A Poly(cobaloxime)/Carbon Nanotube Electrode: Freestanding Buckypaper with Polymer-Enhanced H2-Evolution Performance

Article abstract of DOI:10.1002/anie.201511378

A freestanding H₂-evolution electrode consisting of a copolymer-embedded cobaloxime integrated into a multiwall carbon nanotube matrix by π-π interactions is reported. This electrode is straightforward to assemble and displays high activity towards hydrogen evolution in near-neutral pH solution under inert and aerobic conditions, with a cobalt-based turnover number (TON_Co) of up to 420. An analogous electrode with a monomeric cobaloxime showed less activity with a TON_Co of only 80. These results suggest that, in addition to the high surface area of the porous network of the buckypaper, the polymeric scaffold provides a stabilizing environment to the catalyst, leading to further enhancement in catalytic performance. We have therefore established that the use of a multifunctional copolymeric architecture is a viable strategy to enhance the performance of molecular electrocatalysts.

Full text of DOI:10.1002/anie.201511378

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201511378
German Edition: DOI: 10.1002/ange.201511378
H2 Evolution
Hot Paper
A Poly(cobaloxime)/Carbon Nanotube Electrode: Freestanding
Buckypaper with Polymer-Enhanced H2-Evolution Performance
Bertrand Reuillard+, Julien Warnan+, Jane J. Leung, David W. Wakerley, and Erwin Reisner*
Abstract: A freestanding H2-evolution electrode consisting of
a copolymer-embedded cobaloxime integrated into a multiwall
carbon nanotube matrix by p–p interactions is reported. This
electrode is straightforward to assemble and displays high
activity towards hydrogen evolution in near-neutral pH
solution under inert and aerobic conditions, with a cobalt-
based turnover number (TONCo) of up to 420. An analogous
electrode with a monomeric cobaloxime showed less activity
with a TONCo of only 80. These results suggest that, in addition
to the high surface area of the porous network of the
buckypaper, the polymeric scaffold provides a stabilizing
environment to the catalyst, leading to further enhancement in
catalytic performance. We have therefore established that the
use of a multifunctional copolymeric architecture is a viable
strategy to enhance the performance of molecular electro-
catalysts.
tial[17] and can operate in aqueous solutions[18,19] even under
aerobic conditions.[20,21] Recently, versatile strategies were
reported for their immobilization onto metal-oxide[13,22] and
carbon-based[23–25] surfaces for applications in electro- and
photoelectrocatalytic H2 production. Despite this progress,
a major drawback and limitation in their development is their
poor stability, which is mainly due to degradation of the
equatorial ligand or decoordination of the axial ligand under
catalytic conditions.[13,26]
Carbon nanotubes (CNTs) are widely used as an electrode
material because of their ability to increase the surface
loading of catalytic species whilst maintaining excellent
conductivity.[27,28] They can also be covalently and noncova-
lently functionalized with ease by using a wide range of
methods.[29–31] Strong p–p interactions between pyrene units
and the CNT sidewalls have become a successful approach to
anchor molecular catalysts,[32–35] redox probes,[36] and pro-
teins.[37,38] These noncovalent interactions between hydro-
phobic moieties and CNT sidewalls have been studied to
improve the formation of robust, freestanding CNT electro-
des particularly suited for electrocatalytic applications.[39]
Such CNT films are known as buckypapers (BPs) and can
be easily obtained by vacuum filtration of CNT dispersions to
produce porous networks of nanotubes with unique electrical
conductivity, gas permeability, and mechanical proper-
ties.[39,40] The mechanical stability and high surface area of
BPs have recently been shown to enhance the catalytic
properties of bioelectrodes (high protein loading, efficient
electronic communication, improved stability) for sensors and
enzymatic biofuel cells.[41,42] The freestanding nature of these
BPs precludes the need for an additional conductor or
supporting scaffold, which is a considerable advantage when
large-scale electrodes are required.
