One-Step Electrochemical Preparation Of Graphene And Graphene/Polypyrrole Composites And Their Applications

Owing to the exceptional electrical, mechanical, and thermal properties, graphene has shown greatpromise in various applications such as electronics, transparent electrode, sensors, supercapacitors,lithium-ion batteries and catalysts. Graphene-based composite materials are expected to combine theinherent performance of graphene and composite components, and to produce some novel coordinationeffects. Simple and large-scale production of graphene and graphene-based composites are the first stepfor their prospective applications, and several methods have been proposed in recent years, includingmicromechanical exfoliation, exfoliation, chemical vapor deposition, epitaxial growth, and reduction ofgraphene oxide. However, each method shows advantages and disadvantages, either suffers from lowyield, complicated process, or harsh conditions. Therefore, there is still in a great demand to developsimple, environmentally friendly, and controllable approaches to graphene and graphene-basedcomposites.In this work, we put forward a new, green and controllable method, namely, one-stepelectrochemical deposition to graphene film, and then to graphene/polypyrrole composite film. Thestructure and performance of the prepared materials were characterized, and their applications inelectrochemical sensor or supercapacitors were explored.Details are shown as follows:(1) One-step electrochemical preparation of graphene film and its application in electrochemicalsensor. Graphite oxide, obtained by Hummers method, was dispersed in a phosphate buffer solution byultrasonication, getting a graphene oxide colloidal solution. Graphene nanosheets were directly depositedonto an electrode through cyclic voltammetric electrolysis of the graphene oxide colloidal solution. Themorphology and structures were characterized by scanning and transmission electron microscopy, andelectrochemical properties were characterized by cyclic voltammetry, differential pulse voltammetry, andelectrochemical impedance spectroscopy. The concentration of graphene oxide, the rate of cyclicscanning and the scan number were optimized, and the optimum values are1.0g/L,10mV/s, and10,respectively, in terms of the electrochemical conductivity and electrocatalytic activity of the preparedgraphene film. The electrochemical sensor based on the graphene modified electrode was constructedand used to determine organic pollutants in water. The graphene modified electrodes showed highsensitivity and selectivity in simultaneous determination of the hydroquinone and catechol isomers.(2) One-step electrochemical synthesis of graphene/polypyrrole nanocomposite and its applicationin supercapacitor. Graphene/polypyrrole (EG/PPy) composite films were prepared via one-step cyclicvoltammetric electrolysis of a bath containing both grapehene oxide and pyrrole monomer, and during the synthesis, cationic surfactant cetyltrimethylammonium bromide (CTAB) was found to play animportant role in controlling the morphology of the EG/PPy composite films. The effect of the feedingratios of Py and GO as well as the amount of CTAB on the structure and electrochemical performancesof EG/PPy was investigated. The structure was characterized via scanning electron microscopy,transmission electron microscopy, Raman spectroscopy and X-ray diffraction. The electrochemicalperformance was characterized via cyclic voltammetry, galvanostatic charge-discharge andelectrochemical impedance spectroscopy. The results indicate that at a certain concentration ratio ofgraphene oxide and pyrrole (pyrrole: graphene oxde=80:20), PPy coated homogenously on thegraphene oxide sheets, resulting in the formation of the EG/PPy nanowire array that constitute theEG/PPy composite film on the electrode. Compared to the pure PPy, the EG/PPy showed enhancedelectrical conductivity, and its specific capacitance is595F/g, higher than188F/g of pure PPy, and thestability of the EG/PPy was greatly improved.In short, this work develops a new, green and controllable method to graphene film, and then tographene/conducting-polymer composite film, which provides new insight for designing and controllablesynthesis of graphene materials for various applications especially in the electrochemical fields (such aselectrochemical sensors, supercapacitor, lithium ion battery, electrocatalysis).