Improved hydrogen storage performances of MgH2–NaAlH4 system catalyzed by TiO2 nanoparticles

Abstract The effects of addition of TiO 2 nanoparticles on the hydrogen sorption properties and reaction mechanism of MgH 2 –NaAlH 4 (mole ratios 1:2, 1:1 and 2:1) composites were investigated. The results indicated that TiO 2 nanoparticles were active in improving the dehydriding/rehydriding kinetics and reducing the dehydrogenation temperature of MgH 2 –NaAlH 4 composite. Isothermal volumetric measurements revealed that the kinetics of TiO 2 doped samples were 1.5 and 6 times that of undoped binary and MgH 2 samples. The doped sample displayed substantially reduced activation energies for NaAlH 4 , Na 3 AlH 6 , MgH 2 , and NaH relevant decompositions. TiO 2 doping had also markedly enhanced the reversible capacity of binary composites, persisting well during three dehydrogenation/rehydrogenation cycles. XRD, XPS, and FESEM–EDS analyses had demonstrated that finely dispersed oxygen-deficient titanium species, formed during the first desorption, were migrated to the bulk of composite during cycling. It was suggested that these finely dispersed oxygen-deficient titanium species might contribute to kinetic improvement by serving as active sites to facilitate the hydrogen diffusion during dehydrogenation/rehydrogenation processes.