Two-Dimensional Covalent Organic Frameworks with Cobalt(II)-Phthalocyanine Sites for Efficient Electrocatalytic Carbon Dioxide Reduction

Article abstract of DOI:10.1021/jacs.1c02145

The rapid development in synthesis methodology and applications for covalent organic frameworks (COFs) has been witnessed in recent years. However, the synthesis of highly stable functional COFs still remains a great challenge. Herein two-dimensional poly

Full text of DOI:10.1021/jacs.1c02145

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Article
Two-Dimensional Covalent Organic Frameworks with Cobalt(II)-
Phthalocyanine Sites for Efficient Electrocatalytic Carbon Dioxide
Reduction
Bin Han, Xu Ding, Baoqiu Yu, Hui Wu, Wei Zhou, Wenping Liu, Chuangyu Wei, Baotong Chen,
Dongdong Qi, Hailong Wang,* Kang Wang, Yanli Chen, Banglin Chen,* and Jianzhuang Jiang*
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ABSTRACT: The rapid development in synthesis methodology and applications for
covalent organic frameworks (COFs) has been witnessed in recent years. However, the
synthesis of highly stable functional COFs still remains a great challenge. Herein two-
dimensional polyimide-linked phthalocyanine COFs (denoted as CoPc-PI-COF-1 and
CoPc-PI-COF-2) have been devised and prepared through the solvothermal reaction of the
tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato cobalt(II) with 1,4-
phenylenediamine and 4,4′-biphenyldiamine, respectively. The resultant CoPc-PI-COFs
with a four-connected sql net exhibit AA stacking configurations according to powder X-ray
diffraction studies, showing permanent porosity, thermal stability above 300 °C, and
excellent resistance to a 12 M HCl aqueous solution for 20 days. Current−voltage curves
reveal the conductivity of CoPc-PI-COF-1 and CoPc-PI-COF-2 with the value of 3.7 × 10−3
and 1.6 × 10−3 S m−1, respectively. Due to the same Co(II) electroactive sites together with
similar permanent porosity and CO2 adsorption capacity for CoPc-PI-COFs, the cathodes made up of COFs and carbon black
display a similar CO2-to-CO Faradaic efficiency of 87−97% at applied potentials between −0.60 and −0.90 V (vs RHE) in 0.5 M
KHCO3 solution. However, in comparison with the CoPc-PI-COF-2&carbon black electrode, the CoPc-PI-COF-1 counterpart
provides a larger current density (jCO) of −21.2 mA cm−2 at −0.90 V associated with its higher conductivity. This cathode also has a
high turnover number and turnover frequency, amounting to 277 000 and 2.2 s−1 at −0.70 V during 40 h of measurement. The
present result clearly discloses the great potential of 2D porous crystalline solids in electrocatalysis.
provides more opportunities to improve their function
diversity.31 However, the synthesis of highly stable functional
COFs is still one of the most challenging subjects due to the
contradictory thermodynamic and kinetic balance involved in
the linkage strength and crystallization process, respectively.
Electrocatalytic carbon dioxide reduction reaction (CO2RR)
to obtain fuels/chemicals is one of the sustainable pathways to
solve the energy crisis and global warming issues.32−38 Toward
implementing electrocatalytic CO2RR applicability, various
homogeneous and heterogeneous catalysts with high con-
version efficiency and selectivity have been developed.35−48
Electrochemical active metal-containing molecular (homoge-
neous) systems have been demonstrated to exhibit low
overpotential through the low-valent active intermediate and
excellent selectivity by the smart tailorability.38 However, the
INTRODUCTION
■
Covalent organic frameworks (COFs) with good crystallinity,
as one kind of important porous organic polymers, have
attracted intensive research interests due to their well-defined
and long-range-order structures in addition to their various
applications such as gas separation and storage, catalysis, and
optoelectronics.1−6 As can be easily expected, the definite
architectures of COFs facilitate the deep understanding of
structure−property correlation at the atomic level.7−9 In
particular, the cofacial packing of two-dimensional (2D)
COFs consisting of conjugated molecular building blocks
linked via the in-plane covalent bonds and interlayer π−π
interactions enables the enhanced stability of this kind of
artificial solids and efficient electron transfer in the
optoelectronics.10−18 To date, great efforts in the field of
COFs have been directed toward target synthesis, theoretical
significance, and practical utilization through developing new
synthetic methodologies and applications. In this regard, the
successful predesign and synthesis strategy enabled by dynamic
covalent chemistry reactions such as imine formation, boronic
acid condensation, boronate ester formation, and so on has
generated a vast range of functional COFs.19−30 Furthermore,
incorporation of metal-coordinating building blocks into COFs
Received: February 24, 2021
Published: May 3, 2021
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facile deactivation, inefficient electron transfer, and organic
media requirement in homogeneous systems for molecular
catalysts restrict their further practical applications. Incorpo-
ration of molecular catalysts with conductive substrates into
heterogeneous systems therefore opens an avenue for electro-
catalytic CO2RR, benefiting the catalytic efficiency, separation,
reusability, and stability.39−42 In recent years, COFs, as one of
the important reticular materials platforms, have been
emerging as ideal heterogeneous candidates for electrocatalysis
by integrating catalytically active molecular components in an
accurate connection manner.33,36 As a consequence, electro-
catalytic active metalloporphyrin molecules have been
incorporated into 2D COFs since 2015, exhibiting excellent
heterogeneous electrocatalytic CO2RR properties.46−50 To-
ward further enhancing the electrocatalytic performance, other
tetrapyrrole analogues, metallophthalocyanines, with excellent
molecular electrocatalytic CO2RR activity were assembled into
2D COFs in 2020,15−17,51,52 affording two series of 2D COFs
based on the only two building blocks of 2,3,9,10,16,17,23,24-
octa(hydroxyl)phthalocyanine and 2,3,9,10,16,17,23,24-octa-
(amino)phthalocyanine (Scheme 1a). In this regard, more in-
resistance to even a 12 M HCl aqueous solution for 20 days. In
particular, the electron conductivity of CoPc-PI-COF-1 and
CoPc-PI-COF-2 amounts to 3.7 × 10−3 and 1.6 × 10−3 S m−1,
respectively. The cathodes fabricated by CoPc-PI-COFs&car-
bon black show a similar high CO2-to-CO Faradaic efficiency
(FECO) of 87−97% at various applied potentials of −0.60 to
−0.90 V (vs reversible hydrogen electrode (RHE)) with an
overpotential (η) of −0.49 to −0.79 V in a 0.5 M KHCO3
solution. The CoPc-PI-COF-1&carbon black electrode pos-
sesses a higher current density (jCO) of −21.2 mA cm−2 at
−0.90 V than the CoPc-PI-COF-2-derived electrode associated
with its higher electron conductivity. In addition, the turnover
number (TON) of the CoPc-PI-COF-1 cathode is accumu-
lated to 277 000 with a turnover frequency (TOF) of 2.2 s−1 at
−0.70 V after 40 h of continuous experiment. The present
result clearly discloses the great potential of 2D porous
crystalline solids in electrocatalysis.
EXPERIMENTAL SECTION
■
General Remarks. All regents were commercially available and
directly employed. Co(TAPc) was synthesized referring to the
published procedure.53−57
Synthesis of CoPc-PI-COF-1. A Pyrex tube (9 × 6 mm, o.d. ×
i.d.) was filled with Co(TAPc) (17.0 mg, 0.02 mmol), PD (4.3 mg,
0.04 mmol), N-methylpyrrolidone (NMP) (0.5 mL), 1-butanol (0.5
mL), and isoquinoline (0.05 mL). After sonicating the tube for 10
min followed by flash freezing in a liquid N2 bath, the frozen tube was
degassed and slowly thawed to room temperature. After such a
process was repeated three times, the tube was sealed by flame with a
length of ca. 18 cm. The reaction was performed at 180 °C for 5 days,
generating a black-green precipitate. The solid was isolated via
centrifugation and successively washed with dimethylformamide
(DMF), NMP, and acetone three times. The product was collected
and dried at 100 °C under vacuum overnight to provide a black-green
powder of CoPc-PI-COF-1 (17.1 mg) in a yield of 86% (calculated
based on Co(TAPc)). IR (KBr): 1768, 1712, 1671, 1515, 1357, 1237,
1127, 736, 690 cm−1. The Co content of 3.7 wt % in CoPc-PI-COF-1
was determined by inductively coupled plasma−optical emission
spectrometry (ICP-OES).
