Preparation Of Novel Low-dimensional Functional Materials And Their Energy Storage And Thermal Regulation Properties

With the rapid development of electronic devices and electric vehicles,the power supply system has brought about significant technological renovation.Hydrogen fuel cells have the advantages of high energy utilization,no pollution and no carbon emissions.It not only meets the operating conditions of electronic devices and electric vehicles,but also complies with energy policy of"energy saving and emission reduction"in China.A safe,efficient,lightweight and economical hydrogen storage method is one of the key technologies to realize the practical application of the hydrogen fuel cell system,and it is also an important part of the hydrogen energy industrialization.Compared with gaseous and liquid hydrogen storage materials,solid hydrogen storage materials such as metal hydrides and coordination hydrides have the advantages of high hydrogen storage capacity,high stability and suitable storage and transportation conditions,making it become one of promising candidates for on-board hydrogen storage.However,they also suffer from slow kinetics and poor reversibility.On the other hand,during the operation of electronic devices and power batteries,waste heat is unavoidable,which can seriously affect the operating efficiency and service life of devices and batteries.Therefore,a stable and efficient thermal management system is essential.Organic phase change materials have the advantages of high latent heat,excellent cycle performance,and stable chemical properties,which can realize intelligent adjustment of temperature.However,low thermal conductivity and easy leakage still hinder its practical application.In this paper,on the basis of the research progress of various hydrogen storage technologies and phase change materials-based temperature control technologies,Li Al H₄and lauric acid（LA）-palmitic acid（PA）binary blend materials are selected as the research objects for solid state hydrogen storage materials and phase change materials.Through ball-milling doping and vacuum impregnation,low-dimensional functional materials with high catalytic activity and high thermal conductivity are composited with Li Al H₄ and phase change materials to improve the hydrogen storage properties of Li Al H₄ and the thermal conductivity of phase change materials.The results of the study are as follows:（1）A series of spinel ferrite nanoparticles were successfully obtained by the solvothermal method and introduced into Li Al H₄ by ball milling.Dehydrogenation experiments show that all ferrite nanoparticle dopants can improve the dehydrogenation performance of Li Al H₄,especially Ni Fe₂O₄ nanoparticles.Li Al H₄ doped with 7 wt%Ni Fe₂O₄ can release 6.37 wt%hydrogen gas within 25 min at 180°C.Mechanistic studies show that the presence of Ni Fe2O4 and in situ formed Al4Ni3 can decrease the desorption energy barrier of Al-H bonding of the Li Al H₄ unit and accelerate the breakdown of Al-H bonding through the interfacial charge transfer and the dehybridization of the Al-H cluster.In addition,the doping of Ni in Al₄Ni₃ and Al_1.1Ni_0.9 can also improve the rehydrogenation performance of Li Al H₄.This study provides a reference for the doping modification and mechanism research of solid-state hydrogen storage materials.（2）Ni Fe₂O₄@h-BN nanocomposites were successfully synthesized by mean of one-step hydrothermal route and calcination,and introduced into Li Al H₄ by ball milling.The hydrogen desorption performance of Li Al H₄ is improved due to the synergistic catalytic effect of Ni Fe₂O₄ and h-BN.Li Al H₄ doped with 7 wt%Ni Fe₂O₄@h-BN can release hydrogen at 77.1°C,which is 98.9°C lower than that of pure Li Al H₄.It is found that in situ formed Al₄Ni₃,Li Fe O₂ and Al_1.1Ni_0.9 phases can serve as active sites for the nucleation and growth of dehydrogenation products,accelerating the dehydrogenation kinetics of Li Al H₄.In addition,the doping of Ni from Al₄Ni₃ and Al_1.1Ni_0.9 and the introduction of h-BN can improve the hydrogen absorption performance of Li Al H₄.This study provides a new idea for the design and preparation of multidimensional nano-dopants for solid-state hydrogen storage materials.（3）XTi O₃@h-BN（X=Ni,Co）were successfully obtained by the simple precipitation process and used as catalytic dopants for Li Al H₄.The results show that the doping of XTi O₃@h-BN can significantly improve the dehydrogenation temperature,dehydrogenation kinetics and rehydrogenation performance of Li Al H₄.Li Al H₄ doped with 7 wt%Ni Ti O₃@h-BN can release hydrogen at 68.1°C.Its activation energies（E_a）of the two-step hydrogen release reactions are 45.8%and 69.0%lower than those of as-received Li Al H₄,respectively.In addition,Li Al H₄ doped with 7 wt%Ni Ti O₃@h-BN after dehydrogenation can absorb approximately 1.05 wt%hydrogen under 30 bar hydrogen pressure and 300°C constant temperature,much higher than that of pure Li Al H₄（about 0.10 wt%）and ball-milled Li Al H₄（about 0.17 wt%）.Mechanistic studies show that in situ formed Al Ni₃ and Ni Ti can accelerate the breakdown of Al-H bonding through the interfacial charge transfer and the dehybridization of the Al-H cluster.And,Ni Ti can enhance the adsorption and splitting of H₂,promoting the activation of H₂ molecules during the hydrogen storage process.The doping of Ti phase and Ni atoms from Al Ni₃ can reduce H₂ splitting energy barrier on clean Al（111）.This study provides experimental reference and theoretical support for the design and preparation of solid-state hydrogen storage materials for hydrogen fuel cell systems.（4）The lauric acid（LA）and palmitic acid（PA）binary blend phase change materials synergistically strengthened by h-BN and expanded graphite were prepared by melt impregnation.Benefiting from the multi-layered micro/nano thermal conductive network formed by expanded graphite and h-BN,the composite phase change materials maintain high latent heat of phase transition,good thermal cycle stability and high thermal conductivity.The fusion/crystallization latent heat of the composite phase change materials can reach151.08 J·g^-1 and 149.53 J·g^-1,respectively.After 200 thermal cycles,phase change behavior of 90LP-9.7G-0.3B changes little,and its thermal conductivity is 1.54 W·m^-1·K^-1,which is8.1 times that of binary blended phase change materials.In addition,the composite phase change material exhibits fast thermal response behavior and excellent thermal regulation properties for Li-ion batteries.The center point temperature on the surface of the battery was simulated by a program written in Python during the discharge process.And,the simulation results are very close to the measured result.This study provides new ideas and methods for the research and development of high-performance phase change materials for power battery temperature control systems.