p-Type PdO nanoparticles supported on n-type WO3 nanoneedles for hydrogen sensing

We report the synthesis of palladium nanoparticle (NP) decorated WO3 nanoneedles (NNs) employing a single-step, aerosol assisted chemical vapor deposition approach. Two different Pd precursors were investigated in view of optimizing the morphology and the gas sensing performance of the resulting nanostructured films. In particular, palladium acetylacetonate was found to be more suitable than ammonium hexachloropalladate for obtaining n-type WO3 NNs uniformly decorated with well dispersed p-type PdO NPs. The active films could be directly deposited on the electrode area of microelectromechanical system-based resistive transducers. The morphology and chemical composition of the films was investigated by scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy analysis. PdO-decorated WO3 NNs show a response toward hydrogen that is about 680 times higher than that of bare WO3 NNs. Finally, PdO-loaded sensors display extremely low-cross sensitivity to water vapor, which makes them remarkably immune to changes in the background humidity.