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 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.     

Structural investigation and hydrogen storage properties of Ca3-xLaxMg2Ni13 alloys

The phase structures and hydrogen storage properties of the Ca_3-xLa_xMg₂Ni₁₃ alloys were investigated. It was found that the La substitution is unfavorable for the formation of the Ca₃Mg₂Ni₁₃-type phase. The La-substituted alloys consist of multiple phases. Increasing La content to x = 2.25 leads to a disappearance of Ca₃Mg₂Ni₁₃-type phase. Among these alloys, the Ca_1.5La_1.5Mg₂Ni₁₃ alloy has highest equilibrium pressures of hydrogen absorption–desorption and a highest hydrogen desorption capacity of 1.34 wt.% at 318 K. The discharge capacity decreases for La-substituted alloys. However, the cycling capacity retention rate (S₃₀) increases from 13.7 to 67.6% when x increases from 0 to 3.     

Microstructure and electrochemical investigations of La0.76−xCexMg0.24Ni3.15Co0.245Al0.105 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys

The effects of substitution of Ce for La on the microstructure and electrochemical performance of La_0.76−xCe_xMg_0.24Ni_3.15Co_0.245Al_0.105 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses showed that the main phases of the alloys consist of (La, Mg)Ni₃ phase (PuNi₃-type rhombohedral structure), LaNi₅ phase (CaCu₅-type hexagonal structure) and (La, Mg)₂Ni₇ phase (Ce₂Ni₇-type hexagonal structure). The cell volume of the (La, Mg)Ni₃ phase, (La, Mg)₂Ni₇ phase and LaNi₅ phase decreased monotonously with increasing Ce content. Electrochemical investigations showed a decrease in the discharge capacity, while high rate dischargeability (HRD) first increased and then decreased with increasing Ce content. The Ce substitution for La slightly enhanced the cyclic stability of the alloy electrodes. The pressure–composition (P–C) isotherms showed that the plateau region was broadened with Ce content increased in the alloys, meanwhile, two plateaus appeared and pressure of the hydrogen absorption and desorption increased accordingly.     

Microstructure and electrochemical hydrogen storage characteristics of (La0.7Mg0.3)1−xCexNi2.8Co0.5 (x = 0-0.20) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of (La_0.7Mg_0.3)_1−xCe_xNi_2.8Co_0.5 (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 (S₁₀₀) 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 1200 mA/g. Moreover, the electrochemical kinetic characteristics of the alloy electrodes are also improved by increasing Ce content.     

Synthesis and electrochemical properties of Li[Ni0.45Co0.1Mn0.45−xZrx]O2 (x = 0, 0.02) via co-precipitation method

Li[Ni_0.45Co_0.1Mn_0.45−xZr_x]O₂ (x = 0, 0.02) was synthesized via co-precipitation method. Partial Zr doping on the host structure of Li[Ni_0.45Co_0.1Mn_0.45]O₂ was carried out to improve the electrochemical properties. The Zr-doped Li[Ni_0.45Co_0.1Mn_0.43Zr_0.02]O₂ was evaluated in terms of specific discharge capacity, cycling performance and thermal stability. The Zr-doped Li[Ni_0.45Co_0.1Mn_0.45−xZr_0.02]O₂ shows the improved cycling performance and stable thermal stability. The major exothermic reaction was delayed from 252.1 °C to 289.4 °C.     

Structural characteristics and hydrogen storage properties of Ca3.0−xMgxNi9 (x = 0.5, 1.0, 1.5 and 2.0) alloys

The effect of Mg content on the structural characteristics and hydrogen storage properties of the Ca_3.0−xMg_xNi₉ (x = 0.5, 1.0, 1.5 and 2.0) alloys was investigated. The lattice parameters and unit cell volume of the PuNi₃-type (Ca, Mg)Ni₃ main phase decreased with increasing Mg content. The 6c site of PuNi₃-type structure was occupied by both Ca and Mg atoms. Moreover, the occupation factor of Ca on the 6c site decreased with the increase of Mg content. The hydrogen absorption capacity of the alloys decreased due to higher Mg content. However, the thermodynamic properties of hydrogen absorption and desorption were improved and the plateau pressures were increased. When x = 1.5–2.0, the Ca_3.0−xMg_xNi₉ alloys had favorable enthalpy (ΔH) and entropy (ΔS) of hydride formation.     

