Electrochemically Reduced Graphene Oxide And Its Use For Supercapacitors

Graphene, a one-atom-thick2D single layer of sp2-bonded carbon, has emergedas a new class of promising materials, which are attractive for potential applications inphotonics, optoelectronics, supercapacitors and batteries. In this paper, graphene andits derivatives are fabricated via a simple electrochemical process. The processrequires no special chemical agent, and is mainly implemented by the electronexchange between GO and electrodes. As a merit, this could avoid the use ofdangerous reductants (e.g. hydrazine) and eliminate byproducts. The structure andperformance of the as-prepared graphene and its derivatives are investigated, and theirapplications in supercapacitors are explored. Details are shown as follows:1) A binder-free electrode is prepared by directly depositing electrochemicallyreduced graphene oxide(ERGO) on the metal current collector. Fourier transforminfrared spectroscopy and Raman spectrum have been used to demonstrate theeffective reduction of graphene oxide on the electrode, and the porous structure of theERGO film was further characterized by scanning electron microscopy.Electrochemical measurements showed that the specific capacitance of the ERGOelectrode is126.4F g-1at a current density of0.5mA cm-2. When the scan rateincreases from10to1000mV s-1, the specific capacitance of ERGO decreases from131.6to88F g-1, maintaining66.9%of the initial value. Besides, the CV curves forthe ERGO electrode maintain a relatively rectangular shape with the increasingpotential scan rates, evidently showing the excellent high-rate capability.2) A facile and controllable electrochemical method is adopted for the fabrication ofgraphene-based hydrogel. The porous structure had been demonstrated, whichfacilitated the charge and ion transport in the electrode. As the electrode material forsuperecapacitor, the CV curves of the hydrogel remain rectangular at various scanrates from200to3000mV s-1, indicating good charge propagations at the electrodeinterfaces following the electric double layer charging mechanism.3) The electrochemical co-deposition of nickel sulfide/electrochemically reducedgraphene oxide(ERGO) nanocomposites is presented. During the electrochemicalprocess, the graphene oxide nanosheets loose their hydrophilicity and precipitate ontothe electrode. In the meantime, nickel sulfide is also electrochemically deposited onthe electrode. The CV curves as well as the galvanostatic charge/discharge curves of the nickel sulfide/ERGO nanocomposites exhibit distinct pseudocapacitivecharacteristic. The nanocomposites maintain66.8%of the initial specific capacitancefor the first500cycles, and only4.6%loss of the specific capacitance is experiencedfor the further1500cycles, evidently showing a relatively high cycling stability.