Thermally-driven chemical heterogeneity produces large thermopower and multiday operability in a thermogalvanic cell

Abstract

Thermogalvanic cells, which convert low-grade heat into electricity, usually employ chemically-homogeneous electrolytes that limit the Seebeck response to redox entropy alone. Here, we introduce a redox split thermogalvanic cell in which a temperature gradient drives localized oxidation of a nickel–bipyridine complex at the hot electrode only, creating chemical heterogeneity that augments thermopower via additional concentration gradient effects. We add weakly coordinating anions to stabilize the oxidized species, increase redox entropy change, and balance electrical and thermal transport, and the optimized cell delivers a Seebeck coefficient of 6.44 mV K−1; a maximum power density ~8 Wm−2; and ~0.5 V (open circuit) at a 75 K gradient. It furthermore supplies power for >8 days under load with ~8% relative Carnot efficiency and a figure of merit ZT ~ 0.8, offering a durable, efficient route towards waste heat recovery.