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Supplementary Information For

Comparative Electrochemical Energy Storage Performance of Cobalt Sulfide and Cobalt Oxide Nanosheets: Experiment & Theoretical Insight from Density Functional Theory SimulationsRutuparna Samal,a Soumen Mondal,b Abhijeet Sadashiv Gangan,c Brahmananda Chakraborty,c,d* Chandra Sekhar Routa*

aCentre for Nano and Material Sciences, Jain University, Jain Global Campus, Ramanagaram, Bangalore 562112, India

bSchool of Basic Sciences, Indian Institute of Technology, Bhubaneswar, Odisha 751013, IndiacHigh Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre,

Trombay, Mumbai-400085, India

dHomi Bhabha National Institute, Mumbai-400094, India

Email:*csrout@gmail.com, r.chandrasekhar@jainuniversity.ac.in (CSR), brahma@barc.gov.in (BC)

Experimental SectionMaterials

Cobalt nitrate hexahydrate (Co(NO3)2.6H2O, 97%, Merck, India), thioacetamide (CH3CSNH2, 99%, Alfa Aesar, UK), Potassium hydroxide (KOH, 97%, Merck, India) were used as received without further purification.

Synthesis of cobalt oxide & sulfide on nickel foam using electrodeposition

Cobalt oxide and cobalt sulfide nanosheet arrays were directly grown separately on Ni foam

using electrodeposition technique. For cobalt sulfide precursor solution was obtained by mixing

0.02 M of Co(NO3)2.6H2O and 0.1 M of CH3CSNH2 in 10 mL DI water under sonication. The

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2020

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deposition electrolyte was heated to 500C under constant stirring. For cobalt oxide, the reaction

solution was obtained by mixing 0.02 M of Co(NO3)2.6H2O. The electrodeposition of cobalt

sulfide and oxide were performed using PG262A potentiostat/galvanostat (Techno Science Ltd.,

Bangalore) by chrono-amperometric technique in an electrochemical glass cell in three electrode

configuration. During electrodeposition, Ni foam acts as the working electrode, Ag/AgCl as

reference electrode and Pt as counter electrode. For cathodic deposition we use -1.1 V as

potential and 6 min as deposition time by keeping the electrolyte solution in room temperature

under constant stirring using magnetic stirrer. After the deposition, each of the sample was

washed by DI water and kept in vacuum for drying. Later on, the cobalt oxide sample was kept

in open air oven at 350 oC for 6 hours, where the hydroxide of cobalt convert into Co3O4 and the

cobalt sulfide sample was kept in vacuum oven at 200 oC for 3 hours for annealing. Typical

mass loading on Ni foam for the supercapacitor studies is around 1.5 mg to 1.9 mg. We also

electrodeposited cobalt oxide and sulfide on FTO glasses by following the above mentioned

method for characterization.

Bare Ni Foam

Cobalt Sulfide on Ni

foam

Cobalt Hydroxide on

Ni foam

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Fig. S1. The photographic representation of the thin film grown Ni foam

Characterization

The morphology and elemental composition of the samples were analyzed using FESEM (MERLIN compact with GEMENI electron column, Zeiss Pvt. Ltd, Germany). XRD pattern were obtained by a Brucker D8 advanced diffractometer using Ni filtered Cu-Ka radiation (λ=1.54184 Å). The wettability test was performed using TECH CON-1200 contact angle measuring instrument. Surface morphology were studied using Thermo ScientificTM TalosTM F200S with High-Resolution Transmission Microscopy (HRTEM) at 200 keV.

30 40 50 60 70

$$

2 (degree)

Inte

nsit

y (a

.u.)

$ Co3S4 JCPDS # 47-1738

Ni foam

$

20 30 40 50 602 (degree)

Inte

nsity

(a.u

.)

*

* Co3O4 JCPDS # 73-1701

Ni foam

****

*

*

30 40 50 60 70

$ Co3S4 JCPDS # 47-1738

* Co3O4 JCPDS # 73-1701

Ni foam

2 (degree)

Fig. S2 X-ray diffraction patterns of cobalt sulfide and cobalt oxide on Nickel foam substrate

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Fig. S3 XPS survey spectrum of Co3S4 on Ni foam

Fig. S4 XPS spectrum of Co 2p of Co3O4.

