導電奈米纖維複合RuO2/Graphene應用於超級電容之研製
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2018
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超級電容器(Supercapacitors)依其能量儲存機制可分為靜電儲能的電雙層電容器(Electrical double-layers capacitors, EDLC)與電化學儲能的擬電容器 (Pseudocapacitor)兩大類，比起傳統的電容器(陶瓷電容器、鋁質電解電容器、塑膠薄膜電容器、鉭質電容器等)，具有更高的比功率(Wg-1)和比電容(Fg-1)，並且有很優異的循環壽命與穩定性，故在電動車與消費性電子的應用前景受到注目。然而，目前超級電容器的電極製作，大都只使用平面金屬電極，造成感應電荷的傳輸性與電解液的質傳性受到限制，或者必須使用大量導電高分子(PANi)作為電活性(electroactive)材料，才能達到快速可逆氧化還原反應，獲得高密度儲能的效果。
因此，本研究為實現低成本全碳3D電極之製作，利用2×2 cm2人造石墨作為基板，並使用黃光微影製程以SU-8厚膜光阻，製作1.8×1.8 cm2之陣列圓柱微結構 (ϕ40 μm、深寬比5、間距 80 μm)，接著利用靜電紡絲技術，並以SU-8濃度比例為SU-8:thinner=5:1作為紡絲溶液，製備奈米紡絲纖維 (Nano spinning fiber)。完成後，利用碳-微機電系統(C-MEMS)技術，將上述製備之SU-8圓柱結構與SU-8奈米紡絲纖維，以兩段式升溫方式進行碳化，使SU-8材料轉變成類玻璃碳(Glassy carbon)材料，進而得到導電圓柱結構(Conductive cylindrical structure)與線徑約730 nm碳奈米纖維(Carbon nanofiber)，後續再將碳奈米纖維進行均勻破碎，以便製備複合石墨烯(Graphene)、二氧化釕(RuO2) 之漿料。以NMP@PVDF所製備之黏著劑(Binder)作為溶劑，將石墨烯、二氧化釕與破碎之碳奈米纖維進行混合，分別得到單純碳奈米纖維(CF)、碳奈米纖維複合石墨烯(CF/GN)與碳奈米纖維複合石墨烯/RuO2 (CF/GN/RuO2)等三種不同材料摻入的複合纖維漿料。利用滴定技術分別將上述三種複合漿料，滴置於全碳之3D導電圓柱結構電極板中，藉此沉積複合之碳纖維薄膜(Carbon fiber membrane, CFM)，最終完成三種不同材料摻入的全碳3D電極板之製作。最後，製備完成之全碳對襯電極(Symmetrical electrodes)封裝成超級電容元件，並利用恆電位儀進行C-V特性曲線(C-V curve)、恆電流充放電曲線(Galvanostatic charge/discharge curve)與電荷轉移阻抗(Rct)等量測分析。量測結果發現CF/GN之電容性能以石墨烯摻入比例20 wt%為較理想、CF/GN/RuO2以RuO2摻入比例30 wt%為較理想。在0.5 A/g的電流密度下，CF、CF/GN與CF/GN/RuO2三種電極之比電容值，分別為62.4 F/g、96.5 F/g與219.2 F/g。CF/GN/RuO2電容元件的比電容值相較於CF/GN電容元件高出2.3倍、比CF之電容元件高出3.5倍，且當電流密度增加至3 A/g，CF/GN/RuO2之電容元件仍擁有54.8%的電容保持率。經過1500次的充放電測試，CF/GN之電容元件循環壽命保持率為62.2%，而CF/GN/RuO2之電容元件，仍擁有85.7%的保持率。由於導電圓柱結構與碳奈米纖維具有優異的導電性與比表面積，摻入石墨烯可提升電極之導電率，進而降低電荷轉移阻抗(Rct)，而摻入RuO2可增加電極之電活性，因此提升整體電容的特性。
Supercapacitors, according to their energy storage mechanism, can be divided into two categories of electric double layer capacitor (EDLC) with electrostatic storage and pseudocapacitor with electrochemical storage. Supercapacitors have received much attention on the applications of electric cars and consumer electronics because they have higher specific power (Wg-1) and specific capacitance (Fg-1), and excellent performance of cycle life and stability as compared with traditional capacitors (ceramic capacitors, aluminum electrolytic capacitors, plastic film capacitors, tantalum capacitors, etc.). However, planar metal electrodes as current collectors are mostly used for the production of supercapacitors, result in restricted transmission of induced charge and mass transfer of the electrolyte. Moreover, the electroactive materials such as conducting polymers (PEDOT:PSS, PANi) must be also used massively to achieve rapid reversible redox reactions and performance of a high-density energy storage. Therefore, this study will focus on the low-cost fabrication of 3D electrodes, which will be used to realize supercapacitors. This process uses 2×2 cm2 artificial graphite as the substrate, and uses the lithography process to form a 1.8×1.8 cm2 array cylindrical microstructure (40 μm, aspect ratio 5, pitch 80 μm) with SU-8 thick film photoresist. Nano spinning fiber is prepared by an electrospinning technique using a SU-8 concentration ratio of SU-8 : thinner=5:1 as a spinning solution. SU-8 cylindrical structure and the SU-8 nanospun fiber are carbonized in a two-step heating mode to convert the SU-8 material into a glass-like material (Glassy carbon material). Further, a conductive cylindrical structure and a carbon nanofiber which has a wire diameter about 730 nm are made. Carbon nanofibers are pulverized uniformly to prepare a slurry which are compound graphene and ruthenium dioxide (RuO2). The binder prepared by NMP@PVDF is used as a solvent to compound graphene, ruthenium dioxide and broken carbon nanofibers to obtain carbon nanofiber (CF), carbon nanofiber composite graphene. (CF/GN) and carbon nanofiber composite graphene/RuO2 (CF/GN/RuO2), respectively. The three composite slurries are dropped into the all-carbon 3D conductive cylindrical structure electrode by titration technique respectively. Thereby, a composite carbon fiber membrane (CFM) is deposited, and finally, the production of all-carbon 3D electrodes in which three different materials are completed. The prepared full carbon-based electrodes (Symmetrical electrodes) are packaged into a supercapacitor element and CV curve, galvanostatic charge/discharge curve and charge transfer impedance (Rct) are analyzed using potentiostat measurement. Measurement results show that the capacitance performance of CF/GN is ideal with graphene incorporation ratio of 20 wt%, and CF/GN/RuO2 with RuO2 incorporation ratio of 30 wt%, respectively. The specific capacitance values of CF, CF/GN and CF/GN/RuO2 electrodes are 62.4 F/g, 96.5 F/g and 219.2 F/g respectively in 0.5 A/g current density. Moreover, specific capacitance of CF/GN/RuO2 capacitor is 2.3 times higher