La-doped Sr4Fe4Co2O13-δ as a promising in-situ self-assembled composite cathode for protonic ceramic fuel cells

Protonic ceramic fuel cells (PCFCs) exhibit a lower activation energy compared to conventional oxygen-ion conducting solid oxide fuel cells, which makes them better suited for operating at low temperatures. Regrettably, the use of PCFCs at lower temperatures is restricted due to the absence of durable and highly active cathode materials. Herein, we rationally design in-situ self-assembled composite cathodes with the nominal compositions of Sr4-xLaxFe4Co2O13-δ (SLxFC, x = 0.4, 0.8, 1, and 2) for PCFCs. The SL0.4FC, displays a composite of cubic perovskite phase and spinel phase, the other compositions yield a mixture of both orthorhombic perovskite and spinel phases. The self-assembled SL1FC composite cathode has the highest electrocatalytic activity among all samples, particularly at temperatures (<650 °C). For instance, it demonstrates a very low area-specific resistance (ASR) of 0.465 Ω cm2 at 550 °C. The PCFC with the SL1FC composite cathode provides a high peak power density (PPD) of 518 mW cm−2 at the same temperature. More importantly, the SL1FC electrode demonstrates robust long-term stability (400 h for the symmetrical cell mode and 200 h for the single cell mode). This study shows how La doping enhances the electrochemical activity of Sr4Fe4Co2O13-δ and how the synergistic effect of the two phases boosts the electrochemical performance of the composite cathode.