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The cycling stability of low-Co hydrogen storage alloy was improved by rapid quenching. A low-Co hydrogen storage alloy with outstanding properties was obtained with a content of Co as low as 2.7 wt.%. It was first found that the quenching rate could affect the discharge capacity of the alloy: when the quenching rate was lower than 10 m/s, rapid quenching increased the discharge capacity and when the quenching rate was higher than 15 m/s, it significantly decreased the discharge capacity. In addition, the cycle life of the Mm(NiMnAl)4.9Co0.2 alloy could not be increased when the quenching rate was lower than 10 m/s, but instead, its cycle life was lowered to less than that of the as-cast alloy. The microstructures of the alloy were investigated by XRD and TEM in order to understand and explain these special properties. [Copyright &y& Elsevier]

The rapid quenching technology was used in the preparation of the MmNi3.8Co0.4Mn0.6Al0.2Bx (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were analysed and measured. The effects of boron additive on the microstructures and electrochemical properties of as-cast and quenched alloy MmNi3.8Co0.4Mn0.6Al0.2 were investigated. The experimental results showed that the microstructure of as-cast MmNi3.8Co0.4Mn0.6Al0.2Bx (x=0, 0.1, 0.2, 0.3, 0.4) alloy is composed of CaCu5-type main phase and a small amount of CeCo4B-type secondary phase. The abundance of the secondary phase increases with the increase of the boron content x. The secondary phase in the alloys disappears when quenching rate is larger than 22 m/s. The electrochemical measurement showed that the addition of boron slightly modifies the activation performance and dramatically enhances the cycle life of the alloys, whereas it reduces the capacities of the as-cast and quenched alloys. The influence of boron additive on the electrochemical characteristics of the as-quenched alloy is much stronger than that on the as-cast alloy. It is because boron strongly promotes the formation of the amorphous phase in the as-quenched alloy. [Copyright &y& Elsevier]

In order to improve the electrochemical characteristics of AB2 Laves phase electrode alloys, the rapid quenching technology was used in the preparation of AB2 type Ti- and Ti-Zr-based electrode alloys. The effects of the rapid quenching on the electrochemical characteristics and microstructures of AB2 Laves phase electrode alloys were investigated comprehensively. The experimental results showed that the effects of the rapid quenching on the electrochemical properties and microstructures of AB2 Laves phase electrode alloys were closely relevant with the compositions of the alloys. For Ti-based alloy, the capacity of the as-quenched alloy was enhanced obviously with the increase of the quenching rate, and a maximum capacity could be obtained at a certain quenching rate. The rapid quenching had little effect on the activation capability and improved the cycle stability slightly. For Ti-Zr-based alloy, the cycle stability was exalted significantly and the capacity and activation capability were reduced dramatically with the increase of the quenching rate. The main reason why the rapid quenching can modify the electrochemical performances of AB2 Laves phase electrode alloys was that it has obviously changed the microstructures of the alloys. [Copyright &y& Elsevier]

Abstract: The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10−x Cu x (x = 0, 1, 2, 3, 4) were synthesized by the melt spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that all the as-spun alloys hold typical nanocrystalline structure instead of an amorphous phase. The melt spinning does not modify the major phase Mg2Ni, but it leads to the formation of crystal defects such as stacking faults, dislocations, sub-grain boundary and twin-grain boundary. The melt spinning significantly improves the electrochemical hydrogen storage capacity of the alloys, whereas it slightly impairs the electrochemical cycle stability of the alloys. The substitution of Cu for Ni significantly ameliorates the electrochemical hydrogen storage performances of the alloys, involving both the electrochemical hydrogen storage capacity and the electrochemical charging and discharging stability. [Copyright &y& Elsevier]

Abstract: The electrode alloys La0.7Mg0.3Co0.45Ni2.55− x Fe x (x =0, 0.1, 0.2, 0.3, 0.4) are fabricated by casting and rapid quenching techniques. The effects of the substitution of Fe for Ni on the cycle stabilities as well as the structures of the alloys have been investigated thoroughly. The results indicate that the substitution of Fe for Ni significantly enhances the cycle stability of the alloys. Furthermore, the positive impact of such substitution on the cycle stability has been observed to be more pronounced for the as-quenched alloy as compared to that for the as-cast one. Scanning electron microscopy (SEM) studies demonstrate that all the alloys exhibit a multiphase structure comprising of two major phases (La, Mg)Ni3 and LaNi5 along with a residual phase of LaNi2. The substitution of Fe for Ni has been observed to facilitate the formation of a like amorphous structure in the as-quenched alloy. With an increase in Fe contents, a significant grain refinement of the as-quenched alloy and an obvious enlargement in the lattice constants and the cell volumes of the alloys have been noticed. [Copyright &y& Elsevier]