Scheme 1. (a) Structures of Building Blocks (M = 2H and
Metal): 2,3,9,10,16,17,23,24-Octa(hydroxyl/amino)
Phthalocyanines (i and ii); Tetraanhydrides of
2,3,9,10,16,17,23,24-Octacarboxyphthalocyanine (iii); (b)
Synthesis of CoPc-PI-COF-1 and CoPc-PI-COF-2
Synthesis of CoPc-PI-COF-2. By employing the above-
mentioned procedure for preparing CoPc-PI-COF-1 using BD (7.4
mg, 0.04 mmol) instead of PD as starting material, a black-green
powder of CoPc-PI-COF-2 (20.2 mg, a yield of 88% calculated based
on Co(TAPc)) was obtained. IR (KBr): 1769, 1713, 1671, 1497,
1367, 1237, 1129, 736, 619 cm−1. The Co content in CoPc-PI-COF-2
was determined by ICP-OES with a value of 3.3 wt %.
Carbon Dioxide Electrocatalytic Reduction Measurement.
Before the fabrication of the electrode, a vial containing unsubstituted
phthalocyaninato cobalt(II) compound (CoPc) or CoPc-PI-COFs
(10.0 mg), Ketjen carbon black (10.0 mg), a Nafion perfluorinated
resin solution (Sigma-Aldrich, 30 μL, 10 wt %), and ethanol (1.0 mL)
was sonicated for 60 min to prepare a homogeneous paste. It is worth
noting that the mixture of catalyst and carbon black was ground prior
to sonication. The electrode was fabricated by evenly transferring the
paste (100.0 μL) with a micropipet on a carbon fiber paper (1.0 × 1.0
cm2, TGP-H-60), ensuring a CoPc-PI-COFs loading density of 1.0
mg cm−2. The paper electrode was dried at room temperature
overnight. The experiments for CO2 electrochemical reduction were
conducted in an H-type electrochemical cell consisting of two
compartments separated by an anion exchange membrane (Nafion-
117) on the electrochemical instrument (chi760E) at 25 °C in an air-
conditioned room. Two compartments contained 50.0 mL of
electrolyte (0.5 M KHCO3 aqueous solution) with Pt foil and a
Ag/AgCl electrode in the saturated KCl solution as counter electrode
and reference electrode, respectively. Prior to the electrochemical
measurements, the electrolyte solution was saturated with Ar and CO2
for 30 min. Linear sweep voltammetry (LSV) was operated with a
scan rate of 10 mV s−1 from 0 to −1.63 V vs Ag/AgCl in the CO2-
depth systematical studies toward the exploration of new
molecular building blocks, connection mode, and structure−
function correlation are certainly significant for the rational
design and synthesis of COFs with desired properties.
Herein, a new kind of phthalocyanine building block,
namely, tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxy-
phthalocyanine, were employed toward fabricating new
reticular materials for the first time, Scheme 1a. Reaction of
tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalo-
cyaninato cobalt(II) (Co(TAPc)) with 1,4-phenylenediamine
(PD) and 4,4′-biphenyldiamine (BD), respectively, generates
two 2D polyimide (PI) COFs, denoted as CoPc-PI-COF-1 and
CoPc-PI-COF-2 (Scheme 1b). The robustness of these COFs
is associated with the in-plane rigid imide bonds in a four-
connected square lattice (sql) net and strong π−π interactions
between the AA stacking layers. As a result, CoPc-PI-COFs
display a moderate permanent porosity with a Brunauer−
Emmett−Teller (BET) surface area of 181 and 291 m2 g−1,
good thermal stability above 300 °C, and excellent chemical
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Figure 1. PXRD characterizations of CoPc-PI-COF-1 (a) and CoPc-PI-COF-2 (b): experimental PXRD profile (black), refined profile (red),
difference (orange), and simulation pattern based on the AA stacking manner (cyan). Simulated packing structures of CoPc-PI-COF-1 (c, d) and
CoPc-PI-COF-2 (e, f) via π−π interactions (C: gray; N: cyan; O: red; Co: pink; H: white). SEM, TEM, HRTEM, and EDS mapping photos for
CoPc-PI-COF-1 (g, h, i, j) and CoPc-PI-COF-2 (k, l, m, n).
reticular materials still remain rare, limited to MOF-1992,66
saturated 0.5 M KHCO3 electrolyte (pH = 7.3). In this work, all
CoPc-PDQ-COF,51 MPc-TFPN-COF,52 and MPc-M′-X ser-
mentioned potentials were converted to an RHE scale according to
the equation of E (V vs RHE) = E (vs Ag/AgCl) + 0.059 × pH +
ies,67,68 to the best of our knowledge. As can be found, all the
0.197. During the measurement, CO2 gas at a flow rate of 20 mL
phthalocyanine-involved reticular materials reported thus far
min−1 was transported into the tube, and the product was analyzed by
have been constructed from the 2,3,9,10,16,17,23,24-octa-
gas chromatograph (GC) with the sampling loop (1.0 mL) each 15
(hydroxyl/amino)-substituted phthalocyanine building blocks
(Scheme 1a). Herein, a new phthalocyanine compound,
Co(TAPc), has been used to assemble reticular materials
with the help of the linkers PD and BD, respectively, in NMP
and 1-butanol catalyzed by isoquinoline at 180 °C for 5 days,
Scheme 1b, affording two new 2D PI COFs, CoPc-PI-COF-1
and CoPc-PI-COF-2, with a high yield above 85%. The
resultant COFs with desired porosity and π−π stacking of
metallophthalocyanine-tetraamide units should facilitate sub-
strate diffusion and electron conduction during the electro-
catalytic CO2RR reduction.
Characterization of CoPc-PI-COFs. The structures of the
two CoPc-PI-COFs with high crystallinity were analyzed by
powder X-ray diffraction (PXRD), Figures 1a,b, S1, and S2.
For CoPc-PI-COF-1, there are four obvious diffraction peaks
in its PXRD pattern at 2θ ≈ 4.20°, 8.02°, 11.98°, and 27.01°.
The peak indexing indicates that CoPc-PI-COF-1 is attributed
to the tetragonal system with space group P4/mmm, showing
min. Faradaic efficiency at different potentials was calculated on the
basis of the stable electrocatalytic performance of the CoPc-PI-COFs
electrode monitored by the I−t curve.
RESULTS AND DISCUSSION
■
Design and Fabrication of CoPc-PI-COFs. The imidiza-
tion reaction enables the formation of PI polymers with
excellent thermal stability, chemical resistance, and mechanical
properties.58−60 In addition, the polyimide derivatives,
especially the ones with long-range-order structure (i.e.,
metal−organic frameworks (MOFs) and COFs), have been
widely investigated in the fields of electronics, semiconductors,
and energy storage due to the strong π−π stacking of
conjugated components and redox-active carbonyl sites.61−63
On the other hand, the excellent electrocatalytic CO2RR
properties of metallophthalocyanine compounds have been
demonstrated in recent years.41,64,65 However, examples for
fixation of catalytically active metallophthalocyanine units into
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Figure 2. IR spectra, Co K-edge of EXAFS spectra, and N2 adsorption (solid) and desorption (hollow) curves at 77 K of CoPc-PI-COF-1 (a, c, e)
and CoPc-PI-COF-2 (b, d, f).
the cell parameters a = b = 21.02 Å and c = 3.34 Å. Similar to
the phthalocyanine COFs reported previously, the planar
metallophthalocyanine-tetraamide directs the extension of the
four-connected polyamide sql layer along the a and b axis,
Figure 1c, and an eclipsed AA-stacking of PI-bonded
metallophthalocyanine layers perpendicular to the macrocycle
plane has been built for CoPc-PI-COF-1, Figure 1d. The
simulated PXRD profile deduced from the structural model is
matchable with the experimental curve of CoPc-PI-COF-1,
Figure 1a. The structural model is further verified by the Le
Bail refinement result of CoPc-PI-COF-1 with agreement
factors of Rp = 0.96% and Rwp = 1.24%. As a result, the above-
mentioned four diffraction peaks for CoPc-PI-COF-1 are
assigned to (100), (200), (300), and (001) reflections,
respectively. Compared with CoPc-PI-COF-1, CoPc-PI-COF-
2 constructed from the same phthalocyanine building block
and BD with a longer length than PD possesses an isostructure
but with a bigger cell parameter of a = b = 25.22 Å in addition
to c = 3.30 Å (Rp = 1.28% and Rwp = 1.63% according to the Le
Bail refinement). The corresponding (100), (200), (300), and
(001) reflections shift to 2θ ≈ 3.53°, 7.00°, 10.05°, and 27.00°,
respectively. According to the structural model of CoPc-PI-
COFs, the distance of adjacent cobalt ions in the same layer
amounts to 2.10 and 2.52 nm for CoPc-PI-COF-1 and CoPc-
PI-COF-2, respectively, Figure 1c and e. PI-bonded
phthalocyanine layers are further compiled together to form
a three-dimensional supramolecular architecture via interlay-
ered π−π interactions with the neighboring layers at a distance
of 0.33 nm for these two COFs, Figure 1d and f.
