Time-reduced thermocapacitive cycle with planar supercapacitor for harvesting low-grade thermal energy

Abstract

Most of the energy wasted in the industry has been discarded in the form of low-grade heat (< 130 ℃) energy. However, as the technology for converting thermal energy into electrical energy is developed, thermoelectric power generation with low-grade heat is attracted. Although the thermoelectric materials and the thermogalvanic cells were conducted using thermoelectric gradients, low efficiency was a problem due to heat loss generated in the device itself. The heat loss due to heat gradients was solved by a thermally regenerative electrochemical cycle (TREC) that produced electrical energy through temperature changes in the electrochemical cell. However, there was a problem with wasted thermal energy in that it took at least an hour to charge voltage depending on the temperature change during cycling. In this study, a planar supercapacitor fabricated by MEMs with electric double layers was applied to the TREC system to reduce thermal charging time effectively. As a result, the TREC system with the planar supercapacitor was operated for 102 s, yielding 1.56 mJ/g of specific energy per cycle. The efficiency was performed as 10.47% under 100% of the heat recuperation. The study is expected to develop low-grade heat emitted from power generation such as Rankin cycle or fuel cells.