Fig. 2: Ion distribution.
From: Molecular-scale insights into the electrical double layer at oxide-electrolyte interfaces
a Schematic of the Gouy-Chapman-Stern (GCS) model of the electric double layer (EDL): the outer Helmholtz plane (OHP) separates the EDL into Stern and diffuse layers. Within the Stern layer, the inner Helmholtz plane (IHP) is defined by the distance at which ions specifically adsorb. b Ion density distributions as functions of distance \(\Delta z=z-{z}_{{{\rm{surface}}}}\) from the solid surface, obtained from DPLR simulations of anatase (101) in contact with different electrolytes; the position of the solid surface, \({z}_{{{\rm{surface}}}}\), corresponds to the average position of the O2c sites. Besides the IHP predicted by the GCS model, these simulations reveal two additional ionic density peaks within the Stern layer, which we define as the intermediate Helmholtz planes (IMHPs). The inset in b amplifies the small IMHP1 peak in the neutral system. The computed ion densities are averaged over the two interfaces in the supercell. All results and error bars were derived from simulations using two independent DPLR models. c–e Illustrative snapshots of the microscopic structures of IHP, IMHP1, and IMHP2. Color code: purple (Na+), green (Cl-), white (H), light red (O in water or water ions), dark red (O in TiO2), and gray (Ti). Lines between ions and neighboring oxygens indicate distances smaller than the ionic hydration shell radius. Dashed blue lines indicate hydrogen bonds between water and surface O2c. For visualization purposes, only the most relevant atoms are shown. Source data are provided as a Source Data file.
