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Abstract: Elemental substitution of part Ti by Zr has been carried out for Ti2Ni alloy to form Ti2−x Zr x Ni (x = 0, 0.2, 0.4) alloys. Mechanical milling and subsequent heat treatment have been used to prepare non-equilibrium Ti–Zr–Ni alloys. The effects of Zr addition on the structure and discharge properties of Ti2Ni alloy were investigated. The addition of Zr could enhance the discharge capacity of the non-equilibrium Ti2Ni alloy at electrolyte temperatures of 313 and 333 K. For instance, the non-equlibrium Ti1.6Zr0.4Ni alloy had a stable discharge capacity of about 210 mAh/g at 313 K. However, the protective surface layer formed during heat treatment was destroyed at a high electrolyte temperature of 333 K, and thus a severe capacity loss during cycling. [Copyright &y& Elsevier]

Abstract: The crystal structure and electrochemical properties of the La2MgMn0.3Ni8.7−x (Co0.5Al0.5) x (x = 0, 1.0, 2.0 and 3.0, at%) hydrogen storage alloys are investigated systematically. The results show that all the alloys consist of (La, Mg)Ni3 and LaNi5 phases, the cyclic stability S 60 increases from 61.2% (x = 0) to 78.7% (x = 3.0) after 60 charge/discharge cycles, and the peak high rate dischargeability (HRD) at the discharge current density of 1200 mA/g appears at the alloy of x = 2.0 with the value of 68.3%. Moreover, the electrochemical kinetic properties of the alloys are also improved at different extent with increasing x. All the results indicate that the substitution of Co and Al for Ni in AB3-type hydrogen storage alloys is effective to improving the overall electrochemical properties, and the optimum content is x = 2.0. [Copyright &y& Elsevier]

Abstract: The microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33−x Ca x Ni2.75Co0.25 (x = 0, 0.05, 0.10 and 0.15) alloys are investigated. The results show that all alloys mainly consist of (La, Mg)Ni3 and LaNi5 phases, besides a small amount of (La, Mg)2Ni7 phase. The cycle stability (S 80) after 80 charge/discharge cycles of all alloy electrodes first increases from 60.1% (x = 0) to 64.2% (x = 0.05), then decreases to 45.9% (x = 0.15). The high rate dischargeability of all alloy electrodes first increases from 52.6% (x = 0) to 61.4% (x = 0.10), then decreases to 57.2% (x = 0.15). Moreover, the charge-transfer resistance (R ct) first decreases from 168.2 mΩ (x = 0) to 125.7 mΩ (x = 0.10), then increases to 136.6 mΩ (x = 0.15). All the results indicate that the substitution of Mg with a certain amount of Ca can improve the overall electrochemical characteristics. [Copyright &y& Elsevier]

Abstract: The microstructure and electrochemical hydrogen storage characteristics of (La0.7Mg0.3)1−x Ce x Ni2.8Co0.5 (x =0, 0.05, 0.10, 0.15 and 0.20) alloys have been investigated. The results show that all alloys consist of (La, Mg)Ni3 and LaNi5 phases. The cyclic stability (S 100) of the alloy electrodes increases from 58.7% (x =0) to 69.8% (x =0.20) after 100 charge/discharge cycles. The high rate dischargeability (HRD) increases from 66.8% (x =0) to 69.6% (x =0.10), then decreases to 65.1% (x =0.20) at the discharge current density of 1200mA/g. Moreover, the electrochemical kinetic characteristics of the alloy electrodes are also improved by increasing Ce content. [Copyright &y& Elsevier]

Abstract: The AB5 alloy and Co powders have been mixed at various weight ratios to form AB5–Co composite electrodes. The discharge properties such as discharge capacity, discharge plateau, and cycling stability are investigated by charge and discharge testing using Arbin battery testing equipment. Synergistic effects in the composite electrodes contribute to significant improvements of the discharge behavior. For instance, the composite AB5–25%Co electrode shows a high discharge capacity of 395.1mAh/g, which is significantly higher than that of AB5 or Co electrode, and good cycling stability. The discharge process is also characterized by electrochemical impedance spectroscopy. Moreover, the electrochemical discharge mechanism is discussed. [Copyright &y& Elsevier]

Abstract: Charge and discharge testing, linear polarization, electrochemical impedance spectroscopy (EIS) and potential step chronoamperometry (PSCA) were used to investigate the electrochemical properties of the Ce-rich mischmetal MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy with different particle sizes. At a discharge current density of 900mA/g, the alloy with small original particle size maintained a high rate dischargeability (HRD) above 86% while the alloy with large particle size could not discharge in the same potential region. The alloy with small original particle size also showed lower contact resistances and polarization resistance after full activation. Both the exchange current density and the hydrogen diffusion coefficient increased when the hydrogen concentration decreased. The charge-transfer reaction on the surface of alloy particles with different sizes should be mainly responsible for the differences in electrochemical properties, especially the HRD. [Copyright &y& Elsevier]

Abstract: The effects of polycrystalline nickel and nanocrystalline nickel on the electrochemical properties of the MmNi3.8Co0.75Mn0.4Al0.2 hydrogen storage alloy with an emphasis on the influence of nanocrystalline nickel prepared by mechanical milling are investigated. The electrochemical properties such as the activation, plateau potential and discharge capacity are improved after the modification with the nanocrystalline nickel. The result of linear polarization measurement shows that the exchange current density increases and the polarization resistance decreases after the modification. The result of Tafel polarization measurement also demonstrates the same consequence, shows an increase of the limiting current density and an excellent ability of antioxidation or anticorrosion, and indicates an improvement of the kinetics of the hydrogen absorption/desorption after the modification. [Copyright &y& Elsevier]