Codoped Mesoporous Silicon Load Naaih <sub> 4 </ Sub> Hydrogen Storage Properties Of

As a kind of new hydrogen storage materials, complex hydrides have attracted most of attentions because of their high volumetric and gravimetric hydrogen densities. However, most of these hydrides have poor hydrogen desorbed/absorbed kinetics and limited reversibility for applications. In this paper, hydrogen storage properties of NaAlH4 was improved with codoping TiF3 and porous materials (active carbon AC and mesoporous silica SBA-15) and confining NaAlH4 into SBA-15, and dehydrogenation/rehydrogenation kinetics and reversibility of those two systems were investigated.NaAlH4 co-doped porous materials and TiF3 was prepared by using high energy ball-milling method. Dehydrigenation kinetics and dehydrogenation-rehydrogenation cycling properties of NaAlH4+3mol%TiF3+10wt%AC samples and NaAlH4+3mol%TiF3+10wt% SBA-15 samples have been investigated. Compared to NaAlH4+TiF3+SBA-15, NaAlH4+TiF3+AC exhibits low dehydrogenation temperature of 126℃and 175℃for the first dehydrogenation step and the second dehydrogenation step, decreased by 24℃and 15℃, respectively. Kinetics determination at 160℃shows improved properties after codoped AC, which restrains NaAlH4+TiF3 decomposing during ball-milling process and is helpful to increase its hydrogen storage capacity. Moreover, both of kinetics properties and hydrogen storage capacity of samples codoped SBA-15 were obviously reduced after 3 cycles, however, samples codoped AC show stable cycling properties, which the reversible hydrogen storage capacity can reach 4.8wt% with dehydrogenation at 160℃under vacuum. XRD and SEM-EDS analysis indicates that AC may be helpful to restrain NaH and Al granules conglomeration and growth, which impelled Na3AlH6 fully converted to NaAlH4 and improves kinetics and cycling properties.Dehydrogenation and rehydrogenation properties of NaAlH4 codoped TiF3 and AC was systematically investigated. Dehydrogenation kinetics determination shows that initial dehydrogenation temperature of the samples is lower than doped TiF3 or AC samples, and NaAlH4 codoped TiF3 and AC sample could be able to release hydrogen at 50℃. As dehydrogenation temperature increasing from 140℃to 170℃, the dehydrogenation rate especially for the second step has been greatly enhanced, and the dehydrogenation capacity(base on NaAlH4) increases from 4.0wt% to 5.4wt% in 180 min. Moreover, rehydrogenation kinetics determination shows that codoped AC has an obvious improvement on NaAlH4+TiF3 rehydrogenation properties. Both of the rehydrogenation rate and capacity are swiftly increased with AC codoped contents and hydrogen pressure, and the rehydrogeantion reveals optimum rate at 130℃when the pressure is 11MPa. Considering for practical application,1%CO poisoned properties of NaAlH4+3mol%TiF3+10wt%AC was investigated. The hydrogen storage capacity reduced 22% after CO poisioned, and the CO poisoned was deepened with cycling. It indicates that improved kinetics and stable cycling properties may be partly attribute to Ti-containing phase much uniformly dispersed on NaAlH4 surface after AC codoped and AC may accelerate NaH and Al migrations.NaAlH4 incorporated into SBA-15 was prepared by high-temperature melting method. Without any catalyst, NaAlH4/SBA-15 could be able to dehydrogenate at 160℃under vacuum and rehydrogenate at 130℃with hydrogen pressure of 9MPa. With the NaAlH4 contents increasing from 30% to 70%, samples'hydrogen storage capacity is firstly increasing and then decreasing, which 50wt%NaAlH4/50wt%SBA-15 shows maximum hydrogen desorbed/resorbed capacity. Cycling properties determination reveals that NaAlH4/SBA-15 has more stable properties than NaAlH4 doped Ti-based catalysts, although it has much slower dehydrogenation rate than Ti-based catalysts doped samples.