Metal-Organic Frameworks Mediate Cu Coordination for Selective CO2 Electroreduction

Article abstract of DOI:10.1021/jacs.8b06407

The electrochemical carbon dioxide reduction reaction (CO₂RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity, activity, and efficiency for CO₂RR. Here we report a strategy involving metal-organic framework (MOF)-regulated Cu cluster formation that shifts CO₂ electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clusters with low CN from distorted Cu dimers in HKUST-1 during CO₂ electroreduction. These exhibited 45% C₂H₄ faradaic efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure-activity relationship was established wherein the tuning of the Cu-Cu CN in Cu clusters determines the CO₂RR selectivity.

Full text of DOI:10.1021/jacs.8b06407

Subscriber access provided by EKU Libraries
Article
Metal-Organic Frameworks Mediate Cu
2
Coordination for Selective CO Electroreduction
Dae-Hyun Nam, Oleksandr S. Bushuyev, Jun Li, Phil De Luna, ali seifitokaldani, Cao-Thang Dinh,
F. Pelayo Garcia de Arquer, Yuhang Wang, Zhiqin Liang, Andrew H. Proppe, Chih Shan Tan, Petar
Todorovic, Osama Shekhah, Christine M. Gabardo, Jea Woong Jo, Jongmin Choi, Min-Jae Choi, Se-
Woong Baek, Junghwan Kim, David Sinton, Shana O. Kelley, Mohamed Eddaoudi, and Edward H. Sargent
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b06407 • Publication Date (Web): 16 Aug 2018
Downloaded from http://pubs.acs.org on August 16, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Kim, Junghwan; University of Toronto, Department of Electrical and
Computer Engineering
Sinton, David; University of Toronto, Department of Mechanical and
Industrial Engineering
Kelley, Shana; University of Toronto, Department of Chemistry; University
of Toronto, Department of Pharmaceutical Sciences
Eddaoudi, Mohamed; King Abdullah University of Science and Technology,
Division of Physical Sciences and Engineering, Advanced Membranes and
Porous Materials Center, Functional Ma-terials Design, Discovery and
Development Research Group (FMD3)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Sargent, Edward; University of Toronto, Department of Electrical and
Computer Engineering
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Metal-Organic Frameworks Mediate Cu Coordination for Selective CO2
Electroreduction
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
†
†
†,‡
†,§
†
Dae-Hyun Nam, Oleksandr S. Bushuyev, Jun Li, Phil De Luna, Ali Seifitokaldani, Cao-Thang
†
†
†
†
†,ǁ
Dinh, F. Pelayo García de Arquer, Yuhang Wang, Zhiqin Liang, Andrew H. Proppe, Chih Shan
Tan, Petar Todorovic, Osama Shekhah, Christine M. Gabardo, Jea Woong Jo, Jongmin Choi,
Min-Jae Choi, Se-Woong Baek, Junghwan Kim, David Sinton, Shana O. Kelley, Mohamed Ed-
daoudi, and Edward H. Sargent*
†
†
#
‡
†
†
†
†
†
‡
ǁ,┴
#
,†
†Department of Electrical and Computer Engineering, University of Toronto, 10 King’s College Road, Toronto, Ontario
M5S 3G4, Canada
‡Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ontario
M5S 3G8, Canada
§Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S
3
E4, Canada
ǁDepartment of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3G4, Canada
#
Division of Physical Sciences and Engineering, Advanced Membranes and Porous Materials Center, Functional Mate-
3
rials Design, Discovery and Development Research Group (FMD ), King Abdullah University of Science and Technolo-
gy (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia
┴Department of Pharmaceutical Sciences, University of Toronto, Leslie Dan Faculty of Pharmacy, 144 College Street,
Toronto, Ontario M5S 3M2, Canada
KEYWORDS: Metal-organic framework, CO reduction, Paddle-wheel Cu dimer, Cu cluster, Coordination number
2
ABSTRACT: The electrochemical carbon dioxide reduction reaction (CO
with a judiciously-controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity,
activity, and efficiency for CO RR. Here we report a strategy involving metal-organic framework (MOF)-regulated Cu cluster
formation that shifts CO electroreduction toward multiple-carbon product generation. Specifically, we promoted underco-
2
RR) produces diverse chemical species. Cu clusters
2
2
ordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters.
We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by sepa-
rating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we
modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramag-
netic resonance (EPR) and in-situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clus-
ters with low CN from distorted Cu dimers in HKUST-1 during CO
2
electroreduction. These exhibited 45% C
2
4
H Faradaic
efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure-activity relationship was established wherein the
tuning of the Cu-Cu CN in Cu clusters determines the CO RR selectivity.
2
INTRODUCTION
The surface structure of materials is a critical factor in
determining the reaction pathway. The surface structure
can be understood through the coordination number (CN),
8,9
The electrochemical carbon dioxide reduction reaction
CO RR) enables the storage of renewable energy in chem-
ical form: it reduces CO to products such as carbon mon-
(
2
the number of nearest neighbor atoms. In CO
2
RR, surface
2
coordination control is crucial to CO activation and inter-
2
oxide (CO), methane (CH
4
), ethylene (C
2
H
4
), formate
-
1
mediate stabilization, related ultimately to product selec-
tivity. Theoretical studies have predicted product distribu-
tions by using Cu CN as a descriptor and calculating the
energy of the intermediates: Cu-nanoparticle-covered Cu
(HCOO ), ethanol (C
2
H
5
OH), and propanol (C
3
H
7
OH). Cop-
per (Cu) is capable of forming all of these chemicals, and
efforts have been invested to increase the selectivity of
value-added C2+ hydrocarbons. From a materials view-
point, product selectivity is influenced by the surface struc-
films with a low surface Cu CN show a higher C
2
4
H FE than
ture, oxidation states,3 grain boundaries, vacancies,
2
4
5
an electropolished or sputtered uniform Cu surface due to
2
,10
6
7
high CHO* coverage. Undercoordinated edge and corner
nanostructured morphology, and pore size .
11
sites on Cu surfaces are more active for C-C coupling.
