无镨钕高功率La_(1-x)Ce_x(NiCoM)_5贮氢合金电化学性能的研究(一)

The electrochemical properties of La_(1-x)Ce_x(NiCoM)_5 hydrogen storage alloys

采用真空电弧熔炼-热处理方法制备了一系列无镨钕高功率La1-xCex（NiCoM）5贮氢合金,研究了其相结构和电化学性能,考察了其电化学动力学特性.XRD分析结果表明,合金均为单一的CaCu5型六方结构相,晶胞体积和晶胞参数随Ce含量的增加而减小,导致最大放电容量下降.随Ce含量增加（x=0.08~0.46）,氢的扩散系数由10.5×10-11 cm2/s增加至16.6×10-11 cm2/s,交换电流密度由101.1mA/g增加至123.5mA/g,合金极化电阻由254.0mΩ下降至207.9mΩ,表明合金表面电催化活性和大电流放电循环稳定性有所改善;当Ce的含量达到0.46后,再继续增加,贮氢合金的电化学动力学性能反而下降.试验结果表明：当Ce含量为0.46时,合金电极具有较好的表面电催化活性和电化学动力学性能.此时,合金电极7C放电容量为239.8mA·h/g,大电流充放电循环寿命为310次.

A series of AB5-type PrandNdfree highpower La1-xCex（NiCoM）5hydrogen storage alloys were synthesized in the induction furnace melting-heat treatment process.Electrochemical kinetic properties of these alloys were investigated.XRD results indicate this series of hydrogen storage alloys show a CaCu5-type hexagonal structure,and the unit cell volume and parameter decrease as Ce content increases,which results into the decrease in maximum discharge capacity.When the Ce content increases from 0.08 to 0.46,the hydrogen diffusion coefficient increases from 10.5×10-11 cm2/s to 16.6×10-11 cm2/s,the exchange current density increases from 101.1mA/g to 123.5mA/g,and the polarization resistance decreases from254.0mΩto 207.9mΩ.Results indicate that electrocatalytic activity at the electrode/electrolyte interface and high current cyclic stability of alloys are improved.When the Ce content is more than 0.46,electrochemical kinetic properties of hydrogen storage alloy decrease.In conclusion,when Ce content is 0.46,the alloy electrode has favorable electrocatalytic activity and electrochemical kinetic properties.Specifically,the discharge capacity of 7calloy electrode is 239.8mA·h/g,and high current charge-discharge cycle life is310 cycles.