A-Site Disorder Regulation Enables Simultaneously Steam-Resistant and Kinetically Active Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells

Abstract Reversible protonic ceramic electrochemical cells (R-PCECs) offer efficient energy conversion and storage but remain limited by steam-induced degradation, sluggish air-electrode kinetics, and thermal-expansion mismatch. Here, a targeted A-site disorder regulation strategy is developed for cobalt-based perovskites by co-introducing Pr, Nd, and Sm into La0.8Sr0.2Co0.7Ni0.3O3–δ to form La0.2Sr0.2Pr0.2Nd0.2Sm0.2Co0.7Ni0.3O3–δ (LSPNSCN). The resulting A-site multication disorder drives a rhombohedral-to-cubic phase transition, suppresses cation redistribution and steam-induced Ni segregation, and reduces the thermal-expansion coefficient to 14.7 × 10–6 K–1. Meanwhile, the synergistic effects of the rare-earth cations regulate oxygen-defect chemistry and enhance surface hydration behavior, thereby facilitating oxygen- and proton-involving electrode reactions and improving bifunctional oxygen reduction and evolution reaction (ORR/OER) kinetics. At 650 °C, LSPNSCN-based R-PCECs deliver a peak power density of 1.58 W cm–2 in fuel cell (FC) mode and an electrolysis current density of –2.32 A cm–2 at 1.3 V in electrolysis cell (EC) mode. At 550 °C, independent LSPNSCN-based cells maintain stable operation for over 250 h in FC mode and 140 h in EC mode, respectively. This work demonstrates that targeted A-site disorder regulation can simultaneously improve steam resistance, reaction kinetics, and thermomechanical compatibility, providing a practical design strategy for durable and active R-PCEC air electrodes.