【作者】 樊桢；

【导师】 陈金华；

【作者基本信息】 湖南大学 ， 应用化学， 2008， 博士

【摘要】 电化学电容器是一种新型储能装置,集高能量密度、高功率密度、长使用寿命等特性于一身,具有十分广泛的应用领域。根据不同的储能机理,其主要可分为建立在界面双电层基础上的双电层电容器以及建立在电极材料氧化还原反应基础上的法拉第赝电容器。其中,电极材料是决定电化学电容器性能的核心因素之一,当前主要可以分为三类:碳材料、金属氧化物和导电聚合物。本论文采用多种方法制备了各种金属氧化物、金属氧化物/碳材料复合物并将其作为电极材料应用于电化学电容器的研究。本论文的主要研究工作如下:（1）采用动电位沉积法在无模板条件下成功地在石墨基体上生长了氧化锰纳米线,并将其作为电极材料应用于电化学电容器的研究。纳米线的形貌和晶体结构分别采用扫描电子显微镜和X射线衍射技术进行了表征,其在0.1M Na₂SO₄溶液中的电容性能采用循环伏安法和恒流充放技术进行了研究。结果表明:氧化锰纳米线均匀生长在石墨电极的表面,具有无定形结构。氧化锰纳米线/石墨电极具有良好的电容性能,当充放电电流密度为1 mA cm^-2,充放电范围为0-1V时,电极的比电容值达到208 F g^-1。此外,电极还展示了优异的电化学可逆性和长时间充放电循环稳定性。（2）以直接生长在石墨电极上的碳纳米管为载体,以硝酸钴和硝酸镍为前驱物,采用一种简单的高温热解法成功地制备了具有不同镍/钴摩尔比例的钴-镍氧化物/碳纳米管/石墨电极（（Co-Ni）O_x/CNTs/G）。复合物电极的形貌和晶体结构分别采用扫描电子显微镜和X射线衍射技术进行了表征,其在1M KOH溶液中的电容性能采用循环伏安法和恒流充放技术进行了研究,并详细考察了（Co-Ni）O_x/CNTs/G电极中不同Ni/Co摩尔比例对于电极电容行为的影响。结果表明:复合物中的钴镍氧化物均匀包覆在碳纳米管的表面,分别以四氧化三钴和氧化镍存在。当镍钴摩尔比为1:1时,（Co-Ni）O_x/CNTs/G电极展示了最佳的电容性能:在10 mA cm^-2的充放电电流密度下电极基于（Co-Ni）O_x的比电容值达到569 F g^-1。此外,电极还展示了优异的功率特性和长时间充放电循环稳定性,在10 mA cm^-2下连续充放电2000次后电极比电容值的衰减仅为3.6%。（3）以直接生长在石墨电极上的碳纳米管为载体,以硝酸锰为前驱物,通过简单的高温热解法成功地制备了氧化锰/碳纳米管/石墨电极（MnO₂/CNTs/G）。复合物电极的形貌和结构分别采用扫描电子显微镜和透射电子显微镜进行了表征,其在1M Na₂SO₄溶液中的电容性能采用循环伏安法和恒流充放电技术进行研究,并考察了氧化锰的担载量对复合物电极比电容值的影响。结果表明:氧化锰均匀包覆在碳纳米管表面形成一层连续的薄膜,厚度约20 nm左右。当氧化锰的担载量为36.9μg cm^-2时,MnO₂/CNTs/G电极在1 mA cm^-2充放电电流下,基于氧化锰的比电容值高达568 F g^-1。此外,电极还展示了良好的功率特性和充放电循环稳定性,在10 mA cm^-2下循环充放电2500次后电极的比电容值仍保持了最高值的约88%。（4）首次采用电化学诱导沉积的方法成功地在石墨电极上制备了纳米结构的多孔氢氧化锰薄膜/石墨电极,并将其应用于电化学电容器的研究。薄膜电极的形貌和晶体结构分别采用扫描电子显微镜和X射线衍射技术进行表征,考察了电解液组成和沉积电流对薄膜形貌和结构的影响,并据此初步探讨了多孔氢氧化锰薄膜的沉积机理。薄膜电极的电容性能通过循环伏安法和恒定充放电技术进行研究,并考察了薄膜的沉积条件对其电容性能的影响。结果表明:薄膜的形貌主要依赖于沉积过程中从石墨电极表面析出的氢气泡的数量和大小,通过改变电解质成分和沉积电流密度可以对薄膜的形貌进行有效调控。电极的电容性能受到沉积参数的影响,最佳的沉积参数为:沉积电流密度iD=23 mA cm^-2,沉积液添加量SM=1.25 mL,沉积液添加速度SR=16.7 mL min-1。在最佳沉积参数下制备的多孔氢氧化锰薄膜/石墨复合电极展示了优异的电容性能,当充放电电流为1 mA cm^-2,充放电范围为0-1V时,在0.1M Na₂SO₄溶液中电极的比电容值高达493 F g^-1。此外,电极还展示了优异的电化学可逆性和长时间充放电循环稳定性,在10 mA cm^-2下连续充放电2000次后电极比电容值的衰减仅为2.2%。（5）以直接生长在石墨电极上的无序碳纳米管（CNTs/G）为载体,采用电化学诱导沉积的方法成功地实现了氧化锰在碳纳米管表面的高度分散,制备了氧化锰/碳纳米管/石墨电极（γ?MnO₂/CNTs/G）。采用扫描电子显微镜和X射线衍射技术对γ?MnO₂/CNTs/G电极的形貌和晶体结构进行了表征,电极在0.1M Na₂SO₄溶液中的电容性能采用循环伏安法进行了研究,并对电极的沉积过程进行了探讨。结果表明:氧化锰高度分散且仅沉积在碳纳米管表面形成一层粗糙的薄膜,γ?MnO₂/CNTs/G电极具有与CNTs/G电极类似的三维多孔结构。γ?MnO₂/CNTs/G电极基于氧化锰的最高比电容值达到579 F g^-1。此外,电极还展示了良好的功率特性和长时间充放电循环稳定性。通过对γ?MnO₂/CNTs/G电极沉积过程的探讨表明,沉积过程中H2气泡的逸出及其所引起的溶液对流作用,是导致氧化锰在碳管表面高度分散、均匀沉积的关键。（6）采用热丝辅助加热直流等离子体化学气相沉积方法,在石墨基体上直接生长高度有序碳纳米管,并将其作为载体,通过电化学诱导沉积的方法成功地实现了氧化锰在有序碳管表面的高度均匀分散,制备了氧化锰/有序碳管/石墨（γ-MnO₂/ACNTs/G）电极,并将其应用于电化学电容器的研究。电极的形貌和晶体结构分别采用扫描电子显微镜、透射电子显微镜和X射线衍射技术进行了表征,其在0.1M Na₂SO₄溶液中的电容性能采用循环伏安法和恒流充放技术进行了研究。结果表明:氧化锰高度均匀地包覆在碳纳米管表面,厚度约为12 nm。γ-MnO₂/ACNTs/G电极展现了优异的电容性能,当充放电电流为1 mA cm^-2,充放电范围为0-1V时,其比电容（基于氧化锰）高达784 F g^-1。此外,电极还具有优异的功率特性、电化学可逆性和长时间充放电循环稳定性,在1 mA cm^-2的充放电电流下充放电800个循环后,比电容的衰减仅为0.5%。（7）以普通的滤纸为载体,利用高锰酸钾与碳之间的氧化还原反应并辅以高温热处理的方法,成功地制备了具有高比电容和超高功率特性的MnO-C复合物。复合物的形貌和晶体结构分别采用扫描电子显微镜和X射线衍射技术进行了表征,其在1M Na₂SO₄溶液中的电容性能采用循环伏安法和恒流充放电技术进行了研究。结果表明:所制备的复合物中氧化锰以MnO的形态存在,MnO-C复合物具有纳米级的线状或梭形状结构。MnO-C复合物/石墨（MnO-C/G）电极具有十分优异的电容性能:高的比电容值,在扫描速度为50 mV s-1时,MnO-C/G电极基于MnO-C复合物和MnO的比电容值分别达到248 F g^-1和636 F g^-1;超高的功率特性,当扫速由10 mV s-1增加到1000 mV s-1时,MnO-C/G电极比电容值的衰减仅为1.6%。此外,MnO-C/G电极还展示了优异的电化学可逆性和长时间充放电循环稳定性,在10 mA cm^-2下连续充放电6000次后电极比电容值的衰减仅为6.4%。更多还原

