Thermodynamic NiO exsolution for durable and efficient cobalt-free cathodes in proton-conducting solid oxide fuel cells

Developing high-performance cathodes is critical to advancing proton-conducting solid oxide fuel cells (PCFCs). However, their practical application remains constrained by sluggish oxygen reduction reaction (ORR) kinetics and the instability of nanoscale catalytic features in oxidizing environments. Here, a cobalt-free nanocomposite cathode is rationally engineered via a Mo-induced ion-topological strategy based on the perovskite oxide BaCe_0.26Ni_0.1Fe_0.64O_3−δ (BCNF10). Through the introduction of B-site Mo, the spontaneous exsolution of highly dispersed NiO nanoparticles significantly enhances surface oxygen exchange kinetics and leads to the formation of stable and well-defined heterointerfaces. The single cell with the optimized composite cathode Ba_0.95Ce_0.25Ni_0.1Mo_0.05Fe_0.6O_3−δ (BCNMF10) achieves an outstanding maximum power density (MPD) of 2002 mW·cm⁻² at 700 °C, accompanied by excellent long-term operational durability and humidity tolerance. First-principles calculations further elucidate the underlying mechanism, revealing a thermodynamically favorable, defect-mediated pathway for NiO formation and underscore the crucial role of dopant‒defect interactions in tailoring surface reactivity. This work provides a robust and scalable framework for the development of durable, high-efficiency cathodes for next-generation PCFCs.