E
fficient, inexpensive, and scalable H2 production by water
electrolysis driven by renewable energy sources remains
a major goal towards realizing a sustainable energy cycle.[1–3]
The development of low-cost catalysts, such as those based on
the earth-abundant 3d transition metals Co, Ni, and Fe, offers
a promising route to compete with the performance of the
current benchmark catalysts, including expensive platinum
and fragile H2-producing enzymes known as hydrogenases.[4–8]
Many molecular cobalt-containing H2 evolution catalysts
have been reported,[9] and cobaloximes and their derivatives
are among the most widely studied.[10–13] The advantages of
cobaloximes are their facile synthesis and the tunability of
their catalytic properties by modifying the substituents on the
equatorial and/or axial ligands.[13–16] Moreover, they exhibit
high proton-reduction activity at a relatively low overpoten-
The immobilization of molecular catalysts onto electrodes
with high stability and performance remains a major chal-
lenge in electrocatalysis.[4] Herein, we report the combination
of multiwall carbon nanotubes (MWCNTs) with a pyrene-
bearing cobaloxime copolymer (pPyCo) to produce a func-
tional BP for catalytic hydrogen evolution (Figure 1a,b) and
compare it with an analogous monomeric pyrene-functional-
ized cobaloxime (PyCo). Both catalysts employed the same
4-N-amidylpyridine moiety as a direct or indirect linker
between the catalyst and a pyrene anchoring group in the
monomeric and polymeric architectures, respectively.
Although only a few reports on the use of polymers in H2-
evolution catalysis are available,[43–45] it is well-established
that polymers, and especially copolymers, can provide several
advantages over molecular species as they can incorporate
complementary properties, such as ionic conductivity,[46]
robust immobilization, and a protecting matrix, therefore
[*] Dr. B. Reuillard,[+] Dr. J. Warnan,[+] J. J. Leung, D. W. Wakerley,
Dr. E. Reisner
Christian Doppler Laboratory for Sustainable SynGas Chemistry
Department of Chemistry, University of Cambridge
Lensfield Road, CB2 1EW Cambridge (UK)
E-mail: reisner@ch.cam.ac.uk
Homepage: http://www-reisner.ch.cam.ac.uk
[+] These authors contributed equally to this work.
Supporting information for this article can be found under http://dx.
doi.org/10.1002/anie.201511378. Additional data related to this
publication is available at the University of Cambridge data
repository (https://www.repository.cam.ac.uk/handle/1810/
253645).
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited.
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ation chromatography) are available in the Supporting
Information.
Each monomer unit in pPyCo was chosen to afford
specific properties to the resultant multifunctional copolymer.
The pyrene unit provides a hydrophobic anchor for binding
the MWCNT sidewalls, the pyridine confers a receptor to
coordinate [CoIIICl2(dmgH)(dmgH2)], and the 4EG improves
the polymerꢀs solubility in polar solvents. The natural hydro-
philicity of 4EG also affords a more proton-rich environment
in the vicinity of the catalyst and could reinforce the stability
of the global architecture because of a cross-linked matrix.
The ratio of monomers inside the polymer was estimated
by 1H NMR and elemental analysis (H, C, N, Cl), which
showed a pyrene/pyridine/4EG composition of approximately
1:1:1.3.
Initially, glassy carbon/multiwall carbon nanotube (GC/
MWCNT) electrodes were modified with PyCo and pPyCo in
order to fully characterize the electrochemical behavior of
both the single molecule and the polymer at the surface of the
MWCNTs. These GC/MWCNT electrodes were obtained by
drop-coating 20 mL of a 5 mgmLÀ1 dispersion of MWCNTs in
N-methylpyrrolidone onto the GC disk electrode (1 =
3 mm). After drying under vacuum, a 5 mm thick homoge-
neous MWCNT film was obtained as reported previously.[35]
The GC/MWCNT electrodes were then incubated for 30 min
in a 2.5 mm solution of PyCo (GC/MWCNT-PyCo) or pPyCo
(GC/MWCNT-pPyCo) in DMF and rinsed with DMF and
H2O before running cyclic voltammetry (CV) experiments in
an aqueous pH 6.5 electrolyte solution (Figure 1c). The GC/
MWCNT-PyCo electrodes displayed a reversible redox wave
at E1/2 = 0.24 V versus the standard hydrogen electrode
Figure 1. a) i) Synthetic route to pPyCo: 2,2’-azobisisobutyronitrile
(AIBN), THF, 708C, 16 h, 88%. ii) [CoCl2(dmgH)(dmgH2)], Et3N,
MeOH/CHCl3 (1:4), 458C, 4 h, 69%. b) Schematic representation of
PyCo and pPyCo catalysts attached on the MWCNT sidewalls. c) CV
scans of the bare GC/MWCNTs (black), GC/MWCNTs modified with
PyCo (blue) and with pPyCo (red curve) in phosphate electrolyte
solution (0.1m, pH 6.5; n=100 mVsÀ1) under inert atmosphere and at
room temperature.
