The Hydrogen Storage System Of NaBH₄ Solution And Its' Hydrolysis Catalysts

In this thesis, based on the review of the research work on the catalysts used for hydrogen generation from hydrolysis reaction of NaBH₄ solution, the improvement of Ni-B and Co-B based catalysts with low cost and high performance were proposed as the object of this study. By the means of XRD, TEM, SEM analyses and measurement of hydrogen generation rate, the effects of catalyst composition, structure and reaction conditions (including NaOH concentration in the solution and reaction temperature) on catalytic activity of Fe-doped Ni-Fe-B/Co-Fe-B and Ni-B/Co-B coated on Fe powder were investigated systemically.For Fe-doped Ni-Fe-B catalysts, the catalytic activities of catalysts with different Ni/Fe ratio were comparatively studied. It is found that the catalyst with Ni/Fe ratio of 3:1 (actual composition: Ni2.2Feo.7B) shows the highest activity among the Ni-Fe-B catalysts studied. Its hydrogen generation rate reaches 500 ml/min at 40℃. XRD and TEM observation show that the as prepared Ni-Fe-B catalysts are consisted of nanocystalline. The crystal grain of Ni_2.2Fe_0.7B(1.9 nm) is higher than non-Fe-doped Ni-B, but the average dimension of Ni_2.2Fe_0.7B agglomerate particles (15 nm) is smaller than that of Ni-B (20 nm). It is also found that the hydrogen generation rate was enhanced by adding certain amount of NaOH solution into NaBH₄ solution. In additional, the increase of reaction temperature results in increase of both hydrogen generation rate and conversion rate of NaBH₄. The activation energy for NaBH₄ hydrolysis reaction with Ni2.2Feo.7B is found to be 49.0 kJ/mol. With the reaction temperature of 45°C, the conversion rate of NaBH₄ reaches 92.5% and the maximum hydrogen storage density of alkaline saturated NaBH₄ solution reaches 6.82 wt%.For Fe-doped Co-Fe-B catalysts, the catalytic activities of catalysts with different Co/Fe ratio were comparatively studied. It is found that the catalyst with Co/Fe ratio of 2:1 shows the highest activity among the Co-Fe-B catalysts studied. Its hydrogen generation rate reaches 360 ml/min at 25℃. TEM observation shows that the average dimension of Co₂FeB agglomerate particles is lower than that of Co-B. It is also found that the hydrogen generation rate was enhanced by adding certain amount NaOH solution into NaBH₄ solution. In additional, the increase of reaction temperature results in increase of both hydrogen generation rate and conversion rate of NaBH₄. The activation energy for NaBH₄ hydrolysis reaction with Co₂FeB is found to be 26.0 kJ/mol. With the reaction temperature of 45℃, the conversion rate of NaBH₄ reaches 94.0% and the maximum hydrogen storage density of alkaline saturated NaBH₄ reaches 6.88 wt%. Compared with the Fe-doped Ni-Fe-B catalysts, the Fe-doped Co-Fe-B shows the better catalytic activities.For the catalyst of Ni-B loaded on Fe powders, effects of the amount powder size of Fe powder added on catalytic activity of catalysts were comparatively studied. It is found that the catalyst with 1 g Fe powder (80 mesh) as the carrier shows the highest activity among all the catalysts studied. Its hydrogen generation rate reaches 76ml/min at 25℃. From SEM and TEM observation, most of Ni-B is coated on the surface of Fe powder, but some of the single agglomerate particles of Ni-B are also found, and agglomerate particles coated on Fe powder with a dimension of 30 nm. It is also found that the hydrogen generation rate was enhanced by adding certain amount NaOH solution into NaBH₄ solution, In additional, the increase of reaction temperature results in increase of both hydrogen generation rate and conversion rate of NaBH₄. The activation energy for NaBH₄ hydrolysis reaction with Ni-B loaded on 1 g Fe powder (80 mesh) is found to be 63.0 kJ/mol. With the reaction temperature of 45°C, the conversion rate of NaBH₄ reaches 91.7% and the maximum hydrogen storage density of alkaline saturated NaBH₄ reaches 6.77 wt%.For the catalyst of Co-B loaded on Fe powders, effects of the amount powder size of Fe powder added on catalytic activity of catalysts were comparatively studied. It is found that the catalyst with 1 g Fe powder (80 mesh) as the carrier shows the highest activity among all the catalysts studied. Its hydrogen generation rate reaches 182 ml/min at 25℃. From SEM and TEM observation, most of Co-B is coated on the surface of Fe powder, but some of the single agglomerate particles of Co-B are also found, and agglomerate particles coated on Fe powder with a dimension of 50 nm. It is also found that the hydrogen generation rate was enhanced by adding certain amount NaOH solution into NaBH₄ solution, In additional, the increase of reaction temperature results in increase of both hydrogen generation rate and conversion rate of NaBH₄. The activation energy for NaBH₄ hydrolysis reaction with Co-B loaded on 1 g Fe powder (80 mesh) is found to be 37.1 kJ/mol. With the reaction temperature of 45℃, the conversion rate of NaBH₄ reaches 92.1% and the maximum hydrogen storage density of alkaline saturated NaBH₄ reaches 6.779 wt%. Compared with the Fe powders loaded Ni-B catalysts, he Fe powders loaded Co-B catalysts shows the better catalytic activities.