Seebeck effect in ternary ionic liquids

Abstract

Our previously developed theory of the Seebeck effect for binary full-ionized liquids at steady state  (S. N. Semenov and M. E. Schimpf, Phys. Chem. Chem. Phys., 2025, 27, 23215) is expanded here to include dilute ionic liquids containing a molecular solvent as a third component. Previous studies of the Seebeck effect are restricted to the role of the Soret effect in generating a Seebeck potential. In this work, we elucidate a physical mechanism parallel to the Soret effect that yields thermoelectricity in systems regardless of the presence of a separate Soret effect. In doing so, we examine the relative role of the Soret effect when the Seebeck effect is governed by both temperature and concentration dependence of the component electrochemical potentials. A deeper understanding of the underlying mechanisms of the Seebeck effect is especially important for ionic liquids, where huge Seebeck potentials have been measured (M. Bonetti, S. Nakamae, M. Roger and P. Guenoun, J. Chem. Phys., 2011, 134, 114513). The model is evaluated using empirical values of the Seebeck coefficient in polyethylene glycol (PEG) modified with NaOH. It is shown that the generated concentration and temperature profiles correspond to spatial uniformity in the electrochemical potential throughout the system.