<p>This study reports the synthesis of reduced graphene oxide–infused Ni–Mn–Co phosphate via the polyol-reflux method, demonstrating enhanced crystallinity, well-defined chemical structure, nanoscale morphology, and improved surface area and porosity that collectively contribute to superior electrochemical performance. The electrochemical studies, including cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) tests, reveal the pseudocapacitive nature of the synthesized composites. Notably, the NMCP-C3 composite with 20% reduced graphene oxide exhibits a high specific capacity of 380 C g⁻¹ (specific capacitance of 844 F g⁻¹) at 1 A g⁻¹, with 91% capacitive retention after 5,000 GCD cycles in 1&#xa0;M KOH. The fabricated asymmetric supercapacitor using NMCP-C3 and activated carbon delivers a specific capacity of 560 C g⁻¹ (373 F g⁻¹) at 1 A g⁻¹ in 6&#xa0;M KOH, corresponding to an energy density of 116 Wh kg⁻¹ and a power density of 745 W kg⁻¹. The device demonstrates excellent cycling stability, retaining 81% of its capacity after 5,000 cycles at 5 A g⁻¹. These results suggest that NMCP-C3 is a promising candidate for hybrid supercapacitor electrodes in energy storage applications.</p>