Ti-Mn系储氢合金的研究进展OA北大核心CSTPCD

Hydrogen storage alloys are considered as the most promising solid-state hydrogen storage materials with reliable safety,outstanding hydrogenation/dehydrogenation rate and a large quantity of hydrogen storage capacity.Among the common Mg-based,rare-earth-based,Zr-based and Ti-based hydrogen storage alloys,Ti-based hydrogen storage alloys are rapidly developed due to their low cost and supreme hydrogen storage capacity at room temperature and smooth pressure.Note that the Ti-Mn based AB2-type hydrogen storage alloys(i.e.,A for Ti,Zr,rare metals and other hydride-forming elements,B for late transition metals and other non-hydride-forming elements)have a wide range of adjustable composition and a single Laves hydrogen-absorbing phase.The excellent thermodynamic properties of Ti-Mn alloy make it be an attractive hydrogen storage material,but difficult activation and high plateau pressure are still challenges for the large-scale application of Ti-Mn based hydrogen storage alloys. The optimization of the hydrogen storage properties of the materials is mainly achieved via compositional design of the elements,oxygen content control and achievement of the preparation process.The increase of cell volume brings more space for hydrogen to occupy with the increase of elements with larger atomic radii.Also,the interatomic force or bonding energy weakens,and the energy required for hydride decomposition reduces,which are conducive to the hydrogen absorption and desorption reaction of the material.For instance,an increase in the number of elements(e.g.,Zr)that bind hydrogen more intimately than Ti usually promotes the hydrogen absorption reaction.A small amount of Cr and V instead of Mn can lower the slope of the hydrogen absorption and release plateau and significantly reduce the reaction hysteresis.The phase transition of the metal hydride is restricted,and the plateau pressure is subsequently increased as the valence electron concentration is increased.On this basis,it is still necessary to strengthen the in-depth research on the oxygen control method of materials to improve the hydrogen absorption kinetics of materials.This is because the incubation period before the activation process or the initial hydrogen absorption process is usually caused by the oxide film on the metal surface.The surface oxide scale prevents hydrogen from squeezing into the interior of Ti-Mn based hydrogen storage alloys and reduces the hydrogen absorption kinetic performance of the materials.Also,the oxide scale dissolves at high temperatures,and some oxygen atoms are solidly dissolved into the crystal lattice of the alloy,which reduces the interstitial space available for H to occupy and the hydrogen storage capacity of the material.At present,the commonly used access of oxygen removal is to replace the oxygen in Ti using metals with a lower Gibbs free energy.In addition,unlike conventional methods such as arc melting to prepare Ti-based hydrogen storage alloys,a low-cost,high-performance preparation process is developed for the perspective of modulating the microstructure to provide channels for hydrogen transport.Finally,the application of Ti-Mn hydrogen storage alloys in the field of hydrogen storage tanks is elaborated.The addition of cooling materials inside and outside the tank,the expansion of the contact area between the cooling structure and the hydrogen storage alloys as well as the mixing of phase change material can provide a positive effect of mass and heat transfer for reactor and maintain the hydrogenation/dehydrogenation rate of the metal hydride reactants,which lays the foundation for the design of metal hydride reactors in the future. Summary and prospects Ti-Mn hydrogen storage alloys are practically applied in the field of compressed hydrogen storage due to their advantages of low cost,satisfying dynamics,high hydrogen storage capacity and cycling stability.It is necessary for the further development and application of Ti-Mn hydrogen storage alloys to specifically investigate the bonding of hydrogen atoms with metal atoms as well as the distribution of hydrogen atoms.However,it is difficult to utilize the micro-scale analysis of X-ray diffraction and transmission electron microscopy to achieve this goal.Therefore,some cutting-edge characterization tools,such as differential phase contrast(DPC)imaging,can be used to accurately characterize the positions of interstitial hydrogen atoms as well as the hydrogen binding energies at different positions,which is a key to understanding the hydrogen storage mechanism and chemical properties of metal hydrides.It should not be ignored that the cost issues also need to be considered in the application.At present,the commonly used methods are vacuum self-consuming electrode or induction melting followed by heat treatment to achieve the homogenization of the sample composition.Hence,there is an urgent need to further explore the methods for low-cost and large-scale preparation of Ti-Mn system hydrogen storage alloys in the future.