High Utilization Efficiency of Tetramethylbenzoquinone Hybridized inside the Pores of Activated Carbon for High-Performance Electrochemical Capacitor Electrodes

抄録

High utilization efficiencies of hybridized redox-active materials are of great importance in terms of increasing the capacitance as electrochemical capacitor electrodes. In this study, one of redox active alkylbenzoquiones, tetramethyl-1,4-benzoquinone (TMBQ), is hybridized inside the pores of activated carbon (AC) with the pore sizes of ~4 nm in the gas phase and the electrochemical capacitor performance is evaluated using aqueous 1 M H₂SO₄ electrolyte. The amount of the hybridized TMBQ is examined from 4 to 10 mmol per 1 g of AC and the utilization efficiencies of the resulting AC/TMBQ hybrids are found to be ≥ 85%. The hybridization is not associated with the volume expansion of the AC particles, and therefore, the volumetric capacitances of the hybrids increase with increasing the amount of TMBQ. Consequently, 1 mmol of TMBQ per 1 g of AC allows for the volumetric capacitance enhancement of ~50 F cm⁻³, and the volumetric capacitance is increased to 581 F cm⁻³ at 0.2 A g⁻¹ by hybridizing 10 mmol of TMBQ with 1 g of AC, which is much higher than the volumetric capacitance of the pristine AC: i.e., 99 F cm⁻³. Moreover, despite the substantial contribution of the reversible redox reaction of TMBQ to the capacitance enhancement, capacitance retentions of the hybrids at 10 A g⁻¹ are higher than that of AC up to a TMBQ amount of 8 mmol per 1 g of AC. The gas-phase adsorption does not require any organic solvents or concomitant solvent removal and drying processes, and enables complete adsorption of TMBQ as far as the amount of TMBQ is below the saturation amount of AC. Therefore, this hybridization method is desirable not only for enhancing the electrochemical capacitor performance but also for waste minimization.