高倍率贮氢合金电极的制备及电化学性能研究

【作者】 李傲生；

【导师】 刘开宇；

【作者基本信息】 中南大学 ， 应用化学， 2010， 硕士

【摘要】 本文提出采用低温烧结及在贮氢合金电极中添加Co3O4的两种方法来改善AB5型贮氢合金电极的高倍率性能。采用XRD、SEM、EDX、BET和恒电流充放电,循环伏安以及电化学阻抗等电化学测试手段,研究了不同烧结温度(300℃～700℃)以及时间(0.5 h～5 h)处理的贮氢合金电极的电化学性能和不同Co3O4添加量(2 wt.%～8wt.%)的贮氢合金电极的电化学性能,尤其是两者的电化学动力学性能,初步探讨烧结机理以及Co3O4的作用机理,以求探索出能有效提高贮氢合金电极的高倍率性能的处理方法来满足MH/Ni动力电池发展需要。本文首先研究了烧结温度(300℃～700℃)对于贮氢合金电极电化学性能的影响,研究表明,随着烧结温度的升高,烧结贮氢合金电极的最大放电容量以及放电平台电压逐渐降低,300℃烧结电极放电容量和中值电位最高；极化电阻Rp、电荷转移电阻Pct逐渐增大,交换电流密度I0逐渐减小,烧结温度为300℃时候,Rp和Rct较未烧结合金电极分别降低34.7%和67.5%,I0提高53.0%；阳极极化和电位阶跃测试结果表明,烧结处理后,合金电极的氢扩散系数D明显增大,但随烧结温度升高呈先增大后减小趋势。合金电极的大倍率放电性能的变化规律跟上述几个动力学参数的变化规律基本一致,300℃烧结电极的大倍率性能最好,以1500 mA·g-1电流密度放电时,其HRD值较未烧结电极提高20.92%。研究了300℃不同烧结时间(0.5 h～5 h)对于贮氢合金电极电化学性能的影响。结果表明,烧结电极的活化性能以及放电容量随烧结时间延长逐渐降低,放电平台电压先增大后略有减小,烧结1 h电极放电中值电位最高；Rp和Rct均逐渐增大,I0逐渐减小；阳极极化测试表明,各烧结电极IL均要大于未烧结电极且随烧结时间延长呈先增大后减小的趋势,电极的氢扩散系数也符合这个规律。烧结电极的高倍率放电性能明显优于未烧结合金电极,随烧结时间增加,HRD值呈先增大后减小趋势,烧结1h电极性能最好,以1500mA·g-1电流密度放电时,其HRD值较未烧结电极提高20.92%。研究了不同Co3O4添加量的贮氢合金电极的电化学性能并初步探讨其作用机理。结果表明,添加Co3O4的贮氢合金电极具有较好的活化性能和较高的放电容量,Co3O4添加量越高,电极活化性能越好,放电容量越高,循环稳定性越好；添加Co3O4电极在放电末期1.15 V附近出现2次放电平台,随Co3O4添加量增大,2次放电平台愈加明显,平台电压增高；添加Co3O4贮氢合金电极Rp和Rct减小,10增大,电极表面的电催化活性提高,氢扩散速度加快,电极高倍率性能得到改善,Co3O4添加量越多,HRD值越大,以1500 mA·g-1电流密度放电时,添加8wt.%电极HRD比空白电极提高11.1%。添加Co3O4的贮氢合金电极的循环伏安曲线在阳极分支—0.7V附近出现Co→Co(OH)2氧化峰,峰电流随Co3O4添加量增大而增大。SEM和EDX测试表明,添加的Co3O4在电极表面分布较为均匀,通过电极反应在贮氢合金表明形成了含Co层,有利于增加电极放电容量和提高倍率性能。更多还原

【Abstract】 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.更多还原