A general route for RuO2 deposition on metal oxides from RuO4

Article abstract of DOI:10.1039/c1cc16759f

A novel method for the deposition of RuO₂ from RuO ₄(g) on diverse metal oxides has been developed by grafting dopamine onto the otherwise un-reactive metal oxide surface. Oxygen evolution reaction on TiO₂ and the photoelectrochemical improvement of WO₃ by deposition of RuO₂ are just a few examples where this novel deposition method can be used.

Full text of DOI:10.1039/c1cc16759f

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COMMUNICATION
A general route for RuO deposition on metal oxides from RuO w
2
4
a
a
b
a
a
Alan Kleiman-Shwarsctein, Anders B. Laursen, Filippo Cavalca, Wei Tang, Søren Dahl
a
and Ib Chorkendorff*
Received 1st November 2011, Accepted 16th November 2011
DOI: 10.1039/c1cc16759f
A novel method for the deposition of RuO from RuO (g) on
2
in an economical and easy way. Herein, we describe a 3 step
method that is generally applicable to most metal oxides:
(1) functionalization of the metal oxide host with a grafting agent,
4
diverse metal oxides has been developed by grafting dopamine
onto the otherwise un-reactive metal oxide surface. Oxygen
evolution reaction on TiO
2
and the photoelectrochemical
are just a few
(2) reaction of the functionalized group with gas phase RuO
and (3) post-treatment of the metal-oxide–RuO composite to
4
improvement of WO by deposition of RuO
3
2
2
examples where this novel deposition method can be used.
obtain the required properties. This method is flexible, since the
modification of these 3 steps could be used to include other
families of support materials by changing the grafting molecule
Ruthenium dioxide (and metallic Ru) is widely used, for hetero-
geneous catalysis including oxidation reactions, reduction/hydro-
genation reactions and ammonia synthesis; electrochemical/
2
or the post-treatment conditions after deposition of RuO .
Titanium dioxide (P25 or Degusa Vp Disp ‘‘W2730X’’ on
fluorine doped tin oxide (FTO)) and tungsten trioxide (electro-
deposited on FTO) were chosen as examples of metal oxide
1
photoelectrochemical reactions including Oxygen Evolution
(
OER), Hydrogen Evolution (HER), Oxygen Reduction
2
ORR, combined with Pt or Ir) as well as the chloro-alkali
supports to show how this general RuO deposition method
2
(
works. Many other metal oxides can also been functionalized
process to produce Cl and NaOH. Other applications of Ru and
2
2
with RuO and are shown in Table 1 as a reference. The
RuO are in electronic materials where the high conductivity
2
functionalization (step 1, Scheme 1) of the metal oxide consists
of the grafting of 20 mM dopamine hydrochloride
can be exploited for usage in DRAM capacitors, and battery
3
materials. RuO
2
is especially regarded as being amongst the most
4
(
(HO)
2 6 3 2 2 2
C H CH CH NH HCl) onto the metal oxide, followed
promising electrode materials for super-capacitor applications.
Although there are many uses for Ru and RuO the
by washing of the metal oxide to remove non-grafted dopamine
2
(
see ESIw for full details on the grafting procedure).
X-Ray photoelectron spectroscopy of the N1s region for a
incorporation, of this high-performance material, into industrial
applications, is very limited due to the high cost of Ru. In many
dopamine functionalized TiO sample (Fig. S4a, ESIw) shows
cases the overall cost of utilizing RuO
2
could be decreased if an
2
two peaks at binding energies of 399.8 and 401.7 eV. The peak
economically feasible method, which provides high stability and
increased surface area, could be achieved. Furthermore, due to
2
Table 1 List of metal oxides that have been tested for RuO deposition
the great chemical resistance of RuO it is desirable to make thin
2
coatings that can prevent the support material from being in
contact with the chemical environment. Advances in chemical
RuO
2
deposition
deposition
TiO
Al
SiO
2
, SrTiO
, Li Ti
, FTO
3
, WO
3 2 2 3
, Cu O, a-Fe O ,
2
O
3
4
5
O12, MgAlO, GaN : ZnO
5,6
No RuO
2
2
synthesis have provided mesoporous RuO
provide an increased accessible surface area. In addition, conformal
RuO coating can be achieved by atomic layer deposition (ALD).
2
materials, which
2
However, this requires expensive setups and in many cases exotic
organic Ru complexes which need to be tailored depending on the
metal oxide support that is being used.
Until now there was no general synthesis route in which
RuO2 can be deposited from RuO (g) onto a metal oxide,
4
producing a thin semi-continuous, conformal or thin particulate
coating that can be applied to any geometry and type of substrate
a
Center for Individual Nanoparticle Functionality,
Department of Physics, Building 312, Fysikvej, Technical University
of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark.
E-mail: ibchork@fysik.dtu.dk
Center for Electron Nanoscopy, Building 307, Fysikvej, Technical
University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
b
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c1cc16759f
2
Scheme 1 Deposition process of RuO for powders and thin film
metal oxides.
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 967–969 967

