Supercritical fluid processing for the synthesis of NiS2 nanostructures as efficient electrocatalysts for electrochemical oxygen evolution reactions

Article abstract of DOI:10.1039/c7cy01103b

In this work, the synthesis of NiS₂ nanostructures using a simple and one-step environmentally benign supercritical fluid processing technique within 60 min of reaction time has been demonstrated. Structural and morphological characterization has been performed to confirm that the as-synthesized products are cubic NiS₂ nanostructures. Interestingly, the as-prepared NiS₂ nanostructures exhibit superior electrocatalytic activity towards the oxygen evolution reaction with a small overpotential of 264 mV vs. RHE at 10 mA cm^-2 and a Tafel slope of 105 mV dec^-1. Remarkably, the observed catalytic activity of the NiS₂ nanostructures bears close resemblance to that of the benchmark IrO₂ catalyst, where IrO₂ shows an overpotential of 260 mV with a Tafel slope of 95 mV dec^-1. Thus, the as-synthesized NiS₂ nanostructures can be considered as a promising material for the replacement of noble metal-based IrO₂ catalysts.

Full text of DOI:10.1039/c7cy01103b

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DOI: 10.1039/C7CY01103B
Catalysis Science & Technology
PAPER
Supercritical Fluid Processing for the Synthesis of NiS2
Nanostructures as Efficient Electrocatalyst for Electrochemical
Oxygen Evolution Reaction†
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Pitchai Thangasamya,b, Viruthasalam Maruthapandiana,c, Velu Saraswathya,c and Marappan
Sathisha,b*
www.rsc.org/
In this work, synthesis of NiS2 nanostructures using a simple and one- enhance the efficiency of water splitting process, catalyst is needed
step environmentally benign supercritical fluid processing within 60 to accelerate the rate of reaction.2 Precious metals and their oxides
min reaction time has been demonstrated. The structural and (Pt, IrO2 and RuO2) were used as efficient OER catalysts and they
morphological characterizations have been performed to confirm exhibits a lower overpotential (η). However, it was limited to large
the as synthesized product was cubic NiS2 nanostructures. scale deployment because of their low earth abundance, high cost
Interestingly, the as prepared NiS2 nanostructures exhibit superior and instability under long-term OER condition in acid or alkaline
electrocatalytic activity towards the oxygen evolution reaction with medium.3-6 Numerous efforts have been devoted to develop highly
a small overpotential of 264 mV vs. RHE at 10 mA cm-2 and a Tafel active OER catalysts with low cost and earth abundant. Hence, the
slope of 105 mV dec-1. Remarkably, the observed catalytic activity of non-noble metal based transition metal oxides, hydroxides,
NiS2 nanostructures are very close resemblance to the benchmark oxyhydroxides, phosphides, phosphates, sulphides, selinides,
IrO2 catalyst where IrO2 shows the overpotential of 260 mV with a borates and perovskites have received much attention and
Tafel slope of 95 mV dec-1. Thus, the as-synthesized NiS2 extensively explored due to their good catalytic activity as well as
nanostructures can be considered as promising material for the stability in wide pH range.7-25
replacement of noble metal based IrO2 catalyst.
Generally, Ni based compounds were reported as the attractive
OER catalysts due to the active (γ-NiOOH to β-NiOOH) intermediates
formation in alkaline medium,26 which are mainly responsible for an
enhanced OER. Among the various Ni based compounds, nickel
Introduction
Electrochemical splitting of water (H2O→H2 + 1/2O2) into
molecular hydrogen (H2) and oxygen (O2) is an effective, eco- sulphides have aroused much interest due to its multifarious
applications in various fields and it has the more number of
crystalline phases such as α-NiS, β-NiS, NiS2, Ni3S4, β-Ni3S2, Ni7S6 and
Ni9S8.27 It is important to note that coexistence of nickel sulphides
with different crystalline phases and morphologies is common during
the conventional synthesis. Thus, the phase pure preparation of
nickel sulphide with uniform morphology is highly warranted for
friendly, earth abundant and low cost renewable energy
approaches. It can be considered as clean energy process since
there is no greenhouse gases evolution that damage the
environment as like conventional fossil fuels. The overall water
splitting reaction was mainly hampered by anodic four
electron/proton transfer oxygen evolution reaction (OER)
compared to the two electron/proton transfer cathodic desired applications. Recently, Zhou et.al. reported the fabrication of
Ni3S2 nanorods/Ni foam composite by hydrothermal method and
they explored these composite electrode material for
electrocatalytic OER with a low overpotential of ~157 mV.28 A very
few attempts have been made to synthesis the cubic NiS2
nanostructures for supercapacitor, HER, and oxygen reduction
reaction applications.29-33 Indeed, there are no attempts have been
made to synthesize the NiS2 nanostructures by supercritical fluid
(SCF) processing and also its application in electrocatalytic OER is not
known in literature. Here, the NiS2 nanostructures were prepared
using the environmentally benign SCF processing and exploited for
hydrogen evolution reaction (HER). Hence, the anodic OER is a
rate-limiting and energy intensive process that requires large
overpotential and more energy consumption.1,2 In order to
minimize the energy consumption/overpotential and simultaneously
a.Academy of Scientific and Innovative Research, Karaikudi-630 003, Tamil
Nadu, India.
