Study On The Electrocatalvtic Performance Of Graphene Ateirals

Graphene sheets, one-atom-thick two-dimensional layer of sp2-bonded carbon, havebeen attractinggreatattentionfor their extraordinary electronic, thermal and mechanical properties. Such planar polycyclic aromatic hydrocarbons crystals can be seen as basic structure unit of three kinds of carbon allotrope:zero-dimensional fullerene, one-dimensional carbon nanotube and three-dimensional graphite. Graphene-based materials exhibit excellent electron transfer promoting ability for some redox couples and excellent catalytic behavior toward small biomolecules such as H2O2, NADH. Although a considerable amount of effort has been made to explore the electron transfer properties, it remains difficult for a clear figure and understanding of graphene’s electrochemical activity. On the other hand, to realize graphene-basedapplications in different electrochemical fields, the modulation of its electrocatalytic properties is of great technological importance. Doping graphene with heteroatoms can effectively tune their intrinsic properties, including electronic characteristics, surface and local chemical features. The N atom, having a comparable atomic size and five valence electrons for bonding with carbon atoms, has been widely used for chemical doping of graphene nanomaterials. In this thesis, we studied the electrocatalytic behaviors ofelectrochemically reduced graphite oxide at different potentials. In addition, in order to extend the application of graphene, we proposed a green and facile electrochemical method for the preparation of nitrogen-doped graphene nanosheets at room-temperature and aqueous solutions. 1) Study on the Electrocatalytic Behaviors ofElectrochemically Reduced Graphite OxideBased on the previous work of our research group, the stepwise reduced GO was obtained by using electrochemical reduction route via adjusting electrode’s Femi energy level. Besides, we studied the electrocatalysis of stepwise reduced GO toward various electroactive probes sensitive or non-sensitive to different states of electrode surface, including dopamine (DA), ascorbic acid (AA), hydroquinone (HQ) and β-nicotinamide adenine dinucleotide disodium salt hydrate (NADH, reduced form), positive charged Ru(NH3)3+and negative charged Fe(CN)63". This work discusses the interaction between surface groups and different probes, which provides fundamentals for the construction of graphene-based biosensors and devices.(2) Room temperature electrochemical synthesis of nitrogen-doped Graphene and its electrocatalytic activity for oxygen reductionA green and facile strategy to the synthesis of nitrogen-doped graphene at room-temperature and in aqueous solutions was developed through electrochemical annealing of GO in ammonia. X-ray photoelectron spectroscopy(XPS) study of graphene sheets reveals that N-doping is accompanied by the electrochemical reduction of GO and the highest doping level of3.95%(N/C) is achieved at-1.6V. High-resolution Nls spectra and Raman spectra reveal that the as-made NG mainly contains pyridine-like and pyrrole-like nitrogen atoms. Electrochemical characterizations clearly demonstrate that NG with excellent electrocatalytic activity can catalyze a4electron oxygen reduction reaction in alkaline electrolytes. This energy saving and green electrochemical method could provide the synthesis of nitrogen-doped graphene in large scale for various practical applications.