Effects of addition of rare-earth element on electrochemical characteristics of ZrNi1.1Mn0.5V0.3Cr0.1 hydrogen storage alloy electrodes

The effects of the addition of cerium or Ce-rich mischmetal (Mm) on the ele ctrochemical characteristics of the ZrNi1.1Mn0.5V0.3Cr0.1 hydrogen storage alloy electrodes were investigated. The results showed that a small additio n of Ce or Mm improve greatly the activation behavior of ZrNi1.1Mn0.5V0.3Cr 0.1 alloy electrodes. It was found that Zr0.9M0.1Ni1.1Mn0.5V0.3Cr0.1 (M=Ce, Mm) alloy electrodes can be activated before 3 similar to4 charge/discharg e cycles in comparison with about 27 cycles needed to activate ZrNi1.1Mn0.5 V0.3Cr0.1 alloy electrode. In addition, the maximum discharge capacity was increased from 300 mAh/g to 316 similar to 340 mAh/g owing to the addition of Ce or Mm. However, the addition of Ce or Mm has a negative effect on the cyclic durability of Zr-based alloy electrodes. The dispersive CeNi or MmN i phases in the parent alloy act as active sites for hydrogen electrode rea ction to improve markedly the electrocatalytic activity of the Zr-based all oy electrodes. Therefore, the Zr0.9M0.1Ni1.1Mn0.5V0.3Cr0.1 alloy electrodes exhibited higher exchange current density and lower apparent activation en ergy for the hydrogen electrode reaction than ZrNi1.1Mn0.5V0.3Cr0.1 alloy e lectrode. (C) 2001 Elsevier Science B.V. All rights reserved.