Copper Nanocrystal Morphology Determines the Viability of Molecular Surface Functionalization in Tuning Electrocatalytic Behavior in CO2Reduction

Article abstract of DOI:10.1021/acs.inorgchem.1c00287

Molecular surface functionalization of metallic catalysts is emerging as an ever-developing approach to tuning their catalytic performance. Here, we report the synthesis of hybrid catalysts comprising copper nanocrystals (CuNCs) and an imidazolium ligand for the electrochemical CO2 reduction reaction (CO2RR). We show that this organic modifier steers the selectivity of cubic CuNCs toward liquid products. A comparison between cubic and spherical CuNCs reveals the impact of surface reconstruction on the viability of surface functionalization schemes. Indeed, the intrinsic instability of spherical CuNCs leads to ejection of the functionalized surface atoms. Finally, we also demonstrate that the more stable hybrid nanocrystal catalysts, which include cubic CuNCs, can be transferred into gas-flow CO2RR cells for testing under more industrially relevant conditions.

Full text of DOI:10.1021/acs.inorgchem.1c00287

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Copper Nanocrystal Morphology Determines the Viability of
Molecular Surface Functionalization in Tuning Electrocatalytic
Behavior in CO Reduction
2
James R. Pankhurst, Pranit Iyengar, Valery Okatenko, and Raffaella Buonsanti*
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ABSTRACT: Molecular surface functionalization of metallic catalysts is emerging
as an ever-developing approach to tuning their catalytic performance. Here, we
report the synthesis of hybrid catalysts comprising copper nanocrystals (CuNCs)
and an imidazolium ligand for the electrochemical CO reduction reaction
2
(
CO RR). We show that this organic modifier steers the selectivity of cubic
2
CuNCs toward liquid products. A comparison between cubic and spherical
CuNCs reveals the impact of surface reconstruction on the viability of surface
functionalization schemes. Indeed, the intrinsic instability of spherical CuNCs
leads to ejection of the functionalized surface atoms. Finally, we also demonstrate
that the more stable hybrid nanocrystal catalysts, which include cubic CuNCs, can
be transferred into gas-flow CO RR cells for testing under more industrially
2
relevant conditions.
INTRODUCTION
The electrochemical CO reduction reaction (CO RR) has
gained intense interest from an array of scientific fields because
Ligands can steer the reaction mechanism toward single
products by influencing the binding energies of specific
intermediates, either by modification of the properties of the
■
2
2
23−25
metal itself
the surface.
or by direct interaction with intermediates at
Ligands can also influence the interface
of its potential to address future energy and environmental
26−29
1
demands. By using CO , water, and electrical energy for the
2
between the metal and reaction medium, altering reactant
synthesis of energy-dense hydrocarbons, the storage of
intermittent renewable energy in the form of chemical bonds
while progressing toward a closed carbon cycle is envisioned.
3
0
concentration profiles or even establishing new phase
2
,3
31,32
boundaries.
However, not much attention has been
Copper is the only single metal that is known to form C−C
dedicated so far to the link between the metal catalyst
reconstruction during operation and the effects induced by the
organic modifiers.
In this work, we illustrate how the stability of the nanocrystal
(NC) catalyst is crucial in allowing the effects of surface
ligands to emerge. Specifically, we study CuNCs functionalized
with a disubstituted imidazolium ligand [1-octyl-3-(p-
bonds during the CO RR, leading to desirable products such as
2
hydrocarbons and alcohols. However, this catalyst suffers from
an intrinsic selectivity problem because 16 different products
2
,3
form on a polycrystalline foil. Studies on single crystals have
revealed the structural sensitivity of the reaction, with certain
4
−7
facets being more selective for certain products.
