Development of flexible supercapacitors using an inexpensive graphene/PEDOT/MnO₂ sponge composite

It remains a formidable challenge to develop supercapacitors having both high stretchability and electrochemical performance. A ternary polymer composite was herein developed by engineering graphene platelets (GnPs), poly (3,4-ethylenedioxythiophene) (PEDOT) and manganese dioxide (MnO₂) into a kitchen sponge. Cost-effective GnPs having an electrical conductivity of 1460 S cm^− 1 were deposited onto the sponge pore surface by a simple dipping and drying process, followed by in situ polymerization of 3,4-ethylenedioxythiophene. MnO₂ was then deposited onto the GnPs and PEDOT layers through soaking the GnP/PEDOT sponge into KMnO₄ solution. When the composite was used as the electrodes for a flexible, stretchable supercapacitor, we obtained not only high specific capacitance but a high stretchability up to 400%. The supercapacitor demonstrated a specific capacitance of 802.99 F g^− 1 and an energy density of 55.76 Wh kg^− 1, with 99% capacitance retention over 1000 stretching cycles; these are attributed to the synergy between the composite components as well as the wavy device structure. The mass and thickness of the MnO₂ layer was found to increase with the soak, leading to the enhancement of electrochemical performance of GnP/PEDOT/MnO₂ sponge electrodes, i.e. 368.96 F g^− 1 for 5 min and 740.25 F g^− 1 for 10 min.