Boosting the catalytic activity of high-order Ruddlesden–Popper perovskite SrEu2Fe2O7-δ air electrode by A-site La doping for CO2 electrolysis in solid oxide electrolysis cells

Abstract

Ruddlesden–Popper (R-P) oxides (An+1BnO3n+1) are potential air electrodes for solid oxide electrolysis cells (SOECs) because of their good electrochemical performance. Among them, SrEu2Fe2O7-δ (SEF) with n = 2 has received extensive attention because of its special structure and promising ionic–electronic conductivity. However, the SEF material is prone to degradation at high temperatures (600 °C–800 °C), and its long-term stability is easily affected. In this study, R-P oxide Sr1-xLaxEu2Fe2O7-δ (SLEFx; x = 0, 0.05, 0.1) was successfully synthesized using the sol–gel method. XRD results showed that La-doped SEF displayed good chemical and thermal compatibility with the gadolinia-doped ceria electrolyte. The SLEF0.05 electrode exhibited a polarization resistance of 0.075 Ω cm2 at 800 °C, which was 88.2 % lower than that of SEF. The half-cell based on the SLEF0.05 air electrode exhibited improved performance under the long-term stability test at a current density of − 0.5 A cm−2 for over 110 h at 800 °C, indicating excellent stability. Moreover, an electrolysis current density as high as 0.712 A cm−2 at 1.5 V was obtained for the full cell with the SLEF0.05 air electrode, which was 45.8 % higher than the SEF electrode when the temperature and feed gas were 800 °C and 50 % CO2–50 % CO, respectively. The XPS and cell testing results confirmed that La with high valance and small radius promoted the formation of oxygen vacancies and effectively enhanced the electrochemical performance and structural stability of the SEF material. Therefore, the R-P oxide SLEF0.05 is a promising air electrode material for SOECs.