ACS Paragon Plus Environment

Page 3 of 17
Journal of the American Chemical Society
Compared to films, clusters and nanoparticles exhibit
ylate groups of HKUST-1 generate a 3D structure with
open pore sites (distance between benzene derivatives: 9
Å) and a periodic arrangement of Cu cations. The structure
and elemental composition of as-prepared HKUST-1 in this
work were investigated using scanning electron microsco-
py (SEM) and transmission electron microscopy (TEM)
(Figure 1b-e). The HKUST-1 crystals are symmetric octa-
hedra with flat faces. TEM bright field and high angle annu-
lar dark field (HAADF) images of as-prepared HKUST-1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
high surface-to-volume ratios and high turnover frequen-
cies. As particle size decreases, surfaces tend to bind in-
termediates more strongly than on larger particle surfaces
9
because of d-band narrowing. It has been reported that
hydrocarbon formation was inhibited, and H and CO for-
2
mation promoted, as the nanoparticle diameter decreased
below 5 nm, a regime in which the ratio of low Cu-Cu CN
(
CN < 8) is high.12 Therefore, to achieve high selectivity for
C2 hydrocarbons, it is of interest to optimize the surface
topography and the size of Cu clusters to influence inter-
mediate reaction pathways.
before CO RR and before immersion in high pH solution
2
confirm a homogeneous atomic distribution without ag-
glomerated nanoparticles. The distribution of Cu, C, and O
in TEM energy dispersive spectroscopy (EDS) mapping
matched well with the shape of HKUST-1.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Here we shift CO electroreduction in Cu clusters toward
2
multiple-carbon product generation by promoting under-
coordinated Cu sites using metal-organic frameworks
To modify the symmetric structure of the Cu dimer in
HKUST-1, we attempted to increase the accessibility of the
pentacoordinate Cu atomic center in the paddle-wheel SBU
via thermal treatment. The calcination temperature was
determined from the thermal behavior of HKUST-1 via
thermogravimetric analysis (TGA) in air (Figure 1f). The
weight percent of HKUST-1 (gray line) decreased to 75%
at 200ºC which was attributed to dehydration of physically
adsorbed water in the Cu SBU. When the temperature in-
creased to above 300ºC, 45% mass was lost abruptly with a
total enthalpy of 5965 J/g. The second thermogravimetric
transition occurred at 307ºC with the derivative thermo-
gravimetric (DTG) peak at 324ºC and differential scanning
calorimetry (DSC) exothermic peak at 334ºC (blue and
green line). Abrupt mass loss near 300ºC was attributed to
MOF decomposition (organic combustion) under air.22
(MOFs). MOFs have received increased attention as a class
of crystalline porous materials since they offer a platform
to systematically control the metal site environment and
13,14
porosity.
Controllable pore size/shape, high surface
area, chemical tunability, Lewis acidity, and the open metal
site of MOFs offer avenues to optimize selectivity, activity
and efficiency.1
5–18
Recently, it was reported that Cu clus-
ters form from Cu ions in MOFs and organometallic cata-
1
9
lysts during CO
the CO RR performance of Cu-based MOFs and organome-
tallic catalysts, finding that a major CO RR product of
2
RR. Previous authors have investigated
2
2
1
9
HKUST-1 MOF was hydrogen (H ).
2
In this work, we distort the paddle-wheel structure of the
Cu dimer in HKUST-1 MOF and apply this to modulate the
surface structure of Cu clusters. Controlled calcination
maintains overall MOF crystallinity while detaching car-
boxylate moieties from the Cu dimer in a stepwise manner.
This process allows control over the Cu electronic configu-
ration, local atomic structure, and bonding strain toward
an asymmetric motif, as revealed using Electron Paramag-
netic Resonance (EPR). We utilized in-situ X-ray absorp-
tion spectroscopy (XAS) to track the CN of Cu clusters dur-
The phase and structural changes in HKUST-1 upon
thermal treatment were characterized using X-ray diffrac-
tion (XRD) and SEM (Figure 1g, h). The XRD peak of as-
prepared HKUST-1 matched well with the simulated XRD
23
pattern. When the sample was calcined at 250ºC, no
phase and morphology changes in HKUST-1 were observed.
However, when the temperature increased to 300ºC, the
ing electrochemical CO
2
RR cell operation. Undercoordinat-
XRD peaks for a mixture of Cu O and CuO were detected
2
ed site-promoted Cu clusters from the distorted Cu dimer,
enabling us to increase the Faradaic efficiency (FE) for
while the peaks for the HKUST-1 phase disappeared, indi-
cating that the MOF phase was converted to crystalline Cu
oxide phases. When we increased the temperature to
400ºC, pure CuO nanocrystals with a particle size of ~ 100
nm were formed. Based on these results, 250ºC was chosen
as the temperature at which to distort the symmetric Cu
dimer by detaching carboxylate moieties for catalytic site
activation (Figure 1g).
ethylene (C
decreasing H
insights into the utilization of MOFs as a mediator to modi-
fy the surface structure of Cu clusters for CO RR catalysts;
2
H
4
) from 10% to 45% while simultaneously
2
generation to below 7%. This work provides
2
and it suggests an important role for reticular chemistry in
electrocatalysis.
Materials Characterization vs. Calcination Time. To
modulate the degree of Cu dimer distortion, we kept the
calcination temperature at 250ºC and varied the calcina-
tion isothermal time from 1 to 10 hours. Figure 2 displays
the effect of calcination isothermal time on the crystallinity
and the bonding nature of HKUST-1. With longer calcina-
tion times, the color of HKUST-1 powder changed from
light blue to dark green (Figure S2), while major XRD
peaks for HKUST-1 were maintained even following 10 h
thermal treatment (Figure 2a). Interestingly, the (111)
plane peak began to disappear after 3 h calcination and the
crystallinity of (200) plane decreased (peak intensity de-
crease) at the 10 h mark. 250ºC 1 h calcination shifted the
overall diffraction pattern of HKUST-1 by 0.2º to a higher
angle. However, as
RESULTS AND DISCUSSION
HKUST-1 Synthesis and Thermal Treatment. HKUST-1
(C18
H
6
Cu
tricarboxylate) was fabricated by reacting Cu nitrate
Cu(NO ) and trimesic acid (C , benzene-1,3,5-
3
O
12
,
Cu
3
(btc)
2
∙xH
2
O,
btc=benzene-1,3,5-
(
3
)
2
9
H
6
O
6
20
tricarboxylic acid) in methanol at room temperature. The
secondary building unit (SBU) of HKUST-1 is a paddle-
wheel Cu dimer motif in which the distance between Cu
metal nodes is 2.65 Å (Figure 1a).21 Cu cations in the dimer
are stabilized by the four oxygen atoms of four carboxylate
groups. Cu acetate (CuAc, Cu(CH
3
COO) ) and HKUST-1 are
2
each composed of a paddle-wheel Cu dimer as SBU; but
with acetate pendant groups for CuAc as opposed to ben-
zene tricarboxylates in HKUST-1. The benzene tricarbox-
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 1. (a) Comparison of paddle-wheel structured HKUST-1 vs. CuAc. Structural investigations of as-fabricated HKUST-1
by (b) SEM, (c) TEM bright field image, (d) TEM HAADF, and (e) TEM EDS. (f) TGA of HKUST-1 reveals optimal calcination
temperature region where Cu dimer distortion is possible while maintaining the MOF structure. (g) XRD analysis to investi-
gate the phase of HKUST-1 according to the calcination temperatures. (h) SEM images displaying the structures of HKUST-1
after the calcination.
the calcination time increased to 3 and 10 h, the overall
diffraction pattern of calcined HKUST-1 was shifted by 0.2
was possible only in HKUST-1. It also showed a more sta-
ble thermal behavior than CuAc.
