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

Abstract

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. Using pressure chambers to grow metal oxide nanowires reduces the number of components needed for high-performance supercapacitors. Do-Heyoung Kim from Chonnam National University in South Korea and colleagues report a new hydrothermal synthesis that deposits forest-like arrays of iron—cobalt oxide nanowires directly onto a conductive stainless-steel mesh. This avoids the need to use binding agents or additives, which can increase the electrical resistance. The vertically aligned nanowires were decorated with numerous tiny particles, which provide more active sites for energy storage than bulk electrodes. The team combined this negative electrode with a positive terminal made from manganese oxide, also grown straight onto stainless steel. The complimentary operating voltages and high surface area of the electrodes yielded a supercapacitor device with an excellent energy density and electrochemical stability. SEM image of FeCo2O4 nanowire arrays on a stainless steel mesh with the schematic of MnO2//FeCo2O4 asymmetric cell and its CV curves.