Novel n-i CeO₂/a-Al₂O₃ Heterostructure Electrolyte Derived from the Insulator a-Al₂O₃ for Fuel Cells

Heterostructure technologies have been regarded as promising methods in the development of electrolytes with high ionic conductivity for low-temperature solid oxide fuel cells (LT-SOFCs). Here, a novel semiconductor/insulator (n-i) heterostructure strategy has been proposed to develop composite electrolytes for LT-SOFCs based on CeO₂ and the insulator amorphous alumina (a-Al₂O₃). The constructed CeO₂/a-Al₂O₃ electrolyte exhibits an ionic conductivity of up to 0.127 S cm^-1, and its fuel cell achieves a maximum power density (MPD) of 1017 mW cm^-2 with an open-circuit voltage (OCV) of 1.14 V at 550 °C without the short-circuiting problem, suggesting that the introduction of a-Al₂O₃ can effectively suppress the electron conduction of CeO₂. It is found that the potential energy barrier at the heterointerfaces caused by the ultrawide band gap of the insulator a-Al₂O₃ plays an important role in restraining electron conduction. Simultaneously, the thermoelectric effect of the insulator induces more oxygen vacancies because of interface charge compensation, which further promotes ionic transport and results in high ionic conductivity and fuel cell performance. This study presents a practical n-i heterostructure electrolyte design, and further research confirmed the advanced functionality of the CeO₂/a-Al₂O₃ electrolyte. Our study may open frontiers in the field of developing high-efficiency electrolytes of LT-SOFCs using insulating materials such as amorphous alumina.