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.     

Improved hydrogen storage behaviours of nanocrystalline and amorphous Mg2Ni-type alloy by Mn substitution for Ni

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) were synthesized by melt spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that the as-spun (x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun (x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg₂Ni-type alloy. The hydrogen absorption capacity of the alloys first increases then decreases with rising Mn content, but the hydrogen desorption capacity of the alloys grows with increasing Mn content. Furthermore, the substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn from 0 to 0.4, the discharge capacity of as-spun (30 m/s) alloy grows from 116.7 to 311.5 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle rises from 36.7 to 78.7%.     

Effect of cobalt on the microstructure and hydrogen sorption performances of TiFe0.8Mn0.2 alloy

The microstructures and the hydrogen sorption performances of TiFe_0.8Mn_0.2Co_x (x = 0, 0.05, 0.10, 0.15) and TiFe_0.8Mn_0.2-yCo_y (y = 0.05, 0.10) alloys have been investigated. For TiFe_0.8Mn_0.2Co_x alloys, the lattice parameters of TiFe phase decreased and the Laves phase contents increased with the addition of Co. With the increase of Co content in TiFe_0.8Mn_0.2Co_x alloys, the maximum hydrogen storage capacities of TiFe_0.8Mn_0.2Co_0.05 and TiFe_0.8Mn_0.2Co_0.10 alloys decreased, but the effective hydrogen capacities increased, which is ascribed to the improved flatness of the α-β desorption plateau. Substitution of Co for Mn in TiFe_0.8Mn_0.2-yCo_y alloys can effectively lead to single phase of TiFe alloys. Therefore, TiFe_0.8Mn_0.2-yCo_y alloy showed a deteriorated activation property, but its effective hydrogen capacity increased remarkably due to the obviously improved flatness of the α-β desorption plateau. The addition of Co might adjust the change of the octahedral intersitial environment caused by Mn doping in TiFe phase, which contributes to the improved flatness of the α-β desorption plateau and hence the increased effective hydrogen capacity.     

Effect of substituting Al for Co on the hydrogen-storage performance of La0.7Mg0.3Ni2.6AlxCo0.5−x (x = 0.0–0.3) alloys

La_0.7Mg_0.3Ni_2.6Al_xCo_0.5−x (x = 0.0–0.3) alloys were prepared by induction melting, and the effects of partially substituting Al for Co on the structure and hydrogen-storage properties of the alloys were investigated systematically. It is found that La(Ni, Co, Al)₅ phase with hexagonal CaCu₅-type structure, LaNi₃ phase with PuNi₃ structure and MgNi₂ phase exist as the main phases in La_0.7Mg_0.3Ni_2.6Al_xCo_0.5−x (x = 0.0–0.3) alloys, and the cell volume of the La(Ni, Co, Al)₅ phase increases with the amount of Al added. The results show that the substitution of Al for Co can reduce the plateau pressure and the hysteresis between hydrogen absorption and desorption, and improve the hydrogen-absorption capacity and thermal stability of the hydride. Moreover, the addition of Al can delay the oxidation of the surface layer of the alloy electrodes in electrolyte, slow down the capacity degradation and prolong the cycling lifetime, and enhance the electrocatalytic activity of the hydrogen-storage electrodes for hydrogen oxidation.     

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).     

Properties of La0.2Y0.8Ni5−xMnx alloys for high-pressure hydrogen compressor

Hydrogen absorption/desorption properties of La_0.2Y_0.8Ni_5−xMn_x (x = 0.2, 0.3, 0.4) alloys for high-pressure hydrogen compression application were investigated systematically. The Pressure–Composition isotherms and absorption kinetics were measured at 293, 303 and 313 K by the volumetric method. XRD analyses showed that all the investigated alloys presented CaCu₅ type hexagonal structure and the unit cell volume increased in both a and c lattice axes with Mn substitution. Hydrogen absorption/desorption measurements revealed that Mn could lower the plateau pressure effectively, improve the hydrogen storage capacity and absorption kinetics but slightly increase the slope of the pressure plateau and hysteresis. The study results suggest that La_0.2Y_0.8Ni_4.8Mn_0.2 is suitable for the high-pressure stage compression of the hydrogen compressor and the other two alloys, La_0.2Y_0.8Ni_4.7Mn_0.3 and La_0.2Y_0.8Ni_4.6Mn_0.4, for the preliminary stage.     

