Biomimetic CsCl:EG/PVA–NaOH eutectogels for high-performance ionic thermoelectrics and sustainable low-grade heat harvesting

Abstract

Developing efficient and flexible ionic thermoelectric (i-TE) materials is essential for converting low-grade waste heat into usable electrical energy. In this study, we present a new biomimetic strategy for designing high-performance eutectogels that integrate a cesium chloride–ethylene glycol deep eutectic solvent (CsCl:EG DES) with a poly(vinyl alcohol) (PVA)–sodium hydroxide (NaOH) polymer matrix. The resulting CsCl:EG/PVA–NaOH eutectogel exhibits outstanding thermoelectric performance, achieving a record-high Seebeck coefficient of 1.65 mV K⁻¹ at 355 K, significantly surpassing previously reported PVA/NaOH hydrogels and marking the first successful demonstration of thermoelectric operation in the CsCl–EG system. Comprehensive structural and morphological characterization using FTIR, SEM, and EDX confirms the formation of a robust, well-developed bicontinuous network in which CsCl:EG domains are uniformly distributed within the crosslinked PVA matrix. This architecture enables p-type thermoelectric behavior, where directional ionic transport of Na⁺, Cs⁺, Cl⁻, and OH⁻ ions through interconnected percolation pathways is driven by a thermal gradient. Complementary molecular dynamics simulations (GROMACS) further validate the experimental findings, predicting a Seebeck coefficient of 2.06 mV K⁻¹ within the 298–358 K range. The simulations elucidate that the strong hydrogen-bonding network and the presence of multiple mobile ion species facilitate efficient thermodiffusion while maintaining low phonon transport. The synergistic combination of engineered ionic migration channels and phonon-scattering interfaces yields an optimal balance between a high Seebeck coefficient and low thermal conductivity. These features make the CsCl:EG/PVA–NaOH eutectogel a promising candidate for flexible, sustainable thermoelectric devices capable of harvesting low-grade waste heat under ambient conditions.