石墨烯及其複合材料應用於超級電容之研究

Study on the Application of Graphene and Its Composite Materials to Supercapacitors

石墨烯具有優異的導電性、比表面積以及特殊的形貌結構，非常適合作為超級電容之電極材料。本研究透過化學插層加上熱處理法製備出蓬鬆的石墨烯粉末，並將之應用於超級電容，在第一階段實驗結果中可明顯發現，石墨烯所產生的比電容值 （218 F/g） 遠大於奈米碳管的73 F/g，而且在100 mV/s高掃描速率下，石墨烯的電容維持率 （72%） 也較奈米碳管 （63%） 高。在第二階段，我們將石墨烯與各式碳材料 （奈米碳管、碳黑、石墨） 混合形成複合材料並進行電化學性質比較，結果顯示在石墨烯中加入少量的奈米碳管，在掃描速率10 mV/s下可得到236 F/g的比電容值，因此推斷奈米碳管的加入，可防止石墨烯互相堆疊，因而增加石墨烯表面積利用率，提高比電容值，同時還能在石墨烯片之間形成導電橋梁，提升電極導電率。最後在交流阻抗分析中，也可以發現相較於其他碳材料，奈米碳管與石墨烯複合材料具有較低的內阻，因此具有較高的性能。

Graphene is very suitable for application to supercapacitors as anelectrode material due to its excellent conductivity, specific surface area, and unique shape and structure. In this study, we produced graphene bychemical oxidation/intercalation of graphite, followed by a thermalreduction/exfoliation step. We also studied its application to supercapacitors.In the first part of our experiment, we found that graphene can givea higher specific capacitance (218 F/g) than carbon nanotubes (CNTs) (73F/g). In addition, at a high scan rate of 100 mV/s, the capacitanceretention of graphene (72%) was also higher than that of CNTs (63%). Inthe second part, graphene was mixed with different carbon materials (CNTs,carbon black, and graphite) to form composites and their electrochemicalproperties were compared. The results showed that adding a smallamount of CNTs into graphene gave the best specific capacitance (236 F/gat a scan rate of 10 mV/s). Presumably CNTs can prevent the restackingof graphene flakes and increase the effective utilization of graphene’ssurface area, leading to a higher specific capacitance. In addition, CNTsmay bridge the gaps between graphene flakes and increase the conductivityof the electrode. The AC impedance analysis also revealed that, comparedto other carbon materials, the composite of CNTs and graphene hadthe lowest internal electric resistance and thus the best performances.