COMMUNICATION 1803784 (1 of 6) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advmat.de The Worldwide Graphene Flake Production Alan P. Kauling, Andressa T. Seefeldt, Diego P. Pisoni, Roshini C. Pradeep, Ricardo Bentini, Ricardo V. B. Oliveira, Konstantin S. Novoselov, and Antonio H. Castro Neto* Dr. A. P. Kauling, A. T. Seefeldt, Dr. D. P. Pisoni, R. C. Pradeep, Dr. R. Bentini, Dr. R. V. B. Oliveira, Prof. A. H. Castro Neto Centre for Advanced 2D Materials (CA2DM) Faculty of Science National University of Singapore (NUS) 117546 Singapore E-mail: phycastr@nus.edu.sg Prof. K. S. Novoselov National Graphene Institute and School of Physics and Astronomy University of Manchester Manchester M13 9TX, UK The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201803784. DOI: 10.1002/adma.201803784 lattice (lattice symmetry p3m1, point group D 3 ). [3] Graphene was isolated in 2004 [4] and because of its extraordinary structural, physical, and chemical properties, the industrial interest in exploring graphene applications in many different areas, from inks to transistors, grew exponentially over the last decade. [5] At the same time, dif- ferent routes for production and synthesis of graphene are available with different degrees of success. The original method used for graphene production via direct mechanical exfoliation of graphite with adhesive tape has been very successful in rendering high quality material for scien- tific purposes. However, this method is not scalable for industrial use. The most popular method for creating large area continuous graphene film has been the chemical vapor deposition (CVD). CVD uses hydrocarbon gas as feeding stock and is capable of producing polycrystalline films that can be square meters in size. [6,7] This method is a bottom-up approach since it uses simpler molecules to produce continuous films. Although CVD growth is widely used, it has limited success due to the presence of extended defects and voids that jeopardize the film’s structural stability and spoil its exceptional physical prop- erties. [7,8] However, a common use for CVD graphene is in applications such as touch panels and displays. [9] The produc- tion of graphene via the CVD method is a topic on its own right and will be covered elsewhere. Another route for the large scale graphene production is a top-down approach, which starts with graphite and exfoliates it by mechanical, chemical, or electrochemical means to gra- phene flakes. Two main methods frequently used to produce graphene flakes are • Oxidation of graphite producing graphene oxide (GO) that is partially deoxidized to produce reduced graphene oxide (rGO); [10,11] • Liquid-phase exfoliation (LPE) of graphite. [12] Oxidation via the Hummers and Offeman’s method, [13] and its variations, generically exposes graphite to a solution of potassium permanganate, sodium nitrate, sulfuric acid, and water. In this process, oxygen atoms attach to the carbon scaffold in the form of epoxy, carboxyl, and hydroxyl groups (usually 45% of oxygen content). By the intrinsic nature of the oxidation process, this GO has a high density of defects. Thus, There are hundreds of companies worldwide claiming to produce “graphene,” showing a large variation in its properties. A systematic and reliable protocol is developed to test graphene quality using electron microscopy, atomic force microscopy, Raman spectroscopy, elemental analysis, X-ray photoelectron spectrometry, and scanning and transmission electron microscopy, which is used to study graphene from 60 producers. The statistical nature of the liquid-phase exfoliation of graphite is established. It is shown that the current classification of graphene flakes used in the market is erroneous. A new clas- sification is proposed in terms of distribution functions for number of layers and flake size. It is shown unequivocally that the quality of the graphene produced in the world today is rather poor, not optimal for most applications, and most companies are producing graphite microplatelets. This is possibly the main reason for the slow development of graphene applications, which usually require a customized solution in terms of graphene properties. It is argued that the creation of stringent standards for graphene characterization and production, taking into account both the physical properties, as well as the requirements from the particular application, is the only way forward to create a healthy and reliable worldwide graphene market. Graphene The International Organization for Standardization (ISO) has defined a nanomaterial as a “… material with any external dimension in the nanoscale (length range approximately from 1 to 100 nm) or having internal structure or surface structure in the nanoscale.” [1] It is also accepted that 2D materials are “substances with a thickness of a few nanometers or less.” Hence, according to these definitions 2D materials are nanomaterials. Graphene is the best-known 2D material and the frst one to be isolated in a laboratory. Only recently [2] ISO has established the nomenclature for graphene as a single layer, monocrystal, of carbon atoms organized in a hexagonal Adv. Mater. 2018, 1803784