Achieving active and durable oxygen reduction/evolution reactions on protonic ceramic electrochemical cells with spinel-based air electrodes†

Abstract

Reversible protonic ceramic electrochemical cells (R-PCECs) have demonstrated great potential for efficient energy conversion and storage, and are expected to break through the limitations in traditional cell systems. However, the performance of R-PCECs is often constrained by the air electrode, where oxygen reduction/evolution reactions occur. Herein, we report a composite electrode of spinel oxide MnCo_1.9Cu_0.1O₄ (MCCO) and BaZr_0.8Y_0.2O₃ (BZY), at an optimized ratio of MCCO to BZY = 9 : 1, showing a low area-specific resistance of 0.107 Ω cm² at 700 °C. R-PCECs with this composite air electrode exhibit high performance: a maximum power density (P_max) of 1.81 W cm⁻² in fuel cell mode, and a current density of −3.57 A cm⁻² at 1.3 V in electrolysis mode at 700 °C. Moreover, the cells demonstrate remarkable stability in reversible operation for 70 hours and 15 cycles during cycling testing, at ±0.5 A cm⁻². The enhanced activity and durability are likely attributed to the facilitated oxygen/proton transport and the increased concentration of oxygen vacancies after Cu doping, as indicated by the analyses of X-ray photoelectron spectroscopy and distribution of relaxation time.