Highly enhanced performance of La_0.8Sr_0.2MnO_3-δ cathode by compositing with (Er_0.25Ce_0.05Bi_0.7)₂O_3+δ for low-temperature solid oxide fuel cells

To enhance the redox reaction process of lanthanum manganite (La_0.8Sr_0.2MnO_3−δ, LSM) in intermediate-to low-temperature solid oxide fuel cells (SOFCs) and further reduce polarization resistance, this study develops a high-performance composite cathode material of (Er_0.20Ce_0.05Bi_0.75)₂O_3−δ (ECSB) with LSM. The composite ratios x of ECSB are 40, 50, 60, and 70 wt% (denoted as EL46, EL55, EL64, and EL73), with sintering temperatures of 800, 850, 900, and 950 °C, respectively. The electrolyte matrix consists of Gd_0.1Ce_0.9O_1.95(GDC) doped with 2 mol.% Co as a sintering aid, which allows for dense sintering at 1050 °C. The ECSB-LSM composite cathode can be sintered as low as 800 °C. As the ECSB composite ratio (x) increases from 40 wt% to 70 wt% the polarization resistance of the composite cathode sintered at 850 °C decreases by 56%. EL73 sintered at 800 °C presents the lowest polarization resistance of ∼0.19 Ω cm² at 650 °C. X-ray photoelectron spectroscopy (XPS) analysis indicates that a higher content of ECSB in the composite cathode promotes oxygen ion conduction, thereby accelerating the rate of the redox reaction and reducing polarization resistance. As the sintering temperature increases from 800 °C to 900 °C, the ohmic resistance of the symmetrical cell based on the EL73 cathode decreases by 36%, which is attributed to the diffusion of ECSB along the interface between the cathode and the GDC electrolyte matrix, enhancing the ionic conductivity of the electrolyte. The full cell incorporating the GDC electrolyte matrix and the EL73 cathode achieve an open circuit voltage of 0.943 V at 650 °C, with a maximum power density of 600 mW cm⁻² at 750 °C, representing 1.05- and 2.75-times higher values, respectively, compared to the cell with pure LSM cathodes.