Dynamic Hydrogen Bubble Templated NiCu Phosphide Electrodes for ph-insensitive Hydrogen Evolution Reactions

Transcription

1 Dynamic Hydrogen Bubble Templated NiCu Phosphide Electrodes for ph-insensitive Hydrogen Evolution Reactions Majid Asnavandi +, Bryan H. R. Suryanto +, Wanfeng Yang, Xin Bo and Chuan Zhao* School of Chemistry, The University of New South Wales, High St., Sydney, NSW 2052, Australia + These two authors made equal contribution to this paper. Authors Dr Majid Asnavandi; m.asnavandi@unsw.edu.au Dr Bryan Harry Rahmat Suryanto; bryan.suryanto@unsw.edu.au Ms Wanfeng Yang; wanfeng.yang@student.unsw.edu.au Mr Xin Bo; xin.bo@student.unsw.edu.au *Dr Chuan Zhao (corresponding author); chuan.zhao@unsw.edu.au Totals 19 pages, 1equation, 1 table and 13 figures. S1

2 Fabrication of NiCuP/NM electrode and electrochemical characterization Before deposition of Ni, Cu, NiCu, nickel mesh (purchased from Goodfellow, UK, 99.9% purity and 95% porosity) was sonicated in 5 M HCl for 30 minutes to remove nickel oxide layer and then rinsed with water and ethanol several times and dried in air. All electrodeposition have been carried out via a galvanostatic technique in a two electrode electrochemical cell where a graphite rod was used as the counter electrode and the working electrode area was cm, unless mentioned. Current density, time and the electrolyte chemical composition of electrodeposition are listed in Table S1. The phosphidation of electrodeposited NiCu was achieved through the use of red phosphorus as P source. Only the most active NiCu sample with optimized Ni:Cu content ratio (2:1) was subjected to the phosphidation. Thermal annealing was performed with horizontal tube furnace. Crucible containing 60 mg of red phosphorus is positioned at the up-stream in respect to Ar-gas flow, while another crucible containing 1 g of the electrodeposited NiCu/NM is located 5 cm away down-stream. Annealing was performed at 500 C for 6 hours with a temperature increasing rate of 5 C per minute. HER catalytic activity of all electrodes was examined by a CH760 Electrochemical Workstation (CH Instrument, Texas, USA) using a three-electrode cell arrangement. Saturated calomel electrode (SCE) and graphite rode were used as the reference and counter electrode, respectively. RHE potentials were calculated via E RHE = E SCE V ph. CVs and LSVs showed in the paper were run without any ir-compensation at 5 mv.s -1 scan rate while for Tafel slope determination this value was fixed at 0.1 mv.s -1. The solutions were N 2 saturated before starting HER activity investigations. S2

3 Fabrication of PtC/NM electrode PtC onto the NM has been fabricated by dipping the NM in to a made ink containing 5 mg commercial PtC (20 wt % Pt on Vulcan XC-72), 250 µl ethanol, 750 µl water, and 25 µl Nafion. The electrode dried in air before electrochemical studies. Determination of onset potential (E on ) The onset potential was determined from the x-axis value of intersecting point of the two tangent lines from drawn from background currents and HER currents (see Figure S6). ECSA determination The ECSA of each electrocatalyst is determined by double layer capacitance (C DL ) according to Equation S1: 1 ECSA = C DL / C S (S1) where C S is the specific capacitance of the sample of an atomically smooth planar surface of the material per unit area. Specific capacitances have been measured for a variety of metal electrodes in acidic and alkaline solutions and typical values reported range between C S = mf.cm -2 in NaOH and KOH solutions. 2,3 In this study, C S = 0.04 mf.cm -2 in 1 M KOH 4 was used for estimation of ECSA. C DL (mf) is calculated from absolute average of slopes of lines in the plot of currents versus scan rates. In order to measure the currents (I), open circuit potential (OCP) was measured in the solution and then CV in a window potential of OCP ± 0.05 V at different scan rates was recorded. The anodic and cathodic currents in Figure S2a and S2b were used to plot Figure S2c and S2d. Turnover frequency determination S3

