Humidity-tolerant selective sensing of hydrogen and n-butanol using ZIF-8 coated CuO:Al film

Abstract

Hydrogen and n-butanol are emerging as clean energy carriers, necessitating reliable sensors for their low concentration detection. This study investigates an aluminium-doped CuO (CuO:Al) sensor coated with a zeolitic imidazolate framework-8 (ZIF-8) layer for hydrogen and n-butanol detection. Comprehensive characterization was performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), N₂-adsorption isotherms, and Raman spectroscopy, collectively confirming a crystalline structure, intact chemical composition, beneficial surface morphology, uniform metal–organic framework (MOF) particle distribution, hierarchical porosity, and a high thermal stability of the synthesized materials. CuO promotes interaction with hydrogen and n-butanol, while the ZIF-8 coating enhances selectivity by mitigating the sensitivity to other gases and confers high immunity to elevated relative humidity (RH 81%) for hydrogen gas sensing. The hybrid MOF-ZIF-8/CuO:Al (ZIF-8 coated CuO:Al) sensor demonstrates remarkable thermal and temporal stability and maintains consistent performance even in humid conditions. Electrical activation energy (∼0.2 eV), corresponding to hole trap state (V_Cu), was calculated, confirming the p-type conduction mechanism. A gas sensing response of 400% was observed for 1000 ppm hydrogen gas under low relative humidity (RH 11%), remaining stable over four weeks. The gas sensing response remained at 300% even at a higher relative humidity (RH 50%) and sustained a response of 200% even after four weeks under the same RH. This shows its potential for hydrogen detection in industrial safety, environment monitoring, clinical medical diagnosis, and its reliable deployment in hydrogen generated energy applications.