Quantitative Coordination-Activity Relations for the Design of Enhanced Pt Catalysts for CO Electro-oxidation

Efficient redox transformations of CO are vital for remediating the imbalance of the biogeochemical cycle of carbon and also for the development of next-generation energy technologies such as fuel cells. For instance, CO oxidation is ubiquitous in hydrocarbon-based fuel cells and determines to a large extent their efficiency. As Pt is used in these cells, minimal catalyst loadings that do not compromise the activity are needed. In view of that, we present here a "coordination-activity plot" and electrochemical experiments on electro-oxidation of adsorbed CO to CO₂ to establish quantitative structure-activity relations for various Pt electrodes. We predict theoretically and verify experimentally that catalytic CO oxidation is enhanced by creating surface defects with optimal coordination, without alloying. Both largely overcoordinated and undercoordinated defects on Pt (at rough surfaces with cavities and metal adatoms, respectively) hinder the reaction, so that the maximal activity is reached on sites with a generalized coordination of CN = 5.4. Importantly, this moderate coordination is found at defects such as step edges of electrodes with relatively short terrace lengths of 3-4 metal atoms. (Figure Presented).