Hydrogen storage properties of Ti1.4V0.6Ni + x Mg (x = 1–3, wt.%) alloys

We prepared Ti_1.4V_0.6Ni ribbons by arc-melting and subsequent melt-spinning techniques. Ti_1.4V_0.6Ni + x Mg (x = 1, 1.5, 2, 2.5 and 3, wt.%) composite alloys were obtained by the mechanical ball-milling method. The structures and hydrogen storage properties of alloys were investigated. Ti_1.4V_0.6Ni + x Mg composite alloys contained icosahedral quasicrystalline phase, Ti₂Ni-type phase, β-Ti solid-solution phase and metallic Mg. The electrochemical and gaseous hydrogen storage properties of alloys were improved with Mg addition. Ti_1.4V_0.6Ni + 2 Mg alloy showed maximum electrochemical discharge capacity of 282.5 mAh g⁻¹ as well as copacetic high-rate discharge ability of 82.3% at the discharge current density of 240 mA g⁻¹ compared with that of 30 mA g⁻¹, and the cycling life achieved above 200 mAh g⁻¹ after 50 consecutive cycles of charging and discharging. The hydrogen absorption/desorption properties of Ti_1.4V_0.6Ni + x Mg (x = 1, 2 and 3, wt.%) alloys were better than Ti_1.4V_0.6Ni. Ti_1.4V_0.6Ni + 3 Mg alloy also exhibited a favorable hydrogen absorption capacity of 1.53 wt.%. The improvement in the hydrogen storage characteristics caused by adding Mg may be ascribed to better hydrogen diffusion and anti-corrosion ability.     

Microstructure and hydrogen storage properties of Ti10V84−xFe6Zrx (x = 1–8) alloys

Ti₁₀V_84−xFe₆Zr_x (x = 1, 2, 4, 6, 8) hydrogen storage alloys were prepared by induction melting with magnetic levitation, and the effects of Zr content on the microstructures and hydrogen storage properties have been investigated systematically. The results show that the alloy with x = 1 has a single V-based solid solution phase with BCC structure, while other alloys with x = 2–8 consist of a BCC main phase and a C14 type Laves secondary phase, and the abundance ratio of the secondary phase increases with increasing Zr content. As the Zr content in the alloy increases, the activation behavior is improved, but the hydrogen absorption and desorption capacities decrease gradually. For the alloy with the Zr content of x = 1, the best overall hydrogen storage properties are obtained.     

Kinetic properties of La2Mg17–x wt.% Ni (x = 0–200) hydrogen storage alloys prepared by ball milling

The as-cast La₂Mg₁₇ with different amount of Ni powders were mixed through ball milling to produce a new type of La₂Mg₁₇–x wt.% Ni (x = 50, 100, 150, 200) alloy. The microstructures of the alloys were characterized by XRD technique, the results show that the crystal structure transfers to amorphous one with the increasing amount of Ni powders. La₂Mg₁₇–50 wt.% Ni alloy reaches the highest hydrogen absorption capacity of 5.13 wt.% at 300 °C under 2 MPa hydrogen pressure due to its amorphous structure. Furthermore, La₂Mg₁₇–50 wt.% Ni alloy expresses fast hydriding kinetics and absorbs 4.99 wt.% hydrogen gas in 200 s. The hydrogen desorption ability described as discharge capacity during electrochemical reaction is fade next to La₂Mg₁₇–200 wt.% Ni alloy, attributed to the less Mg₂NiH₄ with lower enthalpies and easier to release H₂. The maximum discharge capacity of La₂Mg₁₇–200 wt.% Ni alloy reaches to exciting 980.90 mAh/g, while the La₂Mg₁₇ alloy is only 18.10 mAh/g with inconspicuous improvement of cycle stability. These dramatic difference in electrochemical performance reflect the consequence of sluggish dehydriding process of La₂Mg₁₇–50 and 100 wt.% Ni alloys again. Whereas La₂Mg₁₇–200 wt.% Ni alloy has lower resistance both on alloy surface and in the bulk.     

