多级孔道结构的稻壳基电容炭材料的制备及其电容性能研究

发布时间：2018-07-29 10:18

【摘要】：超级电容器因其具有功率密度大、循环寿命长、充放电效率高等特点，近年来引起了人们的广泛关注。电极材料作为超级电容器的重要部分是决定超级电容器性能的关键。具有多孔结构的活性炭材料具有成本低廉、比表面积高、来源广泛等优点，目前被广泛应用于超级电容器电极材料。利用稻壳为前驱体制备用于超级电容器的活性炭（电容炭）已经成为一个研究热点。但目前稻壳基活性炭（Rice Husk based activated Carbon, RHC）存在着电容性能不理想、制备成本高且污染环境等问题，限制了RHC在超级电容器中的应用。本文以实现稻壳基电容炭在超级电容器中的应用为目标，，以稻壳为原料，通过化学活化法制备了具有不同孔道结构的稻壳基电容炭材料，研究了制备条件、稻壳的结构、组成与活性炭的孔结构及其电容性能的内在联系，研究了RHC在酸性和碱性电解质溶液中的稳定性，探究了RHC在碱性电解质溶液中的衰减机理，并提出了提高其循环寿命的新方法，设计了稻壳基电容炭的绿色制备工艺，主要研究成果如下：（1）利用稻壳的自身模板结构，通过炭化、碱煮、活化制备出了具有高比表面积的稻壳基多级孔道活性炭（Rice Husk based Hierarchical Activated Carbon,RHHAC），并研究了多级孔道结构的形成机理。RHHAC的表层为三维多孔结构，内部为平行排列大孔通道，在通道壁上同时存在大孔和大量的微介孔。所制得的RHHAC在6mol L-1KOH中表现出优异的电化学性能。电流密度为0.5A g-1时，其比电容为278F g-1。当电流密度由0.5A g-1增大到20A g-1时，其电容保持率为77.2%，表现出较好的倍率特性。由其构成的对称型超级电容器，当功率密度为6195W kg-1时，其能量密度仍保持7.4Wh kg-1，是非常有前景的高性能超级电容器电极材料。（2）研究了稻壳中SiO2对KOH活化过程中孔结构形成的影响。结果表明，未去除稻壳中的SiO2时，所制备的活性炭具有较多微孔；去除稻壳中的SiO2时，活性炭具有介孔、大孔较多。这是由于KOH活化过程中SiO2优先与KOH反应形成K2SiO3，K2SiO3的形成阻碍了KOH对稻壳的上下表皮的活化，同时造成中部的维管束活化过度导致结构破坏，导致介孔形成和扩大以及大孔的形成受阻。（3）研究了RHC在KOH和H2SO4中的循环特性。结果表明，RHC在H2SO4中表现出优异的稳定性，而在KOH中稳定性较差。这是由于在超级电容器循环充放电过程中含氧官能团在两种电解质中发生不同的反应引起了正极电极电势的变化差异，从而导致RHC作为超级电容器在两种电解质中的循环稳定性发生变化。在KOH电解质中，羧基和内酯基团发生水解反应产生的静电排斥和空间位阻效应使得正极电容下降，引起正极电势的增加和正极氧化，从而导致循环寿命的衰减。在H2SO4电解质中，含氧官能团发生可逆的氧化还原反应并不引起正极电势的正移。基于RHC在KOH电解质溶液中衰减过程的研究，通过热处理去除RHC表面含氧官能团，使得其循环稳定性得了大大提升，10000次恒流充放电后的电容保持率由热处理之前的28.3%提升至94.7%，但热处理后材料的比电容降低了30%；提高正负极的质量比抑制了正极电势的正移，改善了RHC在KOH中的循环稳定性，当正负极质量比由最初的1：1提高到2：1时，10000次恒流充放电后电容保持率由最初的28.3%提升至95.3%，电容降低了12%。通过提高正负极质量比的方式来改善RHC在KOH中的循环稳定性，相对于热处理具有操作简单、易于实现的特点。（4）基于稻壳基电容炭的制备，提出了两种绿色制备工艺。在高比电容稻壳基活性炭绿色制备工艺中，将RHC制备过程中产生的废液经酸化和电解之后，获得了纳米SiO2，并可实现活化剂KOH和水的循环利用。相对于普通制备工艺，具有成本低、绿色环保的特点。在稻壳基多级孔道活性炭绿色制备工艺中，利用石灰乳将RHHAC制备过程中产生的废液转化为活化剂KOH，实现活化剂KOH和水的循环利用。
[Abstract]:Because of its high power density, long cycle life and high charging and discharging efficiency, supercapacitor has attracted wide attention in recent years. As an important part of supercapacitor, the electrode material is the key to determine the performance of supercapacitor. The porous structure of activated carbon material has low cost, high surface area and wide source. These advantages are widely used in electrode materials of supercapacitors.
Using rice husk as a precursor to prepare active carbon for supercapacitor (capacitor carbon) has become a hot spot. But at present, the Rice Husk based activated Carbon (RHC) has the problems of low capacitance performance, high preparation cost and pollution environment, which restricts the application of RHC in supercapacitor. The application of rice husk based capacitance carbon in supercapacitor was taken as the target. Rice husk based capacitor carbon materials with different pore structure were prepared by chemical activation method. The preparation conditions, the structure of rice husk, the structure of the rice hull and the pore structure of activated carbon and its capacitive energy were studied. The acid and basic electricity of RHC were studied. The stability of the solution in the solution was solved, and the attenuation mechanism of RHC in alkaline electrolyte solution was explored. A new method to improve its cycle life was proposed. The green preparation technology of rice husk based capacitor carbon was designed. The main research results were as follows:
(1) using the self template structure of rice husk, by carbonization and alkali cooking, the Rice Husk based Hierarchical Activated Carbon, RHHAC, which has high specific surface area, is prepared, and the formation mechanism of the multistage channel structure is studied. The surface of.RHHAC is three-dimensional porous structure, and the interior is parallel to the large pore channel. There is a large pore and a large number of micro mesopore on the channel wall. The obtained RHHAC shows excellent electrochemical performance in 6mol L-1KOH. When the current density is 0.5A g-1, its specific capacitance is 278F g-1. when the current density increases from 0.5A g-1 to 20A g-1, and its capacitance retention rate is 77.2%, showing a better multiplier characteristic. The symmetry of the current density is symmetrical. When the power density is 6195W kg-1, the energy density of the super capacitor is still 7.4Wh kg-1. It is a very promising electrode material for high performance supercapacitors.
