Hexagonal MBene (Hf₂BO₂): A Promising Platform for the Electrocatalysis of Hydrogen Evolution Reaction

Hexagonal MAB (h-MAB) phases and their two-dimensional (2-D) derivatives (h-MBenes) have emerged as promising materials since the discovery of Ti₂InB₂. Herein, we identified that a possible h-MBene, 2-D Hf₂BO₂, 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 Hf₂BO₂. 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 Hf₂BO₂ 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 (ΔG_H*) 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 ΔG_H*. This work suggests that due to its excellent electrocatalysis properties, h-MBenes can open up a new area for 2-D materials and will stimulate researchers to explore the synthesis of h-MAB phases and the stripping of h-MBenes.