Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Charged Soft Matter, Polyelectrolytes and Ionic Liquids II

CPP 50.7: Vortrag

Mittwoch, 14. März 2018, 16:45–17:00, C 243

Temperature dependence and thermal response of electric double layer capacitors — •Mathijs Janssen — Max Planck Institute for Intelligent Systems, Stuttgart, Germany

Where surfaces of charged electrodes meet fluids that contain mobile ions, so-called electric double layers (EDLs) form to screen the electric surface charge by a diffuse cloud of counterionic charge.

In this talk, we discuss the intricate interplay between temperature and EDL characteristics. First, we show that varying the electrolyte temperature gives rise to a temperature-induced surface charge variation [1]. Vice versa, variation of the electrode potential of a thermally insulated EDL capacitor gives rise to a charge-induced temperature variation [2]. Besides irreversible (bulk) Joule heating, this temperature variation is sourced by the reversible ion rearrangements that occur during EDL formation: heating upon charging, and cooling upon discharging. We derive a thermodynamic identity for this isentropic-heating-by-charging effect, and compare to the slow-charging thermal behavior of a Nernst-Planck model [2]. We finally argue that the thermal response to charging in fact contains valuable information on the EDL; we deduce the entropic part of the grand potential from the tiny temperature variations that can be measured during charging and discharging an EDL capacitor [3].

[1] M. Janssen et al., Phys. Rev. Lett. 113, 268501 (2014)

[2] M. Janssen and R. van Roij, Phys. Rev. Lett. 118, 096001 (2017)

[3] M. Janssen et al., Phys. Rev. Lett. 119, 166002 (2017)