Rational design of perovskite ferrites as high-performance proton-conducting fuel cell cathodes

Proton migration barriers in BaFeO3−δ – insights from DFT calculations

“…In ref. [28] , a migration barrier for BaFeO 3 of 0.21 eV was calculated, which is virtually the same as the average value of 0.22 eV obtained in the present study for BaFeO 3 . The range of available literature values strongly overlaps with the values obtained for BaFeO 3-δ in the present study (0.10-0.28 eV) although some of the reported values are higher (e.g.…”

“…7 demonstrates that the migration barrier for proton transfer is very sensitive towards structural and electronic perturbation by oxygen vacancies, even if oxygen ions opposite to vacancies are not directly involved, as shown in Figure 7b. The literature available so far on DFT-based proton migration barriers in triple conducting perovskites shows that proton migration is very sensitive towards the crystallographic structure (layers in Ruddlesden-Popper [26] or Brownmillerite [27] phases) as well as the cation composition [22,23,24,25,28] of the perovskite. The barriers in the literature span a wide range of 0.2 to 0.6 eV for various perovskites [22,23,24,25,28] (excluding outliers of 0.03 [22] and 1.52 eV [24] corresponding to specific chemical environments).…”

“…[21] Some proton migration barriers in triple conducting oxides are obtained from density functional theory (DFT) calculations, e.g. [22,23,24,25,26,27,28] . However, a systematic investigation as a function of cation composition, and correlations with other materials parameters (certain atom distances etc.)…”

“…28 eV, with an average barrier of 0.22 eV. The analysis of geometrical changes and O-H chemical bonding during individual proton transfer events indicated that the proton transfer is a two-step process: in the early stage the energy change is mainly governed by the mutual approach of donor and acceptor oxygen ions (the O-H bond is hardly stretched), and in the second stage near the transition state the O-H bond is broken, further increasing the energy.…”

Understanding and mitigating A-site surface enrichment in Ba-containing perovskites: a combined computational and experimental study of BaFeO3

“…This is a clear shortcoming in the literature, especially considering that Ba-based perovskites have recently received a great deal of attention as high-performance cathodes for PCFCs. [44][45][46][47][48][49][50] In particular, it is still unknown whether the surface Ba excess can be tuned using strain engineering. For instance, since Ba 2+ (1.35 Å) is larger than Sr 2+ (1.18 Å), 51 a longer Ba-O bond than that of Sr-O is expected in Ba-based perovskites.…”