b.Functional Materials Division, CSIR-Central Electrochemical Research Institute,
Karaikudi-630 003, Tamil Nadu, India.
c. Corrosion and Materials Protection Division, CSIR-Central Electrochemical
Research Institute, Karaikudi-630 003, Tamil Nadu, India.
*Corresponding author: marappan.sathish@gmail.com and
msathish@cecri.res.in
†Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
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DOI: 10.1039/x0xx00000x
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electrochemical OER in alkaline medium. Recently, SCF assisted wavelength of 633 nm. The morphological stVuiedwieAsrticolefOnalinse-
DOI: 10.1039/C7CY01103B
synthesis of inorganic nanomaterials has been considered as the synthesized NiS2 product was evaluated using field emission
promising route for diverse applications.34 SCF reaction medium was scanning electron microscopy (FE-SEM; Carl Zeiss AG, Supra
created by increasing the temperature and pressure of the solvents 55VP) and high resolution transmission electron microscopic
above their critical points, where a single homogenous phase was (HR-TEM; Tecnai G2 F20, S-Twin working at an accelerating
formed. Thus, the fluid has both vapour and liquid properties such as voltage of 200 kV) analysis at different locations. The X-ray
gas-like diffusivity, liquid-like solvent properties along with low photoelectron spectroscopy (XPS) analysis was recorded for the
viscosity.35 Remarkably, the particle size distribution and NiS2 nanostructures using Thermo Scientific MULTILAB 2000
morphology of the nanomaterials can be tuned by varying the base system with X-ray, Auger and ISS attachments containing
parameters such as temperature, pressure and fluid medium. Since Twin Anode Mg/Al (300/400 W) as X-ray source.
the physical properties of the fluids such as density, viscosity and
dielectric constant can be altered with temperature and pressure. In Electrochemical measurements
addition, the surface tension of the fluid was completely vanished in
The electrochemical studies were performed using Autolab
the SCF condition which is an essential parameter to control the potentiostat-galvanostat (model PGSTAT-30) electrochemical
surface and interface chemistry of the nanostructures. Recently, the workstation. OER measurements were carried out using cyclic
SCF method has been extended for the preparation of high quality voltammetric (CV) method in a standard three electrode setup
few layer 2D inorganic nanomaterials from their bulk materials in a where 1 M KOH solution and Pt wire were served as the
short reaction time.36-40
electrolyte and counter electrode, respectively. Further,
saturated calomel electrode and NiS2 catalyst modified carbon
paper (CP) were used as the reference electrode and working
electrode, respectively. The catalyst ink was prepared by
dispersion of 2 mg of catalyst in 450 μL of water and 50 μL of
Nafion (5 wt% isopropanol) solution by 30 min ultrasonication.
The working electrode was prepared by drop casting the above
catalyst ink (0.3 mg loading) in the area of 1 cm2 of CP substrate.
CV measurements were conducted at the static condition of
working electrode. Whereas the electrolyte solution was stirred
at constant rotation. The linear portion of anodic curve in CV
was taken as linear sweep and mentioned as a linear sweeping
voltammetry (LSV). The potentials were calibrated to a
In this work, the ethanol-toluene mixture has been utilized as SCF
for the synthesis of NiS2 nanostructures in a short reaction time of 60
min. The as-synthesized NiS2 nanostructures showed the superior
OER catalytic activity with a small overpotential of 264 mV vs. RHE at
10 mA cm-2 and a Tafel slope of 105 mV dec-1.
