掺杂间苯二酚的苯酚基炭气凝胶的制备与电化学研究
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摘要
炭气凝胶是一种新型轻质纳米多孔无定形炭素材料,具有许多优异性能(诸如导电性、绝热性、多孔性等),并可应用于催化剂载体、电吸附除盐、吸附剂、色谱仪填充材料、贮氢材料等方面,也是制备超级电容器和锂电池的理想电极材料。炭气凝胶自1989年诞生后的二十多年时间里,受到了各国广泛地关注及研究,目前在原料的选择、制备工艺及具体应用等方面有了相当程度的改进及创新。
传统的炭气凝胶的制备采用间苯二酚及甲醛为原料,但由于间苯二酚高昂的价格,限制了其制备的炭气凝胶的应用。为了降低成本,提高炭气凝胶的市场竞争力,本文选用酚类同系物中价格最为低廉的苯酚为原料,碱作为催化剂,少量的间苯二酚作为反应成核剂与交联剂,在水相中与甲醛反应通过两步法制得炭气凝胶。
本文考察了不同量的间苯二酚掺杂对催化剂碱用量的影响,以及对随后所制备的炭气凝胶的形貌、密度、体积收缩率及炭化收率等宏观物性的影响,并通过扫描电镜、氮气吸脱附等温线、热重分析等手段分析其对炭气凝胶微观结构的影响。结果表明,极少量的间苯二酚的加入可以极大地减少形成透明有机凝胶所需碱催化剂的用量；一定的少量间苯二酚(10%、20%)的加入时,炭气凝胶的微孔中孔含量轻微减少,并引入少量的大孔,碱催化剂用量的减少可以降低所得炭气凝胶的密度及体积收缩率；而当较多量的间苯二酚(30%)的加入时,炭气凝胶的中孔含量极大减少,大孔含量极大增加,碱催化剂用量的减少却提高了所得炭气凝胶的密度及体积收缩率。
本文还利用恒流充放电实验考察了所得的炭气凝胶在不同电流密度下电化学性能,发现当电流密度从1mA增加至50mA时,纯苯酚炭气凝胶的比电容从146.2 F/g下降至125.1F/g,而加入少量间苯二酚的炭气凝胶的比电容从177.1 F/g略微下降至166.5 F/g,结果表明少量间苯二酚的加入可以增加相应炭气凝胶的比电容,特别是可以提高在高电流密度下的电容性能。
Carbon aerogels (CAs) are a new type of nano-sized porous carbon materials with many outstanding properties such as electrical conductibility, thermal conductivity and porosity, which make it can be used as an ideal electrode material in supercapacitor and lithium cell, as well as in some other aspects such as catalyst supports, adsorbents, chromatography fillers and hydrogen storage materials. In recent more than 20 years since its birth, CAs have got a worldwide attention and a great deal of researches and studies have been carried out to the improvement of CAs in many aspects, such as the selection of raw materials, the optimization of preparation process and the specific applications.
CAs are prepared traditionally using resorcinol and formaldehyde as raw materials. However, the high cost of resorcinol reduces their market competitiveness seriously. To change this situation, in our process, the cheapest phenols, i.e. phenol, was chosen and CAs were successfully obtained via the two-step polycondensation method of phenol and formaldehyde in an aqueous alkaline solution with a small amount of resorcinol used as nucleating and cross-linking agent.
In this paper, the effects of the different dosage of resorcinol and catalyst on gel appearance, bulk density, drying and carbonization shrinkage as well as the microstructure of the resultant organic and carbon aerogels were studied and their surface chemical properties were characterized by Infrared Analysis (IR). Morphology and microstructure of CAs were investigated by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and N2 adsorption-desorption measurement. The experimental results showed that the prepared CAs have a three-dimensional network, consisting of interconnected pearl-like particles with abundance of micropores, controllable amount of mesopores and macropores. Besides, the addition of nucleating and cross-linking agent, i.e. resorcinol, can dramatically decrease the required amount of catalyst to form transparent organic gels. Furthermore, with different additive amounts of resorcinol, the porous microstructure of CAs can be tuned accordingly.
Their electrochemical behaviors of the CAs samples as electrode material in electric double-layer capacitors (EDLCs) were characterized by constant current charge-discharge tests under different current densities. Due to the presence of the advisable amount of macropores, the specific capacitance of the CAs with the addition of resorcinol slightly decreased from 177.1F/g to 166.5F/g when increasing the current density from 1 mAcm-2 to 50mAcm-2, compared to the larger reduction of the CAs without the addition of resorcinol from 146.2F/g to 125.1F/g, indicating that the as-prepared samples have a high-rate charge-discharge performance.
