Search Results (5)

Flexible supercapacitors have emerged as pivotal energy storage components in wearable smart electronic systems, owing to their exceptional electrochemical performance. However, the widespread application of flexible supercapacitors in smart electronic devices is significantly hindered by the developmental bottleneck of high-performance anode materials. In this study, a novel electrode composed of surface-modified Fe₂O₃ nanoneedles uniformly coated with a polypyrrole (PPy) film and anchored on Co-MOF-derived N-C nanoflake arrays (PPy/Fe₂O₃/N-C) is designed. This composite electrode, grown in situ on carbon cloth (CC), demonstrated outstanding specific capacity, rate performance, and mechanical flexibility, attributed to its unique hierarchical 3D arrayed structure and the protective PPy layer. The fabricated PPy/Fe₂O₃/N-C@CC (P-FONC) composite electrode exhibited an excellent specific capacitance of 356.6 mF cm⁻² (143 F g⁻¹) at a current density of 2 mA cm⁻². The current density increased to 20 mA cm⁻², and the composite electrode material preserved a specific capacitance of 278 mF cm⁻² (112 F g⁻¹). Furthermore, the assembled quasi-solid-state Mn/Fe asymmetric supercapacitor, configured with P-FONC as the negative electrode and MnO₂/N-C@CC as the positive electrode, demonstrated robust chemical stability and notable mechanical flexibility. This study sheds fresh light on the creation of three-dimensional composite electrode materials for highly efficient, flexible energy storage systems. Full article

The spread of many infectious diseases by vectors is a globally severe issue. Climate change and the increase of vector resistance are the primary sources of rising mosquito populations. Therefore, advanced approaches are needed to prevent the dispersal of life-threatening diseases. Herein, Mn₂O₃ NPs and MnCoO nanocomposites were presented as mosquitocidal agents. The synthesized samples were prepared by a co-precipitation route and characterized using different techniques indicating the change of host Mn₂O₃ structure to 2D MnCoO nanoflakes with Co³⁺ integration. The thermal decomposition of the nanoparticles was examined by TGA analysis, showing high stability. The energy gap (${\mathrm{E}}_{\mathrm{g}}$) of Mn₂O₃ was estimated within the visible spectrum of the value 2.95 eV, which reduced to 2.80 eV with doping support. The impact of Mn₂O₃ and MnCoO on immature stages was investigated by semithin photomicrographs exhibiting significant changes in the midgut, fat tissue and muscles of the third larval instar. Moreover, the external deformations in pupae were examined using scanning electron microscopy (SEM). Full article

Hierarchical composite films grown on current collectors are popularly reported to be directly used as electrodes for supercapacitors. Highly dense and conductive NiCo₂O₄ nanowires are ideal backbones to support guest materials. In this work, low crystalline MnO₂ nanoflakes are electrodeposited onto the surface of NiCo₂O₄ nanowire films pre-coated on nickel foam. Each building block in the composite films is a NiCo₂O₄–MnO₂ core–shell nanowire on conductive nickel foam. Due to the co-presence of MnO₂ and NiCo₂O₄, the MnO₂@NiCo₂O₄@Ni electrode exhibits higher specific capacitance and larger working voltage than the NiCo₂O₄@Ni electrode. It can have a high specific capacitance of 1186 F·g⁻¹ at 1 A·g⁻¹. When the core–shell NiCo₂O₄–MnO₂ composite and activated carbon are assembled as a hybrid capacitor, it has the highest energy density of 29.6 Wh·kg⁻¹ at a power density of 425 W·kg⁻¹ with an operating voltage of 1.7 V. This work shows readers an easy method to synthesize composite films for energy storage. Full article

Electrostatic capacitors have high power density but low energy density. In contrast, batteries and fuel cells have high energy density but low power density. However, supercapacitors can simultaneously achieve both high power density and energy density. Herein, we propose a supercapacitor, in which etched nickel wire was used as a current collector due to its high conductivity. Two redox reactive materials, MnO₂ nanoflakes and NiCo₂O₄ nanoneedles, were used in a hierarchical structure to cover the roughened surface of the Ni wire to maximize the effective surface area. Thus, a specific capacitance, energy density, and power density of 14.4 F/cm³, 2 mWh/cm³, and 0.1 W/cm³, respectively, was obtained via single-electrode experiments. A fiber-shaped supercapacitor was prepared by twisting two electrodes with solid electrolytes made of KOH and polyvinyl alcohol. Although the solid electrolyte had a low ionic conductivity, the energy density and power density were determined to be 0.97 mWh/cm³ and 49.8 mW/cm³, respectively. Full article

Nano α-MnO₂ is usually synthesized under hydrothermal conditions in acidic medium, which results in materials easily undergoing thermal reduction and offers single crystals often over 100 nm in size. In this study, α-MnO₂ built up of inter-grown ultra-small nanoflakes with 10 nm thickness was produced in a rapid two-step procedure starting via partial reduction in solution in basic medium subsequently followed by co-proportionation in thermal treatment. This approach offers phase-pure α-MnO₂ doped with potassium (cryptomelane type K_0.25Mn₈O₁₆ structure) demonstrating considerable chemical and thermal stability. The reaction pathways leading to this new morphology and structure have been discussed. The MnO₂ electrodes produced from obtained nanostructures were tested as electrodes of lithium ion batteries delivering initial discharge capacities of 968 mAh g⁻¹ for anode (0 to 2.0 V) and 317 mAh g⁻¹ for cathode (1.5 to 3.5 V) at 20 mA g⁻¹ current density. At constant current of 100 mA g⁻¹, stable cycling of anode achieving 660 mAh g⁻¹ and 145 mAh g⁻¹ for cathode after 200 cycles is recorded. Post diagnostic analysis of cycled electrodes confirmed the electrode materials stability and structural properties. Full article