Size distribution of trilayer graphene flakes obtained by electrochemical exfoliation of graphite: Effect of the synthesis parameters

Flake size distribution, one of the important aspects to be addressed for large-scale application of graphene, is largely ignored in the research on graphene synthesis. For the liquid phase methods of graphene synthesis, a systematic study is complicated by a scatter in the number of layers of the obtained graphene. We use, a recently reported, electrochemical exfoliation method for obtaining completely trilayer graphene suspension to study the change in trilayer flake size distribution with a change in the synthesis conditions. XRD analysis shows that the exfoliation current density affects the domain size of the intermediate graphite bisulfate (GB) even though the DLS-measured size of the exfoliated GB particles were similar. The difference in the GB domain size resulted in a very different average size as well as the tail of the size distribution of the final graphene flakes obtained by the ultrasonic cleaving of the intermediate GB particles. The power density employed in the ultrasonic cleaving step and the speed of the centrifugation employed to remove impurities from the graphene suspension also affect the flake size distribution. A trilayer graphene suspension of average flake area ∼15 μm2 with the flake size distribution slightly skewed to the right (larger size) and tail like a normal distribution is obtained by optimizing these three synthesis variables. The graphene flakes also contained minor four-layer regions and the effect of the three synthesis variables on their distribution is also studied.