Highly Electrocatalytic Ethylene Production from CO2on Nanodefective Cu Nanosheets

Article abstract of DOI:10.1021/jacs.0c06420

The electrochemical synthesis of chemicals from carbon dioxide, which is an easily available and renewable carbon resource, is of great importance. However, to achieve high product selectivity for desirable C2 products like ethylene is a big challenge. Here we design Cu nanosheets with nanoscaled defects (2-14 nm) for the electrochemical production of ethylene from carbon dioxide. A high ethylene Faradaic efficiency of 83.2% is achieved. It is proved that the nanoscaled defects can enrich the reaction intermediates and hydroxyl ions on the electrocatalyst, thus promoting C-C coupling for ethylene formation.

Full text of DOI:10.1021/jacs.0c06420

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Article
Highly electrocatalytic ethylene production
from CO2 on nano-defective Cu nanosheets
Bingxing Zhang, Jianling Zhang, Manli Hua, Qiang Wan, Zhuizhui Su, Xiuniang Tan, Lifei Liu, Fanyu
Zhang, Gang Chen, Dongxing Tan, Xiuyan Cheng, Buxing Han, Lirong Zheng, and Guang Mo
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.0c06420 • Publication Date (Web): 13 Jul 2020
Downloaded from pubs.acs.org on July 13, 2020
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Highly electrocatalytic ethylene production from CO2 on nano-
defective Cu nanosheets
Bingxing Zhang1,2, Jianling Zhang1,2,3,* Manli Hua1,2, Qiang Wan1,2, Zhuizhui Su1,2, Xiuniang Tan1,2,
Lifei Liu1,2, Fanyu Zhang1,2, Gang Chen1,2, Dongxing Tan1,2, Xiuyan Cheng1,2, Buxing Han1,2,3 Lirong
Zheng4 and Guang Mo4
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1Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Colloid, Interface and Chemical
Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, P.R.China.
2School of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, P.R.China.
3Physical Science Laboratory, Huairou National Comprehensive Science Center, Beijing 101400, P.R.China.
4Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics, Chinese Academy of Sciences, Beijing
100049, P.R.China.
KEYWORDS: CO2 electroreduction • metallic copper • nanosheet • nanoscale defect • confinement
ABSTRACT: The electrochemical synthesis of chemicals from carbon dioxide, which is an easily available and
renewable carbon resource, is of great importance. However, to achieve high product selectivity for desirable C2 products like
ethylene is a big challenge. Here we design Cu nanosheets with nano-scaled defects (2-14 nm) for the electrochemical production of
ethylene from carbon dioxide. A high ethylene Faradaic efficiency of 83.2% is achieved. It is proved that the nano-scaled defects can
enrich the reaction intermediates and hydroxyl ions on the electrocatalyst, thus promoting C-C coupling for ethylene formation.
Here we design the nano-defective Cu nanosheets as an
INTRODUCTION
electrocatalyst for ethylene synthesis from CO2RR. The nano-
Ethylene (C2H4) is a building block of particular importance due
to its high demand in chemical industry. Usually, ethylene is
prepared from steam cracking of naphtha under harsh
production conditions (800-900 oC). In recent years, the
electrochemical synthesis of ethylene from carbon dioxide
reduction reaction (CO2RR) has attracted increasing attention
because it offers a mild and environmentally benign pathway
for ethylene production.1,2 Up to now, diverse kinds of
strategies have been proposed for ethylene production from
electrocatalytic CO2RR, including constructing Cu
nanostructures,3,4 controlling oxidation state,4-6 using dopants,7,8
alloying9,10 and molecule decoration.1,11-13 Among these
methods, constructing nanostructures of metallic Cu (without
any additive) for C2+ products is much promising, for the simple
synthesis and easy-to-study structure-activity relationship of
catalyst. Kanan and coworkers proposed the control of grain
boundaries in a single electrocatalyst for CO2RR, which has
been demonstrated to be an efficient pathway for CO2
conversion.14-16 In general, C1 products such as carbon
monoxide (CO) and methane and C2+ species like ethane and
ethanol are generated simultaneously with ethylene in
electrochemical CO2RR. To date, the highest Faradaic
efficiency (FE) of ethylene is 72%, which was achieved by the
molecule decorated Cu electrocatalyst using a flow cell system.1
It is urgent to further improve the ethylene selectivity in
electrochemical CO2RR, promisingly through the development
of electrocatalysts with desirable nanostructures.
