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 (AlB2-type) for the hydrogen evolution reaction (HER) to produce hydrogen. Our recent research found that α-MoB2 exhibits high HER activity. In addition, density functional theory (DFT) calculations show that several surfaces of AlB2-type MoB2 (α-MoB2) are active and the optimum evolution of H2 occurs on the graphene-like B-terminated {001} surface. Furthermore, DFT and experiments demonstrate that α-MoB2 is more HER active than β-MoB2, due to the presence of 50% more graphene-like boron layers in the former. It was recently also found that FeB2 is highly active for overall water splitting in basic solution. To examine the distinct activities of metal diboride as HER electrocatalysts and demonstrate how different transition 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 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. We have also recently found an unexpected lattice parameter-dependency on HER of ternary variants crystallizing with the AlB2-type structure. Furthermore, an unexpected boron-chain dependency of the HER activity was discovered in the V-B system, that even allows for the prediction of unknow active HER catalysts. Using a recently developed synthesis, we were able to synthesize most transition metal borides at the nanoscale. Nanoscale VB2 and CoB have indeed shown much improved HER activities if compared to their bulk counterparts.

Earth-abundant boride electrocatalysts for hydrogen production: Importance of 1D and 2D boron units

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.