The electrochemical activation and surface properties of Zr-based AB(2) metal hydride electrodes

The slow activation rate of Zr-based AB(2) metal hydride electrodes is one of the reasons retarding their commercialization. Some activation pretreatments of Zr-based alloy powders and electrodes were examined in this work. It was found that alloy powders and electrodes treated by KOH immersion did not show much improvement in their activation properties and extending the immersion time deteriorated the discharge capacity. In contrast, hot charging pretreatment not only made the electrode fully activated after the first cycle, but also increased its discharge capacity. The different activation properties of the electrodes were analyzed on the basis of surface examinations by SEM, AES and XPS. It was found that an electrochemical active surface of Zr-based alloys should have a metallic Ni-rich layer on top of the surface to catalyze the charge transfer reaction and be porous for hydrogen penetration.