Reversible Heating in Electric Double Layer Capacitors

A detailed comparison is made between different viewpoints on reversible heating in electric double layer capacitors. We show in the limit of slow charging that a combined Poisson-Nernst-Planck and heat equation, first studied by d’Entremont and Pilon [J. Power Sources 246, 887 (2014)], recovers the temperature changes as predicted by the thermodynamic identity of Janssen et al. [Phys. Rev. Lett. 113, 268501 (2014)], and disagrees with the approximative model of Schiffer et al. [J. Power Sources 160, 765 (2006)] that predominates the literature. The thermal response to the adiabatic charging of supercapacitors contains information on electric double layer formation that has remained largely unexplored.