Catechol-TiO2 hybrids for photocatalytic H2 production and photocathode assembly

Article abstract of DOI:10.1039/c7cc05094a

Visible-light driven H₂ evolution in water is achieved using catechol-photosensitised TiO₂ nanoparticles with a molecular nickel catalyst. Layer-by-layer immobilisation of catechol-TiO₂ onto tin-doped indium oxide electrodes generates photocathodic currents in the presence of an electron acceptor. This approach represents a new strategy for controlling photocurrent direction in dye-sensitised photoelectrochemical applications.

Full text of DOI:10.1039/c7cc05094a

ChemComm
View Article Online
View Journal
COMMUNICATION
Catechol–TiO2 hybrids for photocatalytic H2
production and photocathode assembly†‡
Cite this:DOI: 10.1039/c7cc05094a
ab
a
Katherine L. Orchard,
Meng-Ju Chan,
Daisuke Hojo,b Katarzyna P. Sokol,
Naoki Asao, §b Tadafumi Adschiri*b and Erwin Reisner
*
b
a
Received 1st July 2017,
Accepted 5th September 2017
DOI: 10.1039/c7cc05094a
rsc.li/chemcomm
Visible-light driven H2 evolution in water is achieved using catechol-
photosensitised TiO2 nanoparticles with a molecular nickel catalyst.
Layer-by-layer immobilisation of catechol–TiO2 onto tin-doped
indium oxide electrodes generates photocathodic currents in the
presence of an electron acceptor. This approach represents a new
strategy for controlling photocurrent direction in dye-sensitised
photoelectrochemical applications.
Immobilising molecular dyes onto wide band-gap metal oxide
semiconductors is a well-established strategy for preparing tuneable,
visible-light responsive materials from relatively inexpensive compo-
nents. This approach was pioneered for solar energy conversion in
dye-sensitised solar cells (DSCs)1 and is an emerging field in the area
of solar fuels synthesis.2 In the majority of dye-sensitised systems,
photoexcitation occurs in the dye (HOMO–LUMO transition)
followed by fast charge injection into the semiconductor (Type I
sensitisation, Fig. 1a). This approach has been effective in H2
production using dye-sensitised photocatalysis (DSP)2a and in
forming photoanodes for dye-sensitised photoelectrochemical cells
(DSPEC);2b,c however, the translation of DSP systems to photo-
cathodes is more challenging, often relying on low-performance
Fig. 1 (a) Energy transfer in Type I (two-step) and Type II (one-step) dye-
sensitised TiO2 systems; (b) diffuse reflectance absorption spectrum of
catechol-modified TiO2 compared to bare TiO2 and the transmission spectrum
of catechol in water (catechol shown is DHCA); (c) solar H2 production in DSP
system (AA = ascorbic acid); (d) layer-by-layer photocathode incorporating
catechol–TiO2 (A = acceptor; catechol shown is DHSP).
p-type semiconductors (such as NiO)3 or molecular engineering4 low-cost alternative in DSCs5 and solar fuel production.6 Type II
to control the direction of electron transfer. sensitisation is known to occur in TiO2 functionalised with phenol
Charge-transfer sensitisation, in which photoexcitation occurs and enediol groups, such as catechols.5d These groups bind to Ti4+
directly from a surface-adsorbed molecule to the semiconductor ions on the surface of TiO2, forming complexes that absorb visible
conduction band (Type II, Fig. 1a), has recently been explored as a light due to ligand-to-metal charge-transfer (Fig. 1b).7 This one-
step transfer from dye to TiO2 results in very fast electron injection
(on the order of fs),5b and, importantly, by avoiding excitation into
the dye LUMO the charge-transfer is inherently directional (Fig. 1a
and Fig. S1, ESI‡). Type II sensitisation also occurs between carbon
nitride and TiO2, and has been used to enhance solar light-driven
H2 evolution with hydrogenase,8 and to form photoanodes for
photoelectrochemical water oxidation.9
a Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge,
CB2 1EW, UK. E-mail: reisner@ch.cam.ac.uk; Web: http://www-reisner.ch.cam.ac.uk
b WPI Advanced Institute for Materials Research (AIMR), Tohoku University,
2-1-1 Katahira Aoba-ku Sendai, Miyagi, 980-8577, Japan.