Because of
their capability of translating these findings identified on
copper surfaces into more realistic conditions, copper nano-
nitrobenzyl)imidazolium hexafluorophosphate, ImPF ] as
6
CO RR electrocatalysts. This molecule was selected based on
2
crystals (CuNCs) are at the forefront of CO RR re-
2
our recent study where we investigated several disubstituted
4
,5,8−12
search.
For example, cubic CuNCs have attracted
imidazolium ligands as CO RR promoters on the surfaces of
2
particular interest because the interface between the exposed
33
silver nanocrystal (AgNC) catalysts. In addition to the
(
100) facets and (110) edge sites has been found to favor C−
6,10,13−16
interaction of the imidazolium group with CO , we found that
2
C coupling toward ethylene.
the C tail length was optimal for promoting the selectivity
8
In addition to structural modifications, the coupling of pure
metal surfaces with organic coatings and ligands has gained
17−34
Special Issue: Heterogeneous Interfaces through the
Lens of Inorganic Chemistry
increased attention in recent years.
These studies have
revealed the huge potential of combining the fields of
homogeneous and heterogeneous catalysis to steer selectivity
Received: January 28, 2021
2
2−34
in the CO RR.
They have also evidenced that the surface
2
chemistry of modified catalysts is both rich and complex
19−22
because many factors that influence catalysis are at play.
©
XXXX American Chemical Society
https://doi.org/10.1021/acs.inorgchem.1c00287
A
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toward CO RR versus the competing hydrogen evolution
the PF6− stretch is observed at 828 cm . The absorption
−1
2
reaction (HER).
bands corresponding to the imidazolium C−H stretches are
In the case of CuNCs, we observe that the selectivity
changes toward liquid products at intermediate potentials
when functionalized with the imidazolium ligand. More
importantly, a comparison between the cubic and spherical
CuNCs highlights that morphologically stable NCs must be
employed for the study of hybrid catalyst systems. Finally, we
demonstrate that the imidazolium-functionalized cubic CuNC
catalysts can be transferred to gas-flow electrochemical setups
for testing under elevated current densities, thus illustrating the
eventual suitability of these catalysts for commercial
applications.
shifted to lower frequency on the Cu surface, appearing at
cub
−
1
−1
3156 cm compared to 3164 cm for the free ligand. This
suggests that ImPF interacts with the copper surface through
6
the imidazolium ring.
X-ray photoelectron spectroscopy (XPS) confirmed the
presence of the ImPF ligands on the Cu surface (Figures
6
cub
2B and S5). No peaks were observed in the N 1s region for the
as-synthesized CuNCs, but after functionalization with ImPF6,
peaks emerged at 406.1, 401.9, and 400.5 eV, corresponding to
the NO functional group and the two nitrogen atoms in an
2
asymmetric imidazolium ring. XPS spectra in the O 1s region
evidenced a large increase in the amount of organic-based
oxygen compared with the metal oxide content, consistent with
RESULTS AND DISCUSSION
We have synthesized cubic CuNCs (Cu ) according to our
previously reported colloidal synthesis route (Figure S1).
■
the introduction of nitro-containing ImPF ligands. Finally, a
6
cub
10
single peak in the F 1s region was observed following
functionalization with ImPF , showing the presence of the
The native trioctylphosphine oxide (TOPO) ligands were
exchanged with ImPF , according to the scheme illustrated in
Figure 1A.
6
−
PF6 anion. The electronic structure of the copper surface was
6
also investigated by XPS, which revealed that the ImPF ligand
6
does not introduce any significant change (Figure S6 and
Table S1). The Cu 2p photoelectron and Cu LMM Auger
spectra were indicative of a mixture of copper(0) and
copper(I) oxidation states for the Cucub surface, both before
and after functionalization with ImPF6.
