Hierarchical carbon-decorated Fe3O4 on hollow CuO nanotube array: Fabrication and used as negative material for ultrahigh-energy density hybrid supercapacitor

In the supercapacitor field, although many positive electrode materials with high specific capacitance are available, progress in developing the corresponding negative electrode materials has been very sluggish. As a result, practical application of actual devices has been limited severely by their low energy density. Thus there is an urgent need to design and synthesize negative electrode materials with high specific capacitance to match the currently available positive electrode materials. In this work, a new negative electrode material—a carbon-decorated Fe3O4/CuO/copper foam (denoted as Fe3O4@C/CuO/CF) nanotube array—has been successfully obtained using the copper foam (CF) as a substrate. The 2D layered structure of the Fe3O4 nanoflakes affords excellent electrochemical performance by facilitating the surface-dependent electrochemical reaction processes, whilst the carbon layer on the surface of the Fe3O4 enhances the electrical conductivity, and the hollow structure enables effective electrode–electrolyte contact facilitating the electrochemical reactions. When used as a negative electrode material, the Fe3O4@C/CuO/CF exhibits an outstanding electrochemical performance, with an ultrahigh specific capacity (15 F cm−2, 1250 F g−1, at 5 mA cm−2) and good cycle stability (88% of its initial capacity was preserved after 5000 charge/discharge process at 100 mA cm−2). Moreover, in order to demonstrate its application in practice, an asymmetric supercapacitor (ASC) device was fabricated with the Fe3O4@C/CuO/CF as the negative electrode and Ni–Co hydroxide/Cu(OH)2/CF as the positive electrode. The ASC device exhibits high energy densities (90.6 Wh kg−1 at a power density of 188.4 W kg−1) which are comparable to those of commercial Li-ion batteries.