E-mail: ajiri@tagen.tohoku.ac.jp
† Additional data related to this publication are available at the University of
Cambridge data repository (https://doi.org/10.17863/CAM.13111).
‡ Electronic supplementary information (ESI) available: Additional figures,
tables, and experimental details. See DOI: 10.1039/c7cc05094a
§ Current address: Faculty of Textile Science and Technology, Shinshu University,
Ueda 386-8567, Japan.
Catechol-containing dyes based on alizarin red have been
studied for DSP and for photocurrent switching applications;10
however, these dyes are also Type I sensitisers.5d To our knowl-
edge, the only example of purely Type II visible-light driven H2
evolution uses phenolic resin-sensitised TiO2 nanoparticles,
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
with Pt as the H2 evolution catalyst (HEC) in the presence of a spectroscopy (Fig. S3, ESI‡), with an estimated NiP loading of
sacrificial electron donor (SED).6b,c 38 nmol mgÀ1 for caffeic acid (CA)-P25 (calculated using the
Replacing noble metals with inexpensive catalysts and mov- difference in absorption at 450 nm of a NiP solution before and
ing towards SED-free systems are both important goals in after exposure to TiO2). No H2 was detected in control experiments
achieving sustainable fuel synthesis. Here we take steps towards without AA, TiO2 or NiP, or with NiCl2 in place of NiP.
addressing these challenges by developing a new route for
AA can also sensitise TiO2 through charge-transfer interactions,
assembling noble metal-free photocathodes. First, we demon- resulting in small amounts of H2 evolution in the absence of
strate that Pt can be replaced by a 3d transition metal catalyst to additional catechol during visible light irradiation (Fig. 2b, ‘‘none’’);
form an active Type II DSP system (Fig. 1c). We then develop a however, all ex situ functionalised powders enhanced the activity
SED-free photoelectrochemical system, using the directionality compared to bare P25 (Fig. 2b and Fig. S4a, ESI‡). The highest
of the charge-transfer complex to form photocathodes on a activity was obtained with CA (Fig. 2), with an activity with respect
conductive electrode support (Fig. 1d).
to the powder of 273 Æ 29 mmol H2 gÀ1 after 4 h. The activity per
For the DSP system, a range of charge-transfer dye-sensitised hour of 73 Æ 3 mmol H2 (g TiO2)À1 hÀ1 was maintained over the
TiO2 powders were prepared by mixing simple catechol deriva- first 4 h, equivalent to a turnover frequency (TOF) per Ni catalyst of
tives (Fig. 2a) with commercial P25 TiO2 nanoparticles (average 3.6 Æ 0.2 mmol H2 (mmol NiP)À1 hÀ1 and TOF per catechol of 0.6 Æ
crystallite diameter 21 nm, 8 : 2 mixture of anatase : rutile). The 0.2 mmol H2 (mmol CA)À1 À1. This result is comparable to that
h
resulting coloured powders exhibited broad light absorption reported for the phenolic resin system with Pt (105 mmol gÀ1 hÀ1).6b
over the visible range (Fig. S2, ESI‡). The dye loadings ranged The TOFNi is an order of magnitude lower than previously reported
from 75–172 nmol (mg TiO2)À1 (Table S1, ESI‡). These loadings for the equivalent system with a Ru tris(bipyridine) dye, RuP,12 but
correspond to an estimated footprint of 0.5–1.1 nm2 moleculeÀ1
,
RuP can directly reduce NiP in solution, whereas the catechol
consistent with reported ranges for sub-monolayer to monolayer derivatives cannot. The lower extinction coefficient and faster
coverage of catechols on TiO2.11
recombination rate of the charge-transfer band relative to that of
Photocatalysis solutions were prepared by suspending the dye- metal-based dyes (ps13 vs. ns–ms2a) are also expected to contribute
P25 powders (2.5 mg) in aqueous SED solution (ascorbic acid, AA, to the difference in activity.
