Coupling of Cu(100) and (110) Facets Promotes Carbon Dioxide Conversion to Hydrocarbons and Alcohols

Article abstract of DOI:10.1002/anie.202015159

Copper can efficiently electro-catalyze carbon dioxide reduction to C₂₊ products (C₂H₄, C₂H₅OH, n-propanol). However, the correlation between the activity and active sites remains ambiguous, impeding further improvements in their performance. The facet effect of copper crystals to promote CO adsorption and C?C coupling and consequently yield a superior selectivity for C₂₊ products is described. We achieve a high Faradaic efficiency (FE) of 87 % and a large partial current density of 217 mA cm^?2 toward C₂₊ products on Cu(OH)₂-D at only ?0.54 V versus the reversible hydrogen electrode in a flow-cell electrolyzer. With further coupled to a Si solar cell, record-high solar conversion efficiencies of 4.47 % and 6.4 % are achieved for C₂H₄ and C₂₊ products, respectively. This study provides an in-depth understanding of the selective formation of C₂₊ products on Cu and paves the way for the practical application of electrocatalytic or solar-driven CO₂ reduction.

Full text of DOI:10.1002/anie.202015159

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Accepted Article
Title: Coupling of Cu(100) and (110) Facets Promotes Carbon Dioxide
Conversion to Hydrocarbons and Alcohols
Authors: Jinlong Gong
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Angewandte Chemie International Edition
10.1002/anie.202015159
RESEARCH ARTICLE
Coupling of Cu(100) and (110) Facets Promotes Carbon Dioxide
Conversion to Hydrocarbons and Alcohols
Dazhong Zhong,# [a], [b] Zhi-Jian Zhao,# [a] Qiang Zhao,# [b] Dongfang Cheng, Bin Liu, Gong Zhang,
[a]
[a]
[a]
[
a]
[a]
[a]
[a]
[b]
[a], [c]
Wanyu Deng, Hao Dong, Lei Zhang, Jingkun Li, Jinping Li,* and Jinlong Gong*
[
a]
D. Zhong, Prof. Dr. Z. Zhao, D. Cheng, B. Liu, G. Zhang, W. Deng, H. Dong, L. Zhang, Prof. Dr. J. K. Li, Prof. Dr. J. Gong
Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University
Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)
Weijin Road 92, Tianjin, 300072, China
E-mail: jlgong@tju.edu.cn
[
b]
D. Zhong Prof. Dr. Q. Zhao, Prof. Dr. J. P. Li
College of Chemistry and Chemical Engineering, Taiyuan University of Technology
Shanxi Key Laboratory of Gas Energy Efficient and Clean Utilization
Yingze West Street 79, Taiyuan 030024, Shanxi, China
E-mail: jpli211@hotmail.com
[
c]
Prof. Dr. J. Gong
Joint School of National University of Singapore and Tianjin University
International Campus of Tianjin University
Binhai New City, Fuzhou 350207, China
#
These authors contributed equally to this work.
Abstract: Copper can efficiently electro-catalyze carbon dioxide
reduction to C2+ products (e.g., C , C OH, and n-propanol).
The high local pH induced by the increased surface roughness
also plays a role [4e, 7]. Additionally, positively charged Cu
and residual subsurface oxygen [9] are proposed to stabilize CO
adsorption and promote dimerization and thus significantly
enhance the selectivity for C2+ products. However, Cu+ and
subsurface oxygen have been revealed experimentally and
theoretically to be unstable under reduction conditions during
[4a, 8]
H
2 4
2 5
H
However, the correlation between the activity and active sites
remains ambiguous, impeding further improvements in their
performance. This paper describes the facet effect of copper crystal
to promote CO adsorption and C-C coupling and consequently yield
a superior selectivity for C2+ products. We achieve a high Faradaic
efficiency (FE) of 87% and a large partial current density of 217 mA
CO
2
RR [4e, 6, 10]. The geometric structure of surface atoms in
-
2
[11]
cm toward C2+ products on Cu(OH)
2
-D at only -0.54 V versus the
catalysts is significant for the catalytic performance . As of yet,
it is a great challenge to control the surface atom arrangement
due to the random reconstruction of Cu during the reduction
process of Cu oxides. Since the Cu-O bond is broken and O (or
OH) is released under reduction potential, the pre-catalyst plays
a crucial role in the structure reconstruction for Cu preparation.
reversible hydrogen electrode in a flow-cell electrolyzer. With further
coupled to a Si solar cell, record-high solar conversion efficiencies of
2 4
4.47% and 6.4% are achieved for C H and C2+ products,
respectively. This study provides an in-depth understanding of the
selective formation of C2+ products on Cu and paves the way for the
practical application of electrocatalytic or solar-driven CO
2
reduction.
By modifying the structures of precursors (Cu(OH)
Cu O), we predict that the exposed surface on the catalysts can
be regulated.
