Improved Electrochemical Hydrogen Storage Performance Of Ti-based Quasicrystal Alloy By Doping With Li And Composite Materials

Ti-based icosahedral quasicrystals have a high hydrogen storage capacity in theory due to their special structure,but their discharge capacity and cycle stability need to be further improved.In this dissertation,Ti-based quasicrystal composites are prepared by infiltrating lithium into quasicrystal voids,adding transition metal hydrides and substituting elements containing the Ti-V-Ni and Ti-Zr-Ni alloys with icosahedral quasicrystalline phase as main alloying materials.The electrochemical hydrogen storage properties of the samples are discussed,the main research contents and results are as follows:1.Ti₅₅V₁₀Ni₃₅ and Ti_1.4V_0.6Ni quasicrystal ribbons are synthesized by arc melting and quenching techniques,and then the lithium metal is infiltrated into the quasicrystal voids by molten salt electroosmosis method,reversible chemical reaction Li⁺+H^-??LiH can increase the reaction rate of hydrogen adsorption and desorption?charge transfer?.The current densities are 0.3 A/mg,0.6 A/mg and 0.9 A/mg,respectively.The maximum discharge capacities of Ti55V10Ni35-Li composite alloy electrodes are 257.7 mAh/g?0.3A/mg?,301.8 mAh/g?0.6 A/mg?and 238.7 mAh/g.?0.9 A/mg?,respectively,when the discharge current density is 30 mA/g.The maximum discharge capacities of Ti₅₅V₁₀Ni₃₅alloy electrode is 219.8 mAh/g.Thereby the optimum current density for lithium infiltration is determined to be 0.6 A/mg.It is also found that the maximum discharge capacities of Ti_1.4V_0.6Ni and Ti_1.4V_0.6Ni-Li?0.6 A/mg?are 276.8 mAh/g and 307.1 mAh/g at a current density of 30 mA/g.2.Molten salt electroosmosis can improve the electrochemical performance of quasicrystalline electrodes,but the experimental method is relatively complex.Because transition metal hydrides can play a catalytic and synergistic role in the electrochemical reaction process.Therefore,appropriate addition of TiH and ZrH2 to Ti1.4V0.6Ni quasicrystalline alloy is considered.In order to improve the properties of Ti_1.4V_0.6Ni quasicrystal alloy,appropriate amounts of TiH and ZrH₂ are added.The results show that the optimum addition amounts of TiH and ZrH₂ are 15 wt.%and 10 wt.%,respectively,and the composites exhibit good cycle stability and high rate of discharge capacity.The maximum discharge capacities of Ti_1.4V_0.6Ni and Ti_1.4V_0.6Ni+15wt.%TiH are 278.6mAh/g and 339.8 mAh/g,respectively,and the capacity retention rates of them after cycling30 times are75.6%and 86.7%,respectively.The high rate discharge capacity of them have increased from 75.0%to 85.6%.Similarly,the electrochemical performance of Ti1.4V0.6Ni+10 wt.%ZrH₂ composite alloy electrode has significantly improved compared with Ti_1.4V_0.6Ni alloy electrode without addition.3.Owing to the high hydrogen density in LiH,lithium atoms located in the interstices of the quasicrystal lattice can generate hydroxyl ions and deposit LiOH in the voids to prevent corrosion of alkali solution.The maximum discharge capacity of Ti₅₅V₁₀Ni₃₅ and Ti₅₅V₁₀Ni₃₅+6 wt.%LiHcomposite electrodes are 220.1 mAh/g and 292.3 mAh/g,and the capacity retention rates of them are 73.9%and 87.1%.The high rate discharge capacity of them have increased from 78.1%to 87.8%.The maximum discharge capacity of Ti_41.5Zr_41.5N_i17 and Ti_41.5Zr_41.5N_i17+10 wt.%LiH composite electrodes are 96.5 mAh/g and146.6 mAh/g,the high rate discharge capacity of them have increased from 62.7%to76.3%.4.Ti₄₉Zr₂₆Ni₂₅+a MWCNTs+b Pd?a+b=5%?composite alloying electrode exhibits excellent electrochemical activity owing to excellent electrocatalytic activity of Pd,large specific surface area and high conductivity of MWCNTs.Ti₄₉Zr₂₆Ni₂₅ quasicrystals are fabricated by mechanical alloying and annealing processes,the mixtures of different proportions of Pd and/or MWCNTs contents are added into alloy powders by ball milling.Appropriate addition of Fe in Ti-V-Ni alloy can reduce the cost,effectively improve the activation performance and the electrochemical discharge capacity.The electrochemical synergistic effect of Fe and V is better than that of pure V,and the oxide layer of Fe can protect V from corrosion to the greatest extent.