Abstract
AbstractThe selective ion transport characteristics of a conducting polymer electrode, based on poly(3,4‐ethylenedioxythiophene) (PEDOT), is evaluated with respect to its electrocatalytic performance, specifically targeting redox switching of quinone couples. Employing model organic redox quinones, here, the novel phenomenon of ion‐selective electrocatalysis (ISEC) is conceptualized. The effect of ISEC is studied and evaluated using two forms of PEDOT electrodes, which differ in their ion‐exchange characteristics, by comparing the redox transformations of catechol and tiron. It is rationalized that the choice of the specific redox couple and the ion selectivity characteristics of the conducting polymer electrode impacts the activation losses in aqueous organic redox‐flow batteries. By carefully selecting and designing the conducting polymer electrodes, high conversion efficiency on acid‐resistant electrodes is obtained. As far as it is known, this is the first redox flow battery to include conducting polymer electrodes operating in both the posolyte and negolyte configurations, thus the first “all‐organic” RFBs.
Highlights
The selective ion transport characteristics of a conducting polymer electrode, attractive beside the lower energy density (≈
We explore the impact of the counterions, of the conducting polymers (CPs) electrodes, on the rate of electron transfer to and from reactants of the electrolyte solution
We focus on complex electrocatalytic reactions, such as the two proton-coupled electron charge transfer of organic quinones
Summary
Two types of PEDOT electrode materials have been explored and investigated for the operation in ISEC and aqueous organic redox-flow battery (AORFB) setups: 1) PEDOT:PSS containing a nonexchangeable polyanionic primary dopant and PEDOT:Tos including a small anionic primary dopant that is mobile and exchangeable. For the case of the PEDOT:PSS electrode, the tiron-associated redox process is significantly suppressed (Figure 1A) We attribute this result to the noncongruence of selective ionic transport and reactant diffusion within the electrode bulk. The intensity of its current peak currents scale linearly versus the film thickness (Figure 1C) (2.8 times increase in thickness leads to 2.5 times increase in oxidation peak current) or its capacitance (Figure S2, Supporting Information), which implies that the entire CP electrode bulk is accessible for the tiron-associated redox process. Tiron is involved in the congruent ionic transport along with the transferable dopant anions of the conducting polymer PEDOT:Tos while it is repelled from the bulk of PEDOT:PSS This is a first indication that the electrochemical process can be classified as ion-selective electrocatalysis ISEC. The ISEC phenomenon with those quinones is controlled by the chemical design of the conducting polymer electrode
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