前驱体中硫化物对超级电容器活性炭电极电容性能的影响研究

发布时间：2018-08-13 13:30

【摘要】：随着科技和社会的迅速发展,人们对高性能电源的需求量越来越大。超级电容器作为一种新型的储能元件成为了世界各国新能源领域的研究热点之一。目前,高性能电极材料的开发是超级电容器主要的研究目标。活性炭由于具有超高的比表面积、高电导率、原料丰富、价格低廉及较好的电化学稳定性等特点,一直是制造超级电容器电极的首选材料。矿物质及其衍生物(沥青、石油焦、煤等)资源丰富、价格低廉,已成为制备活性炭的重要原料。本文以沥青(Pitch)、石油焦(PC)为原料,通过外加有机硫化物DBT、无机硫化物黄铁矿FeS2合成含硫模拟前驱体(ASCPs),采用KOH化学活化法制备超级电容器活性炭(AC)电极材料。ASCPs实现了单因素系统考察前驱体中硫化物的种类及含量对活性炭结构及其电化学性能影响规律的研究。采用X-射线衍射(XRD)、元素分析、X-射线光电子能谱(xPS)、x-射线近边吸收光谱(XANES)、液相离子色谱等研究测试方法对硫化物的含量及形态,活性炭表面官能团等进行表征分析；扫描电子显微镜(SEM)、透射电子显微镜(TEM)、低温氮气吸附仪等测试手段对样品的孔形貌及孔结构进行表征；通过循环伏安(CV)、恒流充放电(GCD)、交流阻抗(EIS)等电化学方法测试了材料的电化学性能。初步探索了前驱体中的硫化物对AC的孔结构性能及其电极材料电容性能的影响规律及影响机理。主要研究内容及结论如下： (1)系统研究了前驱体中有机硫化物二苯并噻吩(DBT)对活性炭结构及其电极电化学性能的影响规律与机理。结果表明,在AC的制备过程中,随着ASCPs中DBT含量逐渐增大,DBT与KOH反应生成的K2SO4的量逐渐增大,因此实际用于活化拓孔的KOH量逐渐减少,即实际的碱炭比KOH/Pitch逐渐下降,从而使得AC样品的比表面积、孔容、平均孔径等呈现出逐渐降低的趋势。电化学测试表明,随着ASCPs中DBT含量逐渐增大,AC电极的储电性能、倍率特性、循环性能等呈现出逐渐降低的趋势。然而,无论ASCPs中DBT含量如何,活性炭中均未发现有残余硫化物。此外,通过适量增加活化剂KOH的量,补偿活化反应过程中因DBT反应消耗KOH的量,可以完全消除因DBT的存在对活性炭孔结构及电容性能造成的负面影响。对于实际应用而言,含DBT的含硫矿物质前驱体也可以作为制备高性能AC潜在的廉价前驱体。 (2)系统研究了前驱体中典型无机硫化物黄铁矿(FeS2)对活性炭结构及其电极电化学性能的影响规律与机理。结果表明,在活化过程中,FeS2与活化剂KOH发生化学反应生成Fe3O4、K2SO4、K2SO3、K2S2O3、K2S和硫醚C-S-C,并由此导致实际碱/碳比降低,即活化拓孔用KOH量减少,AC活化不足,表现为AC的孔容积、比表面积等参数的降低,进而使得AC电极材料的比电容及倍率特性等呈现出逐渐降低的趋势。此外,FeS2与KOH反应的副产物Fe304难以通过传统的水洗法从活化产物中去除,其会作为杂质存在于AC中,从而导致AC电极储电性能下降。非常有趣的是,S-XANES及XPS分析结果均显示,前驱体中FeS2会导致AC表面生成有机硫醚类C-S-C含硫官能团,这表明经过复杂的KOH活化反应,前驱体中一部分无机类FeS2会转化为有机含硫官能团,并成为活性炭自身的有机组成部分。虽然C-S-C官能团能以赝电容的形式在一定程度上提高AC电极材料的比电容,但总体而言,FeS2对AC电容性能产生的负面影响超过C-S-C含硫官能团产生的促进作用。同时,与有机硫化物DBT相比,无机硫化物FeS2对AC孔结构性能及其电极材料的电化学性能产生的负面影响难以通过简单的增大活化剂KOH的用量加以减小或消除。因此,对于实际应用而言,应当严格控制超级电容器用活性炭矿物质前驱体中FeS2的含量,尽可能降低其含量及其带来的负面影响。
[Abstract]:With the rapid development of science, technology and society, the demand for high-performance power supply is increasing. As a new type of energy storage element, supercapacitor has become one of the hotspots in the field of new energy all over the world. High specific surface area, high conductivity, abundant raw materials, low price and good electrochemical stability have been the preferred materials for the manufacture of supercapacitor electrodes.
In this paper, sulfur-containing analog precursor (ASCPs) was synthesized from pitch and petroleum coke (PC) by adding organic sulfide DBT and inorganic sulfide pyrite FeS2. The electrode material of activated carbon (AC) for supercapacitor was prepared by KOH chemical activation method. The effect of sulfide type and content in precursor on activated carbon was investigated by single factor system with ASCPs. The content and morphology of sulfides and the surface functional groups of activated carbon were characterized by X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray near-edge absorption spectroscopy (XANES), liquid chromatography, scanning electron microscopy (SEM), and so on. The pore morphology and pore structure of the samples were characterized by electron microscopy (TEM) and nitrogen adsorption apparatus at low temperature. The electrochemical properties of the samples were tested by cyclic voltammetry (CV), constant current charge-discharge (GCD) and alternating current impedance spectroscopy (EIS). The main contents and conclusions are as follows:
