Hydrogen diffusion in the proton conductor Gd-doped barium cerate

TL;DR

This study uses density functional theory to analyze proton diffusion mechanisms and energy barriers in Gd-doped BaCeO3, revealing complex pathways and variable barriers unlike simpler perovskites.

Contribution

It provides detailed computational insights into proton diffusion pathways and barriers in Gd-doped BaCeO3, highlighting differences from other perovskites.

Findings

Energy barriers range from 0.02 eV to 0.58 eV.

Inter-octahedral hoppings can be more favorable than intra-octahedral.

No single process is clearly rate-limiting in proton diffusion.

Abstract

The energy landscape and diffusion barriers of protonic defects in Gd-doped BaCeO3, a compound candidate as electrolyte for protonic ceramic fuel cells, have been investigated by density functional theory calculations, starting from a previously computed energy landscape consisting of 16 kinds of stable sites (8 close to dopants and 8 far from them). The simplified string method has been used to determine accurately the Minimum Energy Paths between those sites, that might imply either proton reorientations, intra-octahedral or inter-octahedral hopping mechanisms. At contrast with simple cubic perovskites such as barium stannate or barium zirconate, very different values for energy barriers (from 0.02 eV to 0.58 eV) are found in this highly distorted orthorhombic perovskite, and no specific process appears to be clearly rate-limiting. Some inter-octahedral hoppings (when possible) are found to be more favourable than the intra-octahedral ones, while reorientations exhibit a wide range of energy barriers.