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7
at 399.8 eV can be ascribed to the NH
while the peak at 401.7 eV could be related to NH
The pristine TiO and the TiO with RuO before calcination
2
group of dopamine
+
7,8
3
species.
2
2
2
(
(
R0 and R1) show a peak at 400.1 eV and after calcination
R3) at 400.4 eV, this peak could be related to adsorbed
9
molecular N2 and does not correspond to the binding energy
2
reported for N-doped TiO . The XPS spectra is a clear
indication that the dopamine is attached in a chelating bidentate
structure via the diol groups to the uncoordinated titanium
atoms at the surface of titanium dioxide, which is consistent
7
,10
with DFT calculations.
The absorption of the dopamine on
the TiO results in a slight color change as shown by the UV-Vis
2
absorption properties (Fig. S5, ESIw), in which the bandgap of
TiO is decreased from 3.2 eV to 3. Changes in the absorption
2
properties of TiO are due to the removal of band gap states in
2
7
the TiO valence band caused by adsorption of dopamine.
2
Deposition of RuO on the metal oxides is done by a new
2
4
method, in which gas phase in situ generated RuO is reacted
with the dopamine functionalized metal oxide; this methodology
has never been reported in literature before. Previous work in
11
12
this area was limited to biological samples, polymers and
12
etched metal surfaces since most metal oxides will not reduce
RuO to RuO and therefore the RuO will not be deposited
see ESIw). RuO was synthesized by in situ oxidation of
RuCl with KMnO in a closed container, such that the toxic
4
2
2
1
2
(
4
3
4
RuO gas evolves from the reaction mixture and reacts with
4
Fig. 1 (a) STEM HAADF image of P25 TiO with RuO deposition
2
2
the functionalized metal oxide.
and EDX elemental map, prior to calcination, scale bar 5 nm. (b–c)
Consideration of the type of support must be taken into
STEM HAADF and bright field of a RuO layer on a (123) anatase
2
account when delivering the gas phase RuO
no gas diffusion limitations to the surface in order to ensure a
homogeneous distribution of the RuO on the sample. Thin
film substrates used were attached to the lid of a pyrex
crystallizer (coating by convection of RuO (g)), while powders
were packed in a pressurized glass tube flow reactor (forced
flow, due to mass transport limitations). The loading of RuO
4
, so that there are
2
TiO surface after 450 1C calcination, scale bar 1 nm; and (d) EDX
spectrum profile acquired along the red line in (b–c).
2
present in minute amounts or as small particles. Once the
4
sample is calcined at 450 1C in air, STEM (Fig. 1b) reveals that
RuO predominantly covers the surface of the TiO nanoparticle
2 2
2
and is sintered into large homogeneous amorphous B1 nm thick
layers. The predominantly small cluster from the uncalcined
can be controlled by the amount of RuO (g) that is generated
4
in situ by controlling the amount of RuCl and KMnO used
3
sample disappears leaving behind an empty TiO surface and a
2
4
or by repeating the deposition process several times (safety
very sharp interface where RuO is present. Due to the higher
2
precautions and deposition details given in ESIw). RuO in the
Z number, Ru appears brighter in the HAADF image and
darker in the corresponding BF image. Lattice fringes on the
4
s
gas phase will react with organics such as Kapton , phenol and
paraffin, but will not be reactive to most metal oxides. This is
clear from control experiments, which we have performed—in
2 2
lower side of Fig. 1b and c relate to the TiO particle where RuO
is deposited, while the ones appearing on the uppermost side
come from another particle at a different height. STEM EDX
line scans performed on the calcined sample show that all of the
which no RuO
WO samples; results that were also observed by Rolison et al.
However in the case when dopamine is grafted to a great variety
of metal oxides, which can be coated with hydrated RuO
Table 1), SiO and FTO could not be coated with RuO since
2 2
is observed on the non-functionalized TiO and
12
3
RuO
patterns of the sample calcined at 450 1C do not show any RuO
features but show a decreased crystallinity of the TiO
2 2
is present at the TiO grain boundaries. X-Ray diffraction
2
2
(
2
.
2
2
dopamine adsorbs weakly on these substrates, however by using
a different grafting agent they could be functionalized.
After deposition of RuO2 on the functionalized metal
oxides, a distinct color change is observed, indicative of the
XPS spectra (Fig. S4d, e R2, further details in ESIw) of the
C 1s–Ru 3d XPS region show two peaks at 281.2 and 282.5 eV
in the Ru 3d5/2 region and the corresponding peaks in the Ru
3
+
3d3/2 at 285.7, and 287 eV corresponding to Ru or hydrated
1
3
6+
and Ru respectively;
14,15
deposition of Ru/RuO
ESIw). STEM HAADF imaging (Fig. 1a) shows a P25-Dopamine
particle that has been reacted with RuO (g); STEM EDX
mapping shows the ruthenium distribution on the TiO particle:
the brighter contrast in the image corresponds to that of Ru
nanoclusters covering the darker TiO particle. X-Ray diffraction
patterns of TiO can only be indexed to anatase and rutile phases
x
(see photography S1, and UV-VIS S5,
RuO
2
,
the C 1s region shows two
peaks at 284.9 eV (advantageous carbon) and a second carbon
1
4
4
peak at 288.8 eV. Upon calcination at 250 1C (Fig. S4d, f R3,
ESIw) the XPS spectra show peaks at 280.2 and 281.3 eV for the
Ru 3d5/2 and 284.7 and 285.9 eV for Ru 3d3/2 corresponding
2
4
+
3+
13
2
2
to Ru and Ru or hydrated RuO
respectively. The C 1 s
region has the advantageous carbon peak at 285.3 eV and a
second carbon peak at 288.7 eV.
2
(
S2) indicating that the Ru deposit is not crystalline or/and is
9
68 Chem. Commun., 2012, 48, 967–969
This journal is c The Royal Society of Chemistry 2012

