研究从非均相到光催化的过程的多功能模型系统：TiO2（110）上的外延RuO2（110）
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Versatile Model System for Studying Processes Ranging from
Heterogeneous to Photocatalysis: Epitaxial RuO
2
(110) on TiO
2
(110)
Yunbin He,
†,‡
Daniel Langsdorf,
†
Lei Li,
‡
and Herbert Over*
,†
†
Department of Physical Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 58, D-35392 Gießen, Germany
‡
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials; Key Laboratory of Green Preparation and
Application for Functional Materials, Ministry of Education; Faculty of Materials Science & Engineering, Hubei University, Wuhan
430062, China
*
S
Supporting Information
ABSTRACT: The binary model system RuO
2
/TiO
2
(110) can be
prepared with single crystallinity and excellent control of the
morphology of the RuO
2
(110) nanoislands. The interface of
RuO
2
/TiO
2
(110) is structurally well-defined since RuO
2
grows
with the same lattice constants as TiO
2
(110). The actual growth of
RuO
2
on TiO
2
(110) single crystals starts from square-shaped 3−4
ML thick RuO
2
islands with narrow size and thickness
distributions. After TiO
2
(110) is completely covered by RuO
2
, the further growth proceeds via a step flow mechanism,
forming very large and flat RuO
2
(110) terraces with well-defined thickness. Both the flat RuO
2
(110) films and RuO
2
(110)
nanoislands are very reactive toward CO oxidation, and the RuO
2
(110) nanoislands are robust in the redox reactions, i.e., easily
recovering their morphology after reoxidation from the reduced state. The RuO
2
/TiO
2
(110) heterojunction forms a Schottky
barrier of 1.4 eV which is important for photocatalysis.
1. INTRODUCTION
Molecular insight into physical and chemical processes needs
the intimate collaboration of experiment and theory that in turn
resorts on the design and preparation of highly sophisticated
model systems. Proper model systems are at the heart of
physical chemistry, requiring lowest possible structural
complexity, while still capturing the most important properties
of the real system under study. Always the scientific question in
mind dictates the proper choice of the model system.
In heterogeneous catalysis the active component in the form
of nanoparticles is brought onto a supporting material, most
frequently an oxide support to stabilize the dispersion of the
active component.
1,2
Assuming the interaction between the
support and the active component is important for the catalytic
performance, then in a well-designed model system the support
and the metal particles but also the interfaces should exhibit a
simple structure.
Sumitomo Chemical has demonstrated that the Deacon
process, i.e., the gas phase oxidation of HCl by oxygen to
recover molecular chlorine, is most efficiently catalyzed with
RuO
2
supported on rutile TiO
2
.
3
The choice of the supporting
material has shown to be decisive. The activity is not only
determined by the chemical nature of the support but also by
the type of polymorph. For instance, RuO
2
supported on
anatase TiO
2
is by a factor of 3 less active than RuO
2
supported
on rutile TiO
2
.
3
Transmission electron microscopy (TEM)
investigations of the Sumitomo catalyst indicated that ultrathin
RuO
2
islands are formed on rutile TiO
2
preferentially oriented
along the (110) direction.
4
Obviously, a well-designed model
system for the Deacon reaction over a Sumitomo catalyst
should consist of RuO
2
(110) grown on a single-crystal rutile
TiO
2
(110).
This rutile RuO
2
/TiO
2
(110) heterostructure is also a proper
model system for the electrochemical oxidation of HCl,
mimicking the dimensionally stable anodes (DSA) in the
chlorine evolution reaction (CER).
5,6
Besides the CER, the
oxygen evolution reaction (OER) can be efficiently catalyzed by
DSA. As a four-electron process, the OER is sluggish and
constitutes therefore the bottleneck in various technologically
important electrolysis reactions such as the water splitting to
produce hydrogen.
Photocatalysis can be employed to produce hydrogen by
solar water splitting.
7
Here the photoabsorber generates first an
electron−hole pair by the absorption of a single photon with
suitable energy. Subsequently, the electron and hole can be
utilized in the reduction and oxidation of water to produce
hydrogen and oxygen, respectively. Frequently cocatalysts are
required for speeding up the sluggish OER.
8
A suitable model is
again RuO
2
on TiO
2
(110) where TiO
2
serves as the
photoabsorber, and RuO
2
acts as the cocatalyst to facilitate
the OER. Of particular importance in this system is the
interface between RuO
2
and TiO
2
, since photogenerated holes
need to traverse this interface to induce the OER at the RuO
2
surface.
In this paper we will report on the binary model system
RuO
2
/TiO
2
(110) that can be prepared with single crystallinity
Received: December 5, 2014
Revised: January 12, 2015
Published: January 12, 2015
Article
pubs.acs.org/JPCC
© 2015 American Chemical Society 2692 DOI: 10.1021/jp5121405
J. Phys. Chem. C 2015, 119, 2692−2702
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