Platinum monolayer dispersed on MXenes for electrocatalyzed hydrogen evolution: a first-principles study†

Maximizing platinum's atomic utilization and understanding the anchoring mechanism between platinum moieties and their supports are crucial for the hydrogen evolution reaction (HER). Using density functional theory, we investigate the catalyst of a Pt monolayer on the two-dimensional Mo₂TiC₂ substrate (Pt_ML/Mo₂TiC₂) for the reaction. This Pt monolayer shows a Pt(111)-like pattern, with its Pt–Pt bond elongated by about 0.1 Å compared to Pt(111); charge transfer from Mo₂TiC₂ to the Pt monolayer leads to significant charge accumulation on Pt. This substantial monolayer metal–support interaction optimizes hydrogen adsorption toward optimal HER activity under both constant charge and potential conditions, making Pt_ML/Mo₂TiC₂ a promising HER catalyst. Detailed studies reveal that the dominant Volmer–Tafel mechanism in the HER occurs on the 1 monolayer hydrogen-covered Pt_ML/Mo₂TiC₂ surface. The surface Pourbaix diagram identifies this as the stable surface termination under the electrochemical reaction conditions. These findings provide insights into designing stable, efficient, and low platinum-loaded HER catalysts.