Hydrogen Sorption of Porous Tungsten Oxide Nanomaterial and Effect of a Pd Coating on its Storage Capacity Under Hydrogenation Cycles

The H-2 uptake performance at room temperature of porous tungsten oxide nanomaterials with and without a catalytic Pd coating was studied by the quartz crystal microbalance technique. Tungsten oxide composed mainly of WO3 was synthesized by inert gas condensation method using He. The samples consisted of semi-amorphous nanomaterials of low crystallinity and high porosity, as revealed by SAED, TEM, XRD, Raman spectroscopy and N-2 adsorption desorption isotherms. The H-2 uptake capacity of the porous oxide was studied under increasing H-2 exposure pressures (1000-7000 Pa), with and without Pd coating. After reaching a maximum value of 1.2 H-2 wt.%, at 1160 Pa, the H-2 uptake capacity of the Pd-coated oxide consistently decreased. Successive hydrogenation cycles were carried out on the Pd-coated oxide at 3300 Pa and 6000 Pa to evaluate the H-2 uptake performance of the sample under this H-2 loading and unloading process. It was found that the H-2 uptake capacity decreased from around 1 to values below 0.53 H-2 wt.%, which is the reference H-2 storage capacity achieved by a 15 nm-thick Pd film. We argued that water molecule formation in the Pd/oxide interface and sublayers negatively affects the H-2 uptake capacity of the oxide under successive hydrogenation cycles at room temperature.