Structure and Electrochemical Properties of New Mg-free YNi3.5-xAlx(x=0—0.3) Hydrogen Storage Alloys
DENG Anqiang1, 2, 3, LUO Yongchun1, 2, WANG Hao1, ZHAO Lei1, ZHENG Kun1
1 School of Materials Science and Engineering, Lanzhou University of Technology, Lanzhou 730050, China 2 State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China 3 School of Mechanical Engineering, Ningxia University, Yinchuan 750021, China
Abstract: YNi3.5-xAlx(x=0,0.05,0.1,0.15,0.2,0.3) hydrogen storage alloys were prepared by vacuum arc melting and vacuum annealing heat treatment.Structural analysis of the alloys showed that the main phase of the alloys was A2B7 superlattice structural phase.The main phase of alloys was Gd2Co7-type. When x=0,which transformed to Ce2Ni7-type after adding Al element.Aluminium occurs mainly at the 6h site of CaCu5-type slab in Ce2Ni7 phase althongh the solubility is limited.When x>0.1, the CaCu5 phase as the second phase appears in the alloy, which has the greater solid solution for Al elecment than that of the main phase.The greater the solid solution in Ce2Ni7 phase for Al elecment, the smaller the volume mismatch between Laves slab and CaCu5 slab in superlattice. The plateau pressure during hydrogen absorption/desorption of alloy electrodes decreases with the increase of Al element,while the plateau pressure increases slightly due to the appearance of CaCu5 -type phase after x>0.1. The maximum discharge capacity of alloy electrodes increases from 105.52 mAh·g-1 at x=0 to 282.7 mAh·g-1 at x=0.3 with the increase of Al content. With further increasing Al content, especially when x≥0.1, Al was dissolved greater into the second phase of CaCu5 while the solid solution in the main phase of Ce2Ni7 decreases gradually. The cyclic stability of alloy electrodes decreases from 52.89% at x=0 to 6.5% at x=0.3 due to the increase of volume mismatch between Laves slab and CaCu5 slab.The electrode kinetics of Y2Ni7 alloy electrodes was poor, and the HRD900 was only 5.83%. With increasing the Al content, the dynamic properties of the alloys first increased and then decreased, and HRD900 was 79.04% at x=0.15.High rate dischargeability characteristics of alloy electrode was controlled by the hydrogen diffusion rate in the bulk alloy when x≤0.15 and by the charge transfer rate on the alloy electrode surface when x>0.15.
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2020, Vol. 34 
