Effect of electrolyte on electrochemical characteristics of MmNi3.55Co0.72Al0.3Mn0.43 alloy electrode for hydrogen storage

A series of experiments have been performed to investigate the effects of three electrolytes of different compositions (EO, EA and EM) on the electrochemical characteristics of MmNi_3.55Co_0.72Al_0.3Mn_0.43 hydrogen storage alloy electrode. Electrolytes EA and EM were obtained by adding appropriate amounts of Al₂(SO₄)₃ and MnSO₄ to the original electrolyte EO (6 M KOH + 1 wt% LiOH), respectively. Electrode activation, maximum capacity, cycle life, self-discharge and high-rate discharge characteristics have been studied. It was found that a maximum capacity of about 260 mA h/g has been obtained for the alloy electrodes in all these electrolytes after 5–7 cycles of charging/discharging. The alloy electrodes have a good durability in electrolytes EA and EM, especially after 175 cycles. Using the capacity retention as an indication of self-discharge resistance, almost identical degree of capacity retention (82% after 4 days and 45% after 16 days) has been observed at 298 K, regardless of the electrolytes used. When tested at higher temperature, however, a higher capacity retention (46% after 3 days) at 333 K has been observed for electrodes in electrolyte EA, and about 32% for electrodes in both electrolytes EO and EM. As to high-rate discharge behavior of the results of high-rate discharge tests indicated that about 50% of discharge efficiencies were obtained in the three electrolytes at 333 K by continuous-model high-rate discharge method, at a discharge rate of 7C, and 22% in 298 K. The alloy electrode in electrolyte EM has the best durability, in which about 50% of discharge efficiency at DC = 9C was obtained by step-model high-rate discharge method at 333 K, which was even higher than that at 298 K.     

Electrode characteristics of the Cr and La doped AB2-type hydrogen storage alloys

AB₂-type alloy, a kind of hydrogen storage alloys used as an anode of Ni-MH batteries, has a large discharge capacity but still has several problems such as initial activation, cycle life and self-discharge. In this study, we have investigated the effects of Cr addition and fluorination after La addition on AB₂-type alloy with Zr_0.7Ti_0.3V_0.4Mn_0.4Ni_1.2 composition. The EPMA and SEM surface analysis techniques were used and the crystal structure was characterized by XRD analysis. Metal hydride negative was characterized by galvanostatic cycling test, electrochemical impedance spectroscopy and potentiodynamic polarization. Cr-addition is found to be effective to improve cycle life and self-discharge characteristics but ineffective to promote initial activation due to the formation of stable oxide film on alloy surface. Highly reactive particles have been formed by fluorination after La-addition to the alloys and those particles may remarkably improve the initial activation of MH-negative electrodes.     

Effect of rare earth composition on the high-rate capability and low-temperature capacity of AB5-type hydrogen storage alloys

Effects of rare earth composition on the high-rate capability and low-temperature capacity of AB₅-type hydrogen storage alloys have been studied and analyzed with pattern recognition methods. The results show that the increase of Ce and Pr and the decrease of La and Nd concentration improve the high-rate capability and low-temperature capacity of AB₅-type hydrogen storage alloys, Ce exhibiting better favorable influences than Pr. The improvement of both high-rate capability and low-temperature capacity are mainly ascribed to the lower stability of the hydride. The alloy with the rare earth composition of La_0.1645Ce_0.7277Pr_0.0234Nd_0.0845 shows very good high-rate capability and low-temperature capacity.     

Effects of electrolytes and temperature on high-rate discharge behavior of MmNi5-based hydrogen storage alloys

