Multi-heterojunction engineering of simple oxide electrolyte for high-performance low-temperature solid oxide fuel cells

Achieving high performance in solid oxide fuel cells (SOFCs) under low-temperature operation remains hindered by the lack of efficient electrolytes that can simultaneously ensure fast ions transport and negligible electron leakage. Here, we introduce a ternary multi-heterojunction composite electrolyte based on p-type NiO, n-type Li_0.25Sn_0.75O_2-δ (LS), and Sm_0.2Ce_0.8O_2-δ (SDC) to testify its high-performance capability in low-temperature SOFCs. The unique configuration integrates two p–n and one n–n junctions, which can promote the oxygen ion transport while eliminating electronic short-circuiting. The optimized NLS (NiO-LS 8:9)-SDC 6:4 achieves a record of an ionic conductivity around 0.348 S cm^-1 and a peak power density (PPD) of 916 mW cm^-2 at 550 °C, and a long-term stability of over 280 h operation at 150 mA cm^-2. Multi-scale characterizations coupled with the density functional theory analyses confirm that the interfacial band alignment and oxygen vacancy enrichment synergistically drive the exceptional ions transport properties. This study highlights multi‐heterojunction engineering of simple oxides as a versatile and scalable strategy for next-generation SOFC electrolytes, with broad implications for solid oxide electrolysis, solar energy conversion, and selective ion-conducting membranes.