Widely Controllable Syngas Production by a Dye-Sensitized TiO2Hybrid System with ReIand CoIIICatalysts under Visible-Light Irradiation

Article abstract of DOI:10.1002/anie.201608593

Visible-light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂evolving Co^IIIcatalyst and a CO-producing Re^Icatalyst on TiO₂have been found to produce both H₂and CO (syngas) in CO₂-saturated N,N-dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^Iand Co^IIIcatalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂to each of the CO₂-reduction and hydrogen-evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.

Full text of DOI:10.1002/anie.201608593

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201608593
German Edition: DOI: 10.1002/ange.201608593
Photocatalysis Hot Paper
Widely Controllable Syngas Production by a Dye-Sensitized TiO
Hybrid System with Re and Co Catalysts under Visible-Light
Irradiation
2
I
III
Jong-Su Lee, Dong-Il Won, Won-Jo Jung, Ho-Jin Son,* Chyongjin Pac,* and Sang Ook Kang*
[
7]
[8]
[9]
Abstract: Visible-light irradiation of a ternary hybrid catalyst
CO and water using Ni, Re, and Ru catalysts, little has
2
III
prepared by grafting a dye, an H evolving Co catalyst and
been referred to control the syngas composition. Therefore,
a new protocol that focuses on the adjustability of the H /CO
2
I
a CO-producing Re catalyst on TiO have been found to
2
2
produce both H and CO (syngas) in CO -saturated N,N-
dimethyl formamide (DMF)/water solution containing a 0.1m
ratio in the visible-light-induced syngas production should be
of scientific significance. Here a new type of syngas-evolving
hybrid system has been constructed by immobilizing two
types of transition-metal complex catalysts together with
2
2
sacrificial electron donor. The H /CO ratios are effectively
2
controlled by changing either the water content of the solvent
I
III
or the molar ratio of the Re and Co catalysts ranging from
:2 to 15:1. The controlled syngas formation is discussed in
a visible-light absorbing antenna on TiO particleS; the
2
I
[10]
1
catalysts are a Re complex (ReP) as the CO-producing
site and a Co molecular catalyst (CoP) as the H -generating
III
terms of competitive electron flow from TiO to each of the
2
2
CO -reduction and hydrogen-evolving sites depending on the
site. Recently, Reisner and co-workers have demonstrated
2
efficiencies of the two catalytic reaction cycles under given
reaction conditions.
that the CoP complex displayed high catalytic activity with
a good stability when anchored onto a dye-sensitized TiO
2
[
11]
semiconductor. Herein, we report that this system produces
both H2 and CO under visible-light irradiation in CO2-
saturated N,N-dimethyl formamide (DMF) in the presence of
D
ue to the global climate crisis brought by the continuous
[
1]
increase of CO emission in the atmosphere, the use of CO2
2
as a carbon resource is an important subject in science and
water. The H /CO ratio can be widely controlled by changing
2
industry. The reduction of CO to useable C1 resources is
either or both of the catalyst ratio and the water content.
Scheme 1 illustrates the structure of the essential compo-
nents and the overall reaction pathways of the present
photocatalytic syngas production based on a TiO2 hybrid
system with an antenna and two transition-metal complex
catalysts; the antenna is (E)-2-cyano-3-(5’-(5’’-(p-(diphenyla-
2
a major research target in chemical conversions of solar
energy, together with the hydrogen evolution by water
reduction, to provide a strategic way responding to energy
[2]
and environmental issues. Among visible-light-induced
multi-electron reductions of CO , the two-electron reduction
2
to CO is a kinetically favorable choice because of the
relatively low reaction barrier compared to one-electron
and other higher-reduction reactions. Moreover, CO is
currently used as a carbon source for the production of
chemicals in the petrochemical industry, particularly for the
mino)phenyl)thiophen-2’’-yl)thiophen-2’-yl)-acrylic
(dye), catalyst 1 (ReP) is fac-[Re(4,4’-bis(diethoxyphosphor-
acid
[
3]
ylmethyl)-2,2’-bipyridine)(CO) Cl], catalyst 2 (CoP) is
3
III
À
[Co Cl(dimethylglyoximato) (pyridyl-4-phosphonic acid)] ,
2
and the sacrificial electron donor (SED) is 1,3-dimethyl-2-
methanol production from a mixture of CO and H , so-called
syngas.
phenyl-1,3-dihydrobenzimidazole. These compounds were
2
[
2b,4]
[10a,11a,12,13]
synthesized according to literature methods.