Effects of B addition on the hydrogen absorption–desorption property of Ti0.32Cr0.43V0.25 alloy

The effects of boron addition on the hydrogen absorption–desorption properties of the _{Ti0.32Cr0.43V0.25}${\mathrm{Ti}}_{0.32}{\mathrm{Cr}}_{0.43}{\mathrm{V}}_{0.25}$ alloy were studied. Boron was added either directly or indirectly through a mother alloy _Ti0.75B0.25${\mathrm{Ti}}_{0.75}{\mathrm{B}}_{0.25}$. Direct boron addition caused the decrease in the titanium content of the BCC matrix through formation of Ti–B phases, resulting in the decrease in the lattice constant. Conversely, mother alloy addition increased the titanium content and the lattice constant of the matrix, for it contained enough titanium to contribute to the matrix even after forming the second phase TiB. Such lattice constant changes caused by boron addition resulted in drastic changes in hydrogen plateau pressure and great decrease in effective hydrogen storage capacity.     

Microstructure and hydrogen storage characteristics of nanocrystalline Mg + x wt% LaMg2Ni (x = 0–30) composites

The nanocrystalline Mg + x wt% LaMg₂Ni (x = 0, 5, 10, 20, 30) composites were prepared by reactive ball-milling, their microstructure and hydrogen storage characteristics were investigated. The results show that the addition of LaMg₂Ni improves the hydriding rate and capacity. The hydriding capacity of the Mg + x wt% LaMg₂Ni (x = 5, 10, 20, 30) composites are all above 4.1 wt% at 120 °C and above 4.3 wt% at 180 °C within 6000 s. Moreover, the addition of LaMg₂Ni also improves the dehydriding performance of the composites. The main reason for the improvement of hydriding/dehydriding properties investigated by XRD and SEM shows that the synergistic effect among the multiphase nanocrystalline Mg-based structures make hydrogen easily absorbed/desorbed on the interface of the matrix.     

Influence of Fe content on the microstructure and hydrogen storage properties of Ti16Zr5Cr22V57−xFex (x = 2–8) alloys

The influence of Fe content on the microstructure and hydrogen storage properties of Ti₁₆Zr₅Cr₂₂V_57−xFe_x (x = 2–8) alloys was investigated systematically. The results show that all alloys consist of a BCC main phase and a small amount of C14 Laves secondary phase. The crystal lattice parameters of the BCC main phase in the alloys decrease with the increase of the Fe content. Under moderate conditions, all the alloys have good activation behaviors and hydriding/dehydriding kinetics. As the x increases, the hydrogen desorption plateau pressure of the alloys increases consequently. Among the studied alloys, Ti₁₆Zr₅Cr₂₂V₅₅Fe₂ alloy has suitable hydrogen desorption plateau pressures indicated by the middle value of pressure range. (0.1–1 MPa) at 298 K and the best overall hydrogen storage properties.     

Effects of addition of manganese and LmNi4.1Al0.25Mn0.3Co0.65 alloy on electrochemical characteristics of Ti0.32Cr0.43−xMnxV0.25 (x = 0–0.08) alloys as anode materials for nickel–metal-hydride batteries

This study examines the effects of the addition of Mn and LmNi_4.1Al_0.25Mn_0.3Co_0.65 (Lm: lanthanum-rich mischmetal) alloy on the electrochemical characteristics of body centered cubic (BCC) type Ti_0.32Cr_0.43−xMn_xV_0.25 (x = 0–0.08) alloys as negative electrode (anode) materials for nickel–metal-hydride (Ni-MH) batteries. The activation behaviour and discharge capacity of the BCC alloys are improved significantly by ball-milling with LmNi_4.1Al_0.25Mn_0.3Co_0.65 alloy because this AB₅ alloy acts as a path for hydrogen on the surface of the BCC alloy. Among the Mn-substituted alloys, a Ti_0.32Cr_0.38Mn_0.05V_0.25 alloy ball-milled with the AB₅ alloy yields the greatest discharge capacity of 340 mAh g⁻¹. In addition, compared with the alloy without Mn, the Mn-substituted alloys exhibit a lower plateau pressure for hydrogen, a better hydrogen-storage capacity in the pressure–composition isotherms and faster surface activation.     

