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

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.