scaled defects are in size of 2-14 nm, which can be considered
as a large collection of atomic defects. Such a nano-defective
structure strengthens the adsorption, enrichment and
confinement for reaction intermediates and hydroxyl ions on the
electrocatalyst. The C-C coupling is thus promoted to produce
ethylene efficiently. The maximum ethylene FE can reach
83.2%, which is the highest value among all the studied
electrocatalysts to date. The mechanism for the high ethylene
selectivity on the nano-defective Cu nanosheets was
investigated by a series of experiments and calculations.
RESULTS AND DISCUSSION
The nano-defective Cu nanosheets were prepared by an
electrochemical reduction method17 for the pre-formed CuO
nanosheets in K2SO4 electrolyte (see details in Methods). As
characterized by high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM), the
product has a morphology of nanosheets with a lateral size of 1
µm (Figure 1a). Atomic force microscopy (AFM) image reveals
that the thickness of the nanosheet is ~23 nm (Figure S1). It is
clear that there are numerous pits on each nanosheet (Figure
1b), which is further proved by scanning electron microscopy
(SEM, Figure S2). Enlarged HAADF-STEM image shows that
the pits are 2~14 nm in size (Figure 1c). Figure 1d shows the
HAADF-STEM image of one typical pit. The lattice fringes
around the pit is 0.21 nm, which can be indexed to (111) plane
of face-centered cubic Cu (Figure S3). Figure 1e is the
magnified HAADF-STEM image of the square marked in
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Figure 1d. It reveals a growing number of atomic defects from
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techniques were performed. X-ray photoelectron spectroscopy
(XPS) and X-ray absorption spectroscopy (XAS) are commonly
used technologies for monitoring the valence of Cu in Cu based
materials.7,21,22 Cu 2p and Auger Cu LMM XPS spectra of n-
CuNS and CuNS reveal that the Cu valence is zero (Figure
2a,b). The Cu K-edge X-ray absorption near-edge spectra
(XANES) confirm that n-CuNS and CuNS are metallic Cu
(Figure 2c). The extended Cu K-edge X-ray absorption fine
structure (EXAFS) of the two samples present Cu-Cu
coordinations at 2.23 Å, which is identical to that of Cu foil
(Figure 2d). The above results suggest that the two catalysts
keep the metallic state under X-ray exposure, which is
consistent with the reported results.21,22 By quantitative EXAFS
curve fitting analysis, the coordination configuration of Cu
atom for n-CuNS is confirmed to be 9.7, smaller than those of
CuNS (10.9) and Cu foil (12.0) (Figure 2e,f, Figure S6 and
Table S1), which is consistent with the abundant atomic defects
confined in nano-defective n-CuNS (Figure 1d, g).
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the edge to the center of the pit, which is further proved by the
intensity profile along the line shown in Figure 1d and e (Figure
1f). Here the nanoscale pit on Cu nanosheet is named as nano-
defect,18-20 which can be considered as a collection of many
atomic defects. Similar results were observed for Cu(200) plane
around one nano-defect (Figure 1g-i). All the above results
confirm the formation of nano-defective nanosheets instead of
perforated nanosheet. The nano-defective Cu nanosheets were
further characterized by powder X-ray diffraction (XRD), wide-
angle X-ray scattering two-dimensional map and energy
dispersive spectroscopy (EDS). The results prove the formation
of metallic Cu and the major exposed planes are Cu(111) and
Cu(200) of face-centred cubic Cu (Figure S4), which are in
accordance with the above HAADF-STEM results.
For comparison, other two samples of Cu nanosheets with
smooth surfaces and Cu nanoparticles were synthesized and
characterized. As shown in Figure 1j and k, the Cu nanosheet
has a smooth surface with lateral size of ~2 μm and thickness
of ~20 nm (Figure S5). The Cu nanoparticles have an average
diameter of ~20 nm (Figure 1l). The nano-defective Cu
nanosheets, Cu nanosheets with smooth surfaces and Cu
nanoparticles are defined as n-CuNS, CuNS and CuNP,
respectively.
