Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 60: Chemistry at Solid/Liquid Interfaces
O 60.8: Talk
Wednesday, March 9, 2016, 17:00–17:15, S052
Improved Chemical and Electrochemical Stability on Perovskite Oxides by Oxidizing Cations at the Surface — Qiyang Lu1, Nikolai Tsvetkov1, Lixin Sun1, Ethan Crumlin2, and •Bilge Yildiz1 — 1Massachusetts Institute of Technology, Cambridge MA, USA — 2Lawrence Berkeley National Laboratory, Berkeley CA, USA
Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces is detrimental to the performance of electrocatalytic energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants (Sr2+ on La3+ site) by the positively charged oxygen vacancies enriched at the surface. Here we take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less oxidizing than Co on the B-site of LSC. We utilized ambient pressure X-ray absorption and photoelectron spectroscopy to prove that the dominant role of the oxidizing surface additives is to suppress the enrichment and phase separation of Sr while reducing the concentration of oxygen vacancies at the surface. Consequently, we found the effect of these oxidizing cations to be significantly improved stability, with up to 30x acceleration of the oxygen exchange kinetics. Finally, the results revealed a *volcano* relation between the oxygen reduction reaction (ORR) kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations.