Hybrid density-potential functional theory of electric double layers

We present a field theoretic derivation for the free energy of the electrolyte solution. A reference system is introduced to describe non-electrostatic interactions, notably hard-sphere interactions, between charged particles in the electrolyte solution. The reference system is described by the Bikerman theory - a local density approximation, and the fundamental measure theory (FMT) - a nonlocal density approximation. Combining the classical part for charged particles in electrolyte solution and a quantum mechanical part for interacting electrons, we obtain a hybrid density-potential functional for the grand canonical potential of the electric double layer (EDL). Variation analysis of the hybrid density-potential functional leads to two controlling equations in terms of the electron density and the electric potential, respectively. Numerical implementation of the developed model is demonstrated for a simple EDL without specific adsorption. Particularly, oscillating density of counterions occurs near the metal surface when the FMT is used for the reference system. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study presents a field theoretic derivation for the free energy of electrolyte solution, introducing a reference system to describe non-electrostatic interactions between charged particles. By combining classical and quantum mechanical parts, a hybrid density-potential functional for the electric double layer grand canonical potential is obtained. Numerical implementation demonstrates the model's effectiveness, particularly showing oscillating density of counterions near the metal surface when using the FMT for the reference system.