Structure and electrochemical properties of (La1−xDyx)0.8Mg0.2Ni3.4Al0.1 (x = 0.0–0.20) hydrogen storage alloys

The structure and electrochemical characteristics of (La_1−xDy_x)_0.8Mg_0.2Ni_3.4Al_0.1 (x = 0–0.20) hydrogen storage alloys have been investigated. Dysprosium was adopted as a partial substitution element for lanthanum in order to improve electrochemical properties. The XRD, SEM and EDX results showed that the alloys were composed of (La, Mg)₂Ni₇, LaNi₅ and (La, Mg)Ni₂ phases. The introduction of Dy promoted the formation of (La, Mg)₂Ni₇ phase which possesses high hydrogen storage capacity, and controlling dysprosium content at 0.05 can obtain the maximum (La, Mg)₂Ni₇ phase abundance in the alloys. The maximum discharge capacity was heightened from 382.5 to 390.2 mAh/g, which was ascribed to (La, Mg)₂Ni₇ phase abundance increasing from 54.8% to a maximum (60.5%). Also, the biggest discharge capacity retention remained 82.7% after 100 cycles at discharge current density of 300 mA/g.     

An investigation on electrochemical and gaseous hydrogen storage performances of as-cast La1−xPrxMgNi3.6Co0.4 (x = 0–0.4) alloys

The as-cast RE–Mg–Ni-based AB₂-type La_1−xPr_xMgNi_3.6Co_0.4 (x = 0–0.4) alloys were prepared by vacuum induction furnace with a high purity helium gas as the protective atmosphere. The phase composition and microstructure of the as-cast alloys were characterized by XRD, SEM equipped with EDS. The results indicate that the as-cast alloys consist of two phases of LaMgNi₄ and LaNi₅. The measurements of the electrochemical properties show that the discharge capacity of the alloys slightly decreases with Pr content rising. As the Pr content grows from 0 to 0.4, the maximum discharge capacity decreases from 347.0 to 310.4 mAh/g. However, the cycle stability and the high-rate dischargeability of the alloy obviously augment with the Pr content increasing. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the limiting current density (I_L) first increases then decreases whereas the exchange current density I₀ of the alloys first decreases then increases with the rising amount of Pr substitution, which indicates that the electrochemical dynamic of the alloy electrode are jointly dominated by the charge-transfer resistance and diffusion ability of hydrogen atoms. The measuring of the gaseous hydrogen storage reveals two pressure plateaus appear on each pressure–concentration–isotherm (P–C–T) curve of the as-cast alloys, which correspond to the LaMgNi₄ and LaNi₅ phases. Furthermore, we note that the pressure plateau of the P–C–T curve visibly rises with Pr content increasing.     

Microstructures and electrochemical hydrogen storage performances of La0.75Ce0.25Ni3.80Mn0.90Cu0.30(V0.81Fe0.19)x (x = 0–0.20) alloys

