Capillary slit induced graphene laminate films towards enhanced areal capacitive energy storage

This study presents a novel slit evaporation self-assembly method for fabricating freestanding sulfuric acid-treated reduced graphene oxide/commercial graphene films (S-ATrGO/CG). The unique capillary slit-induced self-assembly process facilitates the alignment and stacking of graphene flakes, resulting in a well-ordered, laminated film. The treatment of graphene oxide (GO) with sulfuric acid facilitates the ring-opening of inert functional groups, converting them into active functional groups. Sulfuric acid-treated graphene oxide (ATGO) can serve as an effective binder for adhering commercial graphene (CG) flakes. XPS was used to quantitatively analyze the oxygen-containing functional groups in GO, ATGO, and S-ATrGO/CG. A series of electrochemical tests were conducted to investigate the behavior of the S-ATrGO/CG films, which exhibited well-defined redox peaks, indicating the contribution of unreduced oxygen-containing groups to redox reactions and pseudocapacitance. The S-ATrGO/CG films exhibit superior electrochemical performance, with an ultra-high area-specific capacitance of 1,589.78 mF cm^-2 at a scan of 5 mV s^-1 and an impressive initial capacitance retention of 99.80% after 20,000 cycles at a current density of 50 mA cm^-2. This study highlights the potential of S-ATrGO/CG films as high-performance electrodes for supercapacitors, contributing to the advancement of sustainable energy storage systems.