Highly conductive carbon–CoO hybrid nanostructure arrays with enhanced electrochemical performance for asymmetric supercapacitors

Abstract

In this work, we report the synthesis of hybrid nanowire arrays by growing highly conductive carbon onto rough CoO nanowire arrays on 3D nickel foam. The CoO@C nanostructure arrays (CCNAs) are obtained via a hydrothermal method, followed by controlling the annealing and carbon deposition process at a relatively low temperature in the chemical vapor deposition (CVD) stage. In the carbon shell, apart from partial amorphous carbon, crystalline carbon was observed via TEM. With deposited carbon, the electrical conductivity and capacitance behaviors are dramatically promoted. The growth mechanism is proposed by TEM and XPS analyses, which firstly indicates that CoO could catalyze the decomposition of C₂H₂ at the low temperature of 427 °C in a reduction and catalytic process. The obtained CCNAs with a more hydrophilic surface and low resistance are tested as the working electrodes of supercapacitors, which lead to an ultrahigh specific capacitance of 3282.2 F g⁻¹ approaching to the theoretical value. Good rate capability and 96.9% capacitance retention after 10 000 cycles suggest that such hybrid electrode possesses a great potential application. After assembling it as the positive electrode and activated carbon as the negative electrode, the aqueous asymmetric supercapacitor demonstrates an energy density value up to ∼58.9 W h kg⁻¹ which is the highest value achieved among the Co-based supercapacitors.