Electrochemical exfoliation of graphene using dual graphite electrodes by switching voltage and green molten salt electrolyte

Abstract

In this study, the switching voltage (sV) technique was applied for graphite exfoliation in eutectic molten salts of NaOH and KOH at 300 °C. Dual graphite pencil cores were used as anode and cathode with two commercial time relays to swap between positive and negative voltages at various application times. The exfoliated graphene samples were analyzed using several characterization techniques. Results indicated that the sV technique was efficient to achieve better exfoliation efficiency compared to the constant voltage (cV). At the optimum voltage application times for anode and cathode relays, few-layer graphene with respective high production yields of 0.50 and 0.43 g min−1, low ID/IG ratios of 0.31 and 0.58, and good electrical conductivities of 75.28 and 182.62 S m−1 were obtained on both anode and cathode, respectively. Moreover, the SEM characterizations showed that the sV technique efficiently produced smooth graphene flakes, with less agglomeration, crumbling, and wrinkling than those exfoliated at a constant voltage. The XRD patterns confirmed that the crystallite size of the exfoliated graphene prepared by the sV method was smaller than those of pristine graphite and the graphene obtained at a cV. The AFM analysis revealed that the thickness of the exfoliated graphene developed by the sV technique was significantly lower than that obtained at cV. The XPS analysis showed that the quality and the purity of the exfoliated graphene obtained using the sV technique was higher than that prepared at a constant voltage due to the effective suppressing of the cations and ions stacking between the graphite layers.