A high-performance oxygen electrode based on double-perovskite Sr₂Co_0.6Mo_0.4FeO_5+δ for tubular reversible solid oxide cells

Reversible solid oxide cells (RSOCs) are promising for energy conversion and storage, but their application is limited by poor oxygen electrode stability and electrocatalytic activity. Here, we report Mo-doped Sr₂Co_0.6Mo_0.4FeO_5+δ (SCMF) as a robust oxygen electrode for RSOCs. SCMF exhibits a cubic structure with mixed- valence states, enhanced electronic conductivity, and catalytic activity. DFT calculations reveal that Mo not only stabilizes the lattice but also decreases the formation energy of oxygen vacancies and accelerates oxygen reduction and evolution processes. The tubular cell with SCMF-3SDC (in a mass ratio of 7:3) as the oxygen electrode achieves a peak power density of 1.044 W cm⁻² in fuel cell mode under a 3% H₂O wet hydrogen environment at 800 °C. In electrolysis mode, it attains an electrolysis current density of 1.32 A cm⁻² at 1.3 V in a 30% H₂O wet hydrogen atmosphere, and demonstrates excellent stability over 80 h of fuel cell-electrolysis cell (FC-EC) cycle testing. These findings demonstrate SCMF as a high-performance, durable oxygen electrode for RSOCs.