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Yuemei Zhang1 Boniface Fokwa1

1, University of California, Riverside, Riverside, California, United States

As one of the cleanest sources of energy, hydrogen is abundant on earth but always found as part of a compound, such as water. The electrolysis of water is considered as a clean mean for large scale hydrogen gas production. However, this large-scale production is still hindered by the high cost and scarcity of noble metal catalysts such as Pt. Recently, non-noble metal materials have emerged as highly active electrocatalysts for the hydrogen evolution reaction (HER) to produce hydrogen gas. Among all the non-noble metal catalysts, our recent research found that MoB2 [1] exhibits high activity and chemical stability. In addition, density functional theory (DFT) calculations show that several surfaces of MoB2 are active and the optimum evolution of H2 occurs on the graphene-like B-terminated {001} surface. Geyer et al. [2] reported that FeB2 is also highly active for overall water splitting in basic solution. However, TiB2 [3] is not as active as MoB2 and FeB2 for HER reaction. To examine the distinct activities of metal diboride as HER catalysts and how the metals could affect the graphene-like boron layer, DFT was applied to investigate the H-surface adsorption process on MB2 (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). Our results indicate that the H-surface binding energy decreases (becomes more negative) as the electronegativity of the metal increases. Therefore, the electron transfer between metal and boron is one of the key parameters to control the HER activity of MB2. In addition, VB2 behaves similarly to MoB2, thus it is predicted to be a highly active HER catalyst candidate. We have also probed the activity of MgB2 and AlB2, both are found to be poor HER catalysts. Hence, the type of chemical bonding (covalent, ionic, metallic) in these compounds also plays an essential role on their catalytic activity.

References
[1] P. R. Jothi, Y. Zhang, J. P. Scheifers, H. Park, B. P. T. Fokwa, Sustainable Energy Fuels 2017, 1, 1928.
[2] H. Li, P. Wen, Q. Li, C. Dun, J. Xing, C. Lu, S. Adhikari, L. Jiang, D. L. Carroll, S. M. Geyer, Adv. Energy Mater. 2017, 7, 1700513.
[3] C. S. Lim, Z. Sofer, V. Mazánek, M. Pumera, Nanoscale 2015, 7, 12527.

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