Ion coordination competition enhanced adsorption strategy for improved thermopower in I−/I3− gel-based thermo-electrochemical cells

Given the widespread availability of low-grade heat (< 100 °C), its conversion into electricity represents a highly promising green technology. Thermo-electrochemical cells (TECs) have garnered significant attention for their potential in low-grade thermal energy harvesting, largely due to their relatively high thermopower. An efficient approach to achieve high thermopower is establish a high and stable concentration gradient (∆C). However, the ∆C construction process is often limited by a false saturation state in conventional I − /I 3 − TECs. To address this issue, we propose a enhancement strategy that utilizes a non-additive ion effect to enhance the free energy of hydrophobic ions. Specifically, the addition of strongly hydrating anions (SO 4 2− ) disrupts the coordination between weakly hydrating I 3 − ions and cations (K + ) by competitively occupying the K + coordination site. The free energy of I 3 − raise effectively and promote the hydrophobic interaction with methyl cellulose (MC), breaking the false saturation state and enabling a significantly greater ∆C. The implement of this strategy gets a high thermopower of 18.41 mV K −1 in this gel-based TECs. Moreover, a module comprising six series-connected devices produce a stable output of 520 mV under a 5 °C temperature difference. This work highlights the untapped potential of traditional systems for efficient thermal energy harvesting, offering a new strategy to overcome this false saturation state.