Free-standing graphene-carbon as negative and FeCoS as positive electrode for asymmetric supercapacitor

Free-standing graphene was synthesized using atmospheric pressure microwave plasma and used as electrode for supercapacitors. The graphene based electrodes demonstrated good supercapacitive and electronic properties and displayed a high rate retention of 78.5% and a low time constant of 0.2 s. It was further studied as conductive agent where the electrode produced after mixing it with activated carbon (AC) in 47.5:47.5 ratio demonstrated a specific capacitance of 208 F g(-1) at 2 A g(-1), rate capability of 70.8% at 10 A g(-1) and a time constant of 4 s, significantly below the 25.1 s one obtained for electrodes made with commercial activated carbon and conductive agents. Electrodeposited FeCoS on stainless steel tested as positive electrode. The ratio of Fe to Co equal to 1:2 showed the best electrochemical performance with specific capacitance of 827.5 F g(-1) at 1 A g(-1) with a rate capability of 84.1% at 10 A g(-1) and long cycling stability of 90.4% up to 5000 cycles. An asymmetric cell made of AC:Graphene - 47.5:47.5||Fe:Co-1:2, displayed good capacitive response in a potential window of 1.2 V, in 1 M KOH, stored a maximum energy density of 67.8 W h kg(-1) at a power density of 1.6 kW kg(-1) and retained 45.2 Wh kg(-1) at a power density of 6.1 kW kg(-1).

Automated summary

Free-standing graphene synthesized using atmospheric pressure microwave plasma showed good supercapacitive properties and was used as an electrode. Electrodes made by mixing graphene with activated carbon demonstrated improved specific capacitance and rate capability compared to commercial activated carbon electrodes.