High proton conductivity state of water in nanoporous materials

Abstract

A simple model has been proposed for water confined in nanochannels of a porous material, where the proton conductivity is six orders of magnitude higher than the value for bulk water. The key concept of the model is topological inconsistency of the ice rules with ordering of interface molecules, which results in the formation of excess charge carriers near the interface and in a sharp increase in the proton conductivity of water confined in channels with diameters of about several nanometers as compared to bulk water. Numerical estimates within our model are in quantitative agreement with measured proton conductivities of nanoporous materials with different chemical compositions, degrees of crystallinity, and morphologies of the structure. The model gives a useful scheme for the interpretation of proton transport in confined water and provides recommendations for the fabrication of nanoporous materials with a high proton conductivity.