Pd-doped WO3 hydrogen sensors with high performances (selectivity, sensitivity and stability) were successfully
prepared. The gas sensing properties towards reducing gases (H2, CO, NH3) were studied and discussed in function
of the morphology and the operating conditions. The sensor with WO3 nanoparticles had shown the best response to
hydrogen in the ppm range, it was also demonstrated that the sensors with low Pd loading had the best stability and
reproducibility. We believe that the catalyst is better dispersed at the WO3 grain surface for low Pd loading ( 0.4 wt%). For the sensors with high Pd loading (3.5 wt%) at working temperature of 200°C (the optimum working
temperature of the sensor with high sensitivity and selectivity to H2), the results suggest that the variation in the
sensor resistance can be associated with Pd catalyst diffusion followed by agglomeration during the sensing tests,
which probably causes an evolution of the sensor resistance. To understand the phenomena, more investigations are
now in progress