Effects of Mm(NiCoAlMn)_5 Hydrogen Storage Alloy Coated with Ni-Co-P Alloy by Electroless Plating on the Electrochemical Properties of Hydride Electrodes

摘要

The effect of chemical plating with Ni-Co-P alloy on the properties of MH electrodes is investigated. The results show that the efficiency of storage alloy and the activation of MH electrode have been improved by introducing 1. 74 percent cobalt in the Ni-Co-P alloy coating. The initial discharge capacity is 208mAh. g~(-1). The maximum discharge capacity gets to 298. 5mAh·g~(-1). At the same time the cycle life of MH electrodes is improved. The discharge capacity of MH electrodes coated with Ni-Co-P is 88 percent of the maximum discharge capacity after 300 cycles. Whereas the discharge capacity of bare alloy electrodes retains 62 percent of the maximum capacity after 300 cycles. An increment of discharge capacity is mainly due to superposition of the oxidation current of Co as well as improved efficiency of microcurrent collection. The effect of Ni-Co-P alloy coating by electroless plating on the kinetic properties of hydride electrode has been systematically investigated by electrochemical techniques. The results indicated that the kinetic properties of MH electrode, including exchange current density i_0 limiting current density i_L have been improved markedly. This improvement of kinetic properties led to the decrease of overpotential of anodic and cathodic polarization.