Enthalpic versus Entropic Contribution to the Quinone Formal Potential in a Polypyrrole-Based Conducting Redox Polymer

A conducting redox polymer (CPR) based on pyrrole with a hydroquinone pendant group was synthesized through electropolymerization of the corresponding monomer. The formal potential (E0′) in aqueous solution at different pH as well as in MeCN containing equal amounts of pyridinium-triflates and the corresponding free pyridine with different pKawas investigated. E0′ could be completely recovered in MeCN, and by utilizing pyridine bases with different donor–acceptor strengths, a decrease of 61 meV/pKawas found that corresponded exactly to the pH dependence of E0′ in aqueous electrolyte. To separate the entropic and enthalpic contributions to E0′, temperature-dependent electrochemistry was performed. Two different modes of operation with changing pH/pKabetween the two media were revealed. In MeCN, E0′ varies only because of the enthalpic contribution as the entropic contribution is unaffected by change in pKa. In water, there is primarily an entropic contribution to E0′ with changing pH due to solvation of the proton. The presented results are expected to open up for new design possibilities of CRPs based on ion-coordinating redox groups for electrical energy storage.