Study On The Hydrogen Storage Properties Of NaAlH₄by Nano-confinement And Catalysis

As a kind of novel hydrogen storage materials, lightweight complex hydrides have attracted intensive attentions because of their high gravimetric hydrogen densities, suitable thermodynamic properties and low materials cost. However, most of them have high dehydrogenation temperature, sluggish kinetics and poor reversibility for application. In this paper, the combination of nano-confinement and catalysis on the hydrogen storage properties of NaAlH4was investigated.Firstly NaAlH4co-doped by microporous CuBTC and Tm2O3was prepared through mechanical ball-milling method plus thermal melting impregnation to solve the sluggish kinetic. And the catalytic and synergistic effects of the co-dopants on the microstructure and reversible dehydrogenation properties of NaAlH4were systematically investigated. It was found that doping with microporous CuBTC obviously facilitated the dehydrogenation kinetics and improved the dehydrogenation capacity of Tm2O3-doped NaAlH4with higher hydrogen storage content of-3.95wt%and faster desorption rate of3.17wt%/h. Besides, microporous CuBTC presented superior performance to mesoporous SiO2in terms of the enhancement of dehydrogenation kinetics. However, the weak structural stability of microporous CuBTC led to the failure of nano-confinement, resulting in the poor reversible hydrogen desorption performance.In addition, mechanical ball-milling method was applied to synthesize NaAlH4co-doped by ordered mesoporous materials and Sm2O3. And the influence of two representative ordered mesoporous materials-Al2O3and SiO2on the hydrogen desorption behavior of Sm2O3-doped NaAlH4were presented by Sievert’s technology test. It was found that NaAlH4catalyzed with Sm2O3, together with mesoporous SiO2presented the fastest desorption kinetics and the highest dehydrogenation capacity, slighter higher than that doped with mesoporous A12O3, attributed to the residues in the pores of A12O3that would react with NaAlH4and partial decomposition of mesoporous structure, while Sm2O3 single-doped NaAlH4evolved only3.6wt%hydrogen. Besides, doping with mesoporous SiO2produced a favorable effect on reducing the dehydrogenation temperature of Sm2O3-doped NaAlH4.Besides, the roles of lanthanide oxides and porous materials in the dehydrogenation of NaAlH4were discussed, suggesting the favorable synergistic effects can be more likely ascribed to the surface catalysis of lanthanide oxides and the nano-confinement of porous materials with high specific surface areas on the basis of the experimental results.