The decisive role of adsorbed OH* in low-potential CO electro-oxidation on single-atom catalytic sites

Abstract

CO impurity-induced catalyst deactivation has long been one of the biggest challenges in proton-exchange membrane fuel cells, with the poisoning phenomenon mainly attributed to the overly strong adsorption on the catalytic site. Here, we present a mechanistic study that overturns this understanding by using Rh-based single-atom catalysis centers as model catalysts. We precisely modulated the chelation structure of the Rh catalyst by coordinating Rh with C or N atoms, and probed the reaction mechanism by surface-enhanced Raman spectroscopy. Direct spectroscopic evidence for intermediates indicates that the reactivity of adsorbed OH*, rather than the adsorption strength of CO*, dictates the CO electrocatalytic oxidation behavior. The RhN4 sites, which adsorb the OH* intermediate more weakly than RhC4 sites, showed prominent CO oxidation activity that not only far exceeded the traditional Pt/C but also the RhC4 sites with similar CO adsorption strength. From this study, it is clear that a paradigm shift in future research should be considered to rationally design high-performance CO electro-oxidation reaction catalysts by sufficiently considering the water-related reaction intermediate during catalysis.