Electrochemical synthesis of graphene and holey graphene: the role of material selection and an approach to a simultaneous synthesis process

Abstract

Exfoliating graphene by employing electrochemical exfoliation (ECE) has emerged as a promising route for obtaining large-scale graphene material at a reasonable cost. However, in addition to the exfoliation parameters, the obtained graphene quality can strongly depend on the graphite electrode type used for exfoliation, and a proper understanding is lacking. In the current work, the impact of graphite electrode types in graphene exfoliation has been investigated. Three different commercially available graphite types, namely, graphite block, graphite foil (compressed), and synthetic graphite foil types, are explored. Electrolyte solutions of H₂SO₄ combined with KOH of molar concentration of 0.1 M − 3 M are used for the ECE. In the case of the graphite block, despite having an exfoliation rate of ∼10⁻³ g/min, no graphene flake was found. Compressed and synthetic type yields graphene material with a rate of 10⁻³ - 10⁻⁴ g/min, depending on the molar concentration and electrical parameter. Raman study reveals exfoliation from compressed type provides I_D/I_G of 1.06, which seems to decrease to 0.19 (lesser defect) after sonication. On the other hand, for the synthetic type, the I_D/I_G value is 1.36. The microstructural configuration of the electrode is found to play a key role in the exfoliation process, and a correlation between the two is established. The study substantially advances our understanding of the electrochemical exfoliation process of graphene. We have also proposed and demonstrated a synthesis process of graphene and holey graphene in a simultaneous fashion using a single-cell, two-compartment design that can efficiently synthesize both materials in a single step. The pores are produced via the reduction of the functionalized graphene part. The pore size can vary from a few nm to hundreds of nm, as validated by the electron microscopy and surface characterization. The demonstrated method has the potential to be scaled up and meet the industrial demand.