Hybrid Ionic Thermoelectric–Galvanic Cell Effects for High Power Density in Gel Thermocell

Gel thermocells, which convert heat into electricity through the ionic thermoelectric (i‐TE) effect, are promising for low‐grade heat harvesting due to their high ionic thermopower, low cost, and excellent flexibility. However, their practical application has been limited by the low output power density. Here, we demonstrate a strategy to significantly enhance the output power density by introducing the galvanic cell effect via an asymmetric electrode configuration. Through systematic optimization of gel composition, operating temperature, and copper electrode, a maximum output power density ( P max ) of 470 mW·m −2 is achieved in a gel thermocell rCu@Au | Gelatin‐FeCN 4−/3− | Gp. Furthermore, the addition of EDTA to i‐TE gels, which complexes Cu 2 + into soluble Cu(EDTA) 2− and suppresses Cu 2 + ‐participation layer, boosts P max to 572 mW·m −2 at 305 K (Δ T = 4 K) in a single rCu@Au | Gelatin‐FeCN 4−/3− ‐EDTA | Gp. High P max from the galvanic cell effect was transient, decaying with copper consumption. A device integrating ten gel thermocells connected in series demonstrates a P max of 226 mW m −2 and voltage of 1.5 V, sufficient to directly power the hygrothermograph and LED array. This study provides practical strategies for leveraging hybrid effects to enhance the performance of i‐TE and other energy‐converting gel cells.