Synthesis of N-Doped Graphene By Sonochemical Liquid Exfoliation and Its Electrochemical Performance for ORR in Alkaline Media

Abstract

The graphene is a promising material for many potential application. However, industrial scale manufacturing has been limited because most of these methods are not readily scalable. The development of strategies that make viable large-scale production of graphene is a great challenge. A promising approach is the production of stable graphene dispersions from the exfoliation of graphite in water and organic solvents. The exfoliation of graphite by ultrasonication is a very versatile technique that has already demonstrated its effectiveness in dispersing graphene in solvents with different physical and chemical properties. In this contribution, we reported a fast and simple synthesis of graphene sheets from graphite flakes through ultrasound assisted method. Pure dimethylformamide (DMF) was used as organic solvent. Ultrasound time was evaluated in a range of 30 to 120 minutes. The quality of exfoliation and the morphology were determined by Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS) and X-Ray diffraction (XRD). Additionally, graphene was functionalized by solvothermal treatment in order to obtain nitrogen doped graphene. Metal-free electrocatalyst were also obtained. The total nitrogen and carbon were determined using a CHNS analyzer. The functional groups determinates by FTIR found in graphene are carboxyl and amine groups. Preliminary results obtained by Raman spectroscopy indicates that nanocarbon materials has a molecular structure composed by a mixture of graphene and exfoliated graphite. The electrochemical performance of the material for the oxygen reduction reaction (ORR) was tested by rotation disk electrode technique (RDE). It was observed that stable graphene suspensions could be prepared using DMF. Results demonstrate that ultrasonication time is a key parameter to control the yield and size of graphene, when sonication time was higher than 60 minutes the production of graphene decreased. Electrochemical evaluation revealed that these materials are electroactive for ORR in alkaline media. Therefore, the sonochemical synthesis is an attractive massively scalable and simple method for preparation of graphene to energy applications.