Electrochemical performance of reduced graphene oxide surface-modified with 9-anthracene carboxylic acid

Abstract

An efficient approach for the preparation of 9-anthracene carboxylic acid (ACA) modified reduced graphene oxide (rGO) was demonstrated in this study. ACA was used as a surface-modifying agent and underwent a reversible redox reaction. The benzene ring of the ACA anion was attached to the rGO surface via π–π interactions, and the carboxylate anions helped to disperse the hybrid materials in water due to hydrogen bonding. Therefore, water-dispersible, ACA-modified rGO (ACA-rGO) improved the wettability and capacitance performance in aqueous electrolyte solutions. The morphology of the ACA-rGO was studied using transmission electron microscopy and atomic force microscopy image analysis. The dispersion characteristics of the exfoliated materials were investigated using UV-vis spectroscopy analysis. The chemical states and natures of the samples were investigated using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). The appearance of a new peak at 288.7 eV in the XPS of ACA-rGO confirmed the successful surface modification of rGO using ACA. Raman spectra were studied to compare the electronic structure and defect concentrations in the ACA-rGO with respect to GO. The low intensity and shifted D- and G-bands indicated non-covalent functionalization of rGO with ACA anions. Electrochemical performances of ACA-rGO, rGO, and GO were evaluated in 1 M aqueous Na₂SO₄ electrolyte. The capacitance performance was investigated through galvanometric charge–discharge with ACA-rGO, rGO, and GO in an operating voltage of −1 to 1 V. The range of specific capacitance in the three-electrode system was 610 to 115 F g⁻¹ at a current density range of 0.8 to 20 A g⁻¹. In addition, the capacitance performance of ACA-rGO was studied in 1 M Na₂SO₄ electrolyte using two-electrode systems. The cell capacitance, energy density, and power density at a current density of 0.2 A g⁻¹ of the asymmetric assembly with multiwall carbon nanotubes were 77 F g⁻¹, 41.3 Wh kg⁻¹, and 200 W kg⁻¹, respectively.