power output and cycle stability.3
Despite the
significant progress made so far, designing efficient electrode
materials for SCs to address the challenges they face remains
elusive to date.4,5
Carbonaceous nanostructures are commonly used as
electrode components owing to their various favorable features,
e.g., high surface area with tunable pore size, high conductivity
with excellent mechanical and electrochemical stability, facile
synthesis procedure, and low cost.6−8
However, their specific
capacitance value remains somewhat constrained because of
their charge storage mechanism (electric double-layer capaci-
tance, EDLC). Nanomaterials such as carbon nanotubes
(CNTs),9,10
activated carbon (AC),11−14
graphene oxide/
reduced graphene oxides (GO/rGO)15−19
have been so far
explored extensively in the SC applications. Moreover, surface
modification with different functionalities (nitrogen or sulfur)
increase the electrode surface’s wettability with electrolytes.20,21
On the other hand, pseudocapacitive materials such as
conducting polymers (COPs)22−24
and transition metal oxides
(TMOs)/sulfides25−27
possess high specific capacitance due to
their ability to perform fast and reversible faradaic reactions
induced by redox functionalities. Conducting polymers have
been studied as pseudocapacitors for an affordable cost,
lightweight behavior, tunable surface properties, and nontoxic
nature. Polypyrrole (PPy), contrarily, is one of the versatile
COPs which exhibits multiple redox states through proton
doping and dedoping.28,29
However, lower surface area and
mechanical degradation over many sweeping cycles restrict their
real-time applications. Swelling and shrinking of COPs during
charge/discharge cycles destroy their hierarchical structure and
polymer backbone. Therefore, redox-active metal oxides are
coupled with polymer backbones, which yields enhanced
pseudocapacitance and the cycle stability.29,30
Received: September 27, 2021
Revised: October 19, 2021
Published: November 5, 2021
Article
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© 2021 American Chemical Society
18824
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Polyoxometalates (POMs), a redox-active metal-oxide
molecular cluster enclosing high-valent transition metal atoms,
possess tunable structure, size, and composition.31−34
Various
Keggin clusters were reported as potential candidates for SC
application because of their high abundance, rich pseudocapa-
citive behavior, fast, reversible, multistep redox reaction, and
stable redox states.35−37
However, their poor intrinsic
conductivity and high solubility in aqueous and polar organic
solvents hinder their application. Accordingly, POMs are often
immobilized on a stable elevated surface area substrate (e.g., AC,
CNTs, GO/rGO, COPs) to improve SC performance.38−40
Nevertheless, the realistic design of incorporating POMs into
micro/mesoporous surfaces to result in required electrical
conductivity and high pseudocapacitance is still a challenge.
We report for the first time a facile synthesis process of
polyoxomolybdate, H4[PVMo11O40] (PVMo11), mediated by a
one-pot oxidation reaction with pyrrole (PPy) on a chemically
exfoliated GO surface. Herein, vanadium substituted polyox-
omolybdate (PVMo11) is preferred since it acts as a multifunc-
tional metal-oxide cluster to initiate in situ polymerization of the
pyrrole monomer. As a pristine form or in composite, PPy and
GO have been extensively investigated as electrode materials for
electrochemical energy storage purposes. Although both
materials suffer from their mechanical and electrochemical
instability, in composites, these two materials complement each
other. The PVMo11 plays dual roles during the polymerization of
pyrrole monomer to polypyrrole. First, PVMo11 supplies
protons to the pyrrole. Second, it oxidizes the pyrrole
monomers, which are deposited in layers on the GO surfaces,
and the GO provides mechanical/electrochemical stability to
PPy backbones. As a result, the nanohybrid exhibits a porous
morphology for faster and effective electrochemical reactions. It
is noteworthy that no external oxidant was applied to synthesize
the PVMo11−PPy/GO nanohybrid, and therefore, our synthesis
process is green, clean, and economical. Furthermore, a series of
microsupercapacitors are assembled using the PVMo11−PPy/
GO nanohybrid as an electrode material to light up the red LED
bulb.
