Counterion-assisted Adsorption Strategy for High-Thermopower Thermo-Electrochemical Cell

Abstract

The constructing of redox ion concentration ratio difference (Δ𝐶) between electrodes offers significant potential for enhancing the thermopower of thermo-electrochemical cells (TECs). Strengthening selective ion interactions is expected to achieve larger Δ𝐶 and higher thermopower. Here, we present a counterion-assisted strategy, which involves adding guanidinium (Gdm⁺) ions to I⁻/I₃⁻ system, where Gdm⁺ ions anchor to polymer chains via hydrogen bonding and dispersion interactions, co-localize with triiodide ions (I₃⁻) in hydrophobic domains. In this way, Gdm⁺ can effectively neutralizes the local charge accumulation associated with sustained I₃⁻ adsorption, thereby shifting the adsorption–repulsion equilibrium toward adsorption dominance. This enhanced Δ𝐶 design enables a gel-based TEC to achieve a p-type thermopower of 25.4 mV K⁻¹ under a 4 °C temperature gradient, representing the record value reported in I⁻/I₃⁻ system. This work not only validates an intriguing heteroion co-adsorption behavior at polymer-ion interfaces, providing an effective means for regulating local ion concentrations at electrochemical interfaces, but also provides a viable strategy for improving the performance of TECs.