Improved Performance of Reversible Solid Oxide Cells with Ba0.9Co0.2Fe0.7Nb0.1F0.1O2.9−δ Semiconductor: Synthesis, Characterization, and Performance Evaluation

Promising energy conversion devices, reversible solid oxide cells (R-SOCs) offer the potential for the efficient conversion of fuel into electrical energy. Nonetheless, the development of a reliable bifunctional electrocatalyst as an electrode material for R-SOC devices presents considerable challenges. Hence, two semiconductors, Ba0.9Co0.2Fe0.7Nb0.1O3−δ (BCFeN) and Ba0.9Co0.2Fe0.7Nb0.1F0.1O2.9−δ (BCFeNF) are synthesized. F doping causes a significant reduction in the average valence states of Co, Fe, and Nb elements, ultimately leading to a rise in the concentration of oxygen vacancies, further enhancing the oxygen migration capability of BCFeN. Furthermore, F doping enhances the catalytic performance for the oxidation of hydrogen and the reduction of oxygen. The rate-determining step (RDS) in hydrogen oxidation reaction on BCFeN and BCFeNF surfaces is the H2 adsorption and dissociation process, while the RDS in oxygen reduction reaction is the reduction of adsorbed oxygen atoms to O– species. Remarkably, the outstanding reversible performance is exhibited by the single cell employing BCFeNF with O2 as the oxidant and humidified H2 (30% H2O) as the fuel. At 700 °C, when operating in solid oxide fuel cell mode, the maximum power density reaches 288.9 mW cm–2, and the R-SOC maintains a current density of −301.6 mA cm–2 at 1.3 V in solid oxide electrolysis cell mode.