2. MATERIALS AND METHODS
Graphite, N-methyl-2-pyrrolidone (NMP), Na2HPO4, sodium meta-
vanadate (NaVO3), sodium molybdate (Na2MoO4), and carbon black
were purchased from Sigma-Aldrich. Pyrrole was purchased from
Spectrochem Pvt. Ltd. Polyvinylidene (PDVF) and potassium
permanganate (KMnO4) were procured from the Alfa Aesar. Carbon
cloth was purchased from Sinergy Fuel Cell India Pvt. Ltd. We used
analytical grade reagents and HPLC grade water to prepare solutions.
H2SO4, HCl, H3PO4, 30% H2O2, acetone, and diethyl ether were
obtained from Loba Chem. Pvt. Ltd. The carbon cloth was washed with
acetone and finally rinsed with HPLC grade water thoroughly before
being used.
2.1. Preparation of PVMo11−PPy/GO Nanohybrid. A one-pot
facile synthesis process was followed to prepare the desired nanohybrid.
First, graphene oxide (GO) was synthesized as reported in the
literature.41
Likewise, the redox-active polyoxometalate cluster
(H4[PVMo11O40]·nH2O, PVMo11) was prepared according to the
procedure published elsewhere.42
In the beginning, 20 mg of GO flakes
were dispersed in 50 mL of water in a beaker and stirred thoroughly.
Following that, 0.135 mL of pyrrole and 1 g of PVMo11 were added to
the GO−water mixture. The reaction was stirred for 24 h at room
temperature at 300 rpm. The solid yield was filtered and washed off
several times with HPLC grade water in order to remove undeposited
PVMo11. Finally, it was air-dried and the compound was used for further
analysis.
2.2. Experimental Methods. The prepared nanohybrid’s struc-
tural analysis was carried out using Fourier transform infrared
spectroscopy (FTIR, Bruker 4000 (USA)) in the spectral range of
4000−500 cm−1
. The X-ray diffraction patterns were recorded using
Rigaku Mini Flex 600 (Japan) diffractometer from 5° to 65° diffraction
angles. The thermal stability was analyzed using a thermogravimetric
analyzer, TGA (PerkinElmer TGA4000, USA), at the heating rate of 5
°C/min and inflow of 20 mL/min of N2 at 77 K. The microstructure
and the topological parameters were investigated using a field emission
scanning electron microscope (FESEM, Carl Zeiss Sigma, Germany;
model Gemini SEM 300) with an accelerating potential of 5 kV under
the magnification range of 40 × 103
−150 × 103
. The transmission
electron microscopy (TEM) was investigated using a JEOL JEM
2100FX transmission electron microscope. The textual properties
(surface area, porosity) were further explored by N2 adsorption/
desorption measurement performed at −196 °C using a Micromeritics
Physisorption analyzer (Model ASAP 2020, USA).
Electrochemical measurements were carried out in two-electrode
symmetric cell arrangements through an electrochemical workstation
(IVIUM Technologies BV Co., Netherlands, model Vertex). The
electrode material was prepared using 80% active materials (PVMo11−
PPy/GO) with 10% carbon black and PVDF each in 1 mL of NMP
solution. Henceforth, the slurry solution was coated on 1 cm × 1 cm size
carbon cloth and air-dried at 60 °C. The coated carbon cloth (active
mass ∼0.8 mg) was treated as the electrode in the symmetric cell
separated by a Whatman filter paper drenched in 0.1 M H2SO4 solution.
Notably, the carbon cloth was thoroughly washed with acetone and
rinsed with HPLC grade water many times before coating.
Figure 1. (a) FT-IR spectra and (b) PXRD pattern of the PVMo11−PPy/GO nanohybrid.
