Role of ion hydration for the differential capacitance of an electric double layer

Autor(es)

Caetano, Daniel L. Z. ; Bossa, Guilherme V. ; de Oliveira, Vinicius M. ; Brown, Matthew A. ; de Carvalho, Sidney J. ; May, Sylvio

• Tipo de documento: Artigo Científico
• Fonte: Physical Chemistry Chemical Physics; v. 18, n. 40, p. 27796-27807, OCT 28 2016.
• Citações Web of Science: 8

Resumo

The influence of soft, hydration-mediated ion-ion and ion-surface interactions on the differential capacitance of an electric double layer is investigated using Monte Carlo simulations and compared to various mean-field models. We focus on a planar electrode surface at physiological concentration of monovalent ions in a uniform dielectric background. Hydration-mediated interactions are modeled on the basis of Yukawa potentials that add to the Coulomb and excluded volume interactions between ions. We present a mean-field model that includes hydration-mediated anion-anion, anion-cation, and cation-cation interactions of arbitrary strengths. In addition, finite ion sizes are accounted for through excluded volume interactions, described either on the basis of the Carnahan-Starling equation of state or using a lattice gas model. Both our Monte Carlo simulations and mean-field approaches predict a characteristic double-peak (the so-called camel shape) of the differential capacitance; its decrease reflects the packing of the counterions near the electrode surface. The presence of hydration-mediated ion-surface repulsion causes a thin charge-depleted region close to the surface, which is reminiscent of a Stern layer. We analyze the interplay between excluded volume and hydration-mediated interactions on the differential capacitance and demonstrate that for small surface charge density our mean-field model based on the Carnahan-Starling equation is able to capture the Monte Carlo simulation results. In contrast, for large surface charge density the mean-field approach based on the lattice gas model is preferable. (AU)

• Processo FAPESP: 15/03549-9 - Interações mediadas por solvente em soluções eletrolíticas
• Beneficiário: Daniel Lucas Zago Caetano
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Doutorado