Enhancing Hydrogen Evolution Activity of Au(111) in Alkaline Media through Molecular Engineering of a 2D Polymer

Article abstract of DOI:10.1002/anie.201915855

The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst—which is scarce and expensive—and ongoing r

Full text of DOI:10.1002/anie.201915855

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
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Accepted Article
Title: Enhancing hydrogen evolution activity of Au(111) in alkaline
media through molecular engineering of a 2D polymer
Authors: Patrick Alexa, Juan Manuel Lombardi, Paula Abufager,
Heriberto Fabio Busnengo, Doris Grumelli, Vijay S. Vyas,
Frederik Haase, Bettina V. Lotsch, Rico Gutzler, and Klaus
Kern
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201915855
Angew. Chem. 10.1002/ange.201915855
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10.1002/anie.201915855
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Enhancing hydrogen evolution activity of Au(111) in alkaline media
through molecular engineering of a 2D polymer
Patrick Alexa,[a] Juan Manuel Lombardi,[b] Paula Abufager,[b] Heriberto Fabio Busnengo,[b] Doris
Grumelli,[c] Vijay S. Vyas,[a,†] Frederik Haase,[a,‡] Bettina V. Lotsch,[a,d] Rico Gutzler,*[a] Klaus Kern[a,e]
[a] Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
E-mail: r.gutzler@fkf.mpg.de
[b] Instituto de Física Rosario and Universidad Nacional de Rosario, CONICET-UNR, S2000EZO Rosario,
Argentina
[c] Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias
Exactas, Universidad Nacional de La Plata, CONICET, 1900, La Plata, Argentina
[d] Department of Chemistry, University of Munich (LMU), Butenandtstraße 5-13, 81377 München,
Germany
[e] Institut de Physique, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
[†] present address: Department of Chemistry, Marquette University, Milwaukee WI - 53233
[‡] present address: Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, iCeMS
Research Bldg, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Abstract
The electrochemical splitting of water holds promise for the storage of energy intermittently produced
by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a
catalyst – which is scarce and expensive – and ongoing research is focused towards finding cheaper
alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous
materials with tunable chemical and electronic structure and can be used for improving catalytic activity
of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an
Ullmann type coupling reaction on Au(111). The polymer patterned gold electrode exhibits up to three
times higher hydrogen evolution reaction activity compared to bare gold. Through rational design of the
polymer on the molecular level we can engineer hydrogen evolution activity in an approach that is easily
extendible to other electrocatalytic reactions.
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Water electrolyzers, in which H2O is split into molecular hydrogen and oxygen, are suitable devices for
the storage of intermittently generated excess energy from renewable energy sources like sun and wind
power.[1,2] This power-to-fuel approach converts electricity into chemical energy and generates an
energy-dense fuel (H2) that can readily be stored and transported. On the route towards cheap and
efficient electrocatalytic water splitting catalysts, the replacement of platinum group metals as catalysts
for the hydrogen evolution (HER) half-cell reaction is a primary milestone.[3] Whereas platinum and
platinum group metals function best under acidic conditions at low pH values,[4] these strongly corrosive
conditions inhibit the use of cheaper transition metal based catalysts, and highly acidic proton exchange
membrane systems are costly and suffer from concerns regarding their stability. More challenging,
however, is the lower activity of hydrogen evolution catalysts in alkaline media compared to acidic
media.[5] For equal overpotentials, exchange current densities are commonly smaller in alkaline
electrolyte compared to acidic electrolyte, and current efforts are underway to close this gap.[6–8] The
rate limiting step here seems to be the scission of the HO‒H bond in the Volmer step, which precedes
the adsorption of hydrogen, and which can be accelerated by designing adequate co-catalysts. One
approach is the deposition of a material that stabilizes H2O close to the electrode via hydrogen
bonding.[6,9] The increased interaction results in faster generation of adsorbed hydrogen, which can then
combine to form H2 on platinum, effectively leading to higher HER activity.
