Structured solvent on a split electron tail: A semiclassical theory of electrified metal-solution interfaces

We develop a comprehensive semiclassical continuum theory of electronic response and structured solvents at electrified metal-solution interfaces. The approach combines an orbital-free density-functional theory of electrons on the metal side with a statistical field theory of a structured electrolyte solution within a grand canonical framework. The resulting grand potential of the entire electrical double layer (EDL) is a hybrid functional of particle density, including metal electrons and classical solution particles, electric potential, and solvent polarization, referred to as density-potential-polarization functional theory (DPPFT). The DPPFT captures major atomistic phenomena within the EDL, including electron spillover, spatially damped oscillations in solvent polarization and electric potential extending toward the bulk solution, and the layered structure of ions. Based on DPPFT, an EDL model for the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <a:mi>Ag</a:mi> <a:mo stretchy="false">(</a:mo> <a:mn>110</a:mn> <a:mo stretchy="false">)</a:mo> </a:math> - <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <f:msub> <f:mi>KPF</f:mi> <f:mn>6</f:mn> </f:msub> </f:math> aqueous solution interface is parameterized using experimental data for the double-layer capacitance (). The calibrated model is employed to study the influence of electronic, ion, and solvent properties on EDL structure. profiles at different crystal faces and in various electrolyte solutions are rationalized by the model coherently. We reveal that intensified ion layering enhances the capacitance at the potential of zero charge and narrowed ionic peaks in the profile. Contrary to classical models, the DPPFT allows coions to have appreciable densities near the metal surface, with their magnitudes depending on the local solvent structure and the correlation strength between ions and solvent. All in all, the presented framework provides a holistic and computationally efficient approach for atomistic-level modeling of EDLs under constant-potential conditions.