Abstract: In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr and the melt spinning technology was used for preparing La0.75−x Pr x Mg0.25Ni3.2Co0.2Al0.1 (x =0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performances of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The results of the electrochemical measurement indicate that the cycle stability of the alloy monotonously rises with increasing Pr content. When Pr content rises from 0 to 0.4, the capacity retaining rate after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for as-spun (20ms−1) alloy. The melt spinning significantly improves the cycle stability of the alloys. When the spinning rate grows from 0 (as-cast was defined as spinning rate of 0ms−1) to 20ms−1, the capacity retaining rate after 100 cycles increases from 65.32 to 73.97% for the (x =0) alloy, and from 79.36 to 93.08% for the (x =0.4) alloy. [Copyright &y& Elsevier]

Abstract: A2B7-type electrode alloys with nominal compositions of La0.75−x Pr x Mg0.25Ni3.2Co0.2Al0.1 (x =0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt-spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage characteristics of the as-cast and spun alloys were measured. The obtained results show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The discharge capacity of the alloys first increases and then decreases with variety of the spinning rate except the (x =0.4) alloy. The cycle stability of the alloy monotonously rises with increasing spinning rate. When spinning rate rises from 0 (as-cast was defined as spinning rate of 0m/s) to 20m/s, the discharge capacity increases from 389.4 (0m/s) to 393.5 (5m/s) and then drops to 374mAh/g (20m/s) for the (x =0) alloy, and it mounts up from 392.4 (0m/s) to 397.9 (5m/s), after that declines to 383.6mAh/g (20m/s) for the (x =0.1) alloy. The capacity retaining rate after 100 cycles increases from 65.32% to 73.97% for the (x =0) alloy, and from 73.65% to 86.91% for the (x =0.1) alloy. [Copyright &y& Elsevier]

Abstract: In order to improve the electrochemical performance of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr and melt spinning technology was used for preparing La0.75−x Pr x Mg0.25Ni3.2Co0.2Al0.1 (x =0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performance of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The results of the electrochemical measurement indicate that the discharge capacity of the alloys first increases and then decreases with variation of the Pr content. The cycle stability of the alloy monotonically rises with increasing Pr content. When the Pr content rises from 0 to 0.4, the discharge capacity increases from 389.4 (x =0) to 392.4 (x =0.1) and then drops to 383.7mAh/g (x =0.4) for the as-cast alloy. Discharge capacity increases from 393.5 (x =0) to 397.9 (x =0.1), and then declines to 382.5mAh/g for the as-spun (5m/s) alloys. The capacity remaining after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for the as-spun (20m/s) alloy. [Copyright &y& Elsevier]

Abstract: In order to improve the electrochemical cycle stability of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Zr and the melt-spinning technology was used for preparing La0.75−x Zr x Mg0.25Ni3.2Co0.2Al0.1 (x =0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM showed that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Zr for La leads to an obvious increase of the LaNi5 phase in the alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. The results of the electrochemical measurement indicated that the substitution of Zr for La obviously decreased the discharge capacity of the as-cast and quenched alloys, but it significantly improved their cycle stability. The discharge capacity of the alloys (x ≤0.1) first increased and then decreased with the variety of the quenching rate. The cycle stability of the alloys monotonously rose with increasing quenching rate. [Copyright &y& Elsevier]