Elaborating on this concept, we use molecular engineering to pattern a well-defined gold electrode
surface with an organic polymer of tunable chemical structure with the aim of increasing HER activity at
pH 13. The 2D porous single-layer polymer is structurally similar to the organic sheets that build up 2D
covalent organic frameworks (COFs). COFs have recently emerged as active photocatalysts for hydrogen
production,[10–12] in which the organic framework can efficiently absorb light due to their suitable band
gap. On single-crystal electrode supports, related single-layer 2D polymers can be fabricated that
pattern the electrode surface with a covalent porous network.[13–15] Through a deliberate choice of the
chemical structure of the polymer, we can pattern the gold electrode on the nanoscale with hydrogen
bonding sites. In this organic-inorganic hybrid catalyst, the polymer functions as a co-catalyst that alters
the binding strength of the reactants at the gold surface, which ultimately increases HER activity.
In this comprehensive study, we use scanning tunelling microscopy (STM), X-ray photoelectron
spectroscopy (XPS), electrochemical (EC) measurements, and density functional theory (DFT)
calculations to draw a concice picture of the catalyst before and after HER. Three different brominated
precursor molecules with varying nitrogen content were used for on-surface polymer synthesis (Fig. 1a)
(1,3,5-tris-(4-bromophenyl)-benzene (N0), 2,4,6-tris-(4-bromophenyl)-1,3,5-triazine (N3), and 2,2’,2’’-
(benzene-1,3,5-triyl)-tris-(5-bromopyrimidine) (N6)). Established Ullmann-type coupling procedures[16–19]
on an atomically clean Au(111) substrate allow patterning the surface with a one-monolayer thin porous
2D network (Fig. 1b). For the three precursor molecules N0, N3, and N6, the corresponding covalent 2D
polymers P-N0, P-N3, and P-N6 exhibit an amorphous network structure with pores of different shapes,
mostly hexagons, pentagons, and heptagons. The repeat unit of the polymer consists of two
debrominated precursor molecules. P-N0 is composed purely of carbon and hydrogen, whereas P-N3
contains triazine heterocycles at the vertices of the network and P-N6 contains pyrimidine groups in the
network’s ‘struts’ (cf. Fig. 1a). All three polymers are physisorbed on the Au(111) surface. The void pores
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expose the underlying bare substrate and leave it accessible to electrolyte molecules. The polymer-
covered gold substrates were tested for their properties as electrocatalysts, in particular for HER.
Figure 1: Tunable 2D polymers for electrocatalytic hydrogen evolution: (a) Synthesis scheme of polymerization
synthesis. (b) STM topograph (I = 175pA, U = −1.2 V) of P-N0, low right corner shows an enlargement of a
hexagonal pore with a molecular model overlaid.
The polymers on the Au(111) surface show characteristic EC signals in cyclic voltammograms (Fig. 2a, P-
N0 (turquoise), P-N3 (blue) and the P-N6 (purple)) in the potential window –0.70 to –0.95 VAg/AgCl which
are not present on the bare Au(111) surface (see supporting Information for further discussion). The
presence of these signals is an electrochemical indicator for the polymers and goes along with an
increased HER activity. Polarization curves at more negative potentials of bare Au(111), P-N0, P-N3 and
P-N6 are shown in Fig. 2b and exhibit different current densities for negative potentials as a
consequence of different HER activities. Current densities are depicted with respect to the geometrical
area of the crystal; electrochemically active surface areas are equal for all considered systems (see Fig.
S3 supporting information). Bare Au(111) shows a current density of −0.16 mA cm−2 at a potential of
−1.3 VAg/AgCl, while the presence of the P-N3 increases this value more than three-fold to −0.55 mA cm−2.
P-N0 and P-N6 reach both a current density of −0.27 mA cm−2, almost twice as large as Au(111). For
comparison, the overpotentials vs. the reversible hydrogen electrode at –0.2 mA cm–2 are –0.23 V (P-
N3), –0.29 V (P-N0), –0.30 V (P-N6), and –0.35 V (gold).
