Micelle-Assisted Electrodeposition of γ-MnO2 on Lead Anodes: Structural and Electrochemical Insights

Abstract

Electrolysis of MnSO₄ in H₂SO₄ with cationic surfactants (tetradecyltrimethylammonium bromide; TTAB and cetyltrimethylammonium bromide; CTAB) led to the formation of γ-MnO₂ with surfactant intercalation in an amorphous matrix. Unlike conventional self-standing EMD electrodes, which limit scalability, this study presents bulk electrodeposition of EMD powder on a lead (Pb) anode. Surface morphology is significantly altered by surfactant presence, though X-ray diffraction and density functional theory analyzes confirms consistent γ-MnO₂ crystallography across samples. Galvanostatic charge–discharge at 0.6 A g⁻¹ reveals that TTAB-assisted EMD achieved a specific capacitance of 478.6 F g⁻¹, double that of pristine EMD (232 F g⁻¹), due to improved ion transport and surface area. In contrast, CTAB-assisted EMD shows reduced capacitance (124.6 F g⁻¹), attributed to early micelle formation and immobilization within the MnO₂ lattice, which promoted SO₄²⁻ insertion over surfactant deintercalation. Surfactant critical micelle concentrations and surface activity are key to electrochemical behavior in 1 M Na₂SO₄. An asymmetric device using TTAB-EMD as the cathode and activated carbon as the anode delivered 106 F g⁻¹ and 40 Wh kg⁻¹, demonstrating practical viability. Band structure calculations support the experimental findings, indicating favorable electronic properties for charge storage.