Metal Sulfides/MXenes Based Nanostructured Electrode Materials for High-Performance Supercapacitors

Abstract

Supercapacitors are one of the most frequently explored devices for energy storage applications. In comparison with conventional dielectric capacitors, supercapacitors have energy storage capacities several orders of magnitude higher, however much lower than those of secondary batteries. Their long-life cycles, high power densities, and relatively less carbon footprint than their counterparts have encouraged industries to explore and build reliable energy systems for the future. These superior properties of the supercapacitors offer an alternative to batteries for high-power applications such as emergency door opening (Airbus A380), cordless tools, low CO2 emission vehicles, ship container loading and unloading, water purification systems, portable electronic devices, and many more. The electrochemical double-layer capacitors (EDLC) stored energy via electrostatic adsorption of the electrolyte ions on the electrode which permits the growth of electrostatic positive and negative charged layers at the interface. In EDLC the charge transfer process is non-faradic, i.e., in an ideal case, there will be no transfer of charges across the interface. Consequently, the capacity of EDLC is limited by the availability of the surface area of the electrode materials for the adsorption of electrolyte ions. In contrast, pseudocapacitors rely on charge storage through the fast-reversible redox reaction between electrode materials and electrolytes. The charge accumulation and transfer processes are faradic. As a result, the pseudocapacitors can have a power density similar to the EDLC and an energy density analogous to the batteries. However, the power density and the life cycles of conventional pseudocapacitors are limited by the poor life cycle stability and the low conductivity of the electrodes. Therefore, the search for high-performance supercapacitor electrode materials is highly required. This Ph.D. research was aimed at shedding light on some of these problems (as much as possible) and establishing scientific understanding about them, finding solutions, and ultimately demonstrating the high electrochemical performance of metal sulfides and MXenes-based electrodes in supercapacitors. The metal sulfide electrodes were prepared using a wet chemical approach while MXene electrodes were prepared using the concentrated hydrofluoric acid etching method. The as-synthesized electrodes were analyzed by X-ray diffraction at 2θ values using Cu-Kα radiation for structural analysis. Scanning electron microscopy was used to investigate the morphology of the electrode materials. The electrochemical measurements were studied by a VMP3