Built-in electric field-assisted heterostructure electrolyte based on K₂NiF₄-type La₂NiO₄ for solid oxide fuel cells

The reduction of the operating temperatures of solid oxide fuel cells (SOFCs) has attracted global research attention and inspired considerable efforts toward the development of new materials for low-temperature (LT) operation, such as K₂NiF₄-type electrode La₂NiO₄ (LNO). In this study, to explore the ion-conducting capability of LNO as an SOFC electrolyte while simultaneously maintaining good catalytic activity, a p–n heterostructure composite was constructed by incorporating p-type LNO with n-type ZnO. The as-prepared LNO–ZnO exhibited a bulk heterostructure with a favorable biphasic distribution and a number of heterointerface contacts. When the as-prepared LNO–ZnO was applied as the electrolyte layer in the SOFC, it exhibited a maximum fuel cell power density of 707 mW cm⁻² with an open-circuit voltage of 1.04 V at 550 °C, as well as considerable stability. According to further measurements, the energy band structures of the two semiconductors and the rectifying characteristics of the LNO–ZnO heterostructure were investigated. The results revealed that the electrolyte functionality of LNO–ZnO is realized predominantly by the built-in electric field of the p–n heterojunction to transport ions while simultaneously blocking electrons. Our results thus demonstrated that K₂NiF₄-type LNO can serve not only as an electrode but also as an electrolyte and suggested that the built-in electric field-assisted heterostructure is a feasible approach for developing LT-SOFC materials.