Self-discharge Performance Research Of R-Mg-Ni Based A₂B₇Type Hydrogen Storage Aolly

In this thesis, previous research works on La-Mg-Ni system alloys had 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 including micro structure and electrochemical properties, mainly focusing on self-discharge. Trying to expound the influence law of self-discharge for Mg elements to the Rare-Mg-Ni hydrogen storage alloy through preparation high phase abundance of the A2B7-type La0.7-xGd0.2MgxNi3.35Al0.15(x=0-0.4)alloys. At the same time, it had discussed the influence of the adding of rare earth oxide on alloy to the self-discharge.The research results indicates that the Mg content has important influence on phase composition of alloys. Annealed alloy phase composition is mainly composed of Ce2Ni7, Gd2Co7, PuNi3,CaCu5type phase. x≤0.17,the main phases are Ce2Ni7and Gd2Co7; when x=0.15, the alloy has the highest abundance of Ce2Ni7type phase; With the increase of Mg, the Ce2Ni7type phase reduces, and the Gd2Co7type phase increases; When x>0.2, both CaCu5and PuNi3type phase abundance are increase obviously.Duing to the influence by the content of Mg alloy to the organization, the electrochemical performance of alloy changed also. With increasing the Mg, the activation performance is significantly improved, while x=0and0.4, the activation process is slow. With the increasing of Mg content in the alloy, the maximum discharge capacity of the alloys electrode increase firstly and reduce later.The maximum discharge capacity is368mAh·g-1(x=0.17).Self-discharge of the alloy mainly include two aspects:reversible self-discharge and irreversible self-discharge. Obtained from the test results, self-discharge of alloy is mainly composed of reversible capacity loss. With the increase of the content of Mg in the alloys, the charge retention (x=0.0) increased from7.9%to59.7%(x=0.17), and then gradually decreased to1.8%(x=0.4). The hydrogen partial pressure of the environment affecte self-discharge of the alloy electrodes seriously, under hydrogen pressure1atm, charge retention has increased significantly. The highest one can reach89.5%(x=0.17). After adding different rare earth oxide, self-discharge of the alloys have different degrees change. The alloys electrode which mixed CeO2, Sm2O3had lower self-discharge, which show that the two kinds of rare earth oxides have a good inhibitory effect on self-discharge. It illustrated that the two kinds of rare earth oxides have a good inhibitory effect on the self-discharge of the alloy electrode. After adding CeO2on the alloy powder,its surface was analyzed, which surface coated with a layer of film restrained the escape of hydrogen to some extent.