Thermoelectric ratchet effect for charge carriers with hopping dynamics

TL;DR

This paper explains how a ratchet effect causes large Seebeck coefficients in ionic conductors and complex systems, using a model that matches experimental data without free parameters.

Contribution

It introduces a model demonstrating the thermoelectric ratchet effect in ionic and molecular systems, explaining large Seebeck coefficients observed experimentally.

Findings

Model reproduces experimental Seebeck coefficients in ionic liquids and hydrated polymers.

Ratchet effect causes ions to move towards colder regions under a temperature gradient.

Diffusiophoretic transport enhances thermoelectric response in complex systems.

Abstract

We show that the huge Seebeck coefficients observed recently for ionic conductors, arise from a ratchet effect where activated jumps between neighbor sites are rectified by a temperature gradient, thus driving mobile ions towards the cold. For complex systems with mobile molecules like water or polyethylene glycol, there is an even more efficient diffusiophoretic transport mechanism, proportional to the thermally induced concentration gradient of the molecular component. Without free parameters, our model describes experiments on the ionic liquid EMIM-TFSI and hydratedNaPSS, and it qualitatively accounts for polymer electrolyte membranes with Seebeck coefficients of hundreds of $k_B/e$.