Built-in Electric Field for Efficient Charge Separation and Ionic Transport in LiCoO₂/SnO₂ Semiconductor Junction Fuel Cells

Built-in electric field (BIEF)-induced charge transfer in planar and bulk junctions has significantly improved electrochemical performance in current and advanced energy storage devices such as lithium, sodium, and aluminum batteries. In this study, fuel cells with different junctions based on semiconductor membranes were designed in thin-film planar, bulk planar, and bulk heterojunction (BHJ) configurations to investigate the BIEF effects on their electrochemical performance. These semiconductor membrane fuel cells were constructed with p-type LiCoO₂ and n-type SnO₂ sandwiched between Ni_0.8Co_0.15Al_0.05LiO₂ (NCAL) electrode semiconductors. At 600 °C, the fuel cells with bulk heterojunction (BHJ), bulk planar p–n junction, and thin-film planar p–n junction deliver remarkable peak power densities of 0.82, 0.61, and 0.28 W/cm² in H₂/air operation, respectively. The band structures were determined and the charge transport properties and device operation were investigated. Our results show that the semiconductor membrane-based devices are a good alternative to replace the conventional electrolyte membrane fuel cells for the next generation of fuel-to-electricity conversion technology.