Hydrogen evolution reaction in high-entropy MXenes: Insights into atomic configurations.

High-entropy (HE) MXenes have recently gained attention for enhancing catalytic activity and improving stability through diverse active sites and compositional tuning. However, solute segregation during synthesis causes preferential atomic distributions that affect catalytic performance. In this study, HE variants of M2C(-T)2 MXenes with different surface terminations were evaluated for hydrogen evolution reaction using density functional theory and crystal orbital Hamilton population analysis. Substituting Ti with other transition metals improved H∗ adsorption and diffusion. Mo atoms showed short-range ordering, with strong Mo-Mo interactions forming preferred H∗ diffusion pathways. The Volmer-Heyrovsky mechanism displayed a 0.40 eV energy barrier, while hydrogen spillover reduced the Volmer-Tafel barrier from 0.94 to 0.48 eV. OH-terminated HE MXenes demonstrated both thermodynamic and mechanical stability, with Young's and shear moduli of approximately 170 and 68 N/m, respectively. Engineering the composition can favorably induce short-range ordering of atoms, facilitating HER by enabling multiple H∗ diffusion routes.