corresponds well to the simulated interlayer distance for these
two materials. The element energy dispersive spectroscopy
(EDS) mapping shows the homogeneous Co, C, O, and N
atomic distribution, Figure 1j and n. ICP-OES analyses reveal a
3.7 and 3.3 wt % Co content in CoPc-PI-COF-1 and CoPc-PI-
COF-2, respectively, indicating metallophthalocyanine con-
tents of 62.7% and 64.3% among total phthalocyanine units for
these two COFs. These values are slightly lower than that for
Co(TAPc) (5.3 wt % Co content and 76% metallophthalo-
cyanine content), indicating the occurrence of slight
demetalation in the reaction process.
Comparison in the Fourier transform infrared (FT-IR)
spectra of Co(TAPc), BD/PD, and CoPc-PI-COFs discloses
the clean disappearance of the characteristic amino band of
PD/BD at around 3300 cm−1 and anhydride bands of
Co(TAPc) at 1881 and 1767 cm−1, Figure 2a and b. Instead,
typical CO bands of the imide moieties appear at ca. 1768
and 1712 cm−1 for both CoPc-PI-COF-1 and CoPc-PI-COF-2,
and the other typical C−N−C stretching vibration for the
imide rings of CoPc-PI-COF-1 and CoPc-PI-COF-2 is
observed at 1357 and 1367 cm−1, respectively.58 These IR
data indicate the complete conversion from molecular
phthalocyanine building blocks to COFs. Thermal gravimetric
analyses disclose that the decomposed temperature for both
CoPc-PI-COFs is above 300 °C, Figures S3 and S4, indicating
the prominent thermostability of these two new PI COFs. The
robustness of these two COFs was also evaluated by immersing
the samples into different solutions containing 0.5 M KHCO3,
concentrated HCl (12 M), NMP, tetrahydrofuran (THF),
water, ethanol (EtOH), and DMF for 20 days. The treated
CoPc-PI-COF-1 and CoPc-PI-COF-2 were revealed to retain
the long-range-order structure by the consistent PXRD
patterns with the as-synthesized samples, implying their
excellent chemical stability, Figures S5 and S6. Composition
of CoPc-PI-COF-1 and CoPc-PI-COF-2 was further detected
by X-ray photoelectron spectroscopy (XPS), revealing the
presence of C, N, O, and Co elements in these two samples,
Scanning electron microscope (SEM) and transmission
electron microscope (TEM) photos manifest the nanoscale
crystallite morphology of these two COFs with an irregular
shape and size of ca. 100−300 nm, Figure 1g, k, h, and l. High-
resolution transmission electron microscope (HRTEM)
photos of CoPc-PI-COF-1 and CoPc-PI-COF-2 show the
lattice fringes, further confirming their long-range order
structures, Figure 1i and m. The d-spacing of 0.33 nm
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Figure 3. LSV curves (a), Faradaic efficiency (b), partial CO current density (c), Tafel plots (d) of CoPc-PI-COF-1, CoPc-PI-COF-2, and CoPc.
(f) Comparison of CO partial current densities between CoPc-PI-COF-1 with porphyrin/phthalocyanine electrocatalysts evaluated in an H-type
electrochemical cell. (e) Stability test at −0.70 V for 40 h.
Figures S7 and S8. In the Co 2p XPS spectra, the peaks at
796.02 eV (Co 2p1/2) and 780.54 eV (Co 2p3/2) for CoPc-PI-
S12), respectively. On the basis of CO2 adsorption data at 196
K, the deduced BET surface area of CoPc-PI-COF-1 and
CoPc-PI-COF-2 is calculated to amount to 230 and 339 m2
g−1, respectively, bigger than the corresponding value fitted
from N2 adsorption at 77 K. Both CoPc-PI-COFs have
moderate CO2 uptake capacities with values of 19.4 and 19.1
cm3 g−1 at 298 K and 1.0 bar for CoPc-PI-COF-1 and CoPc-
PI-COF-2 (Figures S13 and S14), respectively, indicating the
favorable CO2 affinity of these COFs. Thermal programmed
desorption of CO2 was also performed to check the interaction
basic sites with carbon dioxide molecules from room
temperature to 300 °C, Figure S15. The presence of only
one peak at 110 °C for both CoPc-PI-COF-1 and CoPc-PI-
COF-2 indicates the presence of a weak interaction of these
two COFs with carbon dioxide molecules.
Electrocatalytic CO2RR of CoPc-PI-COFs. Given the fact
that CoPc-PI-COF-1 and CoPc-PI-COF-2 possess excellent
chemical and thermal stability as well as permanent porous
structures, both CoPc-PI-COFs can serve as promising
candidates for promoting electrocatalytic CO2RR. The electro-
catalytic performance of CoPc-PI-COF-derived electrodes was
investigated using a H-cell separated by a Nafion-117
membrane with a standard three-electrode configuration. In
order to enhance the electron transfer, a doping mixture of
carbon black and CoPc-PI-COFs was deposited on a piece of
carbon fiber paper as a working electrode. For comparison, the
electrocatalytic activity of CoPc was also evaluated under the
same experimental conditions. LSV measurements were carried
out in Ar and CO2-saturated 0.5 M KHCO3 electrolytes. As
can be seen in Figures 3a and S16, both CoPc-PI-COF-derived
electrodes show much larger current densities at the applied
potential range from −0.50 to −0.90 V (vs RHE) in CO2-
saturated 0.5 M KHCO3 solution than in an Ar-saturated one,
indicating the electrocatalytic CO2RR activity of CoPc-PI-
COFs. The potentiostatic electrolysis was further performed to
investigate the electrocatalytic CO2RR performance of CoPc-
PI-COF-derived electrodes. The constant time-dependent total
COF-1 and 796.22 eV (Co 2p1/2) and 780.71 eV (Co 2p3/2
)
for CoPc-PI-COF-2 are comparable with those for divalent
cobalt ions involved in the metallophthalocyanine deriva-
tives.69 Furthermore, the Co K-edge X-ray absorption near-
edge structure spectroscopy (XANES) studies of CoPc-PI-
COF-1 and CoPc-PI-COF-2 disclose a peak at 7713.96 and
7713.99 eV, respectively, Figures S9a and S10a, which is nearly
identical to that for CoPc, indicating the similar coordination
environment around cobalt ions in these three compounds.
The Co K-edge extended X-ray absorption fine structure
(EXAFS) curves for CoPc-PI-COF-1 and CoPc-PI-COF-2
possess similar profiles to that of the CoPc reference rather
than Co foil, Figure 2c and d. These results suggest that the Co
atoms in CoPc-PI-COF-1 and CoPc-PI-COF-2 are located in a
N4 square-planar coordination geometry. In order to acquire
the detailed coordination information around cobalt(II) atoms,
a square-planar Co−N4 coordination model was applied into
the quantitative EXAFS fitting for both CoPc-PI-COFs,
Figures S9b and S10b. As can be found, the theoretical
curve is comparable with the experimental result, giving the
Co−N distance of 1.89 Å for both COFs and the CoPc
benchmark, Table S1. These results disclose the square-planar
Co−N4 local coordination structure around the Co centers in
COFs as the same as that of CoPc.
Gas Sorption Behaviors of CoPc-PI-COFs. The porous
2D layered structures of CoPc-PI-COF-1 and CoPc-PI-COF-2
might be beneficial to the mass transfer of substrates and
enrichment of CO2. The permanent porosity of CoPc-PI-
COFs was checked by a N2 sorption experiment at 77 K.
