锂空气电池二氧化锰催化剂的制备及性能研究

发布时间：2018-03-15 20:02

本文选题：空气电极催化剂　切入点：二氧化锰　出处：《哈尔滨工业大学》2014年硕士论文　论文类型：学位论文

【摘要】：阴极催化剂是限制锂空气电池性能的一个决定性因素。现有的高效催化剂大部分是贵金属催化剂，其价格昂贵且储量有限。过渡金属氧化物价格低廉且易于制备，作为氧电极催化剂引起了广泛关注。本文研究重点是氧化锰、氧化钴和氧化钴-氧化锰复合材料在中性电解液中的ORR催化性能。在电化学测试中，工作电极首先选择了空气扩散电极，但是由于空气扩散电极导电性差，且手工压制电极的重现性不好，所以工作电极最终选用以催化剂修饰的玻碳电极。本文中LSV曲线在-0.6V左右出现ORR电流峰，所以以该电位下的电流密度表征催化剂性能。本文采用静电纺丝法制备了氧化锰催化剂，并对其电催化性能进行了研究。静电纺丝产物为Mn3O4，其催化性能很低，故选用水热法制备氧化锰材料。采用水热法制备氧化锰，以过硫酸铵为氧化剂，比较了反应温度分别为120oC、140oC、160oC和180oC，反应时间分别为6h、12h和24h时产物的催化性能。反应温度为120oC时材料XRD衍射峰很低且形貌呈现块状，其余反应温度下制备出材料均为β-MnO2纳米线。在反应温度为140oC、反应时间为12h时材料的催化性能最好，电流密度高达-29.07mA·cm-2。为了比较-MnO2与β-MnO2的催化性能，以高锰酸钾为氧化剂制备氧化锰。同样进行反应温度和反应时间的选择，不同温度和时间条件下制备的材料均为-MnO2纳米线，随着反应时间的延长，，材料的长度增大。在反应温度为120oC、反应时间为12h时，-MnO2催化活性最高，电流密度高达-34.50mA·cm-2。以两种材料的最佳反应条件比较，-MnO2的催化活性高于β-MnO2。因此，选择以-MnO2为基体进行Co元素的掺杂。对-MnO2掺杂之前首先研究氧化钴的性能。以硝酸钴为静电纺丝液主盐，在500oC烧结得到块状Co3O4，其电流密度为-1.18mA·cm-2。水热法制备出聚合为块状的Co3O4，加入分散剂PVP和PEG，PEG能够使材料分散，但是两者都不能提高材料的催化性能。最佳反应时间为12h，反应温度为120oC，电流密度达到-3.74mA·cm-2。与静电纺丝法制备的Co3O4相比水热法制备的Co3O4电催化活性较高。以硝酸钴为Co元素来源，采用水热法向-MnO2中掺杂摩尔分数分别为2%、5%和10%的Co元素，能谱测试表明材料中Co与Mn的比例与原料掺杂比例相当，但是复合催化剂电流密度与-MnO2相比反而下降。直接将-MnO2与Co3O4材料混合作为催化剂，其电流密度与-MnO2相比也降低。本文中的掺杂和混合催化剂都没有提高材料的催化性能。
[Abstract]:Cathode catalyst is a decisive factor in limiting the performance of lithium-air battery. Most of the available high-efficient catalysts are precious metal catalysts, which are expensive and have limited reserves. Transition metal oxides are cheap and easy to prepare. As a catalyst of oxygen electrode, this paper focuses on the ORR catalytic properties of manganese oxide, cobalt oxide and cobalt oxide / manganese oxide composites in neutral electrolyte. In electrochemical measurement, air diffusion electrode is first selected as working electrode, but because of the poor conductivity of air diffusion electrode and the poor reproducibility of manually pressed electrode, In this paper, the LSV curve of glassy carbon electrode modified by catalyst appears the peak of ORR current at -0.6 V, so the current density at this potential is used to characterize the performance of the catalyst. In this paper, manganese oxide catalyst was prepared by electrospinning method, and its electrocatalytic activity was studied. The product of electrostatic spinning was Mn3O4, and its catalytic activity was very low. Therefore, the hydrothermal method was used to prepare manganese oxide material, and the hydrothermal method was used to prepare manganese oxide. Using ammonium persulfate as oxidant, the catalytic properties of the product were compared at 120oC 140oC and 180oC, respectively, and the reaction time was 6h / 12h and 24h respectively. The XRD diffraction peak of the material was very low and the morphology was block when the reaction temperature was 120oC. The other materials were 尾 -MnO _ 2 nanowires at the reaction temperature of 140 OC and reaction time of 12 h, and the current density was up to -29.07 Ma 路cm ~ (-2). In order to compare the catalytic properties of -MnO _ 2 with 尾 -MnO _ 2, the catalytic properties of 尾 -MnO _ 2 and 尾 -MnO _ 2 were compared. Manganese oxide was prepared by using potassium permanganate as oxidant. Similarly, the reaction temperature and reaction time were selected. The materials prepared under different temperature and time were -MnO2 nanowires, and with the increase of reaction time, When the reaction temperature is 120oC and the reaction time is 12h, the catalytic activity is the highest and the current density is up to -34.50mA 路cm-2.Compared with the optimum reaction conditions, the catalytic activity of the two materials is higher than that of 尾 -MnO2.Therefore, when the reaction temperature is 120oC and the reaction time is 12h, the catalytic activity of MNO _ 2 is higher than that of 尾 -MnO _ 2. The Co element was doped with -MnO2 as substrate. The properties of cobalt oxide were studied before doping of -MnO2. Bulk Co _ 3O _ 4 was sintered at 500oC with a current density of -1.18mA 路cm ~ (-2) using cobalt nitrate as the main salt of electrospinning solution. Co _ 3O _ 4 was prepared by hydrothermal method, and the dispersant PVP and PEGG were added to disperse the material. But neither of them can improve the catalytic performance of the materials. The optimum reaction time is 12h, the reaction temperature is 120oC, the current density is -3.74mA 路cm-2.The electrocatalytic activity of Co3O4 prepared by hydrothermal method is higher than that of Co3O4 prepared by electrospinning. Cobalt nitrate is the source of Co. The molar fraction of Co doped to -MnO2 by hydrothermal method is 2% and 10%, respectively. The results of energy spectrum analysis show that the ratio of Co to mn in the material is the same as that of raw material. However, the current density of the composite catalyst is lower than that of -MnO2. The current density of the composite catalyst mixed directly with Co3O4 is also lower than that of -MnO2. Neither the doped catalyst nor the mixed catalyst in this paper has improved the catalytic performance of the catalyst.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM911.41;O643.36

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