MH electrodes

Figure 15. Reaction mechanism of the charging-discharging reaction of an MH electrode.

Finally, it should be noted that while small Ni-MH batteries are now an article of commerce, a major challenge still remains. It is to produce a low-cost MH, electrode having a long cycle life and a storage capacity of >300 mAhg-1 which is suitable for use in heavy-duty, long-life batteries such as proposed for electric and hybrid vehicles [38],... 

MH electrodes 210 primary cells 1,282 primary systems 17 prismatic nickel MH battery 29 pristine, CBSEI 438... 

There are two types of nickel-hydrogen cells those that employ a gaseous H2 electrode and those that utilize a metal hydride, MH. The use of MH electrodes in small-scaled. However, the market for consumer-type cells is rapidly growing. The system has also been proposed for electric vehicles. 

The potential of the MH electrode at 298 K changes with the hydrogen pressure according to... 

The impedance spectroscopy is most promising for electrochemical in situ characterization. Many papers have been devoted to the AB5 type MH electrode impedance analysis [15-17]. Prepared pellets with different additives were used for electrochemical measurements and comparing. Experimental data are typically represented by one to three semicircles with a tail at low frequencies. These could be described to the complex structure of the MH electrode, both a chemical structure and porosity [18, 19] and it is also related to the contact between a binder and alloy particles [20]. The author thinks that it is independent from the used electrolyte, the mass of the electrode powder and the preparing procedure of electrode. However, in our case the data accuracy at high frequencies is lower in comparison with the medium frequency region. In the case, the dependence on investigated parameters is small. In Figures 3-5, the electrochemical impedance data are shown as a function of applied potential (1 = -0.35V, 2 = -0.50V and 3 = -0.75V). 

Deterioration of electrode performance due to corrosion of electrode components is a critical problem. The susceptibility of MH electrodes to corrosion is essentially determined by two factors surface passivation due to the presence of surface oxides or hydroxides, and the molar volume of hydrogen, V, in the hydride phase. As pointed out by Willems and Buschow [40], V is important since it governs alloy expansion and contraction during the charge-discharge cycle. Large volume changes... 

The oxygen diffuses through the separator to the MH electrode and there it reacts chemically, producing water (eq. 7) and preventing a pressure rise in the cell as shown in fig. 2. The electrolyte solution should be minimal to facilitate the diffusion of gas through... 

The reactions at the MH electrode (eqs. 10-11) are the same as for the hydrogen diflusion electrode using platinum-containing carbon in an alkali fuel cell. Usually, the reaction... 

The MH electrode should satisfy all performance standards such as capacity, cycle life, charging and discharging efficiency, and charge retention. Research work on battery alloys has concentrated mainly on MmNis-based alloys, followed by Tii 3 Zr3.Ni2+a-based... 

Videm (1978) pointed out that the following alloy properties need attention for optimum use as MH electrode ... 

---