Oxygen Surface Exchange Kinetics of Ce _0.99 Gd _0.01 O _{2− <i>δ</i>} and La ₂ Ce ₂ O _{7− <i>δ</i>}

Exploring the influence of acceptor doping on oxygen exchange is essential to utilize electrochemical transport of oxygen in ceria-based materials. Through gas phase analysis (GPA) we have elucidated the mechanism of oxygen exchange on Ce 0.99 Gd 0.01 O 2− δ and La 2 Ce 2 O 7− δ under dry and humid conditions, scenarios commonly encountered in the practical working conditions of solid oxide electrochemical cells and oxygen transport membranes. The oxygen exchange is rate-limited by the dissociation of adsorbed molecular oxygen for both materials. La 2 Ce 2 O 7− δ exhibits a higher oxygen exchange rate with lower activation energy than Ce 0.99 Gd 0.01 O 2− δ . This has been interpreted to reflect primarily higher concentration of oxygen vacancies in La 2 Ce 2 O 7− δ compared to Ce 0.99 Gd 0.01 O 2− δ . However, this increase remains moderate under conditions of relatively low electron concentration. Humidity diminishes the exchange rate due to the dissociative adsorption of water molecules into the surface oxygen vacancies, forming hydroxyl groups effectively blocking reactive sites for oxygen species.