ANi_(3.33)Mn_(0.17)Co_(0.2)Al_(0.1)(A=La,Sm,Gd,Y)型储氢合金微观结构和电化学性能

Microstructure and electrochemical characteristics of ANi_(3.33)Mn_(0.17)Co_(0.2)Al_(0.1)(A=La,Sm,Gd,Y)type hydrogen storage alloys

设计和制备了ANi_(3.33)Mn_(0.17)Co_(0.2)Al_(0.1)(A=La、Sm、Gd、Y)合金,系统研究了A端稀土元素对合金退火组织与结构以及气态储氢和电化学性能的影响。结果表明,A=La、Sm、Gd合金的退火组织主要由A_(2)B_(7)型(Ce_(2)Ni_(7)+Gd_(2)Co_(7))和A_(5)B_(19)型(Pr_(5)Co_(19)+Ce_(5)Co_(19))相组成,A=Y合金则由Ce_(2)Ni_(7)、YNi_3及CaCu_(5)型相组成。当A端原子半径r_(A)按r_(La)>r_(Sm)>r_(Gd)>r_(Y)依次减小时,合金中各物相的晶胞参数a、c和晶胞体积V均随之减小,合金吸氢PCT曲线平台压力按P_(La)(0.0191 MPa)>P_(Sm)(0.0509 MPa)>P_(Gd)(0.1514 MPa)>P_(Y)(0.2129 MPa)顺序逐渐增高,其最大储氢容量(质量分数)依次为0.845%、1.313%、1.239%和1.383%。A=La、Sm、Gd、Y合金的电化学放电容量分别为255.8、377.7、266.3和205.4 mAh/g,电极容量保持率S_(100)分别为52.3、93.5、98.8和4.5%;A=La、Sm合金在3C放电倍率下的HRD_(900)为84%~85%,A=Gd、Y合金的HRD_(900)分别为46.8%和63.4%。随A端元素r_(A)增大,超点阵结构的堆垛单元体积差V_(d)和循环后的衍射峰宽度FWHM均逐渐增加,此时合金的氢致非晶化倾向逐渐增大,进而影响了合金的电化学循环稳定性。A=Sm、Gd合金不仅具有较小的r_(A)和V_(d)值,其抗耐蚀性也较佳,因而具有优良的电化学循环稳定性(S_(100)=94%~98%),其中A=Sm合金具有最佳的综合电化学性能。

ANi_(3.33)Mn_(0.17)Co_(0.2)Al_(0.1)(A=La,Sm,Gd,Y)alloys were designed and prepared.The effects of A-terminal rare earth elements on the annealed microstructure and structure,gaseous hydrogen storage and electrochemical properties of the alloys were systematically studied.The results show that the annealed microstructures of A=La,Sm,Gd alloys are mainly composed of A2B7-type(Ce_(2)Ni_(7)+Gd_(2)Co_(7))and A5B19-type(Pr_(5)Co_(19)+Ce_(5)Co_(19))phases,while A=Y alloys are composed of Ce_(2)Ni_(7),YNi_(3)and CaCu_(5)-type phases.When the atomic radius r_(A)of A terminal decreases in the order of r_(La)>r_(Sm)>r_(Gd)>r_(Y),the unit cell parameters a,c and the unit cell volume Vof each phase in the alloy decrease.The plateau pressure of the hydrogen absorption PCT curve of the alloy gradually increased in the order of P_(La)(0.0191MPa)>P_(Sm)(0.0509MPa)>P_(Gd)(0.1514MPa)>P_(Y)(0.2129MPa),and the maximum hydrogen storage capacity was 0.845,1.313,1.239and 1.383wt%,respectively.The electrochemical discharge capacities of A=La,Sm,Gd and Y alloys are 255.8,377.7,266.3and 205.4mAh/g,respectively,and the electrode capacity retentions S100are 52.3%,93.5%,98.8%and 4.5%,respectively.The HRD900of A=La and Sm alloys at 3Cdischarge rate is 84%~85%,and the HRD900of A=Gd and Y alloys is 46.8%and 63.4%,respectively.With the increase of the A-terminal element r_(A),the volume difference V_(d)of the stacking unit of the superlattice structure and the width FWHM of the diffraction peak after the cycle gradually increase.At this time,the hydrogen-induced amorphization tendency of the alloy gradually increases,which in turn affects the electrochemical cycle stability of the alloy.A=Sm and Gd alloys not only have small r_(A)and V_(d)values,but also have good corrosion resistance,so they have excellent electrochemical cycle stability(S_(100)=94%~98%).Among them,A=Sm alloy has the best comprehensive electrochemical performance.