Photocatalytic Carbon Dioxide Reduction at p-Type Copper(I) Iodide

Article abstract of DOI:10.1002/cssc.201600289

A p-type semiconductor, CuI, has been synthesized, characterized, and tested as a photocatalyst for CO₂ reduction under UV/Vis irradiation in presence of isopropanol as a hole scavenger. Formation of CO, CH₄, and/or HCOOH was observed. The photocatalytic activity of CuI was attributed to the very low potential of the conduction band edge (i.e., ?2.28 V vs. NHE). Photocurrents generated by the studied material confirm a high efficiency of the photoinduced interfacial electrontransfer processes. Our studies show that p-type semiconductors may be effective photocatalysts for CO₂ reduction, even better than extensively studied n-type titanium dioxide, owing to the low potential of the conduction band edge.

Full text of DOI:10.1002/cssc.201600289

DOI: 10.1002/cssc.201600289
Full Papers
Photocatalytic Carbon Dioxide Reduction at p-Type
Copper(I) Iodide
Tomasz Baran,[a, b] Szymon Wojtyła,[a] Angela Dibenedetto,[b, c] Michele Aresta,[c, d] and
Wojciech Macyk*[a]
A p-type semiconductor, CuI, has been synthesized, character-
ized, and tested as a photocatalyst for CO2 reduction under
UV/Vis irradiation in presence of isopropanol as a hole scav-
enger. Formation of CO, CH4, and/or HCOOH was observed.
The photocatalytic activity of CuI was attributed to the very
low potential of the conduction band edge (i.e., ꢀ2.28 V vs.
NHE). Photocurrents generated by the studied material confirm
a high efficiency of the photoinduced interfacial electron-
transfer processes. Our studies show that p-type semiconduc-
tors may be effective photocatalysts for CO2 reduction, even
better than extensively studied n-type titanium dioxide, owing
to the low potential of the conduction band edge.
Introduction
Photocatalytic CO2 reduction is a challenging process in which,
similarly to photosynthesis, solar light can be converted into
chemical energy. This reaction is the opposite of most com-
monly studied photocatalytic reactions in which pollutants are
photooxidized to CO2. Nevertheless, the same photocatalysts
(mainly TiO2) are usually tested in both cases. Most metal
oxides, being n-type semiconductors, offer high oxidation
properties upon excitation, but at the same time they are rela-
tively mild reductants. In this paper we propose an alternative
approach to photocatalytic CO2 reduction based on the use of
p-type semiconductors, which in general disclose better reduc-
ing and worse oxidation properties in comparison to n-type
semiconductors.
in medicine, as well as for water splitting.[1–3] Shrinking resour-
ces of fossil fuels and an increasing CO2 level in the atmos-
phere, motivate scientists to consider photocatalysis as a po-
tential method enabling CO2 utilization.[4–7] Until now numer-
ous materials were tested as photocatalysts for CO2 reduction,
including: TiO2, CdS, ZnO, ZnS, Cu2O, WO3, BiVO4, Ta2O5, and
SiC, as well as hybrid systems involving co-catalysts.[8–14]
The photocatalytic reduction of CO2 may afford a variety of
products, depending on the photocatalyst, solvent, and elec-
Cꢀ
tron donor.[15–17] Unlike one-electron reduction of CO2 to CO2
,
a proton-assisted multi-electron reduction of CO2 requires
a lower energy (less negative potentials) and leads to stable
products. The final oxidation state of carbon depends on the
number of transferred electrons. Standard redox potentials of
CO2 reduction in water vary from ꢀ0.61 V for CO2/HCOOH
(2 eꢀ reduction) to ꢀ0.24 V for CO2/CH4 (8eꢀ reduction).[18]
Semiconductors may be categorized as intrinsic, p, and n
type.[19] An intrinsic material is a perfect crystalline semicon-
ductor, while n- and p-type materials contain impurities or
dopants in their lattices, having electron acceptor or donor
character, respectively. As the interfacial electron transfer is
a critical step in photocatalytic processes and the excess of
electrons leads to photodegradation of the photocatalyst, p-
type semiconductors, in which holes are majority charges,
seem to be more resistant to photocorrosion than n-type.[20–22]
In fact, the p-type semiconductors have in general lower Fermi
levels than n-type materials; therefore, they are more resistant
to oxidation than n-type semiconductors.
