Dresden 2026 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 13: Solid-liquid interfaces: Reactions and electrochemistry I
O 13.4: Vortrag
Montag, 9. März 2026, 15:45–16:00, TRE/PHYS
Ion-specific charge transfer and capacitance in the compact double layer of solvated cations at metal electrodes — •Fabiola Dominguez Flores, Axel Groß, and Wolfgang Schmickler — Institute of Theoretical Chemistry, Ulm University, 89081 Ulm, Germany
A molecular-scale understanding of the compact double layer is essential for fundamental electrochemistry. Using density-functional theory with a hybrid implicit-explicit solvation model, we investigate the adsorption of solvated cations (K+, Na+, Ca2+, Mg2+) on metal electrodes. This approach captures the local hydration structure while modeling a dilute electrolyte where no diffuse layer forms. Our results reveal two distinct physical regimes: alkali ions retain their unit charge, while divalent ions exhibit substantial partial charge transfer, directly quantified by Bader analysis. This charge transfer governs the interfacial capacitance, which we calculate to be 10-20 µF cm−2, in excellent agreement with experiment. We demonstrate that the electrosorption valency equals the negative of this partial charge. Interpreting these results with a parallel-plate model yields an effective dielectric constant dictated by the polarizabilities of the metal and the water layer. This work provides fundamental microscopic insight into how ion-specific electronic interactions control the properties of the electrochemical double layer.
Keywords: cations; weak adsorption; electrochemical double layer; electrosorption