A series of experiments have been performed to investigate the effects of electrolyte composition and temperature on the high-rate discharge behaviors of MmNi₅-based AB₅ hydrogen storage alloy electrodes. Two types of AB₅ electrodes have been used using different alloys: Ce-rich alloy V (La_0.26 Ce_0.44Pr_0.1Nd_0.2Ni_3.55Co_0.72Mn_0.43Al_0.3) and La-rich alloy N (La_0.58Ce_0.25Pr_0.06 Nd_0.11Ni_3.66Co_0.74Mn_0.41Al_0.18). Electrolytes EN were obtained by adding a saturated amount of Al₂(SO₄) ₃ to the original electrolyte EO (6 M KOH + 1 wt% LiOH). The electrolyte EN has previously been shown to be very effective to stop the self-discharge of the AB₅ electrodes, better charge/discharge cycle life have been observed. The electrochemical properties of the electrodes were measured by two methods: step mode high-rate discharge and continuous mode high-rate discharge. The results indicate that at 298 K and 333 K, high-rate discharge capacity of Ni–MH battery was mostly affected by the chemical composition of the electrolyte, then the type of alloy. Better dischargeabilities in high-rate discharge capacity have been observed in electrolyte EO than in electrolyte EN. The Ce-rich alloy V has a higher high-rate discharge capacity than La-rich alloy N. High-rate discharge capacity decreases in the following order: VEO > NEO > VEN > NEN (VEO denotes the combination of alloy V and electrolyte EO used in the test battery, similarly equivalent representations for NEN, VEO and VEN).     

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.     

Effect of temperature on the discharge capacity of the Laves phase alloy used in nickel/metal-hydride batteries

The discharge capacity, the high-rate dischargeability and the self-discharge characteristics of negative electrodes consisting of the Zr-based, modified AB₂ type alloys of ZrV_0.1Mn_0.7Ni_1.2 alloy and ZrV_0.1Mn_0.5Mo_0.2Ni_1.2 alloy, the latter having the form of partially substituted Mo for Mn sites in the former alloy, are investigated in 6 M KOH solution at 30, 40 and 60°C. It is found that the discharge capacities obtained at 30 and 40°C are almost the same in both alloys, but they decrease at 60°C. The activation process becomes faster in both alloys with increasing temperature. The high-rate dischargeability increases slightly from 85% at 30°C to 90% at 60°C. At the very high discharge current of 5 A g⁻¹, however, the discharge capacity at 60°C was increased by 7× and 17× more than that at 30°C in ZrV_0.1Mn_0.7Ni_1.2 alloy and ZrV_0.1Mn_0.5Mo_0.2Ni_1.2 alloy, respectively. The addition of Mo improved the self-discharge characteristics, especially at 60°C.     

Effect of Al content on structure and electrochemical properties of LaNi4.4 − xCo0.3Mn0.3Alx hydrogen storage alloys

The structure and electrochemical properties of LaNi_4.4 − xCo_0.3Mn_0.3Al_x hydrogen storage alloys have been investigated by XRD and simulated battery test, including maximum capacity, cyclic stability, self-discharge, high-rate dischargeability (HRD). Samples A, B, C and D were used to represent alloys LaNi_4.4Co_0.3Mn_0.3Al, LaNi_4.3Co_0.3Mn_0.3Al_0.1, LaNi_4.2Co_0.3Mn_0.3Al_0.2 and LaNi_4.1Co_0.3Mn_0.3Al_0.3 respectively. The results indicated that as-prepared LaNi_4.4 − xCo_0.3Mn_0.3Al_x alloys are all single-phase alloys with hexagonal CaCu₅ type structure. The maximum discharge capacity is 330.4 mAh g⁻¹ (Alloy C). With the increase of Al content from A to D, cycle life of alloy electrode has been improved. Higher capacity retention of 89.29% (after 50 charge/discharge cycles) has been observed for electrode D, while with a smaller capacity loss of 12.5% in its self-discharge test. Better high-rate charge/discharge behaviors have been observed in electrode B, and the maximum data is 54.7% at charge current of 900 mA/g) and 68.54% at discharge current of 1800 mA/g). Furthermore, the electrochemical impedance spectroscopy (EIS) analysis shown that the reaction of alloy electrode is controlled by charge-transfer step. The addition of Al results in the formation of protective layer of aluminum oxides on the surface of the alloy electrode, which is good for the improvement of electrode properties in alkaline solution and is detrimental for the charge-transfer process. Therefore, a suitable addition of Al is needed to improve its electrode properties.     

