Revealing timescale-dependent oxygen vacancy distributions in solid oxide fuel cell electrodes using frequency-resolved X-ray absorption (FR-XAS)

TL;DR

This paper introduces a novel frequency-resolved X-ray absorption imaging technique that captures spatially and temporally resolved oxygen vacancy distributions in solid oxide fuel cell electrodes, enabling direct analysis of diffusion and reaction kinetics.

Contribution

The study develops and demonstrates a new FR-XAS method for operando imaging of defect distributions, revealing timescale-dependent behaviors in SOFC cathodes.

Findings

First experimental visualization of defect distributions linked to impedance components

Extraction of diffusion and kinetic parameters from spatially resolved data

Identification of timescale-dependent oxygen vacancy behaviors

Abstract

Development of materials for electrochemical energy conversion requires a deep understanding of the factors governing chemical and physical rates at submicron length scales. Many workers have sought to develop chemically sensitive in situ or operando imaging techniques targeting these length scales. However, current methods focus on steady-state or stepwise response. To probe electrode processes both spatially and temporally, we have developed a frequency-resolved implementation of X-ray absorption imaging (FR-XAS) that can measure local electrochemical response in operando during a global sinusoidal impedance measurement. Frequency-resolved 1-D images of the oxygen vacancy distribution in a thin film SOFC cathode material ($La_{1-x}Sr_xCoO_{3- \delta}$) reveal, for the first time experimentally, the defect concentrations associated with a Warburg and Gerischer impedance. Analysis of these images allows direct extraction of diffusion and kinetic rate parameters, independent of the global impedance.