Researches On The Application Of Carbon Nanotubes For Negative Material Of Ni/MH Battery

Since carbon nanotubes(CNTs) were discovered by Iijima in 1991, they have become a hotspot and frontier of carbon materials research and condensed state physics owing to unique structure with one-dimensional inner cavity in nano-size and high specific surface area. Because of these properties, it is very possible that CNTs are as a storage medium of hydrogen energy. Once it comes to be true, it is promising to develop a green battery with a brand-new idea and high performance.In this research, CNTs synthesized by catalytic decomposition were characterized by transmission electron microscopy(TEM) and X-ray diffraction(XRD). The hydrogen storage properties of CNTs were investigated by electrochemical methods including cyclic voltammetry(CV), chronopotentiometry(CP), A.C. impedance and Tafel plot. At the same time, the study on improving electrochemical performance of MmNi5 rare earth alloy as the negative material for nickel/metal hydride batteries by doped CNTs was carried.As the investigation on hydrogen storage properties of CNTs by cyclic voltammetry showed the current of oxidatoin and reduction peak increases with cycle number rising at beginning of scan, it was found that there is an activation process in electrochemical hydrogen storage. Furthermore, the potential of reduction peak of CNTs-Ni electrodes is very consilient with the nickel electrode, and relationship between the current of oxidation peak and scan rate is linear well. It was exhibited that the process of electrochemical hydrogen storage for CNTs-Ni electrodes takes place at nickel active site, and is controlled by the process of hydrogen adsorption and oxidation. According to the charging and the discharging curves, contribution of nickel powder to the capacity for electrochemical hydrogen storage is very limited, and nickel powder is chiefly as catalyst. Moreover, the capacity for electrochemical hydrogen storage increases as the number of cycles rises, and the biggest capacity is 575mAh/g. The results of self-discharge experiments showed that the cohesive force between hydrogen and CNTs was quite weak, so that hydrogen could escape from CNTs. It suggests that the mechanism of electrochemical hydrogen storage in CNTs is mainly physical adsorption.There is an activation process in electrochemical hydrogen storage for MmNi5 and CNTs-MmNi5 electrodes, too. However, hydrogen diffusion controls the process from...