Porous Copper Microspheres for Selective Production of Multicarbon Fuels via CO2 Electroreduction

Article abstract of DOI:10.1002/smll.201902582

The electroreduction of carbon dioxide (CO₂) toward high-value fuels can reduce the carbon footprint and store intermittent renewable energy. The iodide-ion-assisted synthesis of porous copper (P-Cu) microspheres with a moderate coordination number of 7.7, which is beneficial for the selective electroreduction of CO₂ into multicarbon (C₂₊) chemicals is reported. P-Cu delivers a C₂₊ Faradaic efficiency of 78 ± 1% at a potential of ?1.1 V versus a reversible hydrogen electrode, which is 32% higher than that of the compact Cu counterpart and approaches the record (79%) reported in the same cell configuration. In addition, P-Cu shows good stability without performance loss throughout a continuous operation of 10 h.

Full text of DOI:10.1002/smll.201902582

CommuniCation
CO2 Electroreduction
www.small-journal.com
Porous Copper Microspheres for Selective Production
of Multicarbon Fuels via CO2 Electroreduction
Chengqin Zou, Cong Xi, Deyao Wu, Jing Mao, Min Liu, Hui Liu, Cunku Dong,
and Xi-Wen Du*
neither too strong nor too weak, allows
easy dimerization.[6,15] Furthermore, the
adsorption energies of the intermediates
vary with the coordination number (CN)
of the catalyst, which can be tuned by the
structure of catalysts,[16,17] as such, there
also exists a volcano plot between the cata-
lytic activity and CN. Hitherto, the volcano
plots have been established for several
electrochemical reactions (e.g., oxygen
reduction reaction).[16,18] As for CO2RR,
it has been demonstrated that theoreti-
cally, moderate CNs between 6 and 8 can
promote the CO=CO dimerization on Cu
catalyst.[19,20] And experimentally, Cu (100)
The electroreduction of carbon dioxide (CO2) toward high-value fuels can
reduce the carbon footprint and store intermittent renewable energy. The
iodide-ion-assisted synthesis of porous copper (P-Cu) microspheres with a
moderate coordination number of 7.7, which is beneficial for the selective
electroreduction of CO2 into multicarbon (C2+) chemicals is reported. P-Cu
delivers a C2+ Faradaic efficiency of 78 1% at a potential of −1.1 V versus a
reversible hydrogen electrode, which is 32% higher than that of the compact
Cu counterpart and approaches the record (79%) reported in the same cell
configuration. In addition, P-Cu shows good stability without performance
loss throughout a continuous operation of 10 h.
The electrochemical reduction of carbon dioxide (CO2RR) pro-
vides an attractive and viable strategy to produce sustainable
chemical fuels,[1,2] meanwhile, this technique is appealing to
address the storage of intermittent energy and the release of
CO2.[3] A charming goal for CO2RR is to produce high-value
multicarbon (C2+) chemicals, such as ethylene (C2H4), ethanol
(C2H5OH), acetic acid (CH3COOH), and n-propanol (C3H7OH),
which can be achieved with the help of copper (Cu) catalyst.
Compared with other catalysts, Cu is the most efficient one for
the production of C2+ chemicals.[4–7] However, methane (CH4)
and undesired hydrogen (H2) are usually generated in the
presence of Cu catalyst.[8–10] Hence, it is of interest to develop
advanced Cu electrocatalysts in favor of the C2+ production.
It is widely accepted that CO2RR on Cu is initiated by
reducing CO2 to adsorbed CO (*CO), and further dimeriza-
tion of *CO species can lead to C2+ products.[11–14] Particularly,
CO=CO dimerization exhibits a volcano plot related to the
adsorption of *CO, where the optimized adsorption energy,
surface with CN of 8 has been identified as the active site to
catalyze *CO intermediate into C2+ products.[13,21–23] In con-
trast, Cu (111) surface with CN of 9 does not favor the CO=CO
dimerization.[21,22,24] Nevertheless, practical Cu catalysts with
large active surface and moderate CN have not been investi-
gated intensively, and it remains as a great challenge to achieve
Cu catalyst with optimized CN for the production of C2+ fuels.
Halide ions are known as effective inducing reagents for the
synthesis of nanostructured metal due to the strong affinity and
adsorption capability.[25–27] As for CO2RR, Ogura et al. adopted
halide to promote the ethylene production at a three-phase
interface.[28,29] Recently, Yeo et al. found that the addition of
halide ions into electrolyte could improve the current density
and selectivity of CO2RR. In this case, the adsorbed iodide ions
were proposed to increase *CO coverage on Cu surfaces, which
thus lowers the energy barrier for C−C coupling;[30–32] mean-
while, the catalyst morphology was changed in the presence
of iodide ions.[31,32] However, the halide ions have never been
utilized to adjust CN of the catalyst and boost the selectivity of
CO2RR.
