Breaking the limits of Ruddlesden–Popper cathodes to achieve a game-changer for proton-conducting solid oxide fuel cells

Abstract

Ruddlesden–Popper (R–P) structured oxides are promising cathode materials for proton-conducting solid oxide fuel cells (H-SOFCs) due to their excellent thermal compatibility and chemical stability. However, the performance of R–P cathodes has not yet matched that of the widely studied perovskite cathodes, making the enhancement of R–P cathode performance critical for advancing H-SOFC technology. In this study, we introduce a high-entropy R–P oxide, La_0.4Pr_0.4Nd_0.4Ba_0.4Sr_0.4NiO_4+x (LPNBSN), synthesized using an entropy engineering strategy. Compared to conventional R–P oxides, LPNBSN demonstrates significant improvements in oxygen reduction reaction (ORR) activity, interstitial oxygen formation, and proton migration, thereby enhancing its performance as a cathode material for H-SOFCs. The LPNBSN-based fuel cell achieves a record-high peak power density of 2790 mW cm⁻² at 700 °C, surpassing previous R–P oxide cathode performances. Additionally, the high-entropy design induces favorable changes in the coordination environment and electronic state, which suppresses the formation of secondary phases during long-term high-temperature operation—an issue common in conventional R–P oxides—ensuring stable performance under operating conditions. The combination of exceptional power output and long-term stability makes LPNBSN a highly promising cathode material, revitalizing the potential of R–P oxides in H-SOFCs.