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Fig. S5 XPS survey spectrum of Co3O4 on Ni foam.

Fig.S6 EDS spectra of (a) Co3O4 and (b) Co3S4

(a) (b)

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Fig. S7 Elemental mapping of (a) and (b) Co3O4, and (c) and (d) Co3S4.

Fig.S8 Contact angle of (a) cobalt oxide and (b) cobalt sulfide on glass substrate

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Evaluation of electrochemical properties

All the electrochemical measurements for capacity determination of those samples were

performed in a three electrode system using 1 M aqueous KOH solution as the electrolyte. The

cyclic voltammetry (CV) and charge-discharge (CD) measurements of cobalt sulfide were

carried out by keeping the potential window fixed at 0.45 V vs Ag/AgCl. But in case of Co3O4

CVs and CD measurements were performed in the potential window of (0 to 0.5 V) vs Ag/AgCl.

The freshly prepared electrodeposited sample on Ni foam substrate was used as the working

electrode and Platinum wire as the counter electrode. The specific capacitance (Csp) was

calculated from cyclic voltammetry curves using the given equation:

(Fg-1) (1s) 𝐶𝑠𝑝 =

∫𝐼(𝑣)𝑑𝑣

𝑚𝑠 ∗ 2[𝑉𝑓 ‒ 𝑉𝑖]

Where the integral part in the numerator gives the area under the CV curve, “m” is the mass of

the active material, “s” is the scan rate, and [Vf – Vi] is the potential window (Vf and Vi are the

final and initial potential values respectively). From the charge/discharge curves, specific

capacitance of the material was calculated using the following equation:

(Fg-1) (2s)

𝐶𝑠𝑝 = 𝐼

𝑚 ∗𝑑𝑉𝑑𝑡

Where I is the discharge current, m is the mass of the sample deposited on the Ni foam surface

and is the slope of the discharge curve.

𝑑𝑉𝑑𝑡

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0 500 1000 1500 2000 2500

0

20

40

60

80

100

120

140

160

180

200

Co3O4

Co3S4

Cou

lom

bic

effic

ienc

y

No of Cycles

Fig. S8 Stability and Coulombic efficiency plot of Co3O4 and Co3S4 at 20 A/g for over 2500 consecutive cycles.

Table S1. Comparative supercapacitor performance of present work with respect to existing

literature on Co3S4 and Co3O4 based supercapacitors.

Sample Specific Capacitance (Fg-1)

Electrolyte Reference

Co3O4 nanocubes (Hydrothermal) 160 Fg-1 (at 2 Ag-1) 1M KOH 3

Co3O4 3D hollow structures (Chemical method)

710 Fg-1 (at 2 Ag-1) 6M KOH 4

Co3O4 ultralayered (Hydrothermal) 604 Fg-1 (at 4 Ag-1) 1M KOH 5

Co3O4 nanotubes (AAO templates method)

574 Fg-1 (at 0.1 A g-1) 6M KOH 6

Co3O4 nanowires (Hydrothermal) 529 Fg-1 (at 2.03 Ag-1) - 7

Co3O4 nanosheet (Electrodeposition) 200 Fg-1 (at 2 Ag-1) 1M KOH Present Work

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Co3S4 nanosheet (Hydrothermal) 1037 Fg-1 (at 1 A/g-1) 2M KOH 1

Co3S4 nanosheet (Hydrothermal) 1081 Fg-1 (at 1.61 A/g-1) - 6

Co3S4 hollow nanospheres (Hydrothermal)

379.8 F g-1 (at 2 A/g-1) 2M KOH 8

Interlaced nanosheet-like CoS (ED) 1471 F g-1 (at 4 A g-1) 1M KOH 9

Co3S4 crosslinked nanosheets (Hydrothermal)

1369 F g-1 (at 1.5 A/g-1) 6M KOH 2

Co3S4 nanosheet (Electrodeposition) 558 F g-1 (at 2 Ag-1) 1M KOH Present Work

Computational Section

(a) (b)

Fig.S9 Optimized structure of (110) surface of Co3O4 (a) and Co3S4 (b)

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Fig.S10 Partial Density of States of (a) Co d and S p orbital of (110) surface of Co3S4, (b) Co d and O p orbital of (110) surface of Co3O4 .

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8Co3S4 (110)

E-EF (eV)

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