Proton Dynamics at the Water–Silica Interface via Dissociative Molecular Dynamics

Abstract

A robust and accurate dissociative potential that reproduces the structural and dynamic properties of bulk and nanoconfined water, and proton transport similar to ab initio calculations in bulk water, is used for reactive molecular dynamics simulations of the proton dynamics at the silica/water interface. The simulations are used to evaluate the lifetimes of protonated sites at the interfaces of water with planar amorphous silica surfaces and cylindrical pores in amorphous silica with different densities of water confined in the pores. In addition to lifetimes, the donor/acceptor sites are evaluated and discussed in terms of local atomistic structure. The results of the lifetimes of the protonated sites, including H3O+, SiOH, SiOH2+, and Si–(OH+)–Si sites, are considered. The lifetime of the hydronium ion, H3O+, is considerably shorter near the interface than in bulk water, as are the lifetimes of the other protonated sites. The results indicate the beneficial effect of the amorphous silica surface in enhancing proton transport in wet silica as seen in electrochemical studies and provide the specific molecular mechanisms.