High-Voltage Asymmetric Supercapacitors based on Carbon and Manganese Oxide/Oxidized Carbon Nanofiber Composite Electrodes

Asymmetric supercapacitors with high operating voltages have been successfully developed, using manganese oxide/oxidized carbon nanofibers (MnO2/CNFox) composites as the positive electrode and activated carbon (AC) as the negative electrode, in a neutral aqueous 0.5 moll L-1 K2SO4 solution. The assembled MnO2/CNFox//AC supercapacitor can operate reversibly in a wide voltage range up to 2.3 V, showing an excellent stability with only a 7.6% loss of its initial capacitance after 5000 cycles at 1 Ag-1. A high energy density of 24.8 Whkg(-1) at a power density of 100 Wkg(-1) is achieved. This unique electrochemical performance is attributed to the presence of CNFox with hydrophilic surface properties in the MnO2-based electrode, which ensures a perfect dispersion of nanofibers in the bulk MnO2 and a very good adhesion between the components of the MnO2/CNFox composite. The obtained results show great potential in developing asymmetric supercapacitors with high energy and power densities working in neutral aqueous media.