An Interface Heterostructure of NiO and CeO₂ for Using Electrolytes of Low-Temperature Solid Oxide Fuel Cells

Interface engineering can be used to tune the properties of heterostructure materials at an atomic level, yielding exceptional final physical properties. In this work, we synthesized a heterostructure of a p-type semiconductor (NiO) and an n-type semiconductor (CeO₂) for solid oxide fuel cell electrolytes. The CeO₂-NiO heterostructure exhibited high ionic conductivity of 0.2 S cm^-1 at 530 °C, which was further improved to 0.29 S cm^-1 by the introduction of Na⁺ ions. When it was applied in the fuel cell, an excellent power density of 571 mW cm^-1 was obtained, indicating that the CeO₂-NiO heterostructure can provide favorable electrolyte functionality. The prepared CeO₂-NiO heterostructures possessed both proton and oxygen ionic conductivities, with oxygen ionic conductivity dominating the fuel cell reaction. Further investigations in terms of electrical conductivity and electrode polarization, a proton and oxygen ionic co-conducting mechanism, and a mechanism for blocking electron transport showed that the reconstruction of the energy band at the interfaces was responsible for the enhanced ionic conductivity and cell power output. This work presents a new methodology and scientific understanding of semiconductor-based heterostructures for advanced ceramic fuel cells.