Graphene oxide (GO), an important derivative of graphene, is highly desired for printing electronics, optoelectronics, catalysis, energy storage, separation membranes, biomedicine, and composites. However, the present synthesis methods depend on the reactions of graphite with strong oxidizing mixtures containing concentrated acids, and therefore suffer from explosion risk, serious environmental pollution, and long reaction time up to hundreds of hours.

Here, we report a safe, ultrafast and green method to synthesize GO with a high yield based on water electrolytic oxidation of graphite. It is found that the graphite lattice is fully oxidized by highly reactive oxygen radicals within a few seconds, which is over 100 times faster than the present methods. Moreover, this method is easy to scale up and the oxygen degree of GO can be easily controlled. Currently, a production line with a capacity of 10 tons per year has been set up. In terms of applications, based on the theory of fluid mechanics, we developed a continuous centrifugal casting method for highly efficient production of highly aligned and compact GO films. The reduced GO films show high strength (~660 MPa) and conductivity (~650 S/cm) simultaneously. This versatile method also enables the production of reduced GO/single-walled carbon nanotubes hybrid films for flexible supercapacitors with record volumetric energy density, highly anisotropic graphene nanocomposites as well as various 2D nanosheet films and vertical heterostructures. In addition, we synthesized a new class of reduced GO membranes with enlarged interlayer distance by using theanine amino acid and tannic acid as reducing agent and cross-linker, which show superior water permeance, along with good separation efficiency and long-term stability in aqueous solutions.

Green, efficient preparation of graphene oxide by water electrolysis.