0.1 M, 2.25 mL). We selected the HEC [Ni(PPh2NC H CH P(O)(OH) 2)2]Br2,
The high activity of CA relative to the unconjugated analogue
6
4
2
2
NiP (Fig. 1c), as it has previously been shown to be highly active in 3,4-dihydroxyhydrocinnamic acid (DHCA) is consistent with the
aqueous DSP12 and DSPEC.3a,4b NiP (50 nmol) was added to the dye- red-shift in the absorption spectrum and increase in both the
P25 suspension as a solution in methanol (1 mM) before the catechol binding constant and the electron injection efficiency
photoreactors were purged with N2 and irradiated with simulated associated with greater conjugation.5b The activity per dye mole-
solar light (l 4 420 nm, AM 1.5 G, 100 mW cmÀ2). The formation of cule also reflects this trend for 2-(3,4-dihydroxybenzene)thiophene
the hybrid DSP system (Fig. 1c) is supported by FTIR and UV-vis (DHBT; Fig. S4b, ESI‡); however, the lower loading of DHBT on
TiO2 compared to CA (Table S1, ESI‡) resulted in a lower activity
per gram (Fig. 2b). Ring conjugation (2,3-naphthalenediol, ND)
did not enhance activity (Fig. 2b and Fig. S4b, ESI‡), which is
likely due to the comparatively low visible light absorption of
ND-P25 (Fig. S1, ESI‡).
The turnover number per Ni (TONNi) increased with decreasing
NiP loading (Fig. S5a, ESI‡) and increasing CA-P25 powder loading
(Fig. S6a, ESI‡). However, the corresponding activity per gram
decreased with decreasing NiP loading (Fig. S5b, ESI‡) and reached
a maximum at a CA-P25 loading of 1.25 mg (Fig. S6b, ESI‡). Since
increasing the powder loading increases both the dye loading and
the particle : Ni ratio, it can be inferred that the H2 production rate
is limited by the generation and supply of electrons to NiP. This
conclusion is supported by the decrease in activity of the system on
decreasing the light intensity (Fig. S7, ESI‡). The external quantum
efficiency (EQE) of the most active system (5 mg CA-P25, 50 nmol
NiP) was measured to be 0.09 Æ 0.01%.
Since light absorption is related to the number of catechol–
TiO2 surface interactions, light absorption per g can be enhanced
by using smaller nanoparticles to increase the surface area. We
synthesised TiO2 nanoparticles by a previously reported method
(pure anatase, average diameter B7 nm, AN7–TiO2, see Fig. S8,
ESI‡ for TEM)14 and tested both these and commercial pure
anatase nanoparticles (10 nm, AN10–TiO2, Fig. S7, ESI‡) under
the standard DSP conditions (CA–TiO2, 2.5 mg, 50 nmol NiP).
Fig. 2 (a) Chemical structures of charge-transfer dyes used in this study
(catechol = 1,2-dihydroxybenzene, DHBA = 3,4-dihydroxybenzoic acid,
DHCA = 3,4-dihydroxyhydrocinnamic acid, CA = caffeic acid, DHBT =
2-(3,4-dihydroxybenzene)thiophene, ND = 2,3-naphthalenediol, AA = ascorbic
acid); (b) comparison of visible-light driven H2 evolution with charge-transfer
dye-functionalised P25 TiO2 powders in the presence of a molecular
Ni catalyst, NiP (0.1 M AA, pH 4.5, 2.5 mg powder, 50 nmol NiP, 2.25 mL,
l 4 420 nm, AM 1.5 G, 100 mW cmÀ2, 25 1C).