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Figure 2: (a) Cyclic voltammograms in 0.1 M Ar saturated NaOH solution for P-N0 polymer (turquoise), P-N3 (blue)
and P-N6 (purple). (b) Polarization curves at 0.05 V s−1 in 0.1 M Ar saturated NaOH solution for bare Au(111)
(yellow), P-N0 polymer (turquoise), P-N3 (blue) and P-N6 (purple).
To ensure that the polymer is present during catalysis and does not decompose prior or during HER, we
performed X-ray photoelectron spectroscopy (XPS) before and after catalysis of all three polymers.
Exemplarily, Fig. 3 shows the characterization of P-N3 together with typical STM data acquired before
and after HER (three polarization scans up to −1.2 VAg/AgCl), the spectra and images for P-N0 and P-N6 are
shown in the supporting information. No changes are apparent in STM, apart from the filling of the
pores with what presumably are residues of the electrolyte (Fig. 3 a,b), which is also reflected in the
unaltered C 1s core level signal (Fig. 3d). The signal around 284 eV is due to the carbon in the phenyl
rings in the polymer, the smaller signal around 286 eV originates from the carbon atoms in the triazine
ring. In the N 1s spectrum before HER, only one component of the triazine nitrogen atoms is observable
(Fig. 3c). After HER, however, additional signals are observed at higher binding energy around 400 eV
and 401 eV. These additional signals potentially come from the interaction of the nitrogen atoms with
other species like hydrogen. Literature confirms that attaching hydrogen to nitrogen is shifting the core
level to higher binding energy, for example for protonated amino groups[20], where the signal is shifted
from ~399.3 eV to ~401.2 eV, or in free-base porphyrins[21], where the iminic nitrogen is observed at
398.0 eV and pyrrolic nitrogen at 400.1 eV. The hydrogen species attached to the polymer at its nitrogen
sites is an intermediate of HER and its implications for the reaction mechanism will be discussed below.
It is noteworthy that exposure of P-N3 to the electrolyte without applying any potential already leads to
the appearance of a peak at 400 eV, indicative of the interaction of water with the polymer (see Fig. S8
supporting information). From this observation we can infer that the nitrogen in the polymer acts as
interaction site for water molecules, which stabilizes H2O close to the gold electrode. HER activity starts
to decrease after extended catalytic turnover (Fig. S5 supporting information), possibly due to
degradation of the polymer (see XPS in Fig. S7).
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Figure 3: P-N3 characterization before and after HER: (a) STM image before the electrochemical experiment, and (b)
recorded after the electrochemical experiment. (c) XPS spectra of the N 1s core level, orange: before HER, blue: after
HER, (d) XPS spectra of the C 1s core level, orange: before HER, blue: after HER.
Understanding the observed trend in HER activity (P-N3 > P-N6 ≈ P-N0 > Au(111)) calls for the help of
theoretical support that can deliver insight into the different steps of H2O conversion into hydrogen
molecules. Catalytic activity is usually rationalized in terms of the Sabatier principle, which describes the
optimum catalyst such that the interaction of adsorbed intermediate species is neither too weak nor too
strong. If the interaction is too weak, the intermediate does not bind to the catalyst, but if it is too
strong, it is too stable and the reaction cannot proceed. The Sabatier principle is graphically illustrated
by plotting an observable parameter connected with the catalyst activity (e.g. the electrochemical
current in electrocatalysis) as a function of one or more adequate properties quantifying the strength of
the interaction of the reaction intermediates with the catalyst (e.g. heats of adsorption). This gives rise
to the so-called volcano plots, with the largest catalytic activity (i.e. the summit of the volcano) being
obtained for the catalyst characterized by the “just right” value of the reaction descriptor(s).
