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Abstract: The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloys LaNi4.2−x Al0.35Mn0.45Si x (0≤ x ≤0.35) have been investigated with small amount of Si in replacement of Ni. With the increase of Si content, the maximum discharge capacity and the high rate discharge (HRD) ability gradually decrease, however the cycle stability is improved correspondingly. The lowest capacity decay rate can remain 19.4% (x =0.35) after 300 charge/discharge cycles. The lower corrosion current densities of the alloys with the addition of Si can explain the good cycle life for them. It is found that all of the alloys are single CaCu5 phase structure through XRD analysis. But some white dot-like LaNi3 phase separated out in the matrix only for the alloy x=0.35 through further EDX analysis. [Copyright &y& Elsevier]

Abstract: A new Cu coating technique is adopted for a Co-free alloy La(NiMnAlFe)5 to improve its electrochemical properties. Compared with unmodified alloy, the Cu-coated alloys show improved electrochemical performances. The activation number decreased from 19 to 3 cycles and discharge capacity increased from 282 to 307mAh/g. The optimal high rate discharge ability (HRD) is 25.4% (1200mA/g) for the sample with 5wt.% Cu. EIS reveals that decreased charge-transfer resistances and cyclic voltammograms show the higher anodic current peaks, which indicate the high electronic conductivity and electrochemical activity of alloys after Cu coating. The hydrogen diffusion coefficient increases accordingly and the cycle life is also improved. [Copyright &y& Elsevier]

Abstract: The alloy was modified with various metal oxides (, , , ZnO), and the effects of metal oxides addition on the electrochemical properties of the hydrogen storage alloy were investigated. The catalytic effects of metal oxides are found. Not only the discharge capacity but also the high-rate dischargeability (HRD) is improved by addition of 5wt% , , and ZnO, while the cyclic stability does not change except for addition of . The low-temperature property is enhanced more obviously by addition of , , and ZnO. The electrochemical kinetics is also measured by the linear polarization and electrochemical impedance spectroscopy (EIS). In addition, the hydrogen absorption kinetic behavior is measured by gas–solid reaction. [Copyright &y& Elsevier]

Abstract: The structure and electrochemical properties of a cobalt-free hydrogen storage electrode alloy LaNi4.05−x Al0.45Mn0.5Fe x (0≤ x ≤0.5) have been investigated with different additions of Fe in replacement of Ni. With the increase of Fe content the maximum discharge capacity gradually decreases from 334.8mAhg−1 to 292.8mAhg−1, however the cycle stability is improved correspondingly. The capacity decay can remain 28.6% (x =0.5) after 300 charge/discharge cycles. The high rate discharge (HRD) ability of the alloys (x ≤0.5) is improved with the increase of Fe content. It is found that all of the alloys are single CaCu5 phase structure disclosed by XRD pattern. However, small amount of the La2O3 phase, observed from SEM photographs, exists on the matrix of all the alloys and when x =0.5, some web-like LaNi2.28 phase is segregated out along the crystal boundary. [Copyright &y& Elsevier]

Abstract: The microstructural and electrochemical properties of La2.3−x Ca x Mg0.7Ni9 hydrogen storage alloys have been studied systematically. The microstructure examined by XRD, SEM and EDX shows that the alloys consist of multi-phases, which are (La, Mg)2Ni7 phase, LaMgNi4 phase, (La, Mg)Ni3 phase and LaNi5 phase. It is can be found that Ca does not appear to segregate. This phenomenon is different from Mg. With increasing Ca content, the main phase varies from (La, Mg)2Ni7 phase (x =0) to (La, Mg)Ni3 phase (x =0.3), LaNi5 phase (x =0.6, 0.8) and (La, Mg)Ni3 phase (x =1.0, 1.3). The maximum discharge capacities of the alloy electrodes increase from 244.6mAh/g (x =0) to 380mAh/g (x =1.0), and then decrease to 353.6mAh/g (x =1.3). The discharge capacities of the alloys are related to phase content. Cell volumes of LaNi5 phase, (La, Mg)2Ni7 phase and (La, Mg)Ni3 phase all decrease and the high rate dischargeability (HRD) is improved by adding Ca. The alloy electrodes also show relative good cycling stability up to 100 cycles. [Copyright &y& Elsevier]

Abstract: La1.3− x Sm x CaMg0.7Ni9 (x =0–0.3) hydrogen storage alloys were prepared by inductive melting and the effect of the Sm content on the structure and electrochemical properties was investigated in the paper. The Sm substitution for La in La1.3− x Sm x CaMg0.7Ni9 (x =0–0.3) alloys does not change the main phase structure (the rhombohedral PuNi3-type structure), but leads to a shrinkage of unit cell and a decrease of hydrogen storage capacity. With the increase of the Sm content in the alloys, the maximum discharge capacity of electrode decreases from 400.2 (x =0) to 346.6mAhg−1 (x =0.3), but the high-rate dischargeability and cycling stability is improved. After 100 cycles, the capacity retention rate increases from 75 (x =0) to 85% (x =0.3). [Copyright &y& Elsevier]

