Supplemental Information. In Situ Electrochemical Production. of Ultrathin Nickel Nanosheets. for Hydrogen Evolution Electrocatalysis

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1 Chem, Volume 3 Supplemental Information In Situ Electrochemical Production of Ultrathin Nickel Nanosheets for Hydrogen Evolution Electrocatalysis Chengyi Hu, Qiuyu Ma, Sung-Fu Hung, Zhe-Ning Chen, Daohui Ou, Bin Ren, Hao Ming Chen, Gang Fu, and Nanfeng Zheng

2 Figure S1. Structural characterization of -Ni(OH) 2. (a, b) SEM, (c) TEM images and (d) XRD pattern of -Ni(OH) 2 grown on carbon cloth. Intensity (a.u.) Ni-BDT (degree) Figure S2. XRD pattern of the as-prepared Ni-BDT (the two broad peaks come from carbon cloth). S1

3 Figure S3. Experimental and simulated Raman spectra of Ni-BDT. (Inset: model used for simulation) The peak assignment was shown in Table S1. Ni-BDT Ni 3p Intensity (a.u.) Ni 2p 3/2 Ni LMM O 1s S 2p S 2s C 1s Figure S4. XPS survey spectrum of Ni-BDT. Binding Energy (ev) S2

4 Figure S5. (a) Cyclic voltammetry curves of Ni(OH) 2, Ni-BDT and Ni-BDT-A in the region of V vs. RHE. The differences in current density variation ( J=J a-j c) at an overpotential of 0.15 V plotted against scan rate fitted to a linear regression enables the estimation of C dl. Figure S6. (a-c) SEM images at 0h, 1h and 12h of the activation process of Ni-BDT. (d) EDS spectra of the catalysts in (a-c). S3

5 Figure S7. (a) Thickness distribution of Ni-BDT-A from TEM. (b) HAADF-STEM image and EDS elemental mapping images of Ni-BDT-A. (c) HRTEM image of Ni-BDT-A. Figure S8. (a) AFM image, (b) corresponding height profile and (c) thickness distribution of Ni- BDT. (d) AFM image, (e) corresponding height profile and (f) thickness distribution of Ni-BDT-A. S4

6 Ni-BDT Ni-BDT-A Normalized Intensity Raman Shift / cm -1 Figure S9. Raman spectra of Ni-BDT and Ni-BDT-A. Figure S10. (a) XPS survey spectra, (b) Ni 2p region, (c) S 2p region and (d) fitting results of S 2p region of Ni-BDT and Ni-BDT-A. S5

7 Figure S11. Electrochemical in-situ XAS of Ni-BDT. (a) Ni K-edge XANES, (b) k-space, and (c) Fourier transformed R-space of Ni-BDT during HER activation. The cathodic current was set as 50 ma cm -2 during the activation. The in-situ XAS measurement was performed at 0.5h, 1h and 1.5h at the voltage of -1 V to keep the situation of reduction and to avoid the disturbance of bubbles that interfered the measurement. Figure S12. Experimental and simulated XAFS spectra of Ni-BDT and Ni-BDT-A catalysts at the Ni K-edge. The χ(k) data weighted by k 3 and Fourier transformed (FT) to R-space (the k-space ranging from 3 to 10.5 Å 1 ) to isolate the EXAFS contributions from each coordination shell. The quantified fitting results are shown in Table S2. S6

8 Figure S13. (a) EXAFS spectra and (b) HER performance of Ni-BDT-A catalysts after exposing to air at room temperature for different time. The catalysts were easily oxidized by air to form Ni(OH) 2 due to the ultrathin structure, resulting in the decrease of HER activity Ni(OH) 2 Ni-BDT-A air 24h j (ma cm -2 ) mf cm mf cm Scan Rate (mv/s) Figure S14. Double-layer capacitance of pristine Ni(OH) 2 and Ni-BDT-A derived Ni(OH) 2 (air oxidation for 24h). S7

9 Figure S15. (a) SEM image and (b) EDS spectrum of Ni-BDT-A soaked in 0.1 mm Zn(NO 3) 2 solution for 30 s and then washed by deionized water. (c) HER activity of Ni-BDT-A before and after soaking in 0.1 mm Zn(NO 3) 2 solution and H 2O for 30 s with the protection of N 2. Figure S16. (a) HER activity of Ni-BDT-A and (b) Ni foam in 1 M KOH and tetramethylammonium hydroxide (TMAOH) electrolyte. j (ma cm -2 ) Ni foam Ni foam Na 2 S 10s Ni foam Na 2 S 40s Ni foam Na 2 S 100s E (V vs. RHE) E (V vs. RHE) Figure S17. HER activity of Ni foam before and after soaking in 1 mm Na 2S aqueous solution for different time at open circuit potential. S8