Solar energy driven photofixation and photoreduction of
CO2 is a prospective application of semiconductor-based pho-
tocatalysis. Photocatalytic processes have been intensively
studied for water and air purification, photodynamic processes
[a] Dr. T. Baran, S. Wojtyła, Prof. W. Macyk
Faculty of Chemistry
Jagiellonian University
Ingardena 3
30-060 Krakꢀw (Poland)
E-mail: macyk@chemia.uj.edu.pl
[b] Dr. T. Baran, Prof. A. Dibenedetto
Department of Chemistry
University of Bari
Orabona, 4
70125 Bari (Italy)
[c] Prof. A. Dibenedetto, Prof. M. Aresta
CIRCC
CuI is a direct semiconductor with a zincblende structure
below 643 K (g-CuI), a wurtzite structure between 643 and
673 K (b-CuI) and a rock salt structure above 673 K (a-CuI).[23]
The low temperature g-phase is a wide-band gap semiconduc-
tor with the band gap energy close to 3.1 eV and a potential
of the conduction band edge at ꢀ2.1 V vs. SHE (calculated
from data reported elsewhere).[24,25] The valence band is consti-
tuted of Cu-d and I-p orbitals.[23,26] g-CuI is a p-type semicon-
Via Celso Ulpiani, 27
70126 Bari (Italy)
[d] Prof. M. Aresta
IC2R srl, Technopolis
via Casamassima km 3, Valenzano
Bari 70100 (Italy)
Supporting Information for this article can be found under:
http://dx.doi.org/10.1002/cssc.201600289.
ChemSusChem 2016, 9, 1 – 7
1
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
ductor, while b- and particularly a-phases show the character
of an ionic conductor.
Recent studies show that CuI is a promising material for ap-
plication in organic electronic devices. CuI is characterized by
a high conductivity and exhibits a high optical transparency
under visible light. These properties make CuI thin films very
useful in dye-sensitized solar cells[27] or as hole-injection layers
in organic light-emitting diodes.[28] The g-phase CuI can also
find application in bipolar diodes (e.g., p-CuI/n-ZnO)[29] or as
an electrocatalyst.[30] However, the activity of CuI in photocata-
lytic processes remains unraveled. To our best knowledge
there are no reports on application of CuI as a photocatalyst.
Very recently, a CuI-RGO (reduced graphene oxide) system was
tested in photocatalytic degradation of organic dyes; however,
in these studies CuI did not play the role of a photocatalyst
(did not absorb light), but it was used as a core in the core–
shell structure of CuI-RGO.[31]
Figure 1. SEM images of (a) commercial and (b) recrystallized CuI.
In our recent papers on CO2 utilization, we described semi-
conductor systems capable of one-[32,33] and multi-electron re-
duction of CO2,[14] as well as a hybrid photocatalytic–enzymatic
reduction of CO2 to methanol.[34,35] The use of p-type photoca-
talysts for CO2 reduction can be justified by considerably low
potentials of conduction band edges offering significantly
better reduction properties compared to those characteristic
for a majority of n-type materials. Thus, here we report the
first evidence of the photocatalytic activity of CuI and the first
studies on the application of this material for photocatalytic re-
duction of CO2.
Figure 2. XRD pattern of the recrystallized CuI material (green), commercial
CuI (orange line), and the reference pattern of g-CuI (JCPDS card no. 06–
0246) (black).
Results and Discussion
The commercial CuI powder is composed of particles
in a random size range of several tens of microme-
ters, as shown in the scanning electron microscopy
(SEM) image in Figure 1a. When water was quickly in-
jected into the CuI acetonitrile solution, a white pre-
cipitate was instantly formed owing to the strong an-
tisolvent effect of water. Recrystallized CuI forms ir-
regular aggregates of 50–300 nm (Figure 1b).
The crystal structure of recrystallized CuI was de-
termined by X-ray diffraction (XRD, Figure 2). The
main phase of the as-prepared material is g-CuI with
Figure 3. Transformed diffuse reflectance spectrum of recrystallized CuI (left) and estima-
the diffraction peaks at 25, 29, 43, 50, 52, 62, 67, and
698, attributed to (111), (200), (220), (311), (222),
(400), (331), and (420) planes, respectively (JCPDS,
tion of its band gap energy (right).
No. 06-0246). The structure of g-CuI was refined in the F4-3m
space group. Particle sizes calculated from Scherrer equation
are 60 and 20 nm for commercial and recrystallized CuI, re-
spectively.
of commercial CuI is 3.15 eV, as measured for the material ob-
tained from Sigma–Aldrich.
