High-entropy perovskite oxide BaCo_0.2Fe_0.2Zr_0.2Sn_0.2Pr_0.2O_3-δ with triple conduction for the air electrode of reversible protonic ceramic cells

Reversible protonic ceramic cells (RPCCs) show great potential as new-generation energy conversion and storage devices. However, the mature development of RPCCs is seriously hindered by the inactivity and poor stability of air electrodes exposed to concentrated vapor under operating conditions. Herein, we report a high-entropy air electrode with the composition BaCo_0.2Fe_0.2Zr_0.2Sn_0.2Pr_0.2O_3-δ (BCFZSP), which shows integrated electronic, protonic and oxygenic conduction in a single perovskite phase and excellent structural stability in concentrated steam. Such triple conduction can spread the electrochemically active sites of the air electrode to the overall electrode surface, thus optimizing the kinetics of the oxygen reduction and evolution reactions (0.448 Ω cm² of polarization resistance at 550 °C). As-prepared RPCCs with a BCFZSP air electrode at 600 °C achieved a peak power density of 0.68 W/cm² in fuel-cell mode and a current density of 0.92 A/cm² under a 1.3 V applied voltage in electrolysis mode. More importantly, the RPCCs demonstrate an encouragingly high stability during 120 h of reversible switching between the fuel-cell and electrolysis modes. Given their excellent performance, high-entropy perovskites can be promising electrode materials for RPCCs.