The CO RR performance of the CuNC catalysts was first
2
assessed using an H-cell configuration, where the catalysts were
drop-cast on glassy carbon electrodes. Previous studies have
shown that an optimal CO RR performance is achieved for
2
cubic CuNCs in 0.1 M KHCO at −1.1 V
(RHE =
and the catalysts in this
3
RHE
5
,8−12
reversible hydrogen electrode),
study were therefore tested at a range of potentials around this
value (more than 80% hydrogen is generated at potentials
more positive than −1.05 VRHE). Solvent washing of the as-
synthesized Cu was carried out after drop-casting to remove
cub
the native TOPO ligands so as to provide a naked reference
sample. The Cucub-ImPF catalyst was tested after deposition
6
without any additional solvent washing. In line with previous
studies, Cucub produced mainly hydrogen at −1.05 VRHE, then
ethylene as the major CO RR product at −1.10 V
with a
2
RHE
Faradaic efficiency (FE) of 36%, and finally methane as the
dominant CO RR product as the potential became more
2
35
negative, with a FE of 23% at −1.20 V
After functionalization with ImPF , the overall CO RR vs
(Figure 3A).
RHE
6
2
Figure 1. (A) Overview of the ligand-exchange procedure to obtain
HER selectivity remained similar to the pristine Cucub at −1.05
imidazolium-functionalized CuNCs (Cucub-ImPF ). (B) TEM images
6
and −1.10 V , while hydrogen was suppressed at −1.15 and
RHE
of as-synthesized Cucub, functionalized with TOPO, and of Cucub
ImPF6.
-
−1.20 V
. At −1.20 V , FE was only 24% for Cu -
cub
RHE
RHE
H2
ImPF against 40% for Cucub, indicating that the imidazolium
6
ligand inhibits HER at more negative potentials, which is
3
3
Solvent washing was used to remove the native TOPO from
the as-synthesized Cucub (Cucub-TOPO) before functionaliza-
tion with ImPF to form the Cu -ImPF hybrid catalyst
consistent with our previous work. Among the CO RR
2
products, the CO selectivity was equivalent for both catalysts
across the range of potentials. Conversely, ethylene formation
6
cub
6
(
Figure 1A). Transmission electron microscopy (TEM)
was suppressed on the Cucub-ImPF catalyst at −1.05, −1.10
6
characterization shows that no sintering or etching of the
particles occurred using this procedure (Figure 1B). We note
that, compared with our previous work on AgNCs, exchange of
and −1.15 V
(the F.E. is only 22% at −1.10 V ).
RHE
RHE
Concomitantly, an increase in the liquid products was
observed, with formate being the major product (Figure 3A).
This is seen more clearly when the liquid/gas product ratios
are compared across the studied potential range (Figure 3B),
with the maximum change in selectivity being observed at
−
−
the Br counterion for PF6 was necessary because the former
induced severe restructuring in the CuNCs (Figures S2−S4),
34
which is consistent with other work involving copper foils.
Successful ligand exchange on Cucub was supported by
Fourier transform infrared (FT-IR) spectroscopy (Figure 2A).
−1.10 V . At the most negative potential of −1.20 VRHE, the
RHE
gas and liquid product selectivities are again similar to those of
Cucub, as the strongly negative potential still favors methane
formation even in the presence of ImPF6.
The strong absorption bands for the ImPF nitro groups are
6
−
1
observed at 1517 and 1341 cm , and the band arising from
B
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Figure 2. (A) FT-IR spectra of TOPO, Cucub, ImPF , and Cu -ImPF . The absorption bands corresponding to the ImPF imidazolium C−H,
6
cub
6
6
nitro N−O, and P−F stretches are highlighted in red, green, and blue, respectively. (B) XPS spectra evidencing the introduction of the ImPF
ligand are shown for the F 1s, O 1s, and N 1s regions.
