Electrochemical behavior of amorphous MgNi as negative electrodes in rechargeable Ni-MH batteries

A cyclic voltammogram (CV) of amorphous MgNi clearly showing the hydrogen absorption-emission processes of amorphous MgNi was obtained by using a micropaste electrode technique. The hydrogen absorption was observed as an increase in the cathodic current below -0.9 V vs. Hg/HgO, and the emission as a broad anodic peak at similar to-0.9 V These processes were considerably affected by immersion of the electrode in a KOH solution prior to measurements. The rising part of the cathodic current shifted to the cathodic direction depending on the immersion time. A decrease in the anode peak current and a remarkable shift of the anode peak potential were also observed. Using X-ray diffraction analyses, the deterioration of such electrode properties was attributed to formation of Mg(OH)(2) by the alkaline immersion. Potential step measurements gave an apparent diffusion constant (D-app) of the hydrogen in the material of 6.8-9.4 X 10(-10) cm(2)/s, irrespective of the immersion time. These results show that the Mg(OH)(2) formed has almost no effect on the diffusion of hydrogen but disturbs electron transfer processes on the electrode surface. (C) 2002 Elsevier Science BY All rights reserved.