New Thermoelectricity Utilization System Based on Aqueous Organic Redox Flow Battery Involving the Tripyridinium–Triazine Radicals

Graphical A new thermoelectricity utilization system is established using tripyridinium–triazine compound for low-grade heat harvesting. The thermally induced potential shift arises from temperature-dependent interconversion between singlet and triplet states of the tripyridinium–triazine diradical. New energy technology is in urgent demand for waste heat harvesting and utilization for energy saving and renewable energy development. Herein, an aqueous organic redox flow battery (AORFB) with designed tripyridinium–triazine radicals ((TPyTz) ··4+ )/(TPyTz) ·5+ ) as the negative redox couple is constructed as a thermoelectricity utilization system. The electrochemical test indicates that the (TPyTz) ··4+ /(TPyTz) ·5+ couple shows an interesting potential change about 27 mV accompanied by system temperature varying from 298 K to 343 K. Nuclear magnetic resonance and electron paramagnetic resonance spectra approve that the population of high-energy (TPyTz) ··4+ triplet state increases with temperature rise. This shifts the potential of the (TPyTz) ··4+ /(TPyTz) ·5+ couple to a much more negative position. While the 2,2,6,6-tetramethylpiperidin-1-oxyl derivative (TPABPy)Cl 3 is used as the positive electrolyte with no temperature-dependent potential change, the AORFB established by these two couples displays a thermally induced potential change from 1.39 V to 1.42 V.