Catalytic Performance of Single and Double Metal MXenes for the Hydrogen Evolution Reaction

MXenes constitute a rapidly expanding family of two-dimensional materials with significant potential for the hydrogen evolution reaction (HER), but their vast chemical and structural diversities remain largely unexplored. Here, we perform a systematic thermodynamic analysis of H adsorption on 11 MXenes with the general formula (M′M″)n+1(X′X″)nO2, where M = Mo, Mn, Nb, V, Ti, and Y and X = C, N, or B. Using density functional theory calculations within van der Waals corrections, including Hubbard corrections U (d states) for systems containing Mn and V, we determine adsorption energies referenced to both atomic and molecular hydrogen and incorporate Gibbs free-energy corrections accounting for zero-point energy, entropy, and heat-capacity contributions. Our results show that H adsorption is generally exothermic across all 11 MXenes; several MXenes exhibit adsorption free energies comparable to or closer to zero or even with values smaller than those for H/Pt(111), highlighting the potential of MXenes as HER electrocatalysts. Notable exceptions include MoVCO2, MoNbNO2, and Nb3CNO2, which display less favorable adsorption thermodynamics. As expected, we find that O acts as preferential adsorption sites in most materials. To discover the factors that govern HER activity, we analyze the correlations between Gibbs free energies and various electronic descriptors. Among these, the projected integrated covalent bond energy and the work function changes during H adsorption exhibit the strongest relationships (rs ≈ 0.6). This indicates that covalent interactions of H with the surface of MXenes and the changes in the electronic structure of the surface play a key role in determining the catalytic behavior.