Influence of Temperature on ZnO/Co₃O₄ Nanocomposites for High Energy Storage Supercapacitors

Abstract

We developed a two-step chemical bath deposition method followed by calcination for the production of ZnO/Co 3 O 4 nanocomposites. In aqueous reactions, ZnO nanotubes were first densely grown on Ni foam, and then flat nanosheets of Co 3 O 4 developed and formed a porous film. The aspect ratio and conductivity of the Co 3 O 4 nanosheets were improved by the existence of the ZnO nanotubes, while the bath deposition from a mixture of Zn/Co precursors (one-step method) resulted in a wrinkled plate of Zn/Co oxides. As a supercapacitor electrode, the ZnO/Co 3 O 4 nanosheets formed by the two-step method exhibited a high capacitance, and after being calcined at 450 °C, these nanosheets attained the highest specific capacitance (940 F g −1 ) at a scan rate of 5 mV s −1 in the cyclic voltammetry analysis. This value was significantly higher than those of single-component electrodes, Co 3 O 4 (785 F g −1 ) and ZnO (200 F g −1 ); therefore, the presence of a synergistic effect was suggested. From the charge/discharge curves, the specific capacitance of ZnO/Co 3 O 4 calcined at 450 °C was calculated to be 740 F g −1 at a current density of 0.75 A g −1 , and 85.7% of the initial capacitance was retained after 1000 cycles. A symmetrical configuration exhibited a good cycling stability (Coulombic efficiency of 99.6% over 1000 cycles) and satisfied both the energy density (36.6 Wh kg −1 ) and the power density (356 W kg −1 ). Thus, the ZnO/Co 3 O 4 nanocomposite prepared by this simple two-step chemical bath deposition and subsequent calcination at 450 °C is a promising material for pseudocapacitors. Furthermore, this approach can be applied to other metal oxide nanocomposites with intricate structures to extend the design possibility of active materials for electrochemical devices.

Simultaneous Electrodeposition of Ternary Metal Oxide Nanocomposites for High-Efficiency Supercapacitor Applications

“…The cathode materials exhibited nanosheet structures and changed their morphologies from spherical nanoflowers (cathode-1) to flat porous films as the concentration of the Co 2+ precursor increased, as reported previously for Mn oxides and Co oxides. 11 , 20 The nanosheets of cathode-3 had a mean thickness and length of ∼10 and 197 nm, respectively, and interconnected with each other. The thickness and length of the nanosheets increased and decreased (to ∼22 and 87 nm), respectively, as the precursor concentration of Co 2+ increased to 120 mM (cathode-4); that is, the network density of the metal oxides increased.…”

“…In our previous study, ZnO nanotubes were first deposited, and then secondary Co hydroxide nanoplates were hybridized. 20 In this study, the simultaneous deposition of Zn and Co hydroxide/oxide was not effective because the structure of the obtained Zn/Co oxides was not adequate for rapid ion adsorption/desorption and charge transfer. The simultaneous deposition of multiple metal ions is a simple method; however, investigations of the simultaneous deposition of complex TMOs for pseudocapacitor electrodes are rare.…”

“…The electrolyte solution for deposition was prepared from a powder of Ni(NO 3 ) 2 •6H 2 O, Co(NO 3 ) 2 •6H 2 O, and Mn(NO 3 ) 2 •4H 2 O dissolved in 50 mL of deionized water. The Ni 2+ (80 mM) and Mn 2+ (40 mM) concentrations were fixed, whereas that of Co 2+ was varied (20,40,80, and 120 mM). Electrodeposition was carried out in a standard three-electrode glass cell consisting of two pieces of precleaned Ni foam with an apparent exposed area of 2 cm 2 as the working electrode and counter electrode and Ag/AgCl in a saturated KCl solution as the reference electrode.…”

“…To prepare complex TMOs for pseudocapacitors, stepwise deposition can be applied. In our previous study, ZnO nanotubes were first deposited, and then secondary Co hydroxide nanoplates were hybridized . In this study, the simultaneous deposition of Zn and Co hydroxide/oxide was not effective because the structure of the obtained Zn/Co oxides was not adequate for rapid ion adsorption/desorption and charge transfer.…”

Effect of Molar Ratio Modulation of Cobalt Precursors on Supercapacitor Behavior of Engineered Co–Co3O4 Nanocomposite Electrodes

“…So far, a myriad of techniques including chemical precipitation, sol–gel, hydrothermal, chemical bath deposition, spray pyrolysis, direct magnetron sputtering, and electrodeposition have been explored to develop nanostructured Co 3 O 4 materials. − Among these deposition techniques, the electrodeposition method is found to be a simple, low temperature, and cost-effective technique for growing well adhered Co 3 O 4 nanostructures with desired morphological features and composition directly onto conductive substrates without the use of binders and conductive additives. Furthermore, in electrodeposition, factors such as the composition of the electrolyte, type of electrodeposition mode, and duration of the process can be regulated to achieve the desired morphology and texture, including nanoplates, nanoflowers, nanosheets, and nanotubes. ,,,, Subsequently, previous studies have reported a variation in morphological features, microstructure, and corresponding electrochemical performance of Co 3 O 4 materials when different types of cobalt precursor salts, namely, cobalt chloride, cobalt acetate, cobalt sulfate, and cobalt nitrate, are used. ,, The growth rate of Co 3 O 4 was observed to be higher when chloride was used as compared to acetate. Thus, a novel approach will be combining two different cobalt precursors with different anion sizes to control growth rate and tune morphology to achieve high specific capacitance.…”