Pomegranate-Like N, P-Doped Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution

Transcription

1 Supporting Information Pomegranate-Like N, P-Doped Nanospheres as Highly Active Electrocatalysts for Alkaline Hydrogen Evolution Yu-Yun Chen,,,# Yun Zhang,,# Wen-Jie Jiang,, Xing Zhang,, Zhihui Dai,,* Li-Jun Wan,, Jin-Song Hu, * Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Nanostructure and Nanotechnology, Institute of Chemistry, Chinese Academy of Science, 2 North 1 st Street, Zhongguancun, Beijing , China Jiangsu Key Laboratory of Biofunctional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing , China University of Chinese Academy of Science, Beijing , China # These authors contributed equally to this work. This file includes supplementary Figures S1-S10, and Table S1 and S2. S1

2 Figure S1. Typical HRTEM image of nanospheres S-800. Figure S2. SEM images of (a) S-700 and (b) S-900. S2

3 Figure S3. TGA profile of S-800 obtained under air flow. As shown in TGA curve, the initial weight losses below 150 o C is ascribed to the water evaporation. The weight gains between 150 o C and 300 o C should be caused by the gradual oxidation and transformation of Mo2C to MoO3, which followed by an obviously weight loss due to the combustion of carbon. The remaining weight after heating to 500 o C is about 93.4 wt.%. Accordingly, the Mo2C content wasa calculated from the following equation: 1 m%(mo2c) = residual mass * M(Mo2C)/2M(MoO3) = 93.4 wt.%*204/(2*144) 66.1 wt.% S3

4 Table S1. Summary of Mo-based electrocatalysts for HER in alkaline electrolytes. Materials Current density (ma cm -2 ) Overpotential (mv) Electrolyte Ref. MoxC-Ni@NCV M KOH 2 MoC-Mo2C M KOH 3 β-mo2c M KOH 1 MoCx M KOH 4 Mo2C@NC M KOH 5 pomegranate-like N, P-doped Mo2C@C nanospheres M KOH This work S4

5 Figure S4. CV curves measured at different scan rates from 10 to 100 mv s -1 in 1 M KOH and capacitive current at 0.2 V as a function of scan rates for diffrent catalysts: (a, b) S-700, (c, d) S-900, and (e, f) Pt/C. S5

6 ECSA and TOF calculation: The electrochemical active surface area (ECSA) can be estimated using the capacitance (C). The specific capacitance for a flat surface is generally found to be in the range of 20~60 μf cm μf cm -2 was used in the following calculations of the ECSA and turnover frequency (TOF) as literatures generally did. 6, 7 The following formula was used to calculate ECSA: ECSA C 40 μf cm per cm The following formula and ECSA was used to calculate TOF: number of total hydrogen turnover per cm # j TOF number of active sites per cm active sites ECSA The number of total hydrogen turnovers (# ) was calculated from the current density according to the formula: # j ma 1C s cm 1000 ma 1mol H C 1mol H 2mol of e H moleculars 1mol H H /s cm per ma cm The number of active sites per surface area was calculated according to the crystal data as follows: 7 2 atom/unit cell Active sites 37.2 Å /unit cell atom per cm 4 atom/unit cell Active sites Å /unit cell atom per cm S6

7 The TOF values per active site for S-800 and Pt-C were calculated and then plotted as a function of the overpotential in Figure S5. Particularly, at an overpotential of 10 mv, the jecsa is 0.59 μa cm -2 for S-800 (Figure 5), and the TOF value of S-800 was calculate to be: TOF H /s μa μa cm per cm 0.59 cm atom per cm 350 cm per s Similarly, the TOF value of Pt/C at the same overpotantial was calculate to be: TOF / H /s μa μa cm per cm 1.07 cm atom per cm 375 cm per s Figure S5. Comparison of the TOFs of S-800 and Pt/C. S7

8 Figure S6. SEM images of (a, b) S-800-rGO and (c) S-800-Phy. (d) Polarization curves of S-800-rGO, S-800-Phy, S-800, and reference Pt/C, recorded in 1 M KOH at a scan rate of 2 mv s -1. S8

9 Figuer S7. (a) XRD patterns of com-mo2c and (b) SEM image of TEM images of (c) com-mo2c and (d) Figure S8. Polarization curves of com-mo2c and recorded in 1 M KOH at a scan rate of 2 mv s-1. S9

10 Figure S9. (a) Wide-scan survey XPS spectrum, (b) XRD pattern, and (c) SEM image of the control catalyst no-p. (d) Polarization curves of the catalyst no-p, S-800, and reference Pt/C recorded in 1 M KOH at a scan rate of 2 mv s -1. The successful preparation of the control catalyst no-p was evidenced by the following facts: i) No signal of P 2p (~130 ev) was detected in XPS spectrum; ii) XRD pattern disclosed the feature of C and the diffractions of Mo2C phase (JCPDS ); SEM image displayed that the catalyst no-p was composed of nanoparticles in tens of nanometers. Although the morphology of the catalyst no-p was slightly different from the catalyst S-800, it could be concluded that the co-doping of P should play an important role in enhancing the HER activity in view of the significant enhancement of HER activity after N,P co-doping. S10

11 Table S2. Summary of Mo-based electrocatalysts for HER in acidic electrolytes. Materials Current density (ma cm -2 ) Overpotential (mv) Electrolyte Ref. MoS0.86P0.57/CB M H2SO4 8 MoSx@Mo2C M H2SO4 7 PDAP-MoCN-CO H2SO4 and Na2SO4 (0.5 M) 9 NS-doped Mo2C M H2SO4 10 CoMoS M H2SO4 11 nw-w4moc M H2SO4 12 MoxSoy (Mo2C) M HClO4 13 Mo2C/CNT M HClO4 14 M-MoS M H2SO4 15 MoxC-Ni@NCV M H2SO4 2 MoC Mo2C M H2SO4 3 MoCx M H2SO4 4 Mo2C@NC M H2SO4 5 pomegranate-like N, P-doped Mo2C@C nanospheres M H2SO4 This work S11

12 Figure S10. Polarization curves of S-800 with different loadings on a glassy carbon electrode in (a) 1 M KOH and (b) 0.5 M H2SO4. References in the supporting information (1) Ma, F. X.; Wu, H. B.; Xia, B. Y.; Xu, C. Y.; Lou, X. W. Hierarchical β-mo2c Nanotubes Organized by Ultrathin Nanosheets as a Highly Efficient Electrocatalyst for Hydrogen Production. Angew. Chem. Int. Ed. 2015, 54, (2) Wang, S.; Wang, J.; Zhu, M.; Bao, X.; Xiao, B.; Su, D.; Li, H.; Wang, Y. Molybdenum-Carbide-Modified Nitrogen-Doped Carbon Vesicle Encapsulating Nickel Nanoparticles: A Highly Efficient, Low-Cost Catalyst for Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2015, 137, (3) Lin, H.; Shi, Z.; He, S.; Yu, X.; Wang, S.; Gao, Q.; Tang, Y. Heteronanowires of MoC-Mo2C as Efficient Electrocatalysts for Hydrogen Evolution Reaction. Chem. Sci. 2016, 7, (4) Wu, H. B.; Xia, B. Y.; Yu, L.; Yu, X. Y.; Lou, X. W. Porous Molybdenum Carbide S12

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