The usual descriptor used for the HER is the hydrogen binding energy (HBE).[22–24] However, since the
HBE is an intrinsic property of the catalyst, it is not suitable to account for the effect of external
parameters like the pH of aqueous electrolytes. Since the electrode surface in an aqueous electrolyte is
covered with water, it is likely that the adsorption/desorption of hydrogen is accompanied by
desorption/readsorption of water.[25,26] Thus, a more suitable descriptor proposed recently is the
apparent hydrogen binding energy (HBEapp), which also takes the water binding energy (WBE) into
account, HBEapp=HBE−WBE.[25] The HBEapp descriptor includes pH-dependency in describing
electrocatalytic activities, whereby H adsorption remains as a microscopic reaction step for both acid
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and base electrolytes. Since it was recently shown that the adsorption of hydrogen is the critical reaction
step for all pH values,[27] we rationalize in the following our observed HER activities using the modified
H-binding energy HBEapp as a descriptor.
As Pt(111) is the benchmark catalyst for HER, it is expected that the most active catalyst of the
investigated systems has an HBEapp value close to Pt(111). We used DFT to compute HBE, WBE, and
HBEapp for P-N3, P-N0, P-N6, and Au(111) as well as for Pt(111). This requires searching for the optimum
adsorption geometry of H and H2O on all the investigated systems. We found the optimum adsorption
geometry for H2O on all investigated polymers at the vertices of the organic network where water
molecules form hydrogen bonds with the polymers involving the N atoms for P-N3 and P-N6 (see
supporting information Figs. S9).
For atomic hydrogen on P-N3 and P-N6, the most favorable adsorption site is at the nitrogen atoms, in
line with the N 1s XPS data shown above. These results point to N atoms acting as docking sites for both
H2O and H. In contrast, the optimal adsorption environment of H on P-N0 is the same as on bare
Au(111). H prefers the adsorption site on threefold-hollow sites of Au(111) rather than in proximity to
the polymer (Supporting Information, Fig. S10), which is also in line with the unaltered C 1s XPS signal.
Figure 4a shows the values of WBE and HBEapp corresponding to the optimum adsorption geometries
found for the three polymer-decorated surfaces and for Au(111). The HBEapp (WBE) values obtained for
P-N3, P-N6, P-N0, and Au(111) are +0.02 eV (−0.38 eV), +0.32 eV (−0.77 eV), +0.64 eV (−0.44 eV), and
+0.51 eV (−0.31 eV) respectively. The HBEapp in Fig. 4a is the energy difference between the energies
represented in the right gray panel (H adsorption) and in the central panel (H2O adsorption). In light of
the previous discussion, the activity of each catalyst correlates with its HBEapp value and can be
compared to the one of Pt(111), which is HBEapp,Pt=−0.07 eV. The measured values of the current
densities (j) as a function of the computed values of HBEapp are shown in Fig. 4b. The value of HBEapp,Pt is
indicated with a vertical dashed line. According to the previous analysis, the polymer with the HBEapp
value closest to Pt is P-N3, which is the one with the largest HER activity. We connect the high activity of
P-N3 to an optimized balance between water and hydrogen binding energies that are similar to Pt(111).
Compared with P-N3, P-N6 binds H2O stronger than H, which diminishes electrocatalytic activity, in good
agreement with experiments. Hydrogen adsorption on Au(111) becomes endothermic when considering
WBE, inducing a further increase of HBEapp and a reduction of its expected catalytic activity with respect
to P-N3 and P-N6. Thus, our theoretical results are in line with the experimental trend of HER activities:
P-N3 > P-N6 > Au(111), although there remains a discrepancy concerning the P-N0 system. The HBEapp
descriptor does not account for the measured activity of P-N0, which is higher than the activity of
Au(111) and similar to the one obtained for P-N6. This result indicates that other reaction steps might be
rate delimiting and further parameters are required for a full description of all the investigated systems.
For instance, the activity of the supported P-N0 and P-N3 polymers might be reinforced due to the
particular binding geometry. Our calculations show that single H2O molecules adsorb parallel to the
surface on top sites, which is in good agreement with previous theoretical results.[28] In the case of P-N0
and P-N3 one hydrogen atom of the water molecule points downwards towards the gold electrode (H-
down configuration) while for P-N6, H2O lies parallel to the surface forming H-bonds with two N atoms of
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the polymer. The H-down geometry of H2O (Fig. 4a) favors interaction with the gold electronic states,
and consequently electrons transfer into the antibonding 4a1 and 2b2 orbitals of water (Fig. 4c). As a
consequence, this might destabilize the H−O bond, increasing water dissociation and generation of H.