传统的炭气凝胶的制备采用间苯二酚及甲醛为原料,但由于间苯二酚高昂的价格,限制了其制备的炭气凝胶的应用。为了降低成本,提高炭气凝胶的市场竞争力,本文选用酚类同系物中价格最为低廉的苯酚为原料,碱作为催化剂,少量的间苯二酚作为反应成核剂与交联剂,在水相中与甲醛反应通过两步法制得炭气凝胶。
本文考察了不同量的间苯二酚掺杂对催化剂碱用量的影响,以及对随后所制备的炭气凝胶的形貌、密度、体积收缩率及炭化收率等宏观物性的影响,并通过扫描电镜、氮气吸脱附等温线、热重分析等手段分析其对炭气凝胶微观结构的影响。结果表明,极少量的间苯二酚的加入可以极大地减少形成透明有机凝胶所需碱催化剂的用量；一定的少量间苯二酚(10%、20%)的加入时,炭气凝胶的微孔中孔含量轻微减少,并引入少量的大孔,碱催化剂用量的减少可以降低所得炭气凝胶的密度及体积收缩率；而当较多量的间苯二酚(30%)的加入时,炭气凝胶的中孔含量极大减少,大孔含量极大增加,碱催化剂用量的减少却提高了所得炭气凝胶的密度及体积收缩率。
本文还利用恒流充放电实验考察了所得的炭气凝胶在不同电流密度下电化学性能,发现当电流密度从1mA增加至50mA时,纯苯酚炭气凝胶的比电容从146.2 F/g下降至125.1F/g,而加入少量间苯二酚的炭气凝胶的比电容从177.1 F/g略微下降至166.5 F/g,结果表明少量间苯二酚的加入可以增加相应炭气凝胶的比电容,特别是可以提高在高电流密度下的电容性能。
Carbon aerogels (CAs) are a new type of nano-sized porous carbon materials with many outstanding properties such as electrical conductibility, thermal conductivity and porosity, which make it can be used as an ideal electrode material in supercapacitor and lithium cell, as well as in some other aspects such as catalyst supports, adsorbents, chromatography fillers and hydrogen storage materials. In recent more than 20 years since its birth, CAs have got a worldwide attention and a great deal of researches and studies have been carried out to the improvement of CAs in many aspects, such as the selection of raw materials, the optimization of preparation process and the specific applications.
CAs are prepared traditionally using resorcinol and formaldehyde as raw materials. However, the high cost of resorcinol reduces their market competitiveness seriously. To change this situation, in our process, the cheapest phenols, i.e. phenol, was chosen and CAs were successfully obtained via the two-step polycondensation method of phenol and formaldehyde in an aqueous alkaline solution with a small amount of resorcinol used as nucleating and cross-linking agent.
In this paper, the effects of the different dosage of resorcinol and catalyst on gel appearance, bulk density, drying and carbonization shrinkage as well as the microstructure of the resultant organic and carbon aerogels were studied and their surface chemical properties were characterized by Infrared Analysis (IR). Morphology and microstructure of CAs were investigated by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and N2 adsorption-desorption measurement. The experimental results showed that the prepared CAs have a three-dimensional network, consisting of interconnected pearl-like particles with abundance of micropores, controllable amount of mesopores and macropores. Besides, the addition of nucleating and cross-linking agent, i.e. resorcinol, can dramatically decrease the required amount of catalyst to form transparent organic gels. Furthermore, with different additive amounts of resorcinol, the porous microstructure of CAs can be tuned accordingly.
Their electrochemical behaviors of the CAs samples as electrode material in electric double-layer capacitors (EDLCs) were characterized by constant current charge-discharge tests under different current densities. Due to the presence of the advisable amount of macropores, the specific capacitance of the CAs with the addition of resorcinol slightly decreased from 177.1F/g to 166.5F/g when increasing the current density from 1 mAcm-2 to 50mAcm-2, compared to the larger reduction of the CAs without the addition of resorcinol from 146.2F/g to 125.1F/g, indicating that the as-prepared samples have a high-rate charge-discharge performance.
引文
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[5]Farmer J C, Ftx D V, Mack G V, et al. Capacitive deionization of NaCl and NaNO3 solutions with carbon aerogel electrodes [J]. Journal of Electrochemical Society,1996, 143(1):159-169
[6]Gabelich J, Tran T D, Suffet I H. Electrosorption of inorganic salts from aqueous solution using carbon aerogels [J]. Environmental Science and Technology,2002,36:3010-3019
[7]Yang W, Wu D, Fu R. Effect of surface chemistry on the adsorption of basic dyes on carbon aerogels[J]. Colloids and Surfaces A:Physicochem. Eng. Aspects,2008,312(2-3): 118-124
[8]Fang Y, Hu H. Zeolite with tunable intracrystal mesoporosity synthesized with carbon aerogel as a secondary template [J]. Microporous and Mesoporous Materials,2008,113: 481-489
[9]Tian H, Buckley C E, Wang S, Zhou M. Enhanced hydrogen storage capacity in carbon aerogels treated with KOH [J]. Carbon,2009,47:2128-2130
[10]Li J, Wang X, et al. Studies on preparation and performances of carbon aerogel electrodes for the application of supercapacitor [J]. Journal of Power Sources,2006,158:784-788
[11]吴丁财,刘晓方,符若文.炭气凝胶及其有机气凝胶前驱体的吸附性能[J].新型炭材料,2005,20(4)：305-311
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[13]Zhu Y, Hu H, et al. Cresol-formaldehyde based carbon aerogel as electrode material for electrochemical capacitor [J]. Journal of Power Sources,2006,162:738-742
[14]Wu D, Fu R, et al. Low-density organic and carbon aerogels from the sol-gel polymerization of phenol with formaldehyde[J]. Journal of Non-Crystalline Solids, 2005,351:915-921
[15]Scherdel C, Reichenauer G Carbon xerogels synthesized via phenol-formaldehyde gels[J]. Microporous and Mesoporous Materials,2009,126:133-142
[16]Long D, Ling L, et al. Chemical state of nitrogen in carbon aerogels issued from phenol-melamine-formaldehyde gels[J]. Carbon,2008,1253-1269
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