| NaAlH4have been considered as the first complex hydride hydrogen storage material to be researched, and is one of the most potential hydrogen storage materials, due to its high hydrogen capacity and low dehydriding temperature. However, reversibility and hydriding/dehydriding kinetics of NaAlH4is poor, especially in rehydriding. At present, improve its kinetics by adding catalyst have been regarded as a very important research on hydrogen storage materials.In all transition elements which have better catalytic effect on hydriding and dehydriding kinetics of NaAlH4, Ti is the most tipical element. In addition, Ce has catalytic effect on hydriding and dehydriding reaction of NaAlH4, and it has been reported in many published articles. Considering the rare-earth element and transition element have different catalytic effect on hydriding and dehydriding kinetics of NaAlH4. The advantage of both Ti-Ce elements may be obtained by Ti-Ce co-doped. In this work, the effect of cooperative catalytic of Ti-Ce binary elements on hydrogen storage properties of NaAlH4was studied. At first, we researched the feasibility of cooperative catalytical effect of Ti-Ce on hydriding/dehydriding of NaAlH4, then investigated how to improve their cooperative catalytic extent. In the work, the catalyst-NaAlH4systems were prepared by in-situ high energy vibration ball milling under high pressure hydrogen atmosphere. In this way, the catalytic have better contact with NaAlH4, so as to have better catalysis effect on hydriding and dehydriding kinetics properties of NaAlH4.The experimental results shows that the hydriding/dehydriding kinetics properties, the effect of in situ synthesis NaAlH4, and the hydrogen srorge capacity of the sample doped with Ti-Ce binary elements were better than the sample which single doped with single Ti or Ce. Therefore, Ti-Ce binary catalytic have synergistic effect on hydriding and dehydriding of NaAlH4.It was found from the investigations that the samples prepared by Ti-Al or Ce-Ti-Al pre-melting alloys shows better hydrogen storage capacity and better kinetic properties than the sample which prepared by elemental powder. The reason is that after pre-smelting, the contact between catalyst and Al increase greatly due to more interfaces produced. Consiquently, more interface between catalyst and NaAlH4will producted after in situ milling. The sample which prepared by the2Ti-Ce-60Al melting alloys as initial material, the decomposition temperature at the first and second dehydriding step at100℃and170℃respectively, and hydrogen capacity is3.25wt%. As for rehydrogenation aspect, under110℃and8MPa hydrogen back-pressure condition, it can absorb hydrogen3.89wt%in total and complete90%of its maximum hydrogen capacity in2h, which is also superiorty than the sample without pre-melting.Commently, higher content of Catalytic components lead to better catalytic effects. At the same time, the hydrogen storage capacity of systems would be reduced when adding too many catalytic components. Keeping the ratio between Ti and Ce to2:1, we increased the content percentage of Ti-Ce from3mol%to6mol%. It is founded in experiments that, when the proportion of Ti-Ce increased, the kinetic properties and hydrogen storage capacity of sample increase at first and than decrease. The sample with5mol%Ti-Ce had faster hydriding and dehydriding speed and also with higher hydrogen capacity (3.76wt%). At the temperature of150℃, the sample release hydrogen completely in16minutes. Under110℃and8MPa hydrogen back-pressure, the rehydriding of sample reach saturation after rehydriding2.5h, rehydriding capacity was3.9wt%.Catalytic effect of Ti-Ce is influenced by the ratio between Ti and Ce. We founded that, in the total proportion of5mol%(Ti-Ce), charge the ratio between Ti and Ce, from2:1to5:1, the hydrogen storage performance was increased and the kinetic properties was enhanced. The sample with Ti and Ce at the ratio of5:1had the fastest rehydrogenation rate and highest reversibility hydrogen storage capacity. The reversible hydrogen storage volume reached more than4.5wt%. At the temperature of150℃, the sample dehydriding completely within12minutes, and the released hydrogen content was2.2wt%. According to the isothermal rehydrogenation at110℃and8MPa hydrogen back-pressure, the sample can absorb hydrogen4.55wt%, which is the highest hydrogen storage capacity in all experimental samples in this work. |
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