C. Q. Zou, C. Xi, D. Y. Wu, Dr. J. Mao, Dr. H. Liu,
Dr. C. K. Dong, Prof. X.-W. Du
Institute of New Energy Materials
School of Materials Science and Engineering
Tianjin University
In this work, we report the synthesis of porous Cu (P-Cu)
with moderate CN (7.7) via electroreduction of Cu2O micro-
spheres in aqueous solution of KI. We demonstrate that the
adsorption of iodide ions on the product surface plays a cru-
cial role in the formation of P-Cu. As a CO2RR catalyst, P-Cu
achieves a C2+ Faradaic efficiency (FE) of 78%, being 32%
higher than that achieved on the compact Cu catalyst. More-
over, P-Cu exhibits a good durability without loss of C2+ pro-
ductivity during 10 h of continuous operation. The high CO2RR
performance was found to originate from the moderate CN
of P-Cu according to the X-ray absorption spectroscopy (XAS)
analysis.
Tianjin 300072, China
E-mail: xwdu@tju.edu.cn
Prof. M. Liu
Institute of Super-Microstructure and Ultrafast
Process in Advanced Materials
School of Physics and Electronics
Central South University
932 South Lushan Road, Changsha, Hunan 410083, China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.201902582.
The starting Cu2O microspheres were synthesized via a
modified precipitation method.[33] Subsequently, P-Cu was
DOI: 10.1002/smll.201902582
©
1902582 (1 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Small 2019, 1902582

www.advancedsciencenews.com
www.small-journal.com
obtained by the electroreduction of Cu2O microspheres at
−1.1 V versus reversible hydrogen electrode (RHE) for 3 h in
the CO2-saturated electrolyte with 0.05 m KI and 0.05 m KHCO3.
For comparison, compact Cu (C-Cu) microspheres were pre-
pared with the same procedure in the electrolyte without KI.
The as-prepared Cu2O sample comprises many agglom-
erate particles with size around 700 nm, as revealed by
scanning electron microscopy (SEM) and transmission elec-
tron microscopy (TEM; Figure S1a–c, Supporting Informa-
tion). Selected area electron diffraction (SAED) suggests a
polycrystalline cubic phase (Figure S1d, Supporting Informa-
tion), which was confirmed by X-ray diffraction (XRD) pattern
(Figure S2, Supporting Information). After electroreduction in
the electrolyte with KI, the compact Cu2O microspheres trans-
form into porous particles as indicated by SEM (Figure 1a and
Figure S3a–c, Supporting Information) and high-angle annular
dark-field scanning transmission electron microscopy (HAADF-
STEM) (Figure 1b and Figure S3d, Supporting Information).
XRD pattern indicates pure metallic Cu phase without residual
oxide (Figure 1c), and an average crystallite size of 4.4 nm is
determined by the Scherrer equation (Figure S4, Supporting
Information). In contrast, after Cu2O microspheres being
electrochemically reduced in the electrolyte without KI, their
structure maintains compact as indicated by SEM (Figure 1d),
HAADF-STEM (Figure 1e), and TEM (Figure S5, Supporting
Information). XRD analysis indicates that residual oxide coex-
ists with metallic copper in the product (Figure 1f). The phase
constitutions of P-Cu and C-Cu are further verified by the SAED
results (Figure S6, Supporting Information). Moreover, energy
dispersive spectrum (EDS) mapping shows distinct iodine dis-
tribution in P-Cu (Figure S7, Supporting Information).
To understand the formation mechanism of P-Cu, we
observed the structure change of big Cu2O particles with several
microns in size (M-Cu2O, see Figures S8 and S9, Supporting
Information). The M-Cu2O was electrochemically reduced at
−1.1 V versus RHE in CO2-saturated electrolytes with KI or
without KI, respectively. As expected, a porous structure could
be observed in the presence of KI (Figure S10, Supporting Infor-
mation), whereas discrete particles formed on the surface of
M-Cu2O in the absence of KI (Figure S11, Supporting Informa-
tion). Specifically, smooth M-Cu2O surface became rough after
1 h of electroreduction in electrolyte with KI (Figure S10a,b,
Supporting Information), and further transformed into porous
structure as the reduction proceeded (Figure S10c,d, Sup-
porting Information). At the same time, the diffraction peaks
related to Cu2O weakened obviously (Figure S12, Supporting
Information). Those results imply that the porous Cu structure
initiates from the surface of M-Cu2O and develops inward. In
this process, the iodide ions are supposed to adsorb onto both
Cu2O and Cu surface due to strong affinity between Cu2O/Cu
and iodide ions.[34–36] The adsorption of iodide ions can cause
a regulation effect, namely, Cu2O matrix is reduced unevenly,
and Cu skeleton grows gradually from surface to internal,
leading to the formation of porous Cu structure (Figure 2).
