Issue 1, 2024

Exploring the local solvation structure of redox molecules in a mixed solvent for increasing the Seebeck coefficient of thermocells

Abstract

A thermocell is an emerging alternative to thermoelectric devices and exhibits a high Seebeck coefficient (Se) due to the large change of solvation entropy associated with redox reactions. Here, the Se of p-chloranil radicals/dianions (CA˙−/2−) in acetonitrile was drastically increased from −1.3 to −2.6 mV K−1 by the addition of ethanol, and the increment surpassed the estimation of the classical Born model with continuum solvent media. UV-vis spectroscopy and electrochemical measurements at various mixing ratios of acetonitrile to ethanol revealed that the strong hydrogen bonding between ethanol and oxygen atoms of CA2− forms a 4 : 1 solvent–ion pair, while the ethanol molecules binding to CA2− dissociate upon its oxidation to CA˙. The local solvation structures of CA2− are in good agreement with density functional theory. This order–disorder transition of the local solvation structure around the CA˙−/2− ions produces a large entropy change and results in a large Se value. The tailored solvation structure of redox ions by hydrogen bonding is a versatile method applicable to a variety of redox pairs and solvents, contributing to the development of electrolyte engineering for thermocells.

Graphical abstract: Exploring the local solvation structure of redox molecules in a mixed solvent for increasing the Seebeck coefficient of thermocells

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Article information

Article type
Edge Article
Submitted
20 Sept. 2023
Accepted
24 Nov. 2023
First published
27 Nov. 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2024,15, 146-153

Exploring the local solvation structure of redox molecules in a mixed solvent for increasing the Seebeck coefficient of thermocells

H. Inoue, H. Zhou, H. Ando, S. Nakagawa and T. Yamada, Chem. Sci., 2024, 15, 146 DOI: 10.1039/D3SC04955H

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