6
While the FEs provide a clear idea of product distribution,
information regarding changes of the intrinsic catalytic activity
can be derived only from current densities normalized by the
electrochemically active surface areas (ECSAs). Similar ECSAs
of the CO RR versus HER activity at higher potential, as we
2
33
commented on in our previous work. Explaining the change
in selectivity from ethylene to formate is more challenging. In
the absence of comprehensive mechanistic studies combined
with theory, only speculations can be made for now. Overall,
we suspect a convolution of multiple ligand effects at the
surface. In addition to those mentioned above, we should also
were measured for both Cu and Cucub-ImPF (S = 5.7
cub
6
ECSA
2
cm ; Figure S8), indicating that the number of active sites does
not change (i.e., the functionalized CuNCs still retain a large
36−38
number of free active sites for CO RR and/or new ones are
consider the stabilization or trapping of intermediates.
It
2
created post-functionalization). As for the overall current
is interesting to note that a recent study by Etzold et al.
showed that functionalization of a copper foam with ionic
liquid ligands resulted in the suppression of ethylene formation
densities for Cucub and Cucub-ImPF (Figure 4A), they were
6
very similar across the entire potential window studied, thus
38
showing that functionalization with ImPF neither boosts nor
and promotion of liquid products, being mainly formate.
6
inhibits the overall intrinsic activity of the CuNC catalyst
This behavior was indeed attributed to the interaction of the
toward the CO RR. Inspection of the partial current densities
ionic liquid ligands with the reaction intermediates, specifically
2
38
for the different products reinforces the above-mentioned
trapping of the *CH carbene.
2
observations. Namely, they indicate that, on Cucub-ImPF , the
Suppression of ethylene formation after functionalization of
the Cucub catalyst is particularly interesting because ethylene
should be the main product from the (100) facet of the cubic
CuNCs. One of the strengths of colloidal synthesis is the
accessibility of preparing NCs with different shapes, which
expose different crystal facets on the surface. We took
advantage of this to explore the possibility of facet dependence
of the reaction pathway for functionalized CuNCs. Spherical
CuNCs (24 nm) were synthesized and also functionalized with
6
intrinsic activity for hydrogen is suppressed at higher
overpotential (Figure 4B). The activity for ethylene decreases
at −1.10 and −1.15 V
but remains practically unchanged at
(Figure 4C). Finally, the intrinsic activity for
RHE
−1.20 V
RHE
formate is enhanced across the entire potential range (Figure
D).
To explain the discussed changes in the selectivity and
4
intrinsic activity due to the presence of ImPF on the copper
6
surface, we should consider three main roles that ligands can
play on the NC surface at the very least. First, ligands can
influence the electronic structure of the metal; this was already
excluded by XPS measurements, as discussed above. The other
possible roles are to influence the metal/electrolyte interface
and to interact with incoming reactants or intermediates at the
ImPF , which are referred to as Cu
and Cusph-ImPF6,
6
sph
respectively. The same ligand-exchange procedure as that for
Cucub was employed, and similar characterizing data that
supported the successful ligand exchange were obtained
(Figures S11−S13 and Table S3). Surprisingly, after
functionalization with ImPF , we found that the CO RR
6
2
1
7
surface.
product ratio remained essentially unchanged in the case of the
spheres (Figure S14). Therefore, we moved on to study the
persistence of the ligands on the surface during the CO RR at
Ionic liquids have classically been recognized as interacting
36
strongly with CO and contributing to its activation. A higher
2
2
surface hydrophobicity has also been demonstrated to promote
−1.1 VRHE. Figure 5 provides an overview of these results.
30,33
the CO RR versus HER.
In our system, the presence of the
XPS measurements after CO RR electrolysis confirmed that
2
2
imidazolium ring in ImPF , together with a slight increase in
the imidazolium ligand is still present on the surface of CuCub
because N 1s peaks were observed at 400 and 404 eV that can
be ascribed to the imidazolium ring and nitro group of ImPF6,
6
the hydrophobicity for Cucub-ImPF compared to washed
6
Cucub (Figure S10), might contribute to the observed increase
C
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Figure 3. (A) FEs for gas and liquid products and (B) liquid/gas
product ratios for Cucub and Cucub-ImPF6 measured at different
potentials versus RHE. CO RR electrolysis was carried out in a liquid
2
Figure 4. (A) Total current densities and (B−D) partial current
H-cell for 75 min, using 0.1 M KHCO as the electrolyte. The mass
3
densities for hydrogen, ethylene, and formate, respectively, for Cu
cub
loading was 15 μg based on copper in all cases. The error bars show
the standard deviation following three independent measurements.
