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.