Mixed-Potential-Driven Catalysis: An Electrochemical Mechanism for Room-Temperature CO Oxidation on Gold Catalysts.

Gold is an effective catalyst for low-temperature CO oxidation, yet its mechanism remains debated. Among the various proposed mechanisms, increasing attention has been given to a possible electrochemical pathway in recent studies. Here, experimental evidence is reported that CO oxidation at room temperature in electrolytes proceeds via coupled electrochemical CO oxidation and oxygen reduction half-reactions, i.e., the mixed-potential-driven mechanism. A model system is designed with deposited Au nanoparticles (NPs) and nitrogen-doped reduced graphene oxide (NrGO) on carbon paper acting as spatially separated electrodes in a single electrolysis cell. After shorting the two electrodes, the reaction current and mixed potential of the overall CO oxidation are measured without any externally applied bias. Independent current-potential curves for each half-reaction are also obtained under identical experimental conditions. The intersection points of these curves, representing the predicted mixed potential and net current, showed good agreement with the values measured in the short-circuited system. These results provide clear evidence that CO oxidation in aqueous media proceeds via a mixed-potential-driven mechanism, analogous to corrosion. This finding provides strong support for the hypothesis that low-temperature CO oxidation over-supported Au catalysts in the presence of water vapor proceeds via a similar electrochemical pathway in gas-phase heterogeneous catalysis.