A surface reconfiguration of a perovskite air electrode enables an active and durable reversible protonic ceramic electrochemical cell

Reversible protonic ceramic electrochemical cells (R-PCECs) are promising devices for efficient energy storage and conversion. One key technical challenge facing the development of R-PCECs is the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode. Moreover, under typical operating conditions of R-PCECs, the surface of air electrodes readily interacts with the steam, causing severe cation segregations and performance degradations. Here, we report a perovskite-type air electrode with a nominal composition of Ba0.8Gd0.8Pr0.4Co2O5+δ, naturally reconfiguring to a double perovskite Ba0.8Gd0.8-xPr0.4Co2-yO5+δ (BGPC) and in situ formed GdxCoyO3-δ (GCO) nanoparticles (NPs) on the surface of BGPC. Accordingly, the GCO-coated BGPC (GCO-BGPC) electrode shows a low polarization resistance of 0.136 Ω cm2 at 650 °C in a symmetrical cell in wet air (3 vol% H2O). When applied as an air electrode on a fuel electrode-supported cell, the cell demonstrates a good electrochemical performance at 650 °C (a peak power density of 0.909 W cm−2 in fuel cell mode and a current density of 2.336 A cm−2 at 1.3 V in electrolysis cell mode) while maintaining robust reversible operational stability and reasonable Faradaic efficiencies.