10 Figure S18. SEM images and EDS of Ni thiolate synthesized by using 1,2-benzenedithiol as ligand (a, c) before and (b, d) after electrochemical activation. Figure S19. SEM images and EDS of Ni thiolate synthesized by using 1,3-benzenedithiol as ligand (a, c) before and (b, d) after electrochemical activation. S9

11 Figure S20. HER polarization curves of (a) Ni-12BDT and (b) Ni-13BDT before and after activation. Figure S21. (a) LSV plots of Ni(OH) 2 and Ni-BDT-A in 1 M KOH electrolyte with and without 0.33 M urea. (b) Optical image of urea electrolysis device. (c) LSV plots of urea electrolysis using Ni(OH) 2 or Ni-BDT-A as both HER and UOR catalysts in 1 M KOH and 0.33 M urea. (d) Chonopotentiometry of urea electrolysis using Ni-BDT-A as both HER and UOR catalyst at a constant current density of 20 ma cm -2 (without ir compensation). All polarization curves were ir corrected. S10

12 Figure S22. SEM images of (a, b) NiFe-BDT and (c, d) NiFe-BDT-A. EDS of (e) NiFe-BDT and (f) NiFe-BDT-A. Figure S23. Polarization curves for (a) HER and (b) OER of NiFe-BDT before and after activation. S11

13 Table S1. Theoretical frequencies of selected fundamental vibrational bands of Ni-BDT within the frequency range of cm -1. Peak position (cm -1 ) 170 m Ni-S Assignment 227 w Ni-S C-S 303 m Ni-S C-S 344 s Ni-S + ring 544 w C-S Ni-S 753 m C-S + ring 768 m C-S + ring Abbreviation:, stretching;, in-plane ring deformation; β, in-plane bending Relative intensity: s (strong); m (medium); w (weak) Table S2. EXAFS fitting parameters of Ni-BDT and Ni-BDT-A. Sample Shell CN R / Å Δσ 2 / x10-3 Å 2 ΔE0 / ev Ni foil Ni-Ni ± ± ±0.2 Ni-BDT Ni-S 3.6± ± ± ±0.6 Ni-BDT-A Ni-S 1.3± ± ± ±1.4 Ni-Ni 4.9± ± ± ±1.4 CN, coordination number; R, bonding distance; Δσ 2, Debey-Waller factor; ΔE 0, inner potential shift, 2 amplitude reduction factor S 0 was set as 0.8 for all the samples. Table S3. Comparison of the electrocatalytic HER performance of Ni-BDT-A with 2D metal organic polymers reported recently. Catalyst Electrode Loading Electrolyte (mv)@ (mv)@ Tafel slop Reference (mg cm -2 ) 10 ma cm ma cm -2 (mv/dec) Ni-BDT-A CC 0.3 1M KOH This work Co-BHT GC H 2SO 4 ph 1.3 ~ [29] mol Co cm -2 Co-THT GC H 2SO 4 ph 1.3 ~ mol Co cm -2 Co-BTT GC H 2SO 4 ph 1.3 ~550 [30] mol Co cm -2 Ni-THT GC 0.5M H 2SO [31] GC 0.05M KOH ~570 S12

14 Table S4. Comparison of the electrocatalytic HER performance of Ni-BDT-A with metal sulfide electrocatalysts in alkaline electrolyte reported recently. Catalyst Electrode Loading Electrolyte Tafel slop Reference (mg cm -2 ) 10 ma cm ma cm -2 (mv/dec) Ni-BDT-A CC 0.3 1M KOH This work Ni 3S 2 Ni foam 1.6 1M KOH 223 [48] NiCo 2S 4 Ni foam 1M KOH ~ [49] CoMn-S@NiO CC 1M KOH ~ [50] NiS Ni foam 1 1M KOH ~ [51] Ni 3S 2 Ni foam 1M KOH [52] MoS 2/Ni 3S 2 Ni foam 9.7 1M KOH [53] Ni-MoS 2 CC M KOH [54] MoS x FTO M KOH [55] Ni foam 1M KOH ZnCoS GCE M KOH [56] NiCoS Ti foil 0.3 1M KOH [57] Table S5. Comparison of the electrocatalytic HER performance of Ni-BDT-A with metal/metal oxide electrocatalysts in alkaline electrolyte reported recently. Catalyst Electrode Loading Electrolyte (mv)@ (mv)@ Tafel slop Reference (mg cm -2 ) 10 ma cm ma cm -2 (mv/dec) Ni-BDT-A CC 0.3 1M KOH This work Ni/NiO-CNT GC M KOH [13] Ni foam 8 1M KOH 95 Ni/NiO-Cr 2O 3 Ni foam 8 1M KOH 150 (no ir) [14] Ni foam 24 1M KOH 115 (no ir) Ni/NiO Ni foam M KOH ~120 ~ [15] Ni-Mo Ti foil 1 1M NaOH 80 [12] 2-cycle NiFeOx CFP 1.6 1M KOH 220 [58] Co/CoO GC M KOH 232 [59] Ni foam 2.1 1M KOH ~210 S13