An universal oxygen electrode for reversible solid oxide electrochemical cells at reduced temperatures

Solid oxide electrochemical cells (SOCs) are promising energy storage and conversion devices that represent a facile and sustainable route for converting chemical fuels into electricity and vice versa on demand. In particular, the discovery of oxygen-electrode materials that exhibit excellent reactivity and durability is the key to related device technology. Here, we present Ta-doped BaCoO_3−δ catalysts that exhibit record-breaking electrode performance in both fuel cell and electrolysis operations, which were demonstrated with two types of SOCs using oxygen ion- and proton-conducting electrolytes. The introduction of pentavalent Ta ions allows the parent oxide to maintain a cubic perovskite structure with high symmetry, which substantially improves its phase stability and electronic and ionic conductivity, and even catalytic activity for oxygen reduction and evolution. Hence an assortment of best-performing fuel cell and electrolysis cell results are recorded; for example, a proton-conducting SOC conveying a peak power density of 2.26 W cm⁻² at 650 °C. The design principle of the versatile electrode presented in this study not only allows for the realization of high-performance SOCs but also contributes to a broader-real world impact: a multipurpose, standardized electrode of high demand will result in significant cost reductions for related electrochemical devices.