Journal
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Volume 43, Issue 18, Pages 8655-8661Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2018.03.155
Keywords
Hydrogen; ZnO; Surface; AP-XPS; TPD; Pressure-gap
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Funding
- National Research Foundation of Korea [2011-0014157]
- SRC (C-AXS) [NRF-2015R1A5A1009962]
- National Natural Science Foundation of China [11227902]
- [NRF-2015R1A2A2A01004084]
- National Research Foundation of Korea [10Z20130012677, 2015R1A5A1009962] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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The interaction of H-2 molecules with a ZnO (0001) single crystal surface has been studied over a wide pressure (10(-6)-0.25 Torr) and temperature (300-600 K) range using ambient pressure X-ray photoelectron spectroscopy (AP-XPS). ZnO is well-known for interstitial hydrogen and hydrogen atoms in ZnO are believed to be incorporated by the dissociative adsorption of H-2 molecules in the atmosphere and their subsequent diffusion into the bulk. The dissociative adsorption of H-2 has been investigated at elevated pressures because H-2 molecules are not dissociated on the ZnO single crystal surface under ultrahigh vacuum (UHV) conditions. When the pressure is increased to several mTorr, the dissociative adsorption of H-2 takes place to form OH bonds on the surface. At 0.25 Torr, the ZnO surface is saturated with H atoms and the coverage is estimated to be 1.1 x 10(15) atoms/cm(2) at 300 K. At higher surface temperatures, the equilibrium between the dissociative adsorption of gas-phase H-2 molecules and the associative desorption of surface H atoms is established. While maintaining the equilibrium, the surface has been monitored successfully in situ by utilizing AP-XPS. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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