~
0.3º to a lower angle compared to that of as-prepared
FT-IR spectroscopy and Raman analysis were performed
to investigate the bonding features of organics in HKUST-1
using the isothermal time at 250ºC calcination. The FT-IR
peak (Figure 2c) wave numbers for the symmetric vibra-
2
4
HKUST-1 (Table S1). Examination of the crystal structure
of HKUST-1 revealed that a majority of the paddle-wheel
Cu dimers are positioned within the (111) plane (Figure
2
b). Crystallinity loss of the (111) plane can be interpreted
-1
tion mode of C=O (1618 cm ), asymmetric vibration mode
as structural distortion and ordering loss in the Cu dimers
of the paddle-wheel SBU. Compared to HKUST-1, CuAc
showed different phase transformation behavior upon
calcination (Figure S4). The transition temperature for Cu
oxide was lower than in HKUST-1 (300 → 250ºC). CuAc
changed to Cu oxide when isothermally treated at a con-
stant temperature.25 Although each has a similar SBU, the
control of crystallinity of a specific plane by calcination
-1
of O=C-O (1645, 1440 cm ), symmetric vibration mode of
-1
-1
O=C-O (1370 cm ), vibration mode of C-O (1114 cm ) and
-1
the vibration mode of phenyl (752, 729 cm ) were identi-
cal for both as-prepared and calcined samples (1, 3, 10
26–28
h).
The presence of major peaks for the C=C symmetric
stretch of the benzene ring, C-H bend, Cu-O stretch were
observed in the Raman spectra of both as-prepared and
calcined HKUST-1 (Figure 2d), confirming that the main
frame and
ACS Paragon Plus Environment

Page 5 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 2. (a) XRD analysis of HKUST-1 calcined at 250ºC. As the isothermal time increases, the (111) plane crystallinity de-
creases. (b) Schematic of HKUST-1 to investigate the atomic arrangement in the (111) plane. (c) FT-IR analysis to relate
HKUST-1 atomic bonding with isothermal calcination time at 250ºC. The spectra reveal that HKUST-1 structures are main-
tained following calcination. (d) Raman analysis to investigate the difference in the structural symmetry and bonding in
HKUST-1 as a function of isothermal calcination time at 250ºC. The spectra indicate that carboxylate groups are detached
from Cu after calcination.
organic bonding of HKUST-1 were maintained at
tron spin induced by a magnetic field (Zeeman effect).31,32
The EPR signal and related parameters provide the infor-
mation on the local atomic structure of a metal site: the
unpaired electrons are directly affected by the atomic dis-
tance, bonding strain, and oxidation state. Cu 2+ exhibits a
2
7,29,30
2
50ºC.
However, the relative peak intensity of the
symmetric stretch in O=C-O decreased and the asymmetric
stretch of O=C-O disappeared as the calcination isothermal
time increased from 1 h to 10 h. Also, the full width at half
maximum (FWHM) associated with the C=C symmetric
stretch of the benzene ring peak and C-H bend peak in-
creased with decreasing peak intensity. Considering the
atomic bonding nature of HKUST-1, we propose that car-
boxylic moieties are sequentially detached in the thermal
activation process.
9
d-orbital electron configuration of d , spin state of S=1/2,
and axial EPR spectrum (g = g < g ). The electronic struc-
1
2
3
ture of Cu dimers (oxidation state: 2+) in the paddle-wheel
structures of HKUST-1 is in the antiferromagnetic singlet
state (opposite spin direction of unpaired electron in dx2-y2
orbital) and the wave function is delocalized to the carbox-
2
4,33
ylate group.
HKUST-1 Cu Dimer Distortion. For detailed verification
of Cu dimer atomic site modulation as a function of the
degree of carboxylic moiety detachment, we used EPR, X-
ray photoelectron spectroscopy (XPS), and SEM (Figure 3).
EPR spectroscopy evaluates the unpaired electrons in
atomic orbitals by detecting the magnetic moment of elec-
The ground state of the electron configuration in as-
prepared HKUST-1 was confirmed via EPR (Figure 3a). The
Cu 2+ oxidation state of the dimer agrees with that deter-
mined
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. Effect of thermal calcination on the electron configuration and local atomic structure of paddle-wheel structured
Cu dimer in HKUST-1. The distortion of symmetric Cu dimer toward the asymmetric structure was verified by EPR and XPS.
Surface structure of HKUST-1 was investigated by SEM. They were compared according to the degree of thermal calcination.
(a-c) as-prepared HKUST-1, (d-f) 250ºC 1 h calcined HKUST-1, (g-i) 250ºC 3 h calcined HKUST-1, and (j-l) 250ºC 10 h cal-
cined HKUST-1.
using XPS (Figure 3b). SEM images of the as-prepared
HKUST-1 show a uniform surface (Figure 3c). Following 1
h calcination at 250ºC, the EPR signal intensity of HKUST-1
increased and the peak became sharper compared to the
as-prepared HKUST-1 (Figure 3d). Compared to the EPR
1+.34,35 This Cu 1+ oxidation state generation can be ob-
served in the Raman analysis. In Figure 2d, a Cu-O bonding
-1
peak of Cu 1+ around 600 cm was observed in 250ºC 3 h,
3
6
10 h calcined HKUST-1. Also, the X-ray absorption near
edge structure (XANES) of HKUST-1 reveals that the Cu
oxidation state was reduced with increasing isothermal
time of 250ºC calcination (Figure S5). Based on SEM imag-
es for surface structure investigation, we conclude that a
porous structure was generated at the surface of HKUST-1
(Figure 3i, l). Overall, the isothermal time at 250ºC controls
the local atomic structure and electron configuration of Cu
atoms toward asymmetric paddle-wheel dimer. Since this
EPR signal trend was not observed in CuAc, this Cu dimer
distortion is specific to the HKUST-1 MOF (Figure S6).