The photoactivity of CuI was analyzed by photocurrent
measurements in the potential range of 0.65 to 0.15 V versus
RHE (at pH 6.9, irradiation at 390 nm; Figure 4). Only cathodic
photocurrents, typical for p-type semiconductors, were gener-
ated under the applied conditions. Under nitrogen atmos-
phere, the photocurrent density varied from a few up to
70 mAcmꢀ2. In the presence of CO2, a significant increase of
the photocurrent density was observed (up to 200 mAcmꢀ2).
Under oxygen-free atmosphere, the cathodic photocurrent re-
sults from two parallel processes: water splitting and CO2 re-
Diffuse reflectance spectra of the prepared CuI, converted to
Kubelka–Munk function, are presented in Figure 3. CuI shows
absorption of light of wavelength lower than 420 nm. The
band gap energy was estimated from Tauc’s plot, [KMꢁE]n
versus E, where E is the photon energy, KM is the Kubelka–
Munk function, and n is the index and is equal to 2 for direct
allowed transition. The calculated band gap energy (EBG) for
the direct semiconductor is equal to 3.30 eV. The value of EBG
&
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
2
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
Figure 5. Nyquist plots measured in the dark at various potentials in the
range of 0 to 0.6 V versus SCE. The inset presents the equivalent circuit used
to fit the impedance data.
Figure 4. Photocurrents recorded for CuI as a function of the applied poten-
tial. Measurements with chopped incident light (390 nm). The electrolyte
(pH 6.9) was saturated with N2 or CO2.
duction. As the pH was kept at the same level in both meas-
urements, the photocurrent amplification under CO2 atmos-
phere can be attributed to the reduction of CO2. Prolonged
photocurrent measurements under chopped light prove the
stability of recrystallized CuI up to more than 5 h (see Fig-
ure S1 in the Supporting Information).
Mott–Schottky measurements (electrochemical impedance
spectroscopy) were employed to determine the flat-band po-
tential of the photocatalyst. The capacitance of the space-
charge layer depends on the applied potential according to
the formula:
ꢀ
ꢁ
Figure 6. Mott–Schottky plot for CuI. EFB was calculated from the linear fit-
ting (red curve; y=ꢀ2.08ꢁ1010x+1.62ꢁ1010).
1
C2SC
2
kt
e
¼
E ꢀ EFB ꢀ
eee0N
recrystallized CuI photocatalyst. The flat-band potential is close
to the potential of the upper edge of valence band for p-type
semiconductors[37] and is equal to 0.78 V versus SCE (1.02 V vs.
NHE). Knowing the flat-band potential and EBG (3.30 eV, vide su-
pra), we can estimate the potential of the conduction band
edge (ECB), which amounts to ꢀ2.28 V versus NHE. It is suffi-
ciently negative to reduce CO2 (redox potentials of CO2 reduc-
where e is the dielectric constant of the sample, e0 is the
vacuum permittivity, e is the charge of electron, N is the con-
centration of hole acceptor (for p-type semiconductors), E is
the applied potential, EFB is the flat band potential, k is the
Boltzmann constant, T is the temperature, and C (or CPE) is the
capacitance of the space charge layer.[36] The impedance ZCPE
of the CPE is given by:
Cꢀ
tion vary from ꢀ1.9 V vs. NHE for CO2/CO2 to ꢀ0.24 V versus
NHE for CO2/CH4 (values for aqueous solutions, pH 7).[18]
1
ZCPE
¼
a
QðjwÞ
The photocatalytic reduction of CO2 in the presence of the
recrystallized CuI has been tested. Irradiation of the suspen-
sions of CuI in chloroform in the presence of isopropanol as H-
transfer agent resulted in the reduction of CO2 to various prod-
ucts, including HCOOH, CO, and CH4, as summarized in
Figure 7 and Table 1. Chloroform has been selected to facilitate
the analysis of products (GC, NMR). HCOOH was determined
by 1H NMR (Figure 7a) while the gaseous products (CO and
CH4) were quantified based on GC analysis (Figure 7b). The
commercial sample of CuI (Sigma–Aldrich) was only able to
reduce CO2 to CO under the same reaction conditions. After
5 h irradiation the concentration of CO in the gas phase above
where w is the frequency and a equals unity for an ideal ca-
pacitor. Figure 5 shows the electrochemical impedance spectra
(Nyquist plots) measured at various potentials in the range of
0 to 0.6 V in the dark. Data shown in Figure 5 are fitted consid-
ering the equivalent circuit depicted in the inset (R1 and R3
refer to the solution and polarization resistances, respectively,
CPE is a constant phase element).
