First-principles study of precise O vacancy-deficient MXene as an ORR/OER bifunctional catalyst

The catalytic activity of MXene catalysts for oxygen reduction and oxygen evolution reaction (ORR and OER) is limited by the coordination environment of the active center. However, the mechanism of how vacancy-induced reconstruction catalysts promote ORR/OER remains unclear. Here, we exploit oxygen vacancies in Mo₂CO₂ to reveal the influence of defects in the reconstruction process and the limitations of active center coordination environments with different TM atom compositions on the catalytic process. Through theoretical calculations, we found that the enhanced adsorption of OOH* by the oxygen defects during the catalytic process drove the catalyst's reconstruction, especially in the OER reaction, where the presence of O vacancies somewhat breaks the linkage between OH* and the overpotential and shows excellent OER activity. It was found that the Os-O_V@Mo₂CO₂ catalyst had the highest activity with theoretical overpotentials η^ORR = 0.43 V and η^OER = 0.49 V, which were close to or better than those of conventional Pt (111) and IrO₂ (110). In addition, we systematically investigated the interactions between the catalyst and the reaction intermediates during the reaction process and elucidated the relationship between the changes in the free energies of different oxygenated intermediates. Overall, this study provides a feasible approach for the design and development of advanced bifunctional electrocatalysts, enriches the application of MXene, a novel two-dimensional material, in the electrochemical energy field, and provides theoretical experience for the design of defective MXene catalysts.