Oxygen-Vacancy-Engineered CaZr1– x Y x O3–δ for High-Performance Low-Temperature SOFCs

Solid oxide fuel cells (SOFCs) are emerging as transformative electrochemical energy-conversion technologies for sustainable and carbon-neutral power generation owing to their exceptional efficiency, fuel flexibility, and ultra-low emissions. However, the inherently limited ionic transport and elevated operating temperatures of conventional electrolytes remain major barriers to efficient low-temperature operation. In recent years, proton-conducting CaZrO3-based electrolytes have attracted increasing attention due to their chemically tunable defect chemistry and structural stability. However, their limited proton concentration and constrained defect mobility continue to limit ionic transport kinetics at reduced temperatures. Here, we report a defect-engineered perovskite electrolyte, CaZr1–xYxO3–δ (CZY; x = 0, 0.1, 0.2, and 0.3), through aliovalent yttrium-mediated defect engineering that generates highly mobile oxygen vacancies and protonic defects. Comprehensive structural and electrochemical investigations, including XPS, FTIR, Raman spectroscopy, impedance spectroscopy, and distribution of relaxation time (DRT) analysis, reveal dynamically activated defect pathways and accelerated cooperative proton/oxide ion transport kinetics. The optimized CZY composition exhibits a remarkable protonic conductivity of 0.132 S/cm together with peak power densities (PPDs) of 863 mW/cm2 at 550 °C and 266 mW/cm2 at 400 °C, whereas optimized CZY (x = 0.2) exhibits a minimized activation energy of 0.34 eV, lower than those of 0.36 eV (CZY, x = 0.3) and 0.46 eV (CZY, x = 0.1), indicating accelerated ion transport. These findings establish defect-engineered zirconated perovskites as a powerful platform for highly efficient reduced-temperature electrochemical energy-conversion and storage technologies.