Reactive Force Field for Proton Diffusion in BaZrO3 using an empirical valence bond approach

TL;DR

This paper develops a reactive force field based on an empirical valence bond approach to simulate proton diffusion in BaZrO3, providing insights into diffusion mechanisms and energetics relevant for solid-oxide fuel cells.

Contribution

It introduces a novel reactive force field model for proton diffusion in BaZrO3 using EVB, validated against quantum mechanical data and experimental activation energies.

Findings

Yttrium doping does not significantly affect hydrogen diffusivity.

The activation energy for diffusion is 0.42 eV, matching experimental data.

Proton trapping near dopants is infrequent, allowing diffusion despite longer residence times.

Abstract

A new reactive force field to describe proton diffusion within the solid-oxide fuel cell material BaZrO3 has been derived. Using a quantum mechanical potential energy surface, the parameters of an interatomic potential model to describe hydroxyl groups within both pure and yttrium-doped BaZrO3 have been determined. Reactivity is then incorporated through the use of the empirical valence bond model. Molecular dynamics simulations (EVB-MD) have been performed to explore the diffusion of hydrogen using a stochastic thermostat and barostat whose equations are extended to the isostress-isothermal ensemble. In the low concentration limit, the presence of yttrium is found not to significantly influence the diffusivity of hydrogen, despite the proton having a longer residence time at oxygen adjacent to the dopant. This lack of influence is due to the fact that trapping occurs infrequently, even when the proton diffuses through octahedra adjacent to the dopant. The activation energy for diffusion is found to be 0.42 eV, in good agreement with experimental values, though the prefactor is slightly underestimated.