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017

View Article Online
ChemComm
Communication
However, despite the increase in catechol loading (505 nmol contrast to the photocatalysis results, the electrodes with the
(mg TiO2)À1; Table S1, ESI‡) and light absorption (Fig. S9, ESI‡) highest photocurrent in the presence of an acceptor (O2) were
compared to P25, these particles displayed less photocatalytic those prepared with AN7–TiO2 nanoparticles (Fig. S14, ESI‡).
activity (Fig. S10, ESI‡). The lower performance was not found The nanoparticles were deposited by immersion of the IO–
to be due to a difference in binding of NiP to the particles (48 ITO|DHSP electrodes in a stock solution of oleic acid-capped
and 51 nmol mgÀ1 for AN10–TiO2 and AN7–TiO2, respectively). AN7–TiO2,18 followed by treatment with NEt3 (10 vol% in
However, it is likely that the smaller, pure anatase particles ethanol) to remove surface oleic acid, as confirmed by FTIR
suffer from less efficient charge separation compared to the spectroscopy (Fig. S15, ESI‡). The formation of the charge-
larger, mixed-phase (anatase/rutile) P25.15 Pure rutile phase transfer complex was evidenced by a change in colour of the
TiO2 nanoparticles (R–TiO2, 10–30 nm) displayed lower activity electrodes from pale yellow/green to peach (Fig. S16, ESI‡). The
than P25, AN10, and AN7–TiO2 (4.9 Æ 0.3 after 3 h, Table S2 and loading of TiO2 was measured to be 212.4 mg cmÀ2 for 12 mm
Fig. S10, ESI‡).
thick IO–ITO (Ti content; Inductively Coupled Plasma-Optical
Having established that catechol–TiO2 hybrids are effective Emission Spectroscopy, ICP-OES), which corresponds to approxi-
light absorbers for (UV-filtered) solar H2 evolution with NiP, we mately 83 nmol of nanoparticles per cm2.
sought to transfer the DSP system onto photoelectrodes. We
Scanning electron microscopy (SEM) of AN7–TiO2 on DHSP-
designed a layer-by-layer route to immobilise the TiO2 nano- functionalised flat ITO showed that an even monolayer of particles
particles onto a degenerately doped n-type metal oxide support is formed (Fig. S17, ESI‡), and energy-dispersive X-ray spectroscopy
(indium tin oxide, ITO) in a directed, sequential fashion (EDX) of the fully assembled IO–ITO|DHSP|AN7–TiO2 electrodes
(Fig. 1d). In order to maximise the deposition of the TiO2 showed that the particles are evenly distributed throughout the
nanoparticles in our system, we used hierarchical inverse opal IO–ITO structure (Ti content of 11.8, 11.4, and 10.7 at% for
mesoporous ITO electrodes (IO–ITO; Fig. S11a, ESI‡). IO–ITO is the top, middle, and bottom part of the IO–ITO structure
an effective support for nanoscale adsorbates such as enzymes respectively; Fig. S18a, ESI‡). In contrast, EDX analysis of
(e.g. Photosystem II, 10.5 Â 20.5 Â 11.0 nm3), owing to their equivalent electrodes prepared with P25 TiO2 showed that these
open, macroporous structure (750 nm pores with 150 nm nanoparticles do not penetrate beyond the surface (10–12 at%
interconnecting chambers) and high surface area mesoporous Ti detected only on the top surface and none at lower layers;
scaffold (formed from o50 nm ITO nanoparticles).16 Meso- Fig. S18b, ESI‡). The difference in particle distribution, and
porous ITO (mesoITO) electrodes (1 mm thickness, Fig. S11b, subsequent performance, is attributed to the better size match
ESI‡) were also prepared for comparison.17
of the macro- and mesopores of the IO–ITO structure to the
By studying the attachment of DHCA to IO–ITO in the small, well-dispersed AN7–TiO2 compared to the larger, aggre-
presence or absence of one equivalent of propylphosphonic gated P25 particles (close to micron-sized aggregates of 20 nm
acid by UV-vis spectroscopy, we found that ITO binds preferen- particles; see Fig. S8, ESI‡ for TEM). AN10–TiO2 nanoparticles
tially to phosphonate groups over catechol groups (83% of also form aggregates (Fig. S8, ESI‡), resulting in low perfor-
DHCA is displaced; Fig. S12a, ESI‡). We therefore synthesised mance (Fig. S14, ESI‡).