(2) the effect of SiO2 on the formation of pore structure in the activation process of KOH in rice husk was studied. The results showed that the activated charcoal prepared by the SiO2 in the rice husk had more micropores. When the SiO2 in the rice husk was removed, the activated carbon had mesoporous and large pores. This was due to the formation of K2SiO3 and the formation resistance of K2SiO3 in the process of KOH activation and the reaction of SiO2 to KOH. The activation of the upper and lower epidermis of the rice hull was hindered by KOH, and the excessive activation of the vascular bundles in the central region resulted in structural damage, which resulted in the formation and expansion of mesoporous and the formation of the macropores.
(3) the cyclic characteristics of RHC in KOH and H2SO4 are studied. The results show that RHC shows excellent stability in H2SO4 and is not stable in KOH. This is due to the difference in the change of the positive electrode potential by the different reactions of oxygen functional groups in the supercapacitor during the cycle charge and discharge process, which leads to RH. The cyclic stability of the C as a supercapacitor in the two electrolytes is changed. In the KOH electrolyte, the electrostatic repulsion and the space hindrance effect produced by the hydrolysis of the carboxyl and lactone groups make the positive pole capacitance decrease, cause the increase of the positive pole potential and the positive pole oxidation, and lead to the decay of the cycle life. In the H2SO4 electrolyte, The reversible oxidation reduction reaction of the oxygen functional group does not cause the positive shift of the positive electrode potential. Based on the study of the decay process of the RHC in the KOH electrolyte solution, the oxygen functional groups on the RHC surface are removed by heat treatment, which makes the cycle stability greatly improved. The capacity retention of the 10000 constant current charge discharge is 28.3% before the heat treatment. Up to 94.7%, but the specific capacitance of the material is reduced by 30% after heat treatment; the mass ratio of the positive and negative pole increases the positive shift of the positive pole potential, and improves the cyclic stability of RHC in KOH. When the positive and negative mass ratio is increased from the original 1:1 to the 2:1, the capacity holding rate of the 10000 constant current charge discharge is raised from the initial 28.3% to 95.3%, and the capacitance is reduced. 12%. improves the cycle stability of RHC in KOH by improving the ratio of positive and negative mass ratio, which is simpler and easier to implement than heat treatment.
(4) based on the preparation of rice husk based capacitance carbon, two green preparation processes were put forward. In the preparation process of high specific capacitance rice husk based activated carbon, the waste liquid produced in the process of RHC preparation was obtained after acidification and electrolysis, and the nano SiO2 was obtained, and the activating agent KOH and water could be used in the circulation. Compared with the common preparation process, the cost was low. In the green preparation process of the multi-stage channel active carbon in the rice husk base, the waste liquid produced in the process of RHHAC preparation is converted into activator KOH by using lime milk to realize the recycling of activator KOH and water.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ127.11;TM53

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