The
Syngas has been also known as a key feedstock for the
production of synthetic bulk chemicals by the Fischer–
Tropsch (F-T) processing. For the production of chemicals
hybrid catalyst was prepared by anchoring the dye, ReP, and
CoP on TiO particles (Hombikat) in this sequence. Success-
2
[
5]
ful anchoring of the components was confirmed by diffuse-
reflectance spectroscopy, IR-absorption spectra, and X-ray
from syngas, the tailoring of H /CO ratio in syngas mixtures is
2
critical, for example, 2:1 H /CO for methanol production and
2
[
2b,4c]
F-T hydrocarbon syntheses
production of aldehydes via hydroformylation of alkenes.
and 1:1 H /CO for the
2
[6]
While the simultaneous formation of H and CO is known to
2
occur by photochemical and electrochemical reductions of
[*] J.-S. Lee, D.-I. Won, W.-J. Jung, Prof. H.-J. Son, Prof. C. Pac,
Prof. S. O. Kang
Department of Advanced Materials Chemistry
Korea University, 2511 Sejong-ro
Sejong 30019 (South Korea)
E-mail: hjson@korea.ac.kr
jjpac@korea.ac.kr
sangok@korea.ac.kr
Supporting information for this article can be found under:
http://dx.doi.org/10.1002/anie.201608593.
Scheme 1. Schematic representation of heterogeneous ternary photo-
catalytic system for syngas production.
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

Angewandte
Communications
Chemie
photoelectron spectroscopy (XPS) of the treated particles
see Figures S1–S3 in the Supporting Information). In each
(
anchoring procedure, the supernatant separated by centrifu-
gation of the treated dispersion was virtually transparent.
Therefore, the amount of each component anchored on TiO2
was estimated to approximately equal that feed. The hybrid
particles were dispersed in DMF-containing SED (0.1m) in
the absence or presence of H O (3, 10, and 20%), saturated
2
with CO and then irradiated at a wavelength longer than
2
4
00 nm using a LED lamp (60 W, Cree Inc.).
Figure 1 shows typical plots for the formation of CO and
H2 for a hybrid system of 0.05 mmol ReP/0.05 mmol CoP
grafted on 10 mg TiO in the presence of various amounts of
2
[
14]
water (0 to 20 vol%).
The efficiency of CO formation
Figure 2. Dependences of H /CO formation on molar ratios of ReP
2
and CoP anchored on TiO ; irradiation of 10 mg dye/TiO /ReP:CoP
2
2
(
total 0.1 mmol) and 0.1m SED in 3 mL DMF/H O mixture solvent
2
(20 vol% water) for 20 h.
quantum yields (AQY) of CO and H formation at 436 nm for
2
the hybrid systems (dye/TiO /ReP:CoP(1:9 to 9:1)) in the
2
presence of 20 vol% water were determined in a linear time-
[
15]
conversion region (see Table S3).
An isotope-labeling
experiment was performed for the dye/TiO /ReP:CoP(5:5)
2
1
3
system in a CO -saturated [D ]DMF/D O mixture solvent
10 vol% D O) containing 0.1m SED. The C NMR spectrum
2
7
2
1
3
(
2
of the irradiated sample shows a sharp signal at d 185.2 ppm in
1
3
accordance with the resonance of CO (Figure S12), proving
that the formed CO is derived from added CO . The origin is
2
1
3
further supported by the C isotope abundance (> 90%) in
the formed CO (analyzed by GC-MS; see Figure S13).
