High‐Powered Nanostructured rGO/g‐C₃N₄/CoSe||AC Electrodes Employed in an Asymmetric Supercapacitor Device

Supercapacitors are increasingly adopting two‐dimensional (2D) carbon‐intercalated transition metal chalcogenide (TMC) composites (C x MX 1− x ) due to their adjustable surface properties, makeup, and structure. Even though they show promise, we still do not know much about how the strain in the structure and changes in electronic properties from 2D carbon intercalation affect them. In this study, we prepared (rGO/g‐C 3 N 4 ) x ‐(CoSe) 1− x nanocomposites using a new one‐step hydrothermal method with very low ( x = 0.01) and higher ( x = 0.10) amounts of carbon to see how they affect lattice strain and electrochemical performance. The results of XRD and Rietveld refinement demonstrated the purity of the materials and revealed an increase in lattice size with the addition of more rGO/g‐C 3 N 4 . Crystallite size decreased from 12.97 nm for CoSe to 9.5 nm for the (rGO/g‐C 3 N 4 ) 0.1 ‐(CoSe) 0.90 sample due to strain introduced by carbon intercalation. TEM analysis showed nanosheet morphologies with visible rGO and g‐C 3 N 4 structures. XPS confirmed the Co 2+ and Se 2− oxidation states and validated the presence of C–C and C–N bonds. The (rGO/g‐C 3 N 4 ) 0.1 ‐(CoSe) 0.90 electrode exhibited a high specific capacitance of 1102 F g −1 at 1 A g −1 and retained 97.1% after 2000 cycles. An asymmetric device using activated carbon (AC) achieved an energy density of 53.31 Wh kg −1 , a power density of 750 W kg −1 , and 97% capacitance retention after 5000 cycles, underscoring the material's potential for durable, high‐performance.