4 The TOF values of the electrodes were calculated according to: TOF = j.a/2.f.n, where j is the current density obtained at overpotential of -400 mv in A cm -2, A is the surface area of the electrode, F is the Faraday efficiency and n is the number of moles of the catalyst deposited onto the nickel mesh. For determination of n, first the catalyst loadings were determined and then the chemical composition were identified by EDS to figure out the alloys molar mass. Physical characterization For characterization of the produced electrodes, SEM was used for morphology studying by FEI Nova NanoSEM 450. XPS was performed on a Thermo ESCALAB250i X-ray Photoelectron Spectrometer and XRD was done on a PANalytical X Pert instrument. References (1) McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J. Am. Chem. Soc. 2013, 135 (45), (2) Joel Fournier, Louis Brosard, Jean-Yves TiIquin, Roland Côté, J.-P. D.; Daniel Guay, H. M. Hydrogen Evolution Reaction in Alkaline Solution. J. Electroanal. Chem. 1996, 143 (3), (3) Mccrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, (4) Asnavandi, M.; Suryanto, B. H. R.; Zhao, C. Controlled electrodeposition of nanostructured Pd thin films from protic ionic liquids for electrocatalytic oxygen reduction reactions. RSC Adv. 2015, 5 (90), (5) Safizadeh, F.; Ghali, E.; Houlachi, G. Electrocatalysis developments for hydrogen evolution reaction in alkaline solutions - A Review. Int. J. Hydrogen Energy 2015, 40 (1), (6) Xiao, P.; Chen, W.; Wang, X. A Review of Phosphide-Based Materials for Electrocatalytic Hydrogen Evolution. Adv. Energy Mater. 2015, 5 (24), S4

5 (7) Morales-guio, C. G.; Stern, L.; Hu, X.; Stern, L. Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution. Chem. Soc. Rev. 2014, 43, (8) Gong, M.; Wang, D. Y.; Chen, C. C.; Hwang, B. J.; Dai, H. A mini review on nickel-based electrocatalysts for alkaline hydrogen evolution reaction. Nano Res. 2016, 9 (1), (9) Gong, M.; Zhou, W.; Kenney, M. J.; Kapusta, R.; Cowley, S.; Wu, Y.; Lu, B.; Lin, M. C.; Wang, D. Y.; Yang, J.; et al. Blending Cr2O3 into a NiO-Ni Electrocatalyst for Sustained Water Splitting. Angew. Chemie - Int. Ed. 2015, 54 (41), (10) Feng, L.-L.; Fan, M.; Wu, Y.; Liu, Y.; Li, G.-D.; Chen, H.; Chen, W.; Wang, D.; Zou, X. Metallic Co 9 S 8 nanosheets grown on carbon cloth as efficient binder-free electrocatalysts for hydrogen evolution reaction under neutral media. J. Mater. Chem. A 2016, 4, (11) Zhang, J.; Baró, M. D.; Pellicer, E.; Sort, J. Electrodeposition of magnetic, superhydrophobic, non-stick, two-phase Cu Ni foam films and their enhanced performance for hydrogen evolution reaction in alkaline water media. Nanoscale 2014, 6 (21), (12) Wei, L.; Goh, K.; BIRER, O.; Karahan, H. E.; Zhai, S.; Chen, X.; Chen, Y. A Hierarchically Porous Nickel-Copper Phosphide Nano-Foam for Efficient Electrochemical Splitting of Water. Nanoscale 2017, 9, (13) Gao, M. Y.; Yang, C.; Zhang, Q. B.; Yu, Y. W.; Hua, Y. X.; Li, Y.; Dong, P. Electrochemical fabrication of porous Ni-Cu alloy nanosheets with high catalytic activity for hydrogen evolution. Electrochim. Acta 2016, 215, (14) Cardoso, D. S. P.; Eugénio, S.; Silva, T. M.; Santos, D. M. F.; Sequeira, C. a. C.; Montemor, M. F. Hydrogen evolution on nanostructured Ni Cu foams. RSC Adv. 2015, 5 (54), Table S1. Parameters of Ni, Cu and NiCu electrodeposition Electrolyte (M) Current density Time Temperature Size Sample NiCl 2 : CuSO 4 : NaCl: NH 4 Cl (A cm -2 ) (s) ( c) (cm cm) Porous Cu@NM 0: 0.1: 1: Porous Ni@NM 0.1: 0: 1: Porous NiCu@NM (Ni:Cu ratio of 2:1) Porous NiCu@NM (Ni:Cu ratio of 1:1) Porous NiCu@NM (Ni:Cu ratio of 1:2) NiCu@NM (Ni:Cu ratio of 2:1) 0.09: 0.01: 1: : 0.02: 1: : 0.04: 1: : 0.01: 1: S5

