Ultrastrong Adhesion of Fluorinated Graphene on a Substrate: In situ Electrochemical Conversion to Ionic-Covalent Bonding at the Interface

Abstract Graphene shows unique properties such as high mechanical strength and high thermal and chemical stability, making it promising for versatile applications. However, the lack of either interlayer or interface covalent bonds causes this type of 2D materials assembled via van der Waals forces to suffer from weak adhesion with the underlying substrates, thus hindering their application. In this study, a novel method based on a hydrothermal reaction was proposed to synthesize fluorinated graphene (FG) through a facile, scalable, and highly safe process, where a mixture of poly(perfluorosulfonic acid) (C7HF13O5S·C2F4, PFSA) and graphene oxide (GO) as the precursor was employed. The FG sheets prepared by the electrophoretic deposition (EPD) method exhibit superior conformity layered structure on a metal foil. Due to the in situ formation of ionic-covalently bonded F-Cu-F and Cu-F-C between fluorine on the FG sheets and dissolved Cu ions from the copper foil, the deposited film shows ultrastrong adhesion that can sustain up to 3 MPa of shear force. Furthermore, by changing the parameters in the EPD process, such as the EPD duration and applied voltage, the thickness and hydrophobicity of the film can be well controlled from 0.20 μm to 2.51 μm with a contact angle from 93.03˚ to 122.44˚. This study provides a new strategy to prepare a robust film for the assembly of 2D materials, not limited to graphene, with ultrastrong adhesion on substrates, which could solve the long-reported issue of weak adhesion and low durability of graphene-/2D-based functional composites and coatings.