Electrochemical hydrogen storage performances of a La_0.75Ce_0.25Ni_3.80Mn_0.90Cu_0.30 alloy are improved by adding V_0.81Fe_0.19 combined with hyper-stoichiometry, and microstructures and electrochemical characteristics of La_0.75Ce_0.25Ni_3.80Mn_0.90Cu_0.30(V_0.81Fe_0.19)_x (x = 0–0.20) hydrogen storage alloys are investigated. X-ray diffraction and backscattered electron results indicate that all alloys are a LaNi₅ phase with a hexagonal CaCu₅-type structure and the lattice parameters a, c and cell volume V of the LaNi₅ phase decrease with increasing x value. The alloy electrodes keep excellent activation performance with increasing V_0.81Fe_0.19 content. Maximum discharge capacity of alloy electrodes first increases from 330.2 (x = 0) to 335.4 (x = 0.10) mAh/g, and then decreases to 328.8 mAh/g (x = 0.20) with further increasing x value. The high-rate dischargeability at the discharge current density of 1200 mA/g first increases from 67.2% (x = 0) to 76.7% (x = 0.10), and then decreases to 65.3% (x = 0.20). The cycling capacity retention rate at the 100th cycle increases from 52.3% (x = 0) to 77.9% (x = 0.20), which is mainly ascribed to the improvement of anti-pulverization.     

The structure and 233 K electrochemical properties of La0.8−xNdxMg0.2Ni3.1Co0.25Al0.15 (x = 0.0–0.4) hydrogen storage alloys

The effect of neodymium content on the structure and low-temperature (233 K) electrochemical properties of the La_0.8−xNd_xMg_0.2Ni_3.1Co_0.25Al_0.15 (x = 0.0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys was investigated systematically. The result of the Rietveld analyses suggested that all these alloys mainly consist of two phases: the (La, Mg)₂Ni₇ phase and the LaNi₅ phase. The electrochemical studies revealed that, at temperature 233 K, the maximum discharge capacity first increased from 188.5 mAh/g (x = 0.0) to 201.7 mAh/g (x = 0.1) and then decreased to 153.9 mAh/g (x = 0.4). The low-temperature dischargeability (LTD) first increased and then decreased with increasing x, also reaching an extreme when x was 0.10. The LTD was in agreement with the I₀, but was irrespective of the diffusion of hydrogen. From our work, the optimum composition of the La_0.8−xNd_xMg_0.2Ni_3.1Co_0.25Al_0.15 (x = 0.0–0.4) alloy electrodes was found to be x = 0.10.     

Influence of the substitution of La for Mg on the microstructure and hydrogen storage characteristics of Mg20−xLaxNi10 (x = 0–6) alloys

In order to enhance the glass forming ability of the Mg₂Ni-type hydrogen storage alloy, the Mg in the alloy was partially substituted by La. The alloys Mg_20−xLa_xNi₁₀ (x = 0, 2, 4, 6) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and the quenched alloys were studied by XRD, SEM and HRTEM. It was found that no amorphous phase was formed in the as-quenched La-free alloy. But the as-quenched alloys containing La held a major amorphous phase, confirming that the substitution of La for Mg significantly enhances the glass forming ability of the alloys. When La content x ≤ 2, the major phase in the as-cast alloys is Mg₂Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni₃ + LaMg₃ phase. Thermal stability of the as-quenched alloys was studied by DSC, showing that La content engenders a negligible influence on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and the quenched alloys were measured by an automatically controlled Sieverts apparatus. The results showed that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly rise with increasing La content. For La content x = 2, the as-quenched alloy displays an optimal hydrogen desorption kinetics at 200 °C. The electrochemical measurement showed that the discharge capacities of the as-cast alloys rose with the increase of La content, but those of the as-quenched alloys obtained the maximum values with the variation of La content. The cycle stability of the as-cast and the quenched alloys significantly improved with increasing La content.     

Structures and electrochemical hydrogen storage behaviours of La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0–0.4) alloys prepared by melt spinning

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 La_0.75−xPr_xMg_0.25Ni_3.2Co_0.2Al_0.1 (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 383.7 mAh/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 382.5 mAh/g for the as-spun (5 m/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 (20 m/s) alloy.     