This paper describes a Cu catalyst with abundant stepped
Cu(110) and highly active Cu(100) sites for CO RR to C2+
products. Our results reveal that Cu(OH) -derived Cu catalysts
2
, CuO and
2
Introduction
2
2
Solar-driven electrocatalytic carbon dioxide reduction reaction
CO RR) to value-added chemicals and fuels is attractive to
simultaneously utilize renewable energy source and reduce
atmospheric CO concentration to solve the environmental
problem [1]. In contrast to mono-carbon products such as CO
and CH , higher value-added C2+ (including C ) hydrocarbons
and alcohols have attracted more attention . Currently, owing
to the specific binding energy of *CO intermediate, copper is the
2
only metal that can effectively catalyze CO .
RR to C2+ products [3]
expose relatively high density of stepped Cu(110) and Cu(100),
which are assembled into Cu(210) and Cu(310). The assembled
Cu(210) and (310) promote CO adsorption and CO dimerization,
(
2
2
2
leading to improved CO RR catalytic activity to C2+ products.
When evaluated in flow-cell with an alkaline aqueous solution as
the electrolyte, the C2+ FE of 87% is achieved with a larger
current density at low overpotential. We also coupled a cheap Si
solar cell with electrochemical cell to construct a PV-EC system
4
2
[
2]
2
for direct solar-driven CO reduction, the most efficient solar
Nonetheless, due to the sluggish kinetics and the competition of
kinetically favorable hydrogen evolution reaction (HER), poor
selectivity and activity still hinder the large-scale implementation
conversion efficiency of 4.47% and 6.4% is achieved for C
and C2+ products, respectively.
2 4
H
of CO
Electroreduction of high-valence-state copper has been
reported to improve CO
RR performance [4]. HER is largely
2
RR electrolyzers.
Results and Discussion
2
suppressed over Cu sites derived from high-valence-state
copper species (e.g., precursor). However, the FE for C2+
products is generally unsatisfied, and the reaction mechanisms
are still under debate. Grain boundaries formed by the reduction
are firstly proposed to be responsible for the enhanced catalytic
activity [1c, 5]. Similarly, the Cu(100) facet preferentially formed on
the surface also contributes to the enhanced performance [6].
Synthesis and characterization of catalysts. We prepared
three types of precursors. Cu(OH) supported on copper foil
Cu(OH) /Cu foil) was prepared by converting commercial Cu foil
in an alkaline solution
foil) and Cu O supported on Cu foil (Cu
from annealing Cu(OH) /Cu foil in air and N
respectively (for details, please see the Methods Section). The
2
(
2
[
12]
. CuO supported on Cu foil (CuO/Cu
O/Cu foil) were obtained
atmosphere,
2
2
2
2
1
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Angewandte Chemie International Edition
10.1002/anie.202015159
RESEARCH ARTICLE
structures of Cu(OH)
confirmed with X-ray diffraction spectroscopy (XRD) patterns,
Raman spectra, X-ray photoelectron spectroscopy (XPS)
2
/Cu foil, CuO/Cu foil, and Cu
2
O/Cu foil are
demonstrate the precursors were converted to metallic Cu,
where exhibit lattice fringes of Cu(200) and (111) (Figure S5).
Transmission electron microscopy (TEM) images show that
(
Figures S1a-c), and scanning electron microscopy (SEM)
Cu(OH)
rod structure of the precursors (Figure S6). Interesting, Cu(OH)
D gives more roughness structure than CuO-D and follows by
Cu O-D, it is large likely due to the more substantial lattice
change during the reduction of Cu(OH) to metallic Cu (the
lattice distance of Cu(OH) , CuO, Cu O, and Cu gives a
decreasing trend observed from the XRD results). Nevertheless,
due to the rough surface structure of Cu(OH) (Figure S6), high-
2 2
-D, CuO-D, and Cu O-D have essentially inherited the
images (Figure S1d-f).
2
-
2
2
2
2
2
index stepped surfaces, such as Cu(310)=3(100)×(110) and
Cu(210)=2(110)×(100), composed by Cu(100) and Cu(110),
can be observed in Cu(OH) -D (Figure. 1, e-g). The Cu(100)
2
domains in Cu(310) and Cu(210) also inherit the nature of the
stepped Cu(110) with low-coordinations (Figure 1g). Additionally,
2
to further validate the surface roughness of Cu(OH) -D/Cu foil,
we compare the double-layer capacitance (Cdl) between the
electrodes and polished Cu foil to calculate their electrochemical
surface area (ECSA) (Figure S7). The Cu(OH)
largest ECSA of 84.3, followed by 72.4 and 64.9 for CuO-D/Cu
foil and Cu O-D/Cu foil, respectively (table S1).
2
-D/Cu foil has the
2
Figure 1. Structure characterization of the catalysts. (a) Schematic illustration
of the preparation of Cu(OH)
situ Raman spectra of (b) Cu(OH)
foil in CO -saturated 0.1 M KHCO
corrected HAADF-TEM images of Cu(OH)
2
-D/Cu foil, CuO-D/Cu foil, and Cu
/Cu foil, (c) CuO/Cu foil, and (d) Cu
at -0.5 V vs. RHE. (e) and (f) Aberration-
-D. (g) Models showing
2
O-D/Cu foil. In
2
2
O/Cu
2
3
2
coordination numbers of (310) and (210) facets; the yellow square marked
area is the square Cu(100).
