Co-precipitation synthesis of a CeO₂−SnO₂ heterostructure electrolyte of low temperature solid oxide fuel cells

Cerium dioxide (CeO₂), especially doped cerium, is widely used as an electrolyte, while stannic oxide (SnO₂) is known as a gas sensor material, but it is exceptionally new in solid-state ionics. In this work, a new semiconductor composite that consists of CeO₂ and SnO₂ was synthesized using a co-precipitation method and investigated for applications in solid oxide fuel cells (SOFCs). The as-prepared CeO₂-SnO₂ composite (n-n type) is employed as an electrolyte sandwiched between two Ni_0.8Co_0.15Al_0.05LiO_2-δ (NCAL) electrodes to fabricate fuel cells with a high power density of 1167 mW cm⁻², accompanied by high open-circuit voltage (OCV) of 1.11 V at 550°C XRD, SEM, and HR-TEM analyses are employed to investigate the microstructure of the composites, illustrating that the as-prepared composite has particles of the nanometer size, without any other impurity phases. The electrical properties of the device are studied by EIS measurements. The results indicate that the synthesized CeO₂-SnO₂ composite exhibits higher ionic conductivity than that of the CeO₂-SnO₂ composite prepared by a dry grinding method. Considerable proton conductivity was also found for the CeO₂-SnO₂ composite. Interestingly, although two n-type semiconductor materials are composited for the electrolyte membrane, there is no short-circuit issue. Hence, the n-n heterojunction is proposed to explain the electron blocking mechanism.