Facile synthesis and electrochemical performances of binder-free flexible graphene/acetylene black sandwich film

Graphene/acetylene black sandwich film was fabricated by a simple vacuum filtration procedure using a stable complex suspension of graphene oxide (GO) and acetylene black followed by a hydroiodic acid (HI) immersion process to fully reduce the GO to graphene sheets. The self-restacking of individual graphene sheets were greatly alleviated and electric conductivity was obviously improved using the acetylene black nanoparticles as both effective spacers to expand the inter-layer interval of the individual graphene sheets during the film assembly course and highly conducting bridges to facilitate the electron/ion transfer between the upper and lower graphene sheets. The flexible graphene/acetylene black film was utilized as supercapacitor electrode without additional conductive additives, binders and current collectors, which achieved an obviously higher specific capacitance (ca. 136.6 F g−1 at 0.5 A g−1) and much better specific capacitance retention at high current densities than that of the pure graphene film electrode, indicating that such a novel sandwich film structure allows for a higher charge storage capability. More importantly, the assembled symmetric supercapacitor device displayed a satisfactory specific capacitance of 59.2 F g−1 at 0.1 A g−1, 47.6 F g−1 at 0.5 A g−1 and 42.8 F g−1 at 1 A g−1, and only negligible 4.05% capacitance degradation have been found after 1000 continuous charge-discharge cycles at 0.5 A g−1, revealing outstanding rate capability, excellent electrochemical reversibility and long-term cyclability. These results proved that such a flexible and highly conductive graphene/acetylene black film can be promising electroactive materials in the development of advanced electrochemical energy storage devices.