四氧化三钴纳米材料的控形制备及其电化学性能研究

发布时间：2018-03-09 17:16

本文选题：四氧化三钴　切入点：水热法　出处：《上海交通大学》2015年博士论文　论文类型：学位论文

【摘要】：四氧化三钴是一种十分具有应用潜力的超级电容器电极材料,具有低成本,高理论比容量(3560F/g)和环境友好性等优点,因此受到越来越多的研究者亲睐。而作为一种赝电容电极材料由于存在与其它过渡族金属氧化物类似的问题限制了其作为新型储能材料应用的空间,其中的关键在于现有的形貌结构无法在超级电容器应用中充分发挥出材料的高电容特点,同时其循环寿命较短,循环过程中比电容值衰减的现象也较为严重。针对这些关键问题,本论文提出利用简单的水热方法,结合热力学依据,系统研究反应中间产物的材料特征,构建反应产物水热生长的动力学模型,通过调控关键工艺参数,获得形态结构可控的四氧化三钴纳米材料,在此基础上,研究其电化学性能与形貌参数之间的内在关系。这一研究对于进一步丰富纳米材料的制备方法和相关的机理研究,发展新型能源材料,具有重要的意义。本论文主要开展的工作如下:1.通过在水热法制备中引入钴氨配合物来降低氧化二价钴所需的热力学势垒,达到降低制备四氧化三钴材料所需水热温度的目的。同时,对钴氨配合物在水热环境下发生二维重构的现象进行研究,确定其在硝酸根协同作用下生成二维薄膜结构所需的特定条件。研究结果表明,通过控制相关的反应参数,可以一步制备得到类石墨烯Co3O4纳米薄膜。Co3O4纳米薄膜的形成需要反应体系中存在过量的游离氨分子,当氨水用量较少时,无法提供二维形核和生长的驱动力,故而产物为少量的纳米薄片和大量树枝状结构共存;而溶液中适量的硝酸根对于抑制Co3O4晶体垂直方向的生长以得到纳米厚度的薄膜结构是尤为关键的。当硝酸根的用量不足时,插入Co-O键之间的硝酸根不能有效抑制所有Co3O4晶体垂直方向的生长,最终得到的是Co3O4片层结构而不是纳米薄膜;反之,当加入的硝酸根过量时,过度的插入Co-O键则会完全破坏游离氨分子对二维生长的促进作用,最终使得Co3O4原位生长,得到球状团聚结构。2.充分利用二价钴氨配合物易于被氧化的特点,以水热反应中H2O2受热分解产生的O2为气泡模板,并结合硝酸根在水热过程中对Co3O4纳米颗粒进行包覆的特点,对在低温水热条件下制备空心Co3O4微球进行探索。研究认为,硝酸根在微球形貌的形成中发挥着重要的影响作用,当硝酸根浓度过低时,插入到Co-O键之间的硝酸根数量不足,无法将Co3O4纳米颗粒相互分开,因为得到的产物相互串接,得不到良好的微球形貌;而硝酸根浓度过高时,溶液中冗余的硝酸根会增大对Co3O4纳米颗粒包覆的表面积,从而引起微球的粒径出现分化,造成产物形貌大小不再均匀。当适当增加H2O2的用量并提高水热温度后,产物形貌将会从实心Co3O4微球转变为空心Co3O4微球。这是因为温度的提高能促进H2O2的分解释放O2充当模板。当H2O2用量过少时,分解产生的O2无法为足量的Co3O4纳米颗粒结晶生长提供构建暂时核壳结构所需的气泡模板,因而对空心Co3O4微球的空心结构产率以及内部空间大小均产生显著影响;当H2O2用量过多时,大量的气泡扰动对水热反应造成较大的冲击,从而影响了硝酸根对于Co3O4纳米颗粒的包覆效果。3.采用表面活性剂辅助的简单水热法一步制备Co3O4纳米立方结构。研究结果表明,当Co(Ac)2/NaOH为1:0.75时,其产物形貌为类立方的颗粒;当Co(Ac)2/NaOH为1:2时,产物为片状六方的形貌;当Co(Ac)2/NaOH为1:1.25时最有利于Co3O4纳米立方的生长。当反应物的浓度相对较低时,此时更倾向于得到表面平整,轮廓分明的Co3O4纳米立方晶体产物。十二烷基苯磺酸钠(SDBS)在水热过程中会促进Co3O4晶体中的(111)晶面的生长,使其远大于(001)晶面的生长速率,因而添加适量的十二烷基苯磺酸钠能够对立方形貌的完整性和尺寸分布的均匀性起到极大的促进。4.对制备得到的不同形貌结构Co3O4材料的电化学性能进行表征,系统研究了材料结构与超电容特性之间的内在联系。结果表明,超薄类石墨烯Co3O4纳米薄膜的超电容性能最为优异,其最大比电容值高达1400F/g,并且在经过后续1500个周期的循环稳定性测试后,比电容较初始值仅仅下降了2.9%,说明该电极材料循环稳定性同样十分出色。而空心Co3O4微球和实心Co3O4微球的最大比电容值则分别为1227和850F/g。Co3O4纳米立方的最大比电容值仅为586F/g。研究认为具有纳米尺寸的薄膜或者薄壁类结构材料能够充分发挥Co3O4的高比电容性特性,此类结构对于纾解电化学过程中的热效应,提高电极的循环稳定性能也有极大的帮助。
[Abstract]:Four oxidation three cobalt is a very potential super capacitor electrode material, has the advantages of low cost, high theoretical capacity (3560F/g) and the advantages of friendly environment, so more and more researchers favor. As a pseudocapacitive electrode material due to the presence of transition metal oxides and other similar problems limit it as a new energy storage material application space, which is the key to the morphology and structure of existing in the super capacitor application cannot give full play to the high capacitance characteristics of the material, and the short cycle life cycle process, the specific capacitance attenuation phenomenon is more serious. To solve these key problems, this paper using a simple hydrothermal method, combined with the thermodynamic basis, material characteristics of intermediate system reaction, dynamics model of reaction product of hydrothermal growth, by adjusting the control key The parameters, obtained four oxidation morphology controllable three cobalt nano materials, on the basis of research on the relation between the electrochemical properties and morphology parameters. This thesis can enrich the research methods and mechanism of nano materials related to preparation, development of new energy materials, has important significance. This thesis mainly carried out the work is as follows: 1. by introducing Cobaltammine in hydrothermal synthesis of complexes to reduce the thermodynamic potential of cobalt two oxidation required for the preparation of four to reduce the oxidation of three cobalt material required for hydrothermal temperature. At the same time, research object reconstruction in the hydrothermal environment with the phenomenon of cobalt ammonia. To determine the specific conditions to generate two-dimensional collaborative film structure required in nitrate. The results show that, by controlling the reaction parameters, can step prepared graphene like Co3O4 nano thin film. The formation of free ammonia molecules to excess in the reaction system of Co3O4 nano film, when the amount of ammonia is small, cannot provide the driving force for growth and nuclear two-dimensional shape of the product is so small and a large number of coexisting nanosheets dendritic structure; and the amount of nitrate solution to inhibit the growth of Co3O4 