Abstract: A new low cobalt hydrogen storage electrode alloys La1− x Ca x Ni3.2Co0.3Al0.3 (0≤ x ≤0.4) was developed. The microstructure and electrochemical properties were investigated and the results showed that the prepared alloys were basically composed of LaNi5 as matrix phase and LaNi3 as second phase (x ≤0.1). The second phase LaNi3 is substituted by a new phase Al(NiCo)3 gradually with increasing Ca content, and cycle stability is improved correspondingly. The highest discharge capacity can reach to 295mAhg−1 (x =0.2) and it can remain 82.5% (x =0.2) after 300 charge/discharge cycles. [Copyright &y& Elsevier]

Abstract: Ml0.8Mg0.2Ni3.2Co0.6−x Al x (x=0–0.6) hydrogen storage alloys were prepared by induction melting and the effect of Al substitution for Co on the structure and hydrogen storage characteristics was investigated. These alloys are confirmed to be composed of LaNi5 as matrix and (LaMg)Ni3 as the secondary phase. The Al substitution leads to an expansion of the unit cell volume of matrix and an enhancement of the stability of the alloy hydrides. The thermodynamic properties such as ΔH and ΔS and the diffusion coefficient of hydrogen in these alloys were also evaluated. [Copyright &y& Elsevier]

Abstract: Ml1−x Mg x Ni2.4Co0.6 (x =0–0.6) hydrogen storage alloys were prepared by inductive melting and the effect of Mg on the crystal structure and hydrogen storage characteristics was investigated. These alloys are confirmed to be LaNi3 phase with the PuNi3 type structure. The Mg substitution for Ml in the alloys leads to a shrinkage of the unit cell volume and a reduction of the stability of alloy hydrides. With increasing the Mg substitution for Ml, the atom ratio of hydrogen to alloy (H/M) decreases, but the weight ratio of H/M and the discharge capacity of electrodes increase in a certain range of Mg content (x ≤0.4). The Ml0.6Mg0.4Ni2.4Co0.6 alloy has the highest weight ratio of H/M (1.75wt.%) at 1MPa H2 and 298K and the largest discharge capacity of electrodes (326mAhg−1). In addition, the increase of Mg substitution for Ml results in better high-rate dischargeability and cycling stability of electrodes. [Copyright &y& Elsevier]

Abstract: Two non-stoichiometric low-Co AB5 alloys, Ml0.95Mg0.05Ni3.8Co0.3Mn0.3Al0.4 (AB4.8) and Ml0.95Mg0.05Ni3.6Co0.3Mn0.3Al0.4 (AB4.6), were designed to reduce the cost of AB5 alloys. The maximum discharge capacities of the two low-Co alloys can reach 307mAh/g for AB4.8 alloy and 298mAh/g for AB4.6 alloy, respectively. After 300cycles, the capacity decay is 23% for AB4.8 alloy and 19.1% for AB4.6 alloy. XRD patterns and the microstructure, examined by optic microscope and SEM, show that both of the two low-Co alloys are composed of three phases, LaNi5 matrix phase, AlMnNi2 secondary phase and LaNi tertiary phase. For the two low-Co alloys, the microhardness (HV) of the secondary phase are only half of that of the matrix phase, which could resist the crack propagating and make the alloys not amenable to pulverization. The small amount of Mg promotes to form the soft secondary phase, which is believed to be the reason for improving the cycling stability. [Copyright &y& Elsevier]

A low-Co Ml0.8Mg0.2Ni3.2Co0.3Al0.3 alloy was prepared and investigated by examining the alloy structure, phase composition, hydrogen absorption/desorption and electrochemical properties. The alloy is composed of Mg-free LaNi5 phase as matrix and Mg-contained LaNi3 phase as secondary phase. The hydrogen storage capacity (1.37 wt%) at 298 K, discharge capacity (320 mA h/g) and cycling stability (where 88% of the initial capacity remained after 300 charge/discharge cycles) of the alloy are as good as those of the commercial MmNi3.55Co0.75Mn0.4Al0.3 alloy. However, the high-rate discharge ability is better than that of the commercial alloy. The Mn-free composition is advantageous to the oxidization-resistant performance of the alloy. The secondary phase is tougher than the matrix, which not only contributes to the high-rate discharge ability, but also improves the fracture ductility and depresses the disintegration during charge/discharge cycle. [Copyright &y& Elsevier]