Resulting Mott–Schottky plot (dependence of the calculated
capacitance on the electrode potential) is shown in Figure 6.
The negative slope of the plot proves the p-type nature of the
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
3
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
products were higher than those recorded for commercial CuI.
For instance, after 5 h of irradiation, HCOOH was found as the
main product in solution, with a concentration exceeding
800 mmoldmꢀ3. A commercial TiO2 photocatalyst (P25; n-type
material) applied under identical conditions showed very low
photocatalytic activity; 5 h irradiation resulted in the produc-
tion of 3 mmoldmꢀ3 of CH4 and 2.7 mmoldmꢀ3 of H2 (Fig-
ure 7c). Neither CO nor HCOOH was detected after irradiation.
To exclude the possibility of other routes of C1 products for-
mation (e.g., oxidation of contaminants originating from an in-
complete removal of organic solvents during preparation of
the photocatalyst or oxidation of isopropanol) additional con-
trol experiments were performed. The suspensions of photoca-
talysts were irradiated in the absence of CO2 (solutions were
purged with Ar to remove CO2 and O2 dissolved in chloroform)
and the presence of isopropanol. Neither CH4 nor CO and any
other carbon-containing products were detected (data not
shown), indicating that all observed products originate from
the reduction of CO2 and not from the oxidation of any organ-
ic component of the system. The reduction did not proceed in
systems lacking one of the following components: the photo-
catalyst, light, electron donor, or CO2 (tested in the systems
with recrystallized and commercial CuI, data not shown). These
experiments prove, that isopropanol acted as the hole scav-
enger giving rise to acetone production, a typical product of
iPrOH oxidation, confirmed also by 13C NMR analysis, peaks
29.6 and 206 ppm shown in Figure S2. Moreover, further oxida-
tion of acetone cannot be excluded, as its oxidation potential
is 0.126 V.[38] To understand better the stability of the material,
the XRD pattern of CuI used previously as a photocatalyst for
5 h has been collected. Results (compare Figure S3) prove that
the material after 5 h of irradiation is composed mainly of CuI;
however, some peaks characteristic for metallic Cu, CuI, and
CuO have been found on the diffractogram.
Figure 7. Products of CO2 reduction in the presence of various photocata-
lysts and isopropanol as the electron donor: a) 1H NMR spectra of the reac-
tion mixture before and just after irradiation in the presence of CuI (spectra
recorded after addition of CD3Cl); b) GC analysis of gas phase above the re-
action mixture (photocatalyst: CuI); and c) summarized results of products
analysis after 5 h irradiation.
Table 1. Comparison of activity of various photocatalyts toward CO2 re-
duction to selected products.[a]
Products
Photocatalyst
CuI commercial
CuI recrystallized
TiO2
CO
H2
CH4
HCOOH
160
–
–
300
11
114
813
–
2.7
3.0
–
2.2
[a] Concentrations of all products in mmol dmꢀ3. Reaction was led in de-
oxygenated chloroform+isopropanol 10 vol% upon irradiation for 5 h by
150 W XBO arc lamp (l>300 nm).
Conclusions
the reaction mixture reached 160 mmoldmꢀ3 (the headspace
volume was 9.5 mL). The use of recrystallized CuI led to gener-
ation of the enhanced amounts of the reduction products
(HCOOH, CO, and CH4; Figure 8). The formation rates of all
Prepared p-type CuI was successfully applied as a photocatalyst
for CO2 reduction. Recrystallization of CuI leads to the forma-
tion of significantly smaller, more photoactive particles. Small
size of particles is reflected in: i) a larger specific surface area,
ii) more efficient transport of photogenerated charges from the
bulk to the surface, and iii) a higher rate of CO2 photoreduction
owing to increased amount of adsorbed CO2.
The analysis of photocurrents generated by the studied ma-
terial confirms a high efficiency of the photoinduced interfacial
electron-transfer processes for CuI. This effect may result either
from a good charge separation or from a less efficient recom-
bination.
