Electrochemical Performance And Surface Modification Of Ti-based Quasicrystal Alloys

Due to their super high amount of hydrogen storage, Ti-based quasicrystals attract extensive attentions. While compared to its hydrogen storage property, there are some problems seriously restricting their applications in electrochemical area such as difficult to be activated, a poor discharge performance at room temperature and a rapidly decreasing cycle life. Further study of the electrochemical active performance and the mechanism of capacity decline of Ti-based composite alloys still needed. Tthis paper is focused on the electrochemical hydrogen storage activity and the influence factors of Ti-based quasicrystals, and a series of surface modifications are carried out. The main contents and results as follows:Ti40.83Zr40.83Ni18.34 quasicrystals alloys are prepared by mechanical alloying and rapid cooling methods, respectively. The alloys prepared by rapid cooling have a better icosahedron quasicrystal structure. While the discharge capacity of the alloys is only 50 mAh g-1 at room temperature, even after treated with hot alkaline the situation is not changed. The alloys have poor electrochemical activity and there is a smooth oxide film on its surface. After ball milling into small size particles, the alloys are coated with graphene oxide films on their surface with a solvothermal method. During the treated processes, alcohol is selected as the dispersant agent in the ball milling which has an excellent protective capability in inhibiting the damage of alloy structural.Ti1.4V0.6Ni alloys are prepared by rapid cooling method, where there are still TiNi phase and amorphous phase besides the icosahedron quasicrystal phase. Different amounts of Cu are coated on the alloys with an electroless method by controlling the concentration of Cu2+ in the solution. After electrochemical measurements, two steps of dissolution of V are found out which are the main factors leading to the discharge capacity decline of the alloys. The first step is happened in the activation stage and the second step is the slow dissolution in the cycle process. The coating layer has an obviously inhibiting effect, and there is almost no extra dissolution of V in the second step when coated with 10 wt.% Cu. After 100 cycles, the capacity retention ratio of the coating alloys is 23% higher than the bare alloys, which indicates the surface oxidation and pulverization of the alloys are effectively inhibited.Different amounts of Ni are modified on the Ti1.4V0.6Ni alloys surface with a liquid phase reduction method by controlling the concentration of Ni2+ and the reactive conditions. After 100 cycles, the discharge capacity of the coating alloys is enhanced by 35%. The Ni layer is more stable than Cu layer which could effectively inhibit the formation of oxide film, alloys pulverization and V dissolution, for there is a synergistic protection effect of Ni layer and the Ni-rich layer on the surface.Different thicknesses of amorphous carbon film are prepared by PECVD on the Ti1.4V0.6Ni alloy electrode surface. The films are smooth and dense, which are composed of sp2 and sp3 hybrid carbon, as the thickness increase the sp3 content is increase. After electrochemical measurements, there is an obvious decline of the charge transfer resistance of the α-C film coating electrode, while a high sp3 carbon content will lead to a higher polarization voltage. The α-C film has a good effect on inhibiting the dissolution of V. The coating layer structure is still stable even after 100 cycles.Reduction graphene oxide film coated on the electrode surface is successfully achieved by a first electro-deposition of GO and subsequently reduction with HI vapor, the prepared coating layer is smooth and has few defects. The testing results show HI has a better reduction effect than the electrochemical reduction and no side reactions occur which would degrad the discharge property of alloys. The EIS and polarization voltage are reduced of the alloyes by the RGO coating. After 50 cycles, the discharge capacity of the coating electrode is 145 mAh g-1 and is 13.8% higher than the bare one.