Figure 1. Characterizations of P-Cu and C-Cu. a) SEM, b) HAADF-STEM, and c) XRD of P-Cu obtained in the electrolyte with KI. d) SEM, e) HAADF-
STEM, and f) XRD of C-Cu obtained in the electrolyte without KI.
©
Small 2019, 1902582
1902582 (2 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.small-journal.com
Figure 2. Schematic illustration of the formation mechanism of P-Cu in the presence of iodide ions. The adsorption of iodide ions can promote the
uneven reduction of Cu2O, giving rise to the porous cooper.
This hypothesis was proved by the distribution of iodide ions
on P-Cu even after being washed for several times (Figure S7,
Supporting Information).
electrochemical surface area (ECSA) of P-Cu is 2.9 times that
of C-Cu according to double-layer capacitance measurements,
and the degree of porosity based on ECSA of P-Cu has been
improved by four orders of magnitude comparing with that
of polycrystalline Cu (Figure S21 and Table S2, Supporting
Information). After normalizing the CO2RR current density to
ECSA, the intrinsic activity of P-Cu is still higher than that of
C-Cu, implying the superiority of porous structure (Figure S22,
Supporting Information). P-Cu also shows a good durability,
achieving 10 h of continuous operation at −1.1 V versus RHE
without loss of performance (Figure 3c). When comparing with
literature reported in the H-type electrocatalytic cell, P-Cu man-
ifests a top level of C2+ FE, which is comparable with the record
(79%) reported so far (Figure 3d and Table S3, Supporting
Information). These performance results, taken together, sug-
gest that the porous Cu structure derived in the presence of KI
is significant for improving the C2+ selectivity in CO2RR.
To understand the specificity of P-Cu, we employed XAS
and X-ray photoelectron spectroscopy (XPS) to investigate its
composition and structure. The X-ray absorption near edge
structures (XANES) at Cu K-edge of P-Cu presents the Cu
characteristic peak at ≈9005 eV, while the characteristic peak of
Cu2O is absent at ≈9013 eV, suggesting the complete reduction
of Cu2O microspheres (Figure 4a and Figure S23, Supporting
Information). Moreover, P-Cu shows a strong peak related to
Cu-Cu bond in its R spacing spectrum based on the extended
X-ray absorption fine structure (EXAFS) measurements,
whereas C-Cu demonstrates a much weaker peak of Cu-Cu
bond accompanying with an obvious Cu-O bond. The standard
EXAFS fitting reveals that the CNs of P-Cu and C-Cu are 7.7
and 4.9, respectively (Figure 4b and Figure S24 and Table S4,
Supporting Information).
CO2RR performance of the catalysts was evaluated in a
H-type electrocatalytic cell (see quantitative methods in the
Experimental Section and Figures S13 and S14, Supporting
Information). Linear sweep voltammetry (LSV) curves of
P-Cu and C-Cu were shown in Figure 3a, the geometric cur-
rent density of P-Cu increases with the applied potential
more rapidly than that of C-Cu. Potential screenings dem-
onstrate the optimal C2+ (C2H4, C2H5OH, CH3COOH, and
C3H7OH) production can be achieved around −1.1 V versus
RHE (Figure S15, Supporting Information). At this poten-
tial, the CO2RR current density of P-Cu reaches 46 mA cm−2,
whereas the current density of C-Cu is merely 20 mA cm−2
(Figure S16, Supporting Information). Based on the evolution
of FE(C2H4), the activation time for P-Cu was determined as
30 min (Figure S17, Supporting Information). Regarding the
CO2RR selectivity at steady states, P-Cu achieves an average
FE for C2+ (FE(C2+)) as high as 78%, including 56% for C2H4,
16% for C2H5OH, 5% for C3H7OH, and 1% for CH3COOH.
