Electrocoagulation Driven Fabrication of Metal-Ion-Containing Graphene Oxide Films

Abstract

The development of simple, solution-based techniques for the formation of graphene oxide (GO) films is of great interest to the materials community due to the potential application of these films in diverse areas such as filtration membranes and anticorrosion coatings. Further, the reduction of graphene oxide (GO) has been a reliable route to restore electrical conductivity and to obtain chemically modified graphene platelets in large scale and low cost for electronic and energy storage technologies. The stability of GO films in aqueous systems (e.g. for coatings or membrane applications) is often driven by the presence of multivalent, cationic metal contaminants that serve as strong cross-linkers between GO platelets. However, the incorporation of the metal ions into GO suspensions used for film formation is often uncontrolled. In contrast, this work demonstrates the rapid formation of GO films containing metal ions that are introduced using an easily implemented, electrochemical approach that enables the metal ion content and resulting film properties to be tailored. Specifically, the method is based on the electrocoagulation of GO particles onto a Cu substrate/electrode. In this process, the Cu ions used to cross-link and form the GO film are electrochemically evolved from the Cu electrode itself. Tuning of EC-driven GO film deposition was explored using a number of approaches, including size tuning of GO particles in suspension via chemical coagulation prior to deposition and the control of applied voltage, deposition time and suspension concentration. Moreover, the frequency dependence of AC-applied voltage on the resulting film evolution and resulting microstructure was also examined. An electrochemical reduction of the resulting GO films was subsequently used to produce reduced graphene oxide. Cyclic voltammetry was successful in identifying the primary reduction potentials for both the Cu2+ and GO present in the film offering a means to selectively reduce these individual constituents. With this information, a constant potential technique was applied to produce reduced graphene oxide films exhibiting greater conductivities than those typically observed in thermally or chemically reduced graphene oxide films (for example: up to 36% increase compared to hydrazine reduction and up to 200% increase compared to thermal exfoliation). These results offer new avenues for employing GO and reduced GO in a wide variety of technology, energy, and membrane applications.