Graphene And Its Functions And Application In Activated Carbon Supercapacitors

In this thesis, we study systematically the synthesis, characterization, functions, andapplication of graphene in activated carbon supercapacitors. We explored combustion andchemical oxidation-reduction methods to produce graphene and examined their use as as aconductive additive in supercapacitors to improve the electrochemical performance of activatedcarbonsupercapacitors.We studied and compared the electrochemical performance of two types of activated carbonmaterial (YP and8B) supercapacitors in different electrolytes, including6M KOH aqueouselectrolyte,1M Et4NBF4/PC organic electrolyte, and EMI-TFSI ionic liquid. It was found that themesopore concentration, the electrolyte ion size, the activated carbon particle size, the oxygen-containing functional groups, and the graphite crystallite structure all had important roles inaffecting the electrochemical performance of the supercapacitor, including the specific capacitance,theequivalent seriesresistance,andtheratecapability.We have synthesized graphene by the chemical reaction between magnesium metal and carbondioxide. It was found that graphene was grown and deposited on the MgO template. When the as-prepared graphene was used as supercapacitor electrodes, it showed a low specific capacitancebecause of its irreversible re-stacking. However, addition of graphene as a conductive additive intoactivated carbon is beneficial to the electrochemical performance. And thus the graphene/activatedcarbon composite electrode showed a high specific capacitance, indicating a new method toimprovethespecificcapacitanceof activated carbonsuppercapacitors.We also synthesized graphene by the chemical oxidation-reduction method to further imporovethe specific capacitance of activated carbon electrode. Therefore, we examined and compared theelectrochemical performance of activated carbon electrodes incorporated with graphene, single-walled carbon nanotubes，carbon black, and graphite as conductive additives. The sandwichedstructure formed in graphene and activated carbon electrode could improve the accessibility ofelectrolyte to lead a high specific capacitance of nearly300F/g and also improved the electricalconduction of activated carbon electrode. Furthermore, Graphene contributed to the specificcapacitanceofactivated carbon electrode. To explore further use of graphene in supercapacitors, we developed a method to preparegraphene aerogel by using a binder that involved no chemical reaction with graphene oxide. Whenusing PTFE as the binder, we prepared graphene oxide aerogel successfully by adjusting the ratiobetween graphene oxide and PTFE. The graphene aerogel was obtained by reducing the grapheneoxide aerogel. The thus prepared graphene aerogel showed improved electrochemical performancecomparedwithgrapheneaerogel preparedbychemical cross-linking reactionsintheprocess.