Emerging Material Paradigm: Strategic Optimization of Spinel Oxides as High-Performance Air Electrodes for Nanostructured Ceramic Fuel Cells

Hydrogen, renowned for its clean energy profile and high energy density, is a pivotal energy carrier for addressing global energy and environmental challenges. Solid oxide fuel cells (SOFCs) and proton ceramic fuel cells (PCFCs) have garnered significant interest due to their direct chemical-to-electrical-energy conversion, fuel flexibility, high efficiency, and environmental compatibility. However, conventional perovskite-based air electrodes suffer from sluggish oxygen reduction reaction (ORR) kinetics and insufficient structural stability at intermediate temperatures. Spinel oxides, distinguished by excellent chemical stability and thermal expansion compatibility, have emerged as promising alternatives; however, their broader application is constrained by their limited ionic conductivity and catalytic activity. This review systematically elucidates the crystal structure, intrinsic advantages, and advanced design strategies of spinel oxides. It particularly focuses on A- and B-site doping techniques for precise modulation of thermal expansion and enhancement of electrocatalytic performance, alongside high-entropy engineering approaches that bolster high-temperature stability. Finally, the review comprehensively discusses remaining challenges and future prospects for the implementation of spinel oxides in nanostructured ceramic fuel cells.