(Bi₂O₃)_0.705(Er₂O₃)_0.245(WO₃)_0.05–Co₃O₄: A new oxygen electrode material with high oxygen reduction and evolution reaction catalytic activity for low-temperature solid oxide electrochemical cells

The rapid increase in oxygen electrode polarization at reduced operating temperatures is a critical factor limiting the performance of low-temperature solid oxide electrochemical cells (LT-SOCs). To address this issue, a novel composite oxygen electrode material composed of (Bi₂O₃)_0.705(Er₂O₃)_0.245(WO₃)_0.05 (EWSB) and Co₃O₄ is developed. This composite utilizes the high oxygen ion conductivity of EWSB and the robust catalytic activity of Co₃O₄. Compared to conventional composite or mixed ionic–electronic conducting electrodes, this EWSB–Co₃O₄ electrode enhances the density of active sites by increasing the electrode thickness, significantly improving the catalytic activities for both oxygen evolution and reduction reactions. Results indicate that electrode polarization decreases markedly with an increase in electrode thickness. At a thickness of 60 μm, the electrode exhibits the lowest polarization, reaching as low as 0.08 Ω cm² at 600 °C. Furthermore, the EWSB–Co₃O₄ electrode maintains stable performance in both fuel cell and electrolysis modes. It also demonstrates excellent CO₂ tolerance; even at 20 % CO₂ concentration, the electrode polarization impedance does not increase significantly and fully recovers to its initial value once the CO₂ is removed.