Abstract: Nanocrystalline and amorphous Mg2Ni-type Mg20−x La x Ni10 (x =0, 2, 4, 6) electrode alloys were synthesized by the melt-spinning technique. The microstructures of the as-quenched ribbons were characterized by XRD, HRTEM and electron diffraction (ED). The electrode properties of these alloys were measured. The experimental results show that no amorphous phase forms in the as-quenched La-free alloy, but the as-quenched alloys containing La hold a major amorphous phase, confirming that the substitution of La for Mg significantly increases the glass forming ability of the Mg2Ni-type alloys. The discharge capacities of the as-cast alloys increase with rising La content, but those of the as-quenched alloys first increase and then decrease with the variety of La content. The largest discharge capacity reaches around 406.5mAh/g at a discharge current density of 20mA/g for the Mg18La2Ni10 sample quenched at 30m/s. The substitution of La for Mg significantly intensifies the cycle stability of the alloys. When La content grows from 0 to 6, the capacity retaining rate of the as-quenched (15m/s) alloy after 15 cycles rises from 37.18 to 94.93%, and from 35.29 to 95.99% for quenching rate of 30m/s, respectively. Rapid quenching engenders impactful effects on the electrochemical performances of the experimental alloys, involving the increased discharge capacity except x =6 and the strengthened cycle stability, which means that the improvement of electrochemical performances is not only a function of the sample composition but also strongly influenced by the proportion of the nanocrystalline and amorphous phase in the alloys. [Copyright &y& Elsevier]

Abstract: The La–Mg–Ni system PuNi3-type La0.5Ce0.2Mg0.3Co0.4Ni2.6−x Mn x (x =0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and quenching. Ni in the alloy was partially substituted by Mn in order to improve the electrochemical characteristics of the alloys. The effects of the substitution of Mn for Ni and rapid quenching on the structures and electrochemical characteristics of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the alloys have multiphase structures which are composed of two major phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi. The substitution of Mn for Ni leads to an obvious increase of the LaNi5 phase and an decrease of the (La, Mg)Ni3 in the alloys. The electrochemical measurements indicate that the discharge capacities of the as-cast and quenched alloys first increase and then decrease with growing Mn content. The substitution of Mn for Ni clearly improves the high rate discharge abilities (HRDs) and the activation capabilities of the as-cast and quenched alloys, but it slightly impairs the cycle stabilities of the alloys. The rapid quenching significantly improves the cycle stabilities of the alloys, and the discharge capacities and HRDs of the alloys have the maximum values with the variety of the quenching rate. [Copyright &y& Elsevier]

Abstract: Mg2−x Zr x Ni (x =0, 0.15, 0.3, 0.45 and 0.6) electrode alloys were prepared by mechanical alloying (MA). The effects of substituting Mg with Zr on the microstructures and electrochemical performance of the MA alloys were investigated in detail. The results obtained by XRD and TEM show that the substitution of Zr for Mg is favorable for the formation of an amorphous phase. For a fixed milling time, the amorphous phase in the alloy increases with increasing Zr content. The electrochemical measurements indicate that the substitution of Zr can dramatically enhance the discharge capacity with preferable cycle stability, and markedly improve the discharge voltage characteristics of the alloys. The fact that Zr promotes the formation of an amorphous phase is mainly responsible for these effects. [Copyright &y& Elsevier]

Abstract: The effects of the substitution of Mn for Ni on the structures and electrochemical characteristics of the as-cast and quenched (, 0.1, 0.2, 0.3, 0.4) alloys were studied systematically. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases the and and a residual phase LaNi. With increasing Mn content in the alloys, the abundance of the phase decreases and that of the phase increases and both the lattice parameters and the cell volumes of major phases and increase. The as-quenched alloys display a nanocrystalline structure, and the grain sizes of the alloys are in a range of 20–30nm. The results by the electrochemical measurements indicate that the discharge capacities of the as-cast and quenched alloys first increase and then decrease with the variety of Mn content and obtain the maximum values for a Mn content of . The substitution of Mn for Ni clearly improves the high rate discharge abilities (HRDs) and the activation capabilities of the as-cast and quenched alloys, but it slightly impairs the cycle stabilities of the as-cast and quenched alloys. [Copyright &y& Elsevier]

Abstract: The La–Mg–Ni system -type hydrogen storage alloys (, 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. Ni in the alloy was partially substituted by Fe in order to improve the cycle stability of the alloys. The effects of the substitution of Fe for Ni combining rapid quenching on the microstructures and electrochemical performances of the as-cast and -quenched alloys were investigated in detail. The results indicate that the substitution of Fe for Ni obviously decreases the discharge capacity and high rate discharge (HRD) capability as well as the discharge potential of the as-cast and -quenched alloys, but it significantly improves their cycle stabilities. The microstructure of the alloys analyzed by XRD, SEM and TEM shows that the as-cast and -quenched alloys have a multiphase structure which is composed of two major phases (La, Mg) and as well as a residual phase . The substitution of Fe for Ni leads to an obvious increase in the phase in the as-cast alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously enlarge. [Copyright &y& Elsevier]

