2, The University of Texas at Dallas, Richardson, Texas, United States
Continuously operating thermo-electrochemical cells (thermocells) are of interest for harvesting low-grade waste thermal energy because of their potentially low cost compared with conventional thermoelectrics. However, realizing high areal power densities and high temperature operation has been problematic. Pt-free thermocells devised here provide an output power of up to 12 W m-2 for an inter-electrode temperature difference (ΔT) of 81 °C, which is six-fold higher power than previously reported for Pt-free planar thermocells operating at ambient pressure. The previous record power output, normalized to (ΔT)2, for an organic electrolyte thermocell operating above 100 °C, has been tripled. The advances leading to this performance include the use of: 1) multifunctional inter-electrode thermal separators, 2) improved electrolytes, 3) inexpensive carbon fiber textiles as vascular electrodes, and 4) multi-pin or fin electrodes. Transitioning from conventional single-leg thermocells to arrays with n-type and p-type legs produces 2.18 V from a ΔT of only 21 °C, which enables the practical charging of capacitors for energy storage.