Improvement in CO sensing characteristics by decorating ZnO nanorod arrays with Pd nanoparticles and the related mechanisms

Pd nanoparticle functionalized ZnO nanorod arrays are produced by the simple and convenient solution routes of aqueous chemical growth and successive photochemical reduction. In this study, we demonstrate the mechanism of the change of surface states and localized electronic properties of Pd/ZnO NRs to account for the enhanced gas sensing performance, as these are often mentioned in association with superior properties, although no firm links have been proved. A significant enhancement in the CO gas sensing properties of ZnO nanorod arrays can be achieved by decorating Pd nanoparticles on the ZnO nanorod surface, and this improvement is ascribed to both the accelerated sensing reaction due to the emergence of a spillover effect, and the amplification of the resistance variation by the enlargement of the Schottky barrier height. These phenomena originate from catalytic Pd acting as a promoter of oxygen adsorption on the ZnO surface, and the transition between metallic Pd and Pd2+/Pd0 redox couple being accompanied by a variation in the work function.