In order to confirm the persistency of photocatalytic
activity, we performed repetitive irradiation experiments. As
shown in Figure 3, no significant leveling-off tendency was
observed in each cycle and the activity of syngas (CO and H2)
production is almost constant even with the extended
Figure 1. Plots of a) CO and b) H formation (mmol and TON) versus
2
irradiation time for 10 mg dye/TiO /ReP(0.05 mmol):CoP(0.05 mmol) in
2
3
2
mL of DMF/H O solvent containing 0.1m SED: water contents
(
(
vol%)=0% (squares) 3% (circles), 10% (triangles), and 20%
reverse triangles). c) Comparison of H /CO formation (mmol) on the
2
variation of water contents (0–20 vol%).
increased to a maximum in the presence of 3% water, but
decreased at higher contents of water. In contrast, while the
H formation was negligible in the absence of water and still
2
very small in the presence of 3% water, the H production
2
activity dramatically increased in the presence of 10% water
and still more at 20 vol% water. The H /CO ratio can be
2
further controlled by changing the ratio of ReP:CoP grafted
on TiO while fixing the total amount at 0.1 mmol. Upon
2
changing the anchoring ratio of CoP and ReP from 9:1 to 1:9,
the H :CO ratio is systematically tuned from 1:2 to 15:1 as
2
shown in Figure 2. Detailed results with the relating turnover
Figure 3. Formation of CO and H in a 4-cycle repetition at >400 nm
2
frequency (TOF) and number (TON) of CO and H evolution
2
for 400 min after CO bubbling for 30 minutes in the dark; 10 mg
2
per molecular catalyst (ReP or CoP) and per TiO nano-
2
dye(1.5 mmol)/TiO /ReP(0.05 mmol):CoP(0.05 mmol) in 3 mL DMF/
2
particle are listed in Table S3 and Figure S11. The apparent
H O mixture solvent (20 vol% water) containing 0.1m SED.
2
2
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
catalytic cycles from 1st run to 4th run. Overall the photo-
catalytic activities for CO and H production in the prepared
2
present hybrid systems increadsed continuously up to 30 h
with no appreciable leveling off tendency (Figure S8). The
initial gas compositions (H /CO ratio) are invariable during
2
the 10 hour reaction time. However, hydrogen evolution was
a dominant feature in the extended reaction time (see
Figure S9 and Table S).
Scheme 2 shows a working hypothesis for major mecha-
nistic pathways operated in the present photocatalytic
reaction, involving 1) electron injection from the excited-
[16]
state dye into TiO as the initiation process, 2) competitive
2
transfer of the injected electrons to the ReP and CoP catalyst
Figure 4. a) Mott–Schottky plots and b) flat-band potentials (E ) for
fb
TiO nanoparticle films on the FTO electrode in the absence of water
2
and in the presence of 3 vol%, 10 vol%, and 20 vol% water in
acetonitrile containing 0.1m TBAP.
irradiation of the TiO hybrid catalyst with a ReP/CoP ratio of
2
0
.05 mmol:0.05 mmol in the presence of 3 to 20 vol% water are
almost constant independently of the water contents while the
H /CO ratios are variable with the water contents (Figure 1c).
2
In this case, the total amounts of electrons used for the
reductions of both CO and H O would be constant but with
2
2
different branch ratios of electron transfer depending on the
water contents. The higher the water concentration, the faster
Scheme 2. Schematic representation of the electron transfer processes
in visible-light-induced syngas production by the dual molecular
catalytic hybrid system.
the H -generation catalytic cycle should be completed to
2
regenerate CoP. However, the ratios of the final products (CO
and H ) should be determined by complex factors, mainly by
2
sites through TiO , and 3) the chemical processes proceeding
relative flows of both the first and second electrons to ReP
and CoP and by efficiencies of the two-electron reduction
catalytic cycles. In this regard, the CO formation is dominant
even in the presence of 10 vol% water (Figure 1c) where the
concentration of H O (5.6m) is much higher than that of CO
2
on the ReP site (CO reduction) and on the CoP site (H2
2
evolution) under supply of electrons from TiO . This photo-
2
catalytic cycle for syngas production can be closed after the
+
recovery of the dye by reduction of dyeC with SED (4).