【Abstract】 As new energy storage devices, electrochemical capacitors have been applied in many fields because they possess high power density, high energy density, long cycle-life, et al. Two basic types of electrochemical capacitors can be realized using different charge-storage mechanism: electrochemical double-layer capacitors and faradaic pseudocapacitors. The former utilizes the capacitance arising from charge separation at an electrode/electrolyte interface, and the later utilizes the charge transfer pseudocapacitance arising from Faradaic reactions occurring at the electrode surface. The electrode materials are one of the key factors to determine capacitive properties of electrochemical capacitors. There are three kinds of the electrode materials: carbon, metal oxideand conductng polymers. This thesis was focused on the preparation of various metal oxides and metal oxides/carbon composites and their applications as the electrode materials in electrochemical capacitors. The main points of this thesis are summarized as follows:（1） Amorphous manganese oxide nanowires were potentiodynamically deposited onto graphite substrate at room temperature without any templates. The morphology and crystal structure of the prepared manganese oxide nanowires were investigated by scanning electron microscopy （SEM） and X-ray diffraction （XRD）, respectively. Moreover, the prepared manganese oxide nanowires/graphite （MnO_x-NWs/G） electrode was applied as electrode material for electrochemical capacitors and the corresponding capacitive properties were evaluated by cyclic voltammetrty （CV） and galvanostatic charge-discharge method. The results indicate that the MnO_x-NWs/G electrode has excellent capacitive properties: high specific capacitance (208 F g^-1 in 0.1M Na₂SO₄ aqueous solutions from 0 to 1 V at a current density of 1 mA cm^-2), high electrochemical reversibility and excellent long-term charge-discharge cycle stability.（2） The nickel-cobalt oxides/carbon nanotubes/graphite （（Co-Ni）O_x/CNTs/G） electrodes with different Ni/Co molar ratios were prepared by adding and thermally decomposing nickel and cobalt nitrates directly onto the surface of CNTs/G electrode to form nickel and cobalt oxides. CNTs used in this paper were grown directly on graphite substrate by chemical vapor deposition （CVD）. The morphology and crystal structure of （Co-Ni）O_x/CNTs/G electrodes were investigated by SEM and XRD, respectively. The capacitive behavior of （Co-Ni）O_x/CNTs/G electrodes were investigated by CV and galvanostatic charge-discharge method in 1M KOH aqueous solutions. Additionally, the effect of Ni/Co molar ratios on capacitive behaviour of the （Co-Ni）O_x/CNTs/G electrode was also investigated. The results show that nickel-cobalt oxides are coated uniformly on the surface of CNTs and exist as NiO and Co3O4. When the Ni/Co molar ratio is 1:1, （Co-Ni）O_x/CNTs/G electrode shows the best capacitive properits: the highest specific capacitance (569 F g^-1 at 10mA cm^-2), excellent power characteristics and good charge-discharge cycle stability (only 3.6% losses of the specific capacitance are found after 2000 charge-discharge cycles at a discharge density of 10 mA cm^-2).