signal of as-prepared HKUST-1, both the g
1
and the g fac-
2
tor increased (Table S2). Considering the identical XPS
peak positions of Cu 2p1/2, 2p3/2, and the satellite for cal-
cined vs. as-prepared HKUST-1, the increase of the un-
paired electron character in the Cu dimer can be explained
by a change in the atomic distance and bonding strain
(
Figure 3e). The structure of HKUST-1 calcined at 250ºC
for 1 h was similar to that of the as-prepared one (Figure
f). Interestingly, as the isothermal time increased over 3 h,
the EPR signal intensity and g factor increased (g > g
3
1
1
2
)
In-situ XAS for Tracking Cu Cluster CN. In order to study
the effect of Cu dimer distortion upon pre-thermal treat-
ment on Cu cluster CN, we performed real-time catalyst
with decreased peak width compared to as-prepared and 1
h calcined HKUST-1 (Figure 3g, j). This EPR signal sharpen-
ing indicates the transition from antiferromagnetic to fer-
romagnetic states by increased unpaired electrons with
parallel spin direction. This Cu dx2-y2 orbital energy level
transition correlates with a change in the atomic environ-
ment to the asymmetric Cu dimer motif. The EPR peak in-
tensity was higher in the 3 h than 10 h calcination. The
shoulder at a magnetic field of 3250 G appeared and indi-
cated structural distortion to asymmetric Cu dimer. The
XPS peak width of Cu 2p1/2, 2p3/2 in 3 h and 10 h calcined
HKUST-1 increased compared to that of the as-prepared
and 1 h conditions. The shape of the Cu 2+ satellite peak
changed to a single feature related with the ‘shake up’
phenomenon (Figure 3h, k). This reveals that the Cu oxida-
tion state in HKUST-1 was partially reduced from 2+ to
characterization using in-situ XAS under CO
2
RR conditions
(Figure 4). The dependence of the Cu oxidation states,
bonding distance and CN of Cu-Cu and Cu-O on the thermal
activation conditions were evaluated using XANES and
extended X-ray absorption fine structure (EXAFS). We
found that the Cu ion in HKUST-1 was reduced to metallic
Cu clusters during CO
with recently reported results (Figure S7-S11).
2
RR testing conditions, consistent
19
Interestingly, the in-situ EXAFS data showed that the Cu-
Cu CN of the Cu cluster was strongly dependent on the de-
gree
ACS Paragon Plus Environment

Page 7 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 4. In-situ EXAFS for tracking the real-time atomic structure of HKUST-1 derived Cu clusters during CO RR. EXAFS
2
spectra were recorded according to the reaction time at the constant potential of -1.38 V vs. RHE (non-iR corrected) in 1M
KOH, each spectrum was collected with a duration of 9 s. (a) as-prepared HKUST-1, (b) 250ºC 1 h calcined HKUST-1, (c)
2
50ºC 3 h calcined HKUST-1, (d) 250ºC 10 h calcined HKUST-1.
of Cu dimer distortion in HKUST-1 (Table S3). In as-
prepared HKUST-1, the Cu dimer started to reduce to Cu
clusters, and the Cu-Cu CN increased gradually toward 12
with decreasing Cu-O CN as the reaction continued to run
to the case of HKUST-1, agglomerated Cu was found in
CuAc following CO RR (Figure S20).
2
In sum, for HKUST-1, the Cu dimer was distorted to the
asymmetric motif by thermal treatment. As the Cu dimer
was distorted, the Cu-Cu CN of Cu cluster remained low
(Figure 4a). The average Cu-Cu CN of the Cu cluster during
the first 900 s reaction was 11.2 ± 0.6. In the 250ºC 1 h
calcined HKUST-1, the average Cu-Cu CN of Cu cluster was
reduced to 10.7 ± 0.7 (Figure 4b). The 250ºC 3 h calcined
HKUST-1, which showed the asymmetric Cu dimer in EPR,
formed the lowest average Cu-Cu CN of 9.5 ± 0.9 in the Cu
cluster (Figure 4c). When the isothermal time of 250ºC
calcination increased to 10 h, the Cu-Cu CN of Cu cluster
increased to 10.5 ± 0.8 (Figure 4d). The formation of Cu
clusters by the reduction of Cu ions in HKUST-1 and the
change of Cu-Cu CN were confirmed using in-situ XAS. In
ex-situ XAS and XPS experiments (Figure S12, S13), the Cu
oxidation number was the same 2+ before and after the
reaction.37 The ex-situ XAS measurements of oxidized Cu
suggest that the Cu is readily oxidized in air, which is con-
sistent with the reactivity of small-sized clusters. There
was no agglomeration of Cu clusters in SEM after the
during CO RR. However, in CuAc, the Cu dimer was not
distorted by pre-thermal treatment. Instead, as the degree
of pre-thermal treatment increased, the Cu-Cu CN of Cu
2
during CO
2
RR increased. This behavior is due to accelerat-
ed Cu cluster agglomeration by pre-thermal treatment
-
38
induced CH COO decomposition in CuAc. We propose
3
that the surface structure of Cu clusters is controlled only
in HKUST-1 (Cu dimer with benzene tricarboxylates) and
that the low Cu-Cu CN of Cu clusters from 250ºC calcined
HKUST-1 may be explained by the regulating role of organ-
39
ic molecules in the MOF.
CO
2
RR Activity Evaluation. The electrochemical CO RR
2
activity of HKUST-1 was evaluated in a flow cell configura-
4
0
tion using 1M KOH electrolyte. Figure 5 shows the de-
pendence of CO RR performance on the thermal activation
process. In as-prepared HKUST-1, H was generated with
over 20% FE. The main product of CO RR was CO and the
FE was limited to 10%. Additionally, a relatively large
amount of CH was produced with the maximum FE of 15%
Figure 5a). The liquid products of HKUST-1 after CO RR
2
2
CO RR in 250ºC calcined HKUST-1 (Figure S14, S15). Con-
2
2
sidering the in-situ and ex-situ characterization of HKUST-1,
C
2
H
4
the Cu cluster size formed from the reduction of Cu dimer
4
19
in HKUST-1 during CO
In the case of CuAc, it was found that the average Cu-Cu CN
during CO RR increased continuously as a function of the
degree of pre-thermal treatment (Figure S19). In contrast
2
RR was expected to be very small.
