Carbon/Metal Oxide Composites as Electrode Materials for Supercapacitors Applications

Abstract

Energy generation through renewable and sustainable energy sources such as solar, wind and tidal have seen an upsurge in recent years which can be attributed to the depletion in fossil fuel reserves and climatic changes. Due to the intermittent nature of these renewable sources of energy, energy storage and conversion systems have attracted immense attention in recent years. Electrochemical energy conversion and storage systems such as fuel cells, electrochemical batteries and supercapacitors are leading the way owing to their diverse range of applications. Supercapacitors, also known as ultracapacitor or electrochemical capacitors have attracted considerable attention lately due to their outstanding properties such as high power delivery, rapid charge/discharge and long cycle life. Despite these advantageous properties, supercapacitors suffer from inferior energy storage-ability in comparison with other energy storage and conversion devices, such as electrochemical batteries and fuel cells. Energy densities of the electrochemical capacitors can be enhanced by increasing their operating voltage or improving specific capacitance. Higher operating voltages are achievable when non- aqueous solutions such as organic or ionic liquids are adopted as electrolytes however this can result in higher equivalent series resistance (ESR) which can have detrimental effect on power densities of electrochemical capacitor cell. Improving energy densities without scarifying the power densities is achievable through the enhancement of cell’s specific capacitance. Electrode is one of the key components which can have significant effect on the capacitive performance of supercapacitor cell. Carbon based nanomaterials are the most commonly adopted electrodes due to ease of processability and cost-effectiveness, however their charge storage ability is substantially lower when compared with metal oxide or conducting polymers based electrode active materials. Limitations of using metal oxides include elevated material cost poor cycle-ability and lower power densities. Realization of high energy densities without scarifying extraordinary power capabilities is possible in a cost effective manner by using carbon/metal oxide hybrid electrodes in a supercapacitor cell. In this chapter recent development in synthesis and applications of carbon/metal oxide composites has been reviewed when used as active material in a supercapacitor cell.