The structure and high-temperature (333 K) electrochemical performance of La0.8−xCexMg0.2Ni3.5 (x = 0.00–0.20) hydrogen storage alloys

The microstructures and electrochemical properties of La_0.8−xCe_xMg_0.2Ni_3.5 (x = 0.00–0.20) hydrogen storage alloys are investigated systematically. XRD and Rietveld analyses indicate that all these alloys mainly consist of two phases: (La, Mg)₂Ni₇ phase with the hexagonal Ce₂Ni₇-type structure and LaNi₅ phase with the hexagonal CaCu₅-type structure. The lattice parameters of the component phases gradually decreased with increasing Ce content. It is concluded that, compared to that of room temperature (298 K), the deterioration in capacity is due to the enhanced corrosion of electrode active material and self-discharge at 333 K. The electrode corrosion was alleviated effectively with the increasing x, whereas the high-temperature dischargeability decreases from 92.7% (x = 0.00) to 80.5% (x = 0.20) accordingly. As the discharge current density is 1000 mA g⁻¹, the high-rate dischargeability (HRD) increases from 77.2% (x = 0.00) to 89.7% (x = 0.10) and then decreases to 73.5% (x = 0.20).     

The morphology and electrochemical properties of La1-xMgxNi3.4Al0.1 (x = 0.1–0.4) hydrogen storage alloys

In view of the importance of Mg in R-Mg-Ni-type alloys (R generally represents rare earth elements), the effect of Mg on the morphology and electrochemical performance of the as-cast La_1-xMg_xNi_3.4Al_0.1 (x = 0.1, 0.2, 0.3 and 0.4) hydrogen storage alloys were studied in this work. The samples possess multiphase structures, including Gd₂Co₇-, Ce₂Ni₇-, Pr₅Co₁₉-and CaCu₅-type, PuNi₃-and MgCu₄Sn-type phases. It is found that reasonably increasing Mg contents can promote the formation of Gd₂Co₇-and Ce₂Ni₇-type phase as well as Mg contents have important effects on phase morphology. Furthermore, fine-dispersed LaNi₅ structure in (La, Mg)₂Ni₇ matrix is beneficial to facilitate the hydrogen diffusion and exert the electrochemical properties for the alloys.The EIS results indicate that the charge transfer resistance decreases nonlinearly with increase of (La, Mg)₂Ni₇ phase content and presents approximately linear relationship with LaNi₅ phase content. When x equals to 0.2, the alloy displays more optimal comprehensive electrochemical properties, i.e. the discharge capacity reaches 357.4 mA/g, the high rate dischargeability at 1200 mA/g 60.1% and the cycling performance 74.5%.     

Microstructure and hydrogen storage properties of Zr0.8Ti0.2Co1−xFex (x=0, 0.1, 0.2, 0.3) alloys

In the present study, Zr_0.8Ti_0.2Co_1?xFe_x (x = 0, 0.1, 0.2 and 0.3) alloys were prepared by arc melting method. The effect of Fe substitution on microstructure and hydrogen storage properties was studied systematically. The phase structure and hydrogen storage properties were characterized by X-ray diffraction (XRD), Electron Probe Micro-analysis (EMPA) and Sievert's type volumetric apparatus. XRD and EPMA analysis show that Zr_0.8Ti_0.2Co alloy forms cubic phase ZrCo and traces of ZrCo₂, while the alloys of composition with x = 0.1, 0.2 and 0.3 form cubic phase ZrCo with the secondary Laves phases Zr(Co,Fe)₂ and Zr₂Co. The cell volumes and content of the secondary phase increase gradually as the content of Fe substitution increases. The hydrogen storage experiment shows that Fe substitution for Co ameliorates initial hydriding kinetic property and shortens the incubation duration of the Zr_0.8Ti_0.2Co_1?xFe_x (x = 0.1, 0.2 and 0.3) alloys, compared with Zr_0.8Ti_0.2Co alloy. The improved kinetic property is due to the catalyst effect of the secondary phase, which makes it favorable for the application in International Thermonuclear Experimental Reactor (ITER).     