Experimental section
Synthesis of NiS2 nanostructures:
NiS2 nanostructures were synthesized using one-pot SCF
processing. In a typical synthesis, 1 mmol of nickel (II) nitrate
hexahydrate and 2 mmol of commercial sulphur powder was
taken and dissolved in 12.5 mL ethanol and 12.5 mL toluene
solution, respectively. The solutions were mixed together and
ultrasonicated for 15 min. Then, the resulted homogenous
solution mixture was poured into a 35 mL supercritical reactor
and placed in a preheated vertical tubular furnace at 400 °C for
60 min. The reactor was quenched in an ice cold water bath and
the obtained black colour precipitate of NiS2 was collected by
repeated washing with ethanol-water mixture using
centrifugation and then dried in a hot air oven at 70 °C for 6 h.
For comparison, NiS2 nanostructures were also prepared by
solvothermal method using the same precursor solutions in a 50
mL Teflon lined autoclave reactor at 180 °C for 24 h. The
obtained NiS2 nanostructures by SCF and solvothermal methods
are designated as NiS2 SCF and NiS2 Sol in the further results and
discussion, respectively.
reversible hydrogen electrode (RHE) using the relation of ERHE
=
EMeasured + ERef + 0.059*pH. The overpotential (η) was calculated
using the following equation: η = EObserved - EEqu at the current
density of 10 mA cm-2. Electrochemical impedance
spectroscopy (EIS) were measured in the frequency range from
1000 kHz to 10 mHz with an amplitude of 30 mV under the OER
condition (300 mV of η) for the charge transfer kinetics.
Results and Discussion
Fig. 1a represents the typical XRD pattern of as-synthesized
product by one-pot facile SCF processing and the standard
reference pattern of cubic NiS2 (JCPDS No: 01-089-3058). The
observed well-defined diffraction peaks are readily indexed to
the cubic NiS2 phase with lattice parameter of a = 5.67 Å. It is
important to mention here that other non-stoichiometric nickel
sulphide phases and impurities were not detected in the XRD
pattern. It proves that the as-synthesized NiS2 product is in a
single phase with high purity. In addition, the high intense
diffraction lines indicate the obtained NiS2 product is well
crystalline in nature even without any thermal heat treatment.
XRD pattern for the NiS2 product obtained by solvothermal
method is shown in Fig. S1. It clearly indicated that the
significant amount of NiSO4.H2O (JCPDS No: 021-0974) impurity
coexists with cubic NiS2 product. These results clearly revealed
Structural characterizations:
The crystalline nature of as-synthesized NiS2 product was
confirmed by powder X-ray diffraction pattern using BRUKER D8
ADVANCE X-ray Diffractometer with Cu Kα radiation (α = 1.5418
Å). The XRD was recorded from 2θ = 10 to 80° in steps of 0.02°
and a count time of 0.2 s. The formation of NiS2 product was
further confirmed by Raman spectroscopy using RENISHAW
Invia laser Raman microscope system with He-Ne laser having a
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that SCF processing is an effective route for the synthesis of
The formation of NiS2 nanostructures under SCF condition
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DOI: 10.1039/C7CY01103B
phase pure crystalline nanomaterials in a short reaction time. was further confirmed by HR-TEM analysis (Fig. 3). The lateral
Raman spectra of as-synthesized NiS2 SCF product was shown in size of NiS2 nanostructures were in good agreement with FE-
Fig. 1b. The first two broad peaks was deconvoluted and shown SEM analysis. The transparent thin nanostructures observed at
in Fig. S2. The observed peaks in the deconvoluted spectra at the high magnification TEM images (Fig. 3c-d & S3). SAED
237, 272, 507 and 565 cm-1 are the characteristic peaks of NiS2 pattern indicated the crystalline nature of NiS2 under SCF
crystals.41,42 The other two deconvoluted peaks at 164 and 194 condition which is in good agreement with the XRD
cm-1 are assigned to the other stoichiometric nickel sulphide observations. The lattice fringes values have been measured
systems.42 In addition, the observed broad peaks around at 710 and found to be 0.25 nm that corresponds to the (210) plane of
and 1080 cm-1 revealed the formation of NiO nanoparticles over cubic phase of NiS2. To identify the presence of elements in the
NiS2 surface.43 However, these oxide layer was not determined as synthesized NiS2 nanostructures, SEM-EDX analysis have
by the XRD due to very thin layer or amorphous NiO.28 It clearly been performed and it is presented in Fig. S4. It showed the
suggests that the surface of NiS2 nanostructures were oxidized peak that corresponds to Ni, S and O elements. It revealed that
under an air atmosphere or high temperature SCF treatment the as synthesized sample comprised of Ni and S with no other
which is well consistent with XPS analysis.
impurity.
