Depleted Nd–Al-Perovskites for High Proton Conducting Electrolyte Fuel Cells

Depleted perovskites, a new class of functional materials distinct from conventional doped perovskites, present a transformative approach to enhancing proton conduction. This study introduces Nd-alumina as an A-site-depleted perovskite, systematically comparing its properties with those of the well-known BaZr_0.8Y_0.2O_3−δ (BZY) perovskite. Notably, with the same cation deficit concentration, e.g., 20 mol % Nd-depleted alumina (0.8-NAO), achieves three times the oxygen vacancy (O_vac.) concentration compared to 20 mol % Y³⁺ doping in BaZrO₃ (BZY). Electrochemical performance reveals an 0.8-NAO electrolyte with excellent ionic conductivity above 0.20 S cm^–1 and a power density of 966.4 mW cm^–2 at 550 °C. Furthermore, the A-site-depleted perovskite was successfully operated at low temperatures of up to 320 °C, achieving a power density of 109.3 mW cm^–2. Complementary density functional theory (DFT) calculations reveal vacancy-induced midgap states and orbital hybridization effects (O-2p, Al-p, Nd-4f), which rationalize the observed band gap narrowing and enhanced proton mobility. Beyond conductivity, the depleted structure enhances proton transport while maintaining excellent thermal stability under fuel cell conditions. Preliminary results reveal that 0.8-NAO not only enhances proton mobility but also significantly improves thermal stability, outperforming traditional BZY perovskite oxides. These findings underscore the potential of 0.8-NAO as a promising alternative to conventional perovskite designs, making it a superior candidate for fuel cells and relevant proton-conducting applications.