Converting Heat to Electrical Energy Using Highly Charged Polyoxometalate Electrolytes

Thermally regenerative electrochemical cycles and thermogalvanic cells harness redox entropy changes (ΔSrc) to interconvert heat and electricity with applications in heat harvesting and energy storage. Their efficiencies depend on ΔSrc because it relates directly to the Seebeck coefficient, yet few approaches exist for controlling the reaction entropy. Here, we demonstrate the design principle of using highly charged molecular species as electrolytes in thermogalvanic devices. As a proof-of-concept, the highly charged Wells-Dawson ion [P2W18O62]6– exhibits a large ΔSrc (−195 J mol–1 K–1) and a Seebeck coefficient comparable to state-of-the-art electrolytes (−1.7 mV K–1), demonstrating the potential of linking the rich chemistry of polyoxometalates to thermogalvanic technologies.