Improving Accuracy of Electrochemical Capacitance and Solvation Energetics in First-Principles Calculations

TL;DR

This paper introduces the NESS model, a new continuum solvation approach that accurately predicts electrochemical capacitance features of metal-electrolyte interfaces, addressing limitations of previous models.

Contribution

The paper develops the NESS model, incorporating dielectric and ionic nonlinearities, to improve first-principles electrochemical calculations of metal surfaces in aqueous electrolytes.

Findings

Successfully reproduces experimental capacitance features of Ag(100)

Identifies key characteristics for effective electrochemical solvation models

Demonstrates limitations of previous solvation models

Abstract

Reliable first-principles calculations of electrochemical processes require accurate prediction of the interfacial capacitance, a challenge for current computationally-efficient continuum solvation methodologies. We develop a model for the double layer of a metallic electrode that reproduces the features of the experimental capacitance of Ag(100) in a non-adsorbing, aqueous electrolyte, including a broad hump in the capacitance near the Potential of Zero Charge (PZC), and a dip in the capacitance under conditions of low ionic strength. Using this model, we identify the necessary characteristics of a solvation model suitable for first-principles electrochemistry of metal surfaces in non-adsorbing, aqueous electrolytes: dielectric and ionic nonlinearity, and a dielectric-only region at the interface. The dielectric nonlinearity, caused by the saturation of dipole rotational response in water, creates the capacitance hump, while ionic nonlinearity, caused by the compactness of the diffuse layer, generates the capacitance dip seen at low ionic strength. We show that none of the previously developed solvation models simultaneously meet all these criteria. We design the Nonlinear Electrochemical Soft-Sphere solvation model (NESS) which both captures the capacitance features observed experimentally, and serves as a general-purpose continuum solvation model.