Charge injection dynamics in oxygen-functionalized and heteroatom-doped reduced graphene oxide and their impact on supercapacitor performance: An experimental and DFT investigation

Abstract

To elucidate the synergistic effects of oxygen functional groups (OFGs) and heteroatoms (HAs) on charge injection dynamics and the electrochemical performance of reduced graphene oxide (rGO), a combination of experimental techniques and density functional theory (DFT) analyses were employed. GO was synthesized using a modified Hummers method and the sample reduced hydrothermally at 150 °C demonstrated the highest areal capacitance of 817 mF/cm². To understand the diffusion and charge transfer characteristics, the diffusion coefficient and distribution of relaxation time studied using the Electrochemical Impedance Spectroscopy data. Further the X-ray photoelectron spectroscopy (XPS) confirmed the incorporation of OFGs and HAs in the rGO. A partially oxygen-functionalized, nitrogen, and sulfur-doped graphene (NS-POG) model was constructed based on the XPS data and analyzed using DFT. The projected density of states analysis revealed a Fermi level shift, indicating the introduction of excess electrons due to incorporating OFGs and HAs in graphene, thereby improving the charge carrier concentration in the partially reduced or oxidized systems. The NS-POG system exhibited a quantum capacitance of 85.92 μF/cm². Additionally, potassium ion (K⁺) adsorption studies indicated that the adsorption energy was highest near sulfur atoms, suggesting that electrolyte ions exhibit enhanced electrochemical activity in proximity to sulfur. These findings provide insight into the mechanisms by which OFGs and HAs enhance the performance of rGO and highlighting the potential of NS-rGO in supercapacitor applications.