The mechanism of photocatalytic process is shown in
Figure 9. Potentials of the conduction band edges of p-type
semiconductors are usually lower than those of n-type materi-
als (ꢀ2.28 V vs. NHE for CuI estimated from the Mott–Schottky
analysis, compared to about ꢀ1.0 V vs. NHE for P25 TiO2 mea-
sured using spectroelectrochemical method).[39] Reduction of
CO2 requires good reduction properties (e.g., ꢀ1.8 V for one-
Figure 8. Photoreduction of CO2 in the presence of recrystallized (left) and
commercial (right) CuI.
Cꢀ
electron reduction to CO2 or ꢀ0.61 to ꢀ0.24 V for multi-elec-
&
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
4
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Papers
of 0.1 moldmꢀ3 K2HPO4 +KH2PO4 (pH 6.9). Electrolyte was saturated
by N2 or CO2 before each scan. Platinum and saturated calomel
electrode were used as counter and reference electrodes, respec-
tively. The working electrodes were prepared by covering the fluo-
rine-doped tin oxide (FTO) glass with a photocatalyst suspension.
A LED illuminator (l=390 nm) was used for irradiation. The work-
ing electrodes were irradiated from the backside, through the FTO,
to minimize the influence of the thickness of the semiconductor
layer on the photocurrent. The electrochemical measurements
were controlled by the electrochemical analyzer (PGSTAT 302N, Au-
tolab). Electrochemical impedance measurements were performed
in deoxygenated 0.1 moldmꢀ3 K2HPO4 +KH2PO4 electrolyte solu-
tion, pH 7.1. Impedance spectra were recorded at fixed potentials
in the frequency range 1 MHz to 0.1 Hz using Autolab PGSTAT
302N analyzer. The potential was stepped by 50 mV in the range
from 0 to 0.6 V versus SCE with a waiting time of 180 s before the
next spectra were recorded. The impedance data were fitted using
equivalent circuits.
Figure 9. Mechanism of CO2 reduction on the p-type semiconductors.
tron processes leading to the formation of formic acid or
methane, respectively). Therefore, the photocatalytic CO2 re-
duction should be thermodynamically favored in the presence
of p-type semiconductors characterized by low potentials of
conduction band edges. In the case of p-type materials photo-
corrosion leads to the formation of metal(0).[40] This process
may, to some extent, have a positive influence on the CO2 re-
duction efficiency, as the metallic nanoparticles may act as co-
catalysts (e.g., electron sinks); however, this effect requires
a deeper study. Stability and photostability of semiconductors,
both n- and p-type, depends in general on the redox proper-
ties of the system components (in particular of the applied sol-
vent);[41] therefore, it can be controlled, at least to some
extent. This opens a possibility for further improvement of
(photo)stability of the photocatalyst. Our studies show that p-
type CuI may appear an effective photocatalyst of CO2 reduc-
tion. Very likely p-type semiconductors may often appear
better photocatalysts of this reaction than extensively studied
n-type titanium dioxide.[42,43] Other solvents will be considered
in further studies focused on the process optimization and
scaling up.
Photocatalytic tests of CO2 reduction were performed in a quartz
cylindrical cuvette (total volume of 15 mL) equipped with a rubber
septum. The photocatalyst (1 gdmꢀ3) was suspended in distilled,
deoxygenated chloroform (5 mL). Isopropanol was used as an elec-
tron and proton donor (0.5 mL). Noteworthy, isopropanol is used
in industry as an H2-transfer agent. The suspension was purged
with CO2 for 15 min in an ice bath. The suspension was irradiated
in the sealed cuvette using a 150 W XBO arc lamp as a light source
(l>300 nm). Gas samples were collected at fixed time intervals
during irradiation and analyzed by GC (Thermo Scientific Focus GC
with a TCD detector and Carboxen-1000 plot column). Liquid sam-
ples were filtered through syringe filters (0.2 mm) diluted 1:1 with
CD3Cl and analyzed with NMR (Bruker 600 MHz).
Acknowledgements
The authors thank Anna Regiel-Futyra for SEM measurements.
The support from the Foundation for Polish Science within the
VENTURES/2011-8/1 Project and the Project TEAM/2012-9/4, both
co-financed by the EU European Regional Development Fund, is
highly acknowledged. Collaboration with IC2R srl and VALBIOR-
Apulia Network is acknowledged.