（3） Manganese oxide/carbon nanotubes/graphite （MnO₂/CNTs/G） electrodes were synthesized by thermally decomposing manganese nitrates. CNTs used in this paper were grown directly on graphite disk by CVD. The morphology of MnO₂/CNTs/G electrode was characterized by SEM and transmission electron microscopy （TEM）. The capacitive behavior of MnO₂/CNTs/G electrode was investigated by CV and galvanostatic charge-discharge method in 1M Na₂SO₄ aqueous solutions. Moreover, the effect of loading mass of MnO₂ on specific capacitance of the electrode was also investigated. The results show that MnO₂ are covered uniformly on the surface of CNTs and the layer thickness of MnO₂ is about 20 nm. When the loading mass of MnO₂ is 36.9μg cm^-2, the specific capacitance of MnO₂/CNTs/G electrode （based on MnO₂） at 1 mA cm^-2 equals 568 F g^-1. Additionally, good charge-discharge cycle stability (ca. 88% value of specific capacitance is remained after 2500 charge-discharge cycles at a discharge density of 10 mA cm^-2) and power characteristics of the MnO₂/CNTs/G electrode can be observed.（4） A porous Mn（OH）₂ thin film electrode with nanostructure was prepared successfully by electrochemically induced deposition method. The morphology and crystal structure of the prepared film were investigated by SEM and XRD, respectively. The effects of the composition of electrolyte and the deposition current on the morphology of the Mn（OH）₂ film were investigated and the possible deposition mechanism of the film was discussed. Moreover, the capacitive properties of the Mn（OH）₂ film electrode were evaluated by CV and galvanostatic charge-discharge method. The effects of the deposition condition （the deposition current density （iD）, supplied mass （SM） and supplied rate （SR） of the supplied solution） on the capacitive properties of the Mn（OH）₂ film electrode were also examined. The results demonstrate that the morphology of the Mn（OH）₂ film depend on the amount and size of evolved H2 bubbles and can be effectively controlled by changing the composition of electrolyte and the deposition current. The Mn（OH）₂ film electrode prepared under the optimum deposition condition (iD = 23 mA cm^-2, SM = 1.25 mL and SR = 16.7μL min-1) shows excellent capacitive properties: high specific capacitance (493 F g^-1 in 0.1M Na₂SO₄ aqueous solution from 0 to 1 V at 1 mA cm^-2), high electrochemical reversibility and excellent long-term charge-discharge cycle stability (only 2.2% decreases of the specific capacitance are observed after 2000 cycles at a discharge density of 10 mA cm^-2).