Experimental and theoretical investigation of hydrogen sorption by SnO2 nanostructures in a metal-organic framework scaffold

SnO2 nanostructures decorated with Pd clusters were installed in the porous metal-organic framework (MOF) material NU-1000 and investigated as hydrogen storage materials. The proposed concept was to store atomic hydrogen – dissociated by the Pd clusters – within the nanostructured metal oxide to achieve reversible storage of hydrogen at near-ambient temperature and modest pressure using the MOF as a template for the nanostructures. Temperature programmed reduction and X-ray absorption spectroscopy (XANES) provided evidence for the reduction of SnO2 upon exposure to hydrogen. Hydrogen sorption in or on several idealized SnO2 nanostructures was studied using density functional theory (DFT), including the (110) surface of crystalline SnO2 surface and bulk SnO2 to assess the thermodynamic feasibility of hydrogen sorption under the conditions of the experiments, i.e., 1 bar and ambient temperature. Also evaluated computationally was the thermodynamic feasibility of reducing tin by extracting an oxygen atom with H2 and creating a lattice oxygen vacancy with generation of water in the vapor phase. The combined computational and experimental results point to the benefits of metal oxide nanostructuring in enabling reversible dissociative uptake of molecular hydrogen at ambient temperature and moderate pressures.