(
2
included ethanol, acetate, and formate (Figure S25, S26). In
the 250ºC 1 h
2
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 5. Investigation about the effect of Cu dimer distortion and coordination control on CO RR activity of HKUST-1 de-
2
rived Cu clusters. CO reduction product analysis at 1M KOH operation of (a) as-prepared HKUST-1, (b) 250ºC 1 h calcined
2
HKUST-1, (c) 250ºC 3 h calcined HKUST-1, (d) 250ºC 10 h calcined HKUST-1. (e) Comparison of the CO
CuAc (200ºC 1 h calcined) derived Cu and HKUST-1 (250ºC 3 h calcined) derived Cu.
2
RR activity between
calcined HKUST-1, the C
decreased to 7% at all potentials (-0.59 ~ -0.99 V vs. RHE).
CH FE was suppressed to less than 1% (Figure 5b). In the
HKUST-1 calcined at 250ºC for 3 h with the lowest Cu-Cu
2
H
4
FE increased to 35% and H
2
FE
ed sites in Cu clusters increased C
pressing H , CO, and CH production. When the detachment
degree of the benzene tricarboxylate group increased be-
yond the 250ºC 3 h condition, CO RR performance declined
(Figure S27). The CO RR performance improvement by
2
H
4
formation while sup-
2
4
4
2
CN of 9.5 ± 0.9, C
with the current density of 262 mA/cm at -1.07 V vs. RHE
2
H
4
FE was further enhanced up to 45%
2
2
catalytic site activation in reticular chemistry-based mate-
rials is confirmed when one compares the performance of
(Figure 5c). This value is the highest C
2
4
H FE reported
among Cu organometallic and MOF based Cu catalysts to
HKUST-1 and CuAc. The C
higher than CuAc (Figure 5e).
To summarize: the distortion of the Cu dimer in HKUST-1
using thermal energy improved the CO RR performance of
2
H FE of HKUST-1 was up to 20%
4
date (Table S5).1
9,26,37,41–43
When the calcination time in-
FE slightly decreased and H FE
creased to 10 h, the C
2
H
4
2
increased slightly (Figure 5d). Promoting undercoordinat-
2
ACS Paragon Plus Environment

Page 9 of 17
Journal of the American Chemical Society
was verified by XRD with Rigaku MiniFlex 600 diffractom-
Cu clusters, and this enhanced performance was found to
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
be closely related to maintaining a low Cu-Cu CN among
the Cu clusters during the reaction.
eter using Copper Kα radiation (λ=1.5406 Å). XPS for Cu
oxidation state (Cu 2p) investigation was carried out by
Thermo Scientific Al Kα source XPS system with a spot size
of 400 μm. SEM and TEM analysis for HKUST-1 structure
characterization was carried out by Hitachi FE-SEM S-5200
and Hitachi CFE-TEM HF3300. FT-IR was carried out by
Thermo Scientific iS50 with the spectral range of 4600-50
CONCLUSION
In this work, we report a strategy to optimize the CO RR
2
activity of Cu clusters by promoting undercoordinated Cu
sites with the aid of a MOF. This performance tuning was
realized by distorting the symmetric paddle-wheel Cu di-
mer of HKUST-1 to the asymmetric motif using thermal
treatment. The Cu dimer distortion was achieved by sepa-
rating the benzene tricarboxylate moieties. By varying the
calcination isothermal time and keeping the calcination
temperature at 250ºC, we controlled the distortion of
HKUST-1 SBU while maintaining the HKUST-1 structure.
The control of local atomic structure, bond strain, and elec-
tron configuration of the asymmetric Cu dimer motif were
closely related to maintaining a low Cu-Cu CN in MOF-
derived Cu clusters during the reaction. Using this method,
-1
cm . Raman analysis was carried out by a Renishaw mi-
croscope with the 535 nm laser. The power was 0.1% ans.
-1
and we scanned from 100 to 3200 cm . Each scan was tak-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
en in 10 seconds and we repeated the measurement for 6
times. The spectrum is the average of 6 scans.
EPR Measurement. The local atomic structures of the
paddle-wheel Cu dimer in HKUST-1 and CuAc were meas-
ured by EPR. It was carried out by Bruker ECS-EMX X-band
EPR spectrometer at the room temperature of 300K. DPPH
(2,2-diphenyl-1-picrylhydrazyl) was used for standardiza-
tion of the peak position and intensity of the EPR signal. It
has been measured by field sweep mode and modulation
amplitude was 4G. According to the order of as-prepared,
250ºC 1 h, 250ºC 3 h, 250ºC 10 h calcined HKUST-1, the
microwave frequency was 9.369 GHz, 9.372 GHz, 9.370
GHz, 9.371 GHz, center field was 3326.5 G, 3329.9 G,
we improved MOF-derived CO
2
RR performance to achieve
a 45% C FE. The coordination control phenomenon is
2
H
4
specific to the MOF, and the phase transformation during
calcination, EPR signal, in-situ XAS, and catalytic perfor-
mance were appreciably unique for HKUST-1 vs. CuAc.
This work suggests additional avenues to explore metal-
3
5
328.85 G, 3330.05 G, and sweep width was 5347.2 G,
340.0 G, 5340.0 G, 5340.0 G. The g factor and g strain
organic heterogeneous catalysts in CO RR.
2
were calculated by fitting the EPR signal with MATLAB
based EasySpin program (‘pepper’ function: calculation of
field-swept solid-state cw EPR spectra for powders).
