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

The La0.7-xPrxZr0.1Mg0.2Ni3.05Co0.35Fe0.1(x=0,0.05,0.10,0.15) has been prepared with electromagnetic suspension induction under argon gas protection. The physical and chemical properties of the alloys have been test by using (XRD), PCT and electrochemical test method. XRD shows that the LaNi5and La2MgNi9phases are the main phase in La0.7-xPrxZr0.1Mg0.2Ni3.05Co0.35Fe0.1(x=0,0.05,0.10,0.15) alloys, the addition Pr can make the La2Ni7formed priority。The unit cell volume of the main phase LaNi5decreased first and then increased with the increased of the content of Pr。The maximum discharge capacity of the La0.7-xPrxZr0.1Mg0.2Ni3.05Co0.35Fe0.1(x=0.0,0.05,0.10,0.15) alloy electrodes are330(x=0.0),330(x=0.05),323.0(x=0.10) and340.0(x=0.15), respectively; the electrode capacity retention rate of alloys are73.5%(x=0.0,75.6%(x=0.05),74.7%(x=0.10) and76.6%(x=0.15), respectively. It is found that the alloy has good charge and discharge properties with x=0.15. The electrodes HRD1200of La0.7-xPrxZr0.1Mg0.2Ni3.05Co0.35Fe0.1(x=0.0,0.05,0.10,0.15) alloy with high rate discharge performance increased from74.7%(x=0.0) to77.3%(x=0.05), and then decreased to68.6%(x=0.15), the change tendency of the alloy is similar as that of the unit cell volume for La2MgNi9.When the Nd and Al added into the La-Pr-Mg-Co system, the phase structure becomes complexly, when x=0, the main alloying phases are (La,Pr)Ni5, La2Ni7and La2MgNi9; when x=0.05, besides La2Ni7and La2MgNi9, the LaAlNi4and (Nd,Pr)Co5solid solution phases are existed; when x=0.10, the main hydrogen storage phases are LaNi and La2Ni3. The maximum electrode discharge capacity of La0.55Pr0.15Mg0.2Ni3.05Co0.35(NdAl)x alloys are394mAh/g (x=0.0),405mAh/g (x=0.05),166mAh/g (x=0.10),363mAh/g (x=0.15), and336mAh/g (x=0.20), respectively. Due to the single hydrogen storage phase, the voltage width of discharging platform is minium and the discharge performance is worst when x=0.10.After Al and Nd added, the alloy electrodes polarization resistance is increased. The polarization resistance of La0.55Pr0.i5Mg0.2Ni3.05Co0.35(NdAl)x alloys are154.8mΩ,311.0mΩ255.7mΩ440.1mΩ, and222.5mΩ respectively. Adding a small amount of Al and Nd, the surface electrochemical activity of alloys eletrodes and the diffusion ability of hydrogen are decreased. However, with the increasing of the A1and Nd, the electrochemical activity of alloys eletrodes are increased. Therefore, the electric current density of alloys electrodes IL changed from538.6mA/g (x=0.0) to178.2mA/g (x=0.15) firstly, then increased to351.8mA/g(x=0.20).In order to study the hydrogen storage and electrochemical properties of La-Pr-Mg-Co syste, the La0.55Pr0.15Mg0.2Ni3.05Co0.35-x(AlFe)x (x=0.05,0.10,0.15,0.20,0.25) have been prepared by using response furnace. Results show that the LaNis, Pr(Ni,Co)s, LaA1Ni5, and Pr2MgNi9are the main phases.Beaucuse the atomic radius of Al (1.43A) and Fe(1.27A) are all larger than that of Co(1.26A), the unit cell volume of LaNi5is increased with the increased AlFe replace Co.The tendency of the voltage width for discharging platform of Lao.55Pr0.15Mg0.2Ni3.05Co0.35-x(AlFe)x(x=0.05,0.10,0.15,0.20,0.25) is (AlFe)0.05>(AlFe)0.10>(AlFe)0.15>(AlFe)0.20>(AlFe)0.25. The maxium dischaging volume of Lao.55Pro.i5Mgo.2Ni3.o5Coo.35-x(AlFe)x is366.6mAh/g(x=0.05),377.6mAh/g(x=0.10),356.7mAh/g(x=0.15),336.7mAh/g(x=0.20) and323.3mAh/g(x=0.25). It is noted that the dischage volume is maxium at x=0.10. The diffusion coeifficents of H atom in Lao.55Pro.i5Mgo.2Ni3.o5Coo.35-x(AlFe)xare6.78x10-11,10.29×10-11,6.38×10-11,9.96×10-11,7.20×10-11cm2·s-1. When x=0.15, the diffusion ability of H atom is worst. The results of dischaging volume and diffusion coeifficents show that when x=0.10, the electrochemical hydrogen storage properties of the alloys are the best.