Hydrogen storage in CeNiXOY and CeM0.5NiXOY (M = Zr or Al) mixed oxides

CeMZNiXOY mixed oxides (M = Zr or Al, Z = 0 or 0.5, 0 ≤ X ≤ 3) are large catalytic hydrogen reservoirs, called oxyhydrides, once treated in H2. A catalytic chemical reaction is used to reveal and titrate reactive hydrogen species present in the solid. Different physicochemical techniques including XPS, ion sputtering, XRD, TPR, TGA, and inelastic neutron scattering (INS) have been used to characterize the solids. Depending on the composition and metal loading, a solid solution and/or a highly dispersed nickel oxide in ceria (or ceria–zirconia) can be obtained. Ion sputtering followed by XPS analysis has been very useful for estimating the size of NiO clusters (≈10 Å) present in the compounds. INS shows the coexistence of different hydrogen species that can be related to hydride species, hydrogen species in interaction with metallic nickel, as well as hydrogen species from hydroxyl groups.