Effect of the metallicity on the capacitance of gold - aqueous sodium chloride interfaces

TL;DR

This study demonstrates that adjusting the Gaussian charge width in molecular dynamics simulations effectively captures the influence of metallicity on gold's electrode-electrolyte interface capacitance, aligning with experimental and ab initio results.

Contribution

It introduces a method to tune gold's metallicity in simulations by modifying Gaussian charge widths, improving the accuracy of capacitance predictions.

Findings

Capacitance increases with Gaussian width, matching ab initio results.

No structural change in water despite capacitance increase.

Na+ ions adsorb on the surface, forming complexes at high metallicity.

Abstract

Electrochemistry experiments have established that the capacitance of electrode-electrolyte interfaces is much larger for good metals such as gold and platinum than for carbon-based materials. Despite the development of elaborate electrode interaction potentials, to date molecular dynamics simulations were not able to capture this effect. Here we show that changing the width of the Gaussian charge distribution used to represent the atomic charges in gold is an effective way to tune its metallicity. Larger Gaussian widths lead to a capacitance of aqueous solutions (pure water and 1 molar NaCl) in good agreement with recent ab initio molecular dynamics results. For pure water, the increase in the capacitance is not accompanied with structural changes, while in the presence of salt the Na$^+$ cations tend to adsorb significantly on the surface. For a strongly metallic gold electrode, these ions can even form inner sphere complexes on hollow sites of the surface.