Effects of addition of rare-earth element on electrochemical characteristics of ZrNi_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) hydrogen storage alloy electrodes

摘要

The effects of the addition of cerium or Ce-rich mischmetal (Mm) on the electrochemical characteristics of the ZrNi_(1.1)Mn_(0.5)V_(0.3)Cr_(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_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) alloy electrodes. It was found that Zr_(0.9)M_(0.1)Ni_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) (M=Ce, Mm) alloy electrodes can be activated before 3 approx 4 charge/discharge cycles in comparison with about 27 cycles needed to activate ZrNi_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) alloy electrode. In addition, the maximum discharge capacity was increased from 300 mAh/g to 316 approx 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_(0.1)Ni_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) alloy electrodes exhibited higher exchange current density and lower apparent activation energy for the hydrogen electrode reaction than ZrNi_(1.1)Mn_(0.5)V_(0.3)Cr_(0.1) alloy electrode.