To prepare the designed catalysts, the Cu(OH)
2
/Cu, CuO/Cu
and Cu O/Cu foils were placed in a CO -saturated 0.1 M KHCO
2
2
3
aqueous solution and reduced under the bias potential of -0.5 V
versus the reversible hydrogen electrode (vs. RHE) for ~800 s
Figure 2. Surface structure. (a) CV curves collected in Ar-saturated 1 M KOH
(
Figure 1a). The obtained samples were denoted as Cu(OH)
D/Cu foil, CuO-D/Cu foil, and Cu O-D/Cu foil, respectively.
Figure. S2 shows time-dependent current density curves for the
reduction of Cu(OH) /Cu foil, CuO/Cu foil, and Cu O/Cu foil, in
2
-
for Cu(OH)
2
-D/Cu foil, CuO-D/Cu foil and Cu
2
O-D/Cu foil, scan rates = 5 mV s-
-D/Cu foil, CuO-
2
1
.
(b) Grazing incident XRD (α = 0.1°) patterns of Cu(OH)
O-D/Cu foil.
2
D/Cu foil, and Cu
2
2
2
agreement with the reduction of Cu hydroxide/oxide to metallic
Cu [4e]. In situ Raman was employed to investigate the reduction
process (Figure 1b-d). The Raman spectra of these samples
collected in the open circuit are similar to the spectra of
precursors measured ex-situ (Figure S1b). After several minutes
Cyclic voltammetry (CV) curves were collected in Ar-saturated
1 M KOH to further probe the surface structure of Cu(OH) -D/Cu
foil, CuO-D/Cu foil and Cu O-D/Cu foil. Different Cu facets
2
2
exhibit unique OH-adsorption/desorption peaks in the CV curves
[
14]. As displayed in Figure. 2a, the peaks centered at ca. 0.34,
reduction in the CO
at -0.5 V vs. RHE, all of the characteristic Raman bands
associated with Cu(OH) , CuO and Cu O disappear. These
2 3
-saturated 0.1 M KHCO aqueous solution
0.37, and 0.43 V can be assigned to the OH-electrosorption on
Cu(100), Cu(110) and Cu(111), respectively [14]. The peaks of
OH-electrosorption on Cu(100) and Cu(110) are more prominent
2
2
results demonstrate that all three samples are reduced to
metallic copper, agreeing well with the thermodynamics
equilibria displayed in the Cu-pourbaix diagram [13]. Moreover,
other than Cu peaks, no other peaks attributed to Cu
hydroxide/oxide are observed in XRD patterns, further
confirming that all the Cu hydroxide/oxide have been reduced to
metallic Cu (Figure S3). XPS analysis (Figure S4) reveals that
Cu mainly presents a metallic state. Only a small amount of Cu2
is detected, probably due to the surface oxidation during sample
transfer. It should be noted that we could not exclude the
for Cu(OH)
more stepped Cu(110) and Cu(100) surface, followed by CuO-
D/Cu foil and Cu O-D/Cu foil (Figure 2a). As revealed by
2 2
-D/Cu foil, demonstrating Cu(OH) -D/Cu foil expose
2
aberration-corrected HAADF-TEM image mentioned above, the
facets are homogeneously distributed, rather than exist
separately, which can form high-index stepped facets, such as
Cu(210) and Cu(310). Grazing incident XRD (α = 0.1°, probe
depth of ca. 2 nm) also revealed the decreasing trend of
exposed Cu(100) and Cu(110) facets ratio in the surface from
+
+
possible presence of Cu (with the binding energy very closed to
Cu(OH)
2b).
2 2
-D/Cu foil to CuO-D/Cu foil and Cu O-D/Cu foil (Figure.
0
Cu ) due to the oxidation in air. High resolution TEM images also
2
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Angewandte Chemie International Edition
10.1002/anie.202015159
RESEARCH ARTICLE
CO
2
RR performance. CO
-saturated 0.1M KHCO
2
RR performance was carried out in
(pH=6.9) in an anion-conducting
Simultaneously, the FEs towards CH
CuO-D/Cu foil are below 2%, while that for Cu
increased from ~2% to ~24% at the potential lower than ca. -
1.29 V (Figure 3, a-c). Furthermore, Cu(OH) -D/Cu foil gives a
higher maximum C2+/C ratio (ca. 24 at -0.98 V) than that of
4
on Cu(OH)
2
-D/Cu foil and
CO
2
3
2
O-D/Cu foil
membrane separated two-compartment cell (H-cell) with
Cu(OH) -D/Cu foil (CuO-D/Cu foil or Cu O-D/Cu foil) as the
2
2
2
working electrode, saturated Ag/AgCl as the reference electrode
and Pt plate as counter electrodes, respectively. The Faradaic
efficiency (FE) for each product associated with the change of
potential is presented in Figure 3. Similar to previous studies,
the hydrocarbons and alcohols are dominant products at the
1
CuO-D/Cu foil (ca. 23 at -1.14 V) and Cu
1.23 V) (Figure S8).
2
O-D/Cu foil (ca. 0.8 at -
Current density is another key factor in evaluating CO
performance. Cu(OH) -D/Cu foil exhibits a higher current density
than CuO-D/Cu foil, followed by Cu O-D/Cu foil (Figure S9a).