CoPc-PI-COF-1 displays permanent porosity with a BET
surface area of 181 m2 g−1. CoPc-PI-COF-2 has a slightly
bigger BET surface area of 291 m2 g−1 attributed to its larger
structural pore size, Figure 2e and f. Furthermore, the pore size
distribution identifies the channel widths around 1.6 and 1.8
nm for CoPc-PI-COF-1 and CoPc-PI-COF-2 (Figures S11 and
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geometric current density of CoPc-PI-COFs was determined at
the potential range between −0.50 and −0.90 V with each
potential for 20 min (Figures S17 and S18), indicating the
good stability of COFs under the present electrode potential
range.
different scan rates for CoPc-PI-COF-1 is 2.2 × 10−8 mol cm−2
(corresponding to 3.5% cobalt(II)-phthalocyanine moieties as
active sites in CoPc-PI-COF-1), one-sixth higher than those of
CoPc-PI-COF-2 (1.7 × 10−8 mol cm−2 and 3.0%). These
results confirm the enhanced CO2RR activity of CoPc-PI-
COF-1 over CoPc-PI-COF-2, demonstrating the structural
superiority of CoPc-PI-COF-1 in catalyzing CO2RR. As
mentioned above in the structural analysis part, 2D CoPc-PI-
COF-1 and CoPc-PI-COF-2 are isostructural, resulting in their
similar Co(II) electroactive sites, surface area, and CO2
adsorption capability. The only structural difference between
CoPc-PI-COF-1 and CoPc-PI-COF-2 is the longer linker of
CoPc-PI-COF-2 than CoPc-PI-COF-1, which may diminish
the conductivity of CoPc-PI-COF-2. This might be responsible
for the inferior CO2RR activity of CoPc-PI-COF-2 to CoPc-
PI-COF-1. To verify this assumption, electrochemical
impedance spectroscopy (EIS) measurements were performed.
As shown in Figure S28, the CoPc-PI-COF-1 electrode
exhibits a much smaller charge transfer resistance than CoPc-
PI-COF-2. This is beneficial to the charge transfer ability of
CoPc-PI-COF-1 during the electrocatalytic CO2RR process,46
indicating its advantage in the catalytic dynamics. Furthermore,
conductivity measurement was employed to evaluate the
intrinsic electrical conductivity of CoPc-PI-COFs, Figure S29.
Current−voltage curves unveil the conductivity of 3.7 × 10−3
and 1.6 × 10−3 S m−1 for CoPc-PI-COF-1 and CoPc-PI-COF-
2, respectively, indicating their excellent conductive materials
nature through space pathway.70 The higher conductivity of
CoPc-PI-COF-1 then promotes a higher electroactive coverage
than CoPc-PI-COF-2, accounting for its outstanding electro-
catalytic CO2RR performance.49 At−0.70 V (vs RHE), the
TOF (calculated based on the electroactive Co sites in the
electrochemical CO2RR) of CoPc-PI-COF-1 and CoPc-PI-
COF-2 is 2.2 and 1.9 s−1, respectively. It is worth noting that,
by combining the high conductivity, permanent porous
structures, and the excellent CoPc active sites, FECO (93%),
GC and 1H NMR spectroscopic analyses confirm the
evolution of only CO and H2 after the continuous electro-
catalysis at potentials from −0.50 to −0.90 V of CoPc-PI-
COFs in the CO2-saturated 0.5 M KHCO3 electrolyte without
any liquid product, Figure S19. In good contrast, no CO
product was detected in the control electrocatalysis performed
under the Ar-saturated electrolyte and carbon cloth covered
with acetylene black and Nafion in CO2-saturated 0.5 M
KHCO3 electrolyte, in Figures S20−S22, confirming the origin
of a CO product from a CO2 source. The CoPc-PI-COFs
cathodes exhibit a high FECO of 87−97% at an applied
potential range of −0.60 to −0.90 V (vs RHE), similar to the
CoPc electrode, Figure 3b. In particular, at the applied
potential of −0.80 V (vs RHE), FECO is able to reach up to
97% and 96% for CoPc-PI-COF-1 and CoPc-PI-COF-2,
respectively, further demonstrating their excellent electro-
catalytic CO2RR activity. Besides FECO, jCO for CoPc-PI-COF-
1, CoPc-PI-COF-2, and CoPc was comparatively studied,
Figure 3c. As can be found, the jCO values of CoPc-PI-COF-2
at −0.40 to −0.90 V (vs RHE) are almost the same as that for
CoPc. Nevertheless, CoPc-PI-COF-1 shows a significantly
higher jCO at the potential range of −0.60 to −0.90 V (vs
RHE) than CoPc-PI-COF-2 and CoPc, implying the enhanced
CO2RR activity of CoPc-PI-COF-1. For example, at −0.90 V
(vs RHE) CoPc-PI-COF-1 enables a high jCO of −21.2 mA
cm−2 and shows a larger mass activity of 573 mA mg−1
(calculation based on the CO partial current density divided
by total Co(II) amount) than CoPc-PI-COF-2 (482 mA mg−1)
and CoPc (161 mA mg−1). Tafel plots with the logarithm of
current density [log(jCO)] and the overpotential (η) as the x
and y axis, respectively, have been recorded to probe the
possible mechanistic pathway of CO2RR, Figure 3d. The Tafel
slope of the linear part in the low overpotentials between
−0.29 and −0.44 V is 95 and 105 mV dec−1 for CoPc-PI-COF-
1 and CoPc-PI-COF-2, respectively, suggesting the existence of
j
CO (−9.4 mA cm−2), and TOF (2.2 s−1) of CoPc-PI-COF-1 at
−0.70 V (vs RHE) are superior to most tetrapyrrole-containing
porous counterparts reported thus far under similar exper-
imental conditions, such as COF-367-Co (91%, −3.3 mA
cm−2, and 0.5 s−1 at −0.67 V),47 Co-TTCOF (91%, −1.8 mA
cm−2, and 1.3 s−1 at −0.70 V),46 Fe-PB (85%, −0.2 mA cm−2,
and 0.6 s−1 at −0.63 V),42 and CoPc-Cu-NH (72%, −8.4 mA
cm−2, and 1.2 s−1 at −0.74 V).67 After a 2 h durability test at
−0.80 V, the XPS peaks observed at 795.80 and 780.60 eV for
divalent cobalt ions in the electrode, corresponding to Co 2p1/2
and Co 2p3/2, are in good agreement with those found for fresh
CoPc-PI-COF-1, Figure S30. Furthermore, IR spectroscopic
data disclose the lack of any significant band change between
fresh CoPc-PI-COF-1 and used catalyst, Figure S31. These
results indicate their prominent durability associated with the
good chemical stability of these PI-linked COFs in electro-
chemical catalysis. This is also true for CoPc-PI-COF-1 and
CoPc electrodes, Figures S32−S35. Fortunately, a similar
PXRD pattern of CoPc-PI-COF-1@carbon black under the
overpotential of −0.80 V to that of the as-synthesized sample
was observed (Figure S36), indicating the maintenance of the
periodic structure.
•−
single electron transfer to CO2 and the generation of a CO2
intermediate as a possible rate-determining step. In addition,
Tafel slopes for COFs are smaller than that (146 mV dec−1)
for CoPc, hinting at their faster CO2RR kinetics due possibly
to the effective electron transfer and large active surface. The
upward deviation of Tafel slope curvature at overpotentials
above −0.50 V for these three electrodes might be caused by
the mass transport restraint.
Moreover, the control CoPc@black electrode, containing
the same cobalt content as the CoPc-PI-COF-1 electrode,
exhibits an inferior electrochemical performance including
FECO, jCO, and the Tafel slope (167 mV dec−1) to the above-
mentioned CoPc species under the same conditions, Figures
S23−S25. Nevertheless, the TON, which was calculated on the
basis of total cobalt content and the I−t curve at −0.70 V (vs
RHE) for 20 min, is 22, 49, 81, and 71 for CoPc, control CoPc,
CoPc-PI-COF-1, and CoPc-PI-COF-2, respectively, confirm-
ing the excellent electrocatalytic performance of COF
electrodes.