Fig. 1 (a) XRD pattern and (b) Raman spectra of as synthesized NiS2
SCF nanostructures.
Electron microscopic analysis has been employed to
investigate the surface morphology of the as-synthesized
sample obtained by SCF processing. Fig. 2 represents the FE-
SEM images of NiS2 sample that is coated over silica substrate.
It revealed that the obtained NiS2 nanostructures have lateral
dimensions ranging from 50 to 200 nm.
Fig. 3 (a-e) HR-TEM images of the as synthesized NiS2 SCF
nanostructures and (f) the corresponding SAED pattern.
However, the detected oxygen peak indicates that NiS2
surface was mildly oxidized in an atmospheric condition and/or
SCF condition, which is well consistent with XPS analysis results
(Fig. 4). The high resolution Ni 2p spectra shows four peaks in
which the prominent peaks at 854.2 and 871.5 eV are attributed
to Ni 2p3/2 and Ni 2p1/2, respectively.44,45 While, the other two
weak peaks at 860 and 879 eV can be ascribed to the binding
energy values of nickel where it is linked to oxygen species.28 It
suggested that NiS2 nanostructure surfaces were oxidized when
it is exposed to atmosphere and/or under high temperature SCF
Fig. 2 (a-d) FE-SEM images of the as synthesized NiS2 SCF
nanostructures.
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treatment. Fig. 4b shows the deconvoluted S 2p spectra,
wherein 1:2 intensity ratio of S 2p1/2 and S 2p3/2 peaks can be
In the metric relevant to derive the current density of 10 mA cm-
DOI: 10.1039/C7CY01103B
(current density is approximately equal to 10% efficiency of solar to
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2
seen at 163.6 and 162.3 eV, respectively.46,47 Surprisingly, fuel conversion by one time sun light illumination),54 NiS2 SCF-CP was
another broad peak was observed at 166-172 eV is due to the delivered at 1.494 V vs. RHE, which results in an overpotential of 264
oxidized sulphur species.48-50
mV close to IrO2-CP (260 mV). Whereas, NiO-CP and NiS2 Sol-CP
samples exhibited overpotential of 385 and 336 mV, respectively. It
could be attributed to the presence of less accessible active sites for
the adsorption of OH- ions that is well supported by the Faradaic
active site measurement. Further, the obtained catalytic activity for
all the electrocatalysts were compared at an identical conditions (Fig.
5c).
Fig. 4 (a) Ni 2p and (b) S 2p high resolution XPS spectra of NiS2 SCF
nanostructures.
Electrocatalytic OER activity of NiS2 SCF nanostructures on CP
substrate (NiS2 SCF-CP) were examined using CV measurements and
its activity was compared with NiS2 sol (NiS2 Sol-CP), commercially
purchased NiO (Sigma Aldrich) (NiO-CP) and benchmark IrO2 (IrO2-
CP) electrocatalysts. Fig. 5a display the CVs of NiS2 SCF-CP, NiS2 Sol-
CP and NiO-CP were recorded at a scan rate of 2 mV s-1 in 1 M KOH
solution. All the electrocatalysts show a pair of redox peaks around
at 1.35 and 1.25 V vs. RHE in the anodic and cathodic direction,
respectively. It corresponds to the redox reaction between Ni2+ and
Ni3+ (Ni2+ + OH- ↔ NiOOH + e-).16 It is important to mention here that
the similar redox peaks were also observed by Chen et.al, where they
have synthesized the NiSe2 on Ni foam and studied their catalytic
activity towards OER.16 To ensure the extent of adsorption of
OH- ions on the surface of different electrocatalysts during the OER,
Faradaic active sites have been calculated from the voltammetric
charge (q*) based on the eqn 1. The magnitudes of Faradaic active
sites reflects the adsorption capacity of OH* and H2O* on the surface
of electrocatalysts.51-53
Fig. 5 (a) CVs of different electrocatalysts modified CP, (b) LSV of bare
CP and electrocatalysts (NiO, NiS2 Sol, NiS2 SCF and IrO2) on CP at a
scan rate of 2 mV s-1 in 1 M KOH, (c) Comparison of catalytic activity
of all the electrocatalysts under identical conditions and (d) Tafel
plots of NiO, NiS2 Sol, NiS2 SCF and IrO2 on CP.
