| Nowadays,with the development of society and technology,the demand for energy increased rapidly.However,the energy structure of society is mainly dependent on fossil fuels(oil,natural gas,coal,etc.).The unreasonable exploitation and non-renewable nature of fossil fuels has led to a sharp decline in the current stock of fossil fuel.At the same time,the over-used fossil fuels have resulted in a serious deterioration of the global ecological environment.Therefore,it is urgent to find a more suitable and clean alternative energy.Hydrogen,as a kind of new green energy owning high energy density,no pollution,light quality,wide source of has received widespread attention.Especially in recent years,the proton exchange membrane fuel cell(PEMFC)developed so fast.And hydrogen,the fuel of PEMFC,has drawn more and more researchers' attention.However,traditional physical hydrogen storage needs high compression and difficult transportation,so its cost is too high.Sodium borohydride(NaBH4),one of chemical hydrogen storage materials,not only is transported conveniently and safely,but also owns high hydrogen storage capacity.Besides,its other hydrolysis products can be easily separated from H2.The presence of the catalyst is essential for the hydrolytic dehydrogenation of NaBH4.Firstly,it is the "switch" to control the hydrolysis reaction of NaBH4.At the second,it can increase the hydrogen generation rate of NaBH4 and ensure the hydrogen release rate stable.The common catalysts are mainly based on the transition group elements,with noble metals Pt,Pd,Ru,and non-noble metal Co,Ni,Fe as the representative,which have a better catalytic performance of hydrogen production of NaBH4.The catalytic activity for the pure noble metal catalysts is higher,but the cost is too high,resulting in poor practicability.Owing to the addition of small amount of precious metal or other non-noble metals,the activity of the cobalt based catalysts has been greatly improved,which makes cobalt based catalysts to become a hot research topic in the study of NaBH4 hydrolysis.Because of cobalt based catalysts with magnetic.The prepared cobalt based nano-catalyst may easily reunion and decreased activity.Therefore,in order to better stability and dispersion of active metal,the carrier(such as graphene,silica,polymers,and so on)was used to achieve the goal of enhancing the durability of the catalyst.In this paper,the preparation methods,composition and carriers about the cobalt based nano-catalysts were optimized to study the catalytic performance for hydrolysis reaction of the NaBH4 aqueous through a series of characterization methods.This paper mainly consists of two parts:the research progress and the research paper of the catalysts for hydrogen production from NaBH4 hydrolysis.The specific researches are as follows:Part ?:In the first part,the advantages of hydrogen energy,the types of hydrogen storage materials and the principle of hydrogen production by NaBH4 were summarized.In addition,the catalysts and carriers of catalysts for hydrogen production of hydrolysis reaction were introduced in detail.Part ?:Research papers includes the preparation of W doped Co-Pt nano-catalyst,Co-Pt nano-catalyst loaded on the reduced graphene oxide and SiO2-CoFe2O4 loading noble metal catalysts,and the study of catalytic NaBH4 hydrolysis performance about these catalysts.Details are as follows:1.W doped Co-Pt nano catalyst was prepared by using NaBH4 as a reducing agent and polyvinylpyrrolidone as a surfactant.The obtained catalyst had a much higher catalytic activity than Co-Pt catalyst in the absence of W.Through the optimization of metal content,the highest catalytic hydrogen evolution rate of the catalyst reached 6800 mL·min-1·g(catalyst)-1,and had a lower reaction activation energy(31.7 kJ·mol-1).By a series characterization,such as SEM,XRD,XPS,1CP and so on,the morphology,composition and metal content of W doped Co-Pt nano-catalysts were determined.In addition,the effect of W on Co-Pt nano-particles was also discussed in detail.We found that W prevented cobalt particles from coming close enough together to agglomerate into larger particles during the reduction process,which promoted them to amorphous state.And in the presence of W,the catalyst had a lewis acid site,absorbing of OH",and promoting the reaction between OH-and intermediate product to enhance the catalytic activity.2.Using hydrazine hydrate as a electronating agent out of surfactants,Co-Pt nano-particles loaded on the reduced graphene oxide were prepared by a one-step in situ reduction method.The composition and morphology of the prepared Co-Pt catalyst loaded on the reduced graphene oxide was characterized by TEM,EDS,XPS,ICP and so on.The results showed that the catalyst had a better metal loading and dispersion,less agglomeration,and about 2?3nm particle size.Through the study on the catalytic hydrolysis of sodium borohydride properties and optimizing the proportion of metal,the catalyst,with 10 wt.%Pt for the catalyst amounts(20 wt.%Pt for the metal loading content),had a good catalytic activity,and its maximum hydrogen evolution rate was up to 6534 mL·min-1 g(metal)-1,which was significantly higher than Co-Pt catalyst.Besides,activation energy of the reaction is about 57.06 kJ·mol-1 and the catalyst had a better durability and easier recycle because of magnetic characteristics.3.Sodium borohydride was used to reduce noble metal precursors out of surface active agent to prepare noble metal catalysts,Pt/Si02-CoFe2O4 and Ru/SiO2-CoFe2O4,whose carrier is the ferromagnetic CoFe2O4 coated by SiO2.The amorphous and morphology of catalysts was characterized and analysed by means of TEM and XRD.The two kinds of catalysts has been compared to explored the catalytic performance for catalytic dehydrogen of NaBH4 aqueous.The compared results indicated that the prepared Ru/SiO2-CoFe2O4 showed special sphere strucure,and its turnover frequency(TOF)value about catalytic hydrogen evolution vate of sodium borohydride was up to 167.4 mol(H2)·min-1·mol(Ru)-1.Especially,in the catalytic durability test,its hydrogen evolution rate remained in the second cycle almost the original catalytic rate,and had higher catalytic activity,lower the reaction activation energy and better catalytic stability than Pt/SiO2-CoFe2O4. |
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