Degradation mechanism of the misch metal alloy hydride electrodes

Pieces of nonpulverized misch metal (Mm) alloy were used as working electro des (WEs). The WEs were cathodically charged in H-2 and O-2 atmospheres, re spectively, and the electrode potentials were determined. The morphologies of definite areas of WEs were observed by SEM, and the surface composition in chemical elements of these areas were determined by EPMA. The results in dicated that the main causes of the degradation of WEs might be the increas e of internal stress, the expansion of crystal lattice, and the preferentia l dissolution of Mm during charging, rather than the oxidation of the alloy by O-2, which was accordant with the presence of La3+ and Ni2+ in the MH e lectrode of MH/Ni batteries after cycling. (C) 1999 Elsevier Science S.A. A ll rights reserved.