Graphene-based Nanocomposites For High-Efficiency Hydrolysis Of Ammonia Borane

With the continuous development of social economy,human's demand for energies and consumption is growing.Among various renewable clean energies,hydrogen energy has received more and more attention owning for many advantages.However,the efficient storage and controllable release of hydrogen are big problems which have significantly hindered the development of hydrogen economy.In order to solve the problems,many hydrogen storage materials have been developed and among them,ammonia borane(AB)is one of the best chemical storage material owing to its high hydrogen content(19.6 wt%),nontoxicity,high stability in both aqueous solutions and air at room temperature.Controlled release of hydrogen from AB requires effective catalysts.In this work,we have prepared various effective catalysts for the hydrolysis of AB,so as to accelerate the hydrolysis reaction.In this thesis,various methods have been used to improve the catalytic activity and stability.The thesis mainly includes three parts with the preparation of three effective catalysts,which are shown as CuxCo1-xO Nanoparticles(NPs)supported on Graphene Oxide(CuxCo1-xO/GO),Reduced Graphene Oxide immobilized CuxCo1-xPtyO nanoparticles(CuxCoi-xPtyO/RGO)and Reduced Graphene Oxide supported NixRhi-x nanoparticles(NixRh1-x/RGO),respectively.All of them show very good catalytic activity.The detailed contents are shown as following:(1)We describe a facile procedure in a water-isopropanol reaction system,which is capable of in situ depositing CuxCo1-xO nanoparticles on GO sheet.The optimized hybrid(CuxCo1-xO-GO)shows superior catalytic performance in the hydrolysis of AB with a high initial total turnover frequency(TOF)value of 70.0 molH2·molcat-M-1· min-1.Synchrotron radiation-based X-ray absorption spectroscopy(XAS)investigations suggested the enhanced catalytic performance of the hybrid can be ascribed to the interfacial interaction between NPs and GO.Moreover,the catalytic hydrolysis mechanism was studied by in situ XAS experiments for the first time,which reveals a significant water adsorption on the catalyst and clearly confirms the interaction between AB and the catalyst during hydrolysis.(2)By using a two-steps reduction of Cu,Co and Pt precursors,we have successfully prepared RGO immobilized CuxCo1-xPtyO nanoparticles(CuxCo1-xPtyO/RGO),which takes full advantage of the strong synergetic effect of three metal elements and shows a good catalytic activity for the hydrolysis of AB.The catalytic activity of the hybrid is one of the best among all reported Pt-based catalysts.Moreover,the catalyst also shows a good stability.In order to study the hydrolysis mechanism,Synchrotron radiation-based XAS experiments have been performed which probe the electronic structure changes of the catalysts before and after the reaction.The XAS results reveal that the hybrid is formed with the oxidized states of Cu,Co and Pt elements.Interesting,the oxidized states have not been changed after the reaction,which can be the reason for the good stability.(3)By an atomic sacrifice method,NixRh1-x/RGO have been successfully prepared through the displacement between Ni0 atoms on the surface of Ni nanoparLicles in the Ni/RGO and Rh3+ anions in the RhCl3 solution.The newly designed catalysis system showed extremely high activity for the hydrolysis of ammonia borane with the initial turnover frequency value of Ni0.9Rh0.1/RGO reaching 879.4 moIH2·molRh-1 ·min-1,which is higher than most of active Pt-based and Rh-based catalysts.Moreover,it also shows good stability,which retains 80%of initial activity after 8 cycles.