H2 detection mechanism in chemoresistive sensor based on low-cost synthesized WO3 nanorods

Nanostructured WO3 represents a promising material for fast and reliable molecular hydrogen detection through chemo-resistive effect. Here, an extended experimental investigation of WO3-H2 interaction is presented and modeled. A powder of WO3 nanorods (400 nm long, 50 nm large) is produced by hydrothermal technique and drop casted on Pt interdigitated electrode. H2 sensing tests at different concentrations (2000–50,000 ppm) and temperatures (250–400 °C) are reported. Scanning Electron Microscopy (SEM), X-ray Diffraction analysis (XRD), and electrical measurements were performed. The response and recovery kinetics of H2 sensing are carefully described by using a two-isotherms Langmuir model, and kinetics barriers for WO3-H2 interaction are evaluated. Two microscopic processes lead to gas detection. A fast process (shorter than 4 s) is attributed to H2 interaction with adsorbed oxygen at WO3 nanorods surface. A slow process (20–1000 s), with activation energy of 0.46 eV, is attributed to oxygen vacancy generation in WO3. H intercalation in WO3 is ruled out. The recovery of WO3 after H2 exposure is also modeled. The chemo-resistive effect leading to H2 sensing by WO3 is explained through the above processes, whose kinetic barriers have been quantified. These data open the route for the development of fast, sensitive, and low-temperature operating H2 sensors based on WO3.