High-Efficiency Electrochemical System for Harvesting Low-Grade Heat Energy

Tremendous thermal energy exists in low-grade heat sources (<100 °C), so high-efficiency and low-cost thermal energy harvesting system is highly demanded to utilize them. Current technologies, such as thermoelectric device, still have a low efficiency to satisfy commercial application. As an alternative choice, thermogalvanic cell, the electrochemical counterpart of thermoelectric device has benefit of higher electrochemical Seebeck coefficient low thermal conductivity, and material abundance. However, its efficiency is incomparable to thermoelectric system due to the low ionic conductivity. Another approach to utilize the high electrochemical Seeback coefficient is the thermally regenerative electrochemical cycle (TREC) aimed for harvesting high temperature thermal energy (>500 °C) half a century ago.  In this approach, the electrochemical cell is discharged at T₁ and recharged at a different temperature T₂. The electrochemical Seeback effect induces lower charging voltage at T₂ than the discharging voltage at T₁, and thus net electricity is generated as the difference between the discharged and charged energy. This thermal-cycle-like design could lead high efficiency by decoupling electrical conduction and thermal conduction. However, large polarization of electrode materials of TREC has suppressed low temperature thermal energy (<100 °C). Here we demonstrate a new effective TREC to utilize low-grade heat by employing proper materials. The demonstrated system achieved very high efficiency at low temperature range. We believe that the demonstrated system is anticipated to be a good alternative choice of low cost and high efficiency thermal energy harvesting system from various low heat sources such as heat engine system, solar thermal, geothermal, and body heat.