Boosting I–/ I 3 − ${\mathrm{I}}_{3}^{-}$ liquid state thermocells through solubility-driven biphasic system optimization

Abstract

Liquid state thermocells (LTCs) offer a promising approach for harvesting low-grade heat. In exploring the impact of concentration difference (ΔC_r) on the Seebeck coefficient (Se) in LTCs, previous studies mainly focused on two strategies: host–guest complexation and thermosensitive crystallization, which involved adding polymers or cation additives for targeted interaction with the redox couple. However, these methods face challenges in scalability and long-term application due to the selection and costs of additives, along with the stability of recognition. This study pioneers a unique strategy that utilizes solubility differences in an organic-aqueous biphasic system. We investigated an electrolyte consisting of an I⁻/$I_3^{-}$ redox couple, an organic-aqueous solvent, and ammonium sulfate. This biphasic system enables an enriched concentration of $I_3^{-}$ in the upper phase, thereby enhancing the reduction reaction on the hot side. Our approach achieves a Se of 1.8 mV K⁻¹ and a maximum output of 120 μW m⁻² K⁻², representing a substantial improvement, over threefold compared to traditional single-phase systems. Therefore, this cost-effective strategy using a biphasic system establishes a novel pathway for advancing performance of LTCs and presents a promising approach toward achieving carbon neutrality.