Direct electrochemical co-polymerization of EDOT and hydroquinone

Abstract

Quinone–polythiophene composites show much promise as organic electrode materials for energy storage applications due to the combination of conducting properties of the polythiophene matrix with inherently high specific capacity of quinones. To date, composites of this kind were fabricated either as mechanical blends or as true co-polymers from covalently bound quinone–thiophene monomer precursors. The first approach is cheap but often requires the addition of conductive and binding additives implying the domain-like distribution of the conductive and capacitive units. The second approach ensures uniform and highly regular distribution of the quinone units throughout the polythiophene matrix but requires preliminary multi-step synthesis of the organic precursor, which makes this approach less cost-effective in the context of energy storage applications. In this work, an electrochemical method for direct copolymerization of 3,4-ethylenedioxythiophene (EDOT) with hydroquinone (QH₂) is proposed. The method was shown to produce the PEDOT/QH₂ material as a co-(EDOT)–QH₂ polymer where oligothiophene chains are interrupted by quinone units, the length of the oligothiophene chain depending on the QH₂ : EDOT ratio in the polymerization seed. The saturation of the conductive polythiophene matrix with capacitive quinone units can be varied in the same way, yielding specific capacity up to 112 mA h g⁻¹ as calculated per the entire material.