Effects of addition of rare-earth element on electrochemical characteristics of ZrNi 1.1Mn 0.5V 0.3Cr 0.1 hydrogen storage alloy electrodes

Abstract

The effects of the addition of cerium or Ce-rich mischmetal (Mm) on the electrochemical characteristics of the ZrNi 1.1Mn 0.5V 0.3Cr 0.1 hydrogen storage alloy electrodes were investigated. The results showed that a small addition of Ce or Mm improve greatly the activation behavior of ZrNi 1.1Mn 0.5V 0.3Cr 0.1 alloy electrodes. It was found that Zr 0.9 M 0.1Ni 1.1Mn 0.5V 0.3Cr 0.1 ( M=Ce, Mm) alloy electrodes can be activated before 3∼4 charge/discharge cycles in comparison with about 27 cycles needed to activate ZrNi 1.1Mn 0.5V 0.3Cr 0.1 alloy electrode. In addition, the maximum discharge capacity was increased from 300 mAh/g to 316∼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 MmNi phases in the parent alloy act as active sites for hydrogen electrode reaction to improve markedly the electrocatalytic activity of the Zr-based alloy electrodes. Therefore, the Zr 0.9 M 0.1Ni 1.1Mn 0.5V 0.3Cr 0.1 alloy electrodes exhibited higher exchange current density and lower apparent activation energy for the hydrogen electrode reaction than ZrNi 1.1Mn 0.5V 0.3Cr 0.1 alloy electrode.