Flake graphite

Graphene dispersions were created using a modified electrochemical exfoliation method that has been reported previously.59 Briefly, 30 grams of LiCl and triethylamine hydrochloride were dissolved into 1 L of dimethyl sulfoxide (DMSO). Flake graphite (Sigma Aldrich) and PVDF (5 wt. %) were then mixed together in ethanol to make a slurry which was dried in a vacuum oven overnight at room temperature. The dry powder was pressed into pellets and sintered at 450 °C under argon. Then the pellet was used as the working electrode and graphite source for the exfoliation. The pellet, platinum mesh counter electrode and Ag/AgCl reference electrode, were placed into the DMSO solution and the potential was then held at −20 V for 48 hours. The exfoliation products were filtered and then washed with water and ethanol to remove any residual exfoliating ions. Products were dried at 200 °C under an argon atmosphere, with the resulting dry powder being re‐dispersed in NMP before bath sonication (Elmasonic P70H) at 37 kHz and 40 % amplitude for 30 minutes to ensure a homogenous suspension. Dispersions of the CEEG were centrifuged at 500 rpm (21 g) for 30 minutes to remove any unexfoliated material. These graphene dispersions were stable in solution for several months with virtually no detectable sedimentation. The yield of few layer CEEG flakes for this method is typically ∼1–2 %.

Graphene dispersions were created by a liquid phase exfoliation method that has been reported previously.19,40 Briefly, flake graphite (Sigma Aldrich) was dispersed in N‐methyl‐2‐pyrrolidone (NMP) (10 mgml⁻¹) and ultrasonically processed in a bath sonicator (Elmasonic P70H). The bath sonicator was operated at 37 kHz and 40 % amplitude for 12 hours with cooling to maintain a stable temperature of 20 °C. The sonicated dispersions were centrifuged at 6000 rpm (3139 g) for 30 minutes to remove any unexfoliated material. The supernatant was decanted and fresh solvent was added before repeating the centrifugation so that a narrow distribution of flake dimensions and thicknesses was obtained. These graphene dispersions were stable in solution for several months with virtually no detectable sedimentation. The yield of few‐layer LEG flakes for this technique is typically ∼2 %.