Energy & Fuels pubs.acs.org/EF Article
Energy Fuels 2021, 35, 18824−18832
18825

3. RESULT AND DISCUSSION
3.1. Structural, Morphological, and Textual Analysis.
FTIR spectroscopy was used to investigate the structural
modification of the resultant product. As shown in Figure 1a,
the nanohybrid’s FTIR spectra recorded a vibrational band at
3425 cm−1
, which can be assigned to the O−H bond of absorbed
water. A low-intensity band at 2966 cm−1
transpires owing to the
N−H stretching vibration of the pyrrole ring. The bands at 1553
and 1468 cm−1
are ascribed to CC and C−N stretching,
indicating the presence of a pyrrole ring. Vibrational bands that
occur at 1050, 940, 856, 780, and 590 cm−1
are attributed to the
P−O, terminal MoO, V−O bonds, and bridged Mo−O−Mo
bonds, respectively. This affirms the presence of the integrated
PVMo11 polyanion structure. The bands at 2933, 2870, 1630,
1586, 1384, and 1040 cm−1
ascribed to the aliphatic C−H
bonds, CO, C−OH, C−O−C, and C−O, respectively,
upholding the GO integration.42−44
The crystalline nature of the as-derived nanohybrid was
probed using powder X-ray diffraction patterns. Figure 1b
exhibits the diffraction pattern, confirming the integration of
PVMo11 deposited PPy on the GO surface. The strong peak at a
9.5° diffraction angle arises from the merge of (001) planes of
pristine GO with (002) planes of PVMo11 polyanion crystals.
The crystal plane of pristine GO at 9.5° corresponding to the d
spacing of 9.30 Å, which is more significant than pristine
graphite and arises due to the oxygen-containing functional
group alongside interlayer water molecules of it. The amorphous
nature of PPy is well-observed as the broad peak ranges from a
23°−30° diffraction angle. Moreover, the discrete peaks at
diffraction angles of 18° and 26° confirm that PVMo11
polyanions [JCPDS no. 00-045-0611] do not lose any
crystallinity during the nanohybrid formation.42,43
FTIR
spectrum and diffraction pattern of pure PPy, GO, and
PVMo11 are shown in Figure S1 in the Supporting Information
(SI).
The morphological incongruity and microstructure of
constructed nanohybrids were examined using FESEM. Figure
2a shows the FESEM micrograph of PVMo11−PPy/GO,
displaying a sphere like morphology cluttered with nanosheets.
The polymerization of pyrrole that occurred on the GO
nanosheet’s surface with the help of PVMo11 balances the charge
neutrality with PPy. Hence, the nanohybrid forms a layer
structure of PVMo11−PPy/GO, leading to many macropores on
the nanohybrid surface. The GO nanosheets exhibit a thickness
in the range of 38−40 nm, while the polymers’ nanopore
dimensions are in the range of 87−102 nm (Figure 2a). The
average pore diameter measured from the micrograph was
approximately 220 nm. The micrograph of a nanohybrid at
different magnifications shown in Figure S2 exhibits a similar
porous nature. The GO nanosheet offers additional mechanical
strength to the polymer backbones during the repetitive
charging−discharging process. At higher magnification, the
micrograph shows that the polyanions are well decorated
throughout the polymer structure (Figure S2).
Furthermore, the FESEM image of the pristine PVMo11 at
different magnifications confirms the crystalline topography
(Figure S3). Moreover, the micrograph of the pristine PPy
Figure 2. (a) FESEM micrograph, (b) EDX spectrum, and elemental
analysis of the PVMo11−PPy/GO nanohybrid.
Figure 3. HRTEM image of the PVMo11−PPy/GO nanohybrid at
different magnifications.
Figure 4. Indexing of the SAED pattern for the PVMo11−PPy/GO
nanohybrid.
