title: Membrane-free battery for harvesting low-grade thermal energy.
abstract: Efficient and low-cost systems are desired to harvest the tremendous amount of energy stored in low-grade heat sources (<100 °C). An attractive approach is the thermally regenerative electrochemical cycle (TREC), which uses the dependence of electrode potential on temperature to construct a thermodynamic cycle for direct heat-to-electricity conversion. By varying the temperature, an electrochemical cell is charged at a lower voltage than discharged; thus, thermal energy is converted to electricity. Recently, a Prussian blue analog-based system with high efficiency has been demonstrated. However, the use of an ion-selective membrane in this system raises concerns about the overall cost, which is crucial for waste heat harvesting. Here, we report on a new membrane-free battery with a nickel hexacyanoferrate (NiHCF) cathode and a silver/silver chloride anode. The system has a temperature coefficient of -0.74 mV K(-1). When the battery is discharged at 15 °C and recharged at 55 °C, thermal-to-electricity conversion efficiencies of 2.6% and 3.5% are achieved with assumed heat recuperation of 50% and 70%, respctively. This work opens new opportunities for using membrane-free electrochemical systems to harvest waste heat.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.forename: James
authors.initials: J
authors.lastname: Loomis
authors.forename: Hadi
authors.initials: H
authors.lastname: Ghasemi
authors.forename: Seok Woo
authors.initials: SW
authors.lastname: Lee
authors.forename: Yi Jenny
authors.initials: YJ
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
keywords: TREC; battery; electrochemical systems; low-grade thermal energy; membrane-free; thermally regenerative electrochemical cycle