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Figure 2. Spectroscopy characterization of different catalysts. (a,b)
The Cu 2p (a) and Cu LMM (b) XPS spectra of n-CuNS (red) and
CuNS (blue). (c,d) Cu K-edge XANES (c) and EXAFS (d) spectra
of n-CuNS (red), CuNS (blue) and Cu foil (black). (e,f) EXAFS
fitting curves in R space (e) and q space (f) of n-CuNS.
Figure 1. Structural characterization of different catalysts. (a-e,g,h)
HAADF-STEM images of n-CuNS. Inset in (c), size distribution of
the nano-defects on n-CuNS. Insets in (d,g), the corresponding fast
Fourier transform patterns. (e,h) The enlarged area in the square of
(d,g). The cool color (dark spots) and warm color (bright spots)
represent the highly defective area and the less defective area,
respectively. (f,i) The corresponding intensity profile along the line
as shown in (d,g) (top) and (e,h) (bottom). (j-k) TEM images of
CuNS (j,k) and CuNP (l).
The electrochemical CO2RR on n-CuNS, CuNS and CuNP
was conducted using a three electrode H-type cell in a CO2
saturated 0.1 M K2SO4 electrolyte.7 The electrolysis products
were analyzed by 1H nuclear magnetic resonance (NMR)
spectroscopy and gas chromatography. As catalyzed by n-
CuNS, ethylene and H2 in gas phase were detected and no liquid
products were produced (Figure S7). It is obvious that n-CuNS
catalyst presents much enhanced total current density (j) as
compared with the two reference catalysts (Figure 3a). For
example, the current density at -1.18 V versus a reversible
To further gain an insight into the chemical state and local
structure of the as-synthesized sample, a series of spectroscopic
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hydrogen electrode (vs RHE) on n-CuNS is 6 and 1.6 times
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higher than those of CuNS and CuNP, respectively. The
ethylene FE over n-CuNS maintains values of >60% in a wide
potential range of -0.88 to -1.48 V (vs RHE), much higher than
those of CuNS and CuNP (Figure 3b). A maximum ethylene FE
of 83.2% can be achieved at -1.18 V (vs RHE), while those on
CuNS and CuNP are 45.7% and 37.2% (Table S2), respectively.
The partial current density of ethylene for n-CuNS reaches 66.5
mA cm-2 at -1.48 V (vs RHE), whereas those of CuNS and
CuNP are lower than 5 and 8.5 mA cm-2, respectively (Figure
3c). Interestingly, no CO was detected at applied potential range
by n-CuNS, while the other two reference catalysts show
considerable formation of competitive CO (4%-24%) (Figure
S8). It indicates that CO, which is an intermediate for CO2
transformation to ethylene during CO2RR and is often produced
along with ethylene,1,13 is strongly confined on n-CuNS for
efficient C-C coupling rather than desorbed to form gas CO on
CuNS and CuNP. Figure 3d shows a summary for the FE of
ethylene and H2 at various applied potentials on n-CuNS.
The electrochemical double-layer capacitance measurements
were performed to estimate the electrochemical surface area
(ECSA). The ECSA for n-CuNS is roughly 10- and 4-fold those
of CuNS and CuNP, respectively (Figure S9 and Table S3). It
indicates that n-CuNS can afford much more accessible active
sites than the other two catalysts. To compare the intrinsic
activity for CO2RR, the ECSA-normalized current densities of
different products were obtained. It reveals that the activity of
CO2RR to ethylene on n-CuNS is intrinsically higher than those
on CuNS and CuNP (Figure S10). The stability of n-CuNS was
examined at -1.18 V (vs RHE) for 14 h, which shows a stable
ethylene FE of ~80% with current density ~60 mA cm-2 over
the span of stability test (Figure 3e). The slight increase of
ethylene FE at the beginning (~2 h) can be attributed to the
initial activation of the catalyst layer.22,23 The n-CuNS after 14
h CO2RR test was characterized, which shows that the nano-
defective nanosheet morphology can be well maintained
(Figure S11). As compared with all the reported heterogeneous
electrocatalysts, the n-CuNS catalyst displays the highest
ethylene FE and total current density under comparable
conditions (Figure 3f, Table S4).
