Nanostructured MnCo₂S₄/reduced graphene oxide for high performance asymmetric supercapacitor

The performance of semiconducting g-C₃N₄ as anodic material was studied in an asymmetric supercapacitor. The nanohybrid of MnCo₂S₄ with RGO was selected as cathodic material for fabrication of MnCo₂S₄/reduced graphene oxide (RGO)//g-C₃N₄ asymmetric system. To prepare nanohybrid, MnCo₂O₄ was hydrothermally synthesized in the presence of GO and then converted to MnCo₂S₄ during the sulfurization process. Field emission scanning electron microscopy (FE-SEM) images showed the formation of MnCo₂S₄ nanoparticles with size in the range of 10–30 nm on GO nanosheets. Subsequently, nickel foam (NF) was modified with MnCo₂S₄/GO and then GO was reduced electrochemically to RGO. The N-riched g-C₃N₄ showed capacitive behavior in the range of -1 to 0 V in 3 M KOH aqueous solution which makes it suitable choice as negative electrode in the asymmetric supercapacitor. MnCo₂S₄/RGO/NF can store charges in positive potential range in alkaline solution. MnCo₂S₄/NF and MnCo₂S₄/RGO/NF presented specific capacitances of 896 and 1648 F g⁻¹ at current density of 1 A g⁻¹, respectively. For asymmetric supercapacitor composed of MnCo₂S₄/RGO/NF and g-C₃N₄/NF electrodes, the specific capacitance of 87.5 F g⁻¹ was obtained at the current density of 1 A g⁻¹. The highest energy density and power density were obtained equal to 31.11 Wh kg⁻¹ and 16 kW kg⁻¹, respectively. The asymmetric system retained about 97% of its initial capacitance after 2000 cycles at scan rate of 50 mV s⁻¹.