title: Charging-free electrochemical system for harvesting low-grade thermal energy.
abstract: Efficient and low-cost systems are needed to harvest the tremendous amount of energy stored in low-grade heat sources (<100 °C). Thermally regenerative electrochemical cycle (TREC) is an attractive approach which uses the temperature dependence of electrochemical cell voltage to construct a thermodynamic cycle for direct heat-to-electricity conversion. By varying temperature, an electrochemical cell is charged at a lower voltage than discharge, converting thermal energy to electricity. Most TREC systems still require external electricity for charging, which complicates system designs and limits their applications. Here, we demonstrate a charging-free TREC consisting of an inexpensive soluble Fe(CN)6(3-/4-) redox pair and solid Prussian blue particles as active materials for the two electrodes. In this system, the spontaneous directions of the full-cell reaction are opposite at low and high temperatures. Therefore, the two electrochemical processes at both low and high temperatures in a cycle are discharge. Heat-to-electricity conversion efficiency of 2.0% can be reached for the TREC operating between 20 and 60 °C. This charging-free TREC system may have potential application for harvesting low-grade heat from the environment, especially in remote areas.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305;
authors.forename: Seok Woo
authors.initials: SW
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Hadi
authors.initials: H
authors.lastname: Ghasemi
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: James
authors.initials: J
authors.lastname: Loomis
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Daniel
authors.initials: D
authors.lastname: Kraemer
authors.affiliation: Department of Chemical Engineering, Stanford University, Stanford, CA 94305; and.
authors.forename: Guangyuan
authors.initials: G
authors.lastname: Zheng
authors.affiliation: Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305; Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 gchen2@mit.edu yicui@stanford.edu.
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; gchen2@mit.edu yicui@stanford.edu.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
keywords: Prussian blue analog; batteries; nanomaterials; waste heat harvesting