A review on challenges to remedies of MnO2 based transition-metal oxide, hydroxide, and layered double hydroxide composites for supercapacitor applications

Abstract

Supercapacitors are emerging energy storage devices admired in the research field due to their tremendous electrochemical properties parameters. Few peculiar properties parameters such as- high capacitance, large specific power/energy, excellent cyclic life, and rapid charging/discharging make them superior to other existing energy storage/conversion systems. Supercapacitors are predicted to be the potential energy resources for vast number of applications ranging from heavy electric vehicles to portable electrical/personal electronic appliances due to their ultra-fast charging behavior. The working efficiency of any supercapacitor is generally reliant on chosen materials acting as an electrode. In electrode materials series, manganese dioxide (MnO2) has been mostly explored and proven to be very effective and promising material as supercapacitor electrode. This is attributable to its superior theoretical capacitance, environmental friendliness, lower price, and vast profusion. But its deprived electrical conductivity and the volume expansion restrict its practical utility as a preferred electrode material. To make full utility of MnO2 materials, its composites with different type of materials have been tried and tested. The most fascinating composite electrode materials with MnO2 are discussed here in detail. The composites discussed in detail are MnO2/Transition metal oxides, MnO2/Transition metal hydroxides, and MnO2/Layered double hydroxides. A complete overview of these composites has been given and finally the recommendation of the best composites has been figured out systematically. The new opportunities for the future towards the advancement of MnO2 based composites are also being highlighted.