| In this paper, sintered treatment at low temperature and added Co3O4 in hydrogen storage alloy electrode methods were taken to improve the high rate discharge preformance of AB5 type hydrogen storage alloy electrode. electrochemical test methods such as:the galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS)and Cyclic voltammogram (CV) etc and X-ray diffraction (XRD), Scanning electronic microscopy (SEM), Energy dispersive X-ray Spectroscopy (EDX), BET were carried out to study the perofrmance of hydorgen storage alloy electrode sintered at different temperature (300℃-700℃), sintered for different time (0.5 h-5 h) at 300℃and added with different content of Co3O4(2wt.%-8wt.%), especially the electrochemical dynamic performance. The mechanisms of sintered treatment and Co3O4 additive were also superficially disscussed. We aimed at the target, developing new kind of treat methods to improve the high rate discharge performance of AB5 type hydrogen storage alloy electrode effectively, to meet the developing requirement of MH/Ni battery.The effects on electrochemical performances of hydrogen storage alloy electrode sintered at different temperature were studied firstly. The results showed that:with the increasing of sintered temperature, maximum discharge capacity and discharge plat voltage of sintered electrodes decreased gradually, the discharge capacity and mid-voltage of electrode sintered at 300℃was the highest; polarization resistance Rp and charge-transfer resistance Rct increased, exchange current density Io decreased; anodic polarization curves and potential-step tests suggested limmit current density IL and hydrogen diffusion coefficient D firstly increased and then decreased; HRD performance of the electrode sintered at 300°C was the best, which is 20.92% higher comparing to the no-sintered electrode at discharge current denstiy of 1500 mA·g-1.The effects on electrochemical performance of hydrogen storage alloy electrode sintered at 300℃for different time were studied. The results suggested that:with the increasing of sintered time, activiate performance and discharge capacity of sintered electrodes decreased, mid-poteneial of sintered electrode for 1 h was highest; Rp, Rct increased and Io gradually decreased, IL and D firstly increased and then decreased. HRD performance of the electrode sintered for 1h was the best, which is 20.92% higher comparing to the no-sintered electrode at discharge current denstiy of 1500 mA·g-1Different contents of Co3O4 were added in hydrogen storage alloy electrodes and its electrochemical performance were studied. The results showed that:the activiate performance and discharge capacity of electrodes with Co3O4 additive were better than blank electrode, the higher the content of Co3O4 additive was, the better the activiate performance, discharge capacity and cyclic stability was. There was a second plat appearing in the end of discharge near 1.15 V of the electrodes with Co3O4 additive, plat voltage of which increased with the content of Co3O4 additive increased; HRD performance also increased, which is due to electrocataly activity of electrode surface and hydrogen diffusion rate enhanced and Rp decreased much with the content of Co3O4 additive increasing. The HRD of the electrode with 8 wt.% Co3O4 additive was 11.1% than blank electrode at discharge current density of 1500 mA·g-1. Oxidation peak near -0.7 V in anodic blanch corresponding to Co'Co(OH)2 oxidition reaction were observed in cyclic voltammogram curves of the electrodes with Co3O4 additive, the peak current increasing obviously with the content of Co3O4 additive increased. SEM and EDX tests suggented that Co3O4 distributed uniformitily on the surface of hydrogen storage alloy electrode, which came to the reaction of Co←'Co(OH)2, formed a layer with high content of Co on the surface, which helped to increase discharge capacity and improve high rate discharge ability. |
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