Correlating Metal-Water Interactions and Double-Layer Capacitance at Gold and Silver: Revisit of Single-Crystal Experiments Using a Unified Theoretical Model

Abstract

We quantify how metal identity and crystallographic orientation shape the electrical double layer (EDL) and differential capacitance (Cdl) in weakly adsorbing electrolytes. The concentration-dependent Cdl curves of Ag(110), Ag(100), Ag(111), and Au(110) in aqueous KPF6, are quantitatively analyzed using the density-potential functional theory (DPFT). The comparative analysis results in four key findings. First, in accordance with conventional understanding, Cdl is dominated by the diffuse layer and is identical for Ag and Au electrodes near their respective potential of zero free charge (pzfc) at the same low electrolyte concentrations. Second, the Cdl sequence of Ag(110)>Ag(100)>Ag(111) at their pzfc at the same higher electrolyte concentration is attributed to facet-dependent water adsorption. Third, under same solution conditions, Ag(110) shows a higher Cdl peak and smaller peak-to-peak spacing than Au(110), reflecting differences in short-range metal-water interaction, metal-ion interaction and electron spillover at the metal surface. Fourth, partial desolvation under strong interfacial fields further reshapes the ionic distribution and lifts the Cdl curves away from the pzfc. Overall, these results map macroscopic capacitance fingerprints onto microscopic EDL structure within a unified DPFT framework.