2
2
[
19]
According to Scheme 2, the ratio of formed CO and H should
(ca. 0.2m). A possible speculation is that electron supply
2
primarily depend on the relative rates of electron supply from
from TiO would more favorably occur to ReP than to CoP
2
TiO to the two catalysis sites, which would be determined by
due to the different distances from the TiO surface to the
2
2
the relationship between the reduction potentials of ReP and
electron-accepting centers (the bpy ligand across the meth-
ylphosphonate spacer for ReP vs. Co across the pyridyl-
III
CoP with respect to the conduction-band edge of TiO . The
2
reduction potential of CoP is À0.88 V versus saturated
phosphonate bridge for CoP) as well as due to the different
configurational situations of the anchored molecules (double
anchoring with the two phosphonate groups of ReP vs. single
anchoring of the one phosphonate substituent of CoP).
Alternatively, the catalytic cycle on the ReP site would
more efficiently proceed than that on the CoP site in the
presence of 10 vol% water, even though the CO formation on
ReP involves more complex chemical processes than the H2
evolution on CoP. In the presence of 20 vol% water, however,
the formation of H2 is more efficient than that of CO,
probably due to the large amount of water that should
[16d]
calomel electrode (SCE),
significantly less negative than
[
10b]
that of ReP (RePE, À1.34 V vs. SCE)
(Figure S4).
The flat-band potential (E ) of TiO , which has been used
fb
2
as a practical measure of the conduction-band edge, is known
[
17]
[10b]
to depend on solvents. In a previous paper,
we reported
that Efb positively shifts in the presence of water in DMF.
Figure 4 shows four different Mott–Schottky (MS) plots taken
for TiO nanoparticle films in the absence of water and in the
2
presence of 3, 10, and 20 vol% water in acetonitrile. The
increase of added water resulted in substantial positive shifts
of Efb from À1.93 V at 0% H O, to À1.74 V (3% H O), to
accelerate the chemical processes for the H generation. Also,
2
2
2
[18]
À1.56 V (10% H O), and to À1.47 V (20% H O).
this behavior may be supported by the CO concentration
2
2
2
Provided that the E values observed for the TiO2
lessened with higher water content (consequently lowering
the catalytic CO formation efficiency) since the solubility of
fb
nanoparticle films can be applied to those of the TiO2
hybrid particle dispersions in DMF, the electron transfer
[
20]
CO gas is generally much lower in water (ca. 0.034m) than
2
[19]
from TiO to either ReP and CoP should be exergonic enough
in DMF (ca. 0.2m). As shown in Figure 2, the CO formation
is sharply increased upon changing the anchoring amount of
ReP from 0.01 mmol to 0.09 mmol, whereas the dependence of
H2 formation on the anchoring amount of CoP is not so
2
[16c,d,b]
to proceed under the reaction conditions.
In fact, both
CO and H are generated in the presence of water, as shown
2
in Figures 1 and 2. The total amounts of CO and H formed by
2
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

Angewandte
Communications
Chemie
remarkable. In the presence of 20 vol% water, the catalytic
R. Bongartz, A. Schreiber, T. E. Mueller, Energy Environ. Sci.
012, 5, 7281 – 7305.
2
cycle for H generation would be efficient even with 0.01 mmol
2
[
2] a) I. Willner, R. Maidan, D. Mandler, H. Dꢂrr, G. Dçrr, K.
Zengerle, J. Am. Chem. Soc. 1987, 109, 6080 – 6086; b) M. E.
Dry, Catal. Today 2002, 71, 227 – 241; c) G. Centi, S. Perathoner,
Catal. Today 2009, 148, 191 – 205; d) J. Qiao, Y. Liu, F. Hong, J.
Zhang, Chem. Soc. Rev. 2014, 43, 631 – 675; e) A. M. Appel, J. E.
Bercaw, A. B. Bocarsly, H. Dobbek, D. L. DuBois, M. Dupuis,
J. G. Ferry, E. Fujita, R. Hille, P. J. A. Kenis, C. A. Kerfeld, R. H.
Morris, C. H. F. Peden, A. R. Portis, S. W. Ragsdale, T. B.
Rauchfuss, J. N. H. Reek, L. C. Seefeldt, R. K. Thauer, G. L.