Electrocatalytic characteristics of the metal hydride electrode for advanced Ni/MH batteries

The electrocatalytic characteristics of a metal hydride (MH) electrode for advanced Ni/MH batteries include the hydrogen adsorption/desorption capability at the electrode/electrolyte interface. The hydrogen reactions at the MH electrode/electrolyte interface are also related to factors such as the surface area of the MH alloy powder and the nature of additives and binder materials. The high-rate discharge capability of the negative electrode in a Ni/MH battery is mainly determined by the mass transfer process in the bulk MH alloy powder and the charge transfer process at the interface between the MH alloy powder and the electrolyte. In this study, an AB₅-type hydrogen-absorbing alloy, Mm (Ni, Co, Al, Mn)_5.02 (where Mm denotes Mischmetal, comprising 43.1 wt.% La, 3.5 wt.% Ce, 13.3 wt.% Pr and 38.9 wt.% Nd), was used as the negative MH electrode material. The MH electrode was charged and discharged for up to 200 cycles. The specific discharge capacity of the alloy electrode decreases from a maximum value of 290–250 mAh g⁻¹ after 200 charge/discharge cycles. A cyclic voltammetry technique is used to analyze the charge transfer reactions at the electrode/electrolyte interface and the hydrogen surface coverage capacity.     

Effects of pretreatment of LM-Ni3.9Co0.6Mn0.3Al0.2 alloy powders in a KOH/NaBH4 solution on the electrode characteristics and inner pressure of nickel-metal-hydride secondary batteries

The discharge capacities of lanthanum-rich mischmetal (LM)-Ni_3.9Co_0.6Mn_0.3Al_0.2 alloy electrodes are significantly degraded by an increase in the C rate. Nevertheless, the discharge capacity of alloy electrodes pretreated with KOH/NaBH₄ is maintained higher than that of raw alloy electrodes, with the difference in discharge capacities between the raw and pretreated alloy electrodes more prominent at higher C rates. The charge retention of the electrodes decreases with increasing rest time. In particular, the charge retention of the pretreated alloy electrode is lower than that of the raw alloy electrode due to the higher self-discharge rate. The overvoltage for hydrogen evolution of the pretreated alloy electrode is superior to that of the raw alloy electrode, particularly at higher temperatures. This phenomenon indicates that the charge efficiency of the electrode was significantly improved by the surface pretreatment, resulting from its high surface catalytic activity. Repeated charge-discharge increases the inner pressure of the battery. Nevertheless, due to its higher charge efficiency and faster recombination rate, the inner pressure of the battery made using the pretreated alloy electrode is much smaller than that of the battery made using a raw alloy electrode.     

Influence of the synthesis route on hydrogen sorption properties of La2MgNi7Co2 alloy

Solid-gas and electrochemical hydrogenation properties of La₂MgNi₇Co₂ alloy are presented. Hydrogen concentration of 1.90 wt% at hydrogen pressure of 10 bar has been reached. The influence of the fabrication technology of La₂MgNi₇Co₂ alloy on electrochemical performance of the hydride electrode were studied and discussed. To evaluate electrochemical characteristics of La₂MgNi₇Co₂ electrodes including discharge capacity, self-discharge and kinetic parameters the galvanostatic charge/discharge technique was used. The studied samples were a multiphase. The presence of Mg-enriched phases (La₂MgO_x, (La, Mg)Ni₃ and LaMgNi₄) raises hydrogen capacity and makes an electrode less susceptible for the self-discharge effect. On the other hand Mg-presence in MH electrodes lowers the hydrogen desorption rate. It was found that, the dominant abundance of the LaNi₅ phase in the tested materials has a positive effect on the kinetic parameters of the hydride electrode.     

Effect of Sm on hydrogen storage performance of La–Sm–Mg–Ni alloys

Abstract

In this study, Sm was adopted in order to completely replace the expensive Pr/Nd elements in the A2B7 type alloy. The results indicate that Sm is a favourable element for forming Ce2Ni7 type and Ce5Co19 type phases. With the increasing amount of Sm, the discharge capacity of the alloy retains a value of 283·3 mAh g^?1 at the current density of 1200 mA g^?1. The maximum discharge capacity of the alloys increases with the increasing Sm content when Mg content is relatively low. By optimising the composition and processing technology, the cycle life the alloy enhances from 74 cycles to more than 540 cycles, and the maximum discharge capacity also increases from 300 to 355 mAh g^?1.     

