Tuning surface acidity of mixed conducting electrodes: Recovery of Si-induced degradation of oxygen exchange rate and area specific resistance.

Metal oxides are an important class of functional materials, and for many applications, ranging from solid oxide fuel/electrolysis cells, oxygen permeation membranes, and oxygen storage materials to gas sensors (semiconducting and electrolytic) and catalysts, the interaction between the surface and oxygen in the gas phase is central. Ubiquitous Si-impurities are known to impede this interaction, commonly attributed to the formation of glassy blocking layers on the surface. Here, we examine the surface oxygen exchange coefficient (kchem ) of Pr0.1 Ce0.9 O2-δ (PCO), a model mixed ionic electronic conductor, via electrical conductivity relaxation measurements, and the area-specific resistance (ASR) by electrochemical impedance spectroscopy. We demonstrate that even low silica levels, introduced by infiltration, depress kchem by a factor 4,000, while the ASR increases 40-fold and attribute this to its acidity relative to that of PCO. We further show the ability to fully regenerate the poisoned surface by the subsequent addition of basic Ca- or Li-species. This ability to not only recover Si-poisoned surfaces by tuning the relative surface acidity of an oxide surface, but subsequently outperform the pre-poisoned response, promises to extend the operating life of materials and devices for which the catalytic oxygen/solid interface reaction is central. This article is protected by copyright. All rights reserved.