Scaling Relation between Electrochemical Seebeck Coefficient for Fe2+/Fe3+ in Organic Solvent and Its Viscosity

The temperature coefficient α (= dV/dT) of the redox potential (V) in a redox system, or so-called electrochemical Seebeck coefficient, is a key parameter for thermal energy harvesting. We systematically investigated α for Fe2+/Fe3+ in 16 organic solvents, i.e., 8 protic and 8 aprotic solvents. We found that α shows remarkable solvent dependence and is distributed from 0.14 mV/K for glycerin to 3.60 mV/K for acetone. We further found a scaling relation between α and viscosity (η) of the solvent as α ∝ η−0.4. We will discuss solvent dependence of α and the scaling relation in terms of the configuration entropy of the solvent molecules.