Despite the intensive research efforts
devoted to graphene fabrication
over the past decade, the production of high-quality graphene on a
large scale, at an affordable cost, and in a reproducible manner still
represents a great challenge. Here, we report a novel method based
on the controlled electrochemical exfoliation of graphite in aqueous
ammonium sulfate electrolyte to produce graphene in large quantities
and with outstanding quality. Because the radicals (e.g., HO<sup>•</sup>) generated from water electrolysis are responsible for defect formation
on graphene during electrochemical exfoliation, a series of reducing
agents as additives (e.g., (2,2,6,6-tetramethylpiperidin-1-yl)oxyl
(TEMPO), ascorbic acid, and sodium borohydride) have been investigated
to eliminate these radicals and thus control the exfoliation process.
Remarkably, TEMPO-assisted exfoliation results in large graphene sheets
(5–10 μm on average), which exhibit outstanding hole
mobilities (∼405 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>), very low Raman <i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> ratios (below 0.1), and extremely high carbon
to oxygen (C/O) ratios (∼25.3). Moreover, the graphene ink
prepared in dimethylformamide can exhibit concentrations as high as
6 mg mL<sup>–1</sup>, thus qualifying this material for intriguing
applications such as transparent conductive films and flexible supercapacitors.
In general, this robust method for electrochemical exfoliation of
graphite offers great promise for the preparation of graphene that
can be utilized in industrial applications to create integrated nanocomposites,
conductive or mechanical additives, as well as energy storage and
conversion devices