Ba1−xCo0.9−yFeyNb0.1O3−δ (x = 0-0.15, y = 0-0.9) as cathode materials for solid oxide fuel cells

Perovskite oxide Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3−δ has been reported as oxygen transport membrane and cathode material for solid oxide fuel cells (SOFCs). In this study, the effects of A-site cation deficiency and B-site iron doping concentration on the crystal structure, thermal expansion coefficient (TEC), electrical conductivity and electrochemical performance of Ba_1−xCo_0.9−yFe_yNb_0.1O_3−δ (x = 0-0.15, y = 0-0.9) have been systematically evaluated. Ba_1−xCo_0.9−yFe_yNb_0.1O_3−δ (x = 0-0.10, y = 0.2 and x = 0.10, y = 0.2-0.6) can be indexed to a cubic structure. Increased electrical conductivity and decreased cathode polarization resistance have been achieved by A-site deficiency. No obvious variation can be observed in TEC by A-site deficiency. The electrical conductivity and TEC of Ba_0.9Co_0.9−yFe_yNb_0.1O_3−δ decrease while the cathode polarization resistance increases with the increase in iron doping concentration. The highest conductivity of 13.9 S cm⁻¹ and the lowest cathode polarization resistance of 0.07 Ω cm² have been achieved at 700 °C for Ba_0.9Co_0.7Fe_0.2Nb_0.1O_3−δ. The composition Ba_0.9Co_0.3Fe_0.6Nb_0.1O_3−δ shows the lowest TEC value of 13.2 × 10⁻⁶ °C⁻¹ at 600 °C and can be a potential cathode material for SOFCs.     

Investigation on electrochemical performances of melt-spun nanocrystalline and amorphous Mg2Ni1−xMnx (x = 0–0.4) electrode alloys

In order to enhance the glass forming ability of the Mn₂Ni-type electrode alloy, Ni in the Mg₂Ni compound is partially substituted by Mn. The nanocrystalline and amorphous Mg₂Ni-type alloys with nominal compositions of Mg₂Ni_1−xMn_x (x = 0, 0.1, 0.2, 0.3, 0.4) are fabricated by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are successfully obtained. The microstructures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were tested by an automatic galvanostatic system. The electrochemical impedance spectra (EIS) are plotted by an electrochemical workstation (PARSTAT 2273). The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The results show that no amorphous structure is detected in the as-spun Mn-free alloy, whereas the as-spun alloys containing Mn display a nanocrystalline and amorphous structure. The amorphization degree of the alloy increases with rising spinning rate, suggesting that the substitution of Mn for Ni facilitates the glass formation in the Mg₂Ni-type alloy. The substitution of Mn for Ni markedly improves the electrochemical hydrogen storage performances of the Mg₂Ni-type alloy, enhancing both the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with increasing amount of Mn substitution.     

Effect of La–Mg-based alloy addition on structure and electrochemical characteristics of Ti0.10 Zr0.15V0.35Cr0.10Ni0.30 hydrogen storage alloy

Effect of La–Mg-based alloy (AB₅) addition on Structure and electrochemical characteristics of Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 hydrogen storage alloy has been investigated systematically. XRD shows that the matrix phase structure is not changed after adding AB₅ alloy, however, the amount of the secondary phase increases with increasing AB₅ alloy content. The electrochemical measurements show that the plateau pressure Ti_0.10Zr_0.15V_0.35Cr_0.10Ni_0.30 + x% La_0.85Mg_0.25Ni_4.5Co_0.35Al_0.15 (x = 0, 1, 5, 10, 20) hydrogen storage alloys increase with increasing x, and the width of the pressure plateau first increases when x increases from 0 to 5 and then decreases as x increases further, and the maximum discharge capacity changes in the same trend. The activation performance, the low temperature dischargeabilities, high-rate dischargeability and cyclic stability of composite alloy electrodes increase greatly with increasing x. The improvement of the electrochemical characteristics caused by adding AB₅ alloy seems to be related to formation of the secondary phase.