Slurry redox couple thermogalvanic cells with self-sustained stratification and self-replenishment characteristics for efficient body heat harvesting.

Conventional wearable thermogalvanic cells face a core bottleneck: liquid electrolytes leak severely, while quasi-solid ones deliver low power output due to restricted ion transport (typical value <200 mW m-2), insufficient for practical use. Herein, a thermogalvanic cell based on slurry redox couples composed of micron-sized K3/4[Fe(CN)6] crystals and their saturated solution is designed. The as-built system combines high ionic conductivity comparable to liquid electrolytes and superior safety due to suppressed free liquid flow. Its core innovation originates from the synergy of two mechanisms. On one hand, the solid-liquid composite slurry composed of redox-active crystals enables the formation and maintenance of an artificial stratified structure without a separator, thereby significantly enhancing the concentration gradient between the two electrodes. On the other hand, the redox crystals existing in the solid-liquid structure act as a soluble local material reservoir, which can replenish the consumed redox ions to buffer the reaction rate equilibrium for the reactants. At ΔT = 10 K, the single cell achieves an open-circuit voltage of 145 mV and a maximum power density of up to 1180 mW m-2. This strategy possesses outstanding universality: the FeCl3/KI slurry system further elevates the power density to 2053 mW m-2, outperforming reported quasi-solid counterparts by ∼10 times. A stack of six K3/4[Fe(CN)6] and six FeCl2/3 units in series yields a steady 1.8 V driven by human body heat (ΔT = 3 K), enabling continuous operation of a commercial wristwatch. This work develops a novel high-performance, leakage-proof and integrable thermogalvanic system for efficient harvesting of human low-grade waste heat, offering a new route for practical wearable self-powered electronics.