A Review on Electrolyte Materials for Protonic Solid Oxide Cells (P‐SOCs)

ABSTRACT Protonic solid oxide cells (P‐SOCs) have garnered significant attention in energy conversion and storage, due to their high efficiency and reduced environmental footprint. As the central component of P‐SOCs, the electrolyte dictates cell performance and long‐term durability, with its protonic conductivity, chemical stability, and mechanical integrity playing decisive roles. Distinct from previous P‐SOC reviews centered on electrodes or full‐cell architectures, this review provides a comprehensive analysis of proton conduction mechanisms and the current material landscape, focusing particularly on perovskite‐type oxides such as BaCeO 3 , BaZrO 3 , and their derivatives. Specifically, it addresses the critical trade‐off between the poor chemical stability of BaCeO 3 and the refractory nature of BaZrO 3 . To overcome these intrinsic limitations, various modification strategies are critically evaluated, ranging from single and multi‐element co‐doping to the introduction of low‐melting‐point elements at the B‐site and secondary‐phase sintering aids. Beyond material composition, the review examines advanced fabrication techniques for high‐quality electrolyte membranes—including pulsed laser deposition, magnetron sputtering, high‐pressure sintering, and additive manufacturing. Furthermore, it elucidates how interface engineering and multi‐scale structural design can effectively minimize interfacial impedance and suppress electronic leakage. The review concludes by identifying prevailing challenges and outlining strategic research directions for the rational design of next‐generation protonic ceramic electrolytes.