Selective H₂ Gas Sensing Using ZIF-71/In-SnO₂ Bilayer Sensors: A Size-Selective Molecular Sieving Approach

A universal method for creating selective hydrogen (H₂) gas sensors through the integration of microporous zeolitic imidazolate framework (ZIF) filter layers on metal oxide sensing layers is presented. The sensor design consists of an indium-modified tin oxide (In-SnO₂) layer as the gas-sensitive component, topped by a size-selective ZIF filter layer. The ZIF layer is generated by first depositing zinc oxide (ZnO) of variable thickness (20-48 nm) onto the In-SnO₂ layer, followed by in situ conversion to either ZIF-8 or ZIF-71 through solvothermal methods. The resulting bilayer structures are characterized using scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), and N₂ physisorption analysis. Gas sensing measurements at 180 °C reveal that a 57-nm-thick ZIF-71 filter layer enhances the sensor response to H₂ while simultaneously suppressing interference from carbon monoxide (CO) through molecular sieving, as the kinetic diameter of H₂ is significantly smaller than that of CO. The sensor maintains stable performance under varying humidity conditions (25-75% relative humidity). This work demonstrates a promising approach for achieving selective H₂ detection through rational design of microporous filter layers with defined pore apertures.