Co-vacancy-rich Co 1 x S nanosheets anchored on rgo for high-efficiency oxygen evolution

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1 Electronic Supplementary Material Co-vacancy-rich Co 1 x S nanosheets anchored on rgo for high-efficiency oxygen evolution Jiaqing Zhu 1, Zhiyu Ren 1 ( ), Shichao Du 1, Ying Xie 1, Jun Wu 1,2, Huiyuan Meng 1, Yuzhu Xue 1, and Honggang Fu 1 ( ) 1 Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People s Republic of China, School of Chemistry and Materials Science, Heilongjiang University, Harbin , China 2 College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin , China Supporting information to DOI /s Table S1 The experimental parameters of the synthesized samples Sample Inventory Co(NO 3 ) 2 6 H 2 O NH 3 H 2 O C 3 H 7 NO 2 S GO Reaction mode Co 1 x S/rGO 0.05 mmol 1 ml 0.31 mmol 25 mg CoS/rGO 0.05 mmol 0.25 mmol 25 mg Co 1 x S 0.05 mmol 1 ml 0.31 mmol CoS 0.05 mmol 0.25 mmol Co 3 O 4 /rgo 0.05 mmol 1 ml 25 mg Co 1 x S/rGO mmol 1 ml 0.31 mmol 25 mg Co 1 x S/rGO-p 0.05 mmol 1 ml 0.31 mmol 25 mg Address correspondence to Zhiyu Ren, zyren@hlju.edu.cn; Hongang Fu, fuhg@vip.sina.com

2 Table S2 Frequency analysis of the intermediates on {110} surface of Co 1 x S and CoS Sample OH* O* OOH* CoS Computed vibrational (i) frequencies (i) (mev) (i) (i) (i) E ZPE (ev) Co 1 x S Computed vibrational frequencies (mev) (i) (i) (i) (i) E ZPE (ev) Figure S1 XRD pattern of CoS powder.

3 Figure S2 XPS survey spectrum of Co 1 x S/rGO hybrid (a), Co 1 x S (b), and CoS/rGO hybrids (c). Figure S3 SEM image of Co 1 x S/rGO hybrid. Nano Research

4 Figure S4 (a) (c) The SEM images of Co 1 x S, Co 3 O 4 /rgo hybrid and CoS/rGO hybrid; (d) the SEM images of Co 1 x S/rGO-1 hybrid synthesized by one-step hydrothermal reaction. Figure S5 (a) (c) XRD patterns of Co 1 x S/rGO-1 and Co 3 O 4 /rgo hybrids. Figure S6 XPS survey spectrum of Co 1 x S/rGO-P.

5 Figure S7 (a) (d) CVs for Co 1 x S/rGO hybrid, Co 1 x S, CoS/rGO hybrid, and CoS at various scan rate (10, 20, 40, 60, 80, 100, and 120 mv s 1 ); (e) the capacitive current at 0.15 V (vs. RHE) as a function of scan rate for Co 1 x S/rGO hybrid,cos/rgo hybrid, and CoS (Δj 0 = j a j c ). Figure S8 Nitrogen adsorption desorption isotherms of Co 1 x S/rGO hybrid (a), Co 1 x S (b), CoS/rGO hybrid (c), Co 1 x S/rGO-1 hybrid (d), and CoS (e). Nano Research

6 Figure S9 (a) and (b) ir-compensated OER polarization curves and the corresponding Tafel plots for Co 1 x S/rGO-1 and hybrids electrodes in 1.0 M KOH; (c) EIS data collected for Co 1 x S/rGO-1 and hybrids, under OER overpotential = 270 mv. Figure S10 (a) and (b) ir-compensated OER polarization curves and the corresponding Tafel plots for CoS and hybrids electrodes in 1.0 M KOH; (c) EIS data collected for CoS and hybrids, under OER overpotential = 270 mv. Table S3 Comparison of catalytic performance of Co 1 x S/rGO hybrid for OER to reported catalysts Materials Electrode Onset potential (V vs. RHE) Potential (at 10 ma cm 2, V vs. RHE) Tafel slope (mv dec 1 ) Electrolyte Co 9 S 8 /graphene GC M KOH [S1] CoSe 2 GC M KOH [S2] Co 3 S 4 GC [S3] Fe 3 O 9 S 8 /rgo GC [S4] Mn 3 O 4 /CoSe 2 GC M KOH [S5] NG-CoSe 2 GC [S6] CoS 2 /N,S-GO GC M KOH [S7] Co 1 x Fe x S@N-MC GC M KOH [S8] NiCo 2 S GC [S9] Ni 3 S 2 /Ni Ni foam M KOH [S10] Ni 3 S 2 /NF Ni foam M KOH [S11] NiSe Ni foam M KOH [S12] NiCo 2 S 4 Carbon M KOH [S13] Co 1 x S/rGO GC M KOH Ref. This work

7 Table S4 Parameters obtained by fitting the impedance spectra of Co 1 x S/rGO, CoS/rGO, Co 1 x S, CoS, and Co 1 x S/rGO-1 using the equivalent circuit in Fig. 4(c) Sample name R S (Ω) C C (μf) R C (Ω) C CT (μf) R CT (Ω) Co 1 x S/rGO Co 1 x S CoS CoS/rGO Co 1 x S/rGO Figure S11 (a) and (b) Ball models of Co 1 x S and CoS, respectively; Co and S atom is depicted blue and yellow, respectively. Table S5 Atomic populations of (110) facets of Co 1 x S Species Ion s p d f Total Charge (e) S S S S S S S S S S Co Co Co Co Co Co Co Co Nano Research

