The Synthesis Of Ni@C Nanotibers As Catalyst For Enhanced Hydrogen Storage Of MgH₂

The storage of hydrogen is the bottleneck restricting the application of hydrogen energy.A reversible and safe hydrogen storage material with high hydrogen content is urgently needed.Magnesium,with its advantages of light weight,high hydrogen storage capacity(7.6 wt%),wide sources,and no pollution,has attracted much attention in the field of hydrogen storage materials.It's hydrogen-absorbing product magnesium hydride(MgH2)is regarded as one of the most promising hydrogen storage materials and has attracted a lot of research in academia and industry.However,due to its disadvantages such as high temperature of hydrogen absorption and dehydrogenation,slow kinetics and too stable thermodynamics,pure magnesium hydride has not been able to meet the requirements of practical application,and is especially difficult to be widely used in vehicular hydrogen storage system.Therefore,it is necessary to conduct research on its modification.Due to the poor hydrogen decomposition ability on the surface of pure magnesium,the addition of trace catalyst is an effective way to improve the kinetic property of hydrogen absorption and dehydrogenation and reduce the temperature of hydrogen absorption.It is the key to select the appropriate catalyst and design its reasonable structure.At present,the catalysts for absorption and dehydrogenation of magnesium hydride mainly include non-metallic materials(carbon materials),transition metal elements,transition metal oxides,transition metal halides,etc.The nickel elements on magnesium hydride hydrogen performance has great influence,in order to further improve the catalytic performance of nickel and system the cycle of life,based on the electrostatic spinning method to design a load of Ni nanoparticles synthesized carbon fiber structure,system add to MgH2 hydrogen storage performance improvement,optimizing the adding quantity,study its catalytic mechanism.First,the primary fiber was synthesized by electrostatic spinning,and then the morphology of the fiber was stabilized through the pre-oxidation stage.Finally,the Ni nanoparticles supported by carbon nanofibers(Ni@C)were synthesized through one-step carbonization and reduction in a tubular furnace.Then,the catalysts were introduced into MgH2 by high-energy ball milling.In this paper,X-ray diffraction analysis(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM)and other methods were used to characterize the structure of the samples,and TPD testing system was used to study the hydrogen separation and liberation properties of the samples,as well as the kinetic and circulating properties of hydrogen absorption.The main results are as follows:In order to explore the catalytic modification effect of synthesized Ni@C on MgH2,the improvement of hydrogen storage performance of MgH2 with the addition of catalysts of different proportions,the comprehensive conditions of hydrogen discharge amount and hydrogen discharge rate were firstly discussed,and finally the modification effect of MgH2 with the addition of 10 wt%of Ni@C was determined to be the best and the optimal ratio.Therefore,the thermostatic hydrogen absorption performance of MgH2-10wt%Ni@C composite system was further studied.The results showed that the hydrogen absorption and dehydrogenation kinetics of the Ni@C catalytic modified MgH2 system was significantly improved,and 6.1 wt%hydrogen was released within 10min at 325?.The dehydrogenation activation energy was reduced to 93.08 kJ/mol compared with the ball-milling magnesium hydride,and the apparent activation energy was reduced by more than half compared with the ball-milling commercial magnesium hydride(187.41 kJ/mol).Finally,the MgH2-10wt%Ni@C composite system was tested for hydrogen storage performance in a cycle,and it was found that after 10 cycles of hydrogen storage,the system was still able to maintain a hydrogen storage content of 5.8wt%and high efficient hydrogen dehydrogenation kinetics performance.In the process of ball grinding,the surface of Ni@C and MgH2 particles are in close and uniform contact,which not only provides more active sites for hydrogen atoms,but also effectively inhibits the growth and agglomeration of catalyst particles,which is beneficial to improve the cycle life of the system.