One-step solid phase synthesis of highly efficient and robust cobalt

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A summary of the OER performances of cobalt based chalcogenide catalysts in 1.0. M KOH electrolyte.a. Catalysts η@10 mA cm-2. (mV). Onset potential. (V vs.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2016

One-step solid phase synthesis of highly efficient and robust cobalt pentlandite electrocatalyst for oxygen evolution reaction Mohammad Al-Mamun,a Yun Wang,*a Porun Liu,a Yulin Zhong,a Huajie Yin,a Xintai Su,a,b Haimin Zhang,c Huagui Yang,a Dan Wang,a Zhiyong Tang,a Huijun Zhao*ac

aCentre

for Clean Environment and Energy, Griffith University, Gold Coast Campus, QLD 4222, Australia

bMinistry

Key Laboratory of Oil and Gas Fine Chemicals, College of Chemistry and

Chemical Engineering, Xinjiang University, Urumqi 830046, China cCentre

for Environmental and Energy Nanomaterials, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China

*Corresponding authors. Tel.: +61 7 5552 8261; Fax: +61 7 5552 8067 E-mail addresses: [email protected] (H. Zhao); [email protected] (Y. Wang)

Intensity (a.u.)

700C 600C 500C

Co9S8 (JCPDS# 86-2273) CoO (JCPDS# 09-0402)

10

20

30

40 50 60 2 (degree)

70

80

Fig. S1 XRD patterns of the samples prepared at different calcination temperatures (500-700 °C).

S2

20 μm Fig. S2 Low magnification SEM image of Co9S8/CNS nanocomposite prepared at 700 °C.

S3

100 nm Fig. S3 SEM image of CNS prepared at 700 °C showing the lateral size of several µm with the thickness of ~10 nm.

S4

(a)

(b)

200 nm

200 nm

1 μm

1 μm

(c)

(d)

400 nm

400 nm

1 μm

10 μm

Fig. S4 SEM images of the synthesised samples prepared at calcination temperature of (a) 500, (b) 600, (c) 800 and (d) 900 °C.

S5

20 15 10 5 0

60

0.00

0.04

0.08 P/P0

0.12

30 0 0.0

0.2

0.4 0.6 P/P0

0.8

1.0

(b)

Pore Volume (cm3 g-1)

Pore Volume (cm-3 g-1)

90

25 Volume (cm3 g-1)

Volume (cm3 g-1)

120 (a)

10

0

10

15 20 Pore Diameter (nm)

20 30 40 50 Pore Diameter (nm)

60

25

70

Fig. S5 (a) BET and (b) pore size distribution curves of Co9S8/CNS nanocomposite. The insets in (a) and (b) show the enlarged BET curve in low P/P0 range and the distribution curves of mesopores, respectively.

S6

(b)

(a)

2 μm

(d)

2 μm

Co K

(e)

SK

2 μm

2 μm CK

(c)

Overlay

2 μm

Fig. S6 (a) SEM image, and (b) cobalt, (c) sulfur, (d) carbon and (e) overlay elemental mapping of Co9S8/CNS nanocomposite.

S7

Transmission (a.u.)

1417 cm-1

620 cm-1

-1

1620 cm

1100 cm-1

2000

1600 1200 800 Wavenumber (cm-1)

400

Fig. S7 FTIR spectrum of Co9S8/CNS nanocomposite.

S8

(b)

Intensity (a.u.)

(a)

200 nm

JCPDS No# 86-2273

10

20

30

40 50 60 2 (degree)

70

80

5 μm

Fig. S8 (a) XRD pattern and (b) SEM images of Co9S8 NPs prepared by a hydrothermal method reported elsewhere1 and calcined at 700 °C under Ar atmosphere.

