Redox-State-Selective Hydrogen Bonding Enables High Seebeck Coefficient and High Durability of Ruthenium Thermocells
Year: 2026
Type: preprint
Abstract: Thermocells generate electrical voltage from a temperature difference through the temperature dependence of redox potentials. One method for improvement is to make electron transfer trigger a substantial rearrangement of surrounding solvent molecules. Here, we realize this concept by designing hydrogen-bonding interactions that depend strongly on the oxidation state of a ruthenium complex. Tris(4,4′-dioxido-2,2′-bipyridine)ruthenium ([RuII/III(bpy(O)2)3]4−/3−) forms hydrogen bonds with alcohol added in organic solvents, with substantially stronger interactions in the Ru(II) state. This redox-state selectivity was evidenced by a larger blue shift of the MLCT absorption peak for Ru(II) than for Ru(III). Their hydrogen bond interaction can be also controlled by the concentration of alcohol in mixed solvent, evidenced by the systematic redox potential shift with log[CH3OH]. The hydrogen bond affinity was thus dependent strongly on temperature change, and as a result, enhancement of Seebeck coefficient in both DMSO/CH3OH and CH3CN/CH3OH mixed solvents, reaching −2.95 mV K-1 in the CH3CN-based electrolyte. The Ru(II)/(III) couple further sustained power generation for over 50 h under a continuous temperature gradient. These results show that redox-state-selective intermolecular interactions can couple electron transfer to solvent reorganization, providing a molecular strategy for achieving both high Seebeck coefficients and durable thermocell operation.
Source: ChemRxiv
Institution: The University of Tokyo
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204953627