Non-Thermal Reactions in Water Adsorbed on Anion-Doped TiO2(110)
EMSL Project ID
24800
Abstract
This proposal is a continuation of research under EMSL User Proposal #18397. Development of new energy sources and alternative fuels, such as hydrogen, are major needs for the 21st century. In the early 1970s, Fujishima and coworkers discovered that hydrogen could be produced from water electrolysis using electrons photocatalytically generated at TiO2 electrodes coupled with noble metals such as platinum.1 Their discovery continues to motivate research toward development of TiO2-based photocatalysts for water splitting, although emphasis is now shifting toward study of visible light-active photocatalysts because TiO2 absorbs little of the solar spectrum. Numerous groups have shown that ion doping red-shifts the TiO2 absorption spectrum into the visible. In particular, promising results have emerged recently on a new class of visible light-active TiO2 photocatalysts doped with anions (C, N, S). We will use low-energy electron-stimulated desorption (ESD), photon-stimulated desorption (PSD), temperature programmed desorption (TPD), and other surface science techniques to probe the reaction kinetics and dynamics for thin water films adsorbed on regular and anion-doped TiO2(110). To map out the non-thermal reaction "landscape," it is useful to have an easily tunable excitation source (e.g. energetic electrons) with sufficient energy to initiate the reactions so that most or all of the possible reaction pathways can be explored. In contrast, with a lower energy excitation source, such as visible photons, only the lowest energy reaction pathways can be explored. An analogy can be made with hiking in the mountains: One gains a much better idea of the overall topography from the mountain tops versus the valley floors. Understanding the non-thermal reaction landscape for a given system [e.g. undoped TiO2(110)] should provide crucial information necessary to design a new system to achieve hydrogen production via a low-energy pathway (i.e. using visible photons). Specifically, these studies are designed to address the following key scientific issues:
• What are the major non-thermal reaction products, how do they depend on the excitation energy and how do they depend on the type of excitation (photons or electrons)?
• What are the reaction mechanisms, reaction intermediates and kinetic bottlenecks for producing H2 and O2?
• How does anion-doping of TiO2(110) influence non-thermal chemistry? Specifically, does anion-doping favor production of molecular hydrogen via low-energy pathways?
• What is the role of metal co-catalysts such as platinum in the non-thermal water chemistry?
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-05-31
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
45) Nikolay G. Petrik and Greg A. Kimmel, “Hydrogen bonding, H/D exchange and molecular mobility in thin water films on TiO2(110),” Phys. Rev. Lett. 99, 196103 (2007).
Petrik NG, and GA Kimmel. 2011. "Electron- and hole-mediated reactions in UV -irradiated O2 adsorbed on reduced rutile TiO2(110)." Journal of Physical Chemistry C 115(1):152-164. doi:10.1021/jp108909p
Petrik NG, Z Zhang, Y Du, Z Dohnalek, I Lyubinetsky, and GA Kimmel. 2009. "Chemical Reactivity of Reduced TiO2(110): The dominant role of surface defects in oxygen chemisorption." Journal of Physical Chemistry C 113(28):12407-12411. doi:10.1021/jp901989x
Zhang Z, Y Du, NG Petrik, GA Kimmel, I Lyubinetsky, and Z Dohnalek. 2009. "Water as a Catalyst: Imaging Reactions of O-2 with Partially and Fully Hydroxylated TiO2(110) Surfaces." Journal of Physical Chemistry C 113(5):1908-1916.