than CF/GN capacitor and 3.5 times higher than CF capacitor, besides when the current density is increased to 3 A/g, capacitance retention of CF/GN/RuO2 capacitive component still has 54.8%. After 1500 charge and discharge tests, cycle life retention rate of CF/GN capacitive component is 62.2% and CF/GN/RuO2 capacitive component still has 85.7%, respectively. Because conductive cylindrical structures and carbon nanofiber have excellent electrical conductivity and specific surface area, the incorporation of graphene can increase the conductivity of electrode, thereby reducing charge transfer resistance (Rct), and incorporation of RuO2 can increase the electrical activity of electrode which improve the characteristics of overall supercapacitor.
Supercapacitors, according to their energy storage mechanism, can be divided into two categories of electric double layer capacitor (EDLC) with electrostatic storage and pseudocapacitor with electrochemical storage. Supercapacitors have received much attention on the applications of electric cars and consumer electronics because they have higher specific power (Wg-1) and specific capacitance (Fg-1), and excellent performance of cycle life and stability as compared with traditional capacitors (ceramic capacitors, aluminum electrolytic capacitors, plastic film capacitors, tantalum capacitors, etc.). However, planar metal electrodes as current collectors are mostly used for the production of supercapacitors, result in restricted transmission of induced charge and mass transfer of the electrolyte. Moreover, the electroactive materials such as conducting polymers (PEDOT:PSS, PANi) must be also used massively to achieve rapid reversible redox reactions and performance of a high-density energy storage. Therefore, this study will focus on the low-cost fabrication of 3D electrodes, which will be used to realize supercapacitors. This process uses 2×2 cm2 artificial graphite as the substrate, and uses the lithography process to form a 1.8×1.8 cm2 array cylindrical microstructure (40 μm, aspect ratio 5, pitch 80 μm) with SU-8 thick film photoresist. Nano spinning fiber is prepared by an electrospinning technique using a SU-8 concentration ratio of SU-8 : thinner=5:1 as a spinning solution. SU-8 cylindrical structure and the SU-8 nanospun fiber are carbonized in a two-step heating mode to convert the SU-8 material into a glass-like material (Glassy carbon material). Further, a conductive cylindrical structure and a carbon nanofiber which has a wire diameter about 730 nm are made. Carbon nanofibers are pulverized uniformly to prepare a slurry which are compound graphene and ruthenium dioxide (RuO2). The binder prepared by NMP@PVDF is used as a solvent to compound graphene, ruthenium dioxide and broken carbon nanofibers to obtain carbon nanofiber (CF), carbon nanofiber composite graphene. (CF/GN) and carbon nanofiber composite graphene/RuO2 (CF/GN/RuO2), respectively. The three composite slurries are dropped into the all-carbon 3D conductive cylindrical structure electrode by titration technique respectively. Thereby, a composite carbon fiber membrane (CFM) is deposited, and finally, the production of all-carbon 3D electrodes in which three different materials are completed. The prepared full carbon-based electrodes (Symmetrical electrodes) are packaged into a supercapacitor element and CV curve, galvanostatic charge/discharge curve and charge transfer impedance (Rct) are analyzed using potentiostat measurement. Measurement results show that the capacitance performance of CF/GN is ideal with graphene incorporation ratio of 20 wt%, and CF/GN/RuO2 with RuO2 incorporation ratio of 30 wt%, respectively. The specific capacitance values of CF, CF/GN and CF/GN/RuO2 electrodes are 62.4 F/g, 96.5 F/g and 219.2 F/g respectively in 0.5 A/g current density. Moreover, specific capacitance of CF/GN/RuO2 capacitor is 2.3 times higher than CF/GN capacitor and 3.5 times higher than CF capacitor, besides when the current density is increased to 3 A/g, capacitance retention of CF/GN/RuO2 capacitive component still has 54.8%. After 1500 charge and discharge tests, cycle life retention rate of CF/GN capacitive component is 62.2% and CF/GN/RuO2 capacitive component still has 85.7%, respectively. Because conductive cylindrical structures and carbon nanofiber have excellent electrical conductivity and specific surface area, the incorporation of graphene can increase the conductivity of electrode, thereby reducing charge transfer resistance (Rct), and incorporation of RuO2 can increase the electrical activity of electrode which improve the characteristics of overall supercapacitor.
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Keywords
超級電容, 靜電紡絲技術, C-MEMS, RuO2, Supercapacitor, Electrospinning technology, C-MEMS, RuO2