It is persistent to note that current density (mA cm-2) of both
electrodes (NiS2 SCF-CP and IrO2-CP) at constant η and the η at
10 mA cm-2 is a close resemblance to each other. The
comparable OER catalytic activity of NiS2 SCF nanostructures to
benchmark IrO2 electrocatalyst are attributed to the sheet-like
surface characteristics (Fig 3a-d&S3). Tafel slope (η = a + b log
(j); where η, a, b and j is the overpotential, constant, Tafel slope
and current density, respectively) analysis was conducted to
evaluate the kinetic behaviour of the different electrocatalysts
are shown in Fig. 5d. It was noted that comparable Tafel slope
value observed for NiS2 SCF (105 mV dec-1) and IrO2 (95 mV dec-
1) modified CP electrode. While, NiS2 Sol-CP and NiO-CP showed
the Tafel slope values of 112 and 126 mV dec-1, respectively. The
closest Tafel slope values of NiS2 SCF and IrO2 is again proves
the close resemblance of their OER catalytic activities. It is
worthy to mention here that the observed high Tafel slope
values could be attributed to the diffusion limitation through
the CP or Ni foam electrode.9,28,55-57 Though, the Tafel slope
value of NiS2 is much lower than that of recently reported
literatures where the OER electrocatalysts are Ni3S2 in Ni foam
1
퐸2
( )
푖 퐸 푑퐸
q* =
(1)
∫
퐸1
푣푚푆
where q* is the estimated charge (mC cm-2 mg-1) which is directly
proportional to the active sites of catalytic layer, v is the scan rate (V
s-1), m is the mass of catalyst (mg) loaded on the substrate, S is the
geometrical surface area (cm2) of catalyst loaded substrate (CP), E1
and E2 is the range of scanning voltage in CV. The q* values under
the redox peak (Ni2+/Ni3+) in the different electrocatalysts have been
calculated and the results were shown in Fig S5. It clearly suggests
that NiS2 SCF-CP has more accessible active sites for the formation of
surface hydroxides compared to NiO-CP and NiS2 Sol-CP. Fig. 5b
shows the LSV of OER of bare CP, NiS2 SCF-CP, NiS2 Sol-CP, NiO-CP,
and IrO2-CP at a scan rate of 2 mV s-1 in 1 M KOH. It can be clearly
seen that bare CP showed poor catalytic activity for OER compared
to electrocatalysts modified CP. Among the modified CP, NiS2 SCF-CP
shows comparably close catalytic activity to IrO2 and higher than
NiO-CP and NiS2 Sol-CP.
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(150-170 mV dec-1) and Ni3S2/AT Ni foam (159.3 mV dec-1).56,57 observed closest Rct value between NiS2-SCF-CP (7V.7ie1w oArhticmle)Oanlninde
DOI: 10.1039/C7CY01103B
The obtained NiS2 catalytic activity was compared with recent IrO2-CP (6.79 ohm) further confirms the existence of proficient
reports on different nickel sulphide system (Table S1).
catalytic activity in SCF assisted synthesized NiS2 nanostructures
The stability of NiS2 catalyst was assessed through CV with that could replace the IrO2 based electrocatalysts. Further, the
accelerated scan rate (30 mV s-1) for 500 cycles in the potential observed EIS results well coinciding with previous LSV and Tafel
window of 1 to 1.7 V vs. RHE in 1 M KOH solution (Fig. 6a). It slope analysis.
