【作者】 程爽；

【导师】 闫鹏勋；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2012， 博士

【摘要】 电化学电容器,又称超级电容器,作为一种新型的能量存储与转化装置,因为具有高功率,长寿命,高的安全性,及低维护成本等优点,而使其在移动通讯,电动车,电子设备,航空航天等各个领域具有巨大的应用前景。然其较低的能量密度又使得它的应用具有一定的局限性,限制了其取代电池的进程。尤其对于现有的赝电容器,因为在能量存储和释放过程中发生在材料表面的氧化还原反应而造成的相变,使得其能量密度和循环寿命都很有限。因此,如何在保证高功率密度的基础上提高能量密度,平衡成本和性能之间的关系成为科学界的一大挑战。过渡族金属氧化物,RuO2,MnO2,NiO,Co3O4,Fe3O4,VOx等,因其相对于碳基材料和导电聚合物材料来说,具有较高的理论比容量和高的能量密度等优势而成为电化学电容器最有潜力的电极材料。在这些电极材料中,虽然氧化钌的性能最好,但其成本很高,所以寻找低成本的可替代品是目前该领域研究的热点。其中,氧化锰、氧化钴因其成本低廉,制备工艺成熟,比电容高等优势吸引了研究者的注意。本文正是通过一种工艺简单成本低廉的化学方法,在无定型高导电的网状碳纤维纸上生长纳米级的锰氧化物及钴氧化物,将其作为超级电容器的电极材料,制备得到了具有高性能：高比容量(-1200F/g在1mol/L的硫酸钠电解质溶液中)、高功率、高能量密度、长寿命的超级电容器,并且活性材料的负载量高达0.3～1.4毫克每平方厘米,远高于多数文献报道；同时还实现了对经济成本的控制。针对氧化锰电极材料,主要运用同步X射线衍射光谱,扫描电子显微镜,高分辨透射电镜,及原位/非原位的X光吸收近边结构谱等表征技术及密度泛函理论计算,对锰氧化物的能量储存和释放机制进行了研究探讨：纳米级高比表面积的活性材料的使用,大大提高了电容电极的有效表面积；可变价态的金属氧化物的选用,使得利用法拉第反应,即金属元素参与的氧化还原反应,储存释放能量成为可能；各种价态的氧化物共存,对促进了氧元素位周围电子态密度随着充放电而变化有一定的作用。简而言之,活性材料高的比表面积和碳基底高的导电率使所制备的电容器快速充放电成为可能,而物理吸附和金属元素及氧元素共同参与的化学反应储能机制使其高能量密度成为可能,化学制备及退火过程产生的空穴、空位、晶错等缺陷使锰氧化物在数万次的充放电过程保持晶体结构的稳定性(即所谓的长寿命)成为可能。同时,我们也对研究比较多的另一种金属氧化物,Co3O4,做了初步的研究。用水热法制备了两种不同形貌的纳米结构氧化钴均匀覆盖的碳纤维电极,通过XRD、SEM、HR-TEM等手段表征了氧化钻的物相结构和微观形貌(纳米立方体和纳米线),并采用电化学表征手段研究了电极活性材料不同的微观形貌对其电容性质的影响。发现相比生长致密、粒径较大的立方颗粒,具有高比表面积的氧化钻网状纳米纤维具有更好的电容性质。由此我们初步探讨了材料形貌对电容产生影响的机制。更多还原

【Abstract】 The exponential-growth needs of the portable electronic devices together with the electric automobiles have raised an ever-increasing demand for light-weight and compact electric power sources with high energy as well as high power density. Among them, pseudocapacitors (a kind of electrochemical capacitors or supercapacitors), as advanced and clean energy storage and management devices, offering extremely high powers as well as possible high energy densities, are expected to play a crucial role where superior power performance is required. While, existing pseudocapacitors always suffer from limited cycle life and low energy density, due to the phase changes caused by redox reactions when energy is stored/released on the surface or subsurface of the electrode. To emerge as an important energy storage technology in the future, hence, advanced electrode materials for supercapacitor are required to be equipped with higher operating voltage and higher energy and power delivery, while maintaining high cyclability.Transition-metal oxides, i.e. RuO2, MnOx, NiO, CoO, Fe3O4, VOx and MnOx-RuO2, are one kind of the most promising electrochemical supercapacitor materials, which are attracting widely interest owing to their relative high specific capacitance and high energy density, compared with carboneous materials and conducting-metal polymers. Among these materials, amorphous hydrated ruthenium oxide exhibits remarkably high specific capacitance and excellent reversibility because of the ideal solid-state pesudofaradaic reaction. However, the high cost, low porosity and toxic nature of RuO2limit its practical application. Therefore, some cheap and environmentally friendly metal oxides have received more and more attention. Manganese oxide, Cobalt oxide materials, as promising candidates for electrochemical supercapacitors, satisfy these fundamental requirements, low cost, environment friendly and reasonable high specific capacitance, whose theoretical value is of about1500F/g, gets more and more attention. In the work reported here, we made carbon fiber paper (CFP) supported nano-structured MnOx and Co3O4as electrodes for symmetric cells, respectivily. Both of these two kind of active materials can achieve eery high specific capacitance of over1000F/g, superior stability (more than5,000CV cycles, as good as carbon based electrodes) and high reaction rate (high rate capability), rectangular shapes even at a CV scan rate of100mv/s at an operating voltage window of0-0.8V in1M Na2SO4aqueous solution with the loading amount of～mg·cm-2, by preparing nano-structure metal oxide with rather simple chemical solution methods, followed by heat treatment.Scanning electron microscope (SEM Leo/Zeiss1530), the high resolution transmission electron microscope (JEOL4000EX) and Synchrotron-based X-ray analysis (Diffraction XRD and Absorption XANES) were employed to collect the morphology and phase information of the active materials. To characterize their electrochemical performance as super-capacitors, cyclic voltammetry (CV) curves and galvanostatic charge-discharge curves were recorded at room temperature in a symmetric-cell configuration containing1M Na2SO4,1M Ca(NO3)2, or1M H2SO4electrolyte solution. The potential and current were controlled by an Electrochemical Interface (Solartron, SI1286) and the electrochemical impedance spectroscopy (EIS) analysis was conducted using a Frequency Response Analyzer (Solartron SI1255) and SI1286with an applied ac voltage of10mV in the frequency range of0.001Hz to1MHz.更多还原