EXPERIMENTAL SECTION
Cu Dimer Distorted HKUST-1 Fabrication. HKUST-1
Cu Cu (btc) ∙xH O, btc=benzene-1,3,5-
tricarboxylate) was prepared by reacting Cu nitrate
Cu(NO , Sigma-Aldrich) and trimesic acid (C , ben-
In-situ XAS analysis. XAS measurements at the Cu K-edge
were performed at the 9BM beamline of the Advanced
Photon Source (APS, Argonne National laboratory, IL). In-
situ XAS measurements were performed by using a custom
(C
18
H
6
3
O
12
,
3
2
2
(
3
)
2
9
H
6
O
6
zene-1,3,5-tricarboxylic acid, Sigma-Aldrich). 1.82 g Cu
nitrate was dissolved in 50 mL methanol. 0.875 g trimesic
acid was dissolved in 50 mL methanol. After vortexing to
produce a homogeneous solution, Cu nitrate solution was
transferred to the trimesic acid solution. The mixed solu-
tion was stirred for 2 h at room temperature.20 After stir-
ring, a solution containing HKUST-1 was washed by cen-
trifugation with methanol and vacuum dried. Calcination
proceeded at the furnace under ambient air. To investigate
the phase after thermal treatment of HKUST-1, the calcina-
tion was performed at 250ºC, 300ºC, and 400ºC with a
temperature ramping rate of 10ºC/min. After confirming
the HKUST-1 crystalline phase remained at 250ºC, the iso-
thermal time of calcination was varied to 1 h, 3 h, and 10 h
to control the distortion of the symmetric Cu dimer in
flow cell in 1M KOH electrolyte with CO gas flowing from
2
40
the backside of a gas diffusion layer. In-situ XANES and
EXAFS scan data were collected during the cell operation
mode of chronoamperometry at the potential of -2.4 V vs.
Ag/AgCl (-1.38 V vs. RHE, non-iR corrected), same with the
CO
2
RR activity measurement condition.
Electrochemical CO
2
Reduction. CO RR activities of
2
HKUST-1 and CuAc were measured by performing elec-
trolysis in a flow cell. The cathode was composed of
HKUST-1 catalyst spray-coated gas diffusion layer (GDL,
Sigracet), an anion exchange membrane, and Pt foil as an
anode. The spray coating ink on GDL was made by dispers-
ing HKUST-1 powder in nafion + methanol solution fol-
lowed by sonication. The deposited HKUST-1 mass per
2
area was 0.56 mg/cm . CuAc was prepared on GDL with
HKUST-1. CuAc (Cu(CH
3
COO)
2
∙H
2
O, M =199.65 g/mol,
w
the same method of HKUST-1. 1M KOH electrolyte was
Sigma-Aldrich) was used as a control sample. The calcina-
tion of CuAc was carried out at 200ºC and 250ºC to deter-
mine the temperature at which the CuAc crystalline phase
would deteriorate. It was found that the CuAc crystal struc-
ture remained at a thermal treatment of 200ºC 1 h calcina-
tion.
flowed in the cathode and anode chambers separately. CO
2
gas was flowed behind the GDL with a flow rate of 50 sccm.
Chronoamperometry was performed using an electro-
chemical station (Autolab). The applied potentials of -2.4, -
2
.8, -3.2, -3.6 V vs. Ag/AgCl were tested with as-prepared,
250ºC 1 h, 250ºC 3 h, and 250ºC 10 h calcined HKUST-1.
The electrode potentials were converted to RHE based on
the following equation: ERHE=EAg/AgCl+0.197V+0.059∙pH. A
resistance of 4.2 Ω was used to calculate the iR-correction.
Material Characterization. Thermal behavior of HKUST-1
according to the temperature was investigated by TG/DSC
with simultaneous thermal analyzer (NETZSCH STA 449
F3 Jupiter). The experiment was carried out in air flow (50
ml/min) at a heating rate of 10ºC/min using an initial
HKUST-1 mass of 4.95 mg. The phase of HKUST-1 powder
The collected gaseous products (H
CO RR was analyzed in 1 mL volumes by gas chromatog-
raphy (PerkinElmer Clarus 600) with a thermal conductivi-
2
, CO, CH
4
, C
2
H
4
) during
2
ACS Paragon Plus Environment

Journal of the American Chemical Society
ty detector (TCD) and a flame ionization detector (FID).
Page 10 of 17
(1)
Liu, M.; Pang, Y.; Zhang, B.; De Luna, P.; Voznyy, O.; Xu, J.;
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
The number of moles of gas products were calculated from
the gas chromatograph peak area. Liquid products were
analyzed by H NMR (Agilent DD2 500 spectrometer) in 10%
Zheng, X.; Dinh, C. T.; Fan, F.; Cao, C.; de Arquer, F. P. G.; Safaei, T.
S.; Mepham, A.; Klinkova, A.; Kumacheva, E.; Filleter, T.; Sinton, D.;
Kelley, S. O.; Sargent, E. H. Nature 2016, 537, 382-386.
1
(
2)
20, 28125–28130.
(3) Mistry, H.; Varela, A. S.; Bonifacio, C. S.; Zegkinoglou, I.;
Zhao, Z.; Chen, Z.; Zhang, X.; Lu, G. J. Phys. Chem. C 2016,
D
2
O water suppression mode, with dimethyl sulfoxide
1
(DMSO) as an internal standard.
Sinev, I.; Choi, Y.-W.; Kisslinger, K.; Stach, E. A.; Yang, J. C.; Strasser,
P.; Cuenya, B. R. Nat. Commun. 2016, 7, 12123.
ASSOCIATED CONTENT
(
4)
016, 2, 169–174.
5) Zhuang, T.-T.; Liang, Z.-Q.; Seifitokaldani, A.; Li, Y.; De
Feng, X.; Jiang, K.; Fan, S.; Kanan, M. W. ACS Cent. Sci.
Supporting Information. This material is available free of
charge via the Internet at http://pubs.acs.org.
2
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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.;
Yu, S.-H.; Sargent, E. H. Nat. Catal. 2018, 1, 421-428.
Detailed information about material characterization, EPR
analysis, in-situ XANES, EXAFS analysis, CO RR activity meas-
2
urement of HKUST-1 and CuAc, including Figures S1-S29, and
Tables S1-S5.
(
6)
De Luna, P.; Quintero-Bermudez, R.; Dinh, C.-T.; Ross, M.
B.; Bushuyev, O. S.; Todorović, P.; Regier, T.; Kelley, S. O.; Yang, P.;
Sargent, E. H. Nat. Catal. 2018, 1, 103–110.
AUTHOR INFORMATION
(7)
H.; Nam, K. T. Angew. Chemie Int. Ed. 2016, 56, 796–800.
(8) Calle-Vallejo, F.; Tymoczko, J.; Colic, V.; Vu, Q. H.; Pohl,
Yang, K. D.; Ko, W. R.; Lee, J. H.; Kim, S. J.; Lee, H.; Lee, M.
Corresponding Author
Edward H. Sargent
M. D.; Morgenstern, K.; Loffreda, D.; Sautet, P.; Schuhmann, W.;
Bandarenka, A. S. Science 2015, 350, 185–189.
*
E-mail: ted.sargent@utoronto.ca
ORCID
Dae-Hyun Nam: 0000-0002-0871-1355
(9)
Sun, S.; Hensen, E. J. M. Nano Energy 2018, 43, 200–209.