Energy Fuels 2021, 35, 18824−18832
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(Figure S4a) exhibits an internal cavity like structure, enabling
easy transport of the electrolyte to the inner part and the external
surface of the nanotubes. The elemental analysis with an atomic
percentage of the constituent elements was studied employing
energy-dispersive X-ray spectra (as shown in Figure 2b). All the
Figure 5. (a) Thermogravimetric analysis and (b) N2 adsorption−desorption isotherm [(inset) pore size distribution] of the PVMo11−PPy/GO
nanohybrid.
Figure 6. (a) Cyclic voltammetry (b) galvanostatic charge−discharge response, (c) variation of Coulombic eﬃciency and speciﬁc capacitance with
current densities, and (d) Ragone plot of the PVMo11−PPy/GO nanohybrid.
Energy Fuels 2021, 35, 18824−18832
18827

elements (C, N, O, Mo, V, and P) also support the nanohybrid
formation.
Transmission electron spectroscopy (TEM) was carried out
to elucidate the microstructure of the nanohybrid. Figure 3
illustrates the porous morphology, where the polymer clusters
are fastened between GO nanosheets. The darker area specifies
the indistinct stacking of the components. Significantly, the
micrograph confirms the nanohybrid formation, providing a
large surface area for faster operation. Furthermore, the selected
area electron diffraction (SAED) was performed to verify the
indexing of the crystal planes. The concentric bright rings (as
shown in Figure 4) with bright white spots prove the
combination of the polycrystalline PVMo11 with PPy and GO.
The SAED pattern further provides structural insight and
corroborates the microcrystalline properties (crystal planes)
obtained from XRD.
Thermogravimetric analysis (TGA) is a valuable tool for
better understanding the consequences of predetermined
heating range and temperature conditions for nanohybrid.
TGA analysis on the PVMo11−PPy/GO nanohybrid was used to
examine its thermal stability (as shown in Figure 5a). We found
moderately good stability over an extended temperature range
compared with pristine PPy and GO separately.44,45
An initial
mass loss of 8.5% was observed at 110 °C due to the moisture
removal from the crystal. The nanohybrid suffers a steady weight
loss of 29.27% above 200 °C, corresponding to the inorganic
component’s phase transition. PVMo11−PPy/GO decomposes
further at 735 °C owing to the complete structural collapse of
the polyanions, and beyond that, total loss of its structure occurs
over 800 °C (See Figure S5 in the SI).
Next, the nitrogen adsorption isotherm was analyzed to know
the nanohybrid’s textual parameters, porosity, and pore
distribution. Figure 5b shows a steep N2 gas uptake at higher
relative pressure ranging from 0.8 to 1.0, implying the
macropore’s existence. Moreover, a slight N2 uptake observed
in the lower relative pressure regime of less than 0.05 was
attributed to the micropore filling.46
The coexistence of both
micropores and macropores was further confirmed from the
pore size distribution curve, as shown in Figure 5b (inset
Scheme 1. Plausible Oxidation/Reduction Mechanism of
Graphene Oxide (GO) Electrode Coatings Doped with 11-
Molybdovanadophosphoric Acid and Polypyrrole
Figure 7. Response graph of (a) reciprocal of specific capacitance against the square root of scan rate and (b) specific capacitance against reciprocal of
the scan rate for the PVMo11−PPy/GO nanohybrid. (c) Representation of the capacitance distribution.
Energy Fuels 2021, 35, 18824−18832
18828

picture). The specific surface area (SBET) and the average pore
volume of the nanohybrid are 16.0 m2
g−1
and 0.08 cm3
g−1
. The
relative micropore size and area were calculated to be around
19.4 Å and 0.3 m2
g−1
, respectively.
3.2. Supercapacitor Performance. The electrochemical
properties of the symmetric SC cell were first examined by a two-
electrode cyclic voltammetry (CV) system using a 0.1 M H2SO4
solution as the electrolyte. The CV of PVMo11−PPy/GO
nanohybrid was acquired within the potential window of 0 to 1 V
in various scan rates ranging from 100 to 10 mV s−1
(as can be
seen in Figure 6a). Multiple pairs of faradaic peaks on distorted
rectangular voltammograms were observed, reflecting the
coexistence of the cell’s double layer and faradaic behavior.
