Investigation of the Effective Voltage and Performance of Thermocells

Abstract

Thermocells, also called thermogalvanic cells, are a promising technology that can efficiently harvest low-grade waste heat with direct thermoelectric conversion. The cells operate under a temperature difference, with one electrode on the hot side and the other on the cold side. The recently developed electrodes, such as porous carbon materials and pin-structured electrodes, have led to a temperature gradient even inside one of the electrodes. However, it still remains an open question of what temperature difference determines the open-circuit voltage of thermocells. Here, we investigated the effective voltage of a thermocell with thick electrodes. The temperature difference that determines the voltage turned out to be the smallest temperature difference between anode and cathode electrodes, the average temperature difference, or in between, depending on the internal resistances of the cell. We also verified the validity of normalized power density estimated from the open-circuit voltage. In addition, a strategy was demonstrated to improve the power density of a thermocell that consists of thick electrodes. The results provided here would help devise high-performance thermocells with optimized electrode structures.