10) Tang, W.; Peterson, A. A.; Varela, A. S.; Jovanov, Z. P.;
Zhang, X.; Liu, J.-X.; Zijlstra, B.; Filot, I. A. W.; Zhou, Z.;
(
Phil De Luna: 0000-0002-7729-8816
Bech, L.; Durand, W. J.; Dahl, S.; Norskov, J. K.; Chorkendorff, I.
Phys. Chem. Chem. Phys. 2012, 14, 76–81.
Ali Seifitokaldani: 0000-0002-7169-1537
Cao-Thang Dinh: 0000-0001-9641-9815
F. Pelayo García de Arquer: 0000-0003-2422-6234
Andrew H. Proppe: 0000-0003-3860-9949
Osama Shekhah: 0000-0003-1861-9226
Christine M. Gabardo: 0000-0002-9456-6894
Jea Woong Jo: 0000-0001-8086-2644
(
11) Hahn, C.; Hatsukade, T.; Kim, Y.-G.; Vailionis, A.;
Baricuatro, J. H.; Higgins, D. C.; Nitopi, S. A.; Soriaga, M. P.;
Jaramillo, T. F. Proc. Natl. Acad. Sci. 2017, 114, 5918-5923.
(
12) Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.;
Strasser, P. J. Am. Chem. Soc. 2014, 136, 6978–6986.
(13) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.;
O'Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469-472.
(14) Liu, G.; Chernikova, V.; Liu, Y.; Zhang, K.; Belmabkhout,
Y.; Shekhah, O.; Zhang, C.; Yi, S.; Eddaoudi, M.; Koros, W. J. Nat.
Mater. 2018, 17, 283–289.
Junghwan Kim: 0000-0003-3017-5330
David Sinton: 0000-0003-2714-6408
(
15) Diercks, C. S.; Liu, Y.; Cordova, K. E.; Yaghi, O. M. Nat.
Mater. 2018, 17, 301–307.
16) Kornienko, N.; Zhao, Y.; Kley, C. S.; Zhu, C.; Kim, D.; Lin,
S.; Chang, C. J.; Yaghi, O. M.; Yang, P. J. Am. Chem. Soc. 2015, 137,
(
Shana O. Kelley: 0000-0003-3360-5359
Mohamed Eddaoudi: 0000-0003-1916-9837
Edward H. Sargent: 0000-0003-0396-6495
1
4129–14135.
(17) Diercks, C. S.; Lin, S.; Kornienko, N.; Kapustin, E. A.;
Nichols, E. M.; Zhu, C.; Zhao, Y.; Chang, C. J.; Yaghi, O. M. J. Am.
Chem. Soc. 2018, 140, 1116–1122.
Notes
The authors declare no competing financial interest.
(
18) Lin, S.; Diercks, C. S.; Zhang, Y.-B.; Kornienko, N.;
Nichols, E. M.; Zhao, Y.; Paris, A. R.; Kim, D.; Yang, P.; Yaghi, O. M.;
Chang, C. J. Science 2015, 349, 1208–1213.
(19) Weng, Z.; Wu, Y.; Wang, M.; Jiang, J.; Yang, K.; Huo, S.;
Wang, X.-F.; Ma, Q.; Brudvig, G. W.; Batista, V. S.; Liang, Y.; Feng, Z.;
Wang, H. Nat. Commun. 2018, 9, 415.
(20) Wu, R.; Qian, X.; Yu, F.; Liu, H.; Zhou, K.; Wei, J.; Huang, Y.
J. Mater. Chem. A 2013, 1, 11126–11129.
ACKNOWLEDGMENTS
This work was supported financially by the Natural Sciences
and Engineering Research Council (NSERC) of Canada (RGPIN-
2
017-06477), the Ontario Research Fund: Research Excel-
lence Program (ORF-RE-RE08-034). This publication is based
upon work supported by the King Abdullah University of Sci-
ence and Technology (KAUST) Office of Sponsored Research
(OSR) under Award No. OSR-2017-CPF-3325-03. This re-
search was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)
(
21) Chui, S. S.-Y.; Lo, S. M.-F.; Charmant, J. P. H.; Orpen, A. G.;
Williams, I. D. Science 1999, 283, 1148–1150.
22) Nam, D.-H.; Lee, S.; Lee, Y.-J.; Jo, J.-H.; Yoon, E.; Yi, K.-W.;
(
Lee, G.-D.; Joo, Y.-C. Adv. Mater. 2017, 29, 1702958.
(23) Yakovenko, A. A.; Reibenspies, J. H.; Bhuvanesh, N.;
Zhou, H.-C. J. Appl. Crystallogr. 2013, 46, 346–353.
funded
by
the
Ministry
of
Education
(
2017R1A6A3A03004826). The authors thank Dr. T. P. Wu, Dr.
(
24) Todaro, M.; Buscarino, G.; Sciortino, L.; Alessi, A.;
Z. Finfrock, Dr. L. Ma for technical support at the 9BM beam-
line of the Advanced Photon Source (Lemont, IL). C.M.G.
acknowledges NSERC for funding in the form of a postdoctoral
fellowship.
Messina, F.; Taddei, M.; Ranocchiari, M.; Cannas, M.; Gelardi, F. M.
J. Phys. Chem. C 2016, 120, 12879–12889.
(
25) Lin, Z.; Han, D.; Li, S. J. Therm. Anal. Calorim. 2012, 107,
471–475.
(26) Albo, J.; Vallejo, D.; Beobide, G.; Castillo, O.; Castaño, P.;
Irabien, A. ChemSusChem 2016, 10, 1100–1109.
REFERENCES
ACS Paragon Plus Environment

Page 11 of 17
Journal of the American Chemical Society
(
27) Dhumal, N. R.; Singh, M. P.; Anderson, J. A.; Kiefer, J.;
Kim, H. J. J. Phys. Chem. C 2016, 120, 3295–3304.
28) Toyao, T.; Liang, K.; Okada, K.; Ricco, R.; Styles, M. J.;
(36) Gan, Z. H.; Yu, G. Q.; Tay, B. K.; Tan, C. M.; Zhao, Z. W.; Fu,
Y. Q. J. Phys. D. Appl. Phys. 2004, 37, 81-85.
(37) Weng, Z.; Jiang, J.; Wu, Y.; Wu, Z.; Guo, X.; Materna, K. L.;
Liu, W.; Batista, V. S.; Brudvig, G. W.; Wang, H. J. Am. Chem. Soc.