The FE values for individual products are given in Table S2 and
shown in Figure S7.
and Cucub-ImPF measured at different potentials versus RHE. The
6
decrease and increase in the intrinsic activity are indicated by red and
blue arrows, respectively. CO RR electrolysis was carried out in a
2
liquid H-cell for 75 min, using 0.1 M KHCO as the electrolyte. The
3
mass loading was 15 μg based on copper in all cases. The partial
current densities corresponding to the other products are reported in
Figure S9.
respectively (Figure 5A). In contrast, these peaks were not
observed in the case of Cusph (Figure 5B). Furthermore, during
linear-sweep voltammetry (LSV) measurements, a reduction
wave at −0.32 V
was observed for Cusph-3ImPF . This
RHE
6
9
signature is consistent with ligand stripping and thus
have recently demonstrated that an Ostwald-ripening-like
mechanism is involved in such reconstructive processes,
which start at potentials as low as −0.25 VRHE.
Considering the above observations, we can conclude that
indicates that the ImPF ligand readily desorbs from the
spherical CuNCs (Figure 5D). No such desorption wave was
observed for Cucub-ImPF (Figure 5C). Effects related to
6
11,42,43
6
preferential interactions of ImPF with certain facets of the
CuNCs [i.e., stronger binding to the (100) surface of cubic
CuNCs] are possible and might play a role here.
the Cusph-ImPF catalyst is unstable at potentials as low as
6
6
−0.3 VRHE, where a combination of potential-induced ligand
stripping and a change of the NC morphology takes place. We
highlight that this latter point poses a more general implication
for functionalized metal catalysts, where ligands can be
“ejected” from a catalyst surface along with the surface atoms
during restructuring (Figure 5G). A recent study has reported
that ligand desorption can be reversible under those unique
conditions, including the assembly of NC monolayers on the
electrode surface, which enable collective dissociation of
In order to assess the structural stability of the inorganic
component, we then moved to TEM. Consistent with previous
4
0,41
studies on cubic CuNCs,
the Cucub-ImPF6 catalyst
remains stable against restructuring, meaning that they do
not change size or shape over the 75 min of electrolysis
considered in this study (Figure 5E). In contrast, Cusph-ImPF6
converts to larger aggregates containing particles of different
sizes and shapes, including some cubic particles (Figures 5F
and S15). Spherical CuNCs are known to undergo immediate
restructuring when reductive potentials are applied, and we
32
ligands under an applied bias. This phenomenon is certainly
interesting and deserves further investigation. However, we do
not observe any immediate evidence for it (e.g., ligand-induced
D
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Figure 5. (A and B) N 1s XPS analysis of Cucub-ImPF and Cu -ImPF , respectively, following CO RR electrolysis at −1.1 VRHE. (C and D) LSV
6
sph
6
2
of Cucub-ImPF and Cu -ImPF , respectively. (E and F) TEM analysis of Cu -ImPF and Cu -ImPF , respectively, following CO RR
6
sph
6
cub
6
sph
6
2
electrolysis at −1.1 VRHE. (G) Scheme depicting the relative stabilities of cubic and spherical CuNCs during the CO RR.
2
changes in the CO RR performance of spherical CuNCs)
lower overpotentials are needed and suppression of the
reactions that form CH and H is observed, which are
changes connected to the reaction microenvironment created
2
under the high loading densities utilized in our study.
