Selective H Gas Sensing Using ZIF-71/In-SnO Bilayer Sensors: A Size-Selective Molecular Sieving Approach.

A universal method for creating selective hydrogen (H) 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-SnO) 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-SnO 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 N physisorption analysis. Gas sensing measurements at 180 °C reveal that a 57-nm-thick ZIF-71 filter layer enhances the sensor response to H while simultaneously suppressing interference from carbon monoxide (CO) through molecular sieving, as the kinetic diameter of H 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 H detection through rational design of microporous filter layers with defined pore apertures.