Toward practical applications, the long-term durability is
crucial in electrocatalytic CO2RR. For the present CoPc-PI-
COFs electrodes, corresponding electrocatalytic stability
measurement was performed at −0.70 V (vs RHE, η, −0.59
V). After 40 h, the Faradaic efficiency of CO for the CoPc-PI-
The surface concentration of electrochemically active
metallophthalocyanine sites on the CoPc-PI-COFs electrodes
was determined through the integration of the anodic wave at
the CV curve, Figures S26 and S27.47,51 The average value at
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COF-1 electrode can be kept above 91%, with almost no decay
in comparison with the fresh catalyst (93%), indicating its
excellent durability, Figure 3f. During the 40 h electrocatalytic
test at −0.70 V (vs RHE), the TON of CoPc-PI-COF-1 is
accumulated to as large as 277 000. Obviously, according to
the above-mentioned CO2RR studies, the comprehensive
electrocatalytic performance of CoPc-PI-COF-1, in terms of
TOF, TON, FECO, jCO, and durability, is superior to most of
the reticular materials reported thus far under similar
experimental conditions, Figure 3e and Table S2. Moreover,
a flow cell with a gas diffusion electrode composed of CoPc-PI-
COF-1 has been assembled, Figures S37−S40. This flow cell
displays a high FECO of 95% and large jCO of −44 mA cm−2 at a
low potential of −0.50 V (vs RHE), further revealing the
possibility of CoPc-PI-COF-1 in practical electrocatalytic
CO2RR.
V vs RHE) to CoPc (−0.44 V vs RHE) and CoPc-PI-COF-2
(−0.46 V vs RHE) because of the dependence of the
determinant factor on the reduction of catalytic sites rather
than the free energy barrier.41 Additional support for this point
comes from the quite close free energy barrier for A and B but
much smaller onset potential of CoPc-PI-COF-1 than CoPc-
PI-COF-2. The Gibbs free energy of *CO shows the order of
A > B > CoPc, indicating the decreased barrier for the CO
desorption process in the same order. This result reveals that
CoPc-PI-COF-1 is much more favorable for CO desorption.
Investigation of Co−N bond orders reveals that CoPc-PI-
COF-1, CoPc-PI-COF-2, and CoPc have a similar bond order
for Co−N bonds before and after CO desorption, indicating
the similar electrochemical stability of these three materials. In
particular, the density functional theory (DFT)-calculated
Gibbs free energy diagram also well explains the different
CO2RR efficiencies at different potentials. Nevertheless,
despite the similar energy barrier calculated for *COOH
formation between A and B, a much lower energy barrier
revealed for CO desorption for the former species may
contribute to the higher electrocatalytic CO2RR activity of
CoPc-PI-COF-1 than CoPc-PI-COF-2. The theoretical calcu-
lations for hydrogen evolution reaction (HER) and possible
paths of CO2RR with CoPc-PI-COF-1 and CoPc-PI-COF-2
electrocatalysts were also performed, Table S4. On the basis of
simulation results, the high free-energy gap in HER hinders its
competing capability with electrochemical CO2RR. With
regard to other possible paths of CO2RR (for example,
generation of CH4 and CH3OH) with CoPc-PI-COF-1 and
CoPc-PI-COF-2, following the *CO intermediate, the free
energies of *COH and *CHO intermediates were calculated.
It is worth noting that both *COH and *CHO are the
intermediates of CO2RR to generate CH4 and CH3OH. In
comparison with the free energy of CO desorption, the much
higher free energy of *COH is adverse to corresponding
formation. Although *CHO has a similar free energy to that of
CO desorption, carbon substrate and poor dispersion of COFs
in making the present electrodes seem to preclude the
generation of other chemicals such as CH4 and CH3OH.39
At the end of this section, it is noteworthy that the present
theoretical calculations overall rationalize the association of the
electrocatalytic CO2RR activity of phthalocyanine COFs with
their intrinsic structural characteristics. The higher electron
conductivity of CoPc-PI-COF-1 should further facilitate the
charge transportation, therefore promoting its electrocatalytic
CO2RR performance from a kinetic perspective. This is further
rationalized by the calculated electronic coupling result. Based
on the calculation results, the electronic couplings for both
hole and electron transfer between metallophthalocyanine
segments in monolayered A′ and B′ (with a Zn ion to replace
Co for the purpose of calculation) are negligibly small (less
than 1 meV). This corresponds well with the findings derived
from orbital distribution that the conjugation system is
terminated by the imide nitrogen atom. However, the
electronic coupling constants for hole/electron transfer
between double-layered A′ (668/462 meV) are revealed to
be much larger than those between double-layered B′ (294/
156 meV) shown in Table S5, in line with the experimental
fact that CoPc-PI-COF-1 exhibits much larger electron
conductivity than CoPc-PI-COF-2.
Electrocatalytic CO2RR Mechanism. Theoretical simu-
lation has been conducted on the periodic structure of CoPc,
CoPc-PI-COF-1, and CoPc-PI-COF-2, giving an energy gap
value of 1.53, 0.88, and 0.70 eV (Figure 4a and Table S3),
Figure 4. (a) Calculated energy gap of CoPc, CoPc-PI-COF-1, and
CoPc-PI-COF-2. (b) Co−N bond orders of CoPc, A, and B without
and with adsorbed CO. (c) Calculated free energy diagram of CoPc,
A, and B catalyzing CO2RR. Inset represents the optimized
configurations of intermediates with A. H: white; C: gray; N: blue;
O: red; Co: pink.
respectively. In comparison with CoPc, the narrower energy
gap of CoPc-PI-COF-1 and CoPc-PI-COF-2 is helpful for the
electrocatalytic CO2RR. For the purpose of further elucidating
the CO2RR mechanism, finite cluster models of the respective
COF structures (A and B) were built by extracting a structural
segment from respective CoPc-PI-COF-1 and CoPc-PI-COF-2
and neglecting the long-range interaction among cobalt sites.
For details, please see the Supporting Information. The similar
Co−N bond orders calculated for CoPc, A, and B units
indicate the similar coordination environment of Co in these
materials, Figure 4b, in line with EXAFS data.
The calculated Gibbs free energy diagram of three CO2RR
processes for A, B, and CoPc is shown in Figure 4c and Table
S4, including the generation of *COOH, the formation of
*CO, and the CO desorption course. According to the
calculation data, despite that the Gibbs energy barrier to afford
*COOH increases from CoPc to A and B, the onset potential
to initiate the CO2RR decreases from CoPc-PI-COF-1 (−0.36
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University of Science and Technology Beijing, Beijing 100083,
China
CONCLUSIONS
■
In summary, a new tetraanhydride-containing phthalocyanina-
to cobalt(II) building block has been used to construct 2D
polyimide-linked functional COFs, which also provides a new
perspective for constructing diverse phthalocyanine reticular
structures. The porous structure, excellent thermal and
chemical stability, and high electron conductivity for the
newly developed phthalocyanine COFs have been well
disclosed by various crystallographic, spectroscopic, and
electronic measurements. These unique structural character-
istics enable the highly efficient electrocatalysis of CO2RR in
terms of the mass active sites and thus the TOF, TON, and
CO partial current density. These results not only present new
metallophthalocyanine COFs with excellent chemical and
thermal stability but also provide a clear example in
engineering reticular materials electrocatalysts toward CO2RR.
Baoqiu Yu − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China; orcid.org/0000-0003-3379-7581
Hui Wu − Center for Neutron Research, National Institute of
Standards and Technology, Gaithersburg, Maryland 20899-
6102, United States; orcid.org/0000-0003-0296-5204
Wei Zhou − Center for Neutron Research, National Institute of
Standards and Technology, Gaithersburg, Maryland 20899-
6102, United States; orcid.org/0000-0002-5461-3617
Wenping Liu − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c02145.
