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.