(E)-(3,4-dihydroxystyryl)phosphonic acid (DHSP; see Fig. 1d and
In the presence of the electron acceptor O2, cathodic photo-
ESI‡ for synthetic details) as a bifunctional, phosphonated currents were obtained under visible light irradiation (l 4 400 nm,
catechol that is expected to bind to ITO in the correct orientation 100 mW cmÀ2) with IO–ITO|DHSP|AN7–TiO2 electrodes below the
for subsequent formation of the charge-transfer interaction with redox potential of DHSP (Eapplied = 0.3 V vs. RHE, Fig. 3a). Initial
TiO2. In contrast to ITO, TiO2 has an approximately equal binding current spikes were observed in the photocurrent curves of these
affinity for catechol and phosphonic acid groups (45% of DHCA electrodes (Fig. 3a), which likely occur due to rapid polarisation
was displaced in the presence of propylphosphonic acid; and charge accumulation at the electrode.19 A switch to anodic
Fig. S12b, ESI‡). Therefore, formation of the charge-transfer photocurrent was observed at potentials where DHSP is oxidised
complex was only effective if DHSP was anchored to ITO before (Eapplied 4 B0.7 V vs. RHE, Fig. S19, ESI‡). The photocurrent is
adding TiO2; ex situ-prepared DHSP-sensitised P25 powders did attributed to the formation of the charge-transfer complex since
not absorb appreciably in the visible-light region.
little photocurrent is obtained in the absence of the catechol and/or
DHSP was anchored onto ITO by incubating the electrodes in an TiO2 (Fig. 3a). The magnitude of the photocurrent scales with the
aqueous stock solution (1 mM, 2–8 1C, 16 h). Cyclic voltammetry thickness of the ITO scaffold, reflecting the increase in loading of
(CV) of DHSP-functionalised flat ITO shows a quasi-reversible wave the dye–TiO2 complex with increasing ITO surface area (Fig. 3b).
(E1/2 = 0.84 V vs. RHE), which can be assigned to the catechol/ The photocathodic currents obtained with 12 mm thick IO–ITO
semiquinone redox couple (Fig. S13, ESI‡). By monitoring the (70 mA cmÀ2) are comparable to those obtained with Ru-based
change in absorbance of a stock solution of DHSP (1 mM) at Type I dyes in the presence of an acceptor,20 demonstrating the
280 nm after incubation with IO–ITO electrodes, the loading of promise of employing metal-free Type II dyes.
DHSP was estimated to be 64 Æ 11 nmol cmÀ2, which matches
In the absence of O2 (N2 purged solution), small cathodic
the loading estimated from the charge passed during CV currents were maintained for the bare IO–ITO|DHSP|AN7–TiO2
(55.5 nmol cmÀ2, see ESI‡).
electrodes (Fig. S20, ESI‡). Although NiP could be immobilised
The final charge-transfer complexes were formed by depositing onto the electrodes (maximum loading of 29 Æ 3 nmol per cm2;
TiO2 nanoparticles onto the DHSP-functionalised IO–ITO. In UV-vis spectroscopy), photo-driven H2 evolution was not achieved
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
Conflicts of interest
There are no conflicts to declare.
Notes and references
1 A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, Chem.
Rev., 2010, 110, 6595–6663.
2 (a) J. Willkomm, K. L. Orchard, A. Reynal, E. Pastor, J. R. Durrant
and E. Reisner, Chem. Soc. Rev., 2016, 45, 9–23; (b) J. R. Swierk and
T. E. Mallouk, Chem. Soc. Rev., 2013, 42, 2357–2387; (c) L. Alibabaei,
H. Luo, R. L. House, P. G. Hoertz, R. Lopez and T. J. Meyer, J. Mater.
Chem. A, 2013, 1, 4133–4145.
