Role of Ions in Hydrogels with an Ionic Seebeck Coefficient of 52.9 mV K–1

Ionic thermoelectric (i-TE) material with mobile ions as charge carriers has the potential to generate large thermal voltages at low operating temperatures. This study highlights the role of ions in i-TE hydrogels employing a poly(vinyl alcohol) (PVA) polymer matrix and a number of ion providers, e.g., KOH, KNO₃, KCl, KBr, NaI, KI, and CsI. The relationship between the intrinsic physical parameters of the ion and the thermoelectric performance is established, indicating the ability to influence the hydrogen bond by the ion is a crucial factor. Among these i-TE hydrogels, the PVA/CsI hydrogel exhibits the largest ionic Seebeck coefficient, reaching 52.9 mV K^-1, which is the largest of all i-TE materials reported to date. In addition, our work demonstrates the influence of ions on polymer configuration and provides an avenue for ion selection in the Soret effect in ionic thermoelectrics.