HMTA-assisted uniform cobalt ions activated copper oxide microspheres with enhanced electrochemical performance for pseudocapacitors

Abstract

Supercapacitors are being considered to be one of important electrochemical energy storage devices due to their high power density as compared with batteries and have remarkable applications. The large surface area transition metal oxides or hydroxides are excellent conductive materials and have been extensively used for supercapacitors. Herein, uniform copper oxide (CuO) and cobalt (Co) activated CuO (CuO:Co) microspheres were synthesized by a hexamethylenetetramine (HMTA)-assisted hydrothermal method. The HMTA was used as an additive surfactant to acquire the uniform microsphere morphology, which was confirmed by high-resolution field-emission scanning electron microscope and field-emission transmission electron microscope images. The phase form of the pristine CuO and CuO:Co powder samples was examined by X-ray diffraction patterns. For the application of pseudocapacitors, electrochemical studies were performed for the CuO and CuO:Co electrode materials in a three-electrode electrochemical cell system. The cyclic voltammetry and galvanostatic charge-discharge curves were measured at different scan rates and current densities, respectively, in 1 M KOH electrolyte solution. The calculated specific capacitance values of the CuO and CuO:Co electrodes were 77 and 284 F/g at a current density of 1 A/g, respectively. Interestingly, by incorporating small concentration of Co into CuO, the specific capacitance was enhanced approximately 4 times when compared with the pristine CuO electrode. The electrochemical impedance spectroscopy spectrum was analyzed for the pseudocapacitive behavior of CuO:Co electrode material. Furthermore, the CuO:Co electrode showed a capacitance retention (75.6%) after 1000 cycles at a current density of 3 A/g. Therefore, the obtained remarkable electrochemical results suggest that the low-cost CuO:Co electrode materials with improved electrochemical performance have promising applications in the field of pseudocapacitors.