Reaction mechanism and kinetics for carbon dioxide reduction on iron–nickel Bi-atom catalysts

Abstract

The electrochemical CO₂ reduction reaction (CO₂RR) is being accepted as one of the most promising strategies to convert carbon emissions to valuable chemicals and fuels. Among the various types of electrocatalysts, dual-site catalysts have emerged as a new frontier. In particular, the Ni–Fe bi-site not only plays a key role in the biological utilization of CO₂ in enzymes but also shows exceptional activity and selectivity for CO evolution in the heterogeneous CO₂RR. However, an in-depth understanding of the reaction mechanism has not been achieved. In this work, we applied the recently developed grand canonical potential kinetics (GCP-K) method to determine the reaction mechanism and kinetics of the CO₂RR on Fe&Ni@g-N₆. Unlike the traditional CO₂RR mechanism on transition metals or single-atom catalysts, the Fe–Ni dual site is firstly passivated by strongly adsorbed *CO, and the real active site of the CO₂RR cycle is at the exposed single Fe site. The predicted overall kinetics has a U_onset (10 mA cm⁻²) of −0.99 V to generate CO, and the maximum turnover frequency reaches 961 h⁻¹ per site at U = −1.18 V. The competitive hydrogen evolution reaction (HER) has a greater negative onset potential and does not interfere with the CO₂RR. These predictions show a reasonable agreement with the experiment. The promising performance is correlated with the down-shift and localization of the 3d electronic states of Fe atoms. Our analysis provides a defined mechanism and offers useful insight into designing efficient dual-active-site electrocatalysts.