Electrochemical properties of the Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 alloy mixed with Ni powder

Composites of Mm_0.3Ml_0.7Ni_3.55Co_0.75Mn_0.4Al_0.3 alloy and Ni powders were mechanically synthesized and electrochemically tested in 6 M KOH electrolyte. In this work, the electrochemical properties of the alloys were greatly improved by mixing them with Ni, which plays a corrosion-resistance role in the alkali electrolyte and helps electron conduction. It has been shown that the numbers of activation cycles decreased compared with the alloys without Ni powder. All the alloys were activated after the second cycle. Improvements of the maximum discharge capacities were also found in this work. A maximum discharge capacity of 358 mAh g⁻¹ was measured in the Mm_0.3Ml_0.7Ni_3.55Co_0.75Mn_0.4Al_0.3 + 250 wt.% Ni composite. In addition to that, adding Ni was found to enhance the high-rate discharge ability of the alloys, which appear to be good candidates for the realization of MH battery electrodes.     

The electrochemical performances of Ti–V-based hydrogen storage composite electrodes prepared by ball milling method

In order to overcome the inherent disadvantages of Ti–V-based hydrogen storage alloys, such as poor activation behavior and low high-rate dischargeability, the novel composites Ti_0.17Zr_0.08V_0.35Cr_0.1Ni_0.3–x wt.% La_0.7Mg_0.3Ni_2.75Co_0.75 (x = 0, 5, 10 and 20) were successfully synthesized by ball milling method in the present study. And the structure and overall electrochemical properties of as-prepared composites are investigated systemically. The electrochemical studies show that the maximum discharge capacity of the composite electrodes displays no variation with the increase of La_0.7Mg_0.3Ni_2.75Co_0.75 content, whereas the high-rate dischargeability (HRD) and the activation behavior are distinctly improved with increasing x. The electrochemical hydrogen kinetics of composite electrodes is also studied by means of electrochemical impedance spectroscopy (EIS), linear polarization (LP), anodic polarization (AP) and potential-step measurements. It is found that the charge-transfer reaction resistance R_ct is decreased with increasing the amount of La_0.7Mg_0.3Ni_2.75Co_0.75 while exchange current density I₀, limiting current density I_L and hydrogen diffusion coefficient D are all increased with increasing the amount of La_0.7Mg_0.3Ni_2.75Co_0.75. These results suggest that the formation of composite with La_0.7Mg_0.3Ni_2.75Co_0.75 alloy is a promising strategy for improving the HRD, activation behavior and electrochemical kinetics of Ti–V-based alloy electrodes.     

Hydrogen-absorbing alloys for the NICKEL–METAL hydride battery

In recent years, owing to the rapid development of portable electronic and electrical appliances, the market for rechargeable batteries has increased at a high rate. The nickel-metal hydride battery (Ni/MH) is one of the more promising types, because of its high capacity, high-rate charge/discharge capability and non-polluting nature. This type of battery uses a hydrogen storage alloy as its negative electrode. The characteristics of the Ni/MH battery, including discharge voltage, high-rate discharge capability and charge/discharge cycle lifetime are mainly determined by the construction of the negative electrode and the composition of the hydrogen-absorbing alloy. The negative electrode of the Ni/MH battery described in this paper was made from a mixture of hydrogen-absorbing alloy, nickel powder and polytetrafluoroethylene (PTFE). A multicomponent MmNi₅-based alloy (Mm_0.95Ti_0.05Ni_3.85 Co_0.45Mn_0.35Al_0.35) was used as the hydrogen-absorbing alloy. The discharge characteristics of the negative electrode, including discharge capacity, cycle lifetime, and polarization overpotential, were studied by means of electrochemical experiments and analysis. The decay of the discharge capacity for the Ni/MH battery (AA size, 1 Ah) was about 1% after 100 charge/discharge cycles and 10% after 500 charge/discharge cycles.     

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.     

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.     