The anodic oxidation peaks were observed at 0.1, 0.4, and 0.6 V,
with corresponding cathodic reduction peaks at 0.3 and 0.7 V,
corroborating with the literature.47,48
The distinct redox peaks
of pristine PPy and PVMo11 seamlessly demonstrate their faradic
behavior (Figure S6). However, the nanohybrid formation
overlaps the reduction peaks of PPy and PVMo11 into one (0.4
V) while three oxidation peaks are distinguishable. Furthermore,
the reaction mechanism associated with the nanohybrid
provides a better insight into the charge storage, as illustrated
in Scheme 1 below.
With the increase of scan rate, the redox peak current becomes
more prominent, which means that the PVMo11−PPy/GO
nanohybrid facilitates a fast redox reaction. The highest specific
capacitance calculated from the voltammogram’s areal integra-
tion is approximately 359.73 F g−1
with the enhanced specific
energy of 49.96 Wh kg−1
at a scan rate of 10 mV s−1
(using
equation S1 in the SI). Specific capacitance values with
corresponding specific energy at different scan rates are
summarized in Table S1.
For practical applications, such as hybrid vehicles or solid-
state electronic devices, voltage response should remain
unchanged with time for a constant current. The symmetric
cell’s galvanostatic charge−discharge (GCD) was performed to
determine the nanohybrid electrode’s efficiency in SC
applications. The GCD plots of the PVMo11−PPy/GO
nanohybrid (Figure 6b) exhibit typical plateau like deformations
in a triangular shape, demonstrating the coexistence of both the
charge storing mechanism (EDLC + pseudocapacitance
behavior).49,50
The specific capacitance with specific energy
and power densities calculated for various current densities
(from 0.5 to 8 A g−1
) are tabulated in Table S2 (eqs S1−S4).
The PVMo11−PPy/GO nanohybrid offers the maximum
specific capacitance of 354 F g−1
with enhanced specific energy
and specific power of 49.16 Wh kg−1
and 999.86 W kg−1
,
respectively, at a current density of 0.5 A g−1
and Coulombic
efficiency of 71.08% (see Table S2 in the SI). The nanohybrid
exhibits a high specific power of 10 000 W kg−1
at a higher
current density of 5 A g−1
. The variation of specific capacitance
and Coulombic efficiency with the current density change is
Figure 8. (a) Nyquist plot. (inset) Equivalent series circuit. (b) Bode plot. (c) Variation of capacitance with frequency. (d) Cycle stability of the
PVMo11−PPy/GO nanohybrid at a 15 A g−1
current density.
Energy Fuels 2021, 35, 18824−18832
18829

depicted in Figure 6c. Coulombic efficiency (ratio of discharge
time to charging time) increased with the increase in current
density. This implies the electrode’s good energy storage ability
even at high current density. The ratio of specific energy to
power can give us information about the type of cell
(supercapacitor, battery, or plane capacitor). Herein, the
nanohybrid’s Ragone plot (Figure 6d) displays the symmetric
nature of our SC cell. This proves that the nanohybrid could be
effectively used as an efficient energy storage device. The
PVMo11−PPy/GO nanohybrid electrode in SC cells exhibits
maximum specific power and energy of ∼10 000 W kg−1
and
∼50 Wh kg−1
, respectively, demonstrating its enhanced
performance metrics, which can be used for energy storage
purposes.