resulting in a beneficial environment for the catalysts.[47–49] By
embedding a benchmark catalyst in a rationally designed
copolymer, we aim to demonstrate, as a proof of concept, that
tuning the electrocatalyst environment (outer coordination
sphere), instead of the active catalytic center (first coordina-
tion sphere), could be a promising strategy to improve the
performance of a H2 evolution molecular catalyst. This is, to
the best of our knowledge, the first reported attempt at
a rationally designed copolymer for H2 evolution that mimics
the function of the protein matrix surrounding an enzymeꢀs
active site.
(SHE), whereas a reversible process was observed at E1/2
=
0.08 V versus SHE with GC/MWCNT-pPyCo. These redox
processes are attributed to the cobaloximesꢀ reversible CoIII/
CoII redox couple.[16] The small shift in redox potential
between the monomer and polymer is presumably due to
a change in the chemical environment surrounding the cobalt
center upon incorporation into a polymer chain. The small
redox waves observed in the case of GC/MWCNT-PyCo at
Molecular PyCo (Figure 1b) was prepared by coordinat-
ing 4-(pyren-1-yl)-N-(pyridin-4-yl)butanamide (1, see the
Supporting Information) to [CoIIICl2(dmgH)(dmgH2)]
(dmgH2 = dimethylglyoxime). The polymeric pPy intermedi-
ate was obtained from pyridine-based (2) and pyrene-based
(3) methacrylate monomers, which were prepared and
combined together (in stoichiometric amounts) with tetra-
ethylene glycol dimethacrylate (4EG) through free-radical
polymerization (Figure 1a). This polymerization is a versatile
metal-free process, tolerant to a wide range of chemical
functionalities that allows simple tailoring of the polymerꢀs
properties by the incorporation of specific functional groups.
After the polymerization, the cobaloxime was finally intro-
duced through the binding of the free pyridine units to the
[CoIIICl2(dmgH)(dmgH2)] precursor. Compound pPyCo was
found to be soluble in N,N-dimethylformamide (DMF) and
dimethyl sulfoxide (DMSO) despite its cross-linked nature,
probably because of a relatively low average molecular
weight (Mw ꢀ 10.7 kD; “M ꢀ 1.29). All synthetic procedures
and characterization (1H and 13C NMR, FTIR spectra, high-
resolution mass spectra, elemental analysis and gel perme-
E
red = 0.13 V and Eox = 0.08 V may be the result of different
adsorption interactions of the PyCo generating varying
chemical environments on the GC/MWCNT surface. In
contrast, the single redox process observed with GC/
MWCNT-pPyCo results most likely from a more homogenous
environment around the cobalt catalysts, provided by the
polymeric matrix.
Immobilization was further confirmed by the linear
dependence of the CoIII/CoII redox couple current densities
with scan rate for both PyCo and pPyCo (Figure S1). The DE
value for the CoIII/CoII redox couple also increases with scan
rate. According to the Laviron equation for interfacial
electron transfer with adsorbed redox systems, DE observed
for CoIII/CoII corresponds to a heterogeneous electron trans-
fer rate (ks) of 0.23 Æ 0.05 cmsÀ1 and 0.32 Æ 0.08 cmsÀ1 for
PyCo and pPyCo, respectively.[50] The relatively close ks
values are good confirmation that the polymer structure of
pPyCo does not act as an insulating layer and instead retains
electron-transfer properties comparable to PyCo within the
MWCNT electrode.
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A strong wave with a cathodic onset potential of Eonset
=
comparable features compared to those of PyCo and pPyCo
À0.48 V versus SHE is observed for both GC/MWCNT-PyCo
and GC/MWCNT-pPyCo as a result of catalytic reduction of
protons to H2 by the reduced CoI species of the cobaloxime.[16]
This value corresponds to a small overpotential for proton
reduction (h ꢀ 100 mV), which is in agreement with previous
studies for [CoCl(dmgH)2(pyridine)]-type catalysts.[17] There-
fore, the observed redox and catalytic waves on these
modified electrodes demonstrate that both cobaloxime-
based compounds retain their integrity and activity once
immobilized on the MWCNT surface. From the integration of
the CoII to CoIII oxidation wave in the CV scans, the charge
was calculated and the amount of cobalt catalyst immobilized
was estimated to be approximately 33 nmolcmÀ2 and
25 nmolcmÀ2 for PyCo and pPyCo, respectively. These sur-
face coverages are higher than for previously reported
covalently immobilized cobaloximes on CNTs[24] and are
comparable to metal oxide sensitization,[13] thus underlining
the potential of soft and straightforward supramolecular
functionalization methods of CNT to assemble molecular-
based electrodes.
