Preparation and characterization of colorful graphene oxide papers and flexible N‐doping graphene papers for supercapacitor and capacitive deionization

An efficient method that utilizes simple techniques, easy operation, and low‐cost production to create flexible graphene‐based materials is a worthy practical challenge. A rapid strategy for preparing flexible, functional graphene oxide (GO) is introduced using GO‐ethanol dispersion filtration. The filtration process is highly efficient and drying time is significantly reduced by employing ethanol as solvent, due to the fact that ethanol is a volatile liquid. Freestanding GO papers can be harvested with ultralarge size (700 cm2), color variety, and writable characteristics. After reduction, N‐doped graphene (NDG) papers still maintain good foldability with improved electric conductivity and porous structure. When used as an electrode for a supercapacitor, the flexible NDG paper device demonstrates good electrochemical performance even with size expansion and extreme double folding. Moreover, this NDG paper capacitor device shows a good electrosorption performance for capacitive deionization of sulfate and chromate in groundwater system. These flexible GO and NDG papers promise potential to facilitate the production of graphene‐based materials for practical applications in energy and environmental related fields.