Ultra-responsive hydrogen gas sensors based on PdO nanoparticle-decorated WO3 nanorods synthesized by precipitation and impregnation methods

Pd-loaded tungsten oxides are highly promising for hydrogen sensing due to their high response and selectivity derived from widely-accepted spillover mechanisms. Nevertheless, the sensing performances may be further improved by modifying the composite structure with a distinctive preparation process. In this work, high-aspect-ratio WO3 nanorods were produced by a modified precipitation method utilizing ethylene glycol as a dispersing agent and impregnated with Pd nanoparticles to achieve ultra-responsive hydrogen sensors. Characterizations by electron microscopy, X-ray diffraction and X-ray photoemission spectroscopy showed that Pd-loaded WO3 nanostructures comprised 5-20 nm spherical or oval PdO nanoparticles dispersed over the surface of polycrystalline WO3 nanorods. The sensing films were prepared by spin coating of Pd-loaded WO3 nanopowder in an organic paste onto Al2O3 substrates equipped with interdigitated Au electrodes. The hydrogen-sensing performances of Pd-loaded WO3 sensor were systematically investigated at low working temperature ranging from 25 to 350 °C with varying Pd loading levels from 0 to 2 wt%. It was found that 1 wt% Pd loaded WO3 sensing film exhibited the highest response of 3.14 × 106 with a short response time of 1.8 s to 3 vol% H2 at the optimal operating temperature of 150 °C. In addition, it still displayed a good response of 80.4 to 3.0 vol% of H2 at 25 °C. Moreover, the sensor had very high H2 selectivity against C2H5OH, CO, NO2, NH3 and H2S.