Catalytic Dehydrogenation Of Borohydrides And The Corresponding Materials For Energy Storage

The exploitation and utilization of new renewable green energy as well as high-efficient energy storage&conversion technology plays a key role in the sustainable development of human society. Hydrogen with high-energy density and enviromental benignancy is recogniazed as one of the most promising energy for the future. The efficient generation and storage of hydrogen are the main challenge for the development of hydrogen energy. Borohydrides possess high hydrogen storage density, however, their dehydrogenation reactions through hydrolysis and thermolysis always exhibit slow kinetics. The widely application of the borohydride hydrogen generation system depends on the development of the corresponding practical catalysts. Moreover, the direct methanol fuel cells (DMFCs) recently attract much attention as the high-efficient energy conversion apparatus. The anode catalyst is one of the key roles that affect the performance and cost of the DMFCs, and the supporting materials for catalyst is important for the utilization efficiency of the noble metal, the catalytic activity and stability. Based on the above analysis, this dissertation addresses the preparation and characterization of dehydrogenation catalysts for borohydride as well as the porous carbon for catalyst support and the fondamental study of their application in energy storage and conversion.1. Carbon black-supported Co-B catalyst and Porous Co-B hollow spheres were prepared via the impregnation-chemical deposition and template-chemical reduction methods, respectively. The morphology, composition and catalytic activities for NaBH4 hydrolysis reaction of the as-preparted catalysts were investigated. The influence of Co-B loading, reaction temperature, reactant concentration as well as thermal treatment on the catalytic dehydrogenation performance was discussed in detail. In comparison with the Co-B nanoparticles obtained through the traditional method, both of the as-prepared catalyst showed obviously improved catalytic activities. The hydrogen generation rate for thermal-treated Co-B hollow spheres reached 2720 mL min-1 g-1, and the hydrogen production approached the theoretical value of the used hydrolysis system. Experimental results show that the application of the substrate with high surface area for dispersing the catalyst and the construction of porous functional structure are two effective ways to improve the catalytic performance of the non-noble metal catalysts for NaBH4 hydrolysis reaction.2. A new catalytic hydrogen generation system was obtained by using the poly(methyl acrylate) (PMA) to combine with the ammonia borane (AB) through a solution process. In the experiments, the miscibility of PMA and AB was investigated, and the physical properties as well as thermolysis dehydrogenation performance of the composites prepared under different feed ratios were also compared. The as-obtained composite showed a water-resistant property and favorable dehydrogenation kinetics. Study results indicate that the interaction of PMA efficiently lowers the hydrogen-release temperature and depress the generation of detrimental boracic impurities. The thermolysis process can be controlled by changing the reaction temperature, and the results provide a better understanding of the hydrogen release properties from AB with controlled thermodynamics and kineties. In this hydrogen generation system, the application of polymer material with active organic group can also help to broaden the choice of candidates for catalyzing the thermolysis of AB.3. The honeycomb-like hierarchically porous carbons were synthesized by a facile self-assembly strategy. In this strategy, tetraethyl orthosilicate (TEOS) and phenolic resin were used as the template source and carbon source. This synthesis rocess is simple and time-saving in comparison with the conventional casting methods, which is more suitable for mass prodution. The morphology, structure, BET surface area as well as the porosity of the carbon product were characterized in detail. The formation process for the hierarchically porous carbons was discussed and verified. The influence of experimental parameters, such as TEOS concentration, adding speed of aqueous ammonia, on the morphology and porosity of the product was also investigated. Compared with the carbon black-supported Pt catalyst, the porous carbon-supported Pt catalyst exhibits higher catalytic activity and stability for the methanol oxidation reaction, suggesting potential application in the catalysts of direct methanol fuel cells.