Cr2O3-graphene nanocomposites for high-performance supercapacitors and methylene blue degradation: Synthesis and electrochemical analysis

This study aims to enhance the photocatalytic performance of chromium oxide (Cr₂O₃) by incorporating graphene nanoplatelets (GNPs) to form Cr₂O₃/GNPs nanocomposites. Pristine Cr₂O₃, GNPs, and Cr₂O₃/GNPs nanocomposites were synthesized using a cost-effective ex-situ co-precipitation method at different stoichiometric ratios (7:3), (2:3), and (1:9). Structural characterization via X-ray diffraction and Raman spectroscopy confirmed that Cr₂O₃ retained its rhombohedral phase across all compositions, with no evidence of phase transformation. A significant reduction in crystallite size by 50.0 %, 58.4 %, and 72.45 % was observed for the 7:3, 2:3, and 1:9 compositions, respectively, relative to pristine Cr₂O₃. Photocatalytic experiments revealed that the Cr₂O₃/GNPs (1:9) nanocomposite exhibited the highest methylene blue dye degradation efficiency, attributed to defect-induced charge separation and enhanced interfacial electron transport. The rate constant (k_app) and C/C₀ ratio further validated this optimal composition, as UV–Vis spectroscopy demonstrated a substantial decrease in MB absorption intensity, signifying efficient dye removal. Electrochemical investigations using cyclic voltammetry, galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy confirmed the superior energy storage properties of the Cr₂O₃/GNPs (1:9) nanocomposite, which exhibited the highest specific capacitance (462.2 F/g) and the lowest equivalent series resistance (6Ω). The synergistic 2D interfacial interactions between Cr₂O₃ and GNPs facilitated rapid charge transport, efficient electron-hole separation, and enhanced ionic conductivity, making this nanocomposite a promising candidate for both environmental remediation (wastewater treatment) and energy storage (supercapacitor) applications.