Differential capacitance of an electrical double layer with asymmetric ion sizes in the presence of hydration interactions

Author(s)

Bossa, V, Guilherme ; Caetano, Daniel L. Z. ^[1] ; de Carvalho, Sidney J. ^[1] ; May, Sylvio ^[2]

Affiliation

^[1] Bossa, Guilherme, V, Sao Paulo State Univ UNESP, Dept Phys, Inst Biosci Humanities & Exact Sci, Sao Jose Do Rio Preto - Brazil

^[2] North Dakota State Univ, Dept Phys, Fargo, ND 58108 - USA

• Document type: Journal article
• Source: Electrochimica Acta; v. 321, OCT 20 2019.
• Web of Science Citations: 0

Abstract

The differential capacitance is a fundamental property of an electrical double layer and thus important for the development of more efficient and environment-friendly energy storage devices. In addition to the bare electrostatic interactions, the differential capacitance is affected by a complex interplay of ion-specific effects that arise from ion size, shape, and hydration. We employ Monte Carlo simulations to calculate the differential capacitance for size-asymmetric spherical ions, thereby modeling hydration-mediated interactions using Yukawa pair potentials. We also propose a corresponding mean-field theory that includes ion-specific Yukawa pair potentials and accounts for ion size mismatch on the basis of a recently proposed lattice model. Comparison of the two approaches - Monte Carlo simulations and mean-field theory - yields qualitative agreement, irrespective of ion size and size mismatch between cations and anions. The agreement includes the regime of weakly charged electrodes, where we find a growing differential capacitance with growing ion sizes, a behavior that is not consistent with the widely used Stern layer concept. Hence, our study reinforces the predictive power of mean-field theory, but only when the influence of correlations due to excluded volume interactions is diminished by the presence of soft, hydration-mediated ion-ion interactions. (C) 2019 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 17/21772-2 - Extensions of the Poisson-Boltzmann Theory to the study of the differential capacitance of an electrical double layer
• Grantee: Guilherme Volpe Bossa
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/01841-2 - Computational Simulation Studies on the Interaction Between Polyelectrolytes and Macromolecules
• Grantee: Sidney Jurado de Carvalho
• Support Opportunities: Regular Research Grants