ELECTROCHEMICAL PROPERTIES OF HYDROGEN STORAGE ALLOYS MODIFIED WITH FOREIGN METALS

For improving the performance of a Mm(Ni3.6Mn0.4Al0.3Co0.7)0.92 electrode, its surface was modified by the electrodeposition of a foreign metal and the electrochemical characteristics of the resulting electrode were measured. The electrocatalytic activity evaluated from the anodic peak current on the potential sweep voltammograms for hydrogen oxidation was found to increase in the order of Fe < Ni < Co < Pd coatings. The saturation value of discharge capacity and the rate of activation during the charge-discharge cycling were remarkably enhanced by the surface modification with Co and Pd coatings. The surface modification also improved the high-rate dischargeability of Mm(Ni3.6Mn0.4Al0.3Co0.7)0.92 electrode up to the high value comparable to that of a LaNi5 electrode. Such high performance of the modified electrodes was ascribed to the formation of a conducting network and improved electrocatalytic activity for the hydrogen electrode reactions.