title: Direct Observation of Oxygen Dissociation on Non-Stoichiometric Metal Oxide Catalysts.
abstract: 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-δand (La0.8Sr0.2)0.95MnO3±δ, using gas-phase isotope-exchange with a 1:116O2:18O2ratio. 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-δis 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±δshows 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.
authors.affiliation: University of Maryland Energy Research Center, University of Maryland, College Park, MD, 20742, USA.
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Huang
authors.affiliation: University of Maryland Energy Research Center, University of Maryland, College Park, MD, 20742, USA.
authors.forename: Chistopher
authors.initials: C
authors.lastname: Pellegrinelli
authors.affiliation: University of Maryland Energy Research Center, University of Maryland, College Park, MD, 20742, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Wachsman
keywords: heterogeneous catalysis; isotopes; non-stoichiometric compounds; oxygen dissociation; oxygen exchange