Research On Elements And Electrochemiscal Performances Of Nd-free AB₅-type Hydrogen Storage Alloys At -40℃

In this dissertation, the effects of A and B-side elements, non-stoichiometry on structures and electrochemical performances of Mm(NiCoMnAl)5 hydrogen storage alloys at -40℃ were studied, and the following results were obtained:1. The effects of A and B-side elements and non-stoichiometry on the discharge capacity of Mm(NiCoMnAl)5 hydrogen storage alloys at -40℃ were investigated systematically.1) For single-RE hydrogen storage alloys, the capacity of CeB₅ was far higher than that of LaB₅ and PrB₅; For binary-RE hydrogen storage alloys, the increase of Ce content is beneficial to improve the low-temperature discharge capacities of LaCeB₅ alloys. There is a maximum with the increase of Pr content in LaPrB₅ alloys. While the increase of Pr content is baneful to improve the low-temperature discharge capacity of CePrB₅ alloys. For ternary-RE hydrogen storage alloys designed uniformly, the increase of Ce content is beneficial to improve the low temperature discharge capacity in our work. Pr and Ce were further modified around the optimal, and a maximumal discharge capacity exists with the increase of Pr content, while the capacity reduces with the increase of Ce content.2) B-side elements in hydrogen storage alloys were designed uniformly. It was found that the increase of Co content is baneful to improve the low-temperature discharge capacity in our work. Co, Al and Mn were further modified around the optimal, and a minimal discharge capacity with the increase of Co content, while the capacities have increscent current with the increase of Al and Mn content.3) The low-temperature discharge capacities of AB5+X reduce with the increase of stoichiometry. And the low-temperature discharge capacities of AB5_X improve with the increase of stoichiometry.2. The factors, including exchange current density and diffusion coefficient, which evidently influence the low-temperature performances of hydrogen storage alloys, were analyzed.1) For single-RE hydrogen storage alloys, the diffusion coefficient of CeB5 is far higher than the others, and both of the exchange current density and diffusion coefficient of LaB5 is better than those of PrB5. The low-temperature discharge processes of LaCeBs, LaPrBs and ternary-RE hydrogen storage alloys designed uniformly are controlled by diffusion process. The low-temperature discharge capacity of LaPrBs shows positive correlation to the exchange current density to a degree. The low-temperature discharge process of CePrBs is controlled by both superficial electrochemical reaction and diffusion of hydrogen.2) B-side elements in hydrogen storage alloys were designed uniformly. It was found that the low-temperature discharge process is controlled by both superficial electrochemical reaction and diffusion of hydrogen. Co, Al and Mn were further modified around the optimal. The low-temperature discharge process of hydrogen storage alloys with different Co content is controlled by diffusion of hydrogen, while that of alloys with different Al or Mn content is controlled by superficial electrochemical reaction only.3) The low-temperature discharge process of both ABs.x and ABs+x hydrogen storage alloys is controlled by superficial electrochemical reaction.3. The mechanisms that the equilibrium pressure in the P-C-T curve is influenced by the low-temperature discharge process of hydrogen storage alloys were discussed.1) For single-RE hydrogen storage alloys, the diffusion coefficient shows positive correlation to the equilibrium pressure. The diffusion coefficient of LaCeB5shows positive correlation to the equilibrium pressure. While those of LaPrBs and CePrBs don't correlate to the equilibrium pressure. For ternary-RE hydrogen storage alloys designed uniformly, the diffusion coefficient shows positive correlation to the equilibrium pressure. Pr and Ce were further modified around the optimal, and the diffusion coefficient shows positive correlation to the equilibrium pressure with the increase of Pr content, while the diffusion coefficient doesn't correlate to the equilibrium pressure with the increase of Ce content.2) B-side elements in hydrogen storage alloys were designed uniformly. It was found that the diffusion coefficient doesn't correlate to the equilibrium pressure. Co, Al and Mn were furither modified around the optimal, and the diffusion coefficient of Co and Al content shows positive correlation to the equilibrium pressure, the diffusion coefficient of Mn content doesn't correlate to the equilibrium pressure.3) The diffusion coefficient of AB5+X hydrogen storage alloys doesn't correlate to the equilibrium pressure. The diffusion coefficient of ABs-* hydrogen storage alloys shows positive correlation to the equilibrium pressure.4. The structure of hydrogen storage alloys was tested, and the effect of the crystal lattice constants and the cell volume on the low-temperature electrochemical performances was investigated. The hydrogen storage alloys, except that the ABs_x hydrogen storage alloys have multiphase whose kind manifold with the reducing of stoichiometry, are all single-phase structure.1) For single-RE hydrogen storage alloys, the low-temperature exchange current density shows positive correlation to the the crystal lattice constant of c. The low-temperature diffusion coefficient of LaCeB5 shows positive correlation to that of c. The low-temperature exchange current density of LaPrB5 shows positive correlation to that of a. The low-temperature exchange current density and diffusion coefficient of CePrB5 do not correlate to the crystal lattice constants and the cell volume. For ternary-RE hydrogen storage alloys designed uniformly, the low-temperature diffusion coefficient shows positive correlation to the crystal lattice constant of c. Pr and Ce were further modified around the optimal, and thelow-temperature diffusion coefficient shows positive correlation to the cell volume and the exchange current density shows positive correlation to the crystal lattice constant of c with the increase of Pr. While the low-temperature diffusion coefficient and exchange current density do not correlate to the crystal lattice constants and the cell volume with the increase of Ce.2) B-side elements in hydrogen storage alloys were designed uniformly. It was found that the low-temperature diffusion coefficient shows positive correlation to the crystal lattice constant of c. Co, Al and Mn were further modified around the optimal, and the low-temperature diffusion coefficient and exchange current density do not correlate to the crystal lattice constants and the cell volume with the increase of Co, Al and Mn.3) The low-temperature exchange current density of AB5+X hydrogen storage alloys shows positive correlation to the cell volume, and the diffusion coefficient shows positive correlation to the crystal lattice constant of c. Both the low-temperature diffusion coefficient and the exchange current density of ABs* hydrogen storage alloys do not correlate to the crystal lattice constants and the cell volume.