The Interplay of Mass Loading and Active Site Accessibility in Manganese Oxide Thin-Film Electrodes for Electrochemical Capacitor

Abstract

An easy drop coating method on a microfiber carbon substrate was used to fabricate Manganese Oxide (Mn₃O₄) thin-film electrodes with varying mass loadings. The physical and structural properties of the electrodes were characterized by scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD), revealing uniform deposition and crystalline structure. The electrochemical performance was evaluated using cyclic voltammetry (CV) and charge-discharge (CD) tests in 1.0 M Na₂SO₄ solution. Results indicate that increasing the mass loading significantly reduces both specific capacitance and coulombic efficiency due to the limited accessibility of active sites in thicker films. The thin-film electrode with 0.7 mg/cm² mass loading demonstrated optimal capacitive behavior within the potential range of -0.1 to 0.9 V. q-plots further confirmed that thicker electrodes hinder ion diffusion, leading to decreased electrochemical efficiency. These findings suggest that controlling mass loading is crucial for optimizing the performance of Mn₃O₄-based supercapacitors. The study provides practical guidelines for designing thin-film electrodes with improved energy storage capability, highlighting the balance between electrode thickness and electrochemical performance for efficient supercapacitor applications.