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Figure 3. Electrochemical CO2RR performance. (a,b) Total current
density (a) and ethylene FE (b) at various applied potentials for
different catalysts. (c) Ethylene partial current density at various
applied potentials for different catalysts. (d) FE of the products at
various applied potentials for n-CuNS. (e) Chrono-amperometry
and FE results of n-CuNS at a potential of -1.18ꢀV vs RHE. (f)
Performance of n-CuNS catalyst compared with those of other CO2
to ethylene electrocatalysts in H-type cell.
To reveal the mechanism of the high activity of n-CuNS, the
CO2RR process over n-CuNS was traced by in situ XANES and
EXAFS spectra. The results show that the catalyst keeps
identical species of Cu0 during electocatalysis. Thus the
influence of the well-known oxidized and constantly evolved
Cu species for promoting ethylene production4-8,24-27 can be
excluded (Figure 4a,b and Figure S12). Linear sweep
voltammetry (LSV) curve of n-CuNS exhibits an intense peak
at ca. -0.2 V (Figure 4c). It indicates the existence of a large
amounts of atomic defects on n-CuNS,28,29 which is favorable
for promoting the adsorptions to CO and OH- that are crucial to
ethylene formation.4,12,13 In contrast, the CuNS shows a largely
suppressed peak, which is consistent with its smooth surface.
To further confirm this, LSV curves of n-CuNS in N2-saturated
electrolyte and CO-saturated electrolyte were determined,
respectively. It shows that the difference between the current
densities in N2-saturated and CO-saturated electrolytes of n-
CuNS is larger than that of CuNS (Figure 4d), suggesting easier
adsorption of CO on n-CuNS catalyst.30 Moreover, in situ
Raman spectra reveal that the signal of adsorbed CO on n-CuNS
is much more pronounced than that on CuNS (Figure S13). It
suggests the enhanced adsorption of CO on n-CuNS catalyst
during CO2RR, which is consistent with LSV results.1,9
Furthermore the OH- electrosorption (OHads) on n-CuNS was
determined, which is influenced by local pH effect (Figures
S14, 15).31,32 The results show that n-CuNS catalyst has much
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pronounced (100), (110) and (111) OHads features,33,34 while
CuNS only presents a weak (111) OHads peak (Figure 4e).
Such a concentrated effect of CO and OH- components in
nano-defects was further investigated by electrolysis using a
controlled convective flow.35-38 As shown in Figure 4f, the n-
CuNS electrode exhibits a ~50% enhanced CO2RR activity to
ethylene with the increased rotation speed of electrode from 0
to 2000 rpm, while the CuNS electrode shows a decline of ~6%.
It means that the reaction intermediates and OH- are strongly
confined in n-CuNS for producing ethylene even under
vigorous rotation.35-38 Meanwhile, the mass transport can be
accelerated at higher rotation speed.35 Therefore, the CO2RR
efficiency to ethylene on n-CuNS electrode is much improved
with increasing rotation speed of electrode. For CuNS, the
reaction intermediates are weakly confined on its smooth
surface, which can be easily lost by the increased rotation speed
of electrode.37 As a result, a low selectivity of ethylene was
obtained on CuNS electrode with increasing rotation speed of
electrode.
Density functional theory (DFT) calculations were employed
to study the CO dimerization on n-CuNS and CuNS catalysts,
which is a rate-determining step to ethylene production.39,40 It
reveals that the introduced Cu defect facilitates the adsorptions
to the key reaction intermediates (*CO and *OCCO) (Figure
4g) and OH- (Figure S16). With the adsorbed OH-, the defective
Cu (111) surface decreases the energy barrier for 110 meV in
*CO+*CO → *OCCO step than that of the non-defective
Cu(111) surface without OH- (Figure 4h). The calculations
provide molecular-level insights into the enhanced OH- and
reaction intermediate adsorptions on defective Cu, which are
concentrated in one nano-defect for synergistically facilitating
the CO dimerization process (Figures S17-20).
Cu(111) of CuNS (black). Red, grey, white and blue stand for
oxygen, carbon, hydrogen and copper atoms, respectively.
