Distortions induced by Cu-doping enable accelerated oxygen reduction kinetics in Co-free SrFe_0.9Nb_0.1O_3−δ for metal-supported SOFCs

Metal-supported solid oxide fuel cells (MS-SOFCs) offer superior mechanical strength and fast start-up, but the mismatch between metal and cathode (oxygen electrode) components poses challenges for developing compatible, high-activity cathodes at intermediate-to-low temperatures (IL-T). Recently, cobalt-free cathode materials have attracted significant attention, especially donor-doped SrFeO_3−δ. To further improve their redox performance at IL-T, density functional theory (DFT) calculations were employed in this study to design Cu-doped SrFe_0.9Nb_0.1O_3−δ cathodes, revealing the correlation between Cu-doping and lattice distortion. DFT results indicate that moderate Cu-doping at the B site promotes defect formation and effectively reduces the oxygen vacancy formation energy of the parent SrFe_0.9Nb_0.1O_3−δ, while excessive Cu-doping limits the oxygen vacancy formation. Guided by theoretical insights, SrFe_0.9−xNb_0.1Cu_xO_3−δ (SFNCx, x = 0, 0.05, 0.10, 0.15, and 0.20) materials were synthesized, and experimental results further support the DFT conclusions. The optimized SFNC10 composition exhibited the highest oxygen vacancy concentration and achieved a polarization resistance of 0.15 Ω cm² at 650 °C. Moreover, this work provides the first demonstration of the SFNC10 cathode applied in an MS-SOFC, with the configuration of FeCr||NiO-GDC||CoGDC||SFNC10, operating stably at 200 mA cm⁻² for over 60 h and delivering a peak power density of 728.9 mW cm⁻² at 700 °C.