Effects of temperature on the performance of the MmNi3.6Co0.7Mn0.4Al0.3 metal hydride electrode in alkaline solution

In the present study, the electrochemical and hydrogen transport kinetic performance of the MmNi(3.6)Co(0.7)Mn(0.4)Al(0.3) metal hydride electrode has been systematically investigated in the temperature range 0-60 degrees C. The results show that the electrode reaction becomes more reversible and gets faster at higher temperatures. At low-discharge current densities, the charge transfer overpotential is greater than the diffusion overpotential, whereas at high-discharge current densities the diffusion overpotential becomes dominant. At medium-discharge current densities, there is a mixed control with a predominance of the mass-transport conditions at lower temperatures. The calculated kinetic parameters also show that the hydrogen desorption on the metal hydride electrode is easier than the hydrogen absorption into its alloy bulk. Activation energies for charge transfer and for hydrogen diffusion, as well as the hydrogen diffusion coefficients in the electrode, have also been estimated. (c) 2006 The Electrochemical Society.