Polypyrrole and polypyrrole@MnO₂ nanowires grown on graphene foam for asymmetric supercapacitor

The asymmetric supercapacitor with negative electrode by graphene foam loaded Polypyrrole nanowires (PPy NWs/rGOF) and positive electrode by PPy@MnO₂ core–shell nanowires on graphene foam (PPy@MnO₂ NWs/rGOF) was developed. The negative electrode was further converted into the positive electrode by one-step redox reaction at room temperature. Graphene foam (rGOF) with unique flexibility, large surface area and high electric conductivity can favor in situ growth of polypyrrole nanowires (PPy NWs) as well as improve cycling stability of the resultant negative electrode. PPy NWs served as the ideal template for the formation of MnO₂ shell gives rise to the as-prepared positive electrode with fast electron transport and enhanced active material utilization. Owing to the rational design, the assembled asymmetric supercapacitor was able to be repeatedly discharged/charged at 1.6 V, displaying high energy density of 1.04 mWh cm^–3 with improved cycling stability.