Structure of the electrical double layer at the ice-water interface

Area of Science:

• Geochemistry
• Surface Chemistry
• Electrochemistry

Background:

• The ice-water interface possesses protonation/deprotonation sites, acting as adsorption centers for aqueous ions.
• An electrical double layer (EDL) is expected at the ice-water interface, analogous to metal oxide-water interfaces.

Purpose of the Study:

• To modify existing EDL models for the ice-water interface.
• To predict surface charge, potential, and ion occupancy using a surface complexation model.

Main Methods:

• Utilized a surface complexation model.
• Constrained equilibrium constants using literature zeta potential measurements of ice in brines (varying strength and pH).

Main Results:

• Cation adsorption equilibrium constant is >5 orders of magnitude larger than others, dominating at low salinity.
• Deprotonated OH sites are slightly more abundant than dangling O sites.
• Surface charge densities are ~±0.001 C/m², negative at pH 6-9.
• Over 99% of counterions are in the Stern layer at pH 6-9.

Conclusions:

• The cation adsorption reaction is the primary driver of surface charge at the ice-water interface.
• The abundance of deprotonated OH sites aligns with previous research.
• Negligible diffuse layer polarization and Stern layer electrical conduction are predicted due to counterion distribution and mobility.