crystal in vertical direction to get the film structure of nanometer thickness is particularly critical. When the amount of nitrate is insufficient, cannot insert nitrate Co-O bond between the effective inhibition of all Co3O4 crystal growth in the vertical direction, the final Co3O4 lamellar structure rather than the nano film; conversely, when nitrate adding excessive, excessive insertion of Co-O the key will be destroyed completely free ammonia molecules to promote the two-dimensional growth, the in situ growth of Co3O4, by making full use of the two.2. spherical agglomeration structure Cobaltammine complexes to oxygen price The characteristics in the hydrothermal reaction H2O2 produced by decomposing O2 bubble template, combined with the characteristics of nitrate coated Co3O4 nanoparticles in the hydrothermal process, the preparation of hollow Co3O4 microspheres in low temperature hydrothermal conditions were explored. Studies suggest that nitrate play an important role in the formation of the microspheres morphology, when nitrate concentration is too low, the quantity of nitrate into the Co-O bond between the lack of Co3O4 nanoparticles cannot be separated from each other, because the products are connected in series, is not good and the microspheres morphology; nitrate concentration had higher nitrate solution will increase with redundancy the Co3O4 nano particle surface area, thus causing the particle size of the microspheres caused by the morphology of the product differentiation, size is no longer uniform. When appropriate to increase the amount of H2O2 and improve the water temperature, the morphology of the product will be transferred from solid Co3O4 microspheres Into the hollow Co3O4 microspheres. This is because of the increase of temperature can promote the decomposition of H2O2 release O2 as the template. When the H2O2 content is too small, from the decomposition of O2 cannot provide temporary construction growth of core-shell structure required for bubble template crystalline Co3O4 nanoparticles was sufficient, and hence the size of the hollow structure of hollow microspheres and yield Co3O4 the internal space has significant influence; when the content of H2O2 is too much, a lot of bubble disturbance caused by a greater impact on the hydrothermal reaction, thus affecting the nitrate for the coating effect of.3. using surfactant assisted Co3O4 nanoparticles by simple one-step hydrothermal method for preparing Co3O4 nano cubic structure. The results show that, when Co (Ac) 2/NaOH is 1:0.75, the particle morphology is cubic; when Co (Ac) 2/NaOH 1:2, is the product of the six party when the flaky morphology; Co (Ac) 2/NaOH 1:1.25 is the most advantageous to the Co3O4 nanocubes Growth. When the concentration of the reactants is relatively low, the more likely to get a smooth surface, Co3O4 nano cubic crystal product chiseled. Twelve sodium dodecyl benzene sulfonate (SDBS) in the hydrothermal process will promote the Co3O4 crystal (111) surface growth, which is far greater than the average growth rate (001) therefore, adding twelve sodium to the integrity and uniformity of size distribution of cubic morphology to promote the electrochemical performance of different morphologies of.4. Co3O4 materials prepared by the great characterization, system studies the relation and characteristic of super capacitance material structure. The results show that the Supercapacitive properties of ultra-thin type graphene Co3O4 nano film is excellent, the maximum specific capacitance is up to 1400F/g, and after testing the cycle stability of follow-up after 1500 cycles, the specific capacitance than the initial value only decreased 2.9%, the cycle stability of electrode materials also is very good. And the largest hollow Co3O4 microspheres and Co3O4 microspheres than solid capacitance values were 1227 and 850F/g.Co3O4 nanocubes maximum specific capacitance value is only 586F/g. of that of nano-sized thin film or thin wall structure material can give full play to high capacitive characteristics of Co3O4 this kind of structure for relieving heat effect in electrochemical process, improve the cycling performance of the electrode is also a great help.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ138.12;TB383.1

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