Hydrogen Sorption of Porous Tungsten Oxide Nanomaterial and Effect of a Pd Coating on its Storage Capacity Under Hydrogenation Cycles
Abstract
The H2 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 N2 adsorption–desorption isotherms. The H2 uptake capacity of the porous oxide was studied under increasing H2 exposure pressures (1000–7000Pa), with and without Pd coating. After reaching a maximum value of 1.2 H2wt.%, at 1160Pa, the H2 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 H2 uptake performance of the sample under this H2 loading and unloading process. It was found that the H2 uptake capacity decreased from around 1 to values below 0.53H2wt.%, which is the reference H2 storage capacity achieved by a 15nm-thick Pd film. We argued that water molecule formation in the Pd/oxide interface and sublayers negatively affects the H2 uptake capacity of the oxide under successive hydrogenation cycles at room temperature.