By comparison, C-Cu delivers an average FE of 46% for C2+,
including 30% for C2H4, 13% for C2H5OH, 2% for C3H7OH,
and 1% for CH3COOH (Figure 3b and Table S1, Supporting
Information). For C2+ partial current density, P-Cu presents a
value four times that of C-Cu (Figure S18, Supporting Infor-
mation). To exclude the influence of adsorbed iodide ions upon
the C2+ selectivity, CO2RR performance of P-Cu was evalu-
ated in 0.1 m KHCO3 without KI. Inductively coupled plasma
atomic emission spectroscopy (ICP-AES) results demonstrate
that the adsorbed iodide ions on P-Cu leach out after working
in pure KHCO3 for 1 h (Figure S19, Supporting Information),
while no obvious change is found for product constitution and
FE(C2+) (Figure S20, Supporting Information). Moreover, the
In I 3d XPS spectrum of P-Cu, the weak peak at 619.1 eV
arises from the adsorbed KI,[37] whose binding energy is
©
1902582 (3 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Small 2019, 1902582

www.advancedsciencenews.com
www.small-journal.com
Figure 3. CO2 electroreduction performance of P-Cu and C-Cu. a) LSV scans and b) FEs of different CO2RR products of P-Cu and C-Cu. c) Durability
measurement of P-Cu measured at −1.1 V versus RHE. d) Comparison of FE(C2+) with literature reported in the H-type electrocatalytic cell. Error bars
represent standard deviation (n = 3 replicates).
distinct from that of CuI (619.7 eV, Figure 4c). Additionally, the
XANES at I (iodine) LIII-edge of P-Cu does not show any peaks
correlating to CuI, but resembles that of KI (Figure 4d). There-
fore, both XANES and XPS results imply that iodide ions are
adsorbed on the surface of P-Cu, rather than in the form of CuI
compound.
energy for *CO.[6,15] On the other hand, it was verified that the
adsorption energy can be tuned by the CN of the catalyst.[19,20]
Hence, the catalysts with a moderate CN can optimize the
CO=CO dimerization. P-Cu possesses an average CN of 7.7,
which just locates in the appropriate CN range of 6–8.[19] There-
fore, the high C2+ selectivity obtained by P-Cu can be attributed
to the appropriate CN of the unique porous nanostructure.
Based on the literature,[19,38] a scheme is given in Figure S25
in the Supporting Information to visualize CO2 adsorption and
CO=CO dimerization on Cu site with CN = 7 (CN7-Cu): the
CO2 molecules are captured and stabilized on the edge CN7-Cu
sites with the assistance of H2O molecules adsorbed on neigh-
boring Cu sites by forming hydrogen bonds, while the key
intermediates for C2+ production, CO dimers, prefer square-like
CN7-Cu sites. P-Cu possesses an average CN of 7.7, thus con-
tains abundant surface sites with lower CN (such as CN7-Cu
sites). Hence, P-Cu catalyst is advantageous on the conversion
of CO2 to C2+ products.
In conclusion, we synthesized porous Cu with a moderate CN
for selective multicarbon production in CO2 electroreduction.
The porous microspheres were generated by electroreduction
of Cu2O microspheres in the electrolyte containing KI, and
the adsorption of iodide ions on the surface of Cu2O/Cu was
found crucial on the formation of the porous structure. X-ray
absorption spectrum indicated that the porous Cu possesses a
moderate CN, which is beneficial for the production of multi-
carbon chemicals. Eventually, the porous Cu catalyst achieves
It has been reported that the adsorbed iodide ions can
improve the CO2RR selectivity of Cu catalysts by strength-
ening *CO adsorption, enhancing *CO population, and pro-
moting C−C coupling.[29–32] However, iodide ions have never
been utilized to adjust CN of the catalyst and boost C2+ selec-
tivity of CO2RR. Herein, P-Cu catalyst with an average CN
of 7.7 was synthesized with the assistance of iodide ions. As
XAS is also bulk sensitive, the average 7.7 of CN for P-Cu sug-
gests there exist lots of low-coordinated surface atoms with
CN lower than 7.7, consisting with the small crystallite size
of 4.4 nm (Figure S4, Supporting Information) and abun-
dant concave surfaces of P-Cu (Figure 1b and Figure S3d,
Supporting Information). Additionally, the absence of iodide
in the electrolyte leads to the residual oxide in C-Cu (Figure 1f
and Figure S6a, Supporting Information). The residual oxide
not only affects the CN of C-Cu, but also causes excessively
strong adsorption of CO, which is disadvantageous to the
CO=CO dimerization.[38]
In principle, the C2+ formation relies on the C−C coupling
between two *CO molecules, and the optimized C2 production
can be achieved by these catalysts with a moderate adsorption
©
Small 2019, 1902582
1902582 (4 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.small-journal.com
Figure 4. Investigation of the bond structures of P-Cu and C-Cu. a) XANES and b) R-space spectra based on EXAFS of copper at K-edge of P-Cu and
C-Cu. The commercial Cu2O and Cu are plotted as references. c) I 3d XPS spectra of P-Cu and the commercial CuI. d) XANES of iodine at LΙΙΙ-edge of
P-Cu, the commercial KI, and the commercial CuI.
on the TEM (JEM-2100F) instrument with an acceleration voltage of
200 kV. SEM (Hitachi S4800, Hitachi SU5000, and FEI Quanta FEG 250)
was employed to study the morphology changes. XPS measurements
were carried out using a Thermo Scientific K-Alpha system. The binding
an FE (78%) of multicarbon product as well as great durability.