Similar overlap of the unoccupied antibonding orbitals of water is absent on Au(111) and P-N6. We note
that a similar H-down configuration that we propose to facilitate reductive charge transfer into H2O is
observed in calculations for bare Au(111) and Pt(111).[29] At room temperature, the water layer on gold
becomes disordered whereas on platinum it remains at least partially in the H-down configuration;
should this adsorption geometry be responsible for the high activity of Pt, then we can expect P-N0 and
also P-N3 to work along the same way. Acknowledging that hydrogen adsorption is the relevant
descriptor for HER activity, we can thus correlate catalytic activity to the binding energies of H2O and H
on the polymer-decorated surface. Further properties might also influence the details of the reaction
but are probably not the rate-limiting steps; for example, once H2 is formed at a vertex of the polymer,
H2 abstraction is accompanied by a barrier not larger than ~0.17 eV, which is certainly much lower than
all other barriers.
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Figure 4: (a) Energy diagram for H2O and H adsorption and adsorption geometries on Au(111) and at the polymers.
(b) Plot of HER activity vs. calculated HBEapp, the linear line is to guide the eye. (c) Antibonding orbitals of water for
parallel and H-down adsorption configurations.
In conclusion, hydrogen evolution activity of a gold electrode in alkaline electrolyte is enhanced through
patterning the electrode surface with a porous two-dimensional polymer. The polymer provides docking
sites for H2O and H through hydrogen bonds and increases the binding energy and residence time close
to the electrode, which consequently increases catalytic activity. Systematic engineering the hydrogen
bonding sites of the polymer is used to adjust HER activity. Our results highlight the advantage of
controlling reactant interaction with the electrode patterned with porous polymers to achieve hybrid
organic/inorganic catalysts: The interaction of reactants and intermediate products with the electrode is
fine-tuned by providing adequate docking sites. The binding energy can be dialed-in such that the
optimal energy on the abscissa of the corresponding volcano plot can be achieved for any given metal
catalyst just by encoding suitable interaction sites into the precursor molecules. One can envision that
different docking sites such as hydroxyl groups or sulfur hetero atoms on the polymer further tweak
hydrogen bonding interactions and position the reactants in a suitable geometry for increased activity.
This paves the way for enhancing catalytic activity not only of HER but also for other electrocatalytic
reactions on earth-abundant transition metal catalysts.
Acknowledgements
Financial support by the ERC Starting Grant (project COF Leaf, grant number 639233), the DFG cluster of
excellence “e-conversion” and the Center for NanoScience (CeNS) is gratefully acknowledged by B.V.L . J.
M. L, P. A. and H. F. B acknowledge financial support from ANPCyT PICT-2750 and the computational
time provided by the CCT-Rosario computational center and Computational Simulation Center (CSC) for
Technological Applications, members of the High Performance Computing National System (SNCAD-
MincyT Argentina)
Keywords: hydrogen evolution reaction • hybrid catalyst • STM • XPS • DFT
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Bibliography
[1]
[2]
F. M. Mulder, J. Renew. Sustain. Energy 2014, 6, 033105.
J. H. Montoya, L. C. Seitz, P. Chakthranont, A. Vojvodic, T. F. Jaramillo, J. K. Nørskov, Nat. Mater.
2016, 16, 70–81.
[3]
Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov, T. F. Jaramillo, Science 2017,
355, eaad4998.
[4]
[5]
[6]
N. Mahmood, Y. Yao, J.-W. Zhang, L. Pan, X. Zhang, J.-J. Zou, Adv. Sci. 2018, 5, 1700464.
W. Sheng, H. A. Gasteiger, Y. Shao-Horn, J. Electrochem. Soc. 2010, 157, B1529.
R. Subbaraman, D. Tripkovic, D. Strmcnik, K.-C. Chang, M. Uchimura, A. P. Paulikas, V.
Stamenkovic, N. M. Markovic, Science 2011, 334, 1256–1260.
