人造石墨之電化學/機械剪切複合剝離石墨烯與性能評估

Abstract

本研究結合液相剝離法中的電化學剝離法與剪切剝離法(Shear exfoliation)，嘗試由人造石墨粉末剝離出石墨烯，企圖增加製造人造石墨之原料，如重油(Heavy oil)或瀝青焦(Asphalt coke)的經濟價值。傳統電化學剝離法多是以塊狀、棒狀、箔片狀石墨作為研究材料，一旦電解剝離完後，其剩下非石墨烯之產物(細小石墨微粒)無法再反覆剝離成為石墨烯，只能丟棄造成浪費或另尋其他用途。本研究利用電化學剝離法與機械剪切剝離法進行石墨烯剝離實驗，透過此兩種方法的相輔相成，以粉末狀人造石墨材料作為原料，可進行連續性生產，並且非石墨烯之產物也能夠重複剝離，不會造成材料的浪費。本研究亦使用由人造石墨剝離之石墨烯樣品，與由天然石墨剝離之石墨烯樣品相互比較，透過拉曼光譜分析儀(Raman spectroscope)確認石墨烯樣品之缺陷程度(ID/IG)，另以掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)及原子力顯微鏡(AFM)等儀器設備，評估石墨烯片的大小、表面形貌及厚度均勻性。最後，本研究以超級電容器之比電容值表現，作為人造石墨剝離為石墨烯後，性能有無提升之評斷依據。本研究透過電化學插層法配合剪切剝離法，已成功將人造石墨粉末剝離為平均厚度約2.62 nm、平均片徑約2.86 μm之石墨烯薄片，其缺陷程度ID/IG為0.16，並具有122.74 S/cm之導電度表現，皆優於以相同手法由天然石墨材料剝離之石墨烯。本研究亦將成功製備之石墨烯薄片應用於超級電容器，透過石墨烯的添加，使得超級電容之比電容值，較只有使用人造石墨粉末材料者提升超過一倍，代表將人造石墨剝離為石墨烯有助於超級電容性能之提升。This study demonstrated an effective liquid phase electrochemical/mechanical hybrid method to exfoliate artificial graphite into few-layer graphene flakes, and so as to enhance the economic value of useless by-products obtained from oil refining process such as heavy oil and asphalt coke. General electrochemical exfoliation using the massive, clavate and schistose graphite for research material. However, non-graphene of product has become refuse after exfoliation process. This study combined liquid phase electrochemical method and liquid phase mechanical method, realizing a continuous and low-cost process to exfoliate graphene using artificial graphite. The differences between graphene exfoliated from natural graphite and graphene exfoliated from artificial graphite were also be investigated. The crystallinity, defect degree, O/C ratio, surface morphology, size and thickness of the graphene sheet were measured by X-ray powder diffraction (XRD), raman spectroscope, electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and other equipment. Quality of produced graphene was also been evaluated through the application of supercapacitor. The experimental results showed that SEM images clearly show effective exfoliation. The produced graphene are ∼2.62 nm thick and ∼2.86 nm length in average. The conductivity is ~122.74 S/cm and defects degree (ID/IG) is 0.16. The graphene-employed supercapacitor shows a specific capacitance of 41.8 F/g, which is 2.6 times larger than that of the artificial graphite powder (16.1 F/g).