Cathodic exfoliation of graphite into graphene nanoplatelets in aqueous solution of alkali metal salts

Electrochemical exfoliation has emerged as a green, effective and scalable route for mass production of graphene. Cathodic exfoliation of graphite, offers a direct production of high quality and low defect graphene. However, the protocols for cathodic exfoliation reported to date, use mostly non-aqueous electrolytes which require extended period of intercalation, and post-treatment to further exfoliate the intercalated graphene layers. In contrast, the employment of environment friendly aqueous-based electrolytes, coupling with a shorter exfoliation period would be attractive features of any new protocol. Here, we demonstrate efficient cathodic electrochemical exfoliation of graphite to graphene nanoplatelets in aqueous electrolytes using common and inexpensive alkali-metal salts such as KCl. The key driving force to exfoliate graphite successfully in aqueous electrolyte is applying a sufficiently high voltage, and a high salt concentration which facilitate cation intercalation, and promotes hydrogen evolution to exfoliate the graphene. The cathodic exfoliated graphene nanoplatelets using KCl aqueous electrolyte exhibits a low defect density (I-D/I-G of 0.06, a C/O ratio of 57.8), high graphite exfoliation yields (> 80%) in short times (< 10 min for a graphite foil of 1 cm x 1 cm x 0.0254 cm, 30.0 mg). The highly conductive structure consists mainly of 10-13 layers graphene sheets that serve as an excellent support material for electrocatalytic reactions. This environment-benign aqueous-based cathodic electrochemical exfoliation of graphite opens a new opportunity in large-scale and low-cost production of high-quality graphene nanoplatelets.