Influence of rare earth content on electrode kinetics in Misch metal-based AB5 MH alloys – Cyclic voltammetric investigations

The influence of lanthanum/cerium ratio (0.42–14.14) in Misch metal (Mm)-based AB5-type hydrogen storage alloys has been investigated. The samples were subjected to X-ray florescence (XRF) and cyclic voltammetry (CV) studies. The metal hydride electrodes were assembled, and their discharge capacity was determined. These alloys delivered discharge capacity between 118 and 266 mAh/g. CV investigations threw light on charge-transfer reactions at the electrode/electrolyte interface and hydrogen surface coverage capacity. The CV parameters in general indicate that the battery activity increases with lanthanum/cerium ratio. At low lanthanum/cerium values, the discharge reactions proceed at potentials that are more negative. Furthermore, electrochemical reversibility of the hydrogen absorption–desorption on the alloy surface is enhanced at optimum lanthanum/cerium ratio as revealed by decreasing values of peak separation. The slopes of graphical plots of Ipeak (anodic) vs. ν1/2 for the fully charged samples reverse direction at very high lanthanum/cerium values. The results suggest that the discharge plateau is optimum at lanthanum/cerium ratio around 12.