Boosting I^-/I₃^- liquid state thermocells through solubilitydriven biphasic system optimization

Abstract

Liquid state thermocells (LTCs) offer a promising approach for harvesting lowgrade 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 longterm 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^-/I₃^- redox couple, an organic-aqueous solvent, and ammonium sulfate. This biphasic system enables an enriched concentration of I₃^- 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 costeffective strategy using a biphasic system establishes a novel pathway for advancing performance of LTCs and presents a promising approach toward achieving carbon neutrality.

Keywords

biphasic system / liquid state thermocells / low-grade heat harvesting / solubility-driven

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2024 The Author(s). EcoEnergy published by John Wiley & Sons Australia, Ltd on behalf of China Chemical Safety Association.