The Differential Capacitance as a probe for the electric double layer structure and the electrolyte bulk composition

Abstract

In this work we theoretically study the differential capacitance of an aqueous electrolyte in contact with a planar electrode, using classical Density Functional Theory, and show how this measurable quantity can be used as a probe to better understand the structure and composition of the electric double layer at play. Specifically, we show how small trace amounts of divalent ions can influence the differential capacitance greatly, and also how small ions dominate its behaviour for high electrode potentials. In this study, we consider primitive model electrolytes, and not only use the standard definition of the differential capacitance, but also derive a new expression from mechanical equilibrium in a planar geometry. This expression reveals explicitly that the first layer of ions near the charged surface is key to its understanding. Our insights might be used as a guide in experiments to better understand the electrolyte-electrode interface as well as the (composition of the) bulk electrolyte.

References in corpus (8)

• Charge fluctuations in nano-scale capacitors
• Differential capacitance of the electric double layer: The interplay between ion finite size and dielectric decrement
• Surface Tension of Electrolyte Interfaces: Ionic Specificity within a Field-Theory Approach
• Charge fluctuations from molecular simulations in the constant-potential ensemble
• Primitive Model Electrolytes in the Near and Far Field: Decay Lengths from DFT and Simulations
• Capacitance and Structure of Electric Double Layers: Comparing Brownian Dynamics and Classical Density Functional Theory
• Fluctuation profiles in inhomogeneous fluids
• Influence of anisotropic ion shape, asymmetric valency, and electrolyte concentration on structural and thermodynamic properties of an electric double layer

Cited by in corpus (5)

• Force density functional theory in- and out-of-equilibrium
• Learning classical density functionals for ionic fluids
• Local measures of fluctuations in inhomogeneous liquids: Statistical mechanics and illustrative applications
• Extension of the primitive model by hydration shells and its impact on the reversible heat production during the buildup of the electric double layer
• In-plane structure of the electric double layer in the primitive model using classical density functional theory