Nanosized MnO2 spines on Au stems for high-performance flexible supercapacitor electrodes

Electrodes composed of ultrathin MnO2 (thickness 5-80 nm) spines on Au nanowire (NW) stems (length 10-20 mu m, diameter 20-100 nm) were electrochemically grown on flexible polyethylene terephthalate (PET) substrates. The electrodes demonstrated high specific capacitance, high specific energy value, high specific power value, and long-term stability. In Na2SO4(aq.) (1 M), the maximum specific capacitance was determined to be 1130 F g(-1) by cyclic voltammetry (CV, scan rate 2 mV s(-1)) using a three-electrode system. From a galvanostatic (GV) charge/discharge test using a two-electrode system, a maximum capacitance of 225 F g(-1) (current density 1 A g(-1)) was measured. Even at a high charge/discharge rate of 50 A g(-1), the specific capacitance remained at an extremely high value of 165 F g(-1). The flexible electrodes also exhibited a maximum specific energy of 15 W h kg(-1) and a specific power of 20 kW kg(-1) at 50 A g(-1). After five thousand cycles at 10 A g(-1), 90% of the original capacitance was retained. A highly flexible solid-state device was also fabricated to reveal its supercapacitance performance.