2016, 138, 8076–8079.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
Tokudome, Y.; Horiuchi, Y.; Hill, A. J.; Takahashi, M.; Matsuoka, M.;
Falcaro, P. Inorg. Chem. Front. 2015, 2, 434–441.
(
29) Todaro, M.; Alessi, A.; Sciortino, L.; Agnello, S.; Cannas,
(38) Manthiram, K.; Beberwyck, B. J.; Alivisatos, A. P. J. Am.
Chem. Soc. 2014, 136, 13319–13325.
(39) Liu, P.; Qin, R.; Fu, G.; Zheng, N. J. Am. Chem. Soc. 2017,
139, 2122–2131.
M.; Gelardi, F. M.; Buscarino, G. J. Spectrosc. 2016, 2016, 1.
(30) Prestipino, C.; Regli, L.; Vitillo, J. G.; Bonino, F.; Damin,
A.; Lamberti, C.; Zecchina, A.; Solari, P. L.; Kongshaug, K. O.;
Bordiga, S. Chem. Mater. 2006, 18, 1337–1346.
(40) Dinh, C.-T.; Burdyny, T.; Kibria, M. G.; Seifitokaldani, A.;
Gabardo, C. M.; García de Arquer, F. P.; Kiani, A.; Edwards, J. P.; De
Luna, P.; Bushuyev, O. S.; Zou, C.; Quintero-Bermudez, R.; Pang, Y.;
Sinton, D.; Sargent, E. H. Science 2018, 360, 783–787.
(41) Kusama, S.; Saito, T.; Hashiba, H.; Sakai, A.; Yotsuhashi,
S. ACS Catal. 2017, 7, 8382–8385.
(42) Kung, C.-W.; Audu, C. O.; Peters, A. W.; Noh, H.; Farha, O.
K.; Hupp, J. T. ACS Energy Lett. 2017, 2, 2394–2401.
(43) Qiu, Y.-L.; Zhong, H.-X.; Zhang, T.-T.; Xu, W.-B.; Su, P.-P.;
Li, X.-F.; Zhang, H.-M. ACS Appl. Mater. Interfaces 2018, 10, 2480–
2489.
(
31) Ahmad, R.; Kuppusamy, P. Chem. Rev. 2010, 110, 3212–
236.
(32) Junk, M. J. N. Electron Paramagnetic Resonance Theory
BT Assessing the Functional Structure of Molecular
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-
Transporters by EPR Spectroscopy; J.N.Junk, M., Ed.; Springer
Berlin Heidelberg: Berlin, Heidelberg, 2012; pp 7–52.
(
(
Y.; Wӧll, C.; Heine, T. ChemPhysChem 2012, 13, 2025–2029.
(35) Biesinger, M. C.; Lau, L. W. M.; Gerson, A. R.; Smart, R. S.
C. Appl. Surf. Sci. 2010, 257, 887–898.
33) Hendon, C. H.; Walsh, A. Chem. Sci. 2015, 6, 3674–3683.
34) Petkov, P. S.; Vayssilov, G. N.; Liu, J.; Shekhah, O.; Wang,
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 12 of 17
Table of Contents (ToC) Graphic
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
11
ACS Paragon Plus Environment

Page 13 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 1. (a) Comparison of paddle-wheel structured HKUST-1 vs. CuAc. Structural investigations of as-
fabricated HKUST-1 by (b) SEM, (c) TEM bright field image, (d) TEM HAADF, and (e) TEM EDS. (f) TGA of
HKUST-1 reveals optimal calcination temperature region where Cu dimer distortion is possible while
maintaining the MOF structure. (g) XRD analysis to investigate the phase of HKUST-1 according to the
calcination temperatures. (h) SEM images displaying the structures of HKUST-1 after the calcination.
1
70x153mm (300 x 300 DPI)
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 14 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 2. (a) XRD analysis of HKUST-1 calcined at 250ºC. As the isothermal time increases, the (111) plane
crystallinity decreases. (b) Schematic of HKUST-1 to investigate the atomic arrangement in the (111) plane.
(c) FT-IR analysis to relate HKUST-1 atomic bonding with isothermal calcination time at 250ºC. The spectra
reveal that HKUST-1 structures are maintained following calcination. (d) Raman analysis to investigate the
difference in the structural symmetry and bonding in HKUST-1 as a function of isothermal calcination time at
2
50ºC. The spectra indicate that carboxylate groups are detached from Cu after calcination.
1
55x152mm (300 x 300 DPI)
ACS Paragon Plus Environment

Page 15 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. Effect of thermal calcination on the electron configuration and local atomic structure of paddle-
wheel structured Cu dimer in HKUST-1. The distortion of symmetric Cu dimer toward the asymmetric
structure was verified by EPR and XPS. Surface structure of HKUST-1 was investigated by SEM. They were
compared according to the degree of thermal calcination. (a-c) as-prepared HKUST-1, (d-f) 250ºC 1 h
calcined HKUST-1, (g-i) 250ºC 3 h calcined HKUST-1, and (j-l) 250ºC 10 h calcined HKUST-1.
189x102mm (300 x 300 DPI)
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 16 of 17
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 4. In-situ EXAFS for tracking the real-time atomic structure of HKUST-1 derived Cu clusters during
CO RR. EXAFS spectra were recorded according to the reaction time at the constant potential of -1.38 V vs.
2
RHE (non-iR corrected) in 1M KOH, each spectrum was collected with a duration of 9 s. (a) as-prepared
HKUST-1, (b) 250ºC 1 h calcined HKUST-1, (c) 250ºC 3 h calcined HKUST-1, (d) 250ºC 10 h calcined
HKUST-1.
1
83x139mm (300 x 300 DPI)
ACS Paragon Plus Environment

Page 17 of 17
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
Figure 5. Investigation about the effect of Cu dimer distortion and coordination control on CO RR activity of
HKUST-1 derived Cu clusters. CO
HKUST-1, (b) 250ºC 1 h calcined HKUST-1, (c) 250ºC 3 h calcined HKUST-1, (d) 250ºC 10 h calcined
HKUST-1. (e) Comparison of the CO RR activity between CuAc (200ºC 1 h calcined) derived Cu and HKUST-
(250ºC 3 h calcined) derived Cu.
2
reduction product analysis at 1M KOH operation of (a) as-prepared
2
1
1
55x204mm (300 x 300 DPI)
ACS Paragon Plus Environment