revealed that the catalytic activity is increase (η was decreased
The possible mechanism for enhanced OER electrocatalytic
by ~26 mV) upon the electrochemical aging. In addition, the activity and stability of NiS2 catalyst can be described to the
stability of NiS2 catalyst was measured under the OER condition sheet-like nature of NiS2. It provides the freely accessible active
using chronoamperometry method at the applied potential of sites for catalytic OER initially and then the catalytically active
1.7 V vs. RHE (Fig. 6b). It indicates that OER catalytic current metal hydroxide and metal (oxy)hydroxide (NiOOH); (M2+
→
density was increased with an increase in time. It is well M3+) intermediates were formed upon the continuous OER. In
consistent with the accelerated CV stability test and the the meantime, a decrease of sulphur content is also enhancing
previous reports on Ni containing OER catalysts.58-61 Based on the formation of active intermediates in the high alkaline
the observations and previous reported literatures, the condition.16,58 The similar increase in activity on Ni-based
enhancement of NiS2 electrocatalytic activity upon the sulphur systems have also been observed extensively in the
electrochemical aging is due to the formation of catalytically previous reported literatures.16,58,61,62,64
active nickel hydroxide/nickel (oxy) hydroxide intermediates by
the reaction between NiO covered NiS2 and KOH electrolyte. In
addition, the significant decrease in sulphur from the NiS2
surface was observed due to the dissolution of sulphur by
continuous electrochemical cycling that was confirmed by XRF
analysis (Fig. S6 & S7). Similar sulphur dissolution and the
formation of oxygen rich surface were also observed in the
previous studies on NiS@SLS, NiSx and NiSe2,15,16,58,62 which are
more responsible for an enhanced OER catalytic activity upon
the electrochemical aging.16,58 Generally, the leaching of
sulphur from the metal sulphide surface can be observed when
the applied potential was > 1 V vs. RHE in alkaline condition.16,63
Fig. 7 Nyquist plot of electrocatalysts measured at the η of 300
mV.
Conclusions
Noble metal free NiS2 nanostructures were successfully
synthesised by simple and one-pot SCF processing in a short
reaction time of 60 min. Structural and morphological
Fig. 6 (a) Cyclic stability of NiS2 SCF-CP at a scan rate of 30 mV s-1 and
(b) Chronoamperometric stability of NiS2 SCF-CP at the applied
potential of 1.7 V vs. RHE in 1 M KOH.
characterizations confirmed the formation of cubic NiS2
nanostructures. Remarkably, the as-synthesized NiS2
nanostructures showed the superior OER electrocatalytic
activity with a low overpotential of 264 mV vs. RHE and a Tafel
slope of 105 mV dec-1. The obtained catalytic activity of NiS2
nanostructures are very similar to that of benchmark IrO2
catalyst. Hence, the NiS2 nanostructures are the promising
material for the replacement of noble metal based (IrO2) OER
catalyst. In addition, SCF method is a facile and environmental
benign method for the preparation of high quality crystalline
nanomaterials in a short reaction time. Thus, the SCF method
can be utilized for the synthesis of other metal sulphides/oxides
for diverse applications.
Charge transfer kinetics of different electrocatalysts during
the OER was evaluated using EIS Nyquist plot (ZReal vs ZImg).
Solution induced resistance (Rs) with the electrode/catalyst and
charge transfer resistance (Rct) by the redox reaction could be
connected to OER kinetics; which was evaluated from the
impedance spectrum fitting with Randles plot using the simple
and most common equivalent circuit as inserted in Fig 7.
Capacitance (Cdl) parallel with Rct is due to the double-layer
charging at electrode and solution interface. The measured Rs
values are found to be 3.12, 2.82, 3.84 and 2.97 ohm for NiS2
SCF-CP, NiS2 Sol-CP, NiO-CP and IrO2-CP, respectively. While, Rct
values are found to be 7.71, 20.28, 50.20 and 6.79 ohm for NiS2
SCF-CP, NiS2 Sol-CP, NiO-CP and IrO2-CP, respectively. The
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21 L. Cui, F. Qu, J. Liu, G. Du, A. M. Asiri and X. Sun,
Conflicts of interest
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DOI: 10.1039/C7CY01103B
ChemSusChem., 2017, 10, 1370–1374.
There are no conflicts of interest to declare.
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Acknowledgements
We thank CSIR, India for financial support through MULTIFUN
project, (CSC 0101). PT thanks UGC-CSIR, India for SRF fellowship.
Notes and references
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DOI: 10.1039/C7CY01103B
Graphical Abstract:
Supercritical Fluid Processing for the Synthesis of NiS2 Nanostructures as
Efficient Electrocatalyst for Electrochemical Oxygen Evolution Reaction
Pitchai Thangasamya,b, Viruthasalam Maruthapandiana,c, Velu Saraswathya,c and Marappan
Sathisha,b*
A facile supercritical fluid process was demostrated for the synthesis of cubic NiS2 nanostructures for
efficient electrochemical oxygen evoltion reaction.