Experimental Section
Keywords: carbon dioxide reduction
· copper(I) iodide ·
Nanocrystalline CuI has been prepared according to the method
described elsewhere with minor modifications.[44] 0.1 g of commer-
cial CuI powder (Sigma Aldrich) was dissolved in 3 mL of acetoni-
trile by ultrasonication. 15 mL of water was quickly injected into
the CuI solution through a syringe pinhole under vigorous magnet-
ic stirring. Formed white precipitate was collected by centrifuga-
tion, washed with water (3 times) and ethanol (once) and dried in
air at 808C for 12 h.
electron transfer · photocatalysis · p-type semiconductors
[1] S. Fꢂldner, R. Mild, H. I. Siegmund, J. A. Schroeder, M. Gruber, B. Kçnig,
Green Chem. 2010, 12, 400–406.
[2] T. Baran, W. Macyk, J. Photochem. Photobiol. A 2012, 241, 8–12.
[3] K. Szaciłowski, W. Macyk, A. Drzewiecka-Matuszek, M. Brindell, G. Sto-
chel, Chem. Rev. 2005, 105, 2647–2694.
[4] M. Mikkelsen, M. Jørgensen, F. C. Krebs, Energy Environ. Sci. 2010, 3, 43–
81.
UV/Vis diffuse reflectance spectra of CuI were recorded using a UV-
3600 spectrophotometer (Shimadzu) equipped with an integrating
sphere (15 cm diameter). The sample was ground with BaSO4 (1:50
w/w). The prepared material was analyzed using the X-ray powder
diffractometer (MiniFlex 600, Rigaku) operated at 40 kV. Data were
collected in the angular range of 208<2q<708 for a total count-
ing time of 45 min per pattern. SEM images were collected at the
scanning electron microscope (Vega 3 LMU, Tescan) equipped with
an LaB6 cathode. A three-electrode set-up was employed for pho-
tocurrent measurements. The electrolyte solution was composed
ˇ
´
[5] K. Kocꢃ, L. Obalovꢄ, Z. Lacny, Chem. Pap. 2008, 62, 1–9.
[6] J. Albo, M. Alvarez-Guerra, P. CastaÇo, A. Irabien, Green Chem. 2015, 17,
2304–2324.
[7] M. Aresta, A. Dibenedetto, A. Angelini, Chem. Rev. 2014, 114, 1709–
1742.
ˇ
ˇ
ˇ
ˇ
´
[8] K. Kocꢃ, L. Matejovꢄ, M. Reli, L. Capek, V. Matejka, Z. Lacny, P. Kustrowski,
L. Obalovꢄ, Catal. Today 2014, 230, 20–26.
[9] M. Anpo, J. CO2 Util. 2013, 1, 8–17.
[10] S. Wang, X. Wang, Appl. Catal. B 2015, 162, 494–500.
[11] T. Ohno, N. Murakami, T. Koyanagi, Y. Yang, J. CO2 Util. 2014, 6, 17–25.
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

Full Papers
[12] P. Pathak, M. J. Meziani, L. Castillo, Y.-P. Sun, Green Chem. 2005, 7, 667–
670.
[31] J. Choi, D. A. Reddy, M. J. Islam, B. Seo, S. H. Joo, T. K. Kim, Appl. Surf. Sci.
DOI: 10.1016/j.apsusc.2015.07.170.
[13] A. Dhakshinamoorthy, S. Navalon, A. Corma, H. Garcia, Energy Environ.
Sci. 2012, 5, 9217–9233.
[32] M. Aresta, A. Dibenedetto, T. Baran, S. Wojtyła, W. Macyk, Faraday Dis-
cuss. 2015, 183, 413–427.
[14] T. Baran, S. Wojtyła, A. Dibenedetto, M. Aresta, W. Macyk, Appl. Catal. B
2015, 178, 170–176.
[33] T. Baran, A. Dibenedetto, M. Aresta, K. Kruczała, W. Macyk, Chem-
PlusChem 2014, 79, 708–715.
[15] B.-J. Liu, T. Torimoto, H. Matsumoto, H. Yoneyama, J. Photochem. Photo-
biol. A 1997, 108, 187–192.
[34] A. Dibenedetto, P. Stufano, W. Macyk, T. Baran, C. Fragale, M. Costa, M.
Aresta, ChemSusChem 2012, 5, 373–378.
[16] S. N. Habisreutinger, L. Schmidt-Mende, J. K. Stolarczyk, Angew. Chem.
Int. Ed. 2013, 52, 7372–7408; Angew. Chem. 2013, 125, 7516–7557.
