Electric-Field-Triggered Graphene Production: From Fundamental Energy Applications to Perspectives

ConspectusTwo-dimensional sp2-hybridized graphene has been seriously considered and applied in various fields, such as materials science, energy storage/conversion, catalysis, and biomedicine, on account of its unique long-range-ordered and π-conjugated structure as well as excellent thermal and electric conductivity. At present, the adopted methods for graphene synthesis cover micromechanical exfoliation, epitaxial growth, chemical reduction of graphite oxide, chemical vapor deposition, and liquid-phase exfoliation. Nonetheless, a number of issues and challenges still existed in these employed methods in terms of sustainable and green energy chemistry and environmental friendliness. Electrochemical exfoliation is one of the most promising methods for the large-scale production of graphene by virtue of simple/eco-friendly operation and high-efficiency production. Depending on different exfoliation methods (anodic, cathodic, and dual-electrode) and electrochemical exfoliation conditions such as the reaction device, raw material, electrolyte, and power-supply mode, the exfoliated graphene features various and versatile characteristics. The relatively perfect graphene with intrinsic long-range π-conjugated character is accompanied by the fast capability of electron transfer. The defective graphene features the adjustable size and defect density and tunable amphipathicity. As a result, the corresponding graphene has been employed in energy storage/conversion, biology, and medicine fields. In this Account, we summarize the recent progress in the fundamentals of electrochemical exfoliation to produce the graphene and the derivative exfoliation method and their applications in energy-related fields, and the corresponding perspectives are also highlighted. First, we describe the fundamentals for different exfoliation methods and electric-field-induced effects that can help to guide us to prepare and produce graphene with various properties, covering the size, defect density, and surface chemistry. Subsequently, three electric-field-triggered methods (anodic, cathodic, and dual-electrode exfoliation) are discussed in detail. In particular, the effects of various electrolytes and power-supply modes on electrochemically exfoliated graphene (EEG) are systematically underlined in terms of the exfoliation principles and process, which are the significant factors affecting the structure and properties of EEG and the efficiency of intercalation and exfoliation. In addition, the recent progress in multilevel applications of EEG in energy storage/conversion fields such as supercapacitors, secondary batteries, the oxygen evolution reaction, the hydrogen evolution reaction, the carbon dioxide reduction reaction, and so forth is also summarized. Finally, the expectations and future research directions for the EEG in terms of controllably technological parameters and conditions, precise monitoring and in-depth comprehension of the exfoliation processes, multiscale and diverse products (carbon quantum dots, graphene quantum dots, and single-atom catalysts), and large-scale preparation and application are discussed, which hope to provide significant guidance for future research.