Subsequently, MWCNT BPs were prepared in order to
build electrocatalytic freestanding electrodes and to increase
the specific surface area, thereby allowing the immobilization
of a high amount of catalytic centers without any need for an
additional electrode support material. BP-PyCo and BP-
pPyCo were obtained by filtration of a dispersion of
MWCNTs and the corresponding molecular catalysts (1:1
ratio, w/w) in a DMF solution onto a polytetrafluoroethylene
(PTFE) membrane, giving reproducible and stable MWCNT
disks (Figure 2a; a detailed experimental procedure is
described in the Supporting Information). A bare BP and
BP-pPy were also produced by the same procedure for
comparison with the [Co]-functionalized BPs.
(Figure S2). In particular, characteristic bands are observed at
À
˜
the cobaloximeꢀs n(NO ) stretching frequency at around
1240 cmÀ1 (Figure S2a), overlapping with the vibrational
mode of the MWCNTs in the case of the BPs (Figure S2b).[45]
The polymer binding is also observable through the intense
À1
=
˜
n(C O) vibrational mode at 1737 cm that arises from the
ester groups.
X-ray photoelectron spectroscopy (XPS) experiments
show characteristic cobalt, oxygen, and nitrogen binding
energy peaks (Figure S3). In the Co2p region, two broad
signals corresponding to 2p1/2 and 2p3/2 core levels were
observed at 796.8 and 781.8 eV, respectively, after BP
functionalization (similar to values previously reported for
a cobaloxime).[24] Similarly, peaks in the N1s and stronger O1s
core level regions at 400.5 and 532.7 eV, respectively, arise
from the ligands and copolymer components, further indicat-
ing the successful immobilization of both PyCo and pPyCo.
Thermogravimetric analysis (TGA; under N2, gradient
108CminÀ1) showed the presence of degradable materials on
the surface of the functionalized BPs, whereas no significant
loss of weight is detected on the bare BP (Figure S4). Weight
loss of the functionalized BP-PyCo and BP-pPyCo stabilized
at 5008C at approximately 6% and 23%, respectively,
corresponding to the degradation of the organic materials
physisorbed on the CNT surface. These results suggest
a higher loading of material with the polymer pPyCo than
with PyCo.
Finally, scanning electron microscopy (SEM) of BP-PyCo
and BP-pPyCo showed the high surface area of the porous
CNT network of the BP electrodes (Figures 2c,d and S5). The
presence of the polymer seems to limit dense packing of the
CNTs, instead encouraging a rougher and more porous
morphology than its monomeric counterpart.
Attenuated total reflectance Fourier-transform infrared
(ATR-FTIR) spectroscopy of the functionalized BPs shows
The functionalized BPs were employed as freestanding
electrodes (geometric surface = 1 cm2) and connected directly
to a potentiostat in an aqueous electrolyte solution (phos-
phate electrolyte solution, 0.1m, pH 6.5). CV scans of BP-
PyCo and BP-pPyCo exhibit a reversible CoIII/CoII redox
wave at E1/2 = 0.18 V and E1/2 = 0.10 V versus SHE, respec-
tively (Figure 2b and S6). Interestingly, the scale-up process
to the BP electrode did not induce strong changes in the
behavior of PyCo and pPyCo, as they retained environment-
controlled redox activities similar to those seen on the GC
electrodes (see above). The onset potential of the catalytic
proton reduction wave is also observed at around Eonset
ꢀ
À0.48 V versus SHE for both functionalized BPs because of
the presence of the same active species within the free-
standing electrode (Figure S6). Integration of the CoII to CoIII
oxidation wave allowed an estimation of the amount of
immobilized Co of approximately 200 nmolcmÀ2 and
150 nmolcmÀ2 for BP-PyCo and BP-pPyCo, respectively.
