Abstract
The effects of addition of TiO2 nanoparticles on the hydrogen sorption properties and reaction mechanism of MgH2–NaAlH4 (mole ratios 1:2, 1:1 and 2:1) composites were investigated. The results indicated that TiO2 nanoparticles were active in improving the dehydriding/rehydriding kinetics and reducing the dehydrogenation temperature of MgH2–NaAlH4 composite. Isothermal volumetric measurements revealed that the kinetics of TiO2 doped samples were 1.5 and 6 times that of undoped binary and MgH2 samples. The doped sample displayed substantially reduced activation energies for NaAlH4, Na3AlH6, MgH2, and NaH relevant decompositions. TiO2 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.
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