Efficient and Safe One-Step Fabrication of Binder-Free MnO2/rGO Electrodes for High-Performance Aqueous Supercapacitors

A safer and straightforward one-pot synthesis was developed to anchor manganese dioxide nanoparticles on partially reduced graphene oxide (hereafter MnO2/rGO) through an in-situ synthesis approach. The process exploits the oxidizing capability of permanganate within a modified Hummers framework, intentionally excluding nitrate (NaNO3) and peroxide (H2O2) reagents to improve operational safety while maintaining scalability and procedural simplicity. Throughout the oxidation of graphite using KMnO4, manganese dioxide nucleates directly on the developing graphene oxide sheets. Subsequent mild thermal treatment at 300 oC for one hour affords partially reduced graphene oxide (rGO) while preserving nanoscale MnO2 anchoring. Characterization by FT-IR, XRD, and TEM confirms that MnO2 nanoparticles are uniformly distributed across the wrinkled rGO sheets. Thermal analyses (TGA and DSC) display multiple mass-loss events related to the removal of oxygen-containing groups from GO and progressive Mn-oxide transitions. The composite retains approximately 80% of its mass up to 1000 oC, demonstrating excellent thermal endurance and structural stability. In 1 M H₂SO₄ aquas electrolyte, the MnO2/rGO electrode displays quasi-rectangular cyclic voltammograms with clear redox responses, confirming pseudocapacitive behavior. A maximum gravimetric capacitance of about 667 F g-1 is achieved at a scan rate of 10 mV s-1, maintaining roughly 98% of its initial value after 1000 cycles, indicating excellent short-term stability. Galvanostatic charge–discharge curves yield a specific capacitance of approximately 213 F g⁻¹ at 20 A g-1, reflecting robust rate capability. EIS indicates reduced charge-transfer resistance and a rough, porous interface consistent with nanoparticle-spaced graphene layers. Collectively, these results establish a practical and safer one-pot preparation of MnO2/rGO electrodes and a reproducible proof-of-concept for aqueous supercapacitors, with performance arising from intimate oxide–carbon contact and the spacer effect of nanometric MnO2 that suppresses graphene restacking.