Effect of low concentration of impurity gases on the hydrogen absorption performance of uranium

The performance of uranium as a hydrogen storage material has attracted much attention. Herein, the hydrogen absorption properties of depleted uranium in impure hydrogen containing He, Ar, CH4, N2, CO, CO2 and O2 were studied by PVT method and XPS analysis. When these impurity gases were mixed in H2 at low concentrations (0.1%∼1.5%), their behavior can be classified into three categories. The He, CH4 and Ar were chemically inert to the activated uranium powder under room condition. These three gases inhibited the absorption kinetics during the whole stage by hindering the diffusion of H2 molecules, showing a blanketing effect. The N2 and O2 did not affect the absorption kinetics but reduced the capacity by forming nitrides and oxides. The poisoning effect of N2 was weaker than that of O2. The CO and CO2 not only affected the hydrogen absorption capacity, but also strongly inhibited the absorption kinetics. These two gases are chemically adsorbed on the uranium surface to form passivation layers, thus inhibiting the adsorption and dissociation of H2 molecules and the diffusion of H atoms. The poisoning and retardation effect of CO2 were much stronger than that of CO. The above conclusions are important to further study the reactivity of mixed gas with uranium, and can also be used as a reference for other hydrogen storage systems.