Probing the Reaction Mechanism of CO2 Electroreduction over Ag Films via Operando Infrared Spectroscopy

The electrocatalytic reduction of CO 2 to chemical fuels has attracted significant attention in recent years. Among transition metals, silver shows one of the highest faradaic efficiencies for CO formation as the main reaction product; however, the exact mechanism for this conversion is not fully understood. In this work, we study the reaction mechanism of silver as a CO 2 reduction catalyst using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) during electrochemical cycling. Using ATR-FTIR, it is possible to observe the reaction intermediates on the surface of Ag thin films formed during the CO 2 electroreduction reaction. At a moderate overpotential, a proton coupled electron transfer reaction mechanism is confirmed to be the dominant CO 2 reduction pathway. However, at a more negative applied potential, both the COO – and the COOH intermediates are detected using ATR-FTIR, which indicates that individual proton and electron transfer steps occur, offering a different pathway than at lower potentials. These results indicate that the CO 2 reduction reaction mechanism can be potential dependent and not always involving a concerted proton coupled electron transfer, opening alternative pathways to optimize efficient and selective catalysts for desired product formation.