[17] M. Aresta, A. Dibenedetto, A. Angelini, Philos. Trans. R. Soc. A 2013, 371,
20120111.
[35] M. Aresta, A. Dibenedetto, T. Baran, A. Angelini, P. Łabuz, W. Macyk, Beil-
stein J. Org. Chem. 2014, 10, 2556–2565.
[36] S. P. Harrington, T. M. Devine, J. Electrochem. Soc. 2009, 156, C154–
C159.
[18] E. Fujita, Coord. Chem. Rev. 1999, 185–186, 373–384.
[19] A. Hernꢄndez-Ramꢃrez, I. Medina-Ramirez in Photocatalytic Semicond.,
Springer, Cham, 2015.
[20] H. Gerischer, M. Lꢂbke, Ber. Bunsen-Ges. 1983, 87, 123–128.
[21] C. A. Mead, W. G. Spitzer, Phys. Rev. Lett. 1963, 10, 471–472.
[22] M. Grꢅtzel, Nature 2001, 414, 338–344.
[23] M. Grundmann, F.-L. Schein, M. Lorenz, T. Bçntgen, J. Lenzner, H. von
Wenckstern, Phys. Status Solidi A 2013, 210, 1671–1703.
[24] V. P. S. Perera, K. Tennakone, Sol. Energy Mater. Sol. Cells 2003, 79, 249–
255.
[25] K. Tennakone, G. R. R. A. Kumara, I. R. M. Kottegoda, V. P. S. Perera,
P. S. R. S. Weerasundara, J. Photochem. Photobiol. A 1998, 117, 137–142.
[26] K.-S. Song, J. Phys. Chem. Solids 1967, 28, 2003–2009.
[27] A. R. Zainun, M. H. Mamat, U. M. Noor, M. Rusop, Adv. Mater. Res. 2013,
667, 447–451.
[37] Y. Nakabayashi, M. Nishikawa, Y. Nosaka, Electrochim. Acta 2014, 125,
191–198.
[38] H. Adkins, R. M. Elofson, A. G. Rossow, C. C. Robinson, J. Am. Chem. Soc.
1949, 71, 3622–3629.
[39] M. Bledowski, L. Wang, A. Ramakrishnan, O. V. Khavryuchenko, V. D.
Khavryuchenko, P. C. Ricci, J. Strunk, T. Cremer, C. Kolbeck, R. Beranek,
Phys. Chem. Chem. Phys. 2011, 13, 21511–21519.
[40] R. van de Krol in Photoelectrochem. Hydrog. Prod. (Eds.: R. van de Krol,
M. Grꢅtzel), Springer, New York, 2012, pp. 13–67.
[41] H. Gerischer, J. Vac. Sci. Technol. 1978, 15, 1422–1428.
[42] B. Michalkiewicz, J. Majewska, G. Ka˛dziołka, K. Bubacz, S. Mozia, A. W.
Morawski, J. CO2 Util. 2014, 5, 47–52.
[43] J. Fu, S. Cao, J. Yu, J. Low, Y. Lei, Dalton Trans. 2014, 43, 9158.
[44] R. Kozhummal, Y. Yang, F. Gꢂder, U. M. KꢂÅꢂkbayrak, M. Zacharias, ACS
Nano 2013, 7, 2820–2828.
[28] P. Stakhira, V. Cherpak, D. Volynyuk, F. Ivastchyshyn, Z. Hotra, V. Tataryn,
G. Luka, Thin Solid Films 2010, 518, 7016–7018.
[29] F.-L. Schein, H. von Wenckstern, M. Grundmann, Appl. Phys. Lett. 2013,
102, 092109.
Received: March 3, 2016
[30] G. Karim-Nezhad, N. Alipour, Curr. Chem. Lett. 2014, 3, 133–140.
Published online on && &&, 0000
&
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
Enhanced p-type: Copper(I) iodide, a p-
type semiconductor, shows a significant-
ly higher photoactivity toward CO2 re-
duction than extensively studied n-type
titanium dioxide. The enhanced photo-
catalytic activity of CuI is attributed to
the very low potential of the conduc-
tion band edge
T. Baran, S. Wojtyła, A. Dibenedetto,
M. Aresta, W. Macyk*
&& – &&
Photocatalytic Carbon Dioxide
Reduction at p-Type Copper(I) Iodide
ChemSusChem 2016, 9, 1 – 7
www.chemsuschem.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