Significantly Enhanced Electrocatalytic Activity of Air Electrodes in Protonic Ceramic Cells by A-Site Deficiency...

Hydrogen utilization and production through reversible protonic ceramic cells (PCCs) exhibit significant promise as long-term energy storage and conversion systems for renewable sources. However, inadequate intrinsic electrocatalytic activities of the air electrodes for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remain a fundamental bottleneck, severely limiting the enhancement of PCC electrochemical performance. Oxygen vacancies ( $V_O^{··}$ ) in perovskite-based air electrodes play a crucial role because they can simultaneously facilitate faster reaction kinetics for both ORR and OER. Herein, a simple A-site deficiency engineering is applied to effectively regulate the $V_O^{··}$ concentration of perovskite oxides. The designed La_0.85Ba_0.1Co_0.7Ni_0.3O_{3- δ} (L85BCN) demonstrated a high $V_O^{··}$ concentration and significantly boosted the air electrode reaction by accelerating charge transfer kinetics, which is confirmed by integrated experimental characterizations, $V_O^{··}$ formation energy, and Gibbs free energy variation for ORR and OER processes. Consequently, PCC with L85BCN air electrode yields a remarkable peak power density of 0.76 W cm^-2 and current density of 2.12 A cm^-2 at 1.3 V under 600°C, representing the highest performance among PCCs. This effective A-site deficiency engineering strategy not only discovered a novel, promising air electrode but also advanced PCC development for practical applications.