Cu(OH) -D/Cu foil also shows a larger partial current density for
2+ products than CuO-D/Cu foil and Cu O-D/Cu foil (Figures
S9b-d and S10). For CuO-D/Cu foil and Cu O-D/Cu foil, the
peak partial current density for C
is -10.6 and -5.6 mA cm-2 at
ca. -1.14 and -1.23 V, respectively (Figure S9c and d).
2
RR
2
high overpotentials, while H
2
and CO are instead dominant at
2
low overpotentials [15]. Due to the formation path of HCOOH is
different from other products [1a], and usually appeared at low
applied potential with low current density, we don’t evaluate
2
C
2
2
HCOOH product in H-cell. Specifically, the selectivity for H
Cu(OH) -D/Cu foil, CuO-D/Cu foil, and Cu O-D/Cu foil gradually
increasing follows an order of (Cu(OH) -D/Cu foil＜CuO-D/Cu
foil＜Cu O-D/Cu foil). In addition, Cu(OH) -D/Cu foil and CuO-
2
on
2 4
H
2
2
2
Nevertheless, the highest
Cu(OH)
C
2
H
4
-
partial current density on
2
2
2
2
-D/Cu foil is -18.4 mA cm , which is 1.74-fold and 3.29-
D/Cu foil showed relatively higher FE for CO than Cu
foil at low overpotentials.
2
O-D/Cu
fold of aforementioned, respectively, at ca. -1.18 V (Figure S9b).
Additionally, the highest total current density for C2+ products is
ca. -22.7, -15.8, and -5.6 mA cm-2 on Cu(OH)
D/Cu foil and Cu
high C2+ product current density of ca. -22.7 mA cm-2 for
Cu(OH) -D/Cu foil is close to the limiting current density (ca. -20
-D/Cu foil, CuO-
O-D/Cu foil, respectively (Figure S10). Such a
2
2
2
-
2
mA cm ) for CO
2
reduction due to the low solubility of CO
2
in
aqueous solution (ca. 34 mM at 25 ℃) [4c].
The low current densities for CuO-D/Cu foil and Cu
2
O-D/Cu
foil can be attributed in part to their reduced surface area. To
further understand the intrinsic activities of these catalysts,
ECSA was employed to normalize the current density. As
illustrated in Figure S11a, Cu(OH)
largest normalized current density, followed by CuO-D/Cu foil
and Cu O-D/Cu foil. In particular, Cu(OH) -D/Cu foil also exhibit
a larger normalized partial current density of C2+ products than
CuO-D/Cu foil and Cu O-D/Cu foil, indicating the excellent
intrinsic C2+ activity of Cu(OH) -D/Cu foil (Figure S11b). Figure
S12 shows suppressed C partial current density for Cu(OH)
D/Cu foil and CuO-D/Cu foil. The higher C activity of Cu O-
D/Cu foil might be ascribed to the larger proportion of Cu(111)
facet exposed in Cu O-D/Cu foil (Figure 2), which has been
revealed to favor CH by CO RR experiments on a single crystal
. Moreover, local pH has been proposed as another important
factor influencing the selectivity of CO
to a higher OH−production rate per geometric electrode area
during H O/CO reduction for high roughness Cu(OH) -D/Cu foil,
its local pH is higher than that of CuO-D/Cu foil and Cu O-D/Cu
foil. The increased pH suppresses methane production without
affecting intrinsic C2+ activity (Figure S13) [4d, 18]
We also evaluate the stability of Cu(OH) -D/Cu foil at ca. -1.08
V. As displayed in Figure S14a, the FE of C only decreased
less than 4% after 11 h, implying the excellent stability of
Cu(OH) -D/Cu foil. Additionally, there was only a slight reduction
in current density, and the morphologic still maintained after 11 h
Figures S14b, S15 and S16). The excellent stability of our
Cu(OH) -D/Cu foil may be due to the electroreduction of pre-
2
-D/Cu foil still shows the
2
2
2
2
1
2
-
1
2
2
Figure 3. CO
a) Cu(OH) -D/Cu foil, (b) CuO-D/Cu foil, and (c) Cu
saturated 0.1 M KHCO aqueous solution. (d) The C2+ FEs for Cu(OH)
foil, CuO-D/Cu foil, and Cu O-D/Cu foil.
