Synthesis Of Non-noble Metal- Graphene Nanocomposites For Catalytic Hydrogen Generation

Hydrogen has attracted considerable attention as a clean energy with abundant storage capacity and high energy density. The secure storage and transport of hydrogen is the most difficult challenges for the hydrogen technology. Ammonia borane(AB), due to its high hydrogen storage capacity, is considered to be one of most promising candidates for hydrogen storage materials. For the practical application of AB, the search of low-cost and high-performance catalysts becomes the hot topic. Graphene, a new class of two-dimensional carbon nanostructure with one-atom thickness, holding high specific surface area and superior electrical conductivity, could be an ideal substrate for growing and anchoring metal NPs with good dispersion, has potential ability to improve the catalytic activity. In this thesis, graphene supported metal nanoparticles(NPs) were synthesized, characterized and used as highly active catalysts for hydrogen generation from hydrolysis of ammonia borane(AB). The main contents are as follows:Copper NPs supported on reduced graphene oxide(RGO) were synthesized by one-step in situ co-reduction of aqueous solution of copper sulfate and graphene oxide(GO) using AB as the sole reductant at room temperature. Copper NPs with size of less than 5 nm are well-dispersed in the RGO nanosheets. The as-prepared nanocatalysts exert satisfactory catalytic activity with a TOF value of 3.6 mol H2 mol Cu-1 min-1, and appear to be the best Cu nanocatalysts up to now for the dehydrogenation of AB.Bimetallic catalysts usually show enhanced catalytic performance in comparison to their monometallic counterparts. CoNi NPs supported on graphene with magnetic have been synthesized by one-step in situ co-reduction of aqueous solution of cobalt(II) chloride, nickel(II) chloride, and GO with AB as the reducing agent under ambient condition. The characterized results show that the as-synthesized samples are composed of Co-Ni bimetallic NPs and the metal NPs were well dispersed on graphene. The graphene supported CoNi NPs exhibit much higher catalytic activity than the monometallic counterparts, especially for Co0.5Ni0.5/graphene NPs exhibits excellent catalytic activity with a TOF value of 19.5 mol H2 mol metal-1 min-1 and a low activation energy value of 39.9 kJ mol-1 at room temperature. Moreover, by using an external magnet, these catalysts can be readily separated from the solution for recycle purpose, and can keep the high activity even after 5 times of recycle under ambient atmosphere.Ni-CeO2/graphene catalysts were successfully synthesized by one-step co-reduction at room temperature. Compare with Ni/graphene and Ni-CeO2, Ni-CeO2/graphene catalysts show superior catalytic activity for the hydrolysis of ammonia borane. The TOF value is measured to be 68.2 mol H2 mol Ni-1 min-1, which is the highest value of non-noble nanocatalysts reported up to now for the dehydrogenation of AB. The Co-CeO2/graphene was prepared by the similar method, which also exhibit a high catalytic activity for hydrolytic dehydrogenation of AB with a TOF value of 45.1 mol H2 mol Co-1 min-1. Hence, this general method can be easily extended to facile preparation of other RGO-based systems. The catalytic results open up new avenues in the effective application of AB as a promising hydrogen storage material.