Aqueous biphase-boosted liquid-state thermocell for continuous low-grade heat harvesting

Low-grade heat (<100 °C) is widespread and vast potential source of power to be exploited. Liquid-state thermocell (LTC) has provided an alternative approach to directly convert low-grade heat into electricity to help carbon emission reduction. Seebeck coefficient (Se), electrical conductivity (σ) and thermal conductivity (κ) are the three interdependent key factors determining the performance of LTCs. However, most of the previous researches focused on improving Se and σ while ignoring the factor κ. Here, we introduce an aqueous biphasic system as solvent to fabricate electrolytes for LTCs. The aqueous biphasic electrolytes can not only offer different solvation environment near the electrodes, but also suppress the thermal convection, hence result in improved Se and reduced κ. With the aqueous biphasic electrolyte of K3Fe(CN)6/K4Fe(CN)6 as the redox couple, the Se of the LTC was doubled and the output power was improved over 5 times. Furthermore, with the help of porous graphite felt as electrode material, the output power can be improved over 7 times. This work provides a new pathway for the development of high-performance LTC to harvest low-grade heats.