Thermoelectric energy recovery at ionic-liquid/electrode interface

TL;DR

This study demonstrates a thermoelectric energy recovery method using a thermally chargeable capacitor with ionic liquids, showing significant capacitance and robustness, enabling waste-heat conversion without electron exchange.

Contribution

It introduces a novel thermoelectric energy harvesting approach utilizing ionic-liquid/electrode interfaces with high capacitance and demonstrated robustness.

Findings

Capacitance of 36 mF for nanoporous carbon electrodes

Reproducible charging-discharging cycles under temperature gradient

Observed convective flow acceleration enhances charging process

Abstract

A Thermally Chargeable Capacitor containing a binary solution of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide (EMIMTFSI) in acetonitrile is electrically charged by applying a tempera- ture gradient to two ideally polarisable electrodes. The corresponding thermoelectric coefficient is -1.7 mV/K for platinum foil electrodes and -0.3 mV/K for nanoporous carbon electrodes. Stored electrical energy is extracted by discharging the capacitor through a resistor. The measured capacitance of the electrode/ionic- liquid interface is 5 micro $\mu$F for each platinum electrode while it becomes four orders of magnitude larger $\approx 36$ mF for a single nanoporous carbon electrode. Reproducibility of the effect through repeated charging-discharging cycles under a steady-state temperature gradient demonstrates the robustness of the electrical charging pro- cess at the liquid/electrode interface. The acceleration of the charging by convective flows is also observed. This offers the possibility to convert waste-heat into electric energy without exchanging electrons between ions and electrodes, in contrast to what occurs in most thermogalvanic cells.