■
sı
Experimental and theoretical calculation details, PXRD
patterns, TGA curves, XPS spectra, XANES spectra,
CO2 sorption curves, and electrocatalytic performance of
CoPc-PI-COF-1 and CoPc-PI-COF-2 (PDF)
Chuangyu Wei − School of Materials Science and Engineering,
China University of Petroleum (East China), Qingdao
266580, China
Baotong Chen − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China
Dongdong Qi − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China
Kang Wang − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China
AUTHOR INFORMATION
Corresponding Authors
■
Hailong Wang − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China; orcid.org/0000-0002-0138-
2966; Email: hlwang@ustb.edu.cn
Banglin Chen − Department of Chemistry, University of Texas
at San Antonio, San Antonio, Texas 78249-0698, United
States; orcid.org/0000-0001-8707-8115;
Email: banglin.chen@utsa.edu
Jianzhuang Jiang − Beijing Advanced Innovation Center for
Materials Genome Engineering, Beijing Key Laboratory for
Science and Application of Functional Molecular and
Crystalline Materials, Department of Chemistry and
Chemical Engineering, School of Chemistry and Biological
Engineering, University of Science and Technology Beijing,
Beijing 100083, China; orcid.org/0000-0002-4263-
9211; Email: jianzhuang@ustb.edu.cn
Yanli Chen − School of Materials Science and Engineering,
China University of Petroleum (East China), Qingdao
266580, China; orcid.org/0000-0003-3252-7889
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c02145
Authors
Bin Han − Beijing Advanced Innovation Center for Materials
Genome Engineering, Beijing Key Laboratory for Science and
Application of Functional Molecular and Crystalline
Materials, Department of Chemistry and Chemical
Engineering, School of Chemistry and Biological Engineering,
University of Science and Technology Beijing, Beijing 100083,
China; orcid.org/0000-0002-6984-4880
Xu Ding − Beijing Advanced Innovation Center for Materials
Genome Engineering, Beijing Key Laboratory for Science and
Application of Functional Molecular and Crystalline
Materials, Department of Chemistry and Chemical
Engineering, School of Chemistry and Biological Engineering,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the Natural Science Foundation (NSF)
of China (Nos. 21631003 and 21805005), the Fundamental
Research Funds for the Central Universities (No. FRF-BD-20-
14A and FRF-IDRY-19-028), and University of Science and
Technology Beijing is gratefully acknowledged. We are also
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(20) Yan, D.; Wang, Z.; Cheng, P.; Chen, Y.; Zhang, Z. Rational
Fabrication of Crystalline Smart Materials for Rapid Detection and
Efficient Removal of Ozone. Angew. Chem., Int. Ed. 2021, 60, 6055−
6060.
(21) Jin, Y.; Hu, Y.; Zhang, W. Tessellated Multiparous Two-
Dimensional Covalent Organic Frameworks. Nat. Rev. Chem. 2017, 1,
0056.
grateful for the help with theoretical simulations from Prof.
Yuexing Zhang at Hubei University.
REFERENCES
■
(1) Geng, K.; He, T.; Liu, R.; Dalapati, S.; Tan, K. T.; Li, Z.; Tao, S.;
Gong, Y.; Jiang, Q.; Jiang, D. Covalent Organic Frameworks: Design,
Synthesis, and Functions. Chem. Rev. 2020, 120, 8814−8933.
(2) Keller, N.; Bein, T. Optoelectronic Processes in Covalent
Organic Frameworks. Chem. Soc. Rev. 2021, 50, 1813−1845.
(3) Li, J.; Jing, X.; Li, Q.; Li, S.; Gao, X.; Feng, X.; Wang, B. Bulk
COFs and COF Nanosheets for Electrochemical Energy Storage and
Conversion. Chem. Soc. Rev. 2020, 49, 3565−3604.
̂
(22) Coté, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger,
A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks.
Science 2005, 310, 1166−1170.
(23) Dey, K.; Bhunia, S.; Sasmal, H. S.; Reddy, C. M.; Banerjee, R.
Self-Assembly-Driven Nanomechanics in Porous Covalent Organic
Framework Thin Films. J. Am. Chem. Soc. 2021, 143, 955−963.
(24) Evans, A. M.; Parent, L. R.; Flanders, N. C.; Bisbey, R. P.;
Vitaku, E.; Kirschner, M. S.; Schaller, R. D.; Chen, L. X.; Gianneschi,
N. C.; Dichtel, W. R. Seeded Growth of Single-Crystal Two-
Dimensional Covalent Organic Frameworks. Science 2018, 361, 52−
57.
(4) Han, X.; Yuan, C.; Hou, B.; Liu, L.; Li, H.; Liu, Y.; Cui, Y. Chiral
Covalent Organic Frameworks: Design, Synthesis and Property.
Chem. Soc. Rev. 2020, 49, 6248−6272.
(5) Gui, B.; Lin, G.; Ding, H.; Gao, C.; Mal, A.; Wang, C. Three-
Dimensional Covalent Organic Frameworks: From Topology Design
to Applications. Acc. Chem. Res. 2020, 53, 2225−2234.
(6) Wang, Z.; Zhang, S.; Chen, Y.; Zhang, Z.; Ma, S. Covalent
Organic Frameworks for Separation Applications. Chem. Soc. Rev.
2020, 49, 708−735.
(25) Colson, J. W.; Woll, A. R.; Mukherjee, A.; Levendorf, M. P.;
Spitler, E. L.; Shields, V. B.; Spencer, M. G.; Park, J.; Dichtel, W. R.
Oriented 2D Covalent Organic Framework Thin Films on Single-
Layer Graphene. Science 2011, 332, 228−231.
(26) Liu, Y.; Ma, Y.; Zhao, Y.; Sun, X.; Gándara, F.; Furukawa, H.;
Liu, Z.; Zhu, H.; Zhu, C.; Suenaga, K.; Oleynikov, P.; Alshammari, A.
S.; Zhang, X.; Terasaki, O.; Yaghi, O. M. Weaving of Organic Threads
into a Crystalline Covalent Organic Framework. Science 2016, 351,
365−369.
(27) Guan, X.; Li, H.; Ma, Y.; Xue, M.; Fang, Q.; Yan, Y.; Valtchev,
V.; Qiu, S. Chemically Stable Polyarylether-Based Covalent Organic
Frameworks. Nat. Chem. 2019, 11, 587−594.
(28) Wang, P.-L.; Ding, S.-Y.; Zhang, Z.-C.; Wang, Z.-P.; Wang, W.
Constructing Robust Covalent Organic Frameworks via Multi-
component Reactions. J. Am. Chem. Soc. 2019, 141, 18004−18008.
(29) Zeng, Y.; Zou, R.; Luo, Z.; Zhang, H.; Yao, X.; Ma, X.; Zou, R.;
Zhao, Y. Covalent Organic Frameworks Formed with Two Types of
Covalent Bonds Based on Orthogonal Reactions. J. Am. Chem. Soc.
2015, 137, 1020−1023.
(7) Diercks, C. S.; Yaghi, O. M. The Atom, the Molecule, and the
Covalent Organic Framework. Science 2017, 355, No. eaal1585.
(8) Slater, A. G.; Cooper, A. I. Function-led Design of New Porous
Materials. Science 2015, 348, No. aaa8075.
(9) Liang, R.-R.; Jiang, S.-Y.; A, R.-H.; Zhao, X. Two-Dimensional
Covalent Organic Frameworks with Hierarchical Porosity. Chem. Soc.
Rev. 2020, 49, 3920−3951.
(10) Wang, X.; Chen, L.; Chong, S. Y.; Little, M. A.; Wu, Y.; Zhu,
W.-H.; Clowes, R.; Yan, Y.; Zwijnenburg, M. A.; Sprick, R. S.; Cooper,
A. I. Sulfone-Containing Covalent Organic Frameworks for Photo-
catalytic Hydrogen Evolution from Water. Nat. Chem. 2018, 10,
1180−1189.
(11) Liu, W.; Li, X.; Wang, C.; Pan, H.; Liu, W.; Wang, K.; Zeng, Q.;
Wang, R.; Jiang, J. A Scalable General Synthetic Approach toward
Ultrathin Imine-Linked Two-Dimensional Covalent Organic Frame-
work Nanosheets for Photocatalytic CO2 Reduction. J. Am. Chem. Soc.
2019, 141, 17431−17440.
(30) Ma, T.; Kapustin, E. A.; Yin, S. X.; Liang, L.; Zhou, Z.; Niu, J.;
Li, L.-H.; Wang, Y.; Su, J.; Li, J.; Wang, X.; Wang, W. D.; Wang, W.;
Sun, J.; Yaghi, O. M. Single-Crystal X-Ray Diffraction Structures of
Covalent Organic Frameworks. Science 2018, 361, 48−52.
(31) Dong, J.; Han, X.; Liu, Y.; Li, H.; Cui, Y. Metal-Covalent
Organic Frameworks (MCOFs): A Bridge Between Metal-Organic
Frameworks and Covalent Organic Frameworks. Angew. Chem., Int.
Ed. 2020, 59, 13722−13733.
