Flexible supercapacitor based on MnO2 nanowalls vertically grown on ultrathin stainless-steel foils

Vertically aligned nanostructures are usually beneficial for ion diffusion during the charge/discharge process and thereby, are suitable to be electrodes for pseudo-supercapacitor applications. Herein, vertically aligned delta-MnO2 nanowalls are successfully grown on the surface of ultrathin stainless-steel foils by a facile fabrication process that combines the conventional hydrothermal method with the polymer-assisted disposition method. The materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Due to the unique structural characteristics of delta-MnO2 nanowalls, the electrodes exhibit excellent electrochemical capacitive performances. In particular, a quasi-solid-state asymmetric device exhibits a high energy density of 53.24 mu Wh/cm(2) at a power density of 451 mu W/cm(2). The device also exhibits outstanding cycling stability with a high capacitance retention (similar to 94.5 %) after 30,000 cycles.