Our work provides a new avenue toward highly active Cu
catalysts for the production of multicarbon chemicals by CO2
electroreduction.
energy data were calibrated with a reference of carbon C 1s signal at
284.6 eV to correct the charging effect. ICP-AES results were conducted
on Optima 7300.
Preparation of Cathode Electrode: The catalyst inks were prepared by
ultrasonic dispersing 10 mg Cu2O pre-catalysts in 1 mL of methanol
Experimental Section
Synthesis of Compact Cu2O: All chemicals were purchased
from Sigma-Aldrich. The compact Cu2O was prepared following a
modified precipitation method[33] using cupric acetate monohydrate
(Cu(CH3COO)2·H2O), PEG-PPG-PEG (P-123, average Mn ∼ 5800), and
L-ascorbic acid as precursors. First, 50 mL of 0.1 m Cu(CH3COO)2·H2O
was prepared using Millipore water. Next, 1.0 g P-123 and extra 50 mL
water were added to the above Cu(CH3COO)2·H2O solution, which
was stirred till all P-123 dissolved into the solution. After that, 8 mL of
0.1 m ascorbic acid aqueous solution was quickly injected to the mixed
solution, and extra 42 mL water was added with stirring for 1 min.
The 150 mL final solution was incubated for 3 h at room temperature.
Then, the orange precipitates obtained were subsequently washed four
times with 40 mL of water each time and once with 40 mL of acetone to
completely remove the unreacted precursors. Finally, the products were
obtained by centrifugation and blow-dried using pure N2.
Characterization: The as-prepared compact Cu2O pre-catalyst was
characterized after preparation. The commercial micro-Cu2O was
characterized as purchased. For the catalysts after reaction, they
were obtained after CO2RR at −1.10 V versus RHE for 3 h. The crystal
structures of the samples were characterized with a powder XRD (Bruker
D8 Advance) with a copper target (λ = 1.54056 Å). The TEM images,
SAED results, HAADF-STEM images, and EDS mapping were collected
containing 40 µL of 5 wt% Nafion aqueous solution for 30 min. A glassy
carbon electrode (GCE) (diameter: 3 mm, area: 0.07 cm2) that served
as a working electrode was used as a substrate to support the catalysts.
The samples were prepared by drop-casting 5 µL of the as-prepared inks
onto GCE for the subsequent electrochemical measurements.
CO2RR Performance Evaluation: All CO2 reduction experiments were
performed in a gas-tight two-compartment H-cell separated by a proton
exchange membrane (Nafion117) using a three-electrode system. For
all experiments, two kinds of electrolytes were used as the catholyte,
including 30 mL pure electrolyte without KI (0.1 m KHCO3) and 30 mL
mixed electrolyte with KI (0.05 m KHCO3 + 0.05 m KI), while anolytes were
always 30 mL of 0.1 m KHCO3. The catholyte was saturated with CO2, and
CO2 was kept bubbling during the experiments. During CO2RR test, the
activation and performance evaluation of the porous Cu (P-Cu) and the
compact Cu (C-Cu) were carried out in the mixed electrolyte with KI and
the pure KHCO3 electrolyte, respectively. Especially for the experiment of
P-Cu in the electrolyte without KI (Figure S16, Supporting Information),
the P-Cu catalyst was first activated in the electrolyte containing KI,
second washed thoroughly with pure water, and finally transferred to
the pure KHCO3 electrolyte for CO2RR performance evaluation. Pt foil
and Ag/AgCl (3 m KCl) were used as the counter electrode and reference
electrode, respectively. For potential screenings conducted in 0.1
m
©
1902582 (5 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Small 2019, 1902582

www.advancedsciencenews.com
www.small-journal.com
KHCO3 without KI, chronoamperometry measurements were performed
at each fixed potential for 3 h in the CO2-saturated 0.1 m KHCO3. Working
electrode potentials were converted to the RHE reference scale using
ERHE = EAg/AgCl + 0.210 V + 0.0591 × pH. All potentials were corrected
with 95% of iR correction (the series resistance R was determined using
electrochemical impedance spectroscopy). The current densities were
normalized to the geometric surface area.
