Development of a Composite Heterostructure Electrolyte for Low-Temperature Ceramic Fuel Cells: CaSnO3–ZnO Semiconductor Design and Optimization

In recent years, notable interest in developing semiconductor electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs) has been made, and semiconductor heterostructure has shown growing interest due to its fast and high ion-conducting properties. To this end, this study investigates the potential of a semiconductor heterostructure composed of perovskite CaSnO3 and ZnO as an electrolyte for LT-SOFCs. Electrochemical analysis revealed that the synthesized CaSnO3–ZnO heterostructure composite is a mixed ion-electron conductor, exhibiting a high ionic conductivity of 0.16 S cm–1 at 550 °C. Furthermore, a CaSnO3–ZnO fuel cell integrated with this electrolyte displayed a high open-circuit voltage of 1.06 V and achieved an acceptable peak power output of 850 mW cm–2 at 550 °C. We propose a p–n bulk-heterojunction effect at the interface to explain the working principle of the CaSnO3–ZnO for boosting the ionic conduction and blocking the electrical current when using the membrane of a fuel cell. Moreover, the energy band alignment at the interface of CaSnO3 and ZnO could produce the built-in electric field, which further helps promote ionic conduction. Our findings demonstrate the potential of designing highly functional composite electrolytes for LT-SOFCs.