Balanced Electron Donation Governs Adsorption Site Selection in CO2 Electroreduction to HCOOH on Transition Metal-Doped Magnesium Oxides.

Magnesium oxide (MgO) is attractive for CO2 utilization. However, the electronic inertness has limited its application in electrochemical catalysis. Herein, spin-polarized density functional theory (DFT) calculations with the BEEF-vdW functional were performed to evaluate the activity and selectivity of transition-metal-doped MgO (TM-MgO) catalysts for electrochemical CO2 reduction reaction (eCO2RR). Co-, Pd-, and Pt-doped MgO were identified as promising candidates for selective formic acid (HCOOH) production. Mechanistic analysis shows that TM doping induces electron redistribution in MgO, activating neighboring Mg sites while enabling charge transfer between TM dopants and reaction intermediates. The competition between Mg-site activation and TM-intermediate charge transfer determines the site preference and binding strength of the key OCHO* intermediate. Bader charge, density of states, and COHP analyses support this mechanism. This work provides design principles for oxide-based electrocatalysts toward selective HCOOH production from eCO2RR.