S9

Table S1. A summary of the OER performances of cobalt based chalcogenide catalysts in 1.0 M KOH electrolyte.a Catalysts Co9S8/CNS/CNT Co9S8/CNS CP/CTs/Co-S CoOx-CoSe/NF Ni2.3%-CoS2 Fe3O4@Co9S8/rGO Co9S8@NC Co0.85Se Zn0.76Co0.24S/CoS2 CoS Co0.5Fe0.5S@N-MC Co9S8@MoS2/CNFs CoSe2 Co9S8/CNFs

η@10 mA cm-2 (mV) 267 294 300 300(b) ~310 320 320 324 ~325 361 410 430 430 512

Onset potential (V vs. RHE) ~1.45 ~1.45 ~1.50 ~1.50 ~1.53 1.48 ~1.40 ~1.45 ~1.54 ~1.55 ~1.57 ~1.58 ~1.57 ~1.62

Tafel slope (mV dec-1) 48.2 50.7 72.0 68 119 54.5 85 79 64 159 61 50 78

Mass loading (mg cm-2) 0.24 0.24 0.32 1.7 0.97 0.25 0.22 0.6 1.0 0.1 0.21 1.0 0.21

Substrate

Reference

GCE GCE CP Ni foam CC GCE GCE Carbon cloth Ti Ti GCE GCE GCE GCE

This work This work 2 3 4 5 6 7 8 9 10 11 12 11

aThe

table is sorted in descending order by η@10 mA cm-2, the overpotential required to reach the current density of 10 mA cm-2; bthe overpotential @100 mA cm-2.

S10

Table S2. A summary of the OER performances of cobalt based chalcogenide catalysts in 0.1 M KOH electrolyte.a Catalysts Co9S8/CNS/CNT Co9S8/CNS Fe3O4@Co9S8/rGO Co9S8/N-C Co1-xS/G Co3S4 NG-CoSe2 Co9S8@NC CoS2/N,S-GO Co9S8/G Mn3O4/CoSe2 Co3S4/NCNTs NiCo2S4@N/S-rGO CoxSy@C CoSe2 aThe

η@10 mA cm-2 [mV](a) 299 324 340 ~347 ~349 363 366 370 380 409 420 430 470 470 510

Onset potential [V vs. RHE] ~1.46 ~1.46 1.48 ~1.48 ~1.52 ~1.52 ~1.50 ~1.40 ~1.50 ~1.52 ~1.48 ~1.55 ~1.57 ~1.56 ~1.57

Tafel slope [mV dec-1] 59.8 67.9 65.5 69.0 55.6 90 40 124 75 82.7 49 70 67

Mass loading [mg cm-2] 0.24 0.24 0.25 0.80 0.0926 0.283 0.20 0.22 0.25 0.20 0.20 0.20 0.283 0.141 1.0

Substrate

Reference

GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE GCE

This work This work 5 13 14 15 16 6 17 18 19 20 21 22 12

table is sorted in descending order by η@10 mA cm-2.

S11

3 2

180 mV s-1

20 mV s-1

2

(b)

(c)

180 mV s-1

0

20 mV s-1

-1 -2

1.22 1.24 1.26 1.28 1.30 1.32 1.34 Potential (V vs. RHE)

180 mV s-1

1 0

20 mV s-1

-1 -2 1.22 1.24 1.26 1.28 1.30 1.32 1.34 Potential (V vs. RHE)

1.22 1.24 1.26 1.28 1.30 1.32 1.34 Potential (V vs. RHE)

1

-3

Current Density (mA cm-2)

(a)

Current Density (mA cm-2)

Current Density (mA cm-2)

Current Density (mA cm-2)

12 9 6 3 0 -3 -6 -9 -12

7

(d)

6 5 4 3 2 1 0 0

Co9S8/CNS -2 Co9S8 m RuO2 Fc

m .7 7 3

-2

F cm 9.9 m -2 6.5 mF cm 40 80 120 160 Scan rate (mV s-1)

200

Fig. S9 Cyclic voltammograms at scan rates from 20 to 180 mV s-1 under the non-Faradic potential window of 1.224 to 1.324 V (vs. RHE) of (a) Co9S8/CNS, (b) Co9S8 and (c) RuO2; (d) Plots of current densities at 1.275 V vs. scan rates of Co9S8/CNS, Co9S8 and RuO2, respectively.

S12

Current Density (mA cm-2)

30 25 20

1st cycle 1000th cycle

15 10 5 0 1.2

1.3 1.4 1.5 Potential (V vs. RHE)

1.6

Fig. S10 The first and 1000th CV cycle of Co9S8/CNS in 1.0 M KOH electrolyte at a scan rate of 10 mV s-1.