(1) The effects of DBT on the structure and electrochemical properties of activated carbon were studied systematically. The results showed that the amount of K2SO4 produced by the reaction of DBT with KOH increased gradually with the increase of DBT content in ASCPs during the preparation of AC, so the amount of KOH used to activate the rubbing holes increased gradually. The specific surface area, pore volume and average pore size of AC sample decrease gradually with the decrease of the actual alkali-carbon ratio KOH/Pitch. Electrochemical tests show that the storage performance, ratio characteristics and cycling performance of AC electrode decrease gradually with the increase of DBT content in ASCPs. In addition, by increasing the amount of activator KOH and compensating the amount of KOH consumed by DBT reaction, the negative effects of DBT on the pore structure and capacitance properties of activated carbon can be completely eliminated. Material precursors can also be used as potential low-cost precursors for the preparation of high-performance AC.
(2) The effects of typical inorganic sulfide pyrite (FeS2) in precursor on the structure and electrochemical performance of activated carbon were studied systematically. The results showed that during activation, FeS2 reacted with activator KOH to form Fe3O4, K2SO4, K2SO3, K2S2O3, K2S and thioether C-S-C, which resulted in the decrease of the actual alkali/carbon ratio, i.e., the activation. In addition, Fe304, a by-product of the reaction between FeS2 and KOH, is difficult to be removed from the activated products by traditional water washing method and will be stored as impurities. Interestingly, both S-XANES and XPS analysis showed that FeS2 in the precursor could induce the formation of C-S-C sulfur-containing functional groups on the surface of AC, suggesting that a part of inorganic FeS2 in the precursor could be converted into organic sulfur-containing functional groups by complex KOH activation reaction. Although C-S-C functional groups can improve the specific capacitance of AC electrode materials to some extent in the form of pseudo-capacitance, the negative effects of FeS2 on AC capacitance are more than those of C-S-C sulfur functional groups. It is difficult to reduce or eliminate the negative effects of pore structure and electrochemical properties of electrode materials by simply increasing the amount of activator KOH. Therefore, for practical application, the content of FeS2 in the precursor of activated carbon minerals for supercapacitors should be strictly controlled to minimize its content and its negative effects. Influence.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：O646;TM53

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