The electrode alloys were prepared by mechanical alloying (MA). Mg in the alloy was partially substituted with Zr in order to improve the electrochemical characteristics of the -type alloy. The microstructures and the electrochemical characteristics of the experimental alloys were measured systemically. The effects of substituting Mg with Zr as well as the relevant MA technique on the microstructures and electrochemical performances of the alloys were investigated in detail. The results show that the substitution of Zr is favourable for the formation of an amorphous phase. The electrochemical measurement indicated that the substitution of Zr can dramatically enhance the discharge capacity and cycle stability, and it markedly improves the discharge voltage characteristic of the alloys. For a fixed alloy, the electrochemical performances, including the cycle stability, the discharge voltage characteristic and discharge capacity, of the alloys were significantly improved with the increase of the ball-milling duration. [Copyright &y& Elsevier]

Abstract: In order to improve the cycle stability of La–Mg–Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Cu, Cr and Al, respectively. La–Mg–Ni system hydrogen storage electrode alloys La0.7Mg0.3Ni2.55−x Co0.45M x (M=Cu, Cr, Al; x =0, 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. The microstructures of the as-cast and quenched alloys were systematically determined by XRD, SEM and TEM. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni3 phase and the LaNi5 phase as well as the LaNi2 phase. The element substitution and rapid quenching have an inappreciable influence on the phase composition of the alloys, but both change the phase abundance of the alloys obviously. The results obtained by the electrochemical measurement indicated that the substitution decreased the discharge capacities of the as-cast and quenched alloys, whereas it improved the cycle stability, and the effect of three kinds of substitution elements on the cycle life of the alloys increased in the sequence Al>Cr>Cu. The rapid quenching significantly enhanced the cycle stability of the alloys, but it notably decreased the discharge capacity of the alloys. [Copyright &y& Elsevier]

Abstract: In order to enhance the electrochemical capacity of the Co-free AB5-type electrode alloy, Mm in the alloys was substituted with La and Co-free LaxMm1-x(NiMnSiAlFe)4.9 (x = 0, 0.45, 0.75, 1.0) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of the substituting Mm with La on the electrochemical performances of the as-cast and quenched alloys were investigated in detail. The obtained results show that substituting Mm with La can enhance markedly the capacities of the as-cast and quenched alloys. When the amount of substituting Mm with La, x increased from 0 to 1.0, the maximum capacity of the as-cast alloys at 0.2C rate increased from 273.45 to 304.47mAhg-1, and the capacity retaining rate (Rh) increased from 59.16 to 59.86%. The capacity of the as-quenched alloys with a quenching rate of 10ms-1 increased from 236.83 to 300.31mAhg-1, and the capacity retaining rate (Rh) decreased from 78.69 to 62.29%. The substituting Mm with La had an insignificant effect on the activation capabilities of the as-cast and quenched alloys. [Copyright &y& Elsevier]

In order to modify the electrochemical characteristics of low-Co AB5-type electrode alloy, the low-Co AB5-type Mm(NiCoMnAl)5Bx (x=0, 0.1, 0.2, 0.3, 0.4) electrode alloys were quenched by melt-spinning. The phase structure and microstructure morphologies of the as-cast and quenched alloys were analysed and examined by XRD and SEM. The effects of rapid quenching on the microstructures and the electrochemical characteristics of low-Co AB5-type electrode alloys were investigated in detail. The obtained results showed that the as-quenched alloys have an excellent activation performance and can be activated through 2–5 charge–discharge cycles. Rapid quenching can enhance the discharge capacity of the alloys in a certain range of quenching rate. The discharge capacity of the as-quenched alloy was lower than that of the as-cast alloy when the quenching rate is higher than some critical value. The critical quenching rate depends on the compositions of the alloys. The cycle life of the alloys monotonously increased with increasing of quenching rate. [Copyright &y& Elsevier]