2
reduction reaction performance in H-Cell. Faradaic efficiency of
O-D/Cu foil in CO
-D/Cu
4
2
[
16]
(
2
2
2
-
3
2
RR products [4d, 7, 17]. Due
2
2
2
2
2
2
The Cu(OH)
products than CuO-D/Cu and Cu
Cu(OH) -D/Cu displays the maximum FE of ~41%, 21%, and
1% for C , C OH, and n-propanol at ca. -1.08, -0.87, and -
.98 V, respectively. As displayed in Figure. 3D, Cu(OH) -D/Cu
2
-D/Cu electrode exhibits higher selectivity for C2+
2
O-D/Cu (Figure 3). Specifically,
.
2
2
1
0
2
H
4
2 5
H
2
H
4
2
foil exhibits the highest FE of ~59% for C2+ products at ca. -0.98
V, as compared to ~45% for CuO-D/Cu foil and ~21% for Cu O-
D/Cu foil at ca. -1.03 V and -1.23 V, respectively. The trend for
2+ hydrocarbons and alcohols consists well with that of
exposed stepped Cu(110) and Cu(100) surface of Cu(OH)
D/Cu foil, CuO-D/Cu foil and Cu O-D/Cu foil as mentioned
2
2
(
C
2
2
-
catalyst to a relatively stable state during the preparation
process and its large particle size which is unsatisfied for
2
above (Figure. 2 and Figure. 3d), suggesting that the Cu(100)
and stepped Cu(110) surface may be responsible for the
reconstruction [19]
.
enhanced formation of
C2+ products in OD-Cu catalysts.
3
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
Figure 4. DFT calculations and in situ ATR-SEIRAS and in situ Raman spectroscopy characterization. (a) CO
2
reduction procedure. In situ ATR-SEIRAS spectra
2 2
of (b) Cu(OH) -D (c) CuO-D and (d) Cu O-D from 0.2 to -1 V vs. RHE in CO-saturated 0.1 M KOH aqueous solution. The background is collected in the Ar-
saturated electrolyte at 0.2 V vs. RHE. (e) The activation energy barrier of CO dimerization. (f) Configurations of *CO dimerization. The solvent water molecules
are hidden for viewing convenience. The colors are Cu in yellow, C in gray, and O in red. The region of Cu(100) on Cu(210) and Cu(310) are marked as orange.
2
(g) In situ Raman spectra of Cu(OH) -D/Cu foil from -0.1 to -1 V vs. RHE in CO-saturated 0.1 M KOH aqueous solution.
DFT calculations and in situ spectroscopy study. We use
DFT calculations and in situ spectroscopy to gain further insight
into the reaction mechanism. The dimerization of two adjacent
formation energy of *COCOH [20a, 23] on Cu(111), (100), and low-
coordinated (211) and (321) to understand whether the low-
coordinated sites are beneficial for C-C coupling or not (Figure
S18). Our results revealed that the formation energy of *COCOH
on low-coordinated (211) and (321) are higher than that on (100),
implying that low-coordinated sites alone may not help to
promote CO-CO coupling, consisting with previously reported [
24]. Low-coordinated square Cu(100) is essential to improve the
*
CO to form *COCOH is known as the rate-dependent step
RDS) for C2+ products (Figure 4a) [20]. In situ attenuated total
reflectance-surface enhanced infrared absorption spectroscopy
ATR-SEIRAS) was employed to confirm CO adsorption (the key
intermediate to C2+ products) (Figures 4b-d). The spectra were
(
19,
(
2
collected from 0.2 to -1.0 V vs. RHE in CO-saturated 0.1 M KOH. formation of C2+ products in Cu(OH) -D.
As displayed in Figure. 4, B-D, the vibrational bands centered at
ca. 2050 cm , corresponding to linearly-bonded CO (CO ), is
L
observed between 0.2 and -1.0 V [21]. The shift of bands
Additionally, in situ Raman spectroscopy was also employed
to catch the adsorbed intermediate further (Figure S19). As
displayed in Figure 4g, three bands centered at ca. 276, 354 and
-1
associated with the applied potential is caused by the Stack
392 cm-1 are observed on Cu(OH)
2
-D/Cu foil in low-frequency
turning effect [ . The peaks of adsorbed CO
21]
over Cu(OH)
O-D, corresponding
-D with more low-
coordinated stepped (110) surface, followed by CuO-D and
Cu O-D, which is crucial for building up sufficient CO coverage
-D is
area. The band at ca. 276 cm is attributed to the rotation of
adsorbed CO on the Cu surface, and the other two bands at ca.
