Steam‐Induced Surface Reconstruction of Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells

Abstract Reversible protonic ceramic electrochemical cells (R‐PCECs) are promising for efficient energy conversion and storage, but their performance is often limited by the poor stability and inadequate electrocatalytic activity of the air electrode under high‐temperature and steam‐rich environments. In this study, a novel composite air electrode material is successfully synthesized capable of dynamically modulating its composition in response to steam. The electrode consists of a perovskite Sr ₂ Fe _1.5 MoO _6‐δ (SFM) framework integrated with secondary SrMoO ₄ (SMO) and SrSnO ₃ (SSO) phases. Under electrolysis operating conditions, the electrode undergoes a steam‐driven structural transformation that significantly increases the density of catalytically active sites. A single cell based on the Sr ₂ Fe _1.5 Mo _0.5 O _6‐δ ‐0.05SnO ₂ (SFMS50) composite cathode achieves a peak power density of 1.41 cm ⁻² in fuel cell mode at 700 °C and delivers a current density of 1.40 A cm ⁻² under 1.3 V at 600 °C in electrolysis mode. In addition, the cell exhibits excellent long‐term operational stability, with steam‐induced compositional changes under electrolysis conditions further enhancing its performance. These results highlight steam‐driven dynamic reconstruction as an effective and practical strategy for boosting both the activity and durability of air electrodes in R‐PCECs.