The oxygen reduction reaction in solid oxide fuel cells: From kinetic parameters measurements to electrode design

Julián Ascolani-Yael*, Alejandra Montenegro-Hernández, Diana Garcés, Quinyuan Liu, Hongqian Wang, Kyle Yakal-Kremski, Scott Barnett, Liliana Mogni

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The research and development of new Solid Oxide Fuel Cell cathode materials is an area of intense activity. The kinetic coefficients describing the O2-reduction mechanism are the O-ion diffusion (Dchem) and the O-surface exchange coefficients (kchem). These parameters are strongly dependent on the nature of the material, both on its bulk and surface atomic and electronic structures. This review discusses the method for obtaining the kinetic coefficients through the combination of electrochemical impedance spectroscopy with focused ion-beam 3D tomography measurements on porous electrodes (3DT-EIS). The data, together with oxygen non-stoichiometry thermodynamic data, is analysed using the Adler-Lane-Steele model for macro-homogeneous porous electrodes. The results for different families of oxides are compared: single- and double-layered perovskites with O-vacancies defects, based on La-Sr cobalt ferrites (La0.6Sr0.4Co1-xFexO3-δ, x = 0.2 and 0.8) and La/Pr-Ba cobaltites (La0.5-xPrxBa0.5CoO3-δ, x = 0.0, 0.2 and 0.5), as well as Ruddlesden-Popper nickelates (Nd2NiO4 +δ) with O-interstitial defects. The analysis of the evolution of molar surface exchange rates with oxygen partial pressure provides information about the mechanisms limiting the O2-surface reaction, which generally is dissociative adsorption or dissociation-limited. At 700 C in air, the La-Ba cobaltite structures, La0.5-xPrxBa0.5CoO3-δ, feature the most active surfaces (kchem≃0.5-1 102 cm.s1), followed by the nickelate Nd2NiO4 +δ and the La-Sr cobalt ferrites, with kchem≃1-5 105 cm.s1. The diffusion coefficients Dchem are higher for cubic perovskites than for the layered ones. For La0.6Sr0.4Co0.8Fe0.2O3-δ and La0.6Sr0.4Co0.2Fe0.8O3-δ, Dchem is 2.6 106 cm2.s1 and 5.4 107 cm2.s1, respectively. These values are comparable to Dchem = 1.2 106 cm2.s1, observed for La0.5Ba0.5CoO3-δ. The layered structure drastically reduces the O-ion bulk diffusion, e.g. Dchem = 1.3 108 cm2.s1 for the Pr0.5Ba0.5CoO3-δ double perovskite and Dchem≃2 107cm2.s1 for Nd2NiO4 +δ. Finally, the analysis of the time evolution of the electrodes shows that the surface cation segregation affects both the O-ion bulk diffusion and the surface exchange rates.

Original languageEnglish (US)
Article number042004
JournalJPhys Energy
Volume2
Issue number4
DOIs
StatePublished - Oct 2020

Keywords

  • Cathode
  • O-ion diffusion coefficient
  • Solid oxide fuel cell
  • Surface exchange

ASJC Scopus subject areas

  • Energy(all)
  • Materials Chemistry
  • Materials Science (miscellaneous)

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