354 and 392 cm is derived from the Cu-CO stretch [25]. We note
-1
L
2
in higher wavenumbers than CuO-D and Cu
to the strong binding of CO on Cu(OH)
2
-1
L
2
that C≡O stretching modes displayed at ca. 1862, 2073, and
2164 cm-1 and the bands of *CH
at ca. 2855 and 2925 cm can
-1
2
2
to promoting CO-CO coupling (Figure 4b-d) [22]. As shown in
Figure 4e-f, the activation energy of CO dimerization on Cu(100)
facets and the Cu(100) regions in (210) and (310) facets are
similar, and lower than that on Cu(110) and Cu(111) facts
be observed at less negative applied potentials, demonstrating
CO can be easily reduced to hydrocarbons or alcohols on
Cu(OH)
2
-D/Cu foil (Figures 4g and h) [25a]. Whereas, Cu-CO
-1
stretch in the low-frequency area (ca. 354 and 276 cm ) and C
(
(
Figure S17). These results suggest that Cu(100) regions in
210) and (310) with low-coordination, help to build sufficient CO
≡O stretching modes in the high-frequency area (ca. 2073 and
-1
2164 cm ), which are attributed to CO bound on more open Cu
sites, are not obvious on CuO-D/Cu foil and Cu O-D/Cu foil
(Figure S20) [26]. Due to the weak adsorption of CO, the bands of
CH on CuO-D/Cu foil and Cu O/Cu foil are not obvious either
(Figure S20). Besides, we also noted the presence of C≡O
coverage and to facilitate the CO-CO coupling, which is
responsible for the enhanced activity to form C2+ products. It
should be noted that the rougher surface of Cu(OH)
2
2
-D may
2
2
contain more low-coordinated sites. We also calculated the
4
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
-
1
stretching modes displayed slightly lower than 2073 cm (at ca.
exhibits the correlation between product FE and applied
-1
2046 cm ) on Cu(OH)
2
-D/Cu foil, which can be attributed to the
relatively weaker CO bound on fully coordinated Cu(100) or/and
Cu(111) [ . The in situ Raman also indicates that Cu(OH)
foil promotes the adsorption of CO intermediate and C2+ product
formation, agreeing well with the in situ ATR-SEIRAS results
and DFT calculations.
Flow-cell and PV-EC configuration performance. To
2
in aqueous solution
and meet the requirement of industry application (current density
potential. FEs of H
level below 20% in 1 M KOH alkaline electrolyte. Cu(OH)
shows the maximal FE of 58±1%, 21±0.2%, and 7±0.01% for
, C OH, and n-propanol, respectively, at -0.54 V with the
2
at different potential are suppressed at a
2
-D
26]
2
-D/Cu
C
2
H
4
2 5
H
-2
total current density of 250 mA cm (Figure 5b and Figure S21).
FE and partial current density of C2+ products are displayed in
Figure 5C and Figure S21. High C2+ FE of ~87% and partial
current density of ~217 mA cm-2 were achieved simultaneously
at -0.54 V. The power conversion efficiency (PCE) for C2+
products at different potential or current density are also
overcome the low solubility limitation of CO
-2
﹥
200 mA cm ), the performance of Cu(OH)-D for CO
conducted with a flow-cell electrolyzer in 1 M KOH (Figure 5a).
CO molecules directly diffuse across the gas diffusion electrode
2
RR was
2
calculated to evaluate the performance of Cu(OH) -D (Figure
2
S22). The PCEC2+ is increased as the current density or potential
rises in our experiments. The maximum PCEC2+ of 56.5% was
achieved at 250 mA cm-2 (-0.54 V vs. RHE). The excellent
to the electrode/electrolyte interface without dissolved in the
electrolyte firstly [27]. In addition, it is not realistic to use alkaline
electrolytes in batch-cell due to hydroxide ions that can easily
performance is superior to other activities of CO
2
reduction to
combine with dissolved CO
2
to form carbonates. Figure 5b
C2+ products reported so far (Figure S23 and table S2).
Figure 5. CO
2
reduction reaction performance in the flow cell and solar-driven CO
2
reduction performance. (a) Flow cell configuration. Cathode: Cu(OH)
2
-D/CP (1
2
2
cm ); Reference electrode: Hg/HgO (1 M KOH); Membrane: anion-exchange membrane; Anode: Ni foam (1 cm ). (b) Faradaic efficiency, and (c) C2+ partial
current density and faradaic efficiency of Cu(OH)
two-electrode electrochemical cell. (e) Solar driven CO
2
-D evaluated by flow cell in 1 M KOH. (d) I−V curve of the solar cell shown in Figure. S24 and I−V curve of the
reduction current density and faradaic efficiency of products versus time.
2
The solar cell was employed to drive the CO
2
reduction
collected under the illumination of standard AM 1.5G sunlight
with 100 mW cm-2 (1 sun) intensity also displayed in Figure. 5D
under the red line. The power of the solar cell system revealed
that the optimized working condition is at ca. 2.69 V, which gives
the maximum output power (Figure S27). These two I-V curves
crossed at the point where the current and cell voltage were
respectively 50.9 mA and 2.74 V (operating point), which is
close to the maximum power point of the solar cell (Figure 5d).
