Diffusion-controlled H2 sensors composed of Pd-coated highly porous WO3 nanocluster films

The resistive H2 sensing properties of palladium-coated highly porous tungsten oxide nanocluster films (Pd/WO3), with the WO3 layers having different thicknesses (11.2–153 nm) and electrodes at different positions, were investigated at 80 °C. The results were interpreted by using a model involving various mechanisms including surface catalytic dissociation of the H2 and O2 molecules, spillover and diffusion of the split species on the surface and inside the WO3 layer respectively, and the interaction between the species. The validity of the model was further examined by investigating the influences of the WO3 thickness and the electrode position on the H2 sensing properties. The results of data analysis confirm the important role of the diffusion of the split species in the WO3 layer. The optimum sensor is characterized by having an ultrathin WO3 nanocluster film with a thickness ≈11 nm, which exhibits a strong sensor response; short response time and recovery time, and stable resistant output during the hydrogenation process.