Structural optical and electrochemical properties of Cu²⁺ ions substituted α-MnO₂ nanoparticles synthesized by co-precipitation method

Pure and copper (Cu) substituted α-MnO₂ nanoparticles were synthesized by the co-precipitation method. The crystal structure, surface morphology, electrochemical and optical properties were examined and compared with those of Cu:α-MnO₂ and pure α-MnO₂ nanoparticles. XRD analysis confirmed that synthesized samples had a tetragonal crystal structure, and Cu ions did not lead to the formation of secondary phases but slightly reduced the crystallite size. The constituents of the vibrational bands presence in Cu:α-MnO₂ samples were confirmed by FTIR. The HRSEM images of prepared samples showed nanorod structures and length and diameter of nanorods were increased with increasing Cu concentrations. EDS mapping proved the presence of elements such as Cu, Mn, and O. HR-TEM analysis also revealed that pure and Cu substituted α-MnO₂ nanoparticles were polycrystalline in nature. The XPS technique was used to identify the chemical structure of metallic species, such as Mn²⁺ and Cu²⁺. The optical bandgap (Eg) values were found to be increased from 2.64 to 2.83 eV. Electrochemical measurements of the synthesized samples were studied by cyclic voltammetry. The CV curves confirmed the pseudocapacitive behavior, and CuMn-3 sample exhibited a high specific capacitance value that was compared to the pure α-MnO₂ electrode.