Improving Electrocatalytic Activity of Cobalt-Free Barium Ferrite-Based Perovskite Oxygen Electrodes for Proton-Conducting Solid Oxide Cells via Introducing A-Site Deficiency

Proton-conducting solid oxide cells are regarded as promising solid-state energy conversion devices to realize the high-efficiency conversion between electrical energy and chemical energy. However, the high cost, easily reducible ion characteristics, and large thermal expansion coefficient related to the valence state of the traditional high-catalytic cobalt-based oxygen electrode are unavoidable problems. Cobalt-free barium ferrite-based oxides with triple-conducting properties are considered the most promising prospective candidates for highly active oxygen electrode materials because of the increased electrochemical reaction active sites, excellent thermal stability, and low thermal expansion coefficient. In this work, by introducing 5% A-site deficiency at the atomic scale, the oxygen vacancy concentration is increased so that the catalytic reaction kinetics and proton-conduction ability of ABO 3 -type perovskite oxygen electrode material BaFe 0.5 Sn 0.2 Bi 0.3 O 3−δ are improved. The effects of non-stoichiometry on the phase composition, microstructure, hydration capacity, thermal expansion characteristics, conductivity, and chemical stability are investigated. In both fuel cell and electrolysis cell operation modes, the proton-conducting solid oxide cells with the A-site-deficient Ba 0.95 Fe 0.5 Sn 0.2 Bi 0.3 O 3−δ oxygen electrode demonstrate excellent electrochemical performance, giving a peak power density of 0.69 W cm –2 (increased by 19.0%) and an electrolysis current density of 1.64 A cm –2 (increased by 30.2%) at 700 °C. Moreover, even at 600 °C with 50% high steam partial pressure, electrolysis for hydrogen production is maintained for about 100 h without significant attenuation, confirming the vital role of A-site defect engineering in the design of advanced oxygen electrode materials.