Nanoconfinement effects on hydrated excess protons in layered materials.

Thin water layers confined between surfaces are known for their surprising properties. Layered minerals, such as mackinawite, are naturally occurring systems where water is known to intercalate. Here we report, based on ab initio simulations, how excess protons can be hosted by the resulting nanostructured water film depending on the mackinawite interlayer distance. Even extreme nanoconfinement due to the mackinawite sheets is shown to not affect the dynamical nature of the topological defect, thus not localizing the excess protons but rather conserving the efficient structural (Grotthuss) diffusion process known in bulk water. Yet, depending on the width of the slit pore, the defect can bridge the bilayer water structure, thus forcing the excess proton into the water-depleted region between the bilayers.