Low-grade heat having temperatures below 150 °C, which includes waste heat from industrial waste streams, solar heating, geothermal reservoirs, ocean thermal gradients, bio-mass fermentation, and even data centers, provides a major sustainable energy source. Electrochemical thermocells provide a potentially cheaper means to harvest thermal energy than thermoelectrics. These thermocells utilize the tempera-ture dependence of electrode potential to generate electrical power, and redox mediators to transport charge in the electrolyte. Ignoring interfacial charge-transfer resistances and thermal and ionic transport by thermal convection of the electrolyte, the electrolyte in these thermocells functions like semiconductors in conventional thermoelectrics so that the ionic conductivity (σ), thermal conductivity (λ), and Seebeck coefﬁcient (S) of the electrolyte combine to produce the elec-trochemical equivalence of the ZT parameter used for evaluating the performance of thermoelectrics: ZT = σS2T/λ.
- energy harvesting