Finally, another strength of using colloidal NCs as
electrocatalysts is that they can be prepared as inks, which
facilitates their implementation in different device config-
4
2
in the gas-diffusion electrode and are normally attributed to
6
higher local pH. In terms of the CO RR product selectivity,
2
6
,15,44
urations.
In order to verify whether ligand effects still
the same key observations that were made in the liquid H-cell
were also made in the gas-fed cell after functionalization with
hold at higher current densities, which are more relevant for
commercial applications, we tested Cu and Cucub-ImPF in
cub
6
ImPF (Figure 6). Specifically, the ethylene selectivity was
6
a gas-fed cell at 50 mA cm− (Figure 6). Both catalysts formed
stable colloidal inks that could be sprayed onto carbon paper
electrodes. Compared to the measurements in the H-cell,
2
reduced from 40.1% to 29.3%, while the FE for formate
increased from 6.1% to 9.9%. The FE for ethanol also
increased from 0% to 2.16%, as did that for ethylene glycol,
from 0.2% to 2.83%. Overall, the liquid/gas product ratio
increased from 0.15 for Cucub to 0.31 for Cucub-ImPF6,
reflecting the same change in the selectivity that was observed
in the liquid H-cell.
CONCLUSIONS
■
In conclusion, we have synthesized hybrid CO RR catalysts,
comprised of inorganic CuNCs functionalized with an
2
imidazolium ligand. The results of our CO RR studies on
2
cubic CuNCs hint toward the ImPF ligand interacting with
6
CO and the CO RR intermediates to promote the CO RR
2
2
2
versus HER at higher applied potentials and formate over
ethylene across the entire range of investigated potentials
(
from −1.05 to −1.20 V ). After comparing the CO RR
RHE
2
performances of cubic and spherical hybrid CuNCs, we
identified that the structural stability of cubic CuNCs and of
their bonds with the ligands permits such surface modification
studies. In contrast, the reconstruction of spherical CuNCs
means that the promoter effect of the imidazolium ligand is
lost. These results point toward the need to design hybrid
catalysts with stable NC morphologies in mind or perhaps to
conceive ligands that prevent reconstruction processes from
occurring. Finally, we highlight that the transferability of a
surface-modified NC electrocatalyst from a liquid H-cell to a
gas-fed cell is highly encouraging for the future development of
Figure 6. Summary of the CO RR selectivity data for Cu and
2
cub
Cucub-ImPF , showing (A) the FEs for gas and liquid products and
6
(
B) liquid/gas product ratios. CO RR electrolysis was carried out in a
2
gas-fed cell for 50 min, using 1.2 M KHCO as the electrolyte and a
fixed current density of −50 mA cm . The mass loading was 250 μg
based on copper in all cases.
3
−
2
such catalysts in the application of the CO RR.
2
E
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5) Iyengar, P.; Huang, J.; De Gregorio, G. L.; Gadiyar, C.;
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The Supporting Information is available free of charge at
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Buonsanti, R. Size Dependent Selectivity of Cu Nano-Octahedra
Catalysts for the Electrochemical Reduction of CO to CH . Chem.
*
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4
Commun. 2019, 55, 8796−8799.
(6) De Gregorio, G. L.; Burdyny, T.; Loiudice, A.; Iyengar, P.;
Additional experimental details, including information
related to FT-IR, NMR, XPS, contact angle, electro-
catalysis, and TEM results (PDF)
Smith, W. A.; Buonsanti, R. Facet-Dependent Selectivity of Cu
Catalysts in Electrochemical CO Reduction at Commercially Viable
2
Current Densities. ACS Catal. 2020, 10, 4854−4862.
(7) Strasser, P.; Gliech, M.; Kuehl, S.; Moeller, T. Electrochemical
Processes on Solid Shaped Nanoparticles with Defined Facets. Chem.
Soc. Rev. 2018, 47, 715−735.
