Synthesis and Applications of High Quality Graphene Made By a Novel Electrochemical Exfoliation of Natural Graphite Flakes

Since its discovery in 2004, Graphene has been widely study for different applications, noticeable for electrochemical energy devices, due to its excellent properties as a barrier material, electrical conductivity or high surface area. However, it is still an expensive material since it cannot be produced in a large scale. Graphene based materials such as Graphene oxide (GO) or Reduced Graphene Oxide (rGO) also present similar properties than Graphene and can be produce in a more economical way [1]. However, traditional method to produce GO, Hummer’s method, which base on chemical exfoliation of graphite, is a long and tedious process which requires the use of strong oxidants and hazardous chemicals leading environmental pollution that cannot be repaired [2,3]. Recently, electrochemical exfoliation of graphite to produce GO has attracted more and more attention due its environmental protection, low price, easy process and high efficiency [4-7]. Since natural graphite is mostly in the form of flakes and its tiny size is not conducive to its direct use in electrochemical exfoliation, currently, electrochemical exfoliation is mostly made of graphite foil, graphite rod and other graphite processed products. These materials are obtained by using processes such as chemical, thermodynamic, and mechanical compression, leading in physical or chemical changes that alter their original properties or structure. There are also some attempts to use natural graphite flakes for electrochemical exfoliation [8,9]. However, this makes electrochemical exfoliation require more voltage, longer time and less yield. In this work, we present novel design reactor to perform electrochemical exfoliation using natural graphite flakes as raw materials. By using ammonium sulphate as electrolyte, electrochemical exfoliation of natural graphite flakes can be done at low voltage with short time. This achievement also enables the comparison of electrochemical exfoliation products with different raw materials (graphite foil and natural graphite flakes) at the same exfoliation voltage and the same exfoliation time. We explored the properties of the product by raman spectroscopy, ultraviolet–visible spectroscopy (UV-VIS), fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), four-probe method and contact angle measurement. We have found that by combining natural graphite flakes with the reactor, the product obtained is significantly different from the exfoliated product based on graphite foil, achieving better oxidation, better dispersion in deionized water, more defects and greater yield. In addition, the special structure of the reactor allows the exfoliation time to be controlled, and we also compare the products obtained at different exfoliation times. The Exfoliated Graphene Oxide (EGO) obtained it has been used as a filler material in proton exchange membranes for hydrogen fuel cells as well as a support material for electrocalyst to enhance the kinetics for the reactions which take place in these fuel cells. References: [1] Perreault F, De Faria A F, Elimelech M. Environmental applications of graphene-based nanomaterials[J]. Chemical Society Reviews, 2015, 44(16): 5861-5896. [2] Eigler S. Controlled Chemistry Approach to the Oxo‐Functionalization of Graphene[J]. Chemistry–A European Journal, 2016, 22(21): 7012-7027. [3] Eigler S, Hirsch A. Chemistry with graphene and graphene oxide—challenges for synthetic chemists[J]. Angewandte Chemie International Edition, 2014, 53(30): 7720-7738. [4] Gurzęda B, Florczak P, Kempiński M, et al. Synthesis of graphite oxide by electrochemical oxidation in aqueous perchloric acid[J]. Carbon, 2016, 100: 540-545. [5] Su C Y, Lu A Y, Xu Y, et al. High-quality thin graphene films from fast electrochemical exfoliation[J]. ACS nano, 2011, 5(3): 2332-2339. [6] Tian Z, Yu P, Lowe S E, et al. Facile electrochemical approach for the production of graphite oxide with tunable chemistry[J]. Carbon, 2017, 112: 185-191. [7] Liu J, Poh C K, Zhan D, et al. Improved synthesis of graphene flakes from the multiple electrochemical exfoliation of graphite rod[J]. Nano Energy, 2013, 2(3): 377-386. [8] Yu P, Tian Z, Lowe S E, et al. Mechanically-assisted electrochemical production of graphene oxide[J]. Chemistry of Materials, 2016, 28(22): 8429-8438. [9] Lowe S E, Shi G, Zhang Y, et al. Scalable Production of Graphene Oxide Using a 3D-Printed Packed-Bed Electrochemical Reactor with a Boron-Doped Diamond Electrode[J]. ACS Applied Nano Materials, 2019, 2(2): 867-878.