Effect of solvation shell structure on thermopower of liquid redox pairs

Developing redox electrolytes with high thermopower is the key to making efficient thermogalvanic batteries for harvesting low-grade heat. This work applies molecular dynamics simulations to predict the thermopower (i.e. thermogalvanic temperature coefficient) a of the redox pairs Fe(CN)(6)(3-)/ Fe(CN)(6)(4-) and Fe3+/Fe2+, showing excellent agreement with experimental values. We showed that a of the Fe3+/Fe2+ redox pair can be increased from 1.7 +/- 0.4 mV/K to 3.8 +/- 0.5 mV/K with the increased acetone to water fraction. We discovered a significant change in the variance of solvent dipole orientation between Fe3+ and Fe2+, which can serve as a microscopic indicator for large a. In mixed acetone-water solvent, a of Fe3+/Fe2+ showed a rapid increase at high acetone fractions, due to the intercalation of acetone molecules into the first solvation shell of the Fe2+ at high acetone fractions. Our discovery provides insights into how solvation shell order can be engineered to develop electrolytes with high a.

Automated summary

This study used molecular dynamics simulations to predict the thermopower of the redox pairs Fe(CN)6(3-)/Fe(CN)6(4-) and Fe3+/Fe2+, and found excellent agreement with experimental values. It was discovered that the thermopower of Fe3+/Fe2+ can be increased from 1.7+/-0.4 mV/K to 3.8+/-0.5 mV/K by increasing the acetone to water fraction. This increase was attributed to the intercalation of acetone molecules into the first solvation shell of Fe2+ at high acetone fractions.