B-site high-entropy tailoring K2NiF4 oxide as an effective cathode for proton-conducting solid oxide fuel cells

Proton-conducting solid oxide fuel cells (H-SOFCs) are expected to be an ideal energy conversion device operating below 600°C. However, the lack of robust electrodes with high catalytic activity remains a major obstacle to commercialization. Herein, B-site high-entropy modification is first performed on K2NiF4-type oxide to obtain a novel cathode material, La1.2Sr0.8Mn0.2Fe0.2Co0.2Ni0.2Cu0.2O4 + δ (LSMFCNC). By harnessing the unique properties of multiple elements, the B-site transition metals in LSMFCNC evolve into various compound states, resulting in crystal structure expansion and a decrease in the bond strength between cations and oxygen ions, thereby promoting the formation of oxygen vacancies and achieving high proton/oxygen diffusion rates with excellent oxygen reduction reaction (ORR) activity. Ultimately, H-SOFCs using the high-entropy LSMFCNC cathode demonstrate an excellent cell performance with power outputs of 1759 mW/cm2 at 700°C and 1126 mW/cm2 at 600°C. This performance is superior to La1.2Sr0.8NiO4 (LSNO) and other K2NiF4-type cathodes reported in the literature. The outstanding electrochemical performance and fine operational stability suggest that LSMFCNC could be a potential cathode alternative for low-temperature H-SOFC operation. This study provides a new approach to developing highly active and durable cathodes for H-SOFCs.