Degradation mechanism of Ti-Zr-V-Mn-Ni metal hydride electrodes

The degradation mechanism of Ti-Zr-V-Mn-Ni metal hydride electrodes was investigated because they rapidly degraded within 10 cycles despite having a high discharge capacity of 360 similar to 464 mAh g(-1) at the first cycle. It was observed that Ti-oxide formed and grew on the surface of the alloy powder in the early and later stages of degradation using the scanning electron microscopy (SEM) and the auger electron spectroscopy (AES) analyses. Also, it was found that the contact and the reaction resistances for the electrochemical hydrogenation reaction increased as the number of cycles increased using the EIS (Electrochemical Impedance Spectroscopy) analysis. It was suggested that the reason for the degradation of Ti-based hydride electrodes was because it was extremely difficult for hydrogenation to occur through the Ti-oxide film into the inner part of the alloy. This was due to a high polarization resistance during the electrochemical hydrogenation reaction, which included the resistance of the hydrogen diffusion through the Ti-oxide film and the resistance of the electron conduction between Ti-oxide on the surface of the alloy powder and external circuits, as well as between the Ti-oxide layers on the surface of the alloy powders. (C) 1997 Elsevier Science S.A.