Synthesis Of Ni-based Metal Nanocomposites For Hydrogen Production From Hydrous Hydrazine

Hydrogen has attracted much attention as one of ideal clean energy with high power density. Hydrazine monohydrate（N2H4·H2O） has been regarded as a promising liquid chemical hydrogen storage materials due to its high hydrogen content（8.0 wt%）, low cost, safe storage and transport, and the excellent stability of chemical and physical properties under mild conditions. Especially, the complete decomposition of N2H4 can release H2 and the only by-product N2. The development of low cost, high efficient and stable catalysts is the key issue for the decomposition of hydrazine. This thesis mainly focuses on the preparation, characterization, and catalytic performance of Ni-based metal nanocompositions（NCs）. The main contents are as follows:Bimetallic NiRh nanoparticles（NPs） immobilized on the cerium hydroxide carbonate（Ce（OH）CO₃） have been prepared by a facile co-reduction route, and characterized by XRD, SEM, TEM, EDX, ICP, XPS, and TG-DTA. The as-synthesized Ni1-xRhx/Ce（OH）CO₃ NCs were applied as the highly efficient catalysts for hydrogen generation from the decomposition of N2H4·H2O. Especially, the Ni₄₅Rh₅₅/Ce（OH）CO₃ NCs exerted the highly activity and 100% H2 selectivity for the decomposition of hydrazine with a high turnover frequency（TOF） value of 150 h-1 at 30 oC, relative high values for the metal catalysts. The activation energy for the decomposition of hydrazine catalyzed by Ni₄₅Rh₅₅/Ce（OH）CO₃ NCs was measured to be 38.8 kJ mol-1, lower than most of the values reported for this reaction using many different catalysts.Ni1-xPtx/graphene NCs have been successfully synthesized via a galvanic replacement approach at room temperature with a precursor Ni NPs as a sacrificial template. The characterized results showed that NiPt NPs with a small size of around 3.5 nm dispersed on graphene nanosheets. The as-synthesized Ni_0.58Pt_0.42/graphene exhibited a highly activity and 100% hydrogen selectivity for the decomposition of hydrazine with a TOF value of 434 h-1 at 30 oC and a low activation energy value of 23.3 kJ mol-1. The as-synthesized Ni_0.58Pt_0.42/graphene exhibited good durability during five recycle test. These results indicate that the Ni_0.58Pt_0.42/graphene exhibit superior catalytic performance as compared to the previous Ni₄₅Rh₅₅/Ce（OH）CO₃ NCs and other reported catalysts.In order to decrease the cost of catalyst, NiFe-Cr₂O₃ NCs have been successfully synthesized by a facile co-reduction method under ambient atmosphere. The catalytic activity and hydrogen selectivity of Ni_0.9Fe_0.1-Cr₂O₃ were remarkably improved as compared with its mono-/bimetallic counterparts. Ni_0.9Fe_0.1-Cr₂O₃ NCs exhibited a high catalytic activity to make hydrazine release 3.0 equiv.（H2 + N2） in only 8.5 min with a TOF value of 70.6 h-1 at 70 oC, higher than most the previously reported non-noble catalysts. In particular, this catalyst retains 76% of its initial catalytic activity and 100% H2 selectivity even after 10 runs. The excellent catalytic activity of Ni_0.9Fe_0.1-Cr₂O₃ is probably due to the fact that the addition of Cr₂O₃ leads to a decrease in particle size and acts as an electron donor for NiFe NPs.