Defect-driven MXenes for enhanced electrocatalytic nitrogen reduction: a first-principles and microkinetic study

The electrocatalytic nitrogen reduction reaction (ENRR) offers a sustainable pathway for ammonia synthesis under mild conditions, yet its practical implementation is hindered by poor N₂ activation efficiency and the lack of a clear structure-activity relationship for rational catalyst design. Herein, we systematically investigate the electrocatalytic performance of vacancy-engineered M₂CT₂ (M = Ti, Nb, and Mo; T = O, S, Cl, and Br) MXenes for the ENRR using well-defined density functional theory calculations combined with microkinetic modeling. Our results demonstrate that surface vacancies significantly modulate the local electronic structure of MXenes, thereby promoting N₂ adsorption and activation. The results demonstrated that the ENRR proceeded on VT-M₂CT₂ through the distal pathway according to free energy calculations. A novel descriptor, Ψ, based on the valence of the transition metal and the lattice constant, is proposed to establish a quantitative structure-activity relationship, enabling rapid screening of high-performance catalysts. Among the candidates, vacancy-engineered Ti₂CBr₂ exhibits outstanding ENRR activity, as further validated by microkinetic analysis. This work provides a universal strategy for the design of defect-mediated MXene catalysts and paves the way for the development of efficient ENRR electrocatalysts.