6 foil (Ni:Cu ratio of 2:1) 0.09: 0.01: 1: Table S2. HER activities of some benchmark electrocatalysts in alkaline solutions with a current density of -10 and -100 ma cm -2 Catalyst Electrolyte Cathodic overpotential at Tafel Slope j = -10/ -50/ -100 ma cm -2 (mv dec -1 ) Pt-Ce 8 M KOH -154 (-100) -144 CoP nanowire 1 M KOH -209 (-10) -129 FeP nanorod 1 M KOH -218 (-10) -146 Mo 2 C 1 M KOH -190 (-10) -54 NiO/Ni-CNT 1 M KOH -95 (-100) - Ni@NiO-Cr 2 O 3 1 M KOH -115 (-100) - Co 9 S 8 /CC-2 1 M KOH -175 (-10) - Porous NiCu 1 M KOH -400 (-10) - NiCuP 1 M KOH -146 (-50) -47 NiCu nanosheet 1 M KOH -128 (-10) Porous NiCu 8 M KOH -200 (-10) -124 Reference Porous NiCu-P 1 M KOH -175 (-10) -53 This work S6

7 Figure S1. a) SEM images (top view) at high magnification and b) TEM image of a synthesized NiCu-P S7

8 Figure S2. Double-layer capacitance measurements for determining ECSA of NiCu/NM electrodes in 1 M KOH: Cyclic voltammetry in a non-faradaic region at scan rates of 0.005, 0.01, 0.02, 0.025, 0.05, 0.1, 0.2, 0.4, and 0.8 V/s for (a) porous NiCu and (b) non-porous NiCu; Corresponding cathodic and anodic currents versus scan rate for (c) for porous NiCu at a potential of 0.09 V (Ag/AgCl) and (d) for non-porous NiCu at a potential of V (Ag/AgCl); (e) Effect of electrodeposition method on the double-layer capacitance at the scan rate of 0.1 V/s S8

9 Figure S3. EDS mapping and the corresponding analysis of the NiCu-P/NM electrode S9

10 Figure S4. Effect of chemical composition of the HER electrodes on their activity in 1 M KOH. The atomic ratio of Ni:Cu was determined by EDS. S10

11 Figure S5. XRD pattern of Ni-P and Cu-P samples S11

12 Figure S6. Method for determining onset potential (E on ) S12

13 Figure S7. Tafel plots of different electrodes in a) acidic and b) neutral solutions S13

14 Figure S8. Water contact angle measurement of the prepared catalysts; a) NiCu, b) NiCu-P S14

15 Figure S9. Accelerated degradation tests of the NiCu-P/NM electrodes at different phs. The dote curves show the electrodes HER performance after 1000 CV cycles and the solid lines are for fresh samples (before 1000 cycles). The ADTs have been done at potential between V and -0.2 V at ph of 0.3 and 14 and potential window of V and -0.4 V (RHE) at ph of 7. All experiments have been performed at scan rate of 5 mv.s -1 S15

16 Figure S10. Stability test of NiCu-P/NM electrodes under HER condition in a) 0.5 M H 2 SO 4 at -50 ma cm -2, b) 1 M phosphate buffer at -20 ma cm -2, c) 1 M KOH -50 ma cm -2 S16

17 Figure S11. a) XRD pattern, b) SEM and c) TEM images of NiCu-P electrode after stability test in 1 M KOH S17

18 Figure S12. LSV of NiCu-P/NM samples electrodeposited via convenient and hydrogen bubbling method, in 1 M KOH. The current density was normalized by their ECSA S18

19 Figure S13. SEM image of fabricated electrodes at different magnifications; a, c) porous NiCu/NM, b, d) non-porous NiCu/NM S19