Surface Termination (-O, -F or -OH) and Metal Doping on the HER Activity of Mo₂CT_x MXene

Two-dimensional MXenes have recently garnered significant attention as electrocatalytic materials for hydrogen evolution reaction (HER). However, previous theoretical studies mainly focused on the effect of pure functional groups while neglecting hybrid functional groups that are commonly observed in experiments. Herein, we investigated the hybrid functionalized Mo₂CT_x MXene (T=-O, -F or -OH) to probe the HER properties. In binary O/F co-functionalization, the presence of F groups would attenuate the H adsorption and lead to the enhanced HER activity than the fully O-terminated Mo₂CO₂. However, the surface HER activity of ternary O/F/OH functionalized Mo₂CT_x is not satisfactory owing to the relatively weak H adsorption capacity. To further enhance the catalytic activity, modification was performed by introducing another metal element into its lattice structure. The doped metal (Fe, Co, Ni, Cu) exhibits reduced charge transfer to O compared to Mo atoms, leading to enhanced H adsorption and improved overall activity. The synergistic effect of hybrid functionalization and TM modification provides useful guidance for achieving feasible Mo₂CT_x candidates with high HER performance, which can be applied to the electrocatalytic applications of other MXenes.