The gas products from CO2 electroreduction were analyzed using
a PerkinElmer Clarus 680 gas chromatograph (GC) coupled with a
thermal conductivity detector (TCD) and a flame ionization detector
(FID). Gaseous products are separated in a Molecular Sieve 5A capillary
column and a Carboxen-1000 packed column, and the TCD is used to
quantify CO and H2, while the FID is used to quantify the hydrocarbons
such as CH4 and C2H4. Argon (Linde, 99.999%) was used as the
carrier gas.
(DMSO, ≥99.9%; Sigma-Aldrich) to obtain the internal standard. The
1D 1H spectrum was measured with water suppression using a pre-
1
saturation method. One typical H NMR spectrum of P-Cu is shown in
Figure S14 in the Supporting Information.
As the concentration of DMSO is known, the amount of substance
of each liquid product can be calculated based on their relative peak
area comparing to that of DMSO. Finally, the FE for liquid products was
calculated using the following formula
zFnDMSOα yν
FE(y, %)=
× 100
(5)
titotal
∫
0
where z is the number of electrons transferred, F is Faraday’s constant,
nDMSO is the amount of substance of DMSO used, αy is the molar ratio
of the product y and DMSO based on the NMR peak areas (y could
be CH3CH2OH, CH3CH2CH2OH, HCOOH, or CH3COOH, whose αy is
equal to the product of the respective relative NMR peak area and 2, 2,
6, or 2, respectively), ν is the ratio of total catholyte and the collected
catholyte for NMR test, t is the reaction time for collecting liquid
products, and itotal is the total current.
X-Ray Absorption Experiments: Cu K-edge XANES and EXAFS spectra
were performed at the Soft X-ray Microcharacterization Beamline
06B1-1 of Canadian Light Source (CLS). Measurements were performed
in fluorescence using a passivated implanted planar silicon detector.
IFEFFIT software was used to calibrate the energy scale, to correct
the background signal, and to normalize the intensity. The spectra
were normalized with respect to the edge height after subtracting
the pre-edge and post-edge backgrounds using Athena software. All
Fourier transforms were k2-weighted. EXAFS fittings were conducted
at the first shell with Artemis and IFEFFIT software. S0/Δσ2 values of
0.83/0.009 for pure Cu model were determined from the Cu K-edge
XAS of Cu reference (Cu foil, CN = 12), which were directly applied to
the Cu K-edge XAS fittings of P-Cu catalyst. As C-Cu contains residual
oxides, one Cu-O model (with one O atom in a 1 × 1 × 2 Cu supercell)
and S0 value of 0.79 were applied to the Cu K-edge XAS fittings of
C-Cu catalyst. The detailed fitting results are listed in Table S4 in the
Supporting Information.
The FE for gas products was calculated using the following formula
zFGρ
Vmitotal
FE(%)=
× 100
(1)
where z is the number of electrons transferred, F is Faraday’s constant,
G is the flow rate of gas, ρ is the molar fraction of the product, Vm is the
gas molar volume (T = 20 °C, P = 101.3 kPa, Vm = 24 L mol−1), and itotal
is the total current.
For molar fraction ρ, it can be calculated using the following formula
Ax
α x
ρ =
(2)
where Ax is the peak area of x product (x could be C2H4, CH4, CO,
or H2) and αx is the response coefficient of product x in GC. Then,
in combination with Formula (2) and Formula (1), the following
Formula (3) can be obtained
zFGAx
Vmitotalα x
FE(x, %)=
× 100
(3)
Standard gas (C2H4, CH4, CO, or H2 with CO2 as the balance gas) was
used to make calibration to get the response coefficient αx. Generally,
the calibration of each kind of gas was done with three different
concentrations. Here, we take C2H4 as an example for GC calibration
and FE calculation. First, three different concentrations of 226, 673, and
1111 ppm of standard C2H4 gases were injected into GC repeatedly, then
three averaged response peak areas of 31 084, 90 502, and 1 44 359
were obtained. Second, plotted the peak area with concentration using
ppm as x and peak area as y, and get the slope of 130.01 ppm−1 via
linear fitting as shown in Figure S13 in the Supporting Information. This
slope was the response coefficient αx of C2H4 in GC.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
Third, FE of C2H4 was calculated by substituting known data into
Formula (3). Here, 12, 96 485 C mol−1, 20 mL min−1, 24 L mol−1, and
130.01 ppm−1 were used to substitute z, F, G, Vm, and αx, respectively.