S13

(a)

100 0 0

Faradic Efficiency ()

200

= Iring / (Idisk N) 0.95-0.97

0.4 0.2 0.0 0

30

60

90 120 150 180 Time (s) -

-100

-

O2 + 2H2O + 4e 4OH (Pt ring)

30

60

90 120 Time (s)

-120 150

180

20 4OH- O2 + 2H2O + 4e- (glassy carbon disk)

15 Idisk Iring 10

400 200 0 0

5

2H2O- O2 + H2O + 2e- (Pt ring)

50

100 Time (s)

150

Current (A)

300

Idisk Iring -60 -80

0.8 0.6

-20 -40

1.0

600

Current (A)

Current (A)

500 400

(b)

0 4OH- O2 + 2H2O + 4e- (glassy carbon disk)

Current (A)

600

0

Fig. S11 (a) Disk current (Idisk) and ring current (Iring) of Co9S8/CNS using RRDE measurements under the applied potential of 1.52 V (vs. RHE) at the disk (GCE) and 0.4 V (vs. RHE) at the ring (Pt); the inset shows the Faradic efficiency of Co9S8/CNS for OER; (b) Disk current (Idisk) and ring current (Iring) of Co9S8/CNS using RRDE measurements for the detection of H2O2 generation under the applied potential of 1.52 V (vs. RHE) at the disk (GCE) and 1.5 V (vs. RHE) at the ring (Pt). All the RRDE measurements are conducted in N2-saturated, 1.0 M KOH electrolyte.

S14

Intensity (a.u.)

*

47.3% CNT

*

42.0% CNT

*

34.8% CNT 25.3% CNT 16.0% CNT 0% CNT

*

*CNT Co9S8 (JCPDS# 86-2273)

10

20

30

40 50 60 2 (degree)

70

80

Fig. S12 XRD patterns of the nanocomposites prepared with different contents of CNT. CNT peak is highlighted with “*”.

S15

(a)

(c)

(b)

10 μm

10 μm

10 μm

(e)

(d) 200 nm

10 μm

200 nm

200 nm

200 nm

200 nm 500

10 μm

Fig. S13 SEM images of Co9S8/CNS/CNT nanocomposites with CNT weight loadings of (a) 16.0%, (b) 25.3%, (c) 34.8%, (d) 42.0% and (e) 47.3% prepared at calcination temperature of 700°C under Ar atmosphere.

S16

Table S3. Composition of the nanocomposites prepared by the one-step molten-salt calcination method. Catalysts Co9S8 Co9S8/CNS Co9S8/CNS/CNT-1 Co9S8/CNS/CNT-2 Co9S8/CNS/CNT-3 Co9S8/CNS/CNT-4 Co9S8/CNS/CNT-5

Co9S8 (%) 100 48.5 41.2 37.6 31.1 27.8 24.6

CNS (%) 51.5 42.8 37.1 34.1 30.2 28.1

CNT (%) 16.0 25.3 34.8 42.0 47.3

S17

0.36 0.33 Overpotential (V)

S S/CNT-2

1.4 1.5 al (V vs. RHE)

1.6

0.30 0.27 0.24

Co9S8/CNS Co9S8/CNS/CNT-2

-1

c de v -1 m c 9 . de 67 v m .8 59

0.21 0.18

1 10 Current Density (mA cm-2)

Fig. S14 Tafel plots of Co9S8/CNS and Co9S8/CNS/CNT-2 catalysts in 0.1 M KOH electrolyte.

S18

40

RuO2

30 20 10

E(H2O/O2)

Current Density (mA cm-2)

50

RuO2/CNS Co3O4

0 1.2

1.3

1.4 1.5 1.6 1.7 Potential (V vs. RHE)

1.8

Fig. S15 Polarisation curves of RuO2, RuO2/CNS and Co3O4 electrocatalysts measured at a scan rate of 5 mV s-1 in 1.0 M KOH electrolyte. To realise the effect of CNS on the OER performance, 48.5% (wt%) of RuO2 (same weight percentage of Co9S8 in Co9S8/CNS composite) was mixed with CNS to prepare a composite electrocatalyst and the polarisation curves were measured. As evident from Fig. S15, no significant change in the onset potential was observed. However, a slight decrease in the current density was encountered that possibly due to the difference in chemical property of separately prepared CNS compared to that of the in situ grown CNS in Co9S8/CNS nanocomposites. Also, cobalt oxide (Co3O4) nanopowders with the particle size