Physicochemical and electrochemical behaviours of manganese oxide electrodes for supercapacitor application

•MnO2 nanostructures are prepared by chemical reduction of KMnO4 using different reducing agents.•Mn3O4 in Hausmannite structure formed with MnO2 by using the strong reducing agents (NBH, HH).•Morphology of MnO2 changed with reducing agent.•Nanowires of MnO2 prepared by using formic acid shows highest capacitance value of 155 Fg−1 at 0.64 Ag−1.