Tuning the Electrochemical Properties of Manganese Dioxide Based Composites to Enhance Capacitive Properties

Abstract

The design of advanced nanomaterials has significantly transformed the development of innovative electrode materials for energy storage systems. In this study, a ternary composite of manganese dioxide (MnO₂) nanorods, cerium dioxide (CeO₂) nanoparticles, and multi-walled carbon nanotubes (MWCNTs) was synthesized and thoroughly examined for its potential in supercapacitor applications. The combination of these materials results in enhanced electrochemical performance through increased surface defects, higher specific surface area, and improved electron and ion transport. Extensive characterization techniques such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy confirmed the morphology, structure, and successful synthesis of the composite. The well-dispersed MnO₂ nanorods and CeO₂ nanoparticles on the MWCNT framework further supported the integrity of the composite structure. Electrochemical evaluation using cyclic voltammetry (CV), galvanostatic chargedischarge (GCD), and electrochemical impedance spectroscopy (EIS) demonstrated the superior performance of the MnO₂/CeO₂/MWCNT composite, showing a specific capacitance of 1204 F g⁻¹ at 2.5 A g⁻¹. This enhanced capacitance, compared to binary MnO₂/CeO₂ and pristine MnO₂, is attributed to the improved redox activity of MnO₂, defect engineering via CeO₂, and the excellent conductivity of MWCNTs. Additionally, the composite retained 82% of its capacitance at a higher current density of 10 A g⁻¹, indicating excellent rate capability. To demonstrate its practical application, a coin cell asymmetric supercapacitor (ASC) was fabricated using MnO₂/CeO₂/MWCNT as the positive electrode and activated carbon (AC) as the negative electrode. The device exhibited a specific capacitance of 102 F g⁻¹ at 1 A g⁻¹ and operated within a voltage window of 2 V. It achieved an energy density of 36 Wh kg⁻¹ at a power density of 800 W kg⁻¹, making it suitable for high-energy applications. The ASC also showed excellent cycling stability, retaining 94% of its initial capacitance after 10,000 cycles at 10 A g⁻¹. xviii These findings underscore the potential of MnO₂/CeO₂/MWCNT composites in developing high-performance supercapacitors for real-world applications. This work also encourages further exploration into the synergistic effects of combining MnO₂ with other rare earth metal oxides and carbon-based materials to optimize energy storage devices.