system and realize artificial photosynthesis directly (Figures S24
and S25). NiFe double-layer hydroxide on Ni foam (NiFe-
LDH/NF) with excellent oxygen evolution performance was used
as the anode to configure the two-electrode CO
2
reduction cell
(
Figure S26). The ion-exchange membrane was excluded to
minimize the resistance between the two electrodes. The
2
geometric areas of the anode and cathode are 1 cm and 0.2
2
cm , respectively. Potential-dependent current density of the
During the long-time unassisted CO
simulated solar radiation, a C FE of ~50% was obtained
(Figure 5e). The FE of C OH and n-propanol were determined
to be ~18% and ~4%, respectively. Surprisingly, the solar-to-
fuel efficiency of 4.47%, 1.58%, and 0.35% for C , C OH,
2
reduction powered by
electrochemical cell is shown in Figure 5d. The current was
determined to be 50.9 mA at a low cell voltage of 2.74 V
Without iR-compensation). The solar cell is composed of five-
2 4
H
2
H
5
(
junction single-crystal Si photovoltaic, and the I-V curve
2
H
4
2 5
H
5
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
and n-propanol can be achieved, respectively (details see the
Methods Section). The total solar-to-fuel efficiency for C2+
[7]
A. S. Varela, M. Kroschel, T. Reier, P. Strasser, Catal. Today 2016, 260,
8-13.
[
[
8]
9]
P. De Luna, R. Quintero-Bermudez, C.-T. Dinh, M. B. Ross, O. S.
Bushuyev, P. Todorović, T. Regier, S. O. Kelley, P. Yang, E. H. Sargent,
Nat. Catal. 2018, 1, 103-110.
products is as high as 6.4%. The extremely high solar-to-C
2+ efficiency is also higher than all of the reported ones as yet
table S3).
2 4
H or
C
(
a) M. Favaro, H. Xiao, T. Cheng, W. A. Goddard, 3rd, J. Yano, E. J.
Crumlin, Proc. Natl. Acad. Sci. USA 2017, 114, 6706-6711; b) A. Eilert,
F. Cavalca, F. S. Roberts, J. Osterwalder, C. Liu, M. Favaro, E. J.
Crumlin, H. Ogasawara, D. Friebel, L. G. Pettersson, A. Nilsson, J.
Phys. Chem. Lett. 2017, 8, 285-290.
Conclusion
[
[
10] a) A. J. Garza, A. T. Bell, M. Head-Gordon, J. Phys. Chem. Lett. 2018,
9, 601-606; b) Y. Lum, J. W. Ager, Angew. Chem. Int. Ed. 2017, 57,
Comparing the performance of different copper hydroxide/oxides
derived copper, we reveal that the stepped Cu(110) and Cu(100)
sites in Cu(OH) -D/Cu foil are crucial for the enhanced
2
selectivity/activity of C2+ products. In situ ATR-SEIRAS, DFT
calculations, and in situ Raman spectra demonstrate that (110)
facilitating CO adsorption and (100) promoting the C-C coupling
551-554.
11] a) D. Kim, J. Resasco, Y. Yu, A. M. Asiri, P. Yang, Nat. Commun. 2014,
5, 4948; b) Y. Wang, P. Han, X. Lv, L. Zhang, G. Zheng, Joule 2018, 2,
2551-2582.
[
[
12] Y. Luo, H. Zhou, J. Sun, F. Qin, F. Yu, J. Bao, Y. Yu, S. Chen, Z. Ren,
Energy Environ. Sci. 2017, 10, 1820-1827.
to C2+ products. Cu(OH)
2 2 4
-D show the FEs of ~58% for C H and
13] E. McCafferty, in Introduction to Corrosion Science, Springer, 2010, pp.
95-117.
~
87% for C2+ hydrocarbons and alcohols with the C2+ partial
-2
current density of ~217 mA cm only at -0.54 V in the flow-cell
electrolyzer. We achieve a power conversion efficiency of 56.5%
for C2+ hydrocarbons and alcohols at the same potential.
Coupling to a Si solar cell, the solar conversion efficiency for
[14] J. M. Droog, B. Schlenter, J. Electroanal. Chem. 1980, 112, 387-390.
[
15] A. A. Peterson, F. Abild-Pedersen, F. Studt, J. Rossmeisl, J. K.
Nørskov, Energy Environ.l Sci. 2010, 3, 1311-1315.
[
16] a) J. Phys. Chem. B 2002, 15-17; b) K. J. Schouten, Z. Qin, E. Perez
Gallent, M. T. Koper, J. Am. Chem. Soc. 2012, 134, 9864-9867.
17] M Jouny, W. Luc, F. Jiao, Nat. Catal. 2018, 1, 748-755.
2 4
C H and C2+ products is as high as 4.47% and 6.4%,
respectively. This study paves a facile stratagem to develop
efficient catalysts for (solar driven) CRR to C2+ products and
[
[
18] Y. Hori, R. Takahashi, Y. Yoshinami, A. Murata, J. Phys. Chem. B 1997,
101, 7075-7081.
guides the development of Cu catalysts for efficient CO
reduction.
2
[19] J. Huang, N. Hormann, E. Oveisi, A. Loiudice, G. L. De Gregorio, O.
Andreussi, N. Marzari, R. Buonsanti, Nat. Commun. 2018, 9, 3117.
[
[
20] a) T. Cheng, H. Xiao, W. A. Goddard, J. Am. Chem. Soc. 2017, 139,
11642-11645; b) F. Calle-Vallejo, M. T. Koper, Angew. Chem. Int. Ed.