Electrochemical performances of the as-melt La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr,Zr; x = 0, 0.2) alloys applied to Ni/metal hydride (MH) battery

The partial replacement of La by M (M = Pr, Zr) has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni-based A₂B₇-type electrode alloys. For this purpose, we adopt melt spinning technology to prepare the La_0.75−xM_xMg_0.25Ni_3.2Co_0.2Al_0.1 (M = Pr, Zr; x = 0, 0.2) electrode alloys. Then systemically investigate the effects that the preparation methods and M (M = Pr, Zr) substitution have on the structures and electrochemical hydrogen storage characteristics of the alloys. The analysis of XRD and TEM reveals that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)₂Ni₇ and LaNi₅ as well as a trace of residual phase LaNi₂. Besides, the as-spun (M = Pr) alloy displays an entire crystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying the replacement of La by Zr facilitates forming amorphous phase. Based upon electrochemical measurements, an impact engendered by melt spinning on the electrochemical performances of the alloys appears to be evident. The cycle stabilities monotonously augment with the growing of the spinning rate. The discharge capacity and high rate discharge ability (HRD), however, exhibit difference. For the (M = Pr) alloy, they first mount up and then fall with the rising of the spinning rate, whereas for the (M = Zr) alloy, they always decline as the spinning rate elevates. Furthermore, the replacement of La by M (M = Pr, Zr) considerably enhances the cycle stability of the alloys and the replacement of La by Pr clearly increases the discharge capacity, but the Zr replacement results in an adverse impact.     

Effect of non-stoichiometry on hydrogen storage properties of La(Ni3.8Al1.0Mn0.2)x alloys

The La(Ni_3.8Al_1.0Mn_0.2)_x (x = 0.94, 0.96, 0.98, 1.0) hydrogen storage alloys have been investigated to examine the effect of non-stoichiometry on the crystal structure, activation performance, hydrogen absorption/desorption properties and cycle life. It was found that for the stoichiometric compound, only single phase with CaCu₅ type structure exists. However, for B-poor compounds of AB₅ alloys, there is a principal CaCu₅ type phase with a small amount of second phase and the amount of second phase increased with decreasing x when x ≥ 0.96 and reached a maximum when x = 0.96. The activation becomes harder with decreasing x until x = 0.96 and easier when x decreased to 0.94. The plateau pressure increased and the hydrogen uptake capacity decreased with decreasing x when x ≥ 0.96, and then decreased and increased, respectively, when x further decreased to 0.94. Both the change in the lattice strain which could be estimated by FWHM (full width at half maximum) and the degree of slope factor S_f in the alloys show the same trend with the change of x, exhibiting a maximum at x = 0.96. The ΔH decreased with decreasing x when x ≥ 0.96 and then increased when x = 0.94 and it was found that the larger the cell volume, the larger the absolute value of the enthalpy. The pulverization resistance of the alloys was greatly improved by the non-stoichiometric. The kinetics of the alloys was very fast and almost not influenced by the change of non-stoichiometric x. After 300 absorption/desorption cycles, the hydrogen uptake capacity of the stoichiometric and non-stoichiometric alloys almost kept the same, but the particle size decreased greatly.     

