Flexible supercapacitors with tunable capacitance based on reduced graphene oxide/tannin composite for wearable electronics

Abstract

• Flexible supercapacitor with tunable capacitance is achieved by vacuum filtration. • Tannin is served as reducing agent and electroactive material at the same time. • The device exhibits superior mechanical and electrochemical performance. • The preparation method is green, facile, reliable and cost-effective. Realization of flexible supercapacitors with tunable capacitance, high mechanical performance, and superior electrochemical performance has been achieved by precisely controlling the volume of vacuum filtration of reduced graphene oxide/tannin (RGO/TA) mixture slurry in this study. The TA coating on the surface of RGO can not only prevent RGO sheets from aggregation, but also provide extra pseudocapacitance and facilitate the reduction of graphene oxide at the same time owing to the abundant redox-active groups of TA. The capacitance of the RGO/TA film electrode can be continuously adjusted in the range of 40.69 to 234.13 mF cm −2 . The flexible all-solid-state supercapacitor (FASC) based on RGO/TA film electrode exhibits a good capacitance of 40.37 mF cm −2 , superior cycling stability, and good energy density of 3.60 μ W h cm −2 at a power density of 107.6 μ W cm −2 . Due to the 3D network structure of the RGO/TA film electrode and good mechanical properties of the substrate (nylon filter membrane), the FASC also shows acceptable performance at various bending states, which is conducive to expand its application in wearable and portable electronics. Besides, this simple and reliable method can be also applied to fabricate other supercapacitors/electrodes with desired shapes and capacitance, which can more effectively meet the practical needs.