3 (a) M. A. Gross, C. E. Creissen, K. L. Orchard and E. Reisner, Chem.
Sci., 2016, 7, 5537–5546; (b) L. J. Antila, P. Ghamgosar, S. Maji,
¨
H. Tian, S. Ott and L. Hammarstrom, ACS Energy Lett., 2016, 1,
1106–1111; (c) L. Li, L. Duan, F. Wen, C. Li, M. Wang, A. Hagfeldt
and L. Sun, Chem. Commun., 2012, 48, 988–990; (d) F. Li, K. Fan,
B. Xu, E. Gabrielsson, Q. Daniel, L. Li and L. Sun, J. Am. Chem. Soc.,
2015, 137, 9153–9159; (e) Z. Ji, M. He, Z. Huang, U. Ozkan and
Y. Wu, J. Am. Chem. Soc., 2013, 135, 11696–11699.
4 (a) Z. Huang, M. He, M. Yu, K. Click, D. Beauchamp and Y. Wu,
Angew. Chem., Int. Ed., 2015, 54, 6857–6861; (b) B. Shan, A. K. Das,
S. Marquard, B. H. Farnum, D. Wang, R. M. Bullock and T. J. Meyer,
Energy Environ. Sci., 2016, 9, 3693–3697.
5 (a) Y. Ooyama, M. Kanda, K. Uenaka and J. Ohshita, ChemPhysChem,
2015, 16, 3049–3057; (b) E. L. Tae, S. H. Lee, J. K. Lee, S. S. Yoo,
E. J. Kang and K. B. Yoon, J. Phys. Chem. B, 2005, 109, 22513–22522;
(c) B.-K. An, W. Hu, P. L. Burn and P. Meredith, J. Phys. Chem. C,
2010, 114, 17964–17974; (d) Y. Ooyama and Y. Harima, Chem-
PhysChem, 2012, 13, 4032–4080.
Fig. 3 (a) Chronoamperograms under chopped irradiation of (i) IO–ITO|DHSP,
(ii) IO–ITO, (iii) IO–ITO|AN7–TiO2 and (iv) IO–ITO|DHSP|AN7–TiO2 electrodes.
(b) Effect of ITO morphology and thickness on visible-light photocurrent of
ITO|DHSP|AN7–TiO2 electrodes. Due to the hierarchical structure consist-
ing of macro- and mesopores, the effective surface area of IO-2 mm ITO is
lower than 1 mm mesoITO. Conditions: Na2SO4 (0.1 M), pH 4.5, 0.3 V vs.
RHE, 100 mW cmÀ2, l 4 400 nm, room temperature, under air.
6 (a) Z. Tachan, I. Hod and A. Zaban, Adv. Energy Mater., 2014,
4, 1301249; (b) G. Zhang and W. Choi, Chem. Commun., 2012, 48,
10621–10623; (c) G. Zhang, C. Kim and W. Choi, Catal. Today, 2017,
281(Part 1), 109–116.
with these electrodes. It is possible that the phosphonate groups
in NiP may displace either some or all of the DHSP groups from
the surface of TiO2. NiP can also bind directly to ITO,
by-passing the dye–TiO2 construct. Therefore, although the
layer-by-layer design successfully generates a directional, dye-
sensitised electrode, further catalyst design is required in order
to fully translate the DSP system to DSPEC.
In conclusion, we have demonstrated that catechol–TiO2
complexes are effective photosensitisers for driving sacrificial
H2 evolution with an earth-abundant molecular catalyst, form-
ing a fully noble metal-free Type II DSP system. Using a layer-by-
layer method, we have transferred the dye-sensitised TiO2 to an
electrode to form a Type II photocathode. The excellent size
match between the hierarchical IO–ITO support and the TiO2
nanoparticles is critical for high dye–TiO2 loading. The
obtained photocurrents with a sacrificial electron acceptor are
comparable to those obtained with Type I dyes, indicating that
¨
7 P. Persson, R. Bergstrom and S. Lunell, J. Phys. Chem. B, 2000, 104,
10348–10351.
