Degradation of amorphous MgNi electrode and effect of heat treatment in Ar

The mechanism underlying degradation of an amorphous MgNi electrode was studied. Amorphous MgNi powder was prepared by mechanical alloying, and a charge/discharge cycle test was carried out in 6 M KOH solution. The amount of hydrogen absorbed in the charge process was determined by vacuum hydrogen extraction. The discharge capacity decreased rapidly with progress of the cycle test. The results of the hydrogen extraction indicated that almost all hydrogen absorbed in the charge process was released in the discharge process. X-ray diffraction analyses showed that Mg(OH)(2) was formed on the surfaces of MgNi particles after the cycle test, It was deduced that the reduction in the discharge capacity was mainly due to the degradation in absorption capability in the charge process caused by retardation of electron transfer by Mg(OH)(2) layer. The cyclic stability of the discharge capacity was improved by heat treatment in Ar at 573 K. (C) 2002 Elsevier Science BY All rights reserved.