The adoption of green technology is very important to protect the environment and thus there is a need for improving the existing methods for the fabrication of carbon materials. As such, this work proposes to discuss, interrogate, and propose viable hydrothermal, solvothermal, and other advanced carbon materials synthesis methods. The synthesis approaches for advanced carbon materials to be interrogated will include the synthesis of carbon dots, carbon nanotubes, nitrogen/titania-doped carbons, graphene quantum dots, and their nanocomposites with solid/polymeric/metal oxide supports. This will be performed with a particular focus on microwave-assisted solvothermal and hydrothermal synthesis due to their favourable properties such as rapidity, low cost, and being green/environmentally friendly. These methods are regarded as important for the current and future synthesis and modification of advanced carbon materials for application in energy, gas separation, sensing, and water treatment. Simultaneously, the work will take cognisance of methods reducing the fabrication costs and environmental impact while enhancing the properties as a direct result of the synthesis methods. As a direct result, the expectation is to impart a significant contribution to the scientific body of work regarding the improvement of the said fabrication methods.
Lithium manganese phosphate nanoparticles (LiMnPO 4 ; LMP) as well as the nickel-doped (LMNP) and graphenised derivatives (G-LMNP) were synthesized. Electrochemical characteristics of the materials were examined using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge. Lithium ion capacitors (LIC) fabricated using LMP and composite materials as positive electrodes and activated carbon as the negative electrode, exhibited a specific capacitance of 60 F g À 1 at a current load of 0.1 A g À 1 for the AC//G-LMNP LIC. Capacitance retention of 83 % was obtained by the AC//G-LMNP LIC after 750 cycles, with a high specific power of 19 kW kg À 1 at 0.5 A g À 1 .
Nanostructured anilino-functionalized reduced graphene oxide intercalated with Pt metal nanoparticles was successfully synthesized. Graphene oxide nanosheets were synthesized using a modified Hummers method with simultaneous in-situ functionalization with aniline and ionic Pt reduction and dispersion through sonication. The nanomaterial was characterised with FTIR, UV-visible, SEM, TEM, EDX, XRD and Raman spectroscopy to ascertain surface, chemical, elemental and crystalline properties, composite structures, size, morphology and successful entrapment of metal nanoparticles while the electro-conductivity of the nanomaterial was interrogated using CV. The graphene oxide was successfully functionalized with aniline with new peaks belonging to the N-H and C-N group being present and calculated band gaps of 5.35 eV and 4.39 eV which are attributed to functionalization of graphene oxide. The functionalized graphene oxide was successfully loaded with platinum nanoparticles as TEM revealed that the Pt particles are spread out on the graphene sheets and when magnified a uniform distribution of the nanoparticles can be observed. The material (functionalized graphene oxide loaded with platinum nanoparticles) was used in the design of an asymmetric supercapacitor cell using 6M KOH aqueous electrolyte. On testing by galvanostatic charge/discharge, a high specific capacitance value of 605 F/g with a corresponding energy and power densities of 0.021kWh/Kg and 0.372kW/Kg respectively, were obtained.
There is great importance and need of improving existing carbon materials fabrication methods. As such, this work proposes to discuss, interrogate, and propose viable hydrothermal, solvothermal, and other advanced carbon materials synthetic methods. The advanced carbon materials to be interrogated will include the synthesis of carbon dots, carbon nanotubes, nitrogen/titania-doped carbons, graphene quantum dots, and their nanocomposites with solid/polymeric/metal oxide supports. This will be done with special mind to microwave-assisted solvothermal and hydrothermal synthesis due to their favourable properties such as rapidity, low cost, and green/environmentally-friendliness. Thus, these methods are important during the current and future synthesis and modification of advanced carbon materials for application in energy, gas separation, sensing, and water treatment. Simultaneously, the work will pay special cognizance to methods reducing the fabrication costs and environmental impact while enhancing the properties as a direct result of the synthesis methods. As a direct result, the expectation is to impart a significant contribution to the scientific body of work regarding the improvement of the said fabrication methods.
Lithium-ion capacitors (LICs) are a novel and promising form of energy storage device that combines the electrode materials of lithium-ion batteries with supercapacitors. They have the potential to deliver high energy density, power density, and long cycle life concurrently. Due to the good electrochemical performance of lithiated manganese-based materials in LICs, they have received extensive attention in recent years. The latest advancements in lithiated manganese-based materials as electrode materials in lithium-ion capacitors are presented here, including LiMnPO4, LiMn2O4, and Li2MnSiO4. These electrode materials have a lot of potential as high-performance energy storage materials. Apart from capacitive-type electrodes, lithiated manganese-based materials are also used in the creation of LIC battery-type electrodes. The LICs based on lithiated manganese-based electrode materials demonstrated energy density, power density, and cycle life, which are relatively comparable with various electrode material values reviewed in this paper. The electrochemical performance of lithiated manganese-based materials is attributed to the synergistic effect of the doping and the conductive carbon coating which provided new pathways for the movement of Li+ ions and electrons, thus facilitating charge transfer reactions. Although much effort has gone into synthesizing lithium-ion battery electrode materials and contracting LICs based on them because of their higher energy density, there is still work to be carried out. Additionally, the potential barriers and opportunities for LIC-based future research in energy applications are explored.
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