Application of bipolar electrodes in thermocells for efficient waste-heat recovery

Thermocells generate voltage from the temperature difference between a pair of electrodes immersed in a liquid electrolyte. Recent studies showed that natural convection in the liquid thermocells brings a significant amount of heat into the electrolyte, minimizes the temperature gradient, and reduces the open-circuit voltage. Herein, bipolar electrodes (BPEs) are integrated into a thermocell containing aqueous electrolyte of hexacyanoferrate/ferrite to control the natural convection of the thermocell. Simulation of the fluid velocity of the electrolyte showed that the convective flow can be reduced to the half after insertion of one BPE and to the one-third after insertion of two BPEs. The experimental measurement shows the open-circuit voltage was increased by 39% with one BPE and by 55% with two BPEs, because of the enlarged temperature gradient. Further optimization of the position of BPE increased the power output by 54% and the conversion efficiency by 160%, respectively, compared to the conventional single cell. Integration of BPEs is a simple approach to control natural convection in thermocells and can universally be applied to various types of thermocells for increasing the power output and the conversion efficiency for waste-heat recovery.