The effective charge contribution from EDLC and
pseudocapacitance was analyzed using the Trasatti method.51
The total specific capacitance (CT) was calculated from eq 1
(Figure 7a), whereas the surface contribution of the capacitance
(CEDLC) was computed from eq 2 (Figure 7b). Equation 3
represents the relationship of CT with the pseudocapacitance
(CPseudo) part. It has been observed that the PVMo11−PPy/GO
nanohybrid holds 90.08% of pseudocapacitance (contributed
from PVMo11−PPy) and a modest contribution of 9.92% double
layer capacitance (contributed from GO) and the combined
contribution is 100% (Figure 7c). The cyclic voltammogram of
PPy exhibits a perfect pseudocapacitive response (Figure S6a),
and pristine PVMo11 demonstrates a faradaic nature (Figure
S6b), which further experimentally corroborates the results from
eq 1−3.
ν
= × +
− −
C C
constant
1 0.5
T
1
(1)
ν
= × +
−
C C
constant 0.5
EDLC (2)
= +
C C C
T EDLC Pseudo (3)
Electrochemical impedance spectroscopy (EIS) was per-
formed to explore the interface charge transfer phenomenon of
the PVMo11−PPy/GO nanohybrid electrode. Figure 8a exhibits
the Nyquist plot with an equivalent series circuit (Figure 8a
inset), explaining the variation of complex impedance within the
frequency regime of 100 kHz to 10 mHz with the application of
10 mV dc potential. As can be seen in the Nyquist plot, the SC
cell demonstrates a small equivalent series resistance (Rs) of 1.07
Ω (obtained from nonzero intercept in the X-axis), alongside
transfer resistance (RCT) of 5.9 Ω (calculated from the diameter
of the semicircular arc). Rs is responsible for the dissipation of
energy stored in a cell. Besides, the magnitude of Rs also limits
the SC device’s total power and energy efficiency (Table
S3).52,53
A steeper straight line at the low-frequency region
suggests a low diffusion resistance of the electrolyte medium,
providing multiple ion transportation pathways. The Bode plot
(Figure 8b) explains the phase-impedance relation with variable
frequencies. The cell’s phase angle is close to 90° (ϕ ∼ 60°),
revealing an ideal capacitor performance (Figure 8b). The knee
frequency (fk) and relaxation time constant (τ) calculated from
the Bode plot are 63.1 Hz (at a phase angle of −45°) and 15.8
ms, respectively. The device’s electrochemical performance
could also be analyzed by real and imaginary capacitances
(Table S3) corresponding to frequencies, displayed in Figure 8c.
The total impedance is given by, Z(ω) = Z′(ω) + Z″(ω),
where ω = 2πf, f is the frequency of the input ac signal.
The Total capacitance is given as37
ω ω ω
= ′ − ″
c c jc
( ) ( ) ( ) (4)
where
ω
ω
ω ω
ω
ω
ω ω
′ =
″
| |
″ =
′
| |
c
Z
Z
c
Z
Z
( )
( )
( )
and ( )
( )
( )
2 2
(5)
Furthermore, the cycle stability of the SC is another critical
aspect of the device’s performance. Figure 8d displays the
PVMo11−PPy/GO nanohybrid cycle stability over 5000
sweeping cycles at 15 A g−1
current density. The cell can retain
96% of initial capacitance over the 5000 cycles. The SC cell loses
its capacitance for the early 200 cycles, and after that, it
maintains a steady capacitance for the rest of the sweeping
cycles. The inset picture of Figure 8d displays the initial and final
four charge/discharge cycles, demonstrating no change in
response shape. Two of the SC cells were connected in series to
use it as a power source (to light up the LED bulb). Figure 9
shows the light intensity of the LED bulb at discharge time of t =
0 and 90 s. The prototype cell takes 120 s to charge and
completely discharges in 100 s at a discharge current of 15 mA.
4. CONCLUSION
In summary, we developed a simple and efficient strategy to
synthesize PVMo11−PPy/GO nanohybrid via a one-pot
reaction. The following product is employed as an electrode
material in two-electrode SC devices. PPy acts as a linker to the
polyanions and GO nanosheets, restricting GO sheet restacking
Figure 9. (top) Intensity of red LED bulb at discharge time t = 0 s.
