Direct Observation of Oxygen Dissociation on Non‐Stoichiometric Metal Oxide Catalysts

Oxygen dissociation on metal oxides is a key reaction step, limiting the efficiency of numerous technologies. The complexity of the multi‐step oxygen reduction reaction (ORR) makes it difficult to investigate the oxygen dissociation step independently. Direct observation of the oxygen dissociation process is described, quantitatively, on perovskites La0.6Sr0.4Co0.2Fe0.8O3‐δ and (La0.8Sr0.2)0.95MnO3±δ, using gas‐phase isotope‐exchange with a 1:1 16O2:18O2 ratio. Oxygen transport mechanisms between gas–surface reactions and surface–bulk exchange are deconvoluted. Our findings show that regardless of participation of lattice oxygen, La0.6Sr0.4Co0.2Fe0.8O3‐δ is better at oxygen dissociation than (La0.8Sr0.2)0.95MnO3±δ. Heteroexchange, involving lattice oxygen, dominates on La0.6Sr0.4Co0.2Fe0.8O3‐δ. In contrast, (La0.8Sr0.2)0.95MnO3±δ shows both homoexchange and heteroexchange, with the latter only happening above 600 °C. Using a 1:1 isotope mixture, a simple method is presented for separation of the oxygen dissociation step from the overall ORR.