Influência do ph do banho e da densidade de corrente no comportamento capacitivo de eletrodos de mno2 obtidos por eletrodeposição anódica

Abstract

MnO₂ electrodes are obtained by anodic electrodeposition on stainless steel substrate at room temperature from a 0.1 M manganese sulfate bath, under different current densities, ranging from 200 µA·cm⁻² to 5 mA·cm⁻² (galvanostatic mode), and pH values from 2 to 6. The material morphology is analyzed by scanning electron microscopy, revealing compact, homogeneous, and two-dimensional film deposition, with the presence of microcracks that provide active sites for the incorporation of sodium sulfate (Na₂SO₄) electrolyte ions, enhancing the material's specific capacitance. At low current densities, such as 200 and 500 µA·cm⁻², the formed film is homogeneous, while increasing the current density to 2 mA·cm⁻² results in cracks on the material's surface. Morphological changes are also identified as a function of pH: near neutrality (pH 6), cracks become evident, whereas in more acidic pH levels, such as 2 and 3, the structure remains uniform. At pH 4, an irregular structure is observed. The structure of the formed films, analyzed by by X-ray diffraction, reveals the presence of the alpha (α) phase under all studied conditions, regardless of the applied current density and bath pH. Electrochemical characterization of the films, carried out using cyclic voltammetry and charge-discharge curves (chronopotentiometry), indicates a working potential window of 1.1 V and specific capacitance values ranging from 13 to 371.8 F·g⁻¹, depending on the applied current density and bath pH. The highest specific capacitance value is obtained at a current density of 2 mA·cm⁻² and pH 4.