Hydrogen Storage Properties And Electrochemical Characteristics Of La-Mg-Ni-Co Based Alloys

Different element constituents of La-Mg-Ni-Co based alloys were prepared by induction melting under Ar atmosphere. The effects of Zr, Fe, Al, Pr, and annealing treament on phase structures, hydrogen storage and electrochemical properties of La-Mg-Ni-Co based alloys were investigated by XRD, PCT, charge and discharge cycling stability, high rate dichargeability, cyclic voltammograms, linear polarization, and Tafel polarization etc..The x-ray diffraction paterns showed that a series of La-Mg-Ni-Co based alloys mainly consist of LaNis and La2Ni7phases. It can be found that ZnNi phase appears in La0.7Zr0.1Mg0.2Ni2.75Co.75-xFex (x=0,0.05,0.1,0.15,0.2) alloys when;x≥0.15and ZrFe2phase occurs in La0.7Zr0.iMg0.2Ni2.75Co0.75-xFex(x=0,0.05,0.1,0.15,0.2) alloys when x≥0.05. The cell volumes and lattice parameters of LaNis and La2Ni7phases in La0.7Zr0.1Mg0.2Ni2.75Co0.65-xAlxFe0.1(x=0.0-0.4) alloys increased with the increasing of Al content, while cell volume of LaNis in La0.7-xPrxZr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2(x=0.00-0.20) alloys decreased from88.02A3(x=0.00)to86.57A3(a=0.20) with the larger atomic element La (1.69A) substituted by smaller atomic radius element Pr (1.65A) It was showed that hydrogen storage properties of La-Mg-Ni-Co based alloys can be improved by optimizing elemental constituents and proportions. PCT curves show that with increasing of Zr content in La0.7Zr.rMg0.3-xNi2.75Co0.75(x=0-0.2) alloys, maximum hydrogen storage capacity increased from1.36wt%(x=0.00) to1.40wt%(x=0.05) while hydrogen absorption/desorption plateau decreased slightly. With Fe substituting for Co, the maximum hydrogen storage capacity of La0.7Zr0.1Mg0.2Ni2.75Co0.70Fe0.05alloy was larger than La0.7Zr0.1Mg0.2Ni2.75Co0.75alloy’s about0.07wt.%.From charge/discharge cyclic stability curves can be found that the maximum discharge capacity and cyclic stabiltiy of alloy electrodes can be improved by changing A side or B side elements. Though the maximum discharge capacity of La0.7Zx-Mg0.3-xNi2.75Co0.75(x=0,0.05,0.1,0.15,0.2) alloy electrodes reduced slightly with increasing x, the charge/discharge cyclic stability linear increased. It can be seen that the capacity retention rate (S100) of La0.7Zr0.1Mg0.2Ni2.75Co0.75-xFex(x=0-0.2) alloy electrodes increased from44.4%(x=0.00) to55.4%(x=0.20) and the maximum discharge capacity were1.25wt.%(x=0.00),1.32wt.%(x=0.05),1.28wt.%(x=0.10),1.29wt.%(x=0.15),1.27wt.%(x=0.20) respectively. With Pr partial substituting for La on A side, the maximum discharge capacity of La0.7-xrPrxZr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2(x=0.00,0.05,0.10,0.15,0.20) alloy electrodes only slightly change, but cyclic stability S200(S200=C200/CMax) increased from66.2%(x=0.00) to75.1%(x=0.20).The high rate dischargeability investigations revealed that A side elements modified by Zr in La0.7ZrxMg0.3-xNi2.75Co0.75alloy electrodes were disadvantage to the high rate dischargeability. However, with Fe substituting for Co, high rate dischargeability of La0.7Zr0.1Mg0.2Ni2.75Co0.75-xFex(x=0,0.05,0.1,0.15,0.2) alloy electrodes increased firstly then descreased and exhibited better high rate dischargeability when x=0.10. Cyclic voltammograms and Tafel polarization revealed that La0.7Zr0.1Mg0.2Ni2.75Co0.65Fe0.1alloy electrode exhibited relative higher exchange current density Io and hydrogen diffusion coefficient D to La0.7Zr0.1Mg0.2Ni2.75Co0.75-xFex(x=0,0.05,0.15,0.2) alloy electrodes.