An Investigation On The Structural And Electrochemical Properties Of The TiV-Based Hydrogen Storage Electrode Alloys

In this thesis, based on a comprehensive review of the research and development of the Ti-based C14-type Laves phase hydrogen storage electrode alloys, the V-based solid solution type hydrogen storage electrode alloys and the TiV-based hydrogen storage electrode alloys at home and abroad, the TiV-based hydrogen storage electrode alloys were selected and studied in order for optimizing the overall electrochemical properties. By means of XRD, SEM, PCT, XPS, AES and EIS analyses, the effect of elemental substitution, non-stoichiometry, annealing treatment and rapid solidification on the structural and electrochemical properties of the TiV-based hydrogen storage electrode alloys have been systematically studied. The electrochemical hydrogenation and dehydrogenation mechanism and the cycling degradation mechanism of the TiV-based hydrogen storage electrode alloys have also been studied.The study of Zr substitution for Ti on the structural and electrochemical properties of the Ti1-xZrxV1.6Mn0.32Cr0.48Ni0.6 (x = 0.2 ~ 0.5) alloys shows that all alloys are mainly composed of a C14-type Laves phase with hexagonal structure and a V-based solid solution phase with b.c.c. structure. The V-based solid solution phase is dispersed in the C14-type Laves phase in dendritic structure. With the increase of Zr substitution, the electrochemical PCT plateau pressure of the alloy is elevated, while the maximum hydrogen storage capacity [H/M]max is decreased. Electrochemical measurements show that with the increase of Zr substitution, the activation property, the maximum discharge capacity, the high rate dischargeability (HRD), the exchange current density I0, the limiting current density IL of the alloy and the hydrogen diffusion coefficient D in the alloy are all decreased, while the cycling stability and the electrochemical reaction resistance are increased.The structural and electrochemical properties of the non-stoichiometric TiV-based hydrogen storage electrode alloys (Ti0.8Zr0.2)(V0.533Mn0.107Cr0.16Ni0.2)x (x = 2 ~ 6) have been studied systematically. The results show that all alloys are mainly composed of a C14-type Laves phase with hexagonal structure and a V-based solid solution phase with b.c.c. structure. The V-based solid solution phase is dispersed in the C14-type Laves phase in dendritic structure. With increasing x, the content of the C14-type Laves phase in the alloy is decreased continuously, while the gaseous PCT plateau pressure of the alloy is elevated continuously, and the pressure plateau is flattened and broadened, leading to an increase of the effective hydrogen desorption capacity of the alloy. Moreover, the overall electrochemical properties of the alloy is improved greatly with increasing x, and the optimum composition is found to lie in x = 5, at which the maximum discharge capacity, the activation cycles, the capacity retention after 100 cycles, the HRD at the discharge current density 600 mA/g, the exchange current density I0, the limiting current density IL, of the alloy and the hydrogen diffusion coefficient D in the alloy are 379.8 mAh/g, 11, 69.4%, 57.2%, 161.4 mA/g, 1608.3 mA/g and 4.35xl0-11 cm2/s, respectively.The effect of annealing treatment on the (Ti0.8Zr0.2)(V0.533Mn0.107Cr0.16Ni0.2)4 alloy shows that both the as-cast and the annealed alloys are mainly composed of aC14-type Laves phase with hexagonal structure and a V-based solid solution phase with b.c.c. structure. The V-based solid solution phase is dispersed in the C14-type Laves phase in dendritic structure. The alloy composition is homogenized by annealing treatment. With the increase of annealing temperature or the prolongation of holding time, the V-based solid solution phase dendrites grow in size and thickness. The alloy annealed at 1273 K X8 h has the best overall electrochemical properties, of which the maximum discharge capacity, the activation cycles, the capacity decay rate in 100 cycles and the HRD at the discharge current density 600 mA/g are 411.9 mAh/gj 4, 1.66 mAh/g cycle and 66.3%, respectively. The effect o...