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CONCLUSION
Here we demonstrate the efficient production of ethylene from
electrochemical reduction of CO2 on nano-defective Cu
nanosheets. The ethylene FE can reach a high value of 83.2%,
with current density of ~60 mA cm-2. Experimental and
calculation results reveal that the nano-defects on Cu nanosheet
create concentrated atomic defects that favor the adsorption,
enrichment and confinement for the reaction intermediates and
OH-, which synergistically promote the C-C coupling for
ethylene formation. Compared with the usually adopted
strategies of random atomic defects for catalyst design, the
construction of nano-scaled defects is more active and selective
for C2 hydrocarbon production, which have great potential for
practical applications. This work not only paves a promising
approach for selectively producing single multi-carbon product
from CO2 electroreduction, but also provides a new insight for
catalyst design through creating nano-scaled local environment.
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EXPERIMENTAL SECTION
Synthesis of n-CuNS. CuO nanosheets were synthesized in
a high concentrated alkaline solution. 50 mM CuCl2 aqueous
solution was mixed with 3 M NaOH in distilled water. The
solution was vigorously stirred and then transferred into a
Teflon-lined autoclave, sealed and heated at 100 °C for 12 h.
The system was allowed to cool to room temperature naturally
and the resulting product was centrifuged, rinsed with distilled
water and ethanol several times to remove any alkaline salt and
then dried in a vacuum oven at 60 °C for 4 h. The derived n-
CuNS nanocatalyst was prepared via in situ CO2
electroreduction at -1.08 V (vs RHE) from the CuO nanosheet
electrode after an initial electrolysis running for 60 min.
Synthesis of CuNS. The CuNS catalyst was prepared
according to the reported literature with small modification.22
(Cu(NO3)2·3H2O, 100 mg) and l-ascorbic acid (200 mg) were
mixed with 30 ml deionized water were stirred to form a
homogeneous solution. Then CTAB (200 mg) and HMTA (200
mg) were added followed by 30 min of stirring. The mixture
solution was sealed and heated from room temperature to 80 °C
and kept at 80 °C for 3 h in an oil bath. The resulting products
were centrifuged, rinsed with distilled water and ethanol several
times and then dried in a vacuum oven at 60 °C for 4 h.
Synthesis of CuNP. (Cu(NO3)2·3H2O, 300 mg) mixed with
10 mL deionized water were stirred to form a homogeneous
solution. Then NaBH4 (150 mg) was added followed by 10 min
of stirring. The resulting products were centrifuged, rinsed with
distilled water and ethanol several times and then dried in a
vacuum oven at 60 °C for 4 h.
Characterization. Powder X-ray diffraction pattern was
performed on a Rigaku D/max-2500 diffractometer with Cu Kα
radiation (λ = 1.5418 Å) at 40 kV and 200 mA. The
morphologies were characterized by SEM (HITACHI S-4800),
TEM (JEOL-1011) operated at 100 kV and high-resolution
TEM (HRTEM, JEOL-2100F) operated at 200 kV. The
HAADF-STEM characterization was performed on a JEOL
JEM-ARF200F TEM/STEM with a spherical aberration
corrector. AFM image was obtained on a tapping-mode atomic
force microscope (Nanoscope IIIa, Digital Instruments, Santa
Barbara, CA), with a silicon cantilever probes. XPS was
measured by VG Scientific ESCALab220i-XL spectrometer
Figure 4. Mechanism investigation. (a) In situ Cu K-edge XANES
spectra. (b) In situ Cu K-edge EXAFS spectra. (c) LSV curves of
n-CuNS and CuNS. (d) LSV curves obtained on n-CuNS and CuNS
catalysts in N2-saturated and CO-saturated electrolytes. (e)
Voltammograms of OHads peaks collected in a 0.1ꢀM KOH batch
cell. (f) Convective effect on CO2RR, FE and j for ethylene as a
function of rotation rate. (g) Comparison of adsorption energy of
key intermediates that affect selectivity on different facets. (h)
Energy diagrams and geometries of CO dimerisation on OH-
adsorbed and defective Cu(111) of n-CuNS (red) and non-defective
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using Al Kα radiation with 500 μm X-ray spot. The base
the concentration of gas products. The gas chromatograph was
equipped with FID and TCD detectors using helium as the
internal standard. The amounts of gas products were calculated
from the peak areas of gas chromatography with conversion
factors for ethylene, H2 and CO based on calibration of standard
samples at 1.013 bar and 300 K. The liquid product was
pressure was about 3×10-10 mbar in the analysis chamber.