Waldrop, Chem. Rev. 2013, 113, 6621 – 6658.
CoP enough to facilitate sufficient electron flow from TiO to
2
CoP in competition with the electron flow to 0.09 mmol ReP.
This appears to be again true for the CO formation in cases
where the anchoring amount of ReP is greater or equal to
0
.05 mmol. The CO formation competes with or predominates
over the H generation even though the CO concentration is
2
2
much lower than the water concentration. The electron
supply from TiO to ReP and CoP might be dominated by
2
a “seesaw mechanism” depending on the catalytic cycle
efficiencies under given reaction conditions.
[
3] a) A. J. Morris, G. J. Meyer, E. Fujita, Acc. Chem. Res. 2009, 42,
1983 – 1994; b) T. Yui, Y. Tamaki, K. Sekizawa, O. Ishitani, Top.
In summary, we have successfully developed a dual-
function heterogeneous system for the photocatalytic syngas
Curr. Chem. 2011, 303, 151 – 184; c) L. Alibabaei, H. Luo, R. L.
House, P. G. Hoeltz, T. J. Meyer, J. Mater. Chem. A 2013, 1,
4133 – 4145; d) Y. Yamazaki, H. Takeda, O. Ishitani, J. Photo-
chem. Photobiol. C 2015, 25, 106 – 137.
I
production by anchoring both a Re complex (ReP) as the
III
CO -reduction catalyst and a Co complex (CoP) as the
2
[
[
4] a) I. Wender, Fuel Process. Technol. 1996, 48, 189 – 297; b) S. C.
Tsang, J. B. Claridge, M. L. H. Green, Catal. Today 1995, 23, 3 –
hydrogen-evolution catalyst on TiO particles. The ratio of H /
2
2
CO in the formed syngas is widely controlled from 1:2 to 15:1
by the amount of water added and by changing the ratio of
ReP and CoP. To the best of our knowledge, the present
15; c) K. C. Waugh, Catal. Today 1992, 15, 51 – 75.
5] a) A. J. V. Underwood, Ind. Eng. Chem. 1940, 32, 449 – 454;
b) C. K. Rofer-DePoorter, Chem. Rev. 1981, 81, 447 – 474; c) H.
Schulz, Appl. Catal. A 1999, 186, 3 – 12; d) A. Y. Khodakov, W.
Chu, P. Fongarland, Chem. Rev. 2007, 107, 1692 – 1744.
ternary hybrid system (dye/TiO /ReP:CoP) serves as the first
2
example for visible-light-induced syngas production with
a widely tunable H /CO ratio. The concept presented here
[6] M. Beller, B. Cornils, C. D. Frohning, C. W. Kohlpaintner, J. Mol.
Catal. A 1995, 104, 17 – 85.
[7] V. S. Thoi, N. Kornienko, C. G. Margarit, P. Yang, C. J. Chang, J.
Am. Chem. Soc. 2013, 135, 14413 – 14424.
2
will be applicable to other molecular catalyst combinations,
III [11b,21]
II [22]
for example, efficient Co
or Ni
-based H -evolving
2
II [23]
catalysts and various CO reduction catalysts based on Ru ,
2
[
8] B. Kumar, J. M. Smieja, A. F. Sasayama, C. P. Kubiak, Chem.
Commun. 2012, 48, 272 – 274.
II [7,24]
III [25]
II
II [26]
Ni ,
Ir ,
and Fe /Co
molecular complexes. In
addition, introduction of CO-tolerant molecular catalysts
would likely increase the long-term stability of our dual
[
9] P. Kang, Z. Chen, A. Nayak, S. Zhang, T. J. Meyer, Energy
Environ. Sci. 2014, 7, 4007 – 4012.
catalytic system evolving both H and CO.
[10] a) E.-G. Ha, J.-A. Chang, S.-M. Byeong, C. Pac, D.-M. Jang, J.
Park, S. O. Kang, Chem. Commun. 2014, 50, 4462 – 4464; b) D.-I.
