Unveiling the mass-loading effect on the electrochemical performance of Mn₃O₄ thin film electrodes: a combined computational and experimental study

The remarkable storage performance of manganese oxide (Mn₃O₄) makes it an appealing option for use as electrodes in electrochemical capacitors. However, the storage kinetics were significantly influenced by the mass loading of the electrode. Herein, we have inspected the dependency of mass loading on the storage performance of the spray pyrolyzed Mn₃O₄ thin film electrodes along with the correlation of structural and morphological characteristics. X-ray diffraction and Raman spectroscopic studies proven the formation of spinel Mn₃O₄ with a tetragonal structure. Morphological analysis revealed that all films exhibited fibrous structures with interconnected patterns at higher mass loadings. Moreover, the surface roughness and wettability of the electrode surface were influenced by variations in mass loading. Notably, thin-film electrode with a mass loading of 0.4 mg cm⁻² exhibited the highest specific capacitance value of 168 F g⁻¹ at 5 mV s⁻¹ in a three-electrode system. Further, electrochemical impedance spectroscopic studies showed that there were noticeable changes in the capacitive behaviour of the electrode with respect to variations in mass loading. Moreover, the Dunn approach was employed to differentiate the underlying storage mechanism of the Mn₃O₄ electrode. Additionally, first-principles Density Functional Theory (DFT) studies were carried out in connection with the experimental study to comprehend the structure and electronic band structure of Mn₃O₄. This study underscores the critical importance of mass loading for enhancing the storage performance of Mn₃O₄ thin-film electrodes.