Porous manganese oxide nanospheres for pseudocapacitor applications

Mesoporous, uniform manganese oxide nanosphere thin films were grown on a stainless-steel substrate using the successive ionic layer adsorption and reaction (SILAR) method. The amorphous manganese oxide nanosphere thin films (AMONTFs) were characterized by grazing incidence X-ray diffraction (GI-XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The GI-XRD analysis reveals that the manganese oxide nanosphere thin films were present in the forms of α-MnO2 and γ-MnO2. XPS demonstrates that the thin films contain a mixture of manganese oxides: MnO2 (Mn4+) and MnOOH (Mn3+). The effect of the number of SILAR cycles on the morphology was observed systemically by FE-SEM and greatly influences the size of these unique nanospheres. The electrochemical properties of the AMONTF electrodes were analyzed by cyclic voltammetry (CV) and the galvanostatic charge-discharge (CD) method. The outcomes of the FE-SEM and electrochemical measurements reveal that the thin film obtained after 60 SILAR cycles has a uniform nanosphere size distribution and large specific capacitance. The manganese oxide thin films exhibit a maximum specific capacitance, energy, and power density of 262.0 F g−1, 18.3 Wh kg−1, and 7999.4 W kg−1, respectively, in an aqueous 1 M Na2SO4 electrolyte solution.