8 C. A. Caputo, L. Wang, R. Beranek and E. Reisner, Chem. Sci., 2015,
6, 5690–5694.
9 M. Bledowski, L. Wang, A. Ramakrishnan and R. Beranek, J. Mater.
Res., 2013, 28, 411–417.
´
´
10 (a) Y. Di Iorio, H. B. Rodrıguez, E. San Roman and M. A. Grela,
J. Phys. Chem. C, 2010, 114, 11515–11521; (b) Q. Li, Y. Che, H. Ji,
C. Chen, H. Zhu, W. Ma and J. Zhao, Phys. Chem. Chem. Phys., 2014,
16, 6550–6554.
11 (a) P. Z. Araujo, P. J. Morando and M. A. Blesa, Langmuir, 2005, 21,
3470–3474; (b) M. Rodenstein, S. Zu¨rcher, S. G. P. Tosatti and
N. D. Spencer, Langmuir, 2010, 26, 16211–16220.
12 M. A. Gross, A. Reynal, J. R. Durrant and E. Reisner, J. Am. Chem.
Soc., 2014, 136, 356–366.
13 Y. Wang, K. Hang, N. A. Anderson and T. Lian, J. Phys. Chem. B,
2003, 107, 9434–9440.
14 E. T. Hwang, K. Sheikh, K. L. Orchard, D. Hojo, V. Radu, C.-Y. Lee,
E. Ainsworth, C. Lockwood, M. A. Gross, T. Adschiri, E. Reisner,
J. N. Butt and L. J. C. Jeuken, Adv. Funct. Mater., 2015, 25, 2308–2315.
this is a promising means to control photocurrent direction 15 (a) G. Li, C. P. Richter, R. L. Milot, L. Cai, C. A. Schmuttenmaer,
R. H. Crabtree, G. W. Brudvig and V. S. Batista, Dalton Trans., 2009,
10078–10085; (b) J. T. Carneiro, T. J. Savenije, J. A. Moulijn and
G. Mul, J. Phys. Chem. C, 2011, 115, 2211–2217.
and allow the use of n-type metal oxide supports (such as ITO)
in DSPEC applications. This work represents an important first
step in translating functional DSP systems to DSPEC; however, 16 D. Mersch, C.-Y. Lee, J. Z. Zhang, K. Brinkert, J. C. Fontecilla-Camps,
A. W. Rutherford and E. Reisner, J. Am. Chem. Soc., 2015, 137,
8541–8549.
17 M. Kato, T. Cardona, A. W. Rutherford and E. Reisner, J. Am. Chem.
challenges in coupling these electrodes to a H2 evolution
catalyst will need to be overcome in order to apply them for
sustainable solar fuels synthesis.
Soc., 2013, 135, 10610–10613.
18 D. Hojo, T. Togashi, D. Iwasa, T. Arita, K. Minami, S. Takami and
T. Adschiri, Chem. Mater., 2010, 22, 1862–1869.
19 Y. Zhao, J. R. Swierk, J. D. Megiatto Jr., B. Sherman, W. J. Youngblood,
D. Qin, D. M. Lentz, A. L. Moore, T. A. Moore, D. Gust and T. E. Mallouk,
Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 15612–15616.
20 W. Hamd, M. Chavarot-Kerlidou, J. Fize, G. Muller, A. Leyris,
M. Matheron, E. Courtin, M. Fontecave, C. Sanchez, V. Artero and
C. Laberty-Robert, J. Mater. Chem. A, 2013, 1, 8217–8225.
We gratefully acknowledge financial support by the EPSRC
and the World Premier International Research Center Initia-
tive, MEXT, Japan. We also thank Dr Manuela Gross and Dr
Benjamin Martindale for supplying NiP, Mr Alan Dickerson for
ICP-OES measurements, and Dr Janina Willkomm and Mr
Charles Creissen for helpful discussions.
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017