Study On The Preparation And Electrochemical Properties Of Ti-Ai Hydrogen Storage Electrode Alloys

Based on the review of the research and development of hydrogen storage electrode alloys, Ti-Al hydrogen storage alloy was selected as the study object of this work due to its higher storage capacity than commercial rare earth hydrogen storage alloy. During this work, firstly Ti3Al1-xNix(x=0,0.1,0.2,0.3,0.4,0.45) alloys were prepared by levitation melting. Then amorphous electrode hydrogen storage alloys were prepared by ball-milling Ti3Al with certain amounts of Ni, Co or Fe powders. At last, in order to improve the electrochemical properties of the Ti3Al0.55Ni0.45alloy, amorphous alloy by balling it with certain amounts of Ni powder was prepared. By means of XRD, SEM analyses and the electrochemical test methods including the galvanostatic charge-discharge, EIS, linear polarization and anodic polarization, the microstructure and electrochemical properties of the prepared alloys were systematically studied. The study includes the following aspects:(1)the effects of Ni substitution for Al element on the phase structure and electrochemical properties of the as-cast Ti3Al1-xNix alloys;(2)the effects of Ni amounts and ball-milling time on the microstructure and electrochemical properties of the Ti3Al+x wt%Ni alloys, the influence of addition of Co or Fe on the microstructure and electrochemical properties of the ball-milled T13Al+200wt%M alloys;(3) the effects of Ni amounts and ball-milling time on the microstructure and electrochemical properties of the Ti3Al0.55Nio.45+x wt%Ni composite alloys, the influence of small addition of TiO2, MnO2on the microstructure and electrochemical properties of the Ti3Al0.55Ni0.45+200wt%Ni alloys.Firstly, the effects of Ni substitution for Al in the Ti3Al1-xNix alloys on the phase structure and electrochemical properties were studied. The results indicate that discharge capacity of the Ti3Al1-xNix alloys increases as Al is partially substituted by Ni and the maximum discharge capcity of the studied alloys reaches222mAh/g when x is0.45. Meanwhile, Ret of the alloys decreases and I0, IL increase with increasing Ni content. The minimum of Rct is1.156Ω. and the maximum of I0and IL are64.9and1090mA/g respectively. It is found that second phase Ti2Ni appears when Al is partially substituted by Ni. Ti2Ni phase has catalytic effect on the electrochemical charge/discharge properties of Ti3AI phase, and the grain boundaries of the two phases provide more diffusion channels for hydrogen. In a word, these two factors improve the discharge capacity and the dynamic performance of the alloys.Microstructure and electrochemical properties of ball-milled Ti3Al-Ni composite alloys were investigated. The results indicate that structure of Ti3Al will transform to amorphous state when Ti3Al is milled with Ni powder, while this transformation will not occur if Ti3Al is milled at the absence of Ni powder. Electrochemical tests show that the discharge capacity of nickel-free Ti3Al alloy is only100.7mAh/g. Maximum discharge capacity of Ti3Al+x wt%Ni alloys increases first and then decreases with increasing Ni content. The maximum discharge capacity of T13AI alloys with200wt%Ni content reaches476.7mAh/g. For the Ti3Al+200wt%Ni alloy, the maximum discharge capacity increases first and then decreases with increasing milling time. Ni addition promotes the crystalline-amorphous transformation of Ti-Al alloys and improves the electrochemical properties of Ti-Al alloys. In addition, the electrochemical properties of the alloys vary greatly with the Ni content and the milling time. After milling Ti3Al+200wt%Co/Fe for90h, the degree of amorphization is relatively low, the maximum discharge capacity and dynamic performance are lower than the milled Ti3Al+200wt%Ni alloy.Microstructure and electrochemical properties of ball-milled Ti3Alo.55Nio.45-Ni composite alloys were investigated. The results indicate that Ti3Alo.55Nio.45alloy still consists of Ti3Al and Ti2Ni phase when it is milled at the absence of Ni powder. The structure of Ti3Alo.55Nio.45transform to amorphous state when it is milled with Ni powder. Electrochemical tests show that discharge capacity of the alloys increases gradually with increasing Ni content and the maximum capacity reaches498.7mAh/g when the addition of Ni is250wt%. But when the content of Ni powder reaches250wt%, the discharge capacity declines faster and the alloy milled with200wt%Ni has the best cycling stability. The analysis of dynamic performance shows that the alloy milled with200wt%Ni has the best high-rate discharge ability, which indicates the alloy has the highest charge transfer reaction rate and H diffusion rate. When small amount of TiO2or MnO2powder is added for milling, the alloys after milling for90h still exist noticeable Ti3Al and Ti2Ni diffraction peaks, the amorphous transition doesn’t occur and the discharge capacity only raises a little.