Enhancing the Performance of the p‑n Heterostructure Electrolyte for Solid Oxide Fuel Cells via A‑Site-Deficiency Engineering

Semiconductor ionic electrolytes are attracting growing interest for developing low-temperature solid oxide fuel cells (LT-SOFCs). Our recent study has proposed a p-n heterostructure electrolyte based on perovskite oxide BaCo0.4Fe0.4Zr0.1Y0.1O3‑δ (BCFZY) and ZnO, achieving promising fuel cell performance. Herein, to further improve the performance of the heterostructure electrolyte, an A-site-deficiency strategy is used to solely modify BCFZY for regulating the ionic conduction and catalytic activity of the heterostructure. Two new electrolytes, B0.9CFZY-ZnO and B0.8CFZY-ZnO, were developed and systematically studied. The results show that the two samples gain improved ionic conductivity and auxiliary catalytic activity after A-site deficiency as a result of the increment of the surface and interface oxygen vacancies. The single cells with B0.9CFZY-ZnO and B0.8CFZY-ZnO exhibit enhanced peak power outputs at 450–550 °C compared to the cell based on B1.0CFZY-ZnO (typically, 745 and 795 vs 542 mW cm–2 at 550 °C). Particular attention is paid to the impact of A-site deficiency on the interface energy band alignment between B x CFZY and ZnO, which suggests that the p-n heterojunction effect of B x CFZY-ZnO for charge carrier regulation can be tuned by A-site deficiency to enable high proton transport while avoiding fuel cell current leakage. This study thus confirms the feasibility of A-site-deficiency engineering to optimize the performance of the heterostructure electrolyte for developing LT-SOFCs.