Electrochemical Exfoliation of Graphite in Aqueous Sodium Halide Electrolytes toward Low Oxygen Content Graphene for Energy and Environmental Applications

Abstract

Graphene and graphene-based materials have shown great promise in many technological applications, but their large-scale production and processing by simple and cost-effective means still constitute significant issues in the path of their widespread implementation. Here, we investigate a straightforward method for the preparation of a ready-to-use and low oxygen content graphene material that is based on electrochemical (anodic) delamination of graphite in aqueous medium with sodium halides as the electrolyte. Contrary to previous conflicting reports on the ability of halide anions to act as efficient exfoliating electrolytes in electrochemical graphene exfoliation, we show that proper choice of both graphite electrode (e.g., graphite foil) and sodium halide concentration readily leads to the generation of large quantities of single-/few-layer graphene nanosheets possessing a degree of oxidation (O/C ratio down to ∼0.06) lower than that typical of anodically exfoliated graphenes obtained with commonly used electrolytes. The halide anions are thought to play a role in mitigating the oxidation of the graphene lattice during exfoliation, which is also discussed and rationalized. The as-exfoliated graphene materials exhibited a three-dimensional morphology that was suitable for their practical use without the need to resort to any kind of postproduction processing. When tested as dye adsorbents, they outperformed many previously reported graphene-based materials (e.g., they adsorbed ∼920 mg g for methyl orange) and were useful sorbents for oils and nonpolar organic solvents. Supercapacitor cells assembled directly from the as-exfoliated products delivered energy and power density values (up to 15.3 Wh kg and 3220 W kg, respectively) competitive with those of many other graphene-based devices but with the additional advantage of extreme simplicity of preparation.

High quality, low-oxidized graphene via anodic exfoliation with table salt as an efficient oxidation-preventing co-electrolyte for water/oil remediation and capacitive energy storage applications

“…Furthermore, we note that graphite foil could be anodically exfoliated using NaCl or KCl as the only electrolyte (i.e., in the absence of Na 2 SO 4 ) [33]. However, in this case the delamination process was somewhat inefficient, yielding comparatively small amounts of graphene, which can be ascribed to a poor ability of the chloride anion to intercalate graphite on its own.…”

Emerging 2D Materials Produced via Electrochemistry

“…The quality of the exfoliated graphene sheets was further proved by a high hole mobility exceeding 300 cm 2 V −1 s −1 . Later in 2017, Munuera et al proposed an alternative neutral system including sodium halides (such as NaCl, NaBr, and NaI) to delaminate graphite foils . Especially, sodium chloride (0.05 m ) led to single/few‐layer graphene sheets with an average thickness of 2–3 nm, an I D / I G ratio of 0.8, and high C/O ratio of 16.7.…”

Simultaneously electrochemical exfoliation and functionalization of graphene nanosheets: Multifunctional reinforcements in thermal, flame‐retardant, and mechanical properties of polyacrylonitrile composite fibers

“…Electrochemical exfoliation with good overall performance including simpleness, environmental protection and mass production was designed and developed, as a potential method for scalable production of graphene . Parvez et al used aqueous inorganic salts ([NH 4 ] 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , etc.)…”

“…Electrochemical exfoliation with good overall performance including simpleness, environmental protection and mass production was designed and developed, as a potential method for scalable production of graphene. [18,19] Parvez et al [20] used aqueous inorganic salts ([NH 4 ] 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , etc.) as electrolytes to exfoliate graphite by an electrochemical method, resulting in bare graphene with a low oxidation degree (C/O = 17.2) and high yield (≤3 layers, >85%).…”