Novel n-i CeO 2 /a-Al 2 O 3 Heterostructure Electrolyte Derived from the Insulator a-Al 2 O 3 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 CeO 2 and the insulator amorphous alumina (a-Al 2 O 3 ). The constructed CeO 2 /a-Al 2 O 3 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-Al 2 O 3 can effectively suppress the electron conduction of CeO 2 . It is found that the potential energy barrier at the heterointerfaces caused by the ultrawide band gap of the insulator a-Al 2 O 3 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 CeO 2 /a-Al 2 O 3 electrolyte. Our study may open frontiers in the field of developing high-efficiency electrolytes of LT-SOFCs using insulating materials such as amorphous alumina.