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 μm, 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.