Hexagonal MBene (HfBO): A Promising Platform for the Electrocatalysis of Hydrogen Evolution Reaction.

Hexagonal MAB (-MAB) phases and their two-dimensional (2-D) derivatives (-MBenes) have emerged as promising materials since the discovery of TiInB. Herein, we identified that a possible -MBene, 2-D HfBO, can be an excellent platform for the electrocatalysis of hydrogen evolution reaction (HER) by density functional theory calculations. We proposed two approaches of transition metal (TM) modifications by atom deposition and implanting to optimize the HER performance of 2-D HfBO. It is revealed that a moderate charge reduction of surface O, which is induced by the introduction of TM atoms, is conductive to a higher catalytic performance. The synergistic effect between implanted TM atoms and HfBO matrix can efficiently activate the surface by broadening O-p orbitals and shifting up p-band center, especially for V, Cr, and Mo as dopants, which can reduce the Gibbs free energy (Δ) from 0.939 to -0.04, 0.05 and -0.04 eV, respectively. Interestingly, this effect works within a local region and the activity can also be evaluated by bond length of Hf-O, in addition to Δ. This work suggests that due to its excellent electrocatalysis properties, -MBenes can open up a new area for 2-D materials and will stimulate researchers to explore the synthesis of -MAB phases and the stripping of -MBenes.