Developing an ultrafine Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ cathode for efficient solid oxide fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) is an excellent mixed ion/electron conducting cathode among solid oxide fuel cells; however, its electrochemical activity is limited by the sluggish oxygen surface exchange. The application range of the BSCF cathode can be widened by preparing BSCF in the form of an ultrafine powder; however, retaining the microstructure of the powder in the cathode is challenging owing to the sintering of cathodes at high temperatures. In this study, we report a combined modification and direct assembly approach for the fabrication of an ultrafine, multi-phase BSCF-based cathode. This novel BSCF cathode powder is first modified by immersing the pre-synthesised micron-sized BSCF perovskite powder in a weakly acidic chelating solution. The modification treatment changes the composition of the powder and results in the formation of an ultrafine microstructure. The ultrafine microstructure of the powder is further retained in the cathode by direct assembly without high-temperature sintering. The peak power density of the ultrafine, multi-phase BSCF cell is 1.25 W cm⁻² at 750 °C, much higher than the 0.83 W cm⁻² of the pristine BSCF cell. This study provides insights into the facile fabrication and application of ultrafine cathodes for efficient solid oxide fuel cells.