Performance characterization of sintered iron electrodes in nickel/iron alkaline batteries

A nickel/iron storage battery with a porous, sintered, iron negative electrode and a nickel positive electrode is a high power system by virtue of its low internal resistance. A dry-powder sintering procedure is used to fabricate negative and positive electrodes. Negative iron electrodes are activated with various salt solutions such as CdSO₄, BaCl₂, HgCl₂ and sulfur. Positive electrodes are impregnated with nickel hydroxide by a chemical method. Tests are performed in 10 Ah capacity nickel/iron cells and two types of activated iron electrodes are used. The present work deals with electrode fabrication, charge/discharge studies, self-discharge, temperature performance and cycle life. Finally, the best iron electrodes are coupled with nickel electrodes to obtain a 1.37 V, 75 Ah nickel/iron cell. The performance of this cell is discussed.     

High temperature performance of La0.6Ce0.4Ni3.45Co0.75Mn0.7Al0.1 hydrogen storage alloy for nickel/metal hydride batteries

La_0.6Ce_0.4Ni_3.45Co_0.75Mn_0.7Al_0.1 hydrogen storage alloy has been prepared and its electrochemical characteristics and gas hydrogen absorption/desorption properties have been investigated at different temperatures. X-ray diffraction results indicated that the alloy consists of a single phase with CaCu₅-type structure. It is found that the investigated alloy shows good cycle performance and high-rate discharge ability, which display its promising use in the high-power type Ni-MH battery. The exchange current density and the diffusion coefficient of hydrogen in the bulky electrode increase with increasing temperature, indicating that increasing temperature is beneficial to charge-transfer reaction and hydrogen diffusion. However, the maximum discharge capacity, the charge retention and the cycling stability degrade with the increase of the temperature.     

Investigation on microstructures and electrochemical performances of hydrogen storage alloys

In order to improve the cycle stability of La–Mg–Ni system (A₂B₇-type) alloy electrode, a small amount of Co was added in the La_0.75Mg_0.25Ni_3.5 alloy. The effects of Co content on the microstructures and electrochemical performances of the alloys were investigated in detail. The results by XRD and SEM show that the alloys have a multiphase structure which is composed of the LaNi₅, (La,Mg)₂Ni₇ two major phases and a small amount of the LaNi₂ phase. The cell volumes of the LaNi₅ and phases enlarge with the increasing Co content in the alloys. With the increasing Co content, some electrochemical properties and kinetic parameters of the alloy, involving the discharge capacity, high-rate discharge ability (HRD), the polarization resistance (R_p), the loss angle (ψ) and the limiting current density (I_L), first increase and then decrease. The addition of Co slightly improves the cycle stabilities of the alloy electrodes. The mechanism of the efficiency loss of the experimental alloy was investigated by means of SEM and X-ray photoelectron spectroscopy (XPS). The results indicate that the fundamental reasons for the capacity decay of the La_0.75Mg_0.25Ni_3.5Co_x (x=0,0.2,0.4,0.6) alloy electrodes are the pulverization of the alloy particle and corrosion/oxidation of La and Mg in alkaline electrolyte.     

Effect of surface modification on the performance of negative electrodes in Ni/MH batteries

The performance of a Nickel/Metal Hydride (Ni/MH) battery closely depends on the characteristics of the negative MH electrode. Exchange current density, high-rate dischargeability, discharge potential and apparent activation energy of a MH electrode are very important properties, among which the high-rate dischargeability and discharge potential of a MH electrode determine the specific energy and specific power of electric vehicles (EVs) when Ni/MH batteries are applied to EVs. Significant improvements in exchange current density, high-rate dischargeability and discharge potential of a MH electrode have been observed for a $\text{9.0}\text{wt}$% copper coated LaNi_4.7Al_0.3 MH electrode. The high-rate dischargeabilities were determined to be 88.4% for the LaNi_4.7Al_0.3 electrode and 99.4% for Cu-coated LaNi_4.7Al_0.3 electrode. The discharge potential for the Cu-coated LaNi_4.7Al_0.3 electrode is lower (i.e. more negative) than that for the LaNi_4.7Al_0.3 electrode, especially at a large discharge current density (i.e. $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$). The discharge potentials of the Cu-coated LaNi_4.7Al_0.3 electrode are almost the same value (i.e. $\text{−0.930}\text{V}$ vs. Hg/Hgo) at both 20 and $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$ discharge current densities. There is no significant difference between the two apparent activation energies for the electrode reactions for the electrodes with and without the microencapsulation of the MH powders at the same hydrogen concentration.