Importance of the Interlayer Distance of Reduced Graphite Oxide for Reversible Redox Reaction of Quinone-Based Molecules
Authors: Nakasone Kaiya , Sakima Akira , Futamura Ryusuke , Takimoto Daisuke 
Published: December 2024

Introduction

Quinone-based molecules have attracted considerable attention as an electrode material. The electrochemical response of the molecules is typically quasi-reversible because the molecules are dissolved in electrolytes, a diffusion-controlled system. We reported that a flowable electrode composed of activated carbon (AC) and 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate (BQDS) exhibits an adsorption-controlled system; peak-potential separation (ΔE
p) was negligible.1 Herein, we report the dependence of interlayer distance of redox reaction using reduced graphite oxide (rGO) as a model electrode material.

Experimental

The cross-linking of diamine monomers tuned the interlayer distance of GO.2 A diamine monomer (0.1 mol) was added to a GO dispersion (0.4 g L−1). The dispersion was stirred for 1 h, and the powder was collected by suction filtration. This powder was dried at 353 K for 1 h to promote cross-linking between the carbon layer and the diamine, and then it was soaked in methanol for 24 h to remove the weakly adsorbed diamine monomers. The interlayer distance of GO was tuned by using diamine monomers with different chain lengths; the ethylenediamine (denoted as C2NH), hexamethylenediamine (C6NH), and dodecamethylenediamine (C12NH) were used as diamine monomers. Sodium anthraquinone-2-sulfonate monohydrate (AQS) was used as an electroactive molecule. AQS was introduced into the interlayer of GO, and the powder was collected through filtration and dried at 333 K. The GO powder was reduced under hydrogen flow at 473 K (denoted as AQS/C
n
NH-rGO: n = 2, 6, and 12). The working electrode was prepared by casting the electrode material ink onto a mirror-polished 3 mm-diameter glassy carbon rod. The deposited amount of electroactive material was 20 mg cm−2. A Pt mesh and Ag/AgCl (KCl sat.) were used as the counter and reference electrodes.

Results and Discussion

The cross-linkage was confirmed by Fourier transform infrared spectroscopy, elemental analysis, and the presence or absence of GO nanosheet after exfoliation. The interlayer spacing of C
n
NH-rGO (n = 2, 6, 12) was investigated by X-ray diffraction. The d values of C2NH-GO, C6NH-GO, and C12NH-GO were 0.89, 1.00, and 1.45 nm, respectively. The interlayer distance of unmodified GO in the wet state increased compared to that in the dry state, which is attributable to the expansion due to the introduction of water molecules. In contrast, the interlayer space of C
n
NH-rGO (n = 2, 6, 12) was negligible. The interlayer distance did not change after H2 treatment. The current-potential response was rectangular, indicating that the double-layer capacitance is the primary charge storage mechanism. The specific capacitance increased with increasing the interlayer space; the values of C2NH-rGO, C6NH-rGO, and C12NH-rGO were 10.5, 38.4, and 101.2 F g-
1, respectively. The ΔE
p values of AQS/C2NH-rGO, AQS/C6NH-rGO, and AQS/C12NH-rGO are 20, 85, and 110 mV, respectively. The reduced DE
p could be attributed to the confinement effects.3 It is noted that the AQS/C2NH-rGO showed excellent reversibility even at a scan rate of 20 V s−1. In conclusion, we found that the interlayer distance of rGO directly affects the reversibility of the redox reaction of quinone-based molecules.

Acknowledgments

This work was partially supported by the Research Foundation for the Electrotechnology of Chubu, the Kondo Memorial Foundation, and the Tokyo Ohka Foundation for the Promotion of Science and Technology.

References

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