Won, J.-S. Lee, J.-M. Ji, W.-J. Jung, H.-J. Son, C. Pac, S. O. Kang,
J. Am. Chem. Soc. 2015, 137, 13679 – 13690.
2
Acknowledgements
[
11] a) F. Lakadamyali, E. Reisner, Chem. Commun. 2011, 47, 1695 –
1
697; b) J. Willkomm, N. M. Muresan, E. Reisner, Chem. Sci.
This research was supported by Basic Science Research
Program through the National Research Foundation of
Korea(NRF) funded by the Ministry of Education (grant
number NRF-2014R1A6A1030732), the International Sci-
ence and Business Belt Program through the Ministry of
Science, ICT and Future Planning (grant number
2015, 6, 2727 – 2736; c) J. Willkomm, K. L. Orchard, A. Reynal,
E. Pastor, J. R. Durrant, E. Reisner, Chem. Soc. Rev. 2016, 45, 9 –
23.
[12] a) K. R. Justin Thomas, Y.-C. Hsu, J. T. Lin, K.-M. Lee, K.-C.
Ho, C.-H. Lai, Y.-M. Cheng, P.-T. Chou, Chem. Mater. 2008, 20,
1
830 – 1840; b) S.-H. Lee, Y. Park, K.-R. Wee, H.-J. Son, D. W.
Cho, C. Pac, W. Choi, S. O. Kang, Org. Lett. 2010, 12, 460 – 463.
13] X.-Q. Zhu, M.-T. Zhang, A. Yu, C.-H. Wang, J.-P. Cheng, J. Am.
Chem. Soc. 2008, 130, 2501 – 2516.
14] The maximum amount of water in the DMF–water system is
limited to 20 vol% due to the poor solubility of SED in water:
experimentally the dissolved SED begins to be insoluble at
2
015K000287), and the Basic Science Research Program
[
[
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education (grant number
2
014R1A1A1007625).
20 vol% water.
Keywords: heterogeneous catalysis · hydrogen evolution ·
organic–inorganic hybrid systems · photocatalysis · syngas
[
15] We note that the measured AQY is not the real, scientifically
defined quantum yield, but stands for a relative measure of the
CO and H2 production efficiency, because the number of
photons absorbed by the dye cannot be properly determined.
16] a) W.-S. Han, K.-R. Wee, H.-Y. Kim, C. Pac, Y. Nabetani, D.
Yamamoto, T. Shimada, H. Inoue, H. Choi, K. Cho, S. O. Kang,
Chem. Eur. J. 2012, 18, 15368 – 15381; b) H.-J. Son, C. H. Kim,
D. W. Kim, N. C. Jeong, C. Prasittichai, L. Luo, J. Wu, O. K.
Farha, M. R. Wasielewski, J. T. Hupp, ACS Appl. Mater.
Interfaces 2015, 7, 5150 – 5159; c) A. Reynal, F. Lakadamyali,
M. A. Gross, E. Reisner, J. R. Durrant, Energy Environ. Sci.
2013, 6, 3291 – 3300; d) F. Lakadamyali, A. Reynal, M. Kato,
J. R. Durrant, E. Reisner, Chem. Eur. J. 2012, 18, 15464 – 15474.
[
[
1] a) BP statistical Review of World Energy June 2016, Carbon
dioxide emissions http://www.bp.com/content/dam/b/pdf/
energy-economics/statistical-review-2016b/p-statistical-review-
of-world-energy-2016-co2-emissions.pdf; b) M. Aresta, A. Dibe-
nedetto, A. Angelini, Chem. Rev. 2014, 114, 1709 – 1742; c) E. V.
Kondratenko, G. Mul, J. Baltrusaitis, G. O. Larrazꢀbal, J. Pꢁrez-
Rꢀmirez, Energy Environ. Sci. 2013, 6, 3112 – 3135; d) P.
Markewitz, W. Kuckshinrichs, W. Leitner, J. Linssen, P. Zapp,
[17] a) G. Redmond, D. Fitzmaurice, J. Phys. Chem. 1993, 97, 1426 –
1430; b) G. Rothenberger, D. Fitzmaurice, M. Grꢃtzel, J. Phys.
4
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!

Angewandte
Communications
Chemie
Chem. 1992, 96, 5983 – 5986; c) M. D. Ward, J. M. White, A. J.
