High‐Performance Isotropic Thermo‐Electrochemical Cells Using Agar‐Gelled Ferricyanide/Ferrocyanide/Guanidinium

Abstract An isotropic thermo‐electrochemical cell is introduced with a high Seebeck coefficient (Se) of 3.3 mV K−1 that uses a ferricyanide/ferrocyanide/guanidinium‐based agar‐gelated electrolyte. A power density of about 20 µW cm−2 is achieved at a temperature difference of about 10 K, regardless of whether the heat source is on the top or bottom section of the cell. This behavior is very different from that of cells with liquid electrolytes, which exhibit high anisotropy, and for which high Se values are achieved only by heating the bottom electrode. The guanidinium‐containing gelatinized cell does not exhibit steady‐state operation, but its performance recovers when disconnected from the external load, suggesting that the observed power drop under load conditions is not due to device degeneration. The large Se value and isotropic properties can mean that the novel system represents a major advancement from the standpoint of harvesting of low‐temperature heat, such as body heat and solar thermal heat.