Ti-Mn基高容量固态低压储氢合金研究

Properties and Structure of Ti-Mn Based High-Capacity Solid Low Pressure Hydrogen Storage Alloys

为了推动氢储能系统的实用化,需要开展用于规模储氢用途的储氢合金的配方研究。以Ti_(0.9)5Zr_(0.05)Mn_(2)合金作为研究对象,开发储氢量高、平台压力合适且容易活化AB_(2)型储氢合金,系统研究加入V-Fe,调整Mn含量,以及用纯金属V与Fe替代V-Fe等方法对调整储氢合金性能的作用。研究发现加入V-Fe会使得储氢合金晶格参数增大,提高储氢合金的活化性能,但过多V-Fe会大幅度降低合金吸/放氢平台压与储氢量;提高Mn含量会导致吸/放氢平台与上升,储氢量先增后减,在A侧元素稍微过量时(B/A=1.96(摩尔比))有利于获得综合性能较好的合金;用纯金属V与Fe替代V-Fe能进一步提高储氢合金性能,随着Fe/V比例增加,合金储氢量下降,吸/放氢平台压上升,平台斜率下降。最终优化出综合性能良好的Ti_(0.9)5Zr_(0.05)Mn_(1.46)V_(0.39)Fe_(0.13),该合金能在80℃下活化,在20℃吸放氢平台分别为1.812和0.751 MPa,储氢量为1.83%。

In order to promote the practical application of hydrogen storage system,it is necessary to carry on research on large-scale application hydrogen storage alloys.Among the hydrogen storage alloy,Ti-Mn based AB_(2) type hydrogen storage alloy,with high hydro⁃gen storage capacity,adjustable platform pressure,and low raw materials price,is a suitable candidate for large-scale application of hydrogen storage materials.However,Ti-Mn based hydrogen storage alloy suffers from some questions:(1)harsh alloy activation con⁃ditions;(2)high platform pressure of hydrogen absorption/desorption;(3)high slope and hysteresis factor of hydrogen absorption/de⁃sorption platform.Element substitution is an effective method to improve the properties of Ti-Mn based hydrogen storage alloy.To de⁃velop Ti-Mn based hydrogen storage alloy for solid state hydrogen storage system,the effects of adding V-Fe,tuning Mn content and replacing V-Fe with pure metal V and Fe on the properties of hydrogen storage alloys Ti_(0.9)5Zr_(0.05)Mn_(2) were investigated systematically.The activation properties of Ti-Mn based hydrogen storage alloy could be tuned by adding V-Fe,while the platform pressure and plat⁃form features(slope and hysteresis)could be moderated by tuning Mn content,and replacing V-Fe with pure metal V and Fe.Ti-Mn based hydrogen storage alloys were synthesized by vacuum arc melting.Additionally,there was 4%more Mn in the raw materials to make up the loss during the melting.Before testing,the alloys were crushed by hammer to particles less than 150μm.The phases of the alloys were characterized by X-ray diffraction(XRD),while the lattice parameters were computed by Fundamental Parameters Ap⁃proach(TOPAS-5 Academic software).The hydrogen storage properties of alloy were characterized by the pressure-component-temper⁃ature(P-C-T)curves,which were tested by Sieverts type hydrogen storage material performance test system.Before P-C-T testing,al⁃loys were activated twice at the activation condition:vacuum at 80℃for 30 min,and then hydrogenation at 5 MPa H2 and 20℃.The results showed that after element substitution,alloys remained C14-typed Laves phase(P63/mmc;No.194),but the lattice parame⁃ters and hydrogen storage properties were different.By adding V-Fe,the lattice parameters of hydrogen storage alloys were increased and the activation properties of hydrogen storage alloys were improved.Ti_(0.9)5Zr_(0.05)Mn_(2) and Ti0.95Zr0.05Mn1.8(V-Fe)0.21 could not be activat⁃ed by vacuum at 250℃and then hydrogenation at 15 MPa H2 and 20℃,but Ti0.95Zr0.05Mn1.5(V-Fe)0.52 and Ti0.95Zr0.05Mn1.0(V-Fe)1.04 could be activated at the activation condition above.Hydrogen atom could rapidly diffuse en in V element,so the addition of V-Fe could effectively improve the activation properties of alloy.However,excessive addition of V-Fe dramatically reduced the hydrogen platform pressure and storage capacity.The hydrogen absorption platform pressure of Ti0.95Zr0.05Mn1.5(V-Fe)0.52 was 1.124 MPa,while that of Ti0.95Zr0.05Mn1.0(V-Fe)1.04 was only 0.11 MPa.A series of alloys with different Mn contents(Mn1.3~1.5)were prepared to study the role of Mn on the hydrogen storage properties.By increasing the content of Mn,the platform pressure of hydrogen absorption/desorp⁃tion increased,while the hydrogen storage capacity increased in the early stages and then decreased.According to the Local Environ⁃ment Model,there were three kinds of tetrahedral interstices in AB_(2) type hydrogen storage alloy:A2B2(large,number 12),AB3(mid⁃dle,number 4)and B4(small,number 1)tetrahedral interstice.When the alloy was hydrogenation,the large A2B2 tetrahedral inter⁃stices were occupied by hydrogen atom firstly and then AB3 tetrahedral interstices,while the small B4 tetrahedral interstices were hard⁃ly occupied by hydrogen atom.When there was a slight excess of elements in Site A(B/A=1.92 and 1.98(mole ratios)),some B4 tetra⁃hedral interstices were changed into AB3 tetrahedral interstices,and the hydrogen storage capacity was enhanced.Due to the larger atomic radius of Site A element(RTi=0.147 nm,RZr=0.160 nm,R being atomic redius),the excess Site A element leads to the larger lattice parameter of the alloy,resulting in the moderate platform pressure and low platform slope and hysteresis.Thus,Ti0.95Zr0.05Mn1.46(V-Fe)0.52 with 1.80%hydrogen storage capacity,and hydrogen desorption platform of 0.718 MPa,had the best comprehensive hydro⁃gen storage properties in this series alloys.Furthermore,it had the lowest scope factor of 0.754 in hydrogen desorption platform.By re⁃placing V-Fe alloy by pure metal V and Fe,the properties of hydrogen storage alloy were further improved.After the replacement of V and Fe,the hydrogen storage capacities were increased and the hydrogen absorption and desorption platforms reduced.As the Fe/V ra⁃tio increased,the hydrogen absorption and desorption platform pressures increased,while the maximum hydrogen capacity and the platform slope decreased.Among the alloys,Ti0.95Zr0.05Mn1.46V_(0.39)Fe_(0.13) with the highest hydrogen storage capacity of 1.83%hydrogen de⁃sorption platform of 0.751 MPa,and scope factor of 0.567 in hydrogen desorption platform,had the best comprehensive properties.In summary,the activation properties of alloy could be improved by adding V-Fe,and the platform pressure and platform features could be moderated by tuning Mn content.