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in which a reactive moiety such as dopamine is grafted to the
4
metal oxide and afterwards reacted with RuO (g) to form
RuO . This application of the deposition process to synthesize
2
supported RuO is of great interest for many catalysis and
2
energy storage applications. Two examples have been show-
cased to demonstrate some of the potential applications that
2 2
this method has. (1) The deposition of RuO on TiO as an
OER catalyst has been shown to give similar results to those
found in the literature and TEM microscopy has shown that
Fig. 2 (a) Cyclic Voltammogram of TiO
and without RuO in 1 M NaOH, (b) cyclic voltammogram of
electrodeposited WO on FTO with RuO calcined at 250 1C (blue)
and 350 1C (red) and without RuO (black) in 1 M HClO . Dashed
lines show the response in the dark, while continuous lines show the
2
on the FTO substrate with
small RuO
deposited utilizing this method. (2) The application of RuO
an OER catalyst in combination with WO as a photocatalyst
2
clusters with a very homogenous coverage can be
2
2
as
3
2
2
4
3
has shown a superb improvement in performance by the
photoresponse. Photocurrent of WO
scaled to 10 times its original value.
3
without RuO
2
(black) has been
deposition of RuO . These two examples show just how
2
versatile and universal the deposition method of RuO2
described in this communication is and some of the possible
applications for catalysis in the renewable energy area.
This work was supported by the ‘‘Catalysis for Sustainable
Energy’’ (CASE) research initiative, which is funded by the
Danish Ministry of Science, Technology and Innovation.
Center for Individual Nanoparticle Functionality is funded
by The Danish National Research Foundation. A.K.S would
like to thank the Hans Christian Ørsted fellowship. The
authors would like to thank Dr Lone Bech and Mr John
Larsen for technical assistance.
As one of the many potential applications for this RuO2
coating, the electrochemical performance towards OER was
2
tested using spin coated TiO electrodes on FTO as a function
of calcination temperature (see ESIw). From Fig. 2a it can be
seen that activity for OER is negligible for the uncalcined
sample at 100 1C (data not shown). At 170 1C the sample has
the highest OER activity and also shows hysteresis, which is
4
indicative of proton intercalation into the RuO2. However, at
higher calcination temperatures the intercalation is decreased
and the OER performance decreases due to a reduction in the
1
electrochemical active area due to sintering of the RuO . The
2
2
Notes and references
latter is verified by observations from the TEM studies
À2
À2
1
2
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2
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9
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3
2
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3
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4
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 967–969 969