8 Table S6 Atomic populations of (110) facets of CoS Species Ion s p d f Total Charge (e) S S S S S S S S S S Co Co Co Co Co Co Co Co Co Co Figure S12 Calculated projected DOS for bulk Co 1 x S (110) and CoS (110). Table S7 Free energy of (110) facets of Co 1-x S and CoS with intermediates Free energy (ev) Co 1 x S (110) CoS (110) Clean surface 11, , OH* 11, , O* 11, , OOH* 12, ,

9 Table S8 Calculated reaction free energy (ΔG) with the E ZPE corrections ΔG (ev) Reaction step Co 1 x S (110) CoS (110) ΔG 1 * + OH *OH + e ΔG 2 *OH + OH H 2 O + *O + e ΔG 3 *O + OH *OOH + e ΔG 4 *OOH + OH * + O 2 + e References [S1] Dou, S.; Tao, L.; Huo, J.; Wang, S. Y.; Dai, L. M. Etched and doped Co 9 S 8 /graphene hybrid for oxygen electrocatalysis. Energy Environ. Sci. 2016, 9, [S2] Liu, Y. W.; Cheng, H.; Lyu, M. J.; Fan, S. J.; Liu, Q. H.; Zhang, W. S.; Zhi, Y. D.; Wang, C. M.; Xiao, C.; Wei, S. Q. et al. Low overpotential in vacancy-rich ultrathin CoSe 2 nanosheets for water oxidation. J. Am. Chem. Soc. 2014, 136, [S3] Zhao, W. W.; Zhang, C.; Geng, F. Y.; Zhuo, S. F.; Zhang, B. Nanoporous hollow transition metal chalcogenide nanosheets synthesized via the anion-exchange reaction of metal hydroxides with chalcogenide ions. ACS Nano 2014, 8, [S4] Yang, J.; Zhu, G. X.; Liu, Y. J.; Xia, J. X.; Ji, Z. Y.; Shen, X. P.; Wu, S. K. Fe 3 O 4 -decorated Co 9 S 8 nanoparticles in situ grown on reduced graphene oxide: A new and efficient electrocatalyst for oxygen evolution reaction. Adv. Funct. Mater. 2016, 26, [S5] Gao, M. R.; Xu, Y. F.; Jiang, J.; Zheng, Y. R.; Yu, S. H. Water oxidation electrocatalyzed by an efficient Mn 3 O 4 /CoSe 2 nanocomposite. J. Am. Chem. Soc. 2012, 134, [S6] Gao, M. R.; Cao, X.; Gao, Q.; Xu, Y. F.; Zheng, Y. R.; Jiang, J.; Yu, S. H. Nitrogen-doped graphene supported CoSe 2 nanobelt composite catalyst for efficient water oxidation. ACS Nano 2014, 8, [S7] Ganesan, P.; Prabu, M.; Sanetuntiku, J.; Shanmugam, S. Cobalt sulfide nanoparticles grown on nitrogen and sulfur codoped graphene oxide: An efficient electrocatalyst for oxygen reduction and evolution reactions. ACS Catal. 2015, 5, [S8] Shen, M. X.; Ruan, C. P.; Chen, Y.; Jiang, C. H.; Ai, K. L.; Lu, L. H. Covalent entrapment of cobalt-iron sulfides in N-doped mesoporous carbon: Extraordinary bifunctional electrocatalysts for oxygen reduction and evolution reactions. ACS Appl. Mater. Interfaces 2015, 7, [S9] Chen, S.; Qiao, S. Z. Hierarchically porous nitrogen-doped graphene NiCo 2 O 4 hybrid paper as an advanced electrocatalytic water-splitting material. ACS Nano 2013, 7, [S10] Zhou, W. J.; Wu, X. J.; Cao, X. H.; Huang, X.; Tan, C. L.; Tian, J.; Liu, H.; Wang, J. Y.; Zhang, H. Ni 3 S 2 nanorods/ni foam composite electrode with low overpotential for electrocatalytic oxygen evolution. Energy Environ. Sci. 2013, 6, [S11] Feng, L. L.; Yu, G. T.; Wu, Y. Y.; Li, G. D.; Li, H.; Sun, Y. H.; Asefa, T.; Chen, W.; Zou, X. X. High-index faceted Ni 3 S 2 nanosheet arrays as highly active and ultrastable electrocatalysts for water splitting. J. Am. Chem. Soc. 2015, 137, [S12] Liu, X.; Liu, W.; Ko, M.; Park, M.; Kim, M. G.; Oh, P.; Chae, S.; Park, S.; Casimir, A.; Wu, G. et al. Metal (Ni, Co)-metal oxides/graphene nanocomposites as multifunctional electrocatalysts. Adv. Funct. Mater. 2015, 25, [S13] Tang, C.; Cheng, N. Y.; Pu, Z. H.; Xing, W.; Sun, X. P. NiSe nanowire film supported on nickel foam: An efficient and stable 3D bifunctional electrode for full water splitting. Angew. Chem., Int. Ed. 2015, 127, Nano Research