Direct growth of FeCo2O4 nanowire arrays on flexible stainless steel mesh for high-performance asymmetric supercapacitor

Currently, one-dimensional nanostructured binary metal oxides attract a great attention in supercapacitors (SCs) application due to their rapid charge transportation. In this respect, different nanostructures of FeCo2O4 are designed by simply tuning the reaction temperature in hydrothermal synthesis. These nanostructures are directly grown on flexible stainless steel mesh and further applied as binder-free electrodes for SCs. The systematic study is carried out to confirm the relation between surface characteristics and electrochemical properties of FeCo2O4 thin film. Among different nanostructures, FeCo2O4 nanowire arrays exhibit hierarchical mesoporous structure and demonstrate good surface properties including high surface area and appropriate pore volume. As a consequence, relatively high specific capacitance of 1963 F g(-1) is obtained for the FeCo2O4 nanowire electrode. Further, asymmetric SC is fabricated using nanowired-FeCo2O4 and nanoparticulated-MnO2 thin films as negative and positive electrodes with neutral Na2SO4 electrolyte. Impressively, the MnO2//FeCo2O4 cell could be successfully cycled in a wide voltage window of 2.0 V, which can achieve a specific capacitance of 218 F g(-1) and energy density of 43 Wh kg(-1). In addition, the SCs exhibit improved capacitance with cycling, which is attributed to opening of micro-pores occurred by frequent ion transport.