This high Co loading corresponds to an almost tenfold
increase compared to the GC/MWCNT electrodes (see
above) and highlights the ability of the freestanding BP
electrode preparation method to load high amounts of the
molecular catalysts throughout the three-dimensional film.
The slightly lower loading of Co in BP-pPyCo suggests that
more of the degradable material in the TGA measurements
Figure 2. a) Photograph of a BP electrode (1=3.5 cm). b) CV scans
of the different BP electrodes: bare BP (black), BP-PyCo (blue), and
BP-pPyCo (red curve) recorded in phosphate electrolyte solution
(0.1m, pH 6.5; n=5 mVsÀ1) under inert atmosphere and at room
temperature. SEM images of c) BP-PyCo and d) BP-pPyCo.
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stems from the polymeric chain. Ultimately, this BP approach
at a maximal value of 60 mmol H2 after 24 h, which corre-
can be seen as a versatile platform from which further tuning
of catalyst loading and electrode size is possible.
sponds to a TONCo of 420 (Figure 3). The TOFCo with BP-
pPyCo remains stable at approximately 38 hÀ1 for several
hours (Figure S7b), which demonstrates an improved activity
for the pPyCo- over the PyCo-modified BPs. The faradaic
yields calculated from the charge passed during the CPE
measurements confirm BP-pPyCoꢀs superior catalytic activity
compared to BP-PyCo with faradaic yields up to 90% and
70%, respectively (Figure S8). This substantially higher
activity and efficiency of the polymer-based cobaloxime
demonstrates the advantages of the multifunctional polymer
in potentially conferring the composite with a higher proton
affinity and limiting the decomposition of the catalyst.
Concurrently, the greater stability could be a result of the
steric hindrance provided by the polymeric matrix limiting the
loss of individual metal centers from the labile pyridines and
degradation of the cobaloxime. XPS experiments conducted
after electrolysis showed that the Co2p signal maxima shifted
from 796.8 and 781.8 eV to 798.2 and 782.2 eV concomitantly
with the appearance of an overlapping shoulder (Figure S9).
Nevertheless, no metallic cobalt (778.0 eV) was detected. As
the catalytic activity ceased, the modification of the Co
environment is most likely a consequence of the cobaloxime
degrading into an inactive Co species.
A respectable level of hydrogen evolution activity is
maintained under air, with 30 mmol of H2 (TONCo = 180)
evolved in the case of BP-pPyCo and 10 mmol (TONCo = 40)
for BP-PyCo (Figure 3a). These values correspond to 45–
50% of total H2 produced under an inert atmosphere
(Figure 3b). As a result, faradaic yields remain significant
under air with 45% for pPyCo and 30% for PyCo (Figure S9).
Interestingly, these faradaic yields are higher than the values
reported for similar molecular catalysts under air in the
absence of a CNT scaffold,[21] and highlights the protecting
effect of our hybrid composite material. The loss in faradaic
yield under air as compared to that under N2 is due to the
competing reduction of oxygen by the cobaloxime.[25,51]
However, the CNTs themselves can also reduce O2 and
therefore act as a shield protecting the catalyst against the
parasitic reduction of O2 instead of protons, enhancing the
molecular catalystꢀs efficiency under aerobic conditions.[53]
Thus, defensive (reduction of O2 by the electrode scaffold
protecting the catalyst from exposure to O2) and offensive
(the cobaloximeꢀs own reduction of O2 without being
damaged) strategies are used to build a relatively air-tolerant
cathode for H2 evolution.[51]
The freestanding BPs were evaluated for H2 evolution by
controlled-potential electrolysis (CPE) with an applied
potential (Eappl) of À0.7 V versus SHE. CPE was carried out
in aqueous phosphate electrolyte solution at pH 6.5 in an
airtight two-compartment electrochemical cell under an inert
atmosphere (N2/CH4, 98:2; Figure S7a). In a control experi-
ment, the current for the bare BP electrode decreases within
a few seconds to 0.10 mAcmÀ2 and remains stable at this
lower current density for 24 h. BP-PyCo exhibits higher
current densities (> 0.5 mAcmÀ2) for the first 15 min of
electrolysis before slowly decreasing over 8 h and stabilizing
at 0.12 mAcmÀ2. BP-pPyCo displays a substantially improved
performance with higher and more stable current densities of
0.34 mAcmÀ2 for 5 h, before slowly decaying over 10 h to
finally stabilize at 0.12 mAcmÀ2. Knowledge of the amount of
Co on the electrode, along with H2 produced and charge
generated during CPE allowed us to calculate turnover
numbers (TONs), turnover frequencies (TOFs), and faradaic
yields for the functionalized BP electrodes (background
proton reduction activity on cobaloxime-free BP subtracted).
