Structural and Electrochemical Properties of Physisorbed and Chemisorbed Water Layers on the Ceramic Oxides Y₂O₃, YSZ, and ZrO₂

Abstract

A combination of operando Fourier transform infrared spectroscopy, operando electrochemical-impedance spectroscopy, and moisture-sorption measurements has been exploited to study the adsorption and conduction behavior of H2O and D2O on the technologically important ceramic oxides YSZ (8 mol % Y2O3), ZrO2, and Y2O3. Because the characterization of the chemisorbed and physisorbed water layers is imperative to a full understanding of (electro-)catalytically active doped oxide surfaces and their application in technology, the presented data provide the specific reactivity of these oxides toward water over a pressure-and-temperature parameter range extending up to, e.g., solid-oxide fuel cell (SOFC)-relevant conditions. The characteristic changes of the related infrared bands could directly be linked to the associated conductivity and moisture-sorption data. For YSZ, a sequential dissociative water ("ice-like" layer) and polymeric chained water ("liquid-like") water-adsorption model for isothermal and isobaric conditions over a pressure range of 10(-5) to 24 mbar and a temperature range from room temperature up to 1173 K could be experimentally verified. On pure monoclinic ZrO2, in contrast to highly hydroxylated YSZ and Y2O3, a high surface concentration of OH groups from water chemisorption is absent at any temperature and pressure. Thus, the ice-like and following molecular water layers exhibit no measurable protonic conduction. We show that the water layers, even under these rather extreme experimental conditions, play a key role in understanding the function of these materials. Furthermore, the reported data are supposed to provide an extended basis for the further investigation of close-to-real gas adsorption or catalyzed heterogeneous reactions.

Preparation, Characterization, and Evaluation of Humidity-Dependent Electrical Properties of Undoped and Niobium Oxide-Doped TiO2 : WO3 Mixed Powders

“…In terms of surface conductivity in ceramics due to the progressive water adsorption [24], three di erent mechanisms are present [25]. At low RH range, the monomolecular adsorption process takes place as a response to surface modi cation due to water molecule incorporation, reaching a rst complete layer, the chemisorbed one, in the range 20 to 40% RH.…”

Water adsorption at zirconia: from the ZrO2(111)/Pt3Zr(0001) model system to powder samples

“…This is related to the fact that single crystals of pure ZrO 2 grown from the melt exhibit phase transformations upon cooling, thus only crystals of doped zirconia (e.g., YSZ) are available; these retain the hightemperature cubic phase. The surface chemistry of YSZ is much more complex than that of pure ZrO 2 , however, as shown for adsorption of H 2 O, 24 hydrogen, 25 or CO and CO 2 . 26 Therefore, the investigation of pure ZrO 2 , which is needed as a starting point of a well-grounded fundamental understanding, has to rely on thin lms.…”

An Excellent Solid Acid Catalyst Derived from Microalgae Residue for Fructose Dehydration into 5‐Hydroxymethylfurural

“…As was shown by the figure, there was a slight weight loss ( ca . 5.1%) below 230 °C, corresponded to the evaporation of physical and chemisorbed water from the catalyst surface . Then, a noticeable weight loss ( ca .…”