Extension of the primitive model by hydration shells and its impact on the reversible heat production during the buildup of the electric double layer

Abstract

Recently, the reversible heat production during the electric double layer (EDL) buildup in a sodium chloride solution was measured experimentally [Janssen et al., Phys. Rev. Lett. 119, 166002 (2017)] and matched with theoretical predictions from density functional theory and molecular dynamics simulations [Glatzel et al., J. Chem. Phys. 154, 064901 (2021)]. In the latter, it was found that steric interactions of ions with the electrode’s walls, which result in the so-called Stern layer, are sufficient to explain the experimental results. As only symmetric ion sizes in a restricted primitive model were examined, it is instructive to investigate systems of unequal ion sizes that lead to modified Stern layers. In this work, we explore the impact of ion asymmetry on the reversible heat production for each electrode separately. In this context, we further study an extension of the primitive model where hydration shells of ions can evade in the vicinity of electrode’s walls. We find a strong dependence on system parameters such as particle sizes and the total volume taken by particles. Here, we even found situations where one electrode was heated and the other electrode was cooled at the same time during charging, while, in sum, both electrodes together behaved very similarly to the already mentioned experimental results. Thus, heat production should also be measured in experiments for each electrode separately. By this, the importance of certain ingredients that we proposed to model electrolytes could be confirmed or ruled out experimentally, finally leading to a deeper understanding of the physics of EDLs.

Theory and Simulations of Ionic Liquids in Nanoconfinement

“…They even found a situation where one electrode could be heated and the other one cooled during the charging of a two-electrode system. 177 5.2.8. Ion Dynamics in Nanopores.…”

“…Being computationally inexpensive (compared to simulations) and accounting for ion sizes and some correlations, static and dynamic DFTs have become a popular tool to study various phenomena in confined ionic liquids, from anomalous capacitance increase and solvent effects − to charging dynamics − and temperature effects. ,, In this section, we briefly describe the main phenomena studied with DFT. We refer the interested readers to a review by Härtel, which covers the application of DFT to confined ILs before 2017, with a particular focus on technicalities.…”

“…For pores wider than about 4 nm, scriptQ rev becomes relatively small and pore-size independent, because in this case the double-layers practically do not overlap. In follow-up work, Pelagejcev et al showed that hydration shell, ion-size asymmetry, and steric ion–solvent interactions could significantly affect the reversible heat production. They even found a situation where one electrode could be heated and the other one cooled during the charging of a two-electrode system …”

“…In follow-up work, Pelagejcev et al showed that hydration shell, ion-size asymmetry, and steric ion–solvent interactions could significantly affect the reversible heat production. They even found a situation where one electrode could be heated and the other one cooled during the charging of a two-electrode system …”

Modeling the Electric Double Layer at the Liposome Vesicle via Classical Density Functional Theory: Solution of Poisson’s Equations for Curved Membranes

“…The EDL is formed at the contact of the charged surface with an electrolyte solution. − Studies have shown that EDL’s structure is dependent significantly on the type of charged surface curvature, the amount of charge, and electrolyte concentration. In most theoretical studies, the shapes of EDL are usually classified as planar, spherical, and cylindrical based on the charged wall geometry.…”