Doping Ti₃C₂O₂ by metals may effectively reduce the free energy of the hydrogen evolution reaction reaction steps, thereby enhancing electrocatalytic efficiency.

The atomic and electronic structure, thermodynamic stability, and effect of doping the O-terminated Ti₃C₂ MXene (Ti₃C₂O₂) by Hf, Nb, Ta, and Zr on the electrocatalytic activity for the hydrogen evolution reaction (HER) is investigated by means of periodic density functional theory (DFT)-based simulations. The preference of doping Ti₃C₂O₂ with the doping agent either in the outer or inner atomic layers is determined by formation energies’ estimates. Among these studied systems, the case where one Hf substitutes one Ti atom in the Ti₃C₂O₂ inner layer appears to exhibit the optimum HER activity with a ΔG value of −0.27 eV only, lower than the corresponding value of −0.40 eV previously reported for stoichiometric Ti₃C₂O₂, implying an improved HER activity. Thus, doping MXenes with similar metal atoms appears to be an attractive approach to engineer the HER activity of this family of materials.