Effect of synthesis temperature on the characteristics of hydrous manganese oxide deposited using the hydrothermal electrochemical method

Nanometer-scale manganese oxide films were synthesized at various temperatures in the range of 60-150°C using the hydrothermal electrochemical deposition method. Field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were used to verify that the deposits were tri- and divalent hydrous manganese oxides. The electrochemical performance of manganese oxide films was examined by cyclic voltammetry (CV) in the range of 0.0-1.0 V [versus saturated calomel electrode (SCE)] in 0.1 M Na₂SO₄solution at 25 °C. The specific capacitance (SC) increased with decreasing synthesis temperature, with a maximum value of approximately 244F.g^-1at 60 °C. Crystalline manganese oxide prepared at 150 °C improved stability of capacitive performance, which only decreased by 4% after 800 cycles. The SC depended not only on the surface morphology but also on the amount of hydration in the manganese oxide structure. The deposited manganese oxide has the chemical formula Mn₃O₄· nH₂O (n - 1.2), as established using thermogravimetric and differential thermal analysis (TG/DTA).