Figure 3a depicts H2 production over time during CPE of
BP-PyCo and BP-pPyCo under inert atmosphere and under
air. Experiments were performed under air to assess the
catalytic activity and efficiency under demanding aerobic
Figure 3. a) Electrocatalytic H2 production and b) TONCo produced,
during CPE of BP-PyCo (blue) and BP-pPyCo (red curves) at
E
appl =À0.7 V versus SHE in phosphate electrolyte solution (0.1m,
pH 6.5), under N2 (solid) and air (dotted curves) at room temperature.
conditions as some O2 tolerance of a H2-generating cathode is
required in water-splitting applications.[51] Under an N2
atmosphere, BP-PyCo exhibits a linear H2 evolution rate for
the first 3 h before slowing down and becoming almost
inactive after 8 h. The Co-based TON (TONCo) reaches
a maximum of 80 mol H2 (mol Co)À1 (Figure 3b), comparable
to previously reported values for cobaloxime compounds in
solution.[12,20] TOFCo for BP-PyCo reaches a maximum of
32 hÀ1 (Figure S7b) and decreases quickly, thus suggesting
a fairly rapid deactivation of the catalyst during CPE, most
probably arising from decoordination of the cobaloxime from
the labile pyridine ligand during the catalytic cycle,[52] or
degradation of the catalyst.[26]
In summary, we have described the facile association of
a three-dimensional freestanding MWCNT and polymeric
catalyst for H2 evolution. The multifunctional poly(cobalox-
ime)/CNT composite enables a high loading of the molecular
catalyst, catalyst stabilization and a protecting effect against
O2 damage. As a result, the polymeric hybrid material
displays a catalytic activity four times higher and twice as
long compared to its monomeric counterpart. Much like for
an enzyme where the active site is embedded in a protein
matrix, the polymer can be considered as an activating and
protecting environment for the cobaloxime catalyst core. We
demonstrate the possibility to improve the catalytic proper-
ties of a Co-based catalyst by using a simple and tailor-made
The rate of H2 production remains linear for 8 h in the
case of CPE with BP-pPyCo before decaying and stabilizing
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[18] P. Du, K. Knowles, R. Eisenberg, J. Am. Chem. Soc. 2008, 130,
12576 – 12577.
[19] F. Lakadamyali, E. Reisner, Chem. Commun. 2011, 47, 1695 –
1697.
[20] F. Lakadamyali, M. Kato, N. M. Muresan, E. Reisner, Angew.
Chem. Int. Ed. 2012, 51, 9381 – 9384; Angew. Chem. 2012, 124,
9515 – 9518.
[21] D. W. Wakerley, M. A. Gross, E. Reisner, Chem. Commun. 2014,
50, 15995 – 15998.
polymer backbone. The latter confers desirable character-
istics to the composite and therefore prolongs the molecular
catalystꢀs stability on the electrode scaffold without the need
for Nafionꢁ or precious metals. The strategy of integrating
active molecular catalysts in rationally designed polymers
combined with the straightforward and scalable concept of
MWCNT matrices could enable new applications for molec-
ular catalysts in the field of renewable fuel and chemical
synthesis.
[22] N. M. Muresan, J. Willkomm, D. Mersch, Y. Vaynzof, E. Reisner,
Angew. Chem. Int. Ed. 2012, 51, 12749 – 12753; Angew. Chem.
2012, 124, 12921 – 12925.
[23] X.-W. Song, H.-M. Wen, C.-B. Ma, H.-H. Cui, H. Chen, C.-N.
Chen, RSC Adv. 2014, 4, 18853 – 18861.
Acknowledgements
[24] E. S. Andreiadis, P.-A. Jacques, P. D. Tran, A. Leyris, M.
Chavarot-Kerlidou, B. Jousselme, M. Matheron, J. PØcaut, S.
Palacin, M. Fontecave, V. Artero, Nat. Chem. 2013, 5, 48 – 53.
[25] N. Kaeffer, A. Morozan, V. Artero, J. Phys. Chem. B 2015, 119,
13707 – 13713.
