Diffuse-Layer Capacitance at the Potential of Zero Charge in Binary Mixtures

TL;DR

This paper develops an analytical theory for the diffuse-layer capacitance at the potential of zero charge in binary mixtures, revealing divergences and deviations from single-liquid models near surface instabilities.

Contribution

It introduces a new analytical framework for electric double layer capacitance in binary mixtures, highlighting the effects of preferential solvation and surface instability.

Findings

Capacitance diverges at the phase diagram surface instability

Capacitance differs from single-liquid approximation unless solvation energies are equal

Near instability, capacitance significantly deviates from traditional models

Abstract

The capacitance of the electric double layer has potential applications in supercapacitors, and theoretical investigations of the double-layer capacitance in binary mixtures are important. In this work, we develop the theory of the electric double layer in binary mixtures, and the diffuse-layer capacitance at the potential of zero charge is obtained analytically. Furthermore, we observe a divergence of the capacitance in the phase diagram, suggesting a surface instability. The obtained capacitance is different from that derived using single-liquid approximation unless the preferential solvation energies of cations and anions are the same. When the system is close to the surface instability line, the capacitance strongly deviates from the results of single-liquid approximation.