Fabrication of Ultrathin rGO Sheet-Wrapped Mixed-Phase MnSe₂/CoSe₂ Nanocomposite for High-Performance Supercapacitor Electrodes with Long-Term Stability

Binary transition metal chalcogenides and reduced graphene oxide exhibit significant potential for energy storage devices due to their superior electronic conductivity and capacity, surpassing that of single-metal sulfides, owing to their more extensive redox reactions. In this report, we introduce a novel synthesis method for producing a mixed-phase MnSe₂/CoSe₂ nanocomposite wrapped with reduced graphene oxide (rGO) sheets, designed specifically for supercapacitor applications. The MnSe₂/CoSe₂ hybrid material was synthesized using an ultrasonic assisted hydrothermal technique, followed by the preparation of the rGO/MnSe₂/CoSe₂ hybrid composite. The structural characterization was conducted employing x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and Raman techniques. Brunauer–Emmett–Teller (BET) analysis demonstrated a significant specific surface area (66.5 m²/g) and a pore size distribution of 28.4 nm in rGO-MnSe₂/CoSe₂. The interconnected ultrathin rGO nanosheets and conductive carbon layer contributed to the exceptional conductivity and stability achieved by the rGO/MnSe₂/CoSe₂ composite electrode. The electrochemical performance was assessed using a three-electrode setup in a 3 M KOH solution, with nickel foam as the current collector. The working electrode, consisting of rGO/MnSe₂/CoSe₂, acetylene black and PVDF in an 80:15:5 weight ratio, demonstrated specific capacitance of 1214 F g⁻¹ and cycling stability of 88% retention after 5000 cycles at 1 A g⁻¹. An asymmetric supercapacitor, constructed using a tailored electrode composition, achieved energy density of 28.6 Wh kg⁻¹ at 2100 W kg⁻¹ and high power density of 888 W kg⁻¹ at 49.7 Wh kg⁻¹.