（5） Using carbon nanotubes grown directly on graphite substrate as supporting material, theγ-MnO₂/carbon nanotubes/graphite （γ-MnO₂/CNTs/G） electrode with high dispersibility ofγ-MnO₂ was prepared by electrochemically induced deposition method. The morphology and crystal structure of theγ-MnO₂/CNTs/G electrode were investigated by SEM and XRD, respectively. The capacitive properties of theγ-MnO₂/CNTs/G electrode were investigated by CV and the deposition process ofγ-MnO₂/CNTs/G electrode was also discussed. The results indicate thatγ-MnO₂ is only deposited uniformly on the surface of CNTs and form a rough film, which should attribute to the convection of solution caused by H2 bubble motion. Theγ-MnO₂/CNTs/G electrode has three-dimensional porous structure and shows excellent capacitive properties. A specific capacitance based onγ-MnO₂ as high as 579 F g^-1 is obtained at a scan rate of 10 mV s-1 in 0.1M Na₂SO₄ aqueous solution. Additionally, theγ-MnO₂/CNTs/G electrode shows good power characteristics and long-term cycle stability.（6） The well-aligned carbon nanotube arrays （ACNTs） were grown directly on the graphite substrate by plasma-enhanced hot filament chemical vapor deposition and used as supporting material. Theγ-MnO₂/ACNTs/graphite （γ-MnO₂/ACNTs/G） electrode with high dispersibilty ofγ-MnO₂ has been prepared by electrochemically induced deposition method. The morphology and crystal structure of theγ-MnO₂/ACNTs/G electrode were investigated by SEM, TEM and XRD, respectively. The capacitive properties ofγ-MnO₂/ACNTs/G electrode were characterized by CV and galvanostatic charge-discharge method. The results show thatγ-MnO₂ is coated uniformly on the surface of ACNTs and the layer thickness ofγ-MnO₂ is about 12 nm. Theγ-MnO₂/ACNTs/G electrode has three-dimensional porous structure and shows excellent capacitive properties. The specific capacitance of theγ-MnO₂/ACNT electrode based onγ-MnO₂ is as high as 784 F g^-1 in 0.1M Na₂SO₄ aqueous solution from 0 to 1 V when the charge-discharge current density is 1 mA cm^-2. Additionally, the electrode shows excellent power characteristics, high electrochemical reversibility and excellent long-term charge-discharge cycle stability (only 0.5% decreases of the specific capacitance are observed after 800 charge-discharge cycles at a discharge density of 1 mA cm^-2).（7） Using simple filter paper as supporting material, the MnO-C composite with high power density and energy density was prepared by the redox reaction between potassium permanganate and carbons then heat-treatment at high temperature. The morphology and crystal structure of the MnO-C composite were investigated by SEM and XRD. The capacitive properties of the MnO-C composite were evaluated by CV and galvanostatic charge-discharge method. The results indicate that manganese oxide in the prepared composite exists as MnO and the MnO-C composite has nano-shuttle or nanowire structure. The MnO-C composite/graphite （MnO-C/G） electrode has excellent capacitive properties. The specific capacitance of the MnO-C/G electrode based on MnO-C composite and MnO are as high as 248 F g^-1 and 636 F g^-1 at a scan rate of 50 mV s-1, respectively. Additionally, the MnO-C/G electrode has very high power characteristics （only 1.6% decreases in specific capacitance from 10 to 1000 mV s-1）, excellent electrochemical reversibility and long-term charge-discharge cycle stability (only 6.4% decreases in specific capacitance for 6000 charge-discharge cycles at a discharge density of 10 mA cm^-2).更多还原