Hydrogen sensors based on Pd-doped WO3 nanostructures and the morphology investigation for their sensing performances optimization

This paper presents the study of the morphological effects on the performances (sensitivity, response and recovery time) of highly sensitive hydrogen semiconductor sensors based on Pd-doped WO3 nanostructures and the optimization of the parameters influencing their sensing performances. WO3 nanowires, nanospheres and nanolamellae were obtained by hydrothermal, direct precipitation and ionic-exchange methods respectively starting from the same precursor (tungstic acid–gel obtained from sodium tungstate). After annealing in air at 400 °C for 1 hour, the morphologies were observed by SEM and TEM microscopy and the crystal structures were defined by XRD analysis. The prepared WO3 nanopowders were dispersed using sonication in PdCl2 solution and then thick films (∼ 10 μm) were screenprinted on alumina substrates fitted with gold electrodes and annealed at 400 °C for 12 hours. The obtained sensors were exposed to hydrogen (50-200 ppm) at different working temperatures (RH = 50%). The sensors showed high sensitivity and short response time at working temperatures ranging from 200 to 240 °C. The sensors with WO3 nanolamellae showed the highest sensitivity and the shortest response time.