Stratified Triphasic Thermocells with Boosted Thermopower Enabled by Entropy‐Concentration Dual Regulation Strategy

Thermocells (TECs), a booming heat‐to‐electricity conversion technique leveraging redox reactions, face intrinsic challenges in thermopower ( S e ) enhancement, limiting their efficiency in low‐grade heat harvesting. Herein, a stratified triphasic electrolyte (STE) for TECs is presented that synergistically boosts S e via entropy‐concentration dual regulation while inherently suppressing thermal convection. By constructing immiscible neopentyl glycol (NPG)‐rich and water‐rich liquid phases interlaced with Fe(CN) 6 4− crystalline precipitates, the STE synergistically achieves solvation entropy tuning and concentration gradient amplification. The NPG‐rich phase selectively reconstructs redox ion solvation shells to elevate entropy changes, while temperature‐dependent ion solubility disparities between liquid phases generate extreme non‐equilibrium concentration ratio differences. As a result, a significantly boosted S e of 3.61 mV K −1 for Fe(CN) 6 3−/4− ‐based TECs is achieved, outperforming many state‐of‐the‐art systems reliant on singular parameter optimization. The STE‐based TEC delivers a power density of 819.8 mW m −2 at Δ T = 30 K and demonstrates stable continuous operation for hours. An integrated device combining the STE‐based P‐type units with Fe 2+/3+ N‐type counterparts is also fabricated and demonstrated to sustainably power small electronics under low thermal gradients. This work establishes a strategy to harmonize thermodynamic and kinetic optimization in TECs, advancing their viability for scalable low‐grade waste heat recovery and self‐powered Internet‐of‐Things applications.