title: "Thermal Charging" Phenomenon in Electrical Double Layer Capacitors.
abstract: Electrical double layer capacitors (EDLCs) are usually charged by applying a potential difference across the positive and negative electrodes. In this paper, we demonstrated that EDLCs can be charged by heating. An open circuit voltage of 80-300 mV has been observed by heating the supercapacitor to 65 °C. The charge generated at high temperature can be stored in the device after its returning to the room temperature, thus allowing the lighting up of LEDs by connecting the "thermally charged" supercapacitors in a series. The underlying mechanism is related to a thermo-electrochemical process that enhances the kinetics of Faradaic process at the electrode surface (e.g., surface redox reaction of functional group, or chemical adsorption/desorption of electrolyte ions) at higher temperature. Effects of "thermal charging" times, activation voltage, rate, and times on "thermally charged" voltage are studied and possible mechanisms are discussed.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Jianjian
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|Department of Mechanical Engineering, The University of Hong Kong , Pokfulam, Hong Kong.
authors.forename: Shien-Ping
authors.initials: SP
authors.lastname: Feng
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, The University of Hong Kong , Pokfulam, Hong Kong.
authors.forename: Nga Yu
authors.initials: NY
authors.lastname: Hau
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Mary
authors.initials: M
authors.lastname: Munro
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Emerald
authors.initials: E
authors.lastname: Ferreira-Yang
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
keywords: Supercapacitor; chemical adsorption/desorption; electrical double layer; surface functional group; surface redox reaction; “thermal charging”