Graphene Foam (GF)/Manganese Oxide (MnO₂) Nanocomposites for High Performance Supercapacitors

We report supercapacitive characteristics of hierarchically porous architectured graphene foam (GF)/manganese oxide (MnO₂) nanocomposites fabricated via a simple two-step synthesis route. A polyurethane (PU) foam with graphene flakes adsorbed onto the pore walls is pyrolyzed to obtain GF. The MnO₂ is then electrochemically deposited onto GF to form a GF/MnO₂ (with a conductivity of 2.85 and 1.1 Sm⁻¹, respectively) nanocomposite. The GF is an ideal scaffold template for electrochemical deposition of MnO₂ and fast ion transport from MnO₂ to GF. The GF/MnO₂ supercapacitor shows excellent specific capacitance (672 F g⁻¹), rate capability (85% capacity retention over 1 to 20 A g⁻¹), and long cycle life (2% capacity loss after 10000 charge/discharge cycles) for 0.5 mg cm⁻² MnO₂ loading. Furthermore, the optimized supercapacitor delivers a specific energy of 95 Wh kg⁻¹ at a specific power of 1 kW kg⁻¹, which is substantially higher than that of most of the reported GF based supercapacitors. The results obtained here may pave the way for the development of commercial supercapacitors for future energy storage systems.