Graphene-enhanced NiMn₂O₄ composite for high-performance supercapacitor applications

The growing global demand for efficient and sustainable energy storage solutions has highlighted the need for advanced materials to address the energy crisis. In this work, the synthesis and electrochemical performance of a NiMn₂O₄ and Graphene@NiMn₂O₄ (1 : 1) composite for supercapacitor applications has been studied. The novelty lies in the integration of graphene with NiMn₂O₄, enhancing its electrochemical properties. X-ray diffraction (XRD) analysis revealed that NiMn₂O₄ exhibited a crystallite size of 21.4 nm, while the Graphene@NiMn₂O₄ composite showed an increased crystallite size of 28.1 nm. Raman spectroscopy confirmed the successful hybridization of graphene with NiMn₂O₄, exhibiting D and G bands that indicate increased defect density beneficial for charge storage. Scanning electron microscopy (SEM) analysis demonstrated the hierarchical morphology of Graphene@NiMn₂O₄, with well-dispersed NiMn₂O₄ nanoparticles on graphene sheets, which promoted better porosity and electrolyte penetration. Electrochemical results from cyclic voltammetry (CV) showed that Graphene@NiMn₂O₄ exhibited superior capacitance, with a highest capacitance of 301 F g^-1 at 0.8 A g^-1, compared to 229 F g^-1 for pure NiMn₂O₄. Galvanostatic charge-discharge (GCD) tests showed a considerable improvement in energy density for Graphene@NiMn₂O₄, reaching 3.8 Wh kg^-1 at 0.8 A g^-1, compared to 2.9 Wh kg^-1 for NiMn₂O₄. Electrochemical impedance spectroscopy (EIS) exhibited reduced charge transfer resistance (R _ct) and enhanced ion diffusion coefficient for the composite indicating superior charge transport. These findings highlight the potential of Graphene@NiMn₂O₄ as a promising material for high-performance energy storage devices. Future work will focus on optimizing the composite structure for commercial supercapacitor applications.