Outstanding H2 Sensing Performance of Pd Nanoparticle-Decorated ZnO Nanorod Arrays and the Temperature-Dependent Sensing Mechanisms

The nearly monodispersed Pd nanoparticles with controllable density on ZnO nanorod arrays were prepared by the unique PVP-mediated photochemical deposition (PCD). The changes in morphology and dispersion of Pd on ZnO surface are ascribed to the stabilizing property and self-assembly characteristic of PVP being exploited during PCD. There are three temperature-dependent H-2 sensing mechanisms in those Pd/ZnO NRs, including general oxygen adsorption/desorption mode within 200-300 degrees C, surface conductivity mode at 60-120 degrees C and palladium hydride (PdHx) formation at room temperature, which causes a significant discrepancy in sensitivity variations as a function of Pd density. It is also verified that the electronic sensitization related to the transition of Pd2+/Pd-0 redox couple predominates the promoting mechanism in Pd/ZnO NRs used for sensing H-2 at 200-300 degrees C. Therefore, the gas sensitivity to 500 ppm H-2 of Pd/ZnO NRs can be significantly improved by around 553 fold (S, R-a/R-g = 1106) at 260 degrees C through decorating an adequate amount of discrete Pd nanoparticles instead of the Pd clusters, moreover, the corresponding sensitivity at room temperature is 16.9 that is superior to some promising devices reported in the literatures.