[7]
R. Subbaraman, D. Tripkovic, K.-C. Chang, D. Strmcnik, A. P. Paulikas, P. Hirunsit, M. Chan, J.
Greeley, V. Stamenkovic, N. M. Markovic, Nat. Mater. 2012, 11, 550–557.
[8]
[9]
H. Vrubel, X. Hu, Angew. Chemie 2012, 124, 12875–12878.
X. Yu, J. Zhao, L.-R. Zheng, Y. Tong, M. Zhang, G. Xu, C. Li, J. Ma, G. Shi, ACS Energy Lett. 2018, 3,
237–244.
[10] L. Stegbauer, K. Schwinghammer, B. V. Lotsch, Chem. Sci. 2014, 5, 2789–2793.
[11] V. S. Vyas, F. Haase, L. Stegbauer, G. Savasci, F. Podjaski, C. Ochsenfeld, B. V. Lotsch, Nat.
Commun. 2015, 6, 8508.
[12] T. Banerjee, K. Gottschling, G. Savasci, C. Ochsenfeld, B. V. Lotsch, ACS Energy Lett. 2018, 3, 400–
409.
[13] L. Grill, S. Hecht, Nat. Chem. 2020, 12, 115–130.
[14] J. W. Colson, W. R. Dichtel, Nat. Chem. 2013, 5, 453–465.
[15] Q. Shen, H.-Y. Gao, H. Fuchs, Nano Today 2017, 13, 77–96.
[16] W. Wang, X. Shi, S. Wang, M. A. Van Hove, N. Lin, J. Am. Chem. Soc. 2011, 133, 13264–13267.
[17] Q. Fan, J. M. Gottfried, J. Zhu, Acc. Chem. Res. 2015, 48, 2484–2494.
[18] J. Eichhorn, D. Nieckarz, O. Ochs, D. Samanta, M. Schmittel, P. J. Szabelski, M. Lackinger, ACS
Nano 2014, 8, 7880–7889.
[19] S. Clair, D. G. de Oteyza, Chem. Rev. 2019, 119, 4717–4776
[20] N. Graf, E. Yegen, T. Gross, A. Lippitz, W. Weigel, S. Krakert, A. Terfort, W. E. S. Unger, Surf. Sci.
2009, 603, 2849–2860.
[21] M. Chen, X. Feng, L. Zhang, H. Ju, Q. Xu, J. Zhu, J. M. Gottfried, K. Ibrahim, H. Qian, J. Wang, J.
Phys. Chem. C 2010, 114, 9908–9916.
This article is protected by copyright. All rights reserved.

10.1002/anie.201915855
Angewandte Chemie International Edition
[22] S. Trasatti, J. Electroanal. Chem. Interfacial Electrochem. 1972, 39, 163–184.
[23] J. K. Nørskov, T. Bligaard, A. Logadottir, J. R. Kitchin, J. G. Chen, S. Pandelov, U. Stimming, J.
Electrochem. Soc. 2005, 152, J23–J26.
[24] W. Sheng, M. Myint, J. G. Chen, Y. Yan, Energy Environ. Sci. 2013, 6, 1509–1512.
[25] J. Zheng, J. Nash, B. Xu, Y. Yan, J. Electrochem. Soc. 2018, 165, H27–H29.
[26] T. Cheng, L. Wang, B. V. Merinov, W. A. Goddard, J. Am. Chem. Soc. 2018, 140, 7787–7790.
[27] J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz, H. A. Gasteiger, Energy Environ. Sci. 2014, 7,
2255–2260.
[28] P. Tereshchuk, J. L. F. Da Silva, J. Phys. Chem. C 2012, 116, 24695–24705.
[29] S. Schnur, A. Groß, New J. Phys. 2009, 11, 125003.
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