Tailoring p–n heterojunction via high entropy cation integration to improve fuel cell performance

Solid oxide fuel cells face significant challenges in achieving high ionic conductivity and operational stability at low temperatures. Here, we present a high entropy cation integration strategy to engineer next generation semiconductor ionic fuel cells. We synthesized a p-type high entropy Ruddlesden–Popper perovskite oxide, (La_0.2Ca_0.2Sr_0.2Sm_0.2Pr_0.2)₂NiO_4+δ (HEO), and combined it with a conventional n-type ionic conductor, Sm_0.2Ce_0.8O_2–δ (SDC), forming HEO–SDC heterostructure membranes with varying mass ratios. The coherent, diffused interfaces (~2 nm domain boundaries), percolated cation networks, significant lattice strain, and abundant surface-active oxygen species, enhance electronic and ionic conductivity via Ni²⁺/Ni³⁺ hole hopping. Interfacial heterojunctions establish a built-in electric field that suppresses electronic short circuiting while promoting ionic transport. The 5HEO–5SDC achieves a polarization resistance of 0.096 Ω cm² and a peak power density of 1034 mW·cm⁻² at 550 °C, with stable operation over 90 hours. These findings establish high entropy interface engineering as a transformative paradigm for energy conversion devices.