Direct Measurement of Oxygen Mass Transport at the Nanoscale

Abstract

Tuning oxygen mass transport properties at the nanoscale offers a promising approach for developing high performing energy materials. A number of strategies for engineering interfaces with enhanced oxygen diffusivity and surface exchange has recently been proposed. However, the origin and the local magnitude of such local effects remain largely undisclosed to date. This is ascribed to the lack of direct measurement tools with sufficient resolution. In this work, we use atom probe tomography with sub-nanometric resolution to study oxygen mass transport on oxygen-isotope exchanged thin films of lanthanum chromite. We present a direct visualization of nanoscaled highly conducting oxygen incorporation pathways along grain boundaries, with reliable quantification of fast oxygen diffusion at grain boundaries and correlative link to local chemistries. Combined with finite element simulations of the precise 3D nanostructure, we quantify an enhancement in the grain boundary oxygen diffusivity and in the surface exchange coefficient of lanthanum chromite of about 4 and 3 orders of magnitude, respectively, compared to the bulk. This remarkable increase of the oxygen diffusivity in an interface-dominated material is unambiguously attributed to grain boundary conduction highways thanks to the use of a powerful technique that can be straightforwardly extended to the study of currently inaccessible multiple nanoscale mass transport phenomena.