2013, 52, 7282-7285.
Acknowledgements
21] J. Heyes, M. Dunwell, B. Xu, J. Phys. Chem. C 2016, 120, 17334-
7341.
1
We acknowledge the National Key R&D Program of China
2016YFB0600901), the National Natural Science Foundation of
China (21525626, 21761132023), and the Program of
Introducing Talents of Discipline to Universities (No.
BP0618007) for financial support.
[22] a) P. Hollins, Surf. Sci. Rep. 1992, 16, 51-94; b) P. Hollins, K. Davies, J.
Pritchard, Surf. Sci. 1984, 138, 75-83; c) A. Malkani, J. Li, J. Anibal, Q.
Lu, B. Xu, ACS Catal. 2020, 10, 941-946.
(
[
23] Y. Huang, Y. Chen, T. Cheng, L.-W. Wang, W. A. Goddard, ACS
Energy Letters 2018, 3, 2983-2988.
[24] R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J.
Am. Chem. Soc. 2014, 136, 6978-6986.
Keywords: Solar-driven • CO
2
reduction • Cu (100) and (110) •
[25] a) D. Ren, J. Gao, L. Pan, Z. Wang, J. Luo, S. M. Zakeeruddin, A.
Hagfeldt, M. Gratzel, Angew. Chem. Int. Ed. 2019, 131, 15178-15182;
b) T. T. Hoang, S. Verma, S. Ma, T. T. Fister, J. Timoshenko, A. I.
Frenkel, P. J. Kenis, A. A. Gewirth, J. Am. Chem. Soc. 2018, 140,
C2+ products
5
791-5797.
[
1]
a) D. D. Zhu, J. L. Liu, S. Z. Qiao, Adv. Mater. 2016, 28, 3423-3452; b)
R. M. Arán-Ais, D. Gao, B. Roldan Cuenya, Acc. Chem. Res. 2018; c)
C. W. Li, J. Ciston, M. W. Kanan, Nature 2014, 508, 504-507.
[
26] a) C. M. Gunathunge, X. Li, J. Li, R. P. Hicks, V. J. Ovalle, M. M.
Waegele, J. Phys. Chem. C 2017, 121, 12337-12344; b) S. Jiang, K.
Klingan, C. Pasquini, H. Dau, J. Phys. Chem. C 2019, 150, 041718.
27] C.-T. Dinh, T. Burdyny, M. G. Kibria, A. Seifitokaldani, C. M. Gabardo,
F. P. G. de Arquer, A. Kiani, J. P. Edwards, P. De Luna, O. S.
Bushuyev, Science 2018, 360, 783-787.
[
[
2]
3]
M. Jouny, W. Luc, F. Jiao, Ind. Eng. Chem. Res. 2018, 57, 2165-2177.
a) S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S.
Horch, B. Seger, I. E. Stephens, K. Chan, C. Hahn, Chem. Rev. 2019,
[
119, 7610-7672; b) Y. Hori, H. Wakebe, T. Tsukamoto, O. Koga,
Electrochim. Acta 1994, 39, 1833-1839.
[
4]
a) H. Mistry, A. S. Varela, C. S. Bonifacio, I. Zegkinoglou, I. Sinev, Y. W.
Choi, K. Kisslinger, E. A. Stach, J. C. Yang, P. Strasser, B. R. Cuenya,
Nat. Commun. 2016, 7, 12123; b) C. W. Li, M. W. Kanan, J. Am. Chem.
Soc. 2012, 134, 7231-7234; c) D. Ren, J. Fong, B. S. Yeo, Nat.
Commun. 2018, 9, 925; d) K. Jiang, R. B. Sandberg, A. J. Akey, X. Liu,
D. C. Bell, J. K. Nørskov, K. Chan, H. Wang, Nat. Catal. 2018, 1, 111-
119; e) D. Ren, Y. Deng, A. D. Handoko, C. S. Chen, S. Malkhandi, B.
S. Yeo, ACS Catal. 2015, 5, 2814-2821.
[
[
5]
6]
A. Verdaguer-Casadevall, C. W. Li, T. P. Johansson, S. B. Scott, J. T.
McKeown, M. Kumar, I. E. Stephens, M. W. Kanan, I. Chorkendorff, J.
Am. Chem. Soc. 2015, 137, 9808-9811.
M. G. Kibria, C. T. Dinh, A. Seifitokaldani, P. De Luna, T. Burdyny, R.
Quintero‐Bermudez, M. B. Ross, O. S. Bushuyev, F. P. García de
Arquer, P. Yang, Adv. Mater. 2018, 30, 1804867.
6
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
Entry for the Table of Contents
This paper describes the facet effect of copper crystal to promote CO adsorption and C-C coupling and consequently yield a superior
selectivity (87% Faradaic efficiency) for C2+ products. Record-high solar conversion efficiencies of 4.47% and 6.4% are achieved for
C H and C2+ products, respectively.
2 4
7
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