[21] N. M. Muresan, J. Willkomm, D. Mersch, Y. Vaynzof, E. Reisner,
Bard, J. Am. Chem. Soc. 1983, 105, 27 – 31; d) L. A. Lyon, J. T.
Hupp, J. Phys. Chem. B 1999, 103, 4623 – 4628.
Angew. Chem. Int. Ed. 2012, 51, 12749 – 12753; Angew. Chem.
2012, 124, 12921 – 12925.
[
18] The flat-band results determined from MS measurement are not
actually relevant to our actual photocatalysis condition because
of a difference in the solvents used. However, for the MS
measurement in DMF, it was difficult to get reliable/exact data
because the measured Efb value is significantly fluctuant (con-
tinuously lowered) with water adsorption of DMF solvent
[22] a) M. L. Helm, M. P. Stewart, R. M. Bullock, M. R. DuBois,
D. L. DuBois, Science 2011, 333, 863 – 866; b) U. J. Kilgore,
J. A. S. Roberts, D. H. Pool, A. M. Appel, M. P. Stewart, M. R.
DuBois, W. G. Dougherty, W. S. Kassel, R. M. Bullock, D. L.
DuBois, J. Am. Chem. Soc. 2011, 133, 5861 – 5872; c) B. C. M.
Martindale, G. A. M. Hutton, C. A. Caputo, E. Reisner, J. Am.
Chem. Soc. 2015, 137, 6018 – 6025.
(
derived from the significant hygroscopic nature of DMF) over
[
[
[
[
23] Y. Kuramochi, J. Itabashi, K. Fukaya, A. Enomoto, M. Yoshida,
H. Ishida, Chem. Sci. 2015, 6, 3063 – 3074.
24] J. L. Grant, K. Goswami, L. O. Spreer, J. W. Otvos, M. Calvin, J.
Chem. Soc. Dalton Trans. 1987, 2105 – 2109.
25] S. Sato, T. Morikawa, T. Kajino, O. Ishitani, Angew. Chem. Int.
Ed. 2013, 52, 988 – 992; Angew. Chem. 2013, 125, 1022 – 1026.
26] Z. Guo, S. Cheng, C. Cometto, E. Anxolabꢁhꢆre-Mallart, S.-M.
Ng, C.-C. Ko, G. Liu, L. Chen, M. Robert, T.-C. Lau, J. Am.
Chem. Soc. 2016, 138, 9413 – 9416.
time during MS measurement. For this reason, we could not
continue the MS measurement in DMF and, instead, we did the
measurement in CH CN, the water adsorption ability of which is
3
relatively normal (thus resulting in almost constant values for
the measurement).
[
19] A. Gennaro, A. A. Isse, E. Vianello, J. Electroanal. Chem. 1990,
289, 203 – 215.
[
20] The water solubility of CO is calculated using the following
2
À4
3
3
À1
method: 3.3 ꢄ 10 [mol/m pa] ꢄ 101315 [pa] ꢄ 0.001 [m L ] =
.034 mol/L = 0.034 M. The Henryꢅs law constant
[molm pa ]) is obtained from the following reference: R.
Sander, Atmos. Chem. Phys. 2015, 15, 4399 – 4981.
0
(
À3
À1
Manuscript received: September 2, 2016
Revised: October 31, 2016
Final Article published: && &&, &&&&
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Photocatalysis
J.-S. Lee, D.-I. Won, W.-J. Jung, H.-J. Son,*
C. Pac,* S. O. Kang*
&&&& — &&&&
Widely Controllable Syngas Production by
a Dye-Sensitized TiO Hybrid System with
2
I
III
Re and Co Catalysts under Visible-Light
Irradiation
Syngas production: A dye-sensitized TiO2
produced both H and CO (syngas) in
2
hybrid system prepared by grafting a dye,
a CO -saturated dimethyl formamide/
2
III
a H -evolving Co catalyst, and a CO-
water solution. The H /CO ratio was
2
2
I
producing Re catalyst on TiO particles
widely controllable.
2
6
www.angewandte.org
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
These are not the final page numbers!