(32) Nitopi, S.; Bertheussen, E.; Scott, S. B.; Liu, X.; Engstfeld, A. K.;
Horch, S.; Seger, B.; Stephens, I. E. L.; Chan, K.; Hahn, C.; Nørskov,
J. K.; Jaramillo, T. F.; Chorkendorff, I. Progress and Perspectives of
Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte.
Chem. Rev. 2019, 119, 7610−7672.
(33) Diercks, C. S.; Liu, Y.; Cordova, K. E.; Yaghi, O. M. The Role
of Reticular Chemistry in the Design of CO2 Reduction Catalysts.
Nat. Mater. 2018, 17, 301−307.
(34) Nam, D.-H.; Luna, P. D.; Rosas-Hernández, A.; Thevenon, A.;
Li, F.; Agapie, T.; Peters, J. C.; Shekhah, O.; Eddaoudi, M.; Sargent, E.
H. Molecular Enhancement of Heterogeneous CO2 Reduction. Nat.
Mater. 2020, 19, 266−276.
(35) Wei, Y.-S.; Zhang, M.; Zou, R.; Xu, Q. Metal-Organic
Framework-Based Catalysts with Single Metal Sites. Chem. Rev.
2020, 120, 12089−12174.
(36) Liang, Z.; Wang, H.-Y.; Zheng, H.; Zhang, W.; Cao, R.
Porphyrin-Based Frameworks for Oxygen Electrocatalysis and
Catalytic Reduction of Carbon Dioxide. Chem. Soc. Rev. 2021, 50,
2540−2581.
(37) Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M.
Electrocatalytic and Homogeneous Approaches to Conversion of CO2
to Liquid Fuels. Chem. Soc. Rev. 2009, 38, 89−99.
(12) Ma, H.-C.; Zhao, C.-C.; Chen, G.-J. Photothermal Conversion
Triggered Thermal Asymmetric Catalysis within Metal Nanoparticles
Loaded Homochiral Covalent Organic Framework. Nat. Commun.
2019, 10, 3368.
(13) Qian, Y.; Li, D.; Han, Y.; Jiang, H.-L. Photocatalytic Molecular
Oxygen Activation by Regulating Excitonic Effects in Covalent
Organic Frameworks. J. Am. Chem. Soc. 2020, 142, 20763−20771.
(14) Li, W.; Huang, X.; Zeng, T.; Liu, Y. A.; Hu, W.; Yang, H.;
Zhang, Y.-B.; Wen, K. Thiazolo [5,4-d] thiazole-Based Donor-
Acceptor Covalent Organic Framework for Sunlight-Driven Hydro-
gen Evolution. Angew. Chem., Int. Ed. 2021, 60, 1869−1874.
(15) Meng, Z.; Stolz, R. M.; Mirica, K. A. Two-Dimensional
Chemiresistive Covalent Organic Framework with High Intrinsic
Conductivity. J. Am. Chem. Soc. 2019, 141, 11929−11937.
(16) Wang, M.; Ballabio, M.; Wang, M.; Lin, H.-H.; Biswal, B. P.;
Han, X.; Paasch, S.; Brunner, E.; Liu, P.; Chen, M.; Bonn, M.; Heine,
T.; Zhou, S.; Cánovas, E.; Dong, R.; Feng, X. Unveiling Electronic
Properties in Metal-Phthalocyanine-Based Pyrazine-Linked Conju-
gated Two-Dimensional Covalent Organic Frameworks. J. Am. Chem.
Soc. 2019, 141, 16810−16816.
(17) Wang, M.; Wang, M.; Lin, H.-H.; Ballabio, M.; Zhong, H.;
Bonn, M.; Zhou, S.; Heine, T.; Cánovas, E.; Dong, R.; Feng, X. High-
Mobility Semiconducting Two-Dimensional Conjugated Covalent
Organic Frameworks with p-Type Doping. J. Am. Chem. Soc. 2020,
142, 21622−21627.
(18) Ma, H.-C.; Chen, G.-J.; Huang, F.; Dong, Y.-B. Homochiral
Covalent Organic Framework for Catalytic Asymmetric Synthesis of a
Drug Intermediate. J. Am. Chem. Soc. 2020, 142, 12574−12578.
(19) Li, Y.; Chen, W.; Xing, G.; Jiang, D.; Chen, L. New Synthetic
Strategies toward Covalent Organic Frameworks. Chem. Soc. Rev.
2020, 49, 2852−2868.
7112
https://doi.org/10.1021/jacs.1c02145
J. Am. Chem. Soc. 2021, 143, 7104−7113

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
(38) Francke, R.; Schille, B.; Roemelt, M. Homogeneously Catalyzed
Electroreduction of Carbon Dioxide-Methods, Mechanisms, and
Catalysts. Chem. Rev. 2018, 118, 4631−4701.
ing Nature via Peripheral Electron-Withdrawing Octyloxycarbonyl
Substituents. J. Mater. Chem. 2011, 21, 18552−18559.
(55) Wu, Y.; Ma, P.; Wu, N.; Kong, X.; Bouvet, M.; Li, X.; Chen, Y.;
Jiang, J. Two-Step Solution-Processed Two-Component Bilayer
Phthalocyaninato Copper-Based Heterojunctions with Interesting
Ambipolar Organic Transiting and Ethanol Sensing Properties. Adv.
Mater. Interfaces 2016, 3, 1600253.
(56) Kuznetsova, N. A.; Shevchenko, E. N.; Makarov, D. A.; Slivka,
L. K.; Solovyova, L. I.; Kaliya, O. L.; Lukyanets, E. A. Synthesis and
Photophysicochemical Studies of Non-Metal 2,3,9,10,16,17,23,24-
Octacarboxyphthalocyanine. J. Porphyrins Phthalocyanines 2012, 16,
1245−1251.
(57) Dolotova, O.; Yuzhakova, O.; Solovyova, L.; Shevchenko, E.;
Negrimovsky, V.; Lukyanets, E.; Kaliya, O. Water-Soluble Manganese
Phthalocyanines. J. Porphyrins Phthalocyanines 2013, 17, 881−888.
(58) Fang, Q.; Zhuang, Z.; Gu, S.; Kaspar, R. B.; Zheng, J.; Wang, J.;
Qiu, S.; Yan, Y. Designed Synthesis of Large-Pore Crystalline
Polyimide Covalent Organic Frameworks. Nat. Commun. 2014, 5,
4503.
(59) Liu, K.; Qi, H.; Dong, R.; Shivhare, R.; Addicoat, M.; Zhang,
T.; Sahabudeen, H.; Heine, T.; Mannsfeld, S.; Kaiser, U.; Zheng, Z.;
Feng, X. On-Water Surface Synthesis of Crystalline, Few-Layer Two-
Dimensional Polymers Assisted by Surfactant Monolayers. Nat. Chem.
2019, 11, 994−1000.
(60) Maschita, J.; Banerjee, T.; Savasci, G.; Haase, F.; Ochsenfeld,
C.; Lotsch, B. V. Ionothermal Synthesis of Imide-Linked Covalent
Organic Frameworks. Angew. Chem., Int. Ed. 2020, 59, 15750−15758.
(61) Zeng, L.; Liu, T.; He, C.; Shi, D.; Zhang, F.; Duan, C.
Organized Aggregation Makes Insoluble Perylene Diimide Efficient
for the Reduction of Aryl Halides via Consecutive Visible Light-
Induced Electron-Transfer Processes. J. Am. Chem. Soc. 2016, 138,
3958−3961.
(39) Wu, Y.; Jiang, Z.; Lu, X.; Liang, Y.; Wang, H. Domino
Electroreduction of CO2 to Methanol on a Molecular Catalyst. Nature
2019, 575, 639−642.
(40) Han, N.; Wang, Y.; Ma, L.; Wen, J.; Li, J.; Zheng, H.; Nie, K.;
Wang, X.; Zhao, F.; Li, Y.; Fan, J.; Zhong, J.; Wu, T.; Miller, D. J.; Lu,
J.; Lee, S.-T.; Li, Y. Supported Cobalt Polyphthalocyanine for High-
Performance Electrocatalytic CO2 Reduction. Chem. 2017, 3, 652−
664.
(41) Zhang, X.; Wang, Y.; Gu, M.; Wang, M.; Zhang, Z.; Pan, W.;
Jiang, Z.; Zheng, H.; Lucero, M.; Wang, H.; Sterbinsky, G. E.; Ma, Q.;
Wang, Y.-G.; Feng, Z.; Li, J.; Dai, H.; Liang, Y. Molecular Engineering
of Dispersed Nickel Phthalocyanines on Carbon Nanotubes for
Selective CO2 Reduction. Nat. Energy 2020, 5, 684−692.
