Sr-anchoring-directed gradient shell architecture in Sr 2 Fe 1.5 Mo 0.5 O 6- δ cathodes for reversible protonic ceramic electrochemical cells

Strontium segregation remains a critical challenge for Sr-containing double perovskite cathodes, wherein outward-migrating Sr species accumulate at the surface and severely deteriorate interfacial electrochemical kinetics in reversible protonic ceramic electrochemical cells (R-PCECs). Herein, we develop a Sr-anchoring–driven interfacial catalytic architecture on Sr2Fe1.5Mo0.5O6−δ (SFM) via vanadium-assisted near-surface phase engineering. The incorporation of V introduces Lewis-acidic centers that effectively immobilize migrating Sr species and simultaneously induce the in situ reconstruction of a nanoscale SrMoO4/SrVO3 heterointerface. More importantly, this reconstructed interface functions as a catalytically active region with enhanced electronic delocalization and optimized oxygen-defect chemistry, which collectively promote oxygen adsorption, dissociation, and charge-transfer kinetics. The gradient shell architecture not only suppresses detrimental Sr segregation but also establishes fast and continuous pathways for coupled ion–electron transport across the interface. Electrochemical impedance and distribution of relaxation time (DRT) analyses reveal substantially reduced polarization resistance and decreased activation energy, indicating accelerated oxygen electrocatalysis. Consequently, the SFM-V cathode exhibits markedly enhanced reversible electrochemical performance compared to pristine SFM, delivering a peak power density of 1.23 W cm-2 at 650 °C together with high electrolysis activity and robust cycling stability, ranking among state-of-the-art SFM-based air electrodes for R-PCECs. This work demonstrates that Sr-anchoring interfacial engineering is an effective strategy to stabilize perovskite cathodes while maintaining fast interfacial kinetics.