Preparation and structure dependence of H2 sensing properties of palladium-coated tungsten oxide films

This study aims at revealing and explaining the influences of preparation condition on the structure and subsequent hydrogen (H-2) sensing properties of palladium-(Pd-) coated tungsten oxide (WO3) films. The material structure was specified by grain size; porosity, surface roughness and thickness of the WO3 layer; and thicknesses of the Pd coating. The structural parameters are found to be tailorable in broad ranges by applying supersonic cluster beam deposition or magnetron sputtering technique operating at various substrate temperatures (50-550 degrees C) and 20% Ar-80% O-2 pressures (3-60 mTorr). The H-2 sensing response of the sensors, and their response time (t(respond)) for hydrogenation and recovery time (t(recover)) for dehydrogenation are detected and found to be adjustable in a comprehensive manner. Results indicate that Pd/WO3 hydrogen sensors of high sensor response and short t(respond) and t(recover) are achievable if the WO3-based sensor is made to be highly disordered or contain non-crystalline clusters of size <= 5 nm, and have a porosity >= 14%. More details on possible mechanisms responsible for the findings are discussed. (c) 2012 Elsevier B.V. All rights reserved.