Significantly enhanced stability and activity of a perovskite oxygen electrode for reversible protonic ceramic electrochemical cells by heterointerface engineering

Reversible protonic ceramic electrochemical cells (R-PCECs) are considered as the highly promising contraptions for bidirectional electric energy generation or storage, capable of efficiently converting electrical and chemical energy in mutual directions. However, the sluggish electrocatalytic activity at low temperature and unsatisfactory operational durability of oxygen electrodes remains the primary challenges to the commercial application of R-PCECs. Here, the degradation mechanism of the BaFe_0.4Co_0.4Zr_0.1Y_0.1O_3-δ (BFCZY) oxygen electrode under humid conditions is systematically investigated. The degradation can be ascribed to the formation of BaCO₃ caused by the water-facilitated Ba segregation. The activity and stability of the BFCZY oxygen electrode are significantly improved through heterointerface engineering by infiltrating the BaCoO₃ (BCO) catalyst. At 600 °C in 30 vol% H₂O-air, the heterointerface engineering decreases the polarization resistance of the BFCZY electrode by half (from 0.42 to 0.21 Ω cm²) and the decay rate by more than one order of magnitude (from 0.384 to 0.026 Ω cm²/100 h). Meanwhile, a R-PCEC with the BCO-BFCZY oxygen electrode exhibits high activity and stability in both the fuel cell and water electrolysis modes. The substantially increased electrocatalytic activity and stability of the oxygen electrode is primarily ascribed to the improved surface oxygen exchange process and inhibited Ba segregation.