Influence of annealing treatment on the hydrogen storage properties of La2−xTixMgNi9 (x = 0.2, 0.3) alloys

La_2−xTi_xMgNi₉ (x = 0.2, 0.3) alloys have been prepared by magnetic levitation melting under an Argon atmosphere, and the as-cast alloys were annealed at 800 °C, 900 °C for 10 h under vacuum. The effects of annealing on the hydrogen storage properties of the alloys were investigated systematically by XRD, PCT and electrochemical measurements. For the La_2−xTi_xMgNi₉ (x = 0.2, 0.3) alloys, LaNi₅, LaMg₂Ni₉ and LaNi₃ are the main phases and a Ti₂Ni phase appears at 900 °C. The effective hydrogen storage capacity increases from 1.10, 1.10 wt.% (as-cast) to 1.22, 1.16 wt.% (annealed 800 °C) and 1.31, 1.27 wt.% (annealed 900 °C), respectively. The annealing not only improves the hydrogen absorption/desorption kinetics but also increases the maximum discharge capacity and enhances the cycling stability. The La_1.8Ti_0.2MgNi₉ alloy annealed at 900 °C exhibits good electrochemical properties, and the discharge capacities decrease from 366.1 mA h/g to 219.6 mA h/g after 177 charge-discharge cycles.     

Structural and hydrogenation properties of SrAl2−xNix alloys

In this paper, Al was partially substituted by Ni in the Zintl phase alloy SrAl₂ and the structural and hydrogenation characteristics of the SrAl_2−xNi_x (0 ≤ x ≤ 0.4) alloys were studied by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and hydrogenation measurements. The alloy consisted of a single Zintl phase of SrAl₂ when x = 0. However, partial substitution of Al by Ni resulted in multiphase structure of the alloys. When x = 0.1, the alloy was composed of SrAl₂, Sr₅Al₉, SrAl and AlNi phases. With the increase of x, the amount of SrAl₂ and Sr₅Al₉ phases decreased, while the amount of SrAl and AlNi phases increased. Hydrogenation measurements were made at 473 K under 3 MPa hydrogen pressure. It was interesting to find that the hydriding kinetics of the alloy was improved greatly after Ni substitution, which could be attributed to the catalysis of AlNi phase.     

Microstructure and electrochemical hydrogen storage characteristics of La0.67Mg0.33−xCaxNi2.75Co0.25 (x = 0-0.15) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of La_0.67Mg_0.33−xCa_xNi_2.75Co_0.25 (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 (S₈₀) 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.     

Kinetics and electrochemical characteristics of Mg2NiH4-x wt.% MmNi3.8Co0.75Mn0.4Al0.2 (x = 5, 10, 20, 40) composites for Ni-MH battery

The structure, kinetics and electrochemical characteristics of Mg₂NiH₄-x wt.% MmNi_3.8Co_0.75Mn_0.4Al_0.2 (x = 5, 10, 20, 40) composites prepared by mechanical milling have been investigated in this paper. XRD results indicate that the as-milled Mg₂NiH₄ shows nanocrystalline or amorphous-like structure, and it does not react with MmNi_3.8Co_0.75Mn_0.4Al_0.2 during mechanical milling. As the amount of MmNi_3.8Co_0.75Mn_0.4Al_0.2 increases, the maximum discharge capacity decreases initially from 508 mAh/g (x = 5) to 440 mAh/g (x = 10) and then increases to 509 mAh/g (x = 40). Meanwhile, the capacity retention (R₁₀) increases from 12.8% (x = 5) to 23.4% (x = 40), and the corrosion potential of electrode (E_corr) increases from −0.930 V to −0.884 V (vs. Hg/HgO). Especially, the more MmNi_3.8Co_0.75Mn_0.4Al_0.2 content the composite contains, the higher high rate dischargeability (HRD) the electrode exhibits, which could be attributed to the catalytic reaction and reduction of the Mg₂NiH₄ grain size brought by MmNi_3.8Co_0.75Mn_0.4Al_0.2. The improvement in electrode kinetics has been depicted from the bulk hydrogen diffusion coefficient (D), the exchange current density (I₀) and the charge transfer resistance (R_ct) on the alloy surface.     

Effect of rare earth elements on electrochemical properties of La–Mg–Ni-based hydrogen storage alloys

La_0.60R_0.20Mg_0.20(NiCoMnAl)_3.5 (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi₅ phase, La₂Ni₇ phase and LaNi₃ phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g⁻¹ increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g⁻¹ to 220 mAh g⁻¹ for the Ce-substituted alloy.