无镁超点阵结构A_2B_7型La_(1-x)Y_xNi_(3.25)Mn_(0.15)Al_(0.1)合金的储氢和电化学性能

Hydrogen Storage and Electrochemical Properties of the Mg-free A_2B_7-type La_(1-x)Y_xNi_(3.25)Mn_(0.15)Al_(0.1) Alloys with Superlattice Structure

采用真空电弧熔炼和热处理(950℃×10 h)方法制备了新型无镁超点阵结构A_2B_7型La_(1-x)Y_xNi_(3.25)Mn_(0.15)Al_(0.1)(x=0,0.25,0.50,0.67,0.75,0.85,1.00)退火合金,研究了A端稀土Y元素对退火合金微观组织结构、储氢行为及电化学性能的影响.结果表明,退火合金微观组织的主相均由Ce_2Ni_7型结构组成,随稀土Y含量x增大,Ce_2Ni_7型主相丰度呈先增加后减小的规律,同时Ce_2Ni_7型主相的晶胞体积V逐渐减小.气体储氢时,x=0~0.25合金无压力-组成-温度(PCT)曲线平台且易形成氢致非晶化;当x≥0.50时,合金能有效抑制储氢时的氢致非晶化倾向且具有明显的吸/放氢平台特征,吸氢平台压范围为0.026~0.097 MPa,最大储氢量为1.418%~1.48%(质量分数),储氢性能得到极大改善.电化学测试结果表明,x=0.50~0.85的合金具有较高的电化学放电容量(350.4~381 mA·h/g),经100次充放电循环后容量保持率S100=52%~85%,其中稀土Y含量x=0.67~0.75时的合金具有良好的储氢性能及较好的综合电化学性能.合金电极的高倍率放电性能HRD900=64.5%~85.7%,氢原子在合金体相中的扩散是电极反应动力学过程的控制步骤.

The new Mg-free A 2B 7-type La 1-x Y x Ni 3.25 Mn 0.15 Al 0.1(x=0-1.00)annealed alloys with superlattice structure were prepared by vacuum arc melting and heat treatment(950℃×10 h).The influences of Y element on the microstructure,hydrogen storage behavior and electrochemical performance of annealed alloys were investigated systematically.The results show that the main phase of all the annealed alloys is Ce 2Ni 7-type.With the increase of Y content,phase abundance of the Ce 2Ni 7-type phase increases firstly and then decreases,meanwhile the cell volumes decreases gradually.The x=0-0.25 alloys are easy to form hydrogen-induced amorphization(HIA),resulting in the disappearance of the plateau of pressure-composition-temperature(PCT)curves.When x≥0.50,the alloys can effectively avoid the HIA,the PCT curves obviously present an approximately single platform,the maximum hydrogen storage capacity and the plateau pressure of hydrogenation is in the range of 1.418%-1.48%(mass fraction)and 0.026-0.097 MPa,respectively.Therefore,the hydrogen storage performance has been greatly improved.The electrochemical measurement results show that the x=0.50-0.85 alloys exhibit the high discharge capacity of 350.4-381 mA·h/g and the cyclic stability of 52%-85%after 100 cycles,and the alloy with x=0.67-0.75 has good hydrogen storage and comprehensive electrochemical properties.The high rate discharge ability(HRD 900)of the alloys is 64.5%-85.7%and reaction kinetics of the electrode is mainly controlled by the diffusion rate of the hydrogen atom in body phase of the alloys.