Raman spectrum was obtained on a laser confocal Raman
spectroscopy (Labram-010, Horiba-JY) employing the Nd:
YAG laser wavelength of 633 nm). Wide-angle X-ray
scattering measurements were performed at Beamline 1W2A at
Beijing Synchrotron Radiation Facility (BSRF). The XAFS
experiment was carried out at Beamline 1W1B at BSRF. Data
of XAFS were processed using the Athena and Artemis
programs of thee IFEFFIT package based on FEFF 6. Prior to
merging, the spectra were aligned to the first and largest peak
in the smoothed first derivative of the absorption spectrum,
normalized and background removed. Data were processed by
k3-weighting and an Rbkg value of 1.0. Merged data sets were
aligned to the largest peak in the first derivative of the
adsorption spectrum. Normalized μ(E) data was obtained
directly from the Athena program of the IFEFFIT package. The
quantitative structural parameters were obtained using a least-
squares curve parameter fitting method by ARTEMIS module.
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analyzed by H NMR on Bruker AVANCE AV III 400, in
which the used electrolyte was mixed with D2O (deuterated
water). After the quantification, the faradaic efficiencies (FE)
toward each product were calculated as follows:
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Amount of product×n×F
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×100
FE (%) =
C
where n is number of moles of electrons to participate in the
faradaic reaction, F is the Faraday constant (96485 C mol-1),
and C is the amount of charge passed through the working
electrode.
Rotating disk electrode measurements. Rotating disk
electrode measurements was controlled using a Pine Modulated
Speed Rotator in a three-electrode electrochemical cell with an
air-tight seal. The electrodes were polished and sonicated using
a bath sonicator for 5 min prior to each experiment. Rotation
rate dependent product determination were measured by
conducting controlled potential electrolysis at -1.18 V (vs RHE)
in CO2-saturated 0.1 M K2SO4 electrolyte. For a given rotation
rate, the formed gases were detected by GC after the generated
gases were equilibrated in the headspace. The rotation rate was
varied in the following order, 2000, 1000, 1500, 500 rpm.
Preparation of working electrode. The glassy carbon
working electrode was prepared according to the commonly
adopted method.5,7 The catalyst ink was prepared through
ultrasonically dispersing 2 mg of the sample powder with 5 μl
Nafion solution (5%) in 100 μl ethanol for 30 min. Then 10 μl
of the catalyst ink was drop-coated on the glass carbon electrode
with diameter of 3 mm. The electrode was then dried slowly at
room temperature to obtain the working electrode for the
subsequent electrochemical tests.
Electrochemical
measurements.
Electrochemical
measurements and product identification and quantification
were similar to protocols described in our previous work.41,42
Electrocatalytic measurements were performed in a gas-tight
two-compartment H-type cell with three electrode system using
an electrochemical station (Chi660E). Pt gauze and Ag/AgCl
(3.5 M KCl) electrode were used as the counter electrode and
reference electrode, respectively. The working and reference
electrodes keep small spacing (~0.5 cm) to minimize
uncompensated solution resistance. A 0.1 M solution of K2SO4
dissolved in 18.2 MΩcm deionized water was used as the
electrolyte. Each compartment contains 20 ml electrolyte and
the electrolyte in the working-electrode compartment was
bubbled with N2 or CO2 for at least 30 min to form N2 or CO2
saturated solution and maintained this flow rate during
measurements. The working and reference electrodes were
placed in the cathode chamber, while the counter electrode was
placed in the anode chamber, which was separated by a piece of
Nafion 117 ionic exchange membrane to avoid the re-oxidation
of CO2RR-generated products. The measurements were
performed at constant IR-corrected potential. Electrode
potentials were converted to RHE using the following equation,
ERHE=EAg/AgCl+0.21 V+0.0591×pH.
In-situ X-ray absorption spectroscopy. The XAFS
experiment was carried out at Beamline 1W1B at BSRF. A
home-made plastic electrochemical cell was employed for in
situ XAS measurement under the sensitive fluorescence model.
The cell was filled with electrolyte saturated with CO2.
