Catalytic Effect on CO₂ Electroreduction by Hydroxyl-Terminated Two-Dimensional MXenes

Electrocatalysis represents a promising method to generate renewable fuels and chemical feedstock from the carbon dioxide reduction reaction (CO₂RR). However, traditional electrocatalysts based on transition metals are not efficient enough because of the high overpotential and slow turnover. MXenes, a family of two-dimensional metal carbides and nitrides, have been predicted to be effective in catalyzing CO₂RR, but a systematic investigation into their catalytic performance is lacking, especially on hydroxyl (-OH)-terminated MXenes relevant in aqueous reaction conditions. In this work, we utilized first-principles simulations to systematically screen and explore the properties of MXenes in catalyzing CO₂RR to CH₄ from both aspects of thermodynamics and kinetics. Sc₂C(OH)₂ was found to be the most promising catalyst with the least negative limiting potential of -0.53 V vs RHE. This was achieved through an alternative reaction pathway, where the adsorbed species are stabilized by capturing H atoms from the MXene's OH termination group. New scaling relations, based on the shared H interaction between intermediates and MXenes, were established. Bader charge analyses reveal that catalysts with less electron migration in the *(H)COOH → *CO elementary step exhibit better CO₂RR performance. This study provides new insights regarding the effect of surface functionalization on the catalytic performance of MXenes to guide future materials design.