(42) Smith, P. T.; Benke, B. P.; Cao, Z.; Kim, Y.; Nichols, E. M.;
Kim, K.; Chang, C. J. Iron Porphyrins Embedded into a Supra-
molecular Porous Organic Cage for Electrochemical CO2 Reduction
in Water. Angew. Chem., Int. Ed. 2018, 57, 9684−9688.
(43) Zhang, E.; Wang, T.; Yu, K.; Liu, J.; Chen, W.; Li, A.; Rong, H.;
Lin, R.; Ji, S.; Zheng, X.; Wang, Y.; Zheng, L.; Chen, C.; Wang, D.;
Zhang, J.; Li, Y. Bismuth Single Atoms Resulting from Transformation
of Metal-Organic Frameworks and Their Use as Electrocatalysts for
CO2 Reduction. J. Am. Chem. Soc. 2019, 141, 16569−16573.
(44) Yi, J.-D.; Xie, R.; Xie, Z.-L.; Chai, G.-L.; Liu, T.-F.; Chen, R.-P.;
Huang, Y.-B.; Cao, R. Highly Selective CO2 Electroreduction to CH4
by In Situ Generated Cu2O Single-Type Sites on a Conductive MOF:
Stabilizing Key Intermediates with Hydrogen Bonding. Angew. Chem.,
Int. Ed. 2020, 59, 23641−23648.
(45) Cao, C.; Ma, D.-D.; Gu, J.-F.; Xie, X.; Zeng, G.; Li, X.; Han, S.-
G.; Zhu, Q.-L.; Wu, X.-T.; Xu, Q. Metal-Organic Layers Leading to
Atomically Thin Bismuthene for Efficient Carbon Dioxide Electro-
reduction to Liquid Fuel. Angew. Chem., Int. Ed. 2020, 59, 15014−
15020.
(46) Zhu, H.-J.; Lu, M.; Wang, Y.-R.; Yao, S.-J.; Zhang, M.; Kan, Y.-
H.; Liu, J.; Chen, Y.; Li, S.-L.; Lan, Y.-Q. Efficient Electron
Transmission in Covalent Organic Framework Nanosheets for Highly
Active Electrocatalytic Carbon Dioxide Reduction. Nat. Commun.
2020, 11, 497.
(47) 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. Covalent Organic Frameworks Comprising Cobalt Porphyrins for
Catalytic CO2 Reduction in Water. Science 2015, 349, 1208−1213.
(48) Liu, H.; Chu, J.; Yin, Z.; Cai, X.; Zhuang, L.; Deng, H. Covalent
Organic Frameworks Linked by Amine Bonding for Concerted
Electrochemical Reduction of CO2. Chem. 2018, 4, 1696−1709.
(49) Hod, I.; Farha, O. K.; Hupp, J. T. Powered by Porphyrin
Packing. Nat. Mater. 2015, 14, 1192−1193.
(50) Chen, Y.; Li, P.; Noh, H.; Kung, C.-W.; Buru, C. T.; Wang, X.;
Zhang, X.; Farha, O. K. Stabilization of Formate Dehydrogenase in a
Metal-Organic Framework for Bioelectrocatalytic Reduction of CO2.
Angew. Chem., Int. Ed. 2019, 58, 7682−7686.
(51) Huang, N.; Lee, K. H.; Yue, Y.; Xu, X.; Irle, S.; Jiang, Q.; Jiang,
D. A Stable and Conductive Metallophthalocyanine Framework for
Electrocatalytic Carbon Dioxide Reduction in Water. Angew. Chem.,
Int. Ed. 2020, 59, 16587−16593.
(62) Jiang, L.; Tian, Y.; Sun, T.; Zhu, Y.; Ren, H.; Zou, X.; Ma, Y.;
Meihaus, K.; Long, J. R.; Zhu, G. A Crystalline Polyimide Porous
Organic Framework for Selective Adsorption of Acetylene over
Ethylene. J. Am. Chem. Soc. 2018, 140, 15724−15730.
(63) Johnson, B. A.; Bhunia, A.; Fei, H.; Cohen, S. M.; Ott, S.
Development of a UiO-Type Thin Film Electrocatalysis Platform with
Redox-Active Linkers. J. Am. Chem. Soc. 2018, 140, 2985−2994.
(64) Gao, S.; Lin, Y.; Jiao, X.; Sun, Y.; Luo, Q.; Zhang, W.; Li, D.;
Yang, J.; Xie, Y. Partially Oxidized Atomic Cobalt Layers for Carbon
Dioxide Electroreduction to Liquid Fuel. Nature 2016, 529, 68−71.
(65) Ren, S.; Joulié, D.; Salvatore, D.; Torbensen, K.; Wang, M.;
Robert, M.; Berlinguette, C. P. Molecular Electrocatalysts can Mediate
Fast, Selective CO2 Reduction in a Flow Cell. Science 2019, 365, 367−
369.
́
(66) Matheu, R.; Gutierrez-Puebla, E.; Monge, M. A.; Diercks, C. S.;
Kang, J.; Prévot, M. S.; Pei, X.; Hanikel, N.; Zhang, B.; Yang, P.;
Yaghi, O. M. Three-Dimensional Phthalocyanine Metal-Catecholates
for High Electrochemical Carbon Dioxide Reduction. J. Am. Chem.
Soc. 2019, 141, 17081−17085.
(67) Meng, Z.; Luo, J.; Li, W.; Mirica, K. A. Hierarchical Tuning of
the Performance of Electrochemical Carbon Dioxide Reduction Using
Conductive Two-Dimensional Metallophthalocyanine Based Metal-
Organic Frameworks. J. Am. Chem. Soc. 2020, 142, 21656−21669.
(68) Zhong, H.; Ghorbani-Asl, M.; Ly, K. H.; Zhang, J.; Ge, J.;
Wang, M.; Liao, Z.; Makarov, D.; Zschech, E.; Brunner, E.;
Weidinger, I. M.; Zhang, J.; Krasheninnikov, A. V.; Kaskel, S.;
Dong, R.; Feng, X. Synergistic Electroreduction of Carbon Dioxide to
Carbon Monoxide on Bimetallic Layered Conjugated Metal-Organic
Frameworks. Nat. Commun. 2020, 11, 1409.
(52) Lu, M.; Zhang, M.; Liu, C.-G.; Liu, J.; Shang, L.-J.; Wang, M.;
Chang, J.-N.; Li, S.-L.; Lan, Y.-Q. Stable Dioxin-Linked Metal-
lophthalocyanine Covalent Organic Frameworks as Photo-Coupled
Electrocatalysts for CO2 Reduction. Angew. Chem., Int. Ed. 2021, 60,
4864−4871.
(53) Wang, X.; Zhang, Y.; Sun, X.; Bian, Y.; Ma, C.; Jiang, J.
2,3,9,10,16,17,24,25-Octakis(octyloxycarbonyl)phthalocyanines. Syn-
thesis, Spectroscopic, and Electrochemical Characteristics. Inorg.
Chem. 2007, 46, 7136−7141.
(54) Ma, P.; Kan, J.; Zhang, Y.; Hang, C.; Bian, Y.; Chen, Y.;
Kobayshi, N.; Jiang, J. The First Solution-Processable n-Type
Phthalocyaninato Copper Semiconductor: Tuning the Semiconduct-
(69) Zhong, H.; Ly, K. H.; Wang, M.; Krupskaya, Y.; Han, X.;
̈
Zhang, J.; Zhang, J.; Kataev, V.; Buchner, B.; Weidinger, I. M.; Kaskel,
S.; Liu, P.; Chen, M.; Dong, R.; Feng, X. A Phthalocyanine-Based
Layered Two-Dimensional Conjugated Metal-Organic Framework as
a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction.
Angew. Chem., Int. Ed. 2019, 58, 10677−10682.
̌
(70) Xie, L. S.; Skorupskii, G.; Dinca, M. Electrically Conductive
Metal-Organic Frameworks. Chem. Rev. 2020, 120, 8536−8580.
7113
https://doi.org/10.1021/jacs.1c02145
J. Am. Chem. Soc. 2021, 143, 7104−7113