Tuning structural, optical, charge storage, and electronic transport properties of graphene oxide through functional group engineering

Abstract This study investigates the effect of oxidation temperature on the structural, electronic, and electrochemical properties of graphene oxide (GO) synthesized at 75, 95, and 115 °C. Increasing the oxidation temperature resulted in a reduction in crystallite size from 9.95 ± 1.24 to 8.05 ± 0.49 nm and a decrease in the interlayer spacing, accompanied by partial reorganization of the sp² carbon domains. The electrical properties were significantly improved, with enhanced carrier transport at higher oxidation temperatures. The optical band gap decreased from 4.11 to 3.69 eV, while the Urbach energy increased from 285 to 625 meV, indicating enhanced energetic disorder and band-tail formation. Electrochemical analysis revealed improved charge-transfer kinetics, with the charge-transfer resistance decreasing from 911 to 598 Ω and the relaxation time decreasing from 0.842 to 0.671 ms. The electrochemical response also showed a predominantly diffusion-controlled charge-storage contribution, while the apparent diffusion coefficient decreased from 2.094 × 10⁻⁷ to 5.792 × 10⁻⁸ cm²/s with increasing oxidation temperature. In contrast, the specific capacitance decreased from 668 to 328 F/g, which is attributed to the reduction of oxygen-containing redox-active sites and restricted ion accessibility. Despite the reduced capacitive performance, the capacitance retention improved from 84.25% to 95.84% after 6000 cycles. Overall, increasing oxidation temperature promotes electronic transport and electrochemical kinetics while reducing redox-based charge-storage capacity, demonstrating a clear trade-off between electronic conductivity, ion-transport behavior, and capacitive performance.