A Core‐Shell Perovskite Composite Air Electrode With Thermal‐Expansion Offset and Mechanical Support Functions for Highly Durable Reversible Protonic Ceramic Cells

Reversible protonic ceramic cells (RPCCs) offer a promising pathway to efficient and reversible energy conversion, accelerating the global shift to renewables. However, the RPCCs' commercialization faces limitations in air electrode materials. Traditional cobalt-based perovskite air electrodes, while effective, suffer from high cost and environmental concerns. Alternative materials, such as SrFeO_3-δ (SF)-based perovskites, offer potential, yet durability issues, including thermal-expansion mismatch and mechanical instability, hinder their practical application. Here, a unique solid-state reaction between SF and negative-thermal-expansion (NTE) material is demonstrated to yield a core-shell perovskite composite as a highly durable RPCCs air electrode. Specifically, by calcining a mixture of SF and an NTE material, ZrW₂O₈ (ZWO), the in situ incorporation of ZWO into the SF lattice is achieved, resulting in a non-closed core-shell composite, comprising single perovskite Sr_aFe_bZr_cW_dO_3-δ (SP-SFZW) core and B-site cation ordered double perovskite Sr_xFe_yZr_mW_nO_6-δ (DP-SFZW) shell. Both SP-SFZW and DP-SFZW serve as oxygen catalysts, while DP-SFZW shell additionally acts as a thermal expansion suppressor and mechanical support structure, effectively mitigating electrode cracking and delamination from other cell components during RPCC operation. Consequently, the composite electrode demonstrates comparable catalytic activity to SF, coupled with significantly enhanced durability. This work illustrates a novel approach for developing robust RPCCs air electrode.