Counterion-assisted adsorption strategy for a high-thermopower thermo-electrochemical cell

Abstract

Constructing a redox ion concentration ratio difference (ΔC) between electrodes offers significant potential for enhancing the thermopower of thermo-electrochemical cells (TECs). Here, we report a novel counterion-assisted strategy that elucidates a previously unexplored mechanism for interfacial adsorption regulation. By introducing guanidinium (Gdm⁺) ions into the conventional I⁻/I₃⁻ system within a PVA/PNIPAM hydrogel, we demonstrate that Gdm⁺ ions do not merely act as spectators but actively anchor to polymer chains and co-localize with I₃⁻ in hydrophobic domains. Uniquely, this specific interaction effectively neutralizes local charge accumulation, shifting the adsorption–repulsion equilibrium toward an adsorption-dominant regime—a phenomenon distinct from traditional single-ion adsorption models. This mechanistic breakthrough enables a gel-based TEC to achieve a p-type thermopower of 25.4 mV K⁻¹ under a 4 °C temperature gradient. This work establishes a new paradigm for regulating local ion concentrations at electrochemical interfaces via counterion engineering, offering a robust and generalizable strategy to push the performance limits of TECs beyond current boundaries.