Manganese films electrodeposited at different potentials and temperatures in ionic liquid and their application as electrode materials for supercapacitors

Electrodeposition of manganese (Mn) in butylmethylpyrrolidinium bis(trifluoromethylsulfony)imide (BMP-NTf₂) ionic liquid is demonstrated in this study. Crystal structures and surface morphologies of the Mn films deposited at various potentials (from -1.8 V to -2.2 V) and temperatures (from 50 °C to 110 °C) were examined with an X-ray diffractometer (XRD) and a scanning electron microscope (SEM), respectively. Experimental results indicate that the deposited Mn films were amorphous in nature; however, their morphologies strongly depended on the deposition conditions. After being anodized in Na₂SO₄ solution, the deposited Mn was transformed to Mn oxide. Electrochemical properties of the Mn oxides were evaluated using cyclic voltammetry (CV). It was confirmed that the different Mn deposition conditions caused the variations in pseudocapacitive performance of the oxide electrodes. The oxide (∼0.1 mg) anodized from the Mn deposited at -1.8 V and 50 °C had the highest specific capacitance of 402 F/g measured at a CV scan rate of 5 mV/s. Its capacitance retained ratio after 500 CV testing cycles was as high as 94%.