Supporting Information Designing hybrid NiP 2/NiO nanorod arrays for efficient alkaline hydrogen evolution Meng-Ying Wu, Peng-Fei Da, Tong Zhang, Jing Mao,*, Hui Liu,*, and Tao Ling,*, Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China. E-mail: lingt04@tju.edu.cn; cry5501@163.com; maojing@tju.edu.cn S-1
Supplementary Figures Figure S1. (a) TEM image of NiO NRs. (b) XRD spectra of as-prepared NiO NRs and NRs after phosphorization. S-2
0.4 Hydrogen oxidation Current (ma) 0.0-0.4 V RHE = V SCE + 1.049 V Hydrogen evolution -0.8-1.10-1.05-1.00-0.95-0.90 Potential (V vs. SCE) Figure S2. Calibration of the reference saturated calomel electrode (SCE). The calibration was performed in hydrogen saturated electrolyte with a Pt sheet as the working electrode. Cyclic voltammetry run at a scan rate of 1 mv s, and the average of the two potentials at which the -1 current value was zero was taken as the thermodynamic potential. Therefore, in 1 M KOH, VRHE = VSCE + 1.049 V. S-3
Figure S3. Illustration diagram of cation exchange process. S-4
Figure S4. SEM characterizations of hybrid NiP /NiO NRs with varied molar ratios of NiP and NiO NRs. (a1)-(a3) 1:4 NiP /NiO NRs. (b1)-(b3) 1:2 NiP /NiO NRs. (c1)-(c3) 3:2 NiP /NiO NRs. (d1)-(d3) NiP NRs. 2 2 2 2 2 S-5 2
Figure S5. O 1s spectrum of 1:2 NiP 2/NiO NRs after argon sputtering. The large area of peak II suggests that O-vacancies on NiO are present after the phosphorization treatment. Note that this sample was etched with an argon beam for 30 s to remove the surface NiP 2. S-6
NiP 2 /NiO NRs graphite rod Figure S6. Photograph of a home-made electrochemical cell for the hydrogen evolution reaction (HER) measurements. The three electrode system consists of a SCE reference electrode, a graphite rod as the counter electrode and the synthesized catalyst on CFP as the working electrode. S-7
Figure S7. Polarization curves of hybrid NiP 2/NiO NRs with varied NiP 2:NiO composition ratios, NiO NRs, NiP 2 NRs and Pt/C. S-8
Figure S8. EIS spectra of hybrid 3:2 NiP2/NiO NRs and NiP2 NRs at (a) high and (b) low frequencies. It shows that the transfer resistance of 3:2 NiP2/NiO NRs is higher than NiP2 NRs, which may leads to the relatively worse performance of 3:2 NiP2/NiO NRs. S-9
Figure S9. SEM characterization of hybrid 1:2 NiP2/NiO NRs after durability test (@ 10 ma cm - 2 ). (a) and (b) Low magnification. (c) High magnification. S-10
Figure S10. XRD spectrum of hybrid 1:2 NiP2/NiO NRs after durability test (@ 10 ma cm -2 ) compared with that of fresh sample. S-11
Figure S11. Long term durability of 1:2 NiP 2/NiO NRs at a current density of 50 ma cm -2. S-12
Figure S12. Characterization of 1:2 NiP 2/NiO NRs after long-term durability test (@ 50 ma cm - 2 ). (a) and (b) Low and high magnification SEM characterization. (c) XRD spectra of 1:2 NiP 2/NiO NRs. before and after durability test. (d) EDS spectrum. S-13
Figure S13. Characterization of Pt catalysts directly deposited on CFP substrate. It shows that Pt nanoparticles with sizes of about 5 nm are distributed uniformly on CFP substrate. S-14
Supplementary Tables Table S1. Quantitative EDS analysis of hybrid NiP2/NiO NRs in TEM. The average NiP2:NiO data were analyzed based on five nanorods for each phosphorization temperature. Phosphorization temperature ( o C) Element (at %) Ni P O Average NiP2: NiO ratio 360 380 400 Nanorod 1 37.21 20.46 42.33 Nanorod 2 35.79 22.82 41.39 Nanorod 3 39.05 20.49 40.46 Nanorod 4 36.92 20.61 42.47 Nanorod 5 35.72 22.29 41.99 Nanorod 1 34.48 32.58 32.94 Nanorod 2 34.92 31.53 33.55 Nanorod 3 35.50 32.05 32.45 Nanorod 4 36.37 31.40 32.23 Nanorod 5 34.36 33.12 32.52 Nanorod 1 29.33 52.80 17.87 Nanorod 2 27.99 54.24 17.77 Nanorod 3 28.15 54.22 17.63 Nanorod 4 30.43 51.63 17.94 Nanorod 5 30.76 52.48 16.76 1:4 1:2 3:2 Table S2. Summary of the recently reported highly active HER catalysts in alkaline solution. S-15
Catalyst Substrate Loading (mg cm ) -2 Electrolyte Overpotential @ 10 ma cm -2 (mv ) Tafel slope (mv dec -1 ) Reference NiP2/NiO NRs CFP ~0.24 1 M KOH 131 93 This work NixPy CFP ~0.15 1 M KOH ~134 107.3 [1] NiP2 nanosheet CC 4.3 1 M KOH 102 64 [2] Ni-P CFP 25.8 1 M KOH 117 85.4 [3] Ni5P4 Films Ni foil -- 1 M KOH 150 53 [4] Ni2P GCE ~0.12 1 M KOH ~149 65 [5] NiCoP/rGO CFP 0.15 1 M KOH 209 124.1 [6] Co2P nanorods Ti foil 1 1 M KOH ~152 -- [7] Ni-Co-P GCE 0.286 1 M KOH 150 60.6 [8] CoP nanowire CC 0.92 1 M KOH 209 129 [9] CoP@NC GCE 0.306 1 M KOH 129 58 [10] HNDCM Co/CoP CM -- 1 M KOH 138 64 [11] N@MoPCx GCE 0.14 1 M KOH 139 86.6 [12] Co4Ni1P NTs RDE 0.19 1 M KOH 129 52 [13] Abbreviations: NRs=Nanorods; CFP = Carbon fiber paper; CC=Carbon cloth; GCE=Glassy carbon e l e c t r o d e ; rgo = Reduced graphene oxide; NC = N-doped carbon; HNDCM=Nitrogen-doped nanoporous graphitic carbon membranes; CM = Carbon membrane; NTs=Nanotubes;RDE=Rotating disk electrode Supplementary References S-16
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