Physical Chemistry Chemical Physics
Surface chemistry and stability of metastable corundum-type In2O3
Eva-Maria Köck,a Michaela Kogler,a Chen Zhuo,a Lukas Schlicker,b Maged F. Bekheet,b Andrew Doran,c Aleksander Gurlob and Simon Penner*a
a Institut für Physikalische Chemie, Universität Innsbruck, Innrain 52c, A-6020 Innsbruck, Austria
E-mail: simon.penner@uibk.ac.at
Tel: +43 512 507 58003
b Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und-technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany
c Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, USA
To account for the explanation of an eventual sensing and catalytic behavior of rhombohedral In2O3 (rh-In2O3) and the dependence of the metastability of the latter on gas atmospheres, in situ electrochemical impedance spectroscopic (EIS), Fourier-transform infrared spectroscopic (FT-IR), in situ X-ray diffraction and in situ thermogravimetric analyses in inert (helium) and reactive gases (hydrogen, carbon monoxide and carbon dioxide) have been conducted to link the gas-dependent electrical conductivity features and the surface chemical properties to its metastability towards cubic In2O3. In particular, for highly reducible oxides such as In2O3, for which not only the formation of oxygen vacancies, but deep reduction to the metallic state (i.e. metallic indium) also has to be taken into account, this approach is imperative. Temperature-dependent impedance features are strongly dependent on the respective gas composition and are assigned to distinct changes in either surface adsorbates or free charge carrier absorbance, allowing for differentiating and distinguishing between bulk reduction-related features from those directly arising from surface chemical alterations. For the measurements in an inert gas atmosphere, this analysis specifically also included monitoring the fate of differently bonded, and hence, differently reactive, hydroxyl groups. Reduction of rh-In2O3 proceeds to a large extent indirectly via rh-In2O3 → c-In2O3 → In metal. As deduced from the CO and CO2 adsorption experiments, rhombohedral In2O3 exhibits predominantly Lewis acidic surface sites. The basic character is less pronounced, directly explaining the previously observed high (inverse) water–gas shift activity and the low CO2 selectivity in methanol steam reforming.
The article was received on 30 May 2017, accepted on 03 Jul 2017 and first published on 03 Jul 2017
DOI: 10.1039/C7CP03632A
Download Citation: Phys. Chem. Chem. Phys., 2017,19, 19407-19419
E. Köck, M. Kogler, C. Zhuo, L. Schlicker, M. F. Bekheet, A. Doran, A. Gurlo and S. Penner, Phys. Chem. Chem. Phys., 2017, 19, 19407
This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material and it is not used for commercial purposes.
Eva-Maria Köck
Michaela Kogler
Chen Zhuo
Lukas Schlicker
Maged F. Bekheet
Andrew Doran
Aleksander Gurlo
Simon Penner