Controlling oxygen defect chemistry at electrolyte surface of intermediate temperature solid oxide fuel cells

Engineering the anion defect, especially oxygen vacancy, at the electrolyte surface is important because the concentration and distribution of defects at this surface often determine the oxygen reduction reaction (ORR) kinetics and, in turn, the electrochemical performance of intermediate temperature solid oxide fuel cells (<700 °C). However, designing the desired defect structures is a challenging issue because the required concentration and distribution of defects strongly depend on the locations in the electrolyte with different functionalities. In this study, we precisely control the defect chemistry at the electrolyte surface (Gd_0.1Ce_0.9O_2-δ, GDC) through the infiltration method while maintaining the surface structures. The porous GDC scaffold is modified by the conformal GDC layer in a thickness of 7–11 nm with a controlled trivalent dopant (Gd³⁺) ratio in the range of 0–40 mol%. The enriched oxygen vacancies at the electrolyte surface remarkably improve the ORR kinetics, providing extended and more active reaction sites. An optimized cell with the doping ratio of 30 mol% shows 1.81 times increased maximum power density of 1.07 Wcm⁻² at 650 °C compared with a non-infiltrated cell.