Enabling high ionic conductivity in semiconductor electrolyte membrane by surface engineering and band alignment for LT-CFCs

Wide bandgap semiconductor perovskite SrTiO3 (STO) has attracted extensive attention due to its higher kinetics of electrons (electronic conductivity). However, rare studies have been performed to tune the STO semiconductor towards ionic conduction, which could make it a promising candidate for an electrolyte in ceramic fuel cells (CFCs). Herein, we have designed a semiconductor perovskite Co/Fe–SrTiO3 as an electrolyte membrane to tune its semiconducting property to the ionic conduction via surface-enriched O-vacancies. The surface doping of Co/Fe into SrTiO3 resulted in lowering the Fermi level, leading to the space charge region and local electric field on the surficial region, which can enhance the ionic conduction (proton conduction) at the surface. The designed electrolyte exhibited a high ionic conductivity of 0.19 S/cm and the fuel cell employing it delivered a maximum power density of 1016 mW/cm2 at 520 °C. Moreover, the theoretical calculation was performed to support the experimental results, like disorder in lattice and oxygen vacancy formation energy. The surface doping of Co/Fe facilitated the enriched surface channels for quick ion transportation with lower activation energy. The presented methodology of surface doping has proven to be suitable for designing advanced materials for wide bandgap semiconductors with high ionic conductivity to develop next-generation CFCs.