Ag/AgCl and Pt gauze were used as reference electrode and
counter electrode, respectively. The working electrode
compartment had walls with a single square hole of 1.0 cm in
edge length. A catalyst/thin carbon paper as the working
electrode was in contact with a slip of copper tape and fixed
with Kapton (polyimide) tape to the exterior of the wall of the
cell, over the hole, catalyst layer facing inwards. During the
measurement, the XAS data was collected at different time.
Computational details for calculations. Spin-polarized
density functional theory calculations were performed using
DMol3 package with the Perdew-Burke-Ernzerhof (PBE)
generalized gradient approximation (GGA) exchange-
correlation functional. Three layers of 4x4 Cu(111) and Cu
(100) surfaces which contain 48 Cu atoms was chosen as the
catalysts, and the defective 4x4 Cu(111) and Cu(100) surfaces
which contains 47 Cu atoms were comparatively studied. The
density functional semicore pseudopotential (DSPP) was
chosen to describe the Cu atoms. During the geometry
optimization, the tolerances of energy and force were 2×10-5ꢀHa
and 0.004 Ha/Å, and the maximum displacement was 5×10-3 Å,
respectively. The Monkhorst-Pack scheme k-point meshes were
ECSA referred the CV results under the potential windows
of 0.42 V~0.52 V (vs RHE). To compare with the literature,17
the LSV measurements for defective peak were performed
similarly in CO2-saturated 0.1 M KHCO3 electrolyte. LSV
curves in N2-saturated and CO-saturated 0.1 M KHCO3
electrolytes were obtained to detect the CO adsorption
according to the reported literature.18
2×2×1.
The
adjacent
slabs
were
separated
by a vacuum layer of 12 Å thickness along the z-direction, thus
the real Cu surface can be created. The adsorption energy (Eads)
of different adsorbates on both the non-defective and the
defective Cu surfaces were calculated according to:
Product analysis. For product identification and
quantification of gas, 2 ml of collected gas was injected into a
gas chromatograph (GC, HP 4890D) during the
chronoamperometry measurements at each 15 min to analyse
Eads = Etotal –(Esurface+Eadsorbate
)
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(7) Zhou, Y.; Che, F.; Liu, M.; Zou, C.; Liang, Z.; De Luna, P.;
where Eads is the adsorption energy of various adsorbates
which includes the mono or/and the coexisted OH-, CO and
OCCO; Etotal is the total energy for the adsorption state, Esurface
is the energy of either the non-defective or the defective Cu
surface, Eadsorbate is the energy of accumulated adsorbates.
Yuan, H.; Li, J.; Wang, Z.; Xie, H.; Li, H.; Chen, P.; Bladt, E.;
Quintero-Bermudez, R.; Sham, T.-K.; Bals, S.; Hofkens, J.;
Sinton, D.; Chen, G.; Sargent, E. H., Dopant-induced electron
localization drives CO2 reduction to C2 hydrocarbons. Nat.
Chem. 2018, 10, 974-980.
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The coupling energy barrier of OCCO was calculated using
the equations formula:
(8) Zhuang, T.-T.; Liang, Z.-Q.; Seifitokaldani, A.; Li, Y.; De Luna,
P.; Burdyny, T.; Che, F.; Meng, F.; Min, Y.; Quintero-Bermudez,
R.; Dinh, C. T.; Pang, Y.; Zhong, M.; Zhang, B.; Li, J.; Chen, P.-
N.; Zheng, X.-L.; Liang, H.; Ge, W.-N.; Ye, B.-J.; Sinton, D.;
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e1701069.
EOCCO coupling = EOCCO –E2CO
ASSOCIATED CONTENT
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Supporting Information. This material is available free of
charge via the Internet at http://pubs.acs.org. The Supporting
Information including the additional SEM, TEM, EDS Mapping,
AFM and HRTEM images, XRD patterns, XPS spectra,
electrochemical performance of materials andsimulation details.
AUTHOR INFORMATION
Corresponding Author
* E-mail: zhangjl@iccas.ac.cn.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
The authors thank the financial supports from National Natural
Science Foundation of China (21525316, 21673254), Ministry of
Science and Technology of China (2017YFA0403003), Chinese
Academy of Sciences (QYZDY-SSW-SLH013) and Beijing
Municipal
Science
&
Technology
Commission
(Z191100007219009).
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