Electrochemical exfoliation of graphene sheets from a natural graphite flask in the presence of sulfate ions at different temperatures

Abstract

An electrochemical route to functionalize graphene nanosheets (GNs) directly from a natural graphite electrode is described herein in the presence of sulfate ions under constant-voltage (CV) and constant-current (CC) models at a temperature range of 300–333 K. This electrochemical exfoliation process is more effective than chemical exfoliation processes and also provides a means of producing low-defect and high-yield GN products. The influence of exfoliation temperature on the quality of the as-prepared GN products is systematically investigated. To clarify this effect, one mechanism, consisting of (i) ionic intercalation, (ii) anion insertion and polarization, (iii) water electrolysis and SO₂ evolution, and (iv) bubble expansion, is proposed. The interlayer distance, defect concentration, and growth rate of GNs are found to be an increasing function of exfoliation temperature. More than 1.8 g of GNs is produced in less than 1 h by the CC operation in a 250 ml reactor. The growth rate of GNs under the CC model is approximately five times higher than that under the CV one at a fixed temperature. Based on the analysis of Arrhenius plots, the apparent activation energies through the CV and CC models are 20.6 and 23.1 kJ mol⁻¹, respectively. Hence, this exfoliation method using the CC model displays a potentially scalable approach for generating high-quality GN products.