Issue 12, 2016

New mechanistic insight into the oxygen reduction reaction on Ruddlesden–Popper cathodes for intermediate-temperature solid oxide fuel cells

Abstract

Ruddlesden–Popper (R–P) phase materials have been investigated widely as cathode candidates for IT-SOFCs. However, widespread application of R–P phase cathodes demands further improvement in electrode activity whose progress is hindered by the limited information in the oxygen reduction reaction (ORR). The ORR mechanism for the R–P phase is therefore investigated in this paper using (LaSr)2NiOδ as an example. Accurate characterization of the surface oxygen exchange process is realized by developing thin and dense polycrystalline LSNO layers via a versatile spray-modified pressing method we invented before to avoid perceptible bulk diffusion contribution, surface enrichment and geometry complication. The governing factors of the ORR are identified as oxygen adsorption and incorporation based on the findings in reaction orders from electrochemical impedance spectroscopy (EIS), stoichiometry-related chemical capacitance and intrinsic anisotropic properties. The incorporation rate is proven to drastically depend on the amount of interstitial oxygen Image ID:c6cp00056h-t1.gif. Since the unfilled interstitial sites Image ID:c6cp00056h-t2.gif in the R–P phase serve to accommodate the adsorbed oxygen during incorporation, like vacancies in the perovskite structure Image ID:c6cp00056h-t3.gif, more Image ID:c6cp00056h-t4.gif would seem to suppress the kinetics of this process. In regards to this, for the first time, a physical model is proposed to reconcile the discrepancy between the experimental results and intuitive reasoning. Based on supporting evidence, this model illustrates a possibility of how Image ID:c6cp00056h-t5.gif works to regulate the exchange rate, and how the contradiction between Image ID:c6cp00056h-t6.gif and Image ID:c6cp00056h-t7.gif is harmonized so that the latter in the R–P structure also positively promotes the incorporation rate in the ORR.

Graphical abstract: New mechanistic insight into the oxygen reduction reaction on Ruddlesden–Popper cathodes for intermediate-temperature solid oxide fuel cells

Article information

Article type
Paper
Submitted
04 Jan 2016
Accepted
19 Feb 2016
First published
25 Feb 2016

Phys. Chem. Chem. Phys., 2016,18, 8502-8511

New mechanistic insight into the oxygen reduction reaction on Ruddlesden–Popper cathodes for intermediate-temperature solid oxide fuel cells

W. Li, B. Guan, X. Zhang, J. Yan, Y. Zhou and X. Liu, Phys. Chem. Chem. Phys., 2016, 18, 8502 DOI: 10.1039/C6CP00056H

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