Unravelling the oxygen exchange mechanism on La2Ce2O7

Abstract

Understanding the mechanism of the oxygen exchange rate between the gas-phase and the oxide surface is essential to utilize electrochemical transport of oxygen in ceria-based materials for sustainable technologies. This contribution applies pulse isotope exchange (PIE) to investigate the oxygen exchange mechanism on La₂Ce₂O₇ and 5% Pr-substituted La₂Ce₂O₇. The oxygen exchange kinetics is rate-limited by the dissociation of adsorbed molecular oxygen. Pr substitution increases the surface kinetics, presumably due to an increased concentration of electronic defects that enhances charge transfer of electronic defects at the surface. Humidity decreases the exchange rate due to the selective dissociative adsorption of water molecules into surface oxygen vacancies, forming hydroxide defects. This effect diminishes with increasing temperature due to the exothermic nature of hydration.