AUTHOR INFORMATION
Corresponding Author
Raffaella Buonsanti − Laboratory of Nanochemistry for
Energy, Institute of Chemical Sciences and Engineering, Ecole
■
(8) Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser,
P. Particle Size Effects in the Catalytic Electroreduction of CO on Cu
2
́
Nanoparticles. J. Am. Chem. Soc. 2014, 136, 6978−6986.
Polytechnique Fédérale de Lausanne, 1950 Sion, Valais,
Switzerland; orcid.org/0000-0002-6592-1869;
Email: raffaella.buonsanti@epfl.ch
(9) Manthiram, K.; Beberwyck, B. J.; Alivisatos, A. P. Enhanced
Electrochemical Methanation of Carbon Dioxide with a Dispersible
Nanoscale Copper Catalyst. J. Am. Chem. Soc. 2014, 136, 13319−
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H.; Ager, J. W.; Buonsanti, R. Tailoring Copper Nanocrystals towards
C Products in Electrochemical CO Reduction. Angew. Chem., Int.
James R. Pankhurst − Laboratory of Nanochemistry for
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Energy, Institute of Chemical Sciences and Engineering, Ecole
Polytechnique Fédérale de Lausanne, 1950 Sion, Valais,
Switzerland
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(11) Kim, D.; Kley, C. S.; Li, Y.; Yang, P. Copper Nanoparticle
Ensembles for Selective Electroreduction of CO to C -C Products.
Pranit Iyengar − Laboratory of Nanochemistry for Energy,
Institute of Chemical Sciences and Engineering, Ecole
Polytechnique Fédérale de Lausanne, 1950 Sion, Valais,
Switzerland
Valery Okatenko − Laboratory of Nanochemistry for Energy,
Institute of Chemical Sciences and Engineering, Ecole
Polytechnique Fédérale de Lausanne, 1950 Sion, Valais,
Switzerland
2
2
3
́
Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 10560−10565.
(12) Osowiecki, W. T.; Nussbaum, J. J.; Kamat, G. A.; Katsoukis, G.;
Ledendecker, M.; Frei, H.; Bell, A. T.; Alivisatos, A. P. Factors and
Dynamics of Cu Nanocrystal Reconstruction under CO Reduction.
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ACS Appl. Energy Mater. 2019, 2, 7744−7749.
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(13) Mangione, G.; Huang, J.; Buonsanti, R.; Corminboeuf, C. Dual-
Facet Mechanism in Copper Nanocubes for Electrochemical CO2
Reduction into Ethylene. J. Phys. Chem. Lett. 2019, 10, 4259−4265.
(14) Zhu, P.; Xia, C.; Liu, C.-Y.; Jiang, K.; Gao, G.; Zhang, X.; Xia,
Complete contact information is available at:
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Y.; Lei, Y.; Alshareef, H. N.; Senftle, T. P.; Wang, H. Direct and
Continuous Generation of Pure Acetic Acid Solutions via Electro-
catalytic Carbon Monoxide Reduction. Proc. Natl. Acad. Sci. U. S. A.
Author Contributions
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021, 118, No. e2010868118.
15) Wang, Y.; Shen, H.; Livi, K. J. T.; Raciti, D.; Zong, H.; Gregg,
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
J.; Onadeko, M.; Wan, Y.; Watson, A.; Wang, C. Copper Nanocubes
for CO Reduction in Gas Diffusion Electrodes. Nano Lett. 2019, 19,
2
Notes
8461−8468.
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
This work was primarily financed by the H2020 Marie Curie
Individual Fellowship grant SURFCAT with Agreement
37378. V.O. and P.I. acknowledge the Swiss National Science
Foundation (SNSF) under an AP Energy Grant (Project
PYAPP2_166897/1) and Gaznat SA for financial support. The
authors thank Dr. Anna Loiudice for her help with the contact-
angle measurements. This publication was created as part of
NCCR Catalysis, a National Centre of Competence in
Research funded by the SNSF.
■
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