Capacitance of graphene films: effect of the number of layers of the constituent graphene flakes

Assembly of graphene flakes into a film for an electric double-layer capacitor electrode causes restacking and aggregation of the constituent flakes that severely reduces the specific capacitance of the electrode. An understanding of different factors affecting aggregation will lead to strategies for improving the specific capacitance of graphene-based electrodes. In this work, we show that the number of layers of the constituent graphene flakes strongly affects the specific capacitance of the electrodes. For this, we prepared films from completely trilayer- and bilayer-rich graphene suspensions. The average thickness was considerably less, and the electrochemical surface area was considerably higher for the film of bilayer graphene flakes compared with the film of trilayer graphene flakes. The specific capacitance of the film of bilayer graphene (373 F/g) was at least 1.5 times higher than the value (238 F/g) for the film of trilayer graphene. An empirical approach using cyclic voltammetry showed that the amount of film surface easily accessible to the electrolyte was also higher for the film of bilayer flakes compared with the film of trilayer flakes.