So, the following Formula (4) can be obtained
This work was financially supported by the Natural Science Foundation
of China (nos. 51871160, 51671141, 51471115), the Ontario Research
Fund Research-Excellence Program, the Natural Sciences and
Engineering Research Council (NSERC) of Canada, the CIFAR Bio-
Inspired Solar Energy program, and the University of Toronto Connaught
grant. Synchrotron work was carried out at the Canadian Light Source
(CLS). CLS is funded by NSERC, the Canada Foundation for Innovation
(CFI), National Research Council (NRC), Canadian Institute for Health
Research (CIHR), and the University of Saskatchewan. The authors thank
for the technical support from Dr. Y. F. H., Dr. Q. F. X., and Mrs. A. M.
at SXRMB beamline of CLS. The authors thank for the analysis help
from Dr. J. L. at University of Toronto. C.Q.Z. gratefully appreciates the
scholarship under the International Academic Exchange Fund for Joint
Ph.D. Student from Tianjin University.
12⋅96485C mol−1 ⋅20 mL min−1 ⋅AC H
2
4
FE(C2H4, %) =
×100
24L mol−1 ⋅itotal ⋅130.01ppm−1
12⋅96485C mol−1 ⋅20 ×10−6 × 60−1 m3 s−1 ⋅AC H
(4)
2
4
=
×100
24 ×10−3 m3 mol−1 ⋅itotal(mA)×10−3A ⋅130.01×106
A
C2H4
=
i
total(mA)⋅80.9
For P-Cu, the total current was about 3.2 mA at −1.1 V versus RHE,
while the average peak area of C2H4 was about 14 500, thus, the FE of
C2H4 was calculated based on Formula (4) as about 56%.
Regarding the FE for other products, the similar calibration method
and calculation method can be applied.
Liquid products were quantified using a Agilent DD2 500 MHz NMR
spectrometer. Typically, 500 µL of collected catholyte in the reactor was
mixed with 100 µL D2O containing 30 ppm (n/n) dimethyl sulfoxide
Conflict of Interest
The authors declare no conflict of interest.
©
Small 2019, 1902582
1902582 (6 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.small-journal.com
[15] X. Liu, J. Xiao, H. Peng, X. Hong, K. Chan, J. K. Nørskov, Nat.
Commun. 2017, 8, 15438.
[16] F. Calle-Vallejo, J. Tymoczko, V. Colic, Q. H. Vu, M. D. Pohl,
K. Morgenstern, D. Loffreda, P. Sautet, W. Schuhmann,
A. S. Bandarenka, Science 2015, 350, 185.
[17] F. Calle-Vallejo, D. Loffreda, M. T. M. Koper, P. Sautet, Nat. Chem.
2015, 7, 403.
[18] D. Wu, C. Dong, H. Zhan, X.-W. Du, J. Phys. Chem. Lett. 2018, 9,
3387.
Keywords
carbon dioxide electroreduction, coordination number, multicarbon
fuels, porous copper microspheres
Received: May 20, 2019
Revised: August 13, 2019
Published online:
[19] H. Li, Y. Li, M. T. M. Koper, F. Calle-Vallejo, J. Am. Chem. Soc. 2014,
136, 15694.
[1] J. Qiao, Y. Liu, F. Hong, J. Zhang, Chem. Soc. Rev. 2014, 43, 631.
[2] D. D. Zhu, J. L. Liu, S. Z. Qiao, Adv. Mater. 2016, 28, 3423.
[3] R. W. R. Parker, J. L. Blanchard, C. Gardner, B. S. Green,
K. Hartmann, P. H. Tyedmers, R. A. Watson, Nat. Clim. Change
2018, 8, 333.
[20] J. Li, F. Che, Y. Pang, C. Zou, J. Y. Howe, T. Burdyny, J. P. Edwards,
Y. Wang, F. Li, Z. Wang, P. De Luna, C.-T. Dinh, T.-T. Zhuang,
M. I. Saidaminov, S. Cheng, T. Wu, Y. Z. Finfrock, L. Ma,
S.-H. Hsieh, Y.-S. Liu, G. A. Botton, W.-F. Pong, X. Du, J. Guo,
T.-K. Sham, E. H. Sargent, D. Sinton, Nat. Commun. 2018, 9, 4614.
[21] K. J. P. Schouten, Z. S. Qin, E. P. Gallent, M. T. M. Koper, J. Am.
Chem. Soc. 2012, 134, 9864.
[4] Y. Wang, J. Liu, Y. Wang, A. M. Al-Enizi, G. Zheng, Small 2017, 13,
1701809.
