Water, not salt, causes most of the Seebeck effect of nonisothermal aqueous electrolytes

TL;DR

This study shows that in aqueous electrolytes, water layering and orientation near electrodes primarily drive the Seebeck effect, surpassing ionic thermodiffusion, as revealed by molecular dynamics simulations.

Contribution

The paper demonstrates that water, not salt ions, predominantly causes the Seebeck effect in nonisothermal aqueous electrolytes, highlighting the importance of water layering and surface potential differences.

Findings

Water layering causes significant temperature-dependent potential drops.

Surface potential differences dominate ionic thermodiffusion in the Seebeck effect.

Molecular dynamics simulations reveal water's key role in electrolyte thermoelectric phenomena.

Abstract

When two electrolyte-immersed electrodes have different temperatures, a voltage $\Delta \psi$ can be measured between them. This electrolyte Seebeck effect is usually explained by cations and anions flowing differently in thermal gradients. However, our molecular dynamics simulations of aqueous electrolytes reveal a large temperature-dependent potential drop $\chi$ near blocking electrodes caused by water layering and orientation. The difference in surface potentials at hot and cold electrodes is more important to the Seebeck effect than ionic thermodiffusion, $\Delta \psi \sim \chi_{\rm hot}-\chi_{\rm cold}$.