The Effect Of Alloying And Annealing Treatment On Electrochemical Property Of （La, Gd）-Mg-Ni Based A₂B₇Type Hydrogen Storage Alloys

In this paper, previous research works on La-Mg-Ni system alloys have been extensively reviewed. On this basis, the La-Mg-Ni based A2B7-type hydrogen storage alloys was selected as the subject of this study. By means of XRD, SEM, Rietveld analysis and the electrochemical test methods, the hydrogen storage alloys were investigated systemically. The study showed that magnesium and aluminum played an important role on improving the alloys performance. For this we focused on the effect of Mg and Al content on the comprehensive performance of alloy electrodes. Mean while, we designed the new Gd-Mg-Co alloys, the influence of magnesium content on the structure and electrochemical properties of alloys were investigated.Based on low magnesium content of Lao.64Gdo.2Mg0.1(1+x)Ni3.1Coo.3Al0.1alloys with better electrochemical properties. By changing the addition way of Mg, the effect of Mg excess on the microstructure and electrochemical properties of alloys were systematically investigated. The phase structure analyses showed that alloys were mainly consisted of Ce2Ni7/Gd2Co7-type, Pr5Co19-type, PuNi3-type and CaCus-type phases. The Ce2Ni7-type main phase abundance first increased then decreased with the increase of Mg excess. The Ce2Ni7-type phase abundance was81-87.18%when x was from0to50%. The phase abundance decreased below76.3%when x was0and80%. The electrochemical measurements results showed that the maximum discharge capacity of alloy electrodes first increased and then decreased, the electrode exhibited the maximum discharge capacity was384.6mAh·g-1when x=10%. The discharge capacity retention rate S100were maintained more than90%when x was from5to50%. The high rate discharge ability of alloy electrodes showed first increasing then decreasing trend with the increase of Mg excess. The influence of Charge transfer rate of the electrode surface on electrochemical kinetics property was the main control step. Annealing temperature had a great influence on the electrochemical properties of the alloy. The discharge capacity and cyclic stability of alloy electrode were gradually reduced with annealing temperature increased when the value of x was10%,30%and50%. The discharge capacity and cycle stability of the alloy electrode significantly increased when the value of x was80%.On the basis of the La0.8Gd0.2Ni3.3-xCo0.2Alx alloy, the influence of aluminum content on the structure and electrochemical properties of alloys were systematically investigated. The results showed that alloys mainly consisted of PuNi3-type, CaCus-type, MgCu2-type and LaNi phase. The Ce2Ni7-type phase abundance first increased and then decreased and PuNi3-type phase first decreased and then increased. The CaCus-type phase abundance is26.64%when the value of x was0.3. The electrochemical measurements showed that the discharge capacity of alloys increased with the increase of Al content, but the cyclic stability of the alloys first increased and then decreased. The alloy possessd the best electrochemical properties when the value of x was0.2.The effect of Mg on the structure and property of Gd-Mg-Co A2B7-type Gd1-xMgxCo3.25Mn0.15Al0.1hydrogen storage alloys were investigated. The results showed that the as-cast and annealed alloys mainly consisted of CaCus (GdCos)-type, Gd2Co7-type and PuNi3(GdCo3)-type phase. The Gd2Co7-type phase first increased and then decreased with the increase of Mg content, but CaCus-type phase increased. The cell volume of alloys decreased and hydrogen absorption plateau pressure increased. The electrochemical measurements showed that the increase of Mg content can improved the maximum discharge capacity of the alloy electrodes. The high charging voltage and low exchange current density leaded to the electrochemical discharge capacity reduce. The cyclic voltammetry results showed that the reversibility and discharge capacity was improved with the increase of Mg content.