Highly Active Interfacial Sites in SFT‐SnO₂ Heterojunction Electrolyte for Enhanced Fuel Cell Performance via Engineered Energy Bands: Envisioned Theoretically and Experimentally

Extending the ionic conductivity is the pre‐requisite of electrolytes in fuel cell technology for high‐electrochemical performance. In this regard, the introduction of semiconductor‐oxide materials and the approach of heterostructure formation by modulating energy bands to enhance ionic conduction acting as an electrolyte in fuel cell‐device. Semiconductor (n‐type; SnO₂) plays a key role by introducing into p‐type SrFe_0.2Ti_0.8O_3‐δ (SFT) semiconductor perovskite materials to construct p‐n heterojunction for high ionic conductivity. Therefore, two different composites of SFT and SnO₂ are constructed by gluing p‐ and n‐type SFT‐SnO₂, where the optimal composition of SFT‐SnO₂ (6:4) heterostructure electrolyte‐based fuel cell achieved excellent ionic conductivity 0.24 S cm⁻¹ with power‐output of 1004 mW cm⁻² and high OCV 1.12 V at a low operational temperature of 500 °C. The high power‐output and significant ionic conductivity with durable operation of 54 h are accredited to SFT‐SnO₂ heterojunction formation including interfacial conduction assisted by a built‐in electric field in fuel cell device. Moreover, the fuel conversion efficiency and considerable Faradaic efficiency reveal the compatibility of SFT‐SnO₂ heterostructure electrolyte and ruled‐out short‐circuiting issue. Further, the first principle calculation provides sufficient information on structure optimization and energy‐band structure modulation of SFT‐SnO₂. This strategy will provide new insight into semiconductor‐based fuel cell technology to design novel electrolytes.