Effects Of Gd, Co And Mg Element On Electrochemical Properties Of Rare Earth Based A₂B₇-type Hydrogen Storage Alloys

In this thesis, previous research works on R-Mg-Ni (R=La,Ce,Pr,Nd) system alloys had been extensively reviewed. On this basis, the La-Mg-Ni based A2B7-type hydrogen storage electrode alloys was selected as the subject of this study. By means of XRD, EPMA, Rietveld analysis and the electrochemical test methods,the hydrogen storage alloys, which were substituted by Gd, Co, Mg elements, were investigated systemically.The effect of Gd element on the microstructure, hydrogen storage properties and electrochemical properties of La_0.83-xGd_xMg_0.17Ni₍3.05_Co_0.3Al_0.15 (x=0⁰.5) were investigated systematically. The results showed that substitution of La by Gd element led to significant decrease in CaCu₅ type phase abundance and an increase in Ce₂Ni₇-type phase abundance. Meanwhile, with increasing Gd content, Ce₂Ni₇-type phase abundance first increased and then decreased. The plateau pressure of PCT curves rose gradually and became flatter when x increased. The electrochemical measurements showed that the discharge capacity of the alloys first increased and then decreased with the increase of Gd, the maximum discharge capacity of the alloys reached 392.9mAh/g when x was 0.2. After 100 charge-discharge cycles, the discharge capacity retention rate S100 of the alloy electrode(x=0.2) reached 91.2%.The effects of Gd, Co element on the microstructure, hydrogen storage properties and electrochemical properties of La_0.83-xGd_xMg_0.17Ni₍3.35-2x_Co_2xAl_0.15 (x=0⁰.83) hydrogen storage alloys were investigated. The results showed that the increase of Gd and Co could obviously change the microstructure and led to significant increase in Ce2Ni7-type phase abundance. The plateau pressure of PCT curves rose gradually and became flatter when x increased. The electrochemical measurements showed that all these alloys had a good activation performance. The discharge capacity of the alloys first increased and then decreased with the increase of x.Based on La_0.8Gd_0.2Ni_3.1Co_0.3Al_0.1 alloys, the effects of Mg content on La_0.8-xGd_0.2Mg_xNi_3.1Co_0.3Al_0.1 (x=0⁰.4) alloy structure, hydrogen storage properties and electrochemical properties were examined systematically. Experiment results showed that Ce2Ni7-type phase abundance first increased and then decreased with increasing Mg content. When the Mg content was low, alloys would showed hydrogen induced amorphous phenomenon. When Mg content increased, amorphous phenomenon disappeared, alloy electrodes exhibited high discharge capacity and good kinetic properties. When Mg content increased further, and the overall electrochemical properties of alloy electrodes would be deteriorated.