[26] P. -A. Jacques, V. Artero, J. PØcaut, M. Fontecave, Proc. Natl.
Acad. Sci. USA 2009, 106, 20627 – 20632.
[27] J. M. Schnorr, T. M. Swager, Chem. Mater. 2011, 23, 646 – 657.
[28] M. F. L. De Volder, S. H. Tawfick, R. H. Baughman, A. J. Hart,
Science 2013, 339, 535 – 539.
We acknowledge support by the Christian Doppler Research
Association (Austrian Federal Ministry of Science, Research
and Economy and National Foundation for Research, Tech-
nology and Development), the OMV Group, the EPSRC, the
BBSRC (Grant BB/K010220/1), the Woolf Fisher Trust in
New Zealand and the Cambridge Trusts. We also thank the
National EPSRC XPS Userꢀs Service (NEXUS) at Newcastle
University, UK. We thank Dr. K. L. Orchard and J. Willkomm
for helpful discussions and B. C. M. Martindale for help with
XPS.
[29] P. Singh, S. Campidelli, S. Giordani, D. Bonifazi, A. Bianco, M.
Prato, Chem. Soc. Rev. 2009, 38, 2214 – 2230.
[30] N. Karousis, N. Tagmatarchis, D. Tasis, Chem. Rev. 2010, 110,
5366 – 5397.
Keywords: buckypaper · cobaloximes · electrocatalysis ·
[31] Y.-L. Zhao, J. F. Stoddart, Acc. Chem. Res. 2009, 42, 1161 – 1171.
[32] P. D. Tran, A. Le Goff, J. Heidkamp, B. Jousselme, N. Guillet, S.
Palacin, H. Dau, M. Fontecave, V. Artero, Angew. Chem. Int. Ed.
2011, 50, 1371 – 1374; Angew. Chem. 2011, 123, 1407 – 1410.
[33] J. D. Blakemore, A. Gupta, J. J. Warren, B. S. Brunschwig, H. B.
Gray, J. Am. Chem. Soc. 2013, 135, 18288 – 18291.
[34] P. Kang, S. Zhang, T. J. Meyer, M. Brookhart, Angew. Chem. Int.
Ed. 2014, 53, 8709 – 8713; Angew. Chem. 2014, 126, 8853 – 8857.
[35] B. Reuillard, A. Le Goff, S. Cosnier, Chem. Commun. 2014, 50,
11731 – 11734.
[36] A. Le Goff, B. Reuillard, S. Cosnier, Langmuir 2013, 29, 8736 –
8742.
[37] R. J. Chen, Y. Zhang, D. Wang, H. Dai, J. Am. Chem. Soc. 2001,
123, 3838 – 3839.
[38] B. Reuillard, A. Le Goff, M. Holzinger, S. Cosnier, J. Mater.
Chem. B 2014, 2, 2228 – 2232.
[39] Y. Tsarfati, V. Strauss, S. Kuhri, E. Krieg, H. Weissman, E.
Shimoni, J. Baram, D. M. Guldi, B. Rybtchinski, J. Am. Chem.
Soc. 2015, 137, 7429 – 7440.
dihydrogen evolution · polymers
How to cite: Angew. Chem. Int. Ed. 2016, 55, 3952–3957
Angew. Chem. 2016, 128, 4020–4025
[1] J. A. Herron, J. Kim, A. A. Upadhye, G. W. Huber, C. T.
Maravelias, Energy Environ. Sci. 2015, 8, 126 – 157.
[2] N. Armaroli, V. Balzani, ChemSusChem 2011, 4, 21 – 36.
[3] P. D. Tran, V. Artero, M. Fontecave, Energy Environ. Sci. 2010, 3,
727 – 747.
[4] V. S. Thoi, Y. Sun, J. R. Long, C. J. Chang, Chem. Soc. Rev. 2013,
42, 2388 – 2400.
[5] J. R. McKone, S. C. Marinescu, B. S. Brunschwig, J. R. Winkler,
H. B. Gray, Chem. Sci. 2014, 5, 865 – 878.
[6] R. B. Gordon, M. Bertram, T. E. Graedel, Proc. Natl. Acad. Sci.
USA 2006, 103, 1209 – 1214.
[7] W. Lubitz, H. Ogata, O. Rüdiger, E. Reijerse, Chem. Rev. 2014,
114, 4081 – 4148.
