ESI

Hydrothermally Synthesized BiVO4 –Reduced Graphene Oxide

Nanocomposite as a High Performance Supercapacitor Electrode with

Excellent Cycle Stability

Shibsankar Duttaa, Shreyasi Palb and Sukanta Dea*

aDepartment of Physics, Presidency University, 86/1 College Street, Kolkata-700073, India

bDepartment of Physics, Raidighi College, South 24 Parganas, Diamond Harbour subdivision, Raidighi, West Bengal 743383, India

Corresponding Author: Email: sukanta.physics@presiuniv.ac.in

1. Reaction and growth mechanism for BiVO4 nano particle formation

The probable reactions taking place in the BiVO4 formation are shown below

(1)𝐵𝑖(𝑁𝑂3)3.5𝐻2𝑂 + 𝐻𝑁𝑂3 + 𝐻2𝑂 𝐵𝑖𝑂𝑁𝑂3 + 3𝐻𝑁𝑂3

(2)𝐵𝑖𝑂𝑁𝑂3 + 𝑁𝑎3𝑉𝑂4 + 𝐻2𝑂 𝐵𝑖𝑉𝑂4 + 𝑁𝑎𝑁𝑂3 + 𝑁𝑎𝑂𝐻

In the present reaction due to the hydrolysis of , soluble was initially 𝐵𝑖(𝑁𝑂3)3.5𝐻2𝑂 𝐵𝑖𝑂𝑁𝑂3

formed which reacted with the ions provided by at pH ~7 and formed the yellow 𝑉𝑂3 ‒ 𝑁𝑎3𝑉𝑂4

precipitate of tetragonal BiVO4. In the above reaction pH of the solution was controlled by

the NaOH. For the duration of hydrothermal treatment, the formed BiVO4 nuclei was

converted to the well crystalline structure of monoclinic BiVO4 nanocrystals.1 Meanwhile,

the addition of different amount GO into the reaction medium produced the rGO/BiVO4

hybrids.

2. Electrode Preparation:

For electrodes preparation active material, acetylene black and polymer binder (PVDF) in a

ratio of 80:10:10 were mixed with appropriate amount of N-Methyl-2-pyrrolidone to make

slurry. Then the slurry was coated on stainless steel coins and annealed at 180ºC for two

Electronic Supplementary Material (ESI) for New Journal of Chemistry.This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2018

hours in order to remove the binder for the electrodes. Two identical (BiVO4/rGO) electrodes

of mass 2mg with PVA/H2SO4 gel electrolyte were used to construct symmetrical solid state

cell. We have also study the electrochemical performances of the BiVO4/rGO hybrid

electrodes with 1M Na2SO4 solutions as electrolyte using two electrode system. We

systematically study the electrochemical performance of the prepared electrode by two

electrode system using CHI 660E work station.

3. Fabrication of the Solid-State Supercapacitor Device

PVA–H2SO4 gel electrolyte was simply prepared as follows: Initially 3 g H2SO4 was mixed

with 30 mL D.I .water and then 3 g PVA was added to the above mixture under vigorous

stirring at 80°C. The whole mixture was kept at 80°C under continuous stirring until the

solution became clear. Then two electrodes were immersed into the PVA–H2SO4 gel

electrolyte for 5 min. They were then pressed one by one and kept at room temperature for

further measurements.

4. Specific Capacitance Calculation

In the case of two electrodes solid state supercapacitor the specific capacitance value was

calculated using Equation S1. Energy density (E) and power density (P) can also be

calculated from Equation S2 and S3. Where, m was the total mass of the electrode materials,

ΔV (V) is the voltage window, I (A) is the response current, ν (V/s) is the scan rate and Δt

(sec) is the discharge time .2,3

𝐶 =4∫𝐼 𝑑𝑉

𝜈𝑚Δ𝑉 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑆1)

𝐸 =18

𝐶(Δ𝑉)2 (𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑆2)

𝑃 =𝐸Δ𝑡

(𝐸𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑆3)

5. Supplementary Figures

Fig.S1†: XRD pattern of BiVO4 samples synthesized at different reaction time.

Fig.S2†: XRD pattern of BiVO4/rGO samples with GO concentration variation.

Fig.S3†: XPS survey scan of B-90 sample.

Fig.S4†: CV graphs of all BiVO4 samples using both (a) 1 M Na2SO4 aqueous electrolyte

and (b) PVA/H2SO4 gel electrolyte respectively.

Fig.S5†: CV graphs of the BiVO4/rGO hybrids using both (a) 1 M Na2SO4 aqueous

electrolyte and (b) PVA/H2SO4 gel electrolyte respectively.

Fig.S6†: Electrochemical performance of all the BiVO4 and BiVO4/rGO hybrids electrodes

under investigation.

Fig.S7†: CV graphs of (a) BG2 and (b) B-90 at different scan rates and CD graphs of (c)

BG-2 and (d) B-90 at different current density using 1M Na2SO4 electrolyte.

Fig.S8†: (a) Cycling stability of BG2 for 1000 cycles at a scan rate of 100 mV s−1 using 1M

Na2SO4 electrolyte, (b) FESEM image of BG2 sample after cycle test.

Fig.S9†: CV graphs of B-90 and BG2 samples under three electrode configuration.

Table S1. Comparison of the electrochemical performance of the BiVO4/rGO supercapacitor

with ternary transition metal oxides and their rGO composites.

Electrode Electrode configura

tion

Electrolyte medium

Specific capacitance

(F/g)

Scan rate

(mV/s)

Current density (A/g)

Energy density (Wh/kg)

Power density

(KW/kg)

Ref.

CoMoO4/graphene

Three 6 KOH 394.5 1 - 54.8 0.197 4

MnFe2O4/graphene

Two (PVA)-H2SO4

120 - 0.1 5.0 0.4 5

NiCo2O4@RGO Three 2 M KOH 737 - 1 - - 6NiCo2O4-CNT Three 6 M KOH 695 - 1 - - 7

CoMoO4/carbon nanotube

Three 1M KOH 170 - 0.1 - - 8

CuCo2O4/Ni foam

Three 6 M KOH 100 - 1 5.98 4.5 9

ZnCo2O4 porousnanotube

Three - 770 - 10 25 2.55 10

ZnCo2O4microspheres

Three - 953.2 - 4 33.1 8 11

MnCo2O4nanostructure

Three - 346 - 1 - - 12

Self-assembledZnCo2O4

nanosheets

Three 2M KOH 1550 - 1 57.4 34.7 13

3D-nanonetCo3O4

Three 6 M KOH 739 F/g - 1 16.42 3 14

MnCo2O4 Three 2 M KOH 290 1 - 10.04 5.2 15

MnWO4 Nanorods

Three NaOH 256.41 - 0.4 - - 16

rGO/BiVO4 Two 151 - 1.4 33.7 8.0 17SWCNT/BiVO4 Three 2 M NaOH 395 2.5 - - 18

Three 1M Na2SO4 563 5 - 200.1 2.88 1M Na2SO4 245 5 - 21.77 0.3

BiVO4/rGO (BG2) Two

PVA/H2SO4 400 5 - 35.37 2.05

Present

work

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