A Review of MnO2 Composites Incorporated with Conductive Materials for Energy Storage

Developments in conducting polymer-, metal oxide-, and carbon nanotube-based composite electrode materials for supercapacitors: a review

Supercapacitors are the latest development in the field of energy storage devices (ESDs). A lot of research has been done in the last few decades to increase the performance of supercapacitors. The electrodes of supercapacitors are modified by composite materials based on conducting polymers, metal oxide nanoparticles, metal-organic frameworks, covalent organic frameworks, MXenes, chalcogenides, carbon nanotubes (CNTs), etc. In comparison to rechargeable batteries, supercapacitors have advantages such as quick charging and high power density. This review is focused on the progress in the development of electrode materials for supercapacitors using composite materials based on conducting polymers, graphene, metal oxide nanoparticles/nanofibres, and CNTs. Moreover, we investigated different types of ESDs as well as their electrochemical energy storage mechanisms and kinetic aspects. We have also discussed the classification of different types of SCs; advantages and drawbacks of SCs and other ESDs; and the use of nanofibres, carbon, CNTs, graphene, metal oxide-nanofibres, and conducting polymers as electrode materials for SCs. Furthermore, modifications in the development of different types of SCs such as pseudo-capacitors, hybrid capacitors, and electrical double-layer capacitors are discussed in detail; both electrolyte-based and electrolyte-free supercapacitors are taken into consideration. This review will help in designing and fabricating high-performance supercapacitors with high energy density and power output, which will act as an alternative to Li-ion batteries in the future.

Hydrothermal Synthesis of MnO2 Microspheres and Their Degradation of Toluene

Various urchin-like MnO2 materials were obtained with a facile hydrothermal method through controlling the Mn precursor, reaction time, and reaction temperature. The property of MnO2 materials was characterized by scanning electron microscopy, X-ray diffraction, and H2 temperature-programmed reduction. The results showed that the Mn precursor could significantly impact the morphology of as-prepared MnO2. When the precursor was Mn(CH3COO)2·4H2O, the MnO2 morphology consisted of tennis-like microspheres assembled by nanorods. While the precursor was MnCl2·4H2O, the sample morphology was a chestnut shell, and the samples were sea urchin microspheres, as the precursor was MnSO4·H2O. At the same time, the morphology of MnO2 was affected by hydrothermal time and temperature. The nanoneedles on the microsphere surface gradually lengthened with increasing hydrothermal time and hydrothermal temperature, until nanowires were formed. MnO2 crystallinity was also influenced by hydrothermal temperature. It was γ-MnO2 as the temperature was 50 and 80 °C while evolved to be α-MnO2 and β-MnO2 when the temperature increased to 140 °C. As MnO2 (MnO2-1 h, MnO2-2 h, MnO2-4 h, and MnO2-6 h) was prepared to degrade toluene, all the samples could completely catalyze toluene at the temperature of 225 °C. However, the MnO2-4 h showed the best catalytic effect at a lower temperature.

Intrinsically Conducting Polymer Composites as Active Masses in Supercapacitors

Intrinsically conducting polymers ICPs can be combined with further electrochemically active materials into composites for use as active masses in supercapacitor electrodes. Typical examples are inspected with particular attention to the various roles played by the constituents of the composites and to conceivable synergistic effects. Stability of composite electrode materials, as an essential property for practical application, is addressed, taking into account the observed causes and effects of materials degradation.