[40] J. Y. Oh, S. J. Yang, J. Y. Park, T. Kim, K. Lee, Y. S. Kim, H. N.
Han, C. R. Park, Nano Lett. 2015, 15, 190 – 197.
[41] K. Elouarzaki, M. Bourourou, M. Holzinger, A. Le Goff, R. S.
Marks, S. Cosnier, Energy Environ. Sci. 2015, 8, 2069 – 2074.
[42] S. Cosnier, R. Haddad, D. Moatsou, R. K. OꢀReilly, Carbon
2015, 93, 713 – 718.
[8] C. Wombwell, C. A. Caputo, E. Reisner, Acc. Chem. Res. 2015,
48, 2858 – 2865.
[9] N. Queyriaux, R. T. Jane, J. Massin, V. Artero, M. Chavarot-
Kerlidou, Coord. Chem. Rev. 2015, 304 – 305, 3 – 19.
[10] X. Hu, B. S. Brunschwig, J. C. Peters, J. Am. Chem. Soc. 2007,
129, 8988 – 8998.
[43] S. K. Ibrahim, X. Liu, C. Tard, C. J. Pickett, Chem. Commun.
2007, 1535 – 1537.
[11] J. L. Dempsey, B. S. Brunschwig, J. R. Winkler, H. B. Gray, Acc.
Chem. Res. 2009, 42, 1995 – 2004.
[44] D. H. Pool, D. L. DuBois, J. Organomet. Chem. 2009, 694, 2858 –
2865.
[12] N. Kaeffer, M. Chavarot-Kerlidou, V. Artero, Acc. Chem. Res.
2015, 48, 1286 – 1295.
[45] A. Krawicz, J. Yang, E. Anzenberg, J. Yano, I. D. Sharp, G. F.
Moore, J. Am. Chem. Soc. 2013, 135, 11861 – 11868.
[46] S.-J. Park, H. Zhao, G. Ai, C. Wang, X. Song, N. Yuca, V. S.
Battaglia, W. Yang, G. Liu, J. Am. Chem. Soc. 2015, 137, 2565 –
2571.
[47] N. PlumerØ, O. Rüdiger, A. A. Oughli, R. Williams, J. Viveka-
nanthan, S. Pçller, W. Schuhmann, W. Lubitz, Nat. Chem. 2014,
6, 822 – 827.
[13] J. Willkomm, N. M. Muresan, E. Reisner, Chem. Sci. 2015, 6,
2727 – 2736.
[14] B. H. Solis, S. Hammes-Schiffer, J. Am. Chem. Soc. 2011, 133,
19036 – 19039.
[15] C. C. L. McCrory, C. Uyeda, J. C. Peters, J. Am. Chem. Soc. 2012,
134, 3164 – 3170.
[16] D. W. Wakerley, E. Reisner, Phys. Chem. Chem. Phys. 2014, 16,
5739 – 5746.
[17] V. Artero, J.-M. Saveant, Energy Environ. Sci. 2014, 7, 3808 –
3814.
[48] A. A. Oughli, F. Conzuelo, M. Winkler, T. Happe, W. Lubitz, W.
Schuhmann, O. Rüdiger, N. PlumerØ, Angew. Chem. Int.
3956
www.angewandte.org
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 3952 –3957

Angewandte
Communications
Chemie
Ed. 2015, 54, 12329 – 12333; Angew. Chem. 2015, 127, 12506 –
[52] T. M. McCormick, Z. Han, D. J. Weinberg, W. W. Brennessel,
P. L. Holland, R. Eisenberg, Inorg. Chem. 2011, 50, 10660 –
10666.
[53] Y. Zhao, L. Yang, S. Chen, X. Wang, Y. Ma, Q. Wu, Y. Jiang, W.
Qian, Z. Hu, J. Am. Chem. Soc. 2013, 135, 1201 – 1204.
12510.
[49] Z. Xia, S. Wang, L. Jiang, H. Sun, S. Liu, X. Fu, B. Zhang, D. S.
Su, J. Wang, G. Sun, Sci. Rep. 2015, 5, 16100.
[50] E. Laviron, J. Electroanal. Chem. Interfacial Electrochem. 1979,
101, 19 – 28.
[51] D. W. Wakerley, E. Reisner, Energy Environ. Sci. 2015, 8, 2283 –
2295.
Received: December 8, 2015
Published online: February 18, 2016
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ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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