Study Of Phase Structure And Electrochemical Properties Of Low Cost AB₅Type Hydrogen Storage Alloys

The commercial low cost Co-less or Co-free AB5-type alloys are prepared bysubstituting Co element with cheap metal elements, however, the overallelectrochemical properties decrease. The cost performance of low cost AB5-type alloysneeds improving market competition. In other words, the cost of the alloy needsdecreasing and the overall electrochemical properties of the alloys need improving.Therefore, the cheaper FeB and FeV alloys are substituted for Cu or Ni of the low costAB5-type alloys to improve the cost performance.The hydrogen storage alloys La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75-x(Fe_0.43B_0.57)_x,La_0.7Ce_0.3Ni_3.75-xMn_0.35Al_0.15Cu_0.75(Fe_0.43B_0.57)_x, La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75-x(Fe_0.19V_0.81)_x, La_0.7Ce_0.3Ni_3.75-xMn_0.35Al_0.15Cu_0.75(Fe_0.19V_0.81)_x(x=0,0.05,0.10,_0.15,0.20) were prepared in vacuum furnace under the protection of argon atmosphere andthen annealed at1223K for10h. The phase structure of the alloys was characterizedby XRD. The electrochemistry impedance spectroscopy （EIS）, linear polarization,potentialstatic step discharge etc were measured to analyse the kinetics of the alloys.The electrochemical properties were measured by using a galvanostatic method.The results for La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75-x(Fe_0.43B_0.57)_xhydrogen storagealloys shows that La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75alloy consists of a singleCaCu5-type structure phase. The alloys containing FeB are composed of CaCu5-typestructure phase as matrix phase and La₃Ni₁₃B₂as secondary phase, and the abundanceof the secondary phase gradually increases with increasing x value. As x increases from0.00to0.20, the maximum discharge capacity （Cmax） of the alloy electrodesmonotonically decreases from314.0to290.4mAh/g. Cycling stability of the alloyelectrodes increases with increasing x value. High-rate dischargeability at the dischargecurrent density of1200mA/g first increases from51.4%（x=0） to57.2%（x=0.10）,and then decreases to52.7%（x=0.20）. The improvement in electrochemicalcharacteristics is ascribed to the secondary phase La₃Ni₁₃B₂, which improves theelectrochemical activity of electrode surface, as well as to the phase boundary inmultiphase structure, which decreases the lattice distortion and strain energy andenhances the anti-pulverization property of the alloy electrodes. The results for La_0.7Ce_0.3Ni_3.75-xMn_0.35Al_0.15Cu_0.75(Fe_0.43B_0.57)_xhydrogen storagealloys shows that the alloys consist of a single phase with the CaCu5-type structure,and lattice parameters c, cell volume V and c/a ratio increase with increasing x value.The Cmaxof the alloy electrodes first increases from311.0（x=0） mAh/g to316.0mAh/g (x=_0.15), and then decreases to311.0mAh/g （x=0.20）. The HRD1200firstincreases from51.3%（x=0） to6_0.7%(x=_0.15), and then decreases to53.6%（x=0.20）. The charge-transfer reaction at the electrode/electrolyte interface and thehydrogen diffusion in the bulky alloys are responsible for the high-rate dischargeability.Cycling stability first increases with increasing x from0to0.10and then decreaseswhen x increases to0.20, which is resulted from the combined effect of theimprovement of the pulverization resistance and the deterioration of corrosionresistance with increasing x value.The results for La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75-x(Fe_0.19V_0.81)_xhydrogen storagealloys shows La_0.7Ce_0.3Ni_3.75Mn_0.35Al_0.15Cu_0.75-x(Fe_0.19V_0.81)_xalloys consist of a singlephase with CaCu5-type structure, and the lattice parameter a and cell volume Vincrease with increasing x value. The Cmaxfirst increases from319.0（x=0） mAh/g to324.0mAh/g （x=0.05）, and then decreases to307.0mAh/g （x=0.20）. The HRD1200first increases from52.1%（x=0） to59.1%(x=_0.15), and then decreases to55.4%（x=0.20）. The hydrogen diffusion in the bulky alloy is responsible for the high-ratedischargeability. Cycling stability first increases with increasing x from0to0.10andthen decreases when x increases to0.20, which is resulted from the synthesized effectof the improvement of the pulverization resistance and the decrease of corrosionresistance.The results for La_0.7Ce_0.3Ni_3.75-xMn_0.35Al_0.15Cu_0.75(Fe_0.19V_0.81)_xhydrogen storagealloys shows all alloys consist of a CaCu5-type structure single phase. The latticeparameters a and cell volume V increase with increasing x value. The Cmaxmonotonically decreases from320mAh/g （x=0） to299mAh/g （x=0.20）, which isascribed to the decrease of the kinetics property. The HRD1200first increases from52.6%（x=0） to55.6%（x=0.05）, and then decreases to46.7%（x=0.20）. Cyclingstability first increases with increasing x from0to0.10and then decreases when xincreases to0.20, which is resulted from the combined effect of the improvement of the pulverization resistance and the deterioration of corrosion resistance with increasing xvalue.