Cation-driven charge modulation and in-situ exsolved nanoparticles enable a self-assembled cathode for proton ceramic solid oxide cells

Abstract Protonic ceramic fuel cells (PCFCs) offer considerable potential for clean and efficient energy conversion at intermediate temperatures. However, their application is constrained by the trade-off between insufficient electrode activity and limited operational durability. Here, we develop a Zn/Yb B-site codoping strategy combined with temperature-induced nanoparticle exsolution to construct a triple-conducting cathode. This approach introduces cation-driven charge modulation that enhances ionic diffusion and electronic conduction, while the exsolved secondary BaCoO3−δ phase plays a pivotal role in increasing the density of active sites, optimizing interfacial charge transfer, and synergistically promoting oxygen reduction reaction (ORR) kinetics. Zn/Yb codoping redistributes the local charge density, weakens metal–oxygen bonds, and reduces the energy required for oxygen vacancy formation, promoting oxygen vacancy generation. The increased oxygen vacancy concentration facilitates surface oxygen activation and lattice hydration, enhancing oxygen–ion and proton transport. Meanwhile, enhanced d–p orbital hybridization improves the electronic conductivity and accelerates charge transfer kinetics. In addition, the optimized alkaline–earth sites suppress carbonate formation, thereby imparting excellent CO2 tolerance. As a result, the optimized cathode delivers a peak power density of 0.99 W·cm−2 at 600 °C and stable operation over 100 h, with a polarization resistance of 0.110 Ω·cm2 under 20% H2O-air. This work provides a novel strategy for the optimization of activity, conductivity, and stability in PCFC cathodes.