In Situ Measurements on Solid Oxide Fuel Cell Cathodes – Simultaneous X‐Ray Absorption and AC Impedance Spectroscopy on Symmetrical Cells

Abstract

A solid oxide fuel cell in operando is a complex multiphasic entity under electrical polarization and operating at high temperatures. In this work, we reproduce these conditions while studying transition metal redox chemistry in situ at the cathode. This was achieved by building a furnace that allowed for X‐ray absorption near‐edge structure and AC impedance spectroscopy data to be obtained simultaneously on symmetrical cells while at operating temperatures. The cell electrodes consisted of phases from the Ruddlesden–Popper family; La2NiO4+δ, La4Ni3O10–δ, and composites thereof. The redox chemistry of nickel in these cathodes was probed in situ through investigation of changes in the position of the X‐ray absorption K‐edge. An oxidation state reduction (Ni3+ to Ni2+) was observed on heating the cells; this was correlated to changing concentrations of ionic charge carriers in the electrode. Polarizing the cells resulted in dramatic changes to their electrical performance but not to the bulk redox chemistry of the electrode. The implications of this with respect to explaining the polarization behavior are discussed.

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…[ 288,[348][349][350][351][352][353][354] These highorder phases exhibited a better structural stability at elevated temperature and higher electrical conductivity (over 100 S cm −1 ) than those of La 2 NiO 4 phase, as well as a low TEC. [ 349 ] More intriguingly, they may also show an improved ORR activity than La 2 NiO 4 .…”

Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers

“…The bulk composition, crystal and electronic structure may be probed by X-ray and neutron diffraction experiments, and X-ray absorption spectroscopy, respectively. These may be set up in situ together with IS measurements to provide a comprehensive view of the bulk structural changes and electrochemical processes occurring at SOC electrodes 12,13 . Various techniques are used to probe the surface at various depths, including secondary ion mass spectrometry (tens to hundreds of nm) 14,15 , X-ray electron spectroscopy (XPS, 1-10 nm) and low-energy ion scattering (the outer atomic monolayer, i.e.…”

X-ray Absorption under Operating Conditions for Solid-Oxide Fuel Cells Electrocatalysts: The Case of LSCF/YSZ

“…Among synchrotron techniques, X-ray absorption spectroscopy allows one to obtain information about the atomic and electronic structure of the samples, so that it is particularly suited for SOFC electrode materials, often constituted by variable valence elements that can modify their oxidation state and the local structure in dependence of reaction environment and applied potential [6][7][8][9]. Regarding this concern, the development of reliable experimental protocols [10] is essential to obtain significant information on SOFC materials [11][12][13][14]. Among the issues addressed by the above cited authors, Lai et al investigated catalyst poisoning, arguing that deactivation of an LSCF cathode by CO 2 is enhanced under a cathodic bias.…”