The effect of sub-surface strontium depletion on oxygen diffusion in La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ

Abstract

The immediate surface and sub-surface composition of heat treated La0.6Sr0.4Co0.2Fe0.8O3-δ samples was measured by ion beam analysis and compared to oxygen transport properties over the same depth scale. Consistent with...

Visualizing local fast ionic conduction pathways in nanocrystalline lanthanum manganite by isotope exchange-atom probe tomography

“…A progressive decrease of the Mn content towards the free surface of the film ( Z = 0) is highlighted, alongside a very strong accumulation of Sr and La in the sub-surface region ( Z < 10 nm). 38,39 Notably, the thickness of such a region, characterized by different stoichiometry, corresponds to the oxygen isotope accumulation area highlighted in Fig. 1 and can therefore be tentatively accounted for the local low described previously.…”

“…16,35,36 Improved models will be of utmost importance to understand and qualify the recently reported tendency of dopant de-mixing in MIEC materials. 37…”

Investigating oxygen reduction pathways on pristine SOFC cathode surfaces by in situ PLD impedance spectroscopy

“…This degradation is partially reversible at low oxygen partial pressure, hence backwards recorded curves contain inaccuracies at lower p (O 2 ) (more information is presented in S.I.3†). As the atmosphere inside the PLD chamber is very clean, we assume, that a large part of these degradation phenomena at higher pressures is related to Sr migration to the surface due to intrinsic inequilibria in the crystal lattice (details of segregation mechanisms have been investigated by Niania et al 30,31 ), which also explains the slight differences between the materials, as different segregation dynamics in different materials can be expected. 49 Fig.…”

“…They pose, in combination with the reaction order with regard to oxygen partial pressure, the basis for a reaction mechanism analysis. However, surfaces investigated in such experiments are usually far from undisturbed or pristine, for example due to degradation phenomena like Sr-segregation 26–31 or due to various poisoning effects, 32–35 potentially obscuring the true capabilities and properties of SOFC cathode materials.…”

Simulation of the Electrochemical Impedance in a Three-Dimensional, Complex Microstructure of Solid Oxide Fuel Cell Cathode and Its Application in the Microstructure Characterization

“…However, conventional high temperature SOFCs run at 800–1000°C, which makes their operation and maintenance highly cost-ineffective ( Gao et al, 2016 ). The operating temperature has been reduced by the use of electrocatalytically active mixed ion-electron conducting (MIEC) cathodes such as (La,Sr) (Co,Fe)O 3–δ (LSCF) ( Hwang et al, 2005 ; Liu et al, 2013 ; Niania et al, 2020 ) and Sr(Ti,Fe)O 3–δ (STF) ( Yoo and Bouwmeester, 2012 ; Perry et al, 2015 ; Nenning et al, 2017 ), wherein the oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs) occur over the entire surface. To take advantage of this behavior, SOFC cathodes are designed to have complex and porous microstructures with a large specific surface area; however, such designs result in a high degree of tortuosity for ion transport, which limits the performance of SOFCs.…”