Synthesis of Co3O4/CoVxOy core-shell nanosheets arrays with interweaved nanowires as cathode materials for asymmetric supercapacitors

Tailoring the Morphology of α-Cobalt Hydroxide Using Liquid/Liquid Interface and Its Application in Electrochemical Detection of Ascorbic Acid

The exertion of nanomaterials is subjugated by factors such as size, thickness, morphology, crystallinity, and composition, however, the ability to control these parameters, particularly the morphology, through conventional synthesis methods are challenging. Nevertheless, liquid/liquid interface-assisted methods have paved the way for more precise and controlled synthesis of nanomaterials. In this study, an n-butanol/water interface was used to synthesize α-cobalt hydroxide (CH) nanostructures, and the effects of solvent ratio and stirring rate on the properties of the product were examined. The transition from pure water to pure n-butanol alters the morphology from irregular nanoflakes to flower-like structures. A 1:1 solvent ratio produced nonaggregated flower structures with an increased active surface area and minimal charge transfer resistance. The agitation speed also affected the morphology; as the stirring speed increased from zero to 150 rpm, the morphology changed from aggregated needles to flower-like structures. The sample synthesized with a 1:1 solvent ratio and 50 rpm stirring speed (BW2) exhibited enhanced electrochemical activity, which was harnessed for electrochemical sensing with minimal multiwalled carbon nanotube (MWCNT) addition. The CH/MWCNT composite effectively detected ascorbic acid (AA) across a broad linear range of 1-200 μM with a detection limit of 0.0943 μM and provided accurate AA recovery in vitamin C tablets and artificial sweat. A flexible miniature sensor was also developed for AA detection, demonstrating the potential of liquid/liquid interfaces to modulate the morphology and hence the electrochemical properties of transition metal oxides for a wide range of applications.

ZIF-67 Derived Co2VO4 Hollow Nanocubes for High Performance Asymmetric Supercapacitors

In this work, a new type of Co₂VO₄ hollow nanocube (CoVO-HNC) was synthesized through an ion exchange process using ZIF-67 nanocubes as a template. The hollow nanocubic structure of the CoVO-HNC provides an abundance of redox sites and shortens the ion/electron diffusion path. As the electrode material of supercapacitors, the specific capacitance of CoVO-HNC is 427.64 F g⁻¹ at 1.0 A g⁻¹. Furthermore, an asymmetric supercapacitor (ASC) was assembled using CoVO-HNC and activated carbon (AC) as electrodes. The ASC device attains an energy density of 25.28 Wh kg⁻¹ at a high-power density of 801.24 W kg⁻¹, with 78% capacitance retention after 10,000 cycles at 10 A g⁻¹.