Stripping away ion hydration shells in electrical double-layer formation: Water networks matter

SR Alfarano and S Pezzotti and CJ Stein and Z Lin and F Sebastiani and S Funke and C Hoberg and I Kolling and CY Ma and K Mauelshagen and T Ockelmann and G Schwaab and L Fu and JB Brubach and P Roy and M Head- Gordon and K Tschulik and MP Gaigeot and M Havenith, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 118, e2108568118 (2021).

DOI: 10.1073/pnas.2108568118

The double layer at the solid/electrolyte interface is a key concept in electrochemistry. Here, we present an experimental study combined with simulations, which provides a molecular picture of the double-layer formation under applied voltage. By THz spectroscopy we are able to follow the stripping away of the cation/anion hydration shells for an NaCl electrolyte at the Au surface when decreasing/increasing the bias potential. While Na+ is attracted toward the electrode at the smallest applied negative potentials, stripping of the Cl- hydration shell is observed only at higher potential values. These phenomena are directly measured by THz spectroscopy with ultrabright synchrotron light as a source and rationalized by accompanying molecular dynamics simulations and electronic-structure calculations.

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