Role of microstructure on electrode operating mechanisms for mixed ionic electronic conductors: From synchrotron-based 3D reconstruction to electrochemical modeling

A typical La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) electrode was reconstructed by X-ray nanotomography. The new Nano Imaging beamline ID16A-NI of the European Synchrotron Radiation Facility (ESRF) was used to conduct the investigation. Particular attention was paid to prepare samples with a well-adapted shape for the tomographic experiments. The optimized sample preparation and new experimental set-up enables an improved spatial resolution of about 50 nm to be obtained in the electrode reconstruction of 51.2 x 25.6(2) x pi mu m(3). The LSCF microstructural properties were quantified in the 3D volume and used as input data in a dynamic micro scale electrochemical model. The numerical tool includes two parallel reaction pathways with an oxygen exchange at the LSCF/gas surface and a charge transfer at the electrode TPB. Electrochemical impedances were computed in the time domain at OCP, as well as under anodic and cathodic polarizations. Simulations allowed the microstructural parameters to be linked to the basic mechanisms of electrode operation according to the electrode polarization. A microstructural sensitivity analysis was performed on the single-phase LSCF and LSCF-CGO composite electrodes in order to identify the parameters that impact most the electrode response. It was found that the LSCF-CGO composite presents much higher performances compared to the LSCF single phase electrode especially in anodic polarization. (C) 2016 Elsevier B.V. All rights reserved.