Single Atom-Modified Hybrid Transition Metal Carbides as Efficient Hydrogen Evolution Reaction Catalysts

2D transition metal carbides and nitrides (MXenes) are promising hydrogen evolution reaction (HER) catalysts owing to their metallic conductivity, abundant surface active sites, and high specific surface area. The introduction of a single transition metal atom (TM) at the surface is a good way to improve the HER performance of MXenes. However, the effect of TM on MXenes in previous theoretical studies focused on pure functional groups, and ignored the hybrid-functionalized ones, which are mostly observed in experiments. Herein, the HER performance of four O/F ratios stable hybrids MXenes, Ti₂CT_x (T = O, F), is explored. Ti₂CO_1.33F_0.67 exhibits superior HER catalytic activity, comparable to that of platinum metals. Further combinatorial screening of ≈200 TMs based on Ti₂CT_x structures suggests that Rh, Ti, Ir, and Pt are optimal TM candidates that enhance the sensitivity to strain modulation and reduce the activation barrier for hydrogen generation. A descriptor ψ is used to quantify HER performance and reveals the role of the electron filling of TM to the antibonding orbitals. These findings propose feasible candidates with high HER performance through single-atom modification for hybrid-functional MXenes, and a useful descriptor to screen for MXenes with desirable catalytic properties.