[5] C.-T. Dinh, T. Burdyny, M. G. Kibria, A. Seifitokaldani,
C. M. Gabardo, F. P. García de Arquer, A. Kiani, J. P. Edwards,
P. De Luna, O. S. Bushuyev, C. Zou, R. Quintero-Bermudez,
Y. Pang, D. Sinton, E. H. Sargent, Science 2018, 360, 783.
[6] Y. Zhou, F. Che, M. Liu, C. Zou, Z. Liang, P. De Luna, H. Yuan, J. Li,
Z. Wang, H. Xie, H. Li, P. Chen, E. Bladt, R. Quintero-Bermudez,
T.-K. Sham, S. Bals, J. Hofkens, D. Sinton, G. Chen, E. H. Sargent,
Nat. Chem. 2018, 10, 974.
[7] T.-T. Zhuang, Z.-Q. Liang, A. Seifitokaldani, Y. Li, P. De Luna,
T. Burdyny, F. Che, F. Meng, Y. Min, R. Quintero-Bermudez,
C. T. Dinh, Y. Pang, M. Zhong, B. Zhang, J. Li, P.-N. Chen,
X.-L. Zheng, H. Liang, W.-N. Ge, B.-J. Ye, D. Sinton, S.-H. Yu,
E. H. Sargent, Nat. Catal. 2018, 1, 421.
[8] H. Xie, T. Wang, J. Liang, Q. Li, S. Sun, Nano Today 2018, 21, 41.
[9] Q. Lu, F. Jiao, Nano Energy 2016, 29, 439.
[10] Y. Hori, Electrochemical CO2 Reduction on Metal Electrodes In Modern
Aspects of Electrochemistry, Springer, New York 2008.
[11] R. Kortlever, J. Shen, K. J. P. Schouten, F. Calle-Vallejo,
M. T. M. Koper, J. Phys. Chem. Lett. 2015, 6, 4073.
[22] K. J. P. Schouten, E. Pérez Gallent, M. T. M. Koper, ACS Catal. 2013,
3, 1292.
[23] T. Cheng, H. Xiao, W. A. Goddard, Proc. Natl. Acad. Sci. U. S. A.
2017, 114, 1795.
[24] H. Xiao, T. Cheng, W. A. Goddard, J. Am. Chem. Soc. 2017, 139,
130.
[25] S. Ghosh, L. Manna, Chem. Rev. 2018, 118, 7804.
[26] Y. Liu, Y. Xiang, Y. Zhen, R. Guo, Langmuir 2017, 33, 6372.
[27] Z. Zhang, H. Li, F. Zhang, Y. Wu, Z. Guo, L. Zhou, J. Li, Langmuir
2014, 30, 2648.
[28] K. Ogura, H. Yano, T. Tanaka, Catal. Today 2004, 98, 515.
[29] K. Ogura, J. CO2 Util. 2013, 1, 43.
[30] A. S. Varela, W. Ju, T. Reier, P. Strasser, ACS Catal. 2016, 6, 2136.
[31] D. Gao, F. Scholten, B. R. Cuenya, ACS Catal. 2017, 7, 5112.
[32] Y. Huang, C. W. Ong, B. S. Yeo, ChemSusChem 2018, 11, 3299.
[33] C. Young-Sik, H. Young-Duk, Bull. Korean Chem. Soc. 2014, 35,
3239.
[34] G. Lefèvre, A. Walcarius, J. J. Ehrhardt, J. Bessière, Langmuir 2000,
16, 4519.
[12] E. Pérez-Gallent, M. C. Figueiredo, F. Calle-Vallejo, M. T. M. Koper,
Angew. Chem. 2017, 129, 3675.
[13] J. H. Montoya, C. Shi, K. Chan, J. K. Nørskov, J. Phys. Chem. Lett.
2015, 6, 2032.
[35] X. Zhang, P. Gu, X. Li, G. Zhang, Chem. Eng. J. 2017, 322, 129.
[36] Y. Au, Y. Lin, R. G. Gordon, J. Electrochem. Soc. 2011, 158, D248.
[37] W. E. Morgan, J. R. Van Wazer, W. J. Stec, J. Am. Chem. Soc. 1973,
95, 751.
[14] J. H. Montoya, A. A. Peterson, J. K. Nørskov, ChemCatChem 2013,
5, 737.
[38] H. Xiao, W. A. Goddard, T. Cheng, Y. Liu, Proc. Natl. Acad. Sci. U. S.
A. 2017, 114, E7045.
©
1902582 (7 of 7)
2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Small 2019, 1902582