Energy produced by renewable energy sources need to be stored till required. Therefore, the development of high energy density energy storage systems is required to fulfil the energy needs around the world without any significant environmental impact. Recently, energy storage devices such as rechargeable batteries, fuel cells, and supercapacitors have attracted significant attention owing to their diverse applications in hybrid electric vehicles, energy management, and smart portable electronic devices. Rechargeable batteries such as lithium-ion batteries have been widely employed for various commercial application ranging from consumer electronics to hybrid electric vehicles. However, rechargeable batteries possess high energy density but often suffers from slow charging/discharging, limited cycle life, high cost of Li metal, low power density, poor cycle life, and environmental issues. Currently, supercapacitors are becoming more popular to overcome the issues raised by Li on rechargeable batteries such as low power density and limited cycle life.

Various transition metal-based materials such as oxides, sulfide, selenides, nitrides, phosphide are being used for supercapacitor applications due to their high theoretical specific capacitance abundant sources, and low cost. Transition metal oxides have attracted great attention of the researchers for supercapacitor applications because of their multiple oxidation states due to which multiple electrons transfer exists and discharge time extends, resulting in improving energy density in rapid Faraday redox reactions.

Our group is actively engaged in studying supercapacitor behavior of various transition metal oxides, sulfides, and their composites with carbonaceous materials such as carbon nanotube, graphene oxide (GO), reduced graphene oxide(rGO), and carbon nanotubes (CNT). We have synthesized pure MnO₂ and CuS along with their composites with graphene oxide and multiwall carbon nanotube (MWCNT). It was reported that the specific capacitance of CuS and CuS-GO nanocomposite was found to be 158 F/g and 250 F/g, respectively, at a current density of 0.5A/g. The specific capacitance of MnO₂ and MnO_2/MWCNT nanocomposite was found to be as 124 F/g and 145 F/g, respectively, at a current density of 0.5A/g. The detailed studies on electrochemical performances of various transition metal oxide/sulfides and their composite with carbonaceous materials will be presented at 242^nd ECS Meeting.