One-Step Synthesis of Aminobenzoic Acid Functionalized Graphene Oxide by Electrochemical Exfoliation of Graphite for Oxygen Reduction to Hydrogen Peroxide and Supercapacitors

Abstract

Graphene-based materials have attracted considerable attention as promising electrocatalysts for the oxygen reduction reaction (ORR) and as electrode materials for supercapacitors. In this work, electrochemical exfoliation of graphite in the presence of 4-aminebenzoic acid (4-ABA) is used as a one-step method to prepare graphene oxide materials (EGO) functionalized with aminobenzoic acid (EGO-ABA). The EGO and EGO-ABAs materials were characterized by FT-IR spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that the EGO-ABA materials have smaller flake size and higher density of oxygenated functional groups compared to bare EGO. The electrochemical studies showed that the EGO-ABA catalysts have higher activity for the ORR to H₂O₂ in alkaline medium compared to EGO due to their higher density of oxygenated functional groups. However, bare EGO has a higher selectivity for the 2-electron process (81%) compared to the EGO-ABA (between 64 and 72%) which was related to a lower content of carbonyl groups. The specific capacitance of the EGO-ABA materials was higher than that of EGO, with an increase by a factor of 3 for the materials prepared from exfoliation in 5 mM 4-ABA/0.1 M H₂SO₄. This electrode material also showed a remarkable cycling capability with a loss of only 19.4% after 5000 cycles at 50 mVs^-1.

Keywords: amine oxidation; aminobenzoic acid; electrochemical exfoliation of graphite; graphene oxide; oxygen reduction reaction; supercapacitors.

Scheme 1

One-step synthesis of electrochemically exfoliated and aminobenzoic acid functionalized graphene oxide (EGO-ABA). The exfoliation of graphite is carried out in 0.1 M H₂SO₄ with the presence of 4-aminobenzoic acid.

Scheme 2

The chemical reactions describing the grafting of aminobenzoic acid on the basal plane of the graphitic layers and the formation of an azo compound.

Figure 1

FT-IR spectra of EGO, EGO-ABA 5 and 20 materials.

Figure 2

(a) XPS survey spectra; atomic percentage (at% ratio) of (b) total functionalized carbon, (c) each functional group, (d) total nitrogen and (e) each nitrogen type.

Figure 3

(a) The powder XRD patterns of the EGO and EGO-ABA materials. The position of the diffraction peaks of graphene (PDF 65-6212) is included in the lower panels for reference, respectively. (b) Raman spectra of the EGO and EGO-ABA materials.

Figure 4

(a) Cyclic voltammetry of the EGO and EGO-ABAs modified electrodes in N₂-saturated 0.1 M KOH solution after 20 cycles, scan rate 50 mV s⁻¹. (b) The total charge (Q_total) calculated from the voltammograms presented in Supplementary Figure S4a.

Figure 5

(a) Linear sweep voltammograms for the oxygen reduction reaction for EGO and EGO-ABA electrodes 0.1 M KOH at 5 mV s⁻¹ with a rotation of 1600 rpm: disc current (bottom panel) and ring currents (top panel). The potential dependence of (b) number of transferred electrons (n) and (c) of the yield of hydroperoxide formation on EGO and EGO-COOHs based electrodes.

Figure 6

(a) Cyclic voltammograms (CV) of graphene materials, before (EGO) and after surface functionalization (EGO-ABA) collected at the scan rate of 50 mV s⁻¹ from 0 to −1.15 V. (b) Specific capacitance (C_s) versus the scan rate (υ) for EGO and EGO-ABA based electrodes.

Figure 7

Cycling performance of the EGO-ABA-5/NF electrode at 50 mV s⁻¹ for 5000 cycles; the inset shows CV curves for the 1st and 5000th cycles.