Electrospray; Foam substrate; In situ carbonization; Electrochemical oxidation

MnO2 electrode with nanosheet morphology, counter to carbon electrode in a supercapacitor shows promise for energy storage application. In this investigation, film electrodes of Mn-oxide and carbon with much higher and controllable mass loadings are grown by electrospray of respective precursors on Ni foam substrates. The electrospray deposition is conducted at room temperature to simplify the procedure. The evolution of nanosheet morphology of the Mn-oxide film due to electrochemical oxidation of Mn (II, III) to Mn (IV) valence state, implemented by multiple cyclic voltammetry (mCV) cycles on the calcined film is studied here. The CV and the charge-discharge curve show near-ideal behaviour with 0.5 M K2SO4 as electrolyte in asymmetric set-up, logging a capacitance of 115 F g(-1) at 1 mA cm(-2). The capacitance is retained to 93% of initial value after 5000 cycles at 20 mA cm(-2). The specific energy and power are found to the levels of 62.3 Wh kg(-1) and 5.2 kW kg(-1) respectively, which appear promising in comparison to the values, reported in literature. The increase in calcination temperature from 350 degrees C to 500 degrees C resulted in interspersed agglomeration within nanosheet morphology after mCV cycles, and consequent loss of capacitance.