Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures

TL;DR

This study visualizes and analyzes oxygen transport pathways in Sr-doped lanthanum ferrite and heterostructures, revealing complex mechanisms influenced by structural, chemical, and interfacial factors crucial for catalysis and fuel cell applications.

Contribution

It combines isotopic tracing, atom probe tomography, and DFT calculations to directly visualize and understand oxygen diffusion pathways and mechanisms in perovskite heterostructures.

Findings

Multiple oxygen transport pathways identified in heterostructures

Interfacial reactions significantly influence oxygen mobility

DFT explains thermodynamic and kinetic factors affecting oxygen exchange

Abstract

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g. Ni- and Cr-based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real-world environments. Here we use isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory (DFT) calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. Our results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.