Microstructure of Electrical Double Layers at Highly Charged States

While the traditional Gouy-Chapman-Stern (GCS) model can well describe the differential doublelayer capacitance (<i>C</i> _dl) near the potential of zero charge with several empirical parameters, it is insufficient to capture the <i>C</i> _dl profile in a wide potential range and changes in the <i>C</i> _dl profiles with varying electrolyte cations, anions, and solvent, even for the atomistically smooth Mercury-solution interfaces. The extended data set of <i>C</i> _dl at mercury is then analyzed using modified semiclassical, density-potential functional theoretical (DPFT) models. Our analysis highlights the importance of potential-dependent short-range metal-solvent interactions and ion partial desolvation at highly charged surfaces. With the aid of the modified model, the impact of electrolyte cation, anion, and solvent on the EDL structure can be interpreted in an inherent framework. These insights gleaned from the mercury electrodes have crucial implications for the EDLs at gold, silver, and copper, which are usually highly charged in important electrocatalytic reactions like electrochemical CO₂ reduction.