(bottom) Intensity of LED bulb at discharge time t = 90 s.
Energy Fuels 2021, 35, 18824−18832
18830

with a homogeneous distribution of PVMo11 on the surface. On
the other hand, PVMo11−PPy enhanced the pseudocapacitance
via effective charge transfer into the GO nanosheets and created
macropores for a better electrolyte ion diffusion mechanism. As
a result, the SC cell demonstrates enhanced electrochemical
characteristics in 0.1 M H2SO4 solution. The high specific power
of ∼10 000 W kh−1
was recorded with Coulombic efficiency of
92.30%. Furthermore, the specific capacitance of 354 F g−1
is
calculated for 0.5 A g−1
current density with a high specific
energy of 49.16 Wh kg−1
(the same specific capacitance and
energy values were observed from the CV measurements). Thus,
the interfacial design approach at the nanoscale level shows
promising results for high-performance SC applications.
■ ASSOCIATED CONTENT
*
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.energyfuels.1c03300.
FTIR spectrum, and X-ray diffraction pattern of pristine
PPy, PMo11VO40, and GO; FESEM micrograph of the
PVMo11−PPy/GO nanohybrid at different magnifica-
tions; FESEM micrograph of PVMo11 nanocrystals in
different magnifications; FESEM micrograph of pristine
PPy and GO; DTA response of PVMo11−PPy/GO
nanohybrid; cyclic voltammogram of pristine PPy and
PVMo11 at different scan rates; table of specific
capacitance and energy values of the PVMo11−PPy/GO
nanohybrid calculated from CV graphs; table of specific
capacitance, energy, and power of PVMo11−PPy/GO
nanohybrid from GCD graphs; table of Rs, Rct, and cell
capacitance of the PVMo11−PPy/GO nanohybrid from
Nyquist and Bode plots (PDF)
■ AUTHOR INFORMATION
Corresponding Authors
Sib Sankar Mal − Materials and Catalysis Laboratory,
Department of Chemistry, National Institute of Technology
Karnataka, Surathkal 575025, India; orcid.org/0000-
0002-2520-4371; Email: malss@nitk.edu.in
Partha Pratim Das − Low Dimensional Physics Laboratory,
Department of Physics, National Institute of Technology
Karnataka, Surathkal 575025, India; Email: daspm@
nitk.edu.in
Authors
Sukanya Maity − Low Dimensional Physics Laboratory,
Karnataka, Surathkal 575025, India
Madhusree JE − Materials and Catalysis Laboratory,
Department of Chemistry, National Institute of Technology
Bhimaraya R. Biradar − Low Dimensional Physics Laboratory,
Pranay R. Chandewar − Department of Chemical Engineering,
Indian Institute of Technology Hyderabad, Kandi, Sengareddy
502284, India
Debaprasad Shee − Department of Chemical Engineering,
Indian Institute of Technology Hyderabad, Kandi, Sengareddy
502284, India; orcid.org/0000-0002-3503-8098
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.energyfuels.1c03300
Author Contributions
S.M.: Visualization, investigation, original draft preparation,
software work. M.J.E.: Data curation. B.R.B.: Data curation.
P.R.C.: Data curation. D.S.: Writing, reviewing, and editing.
P.P.D.: Supervision, software work, validation, writing, review-
ing, and editing. S.S.M.: Conceptualization, methodology,
writing reviewing, editing, and supervision.
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work was funded by the Science and Engineering Research
Board (SERB), DST, Government of India [EMR/2016/
000808]; Vision Group on Science and Technology (VGST),
Govt. of Karnataka [KSTePS/VGST-RGS-F/2018-19/GRD
no. 827/315]; Vision Group on Science and 490 Technology
(VGST), Govt. of Karnataka [KSTePS/VGSTRGS-F/2018-
19/GRD no. 806/315]. S.M. and B.R.B. acknowledge financial
support from the National Institute of Technology Karnataka
and University Grants Commission India.
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