Recent development of mixed transition metal oxide and graphene/mixed transition metal oxide based hybrid nanostructures for advanced supercapacitors

Nowadays, imminent deficiency of fossil fuels and arising environmental concerns have triggered immense research enthusiasm for the development of green and renewable energy sources. Particularly, supercapacitors are emerging as one of the competent energy storage devices owing to their excellent capacitive properties, long term cycling stability as well as remarkable power density. In this sense, the promising family of transition metal oxides (TMO) and mixed transition metal oxides (MTMO) are felicitous as active electrode materials for supercapacitor due to their multiple oxidations states and ions possess, leading to superior specific capacitance. Moreover, hybridisation of MTMO with graphene nanosheets has received tremendous research interest owing to the peculiar intrinsic properties of graphene, which ameliorate the electrical conductivity and enlarge the specific surface area of the nanocomposite for faradiac redox reaction. In this review article, we emphasised on the current evolution of MTMO and the hybridisation of MTMO with graphene nanosheets as active electrode materials, with a comprehensive study on their synthetic approaches. In addition, the critical factors that influence the electrochemical activities of mixed transition metal oxide based materials are also delineated.