Porphyrin-based NiFe Porous Organic Polymer Catalysts for the Oxygen Evolution Reaction

Article abstract of DOI:10.1002/cctc.202001876

Porphyrin-based NiFe porous organic polymers (POPs) have been synthesized with good porosity and large BET surface areas (261 to 313 m² g^?1). These bimetallic POPs exhibit RuO₂-like OER activity, with the reaction for catalyst FeTAPP-NiTCPP-POP reaching a current density of 10 mA cm^?2 at a low overpotential of 338 mV and with a small Tafel slope of 52 mV dec^?1. FeTAPP-NiTCPP-POP was stable over a long period under reaction conditions. These bimetallic POPs exhibit better catalytic activity than their monometallic counterparts, due to synergetic interactions between the iron and nickel centers to facilitate the electrocatalytic process.

Full text of DOI:10.1002/cctc.202001876

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Porphyrin-based NiFe Porous Organic Polymer Catalysts for the
Oxygen Evolution Reaction
Authors: Jing Meng, Ze Xu, Hongxi Li, David James Young,
Chuanjiang Hu, and Yonggang Yang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemCatChem 10.1002/cctc.202001876
Link to VoR: https://doi.org/10.1002/cctc.202001876
01/2020

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
Porphyrin-based NiFe Porous Organic Polymer Catalysts for the
Oxygen Evolution Reaction
Jing Meng,[a] Ze Xu,[a] Hongxi Li,[a] David James Young,[b] Chuanjiang Hu,*[a] Yonggang Yang*[a]
Dedication ((optional))
Abstract: Porphyrin-based NiFe porous organic polymers (POPs)
have been synthesized with good porosity and large BET surface
areas (261 to 313 m2 g−1). These bimetallic POPs exhibit RuO2-like
OER activity, with the reaction for catalyst FeTAPP-NiTCPP-POP
reaching a current density of 10 mA cm-2 at a low overpotential of 338
mV and with a small Tafel slope of 52 mV dec-1. FeTAPP-NiTCPP-
POP was stable over a long period under reaction conditions. These
bimetallic POPs exhibit better catalytic activity than their monometallic
counterparts, due to synergetic interactions between the iron and
nickel centers to facilitate the electrocatalytic process.
conditions. The easily accessible sulfides, phosphides and
selenides are irreversibly oxidized to form oxide or hydroxide
phases.[4]
Conjugated N4 macrocycles are redox active chelating
ligands with rigid, planar structures that provide good stability for
metal ions. Some metalled macrocycle-based POPs, including
phthalocyanine (Pc) based NiFe POPs, have been reported as
OER catalysts.[5] Jiang’s group has recently reported an
Fe0.5Ni0.5Pc-CP OER catalyst that operates with an overpotential
of 317 mV at 10 mAcm−2. Their studies suggest that the improved
OER performance of Fe0.5Ni0.5Pc-CP relative to the monometallic
analogues can be attributed to the electronic interactions between
the adjacent Fe and Ni atoms.[5a] Liao et al. reported metallic
phthalocyanine-based covalent organic polymers as self-
sacrificial precursors for fabrication of mono- (Fe or Ni) and bi-
metallic (Fe-Ni) heteroatoms/carbon OER catalysts. The as-
prepared FeNi-COP-800 exhibited an IrO2-like OER activity with
a potential of 1.63 V at 10 mAcm−2.[5b]
Metallic porphyrin based POPs could be ideal OER catalyst
candidates due to their potentially high stability， porosity and
well-defined N4-coordination sites. Herein, we report the
bimetallic porphyrin-based porous organic polymers as shown in
Scheme 1, which have been synthesized by amide bond
formation. To the best of our knowledge, they are the first
porphyrin-based NiFe POP OER catalysts. FeTAPP-NiTCPP-
POP exhibited high electrocatalytic OER activity reaching a
current density of 10 mA cm-2 at a low overpotential of 338 mV
and with a relatively small Tafel slope of 52 mV dec-1. The
bimetallic porphyrin polymers exhibit superior OER performance
compared with the monometallic polymers due to the synergetic
interactions between iron and nickel centers.
Introduction
Porous organic polymers (POPs) are a class of porous materials
constructed from covalently linked organic building blocks. They
possess high stability with the potential for high porosity and
easily modified structures.[1] Metal ions can be incorporated by
including coordinating functionality in the framework, leading to
catalytically active POPs. The reactivity of catalytic POPs can be
fine-tuned by modulating the electronic properties of the
monomers and increasing the porosity of the structure, yielding
heterogenous catalysts potentially suitable for use in organic
synthesis, for carbon dioxide reduction and water splitting.[1d, 2]
Efficient electrochemical catalytic water splitting will be an
important element of the future hydrogen economy. The oxygen
evolution reaction (OER) is the key half-cell reaction of electrolytic
water-splitting process, because it is a kinetically sluggish and
complex, involving four proton-coupled electron transfer
processes. OER electrocatalysts are required to facilitate the
reaction and lower the activation energy barriers. Noble metals or
their oxides, such as RuO2 and IrO2, are good catalysts, but
expensive and somewhat unstable under OER conditions. Much
effort has been devoted to developing low-cost, highly efficient
and stable alternatives and non-noble metal electrochemical
catalysts such as NiFe-based compounds have been important
candidates in this respect .[3] However, many NiFe-based OER
catalysts also suffer from instability under prolonged OER
[a]
[b]
J. Meng, Z. Xu, Prof. H.X. Li, Prof. C.J. Hu, Prof. Y.G.Yang,
State and Local Joint Engineering Laboratory for Novel Functional
Polymeric Materials, College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, Suzhou 215123, Jiangsu, P. R.
China
E-mail: cjhu@suda.edu.cn; ygyang@suda.edu.cn
Prof. D. J. Young, College of Engineering, Information Technology and
Environment, Charles Darwin University, Darwin, NT 0909, Australia.
Scheme 1. Schematic of the typical synthesis of porous organic polymers.
Supporting information for this article is given via a link at the end of the
document.
1
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
Results and Discussion
Condensation of FeTAPP and NiTCPP produced bimetallic
FeTAPP-NiTCPP-POP. NiTAPP-FeTCPP-POP, monometallic
FeTAPP-FeTCPP-POP and NiTAPP-NiTCPP-POP were also
synthesized under similar conditions. A strong FTIR peak at 1658
cm-1 is attributable the stretching vibration of C=O bond for
FeTAPP-NiTCPP-POP (Figure 1). Similarly, C=O stretching
bands are located at 1631 cm-1, 1659 cm-1 or 1640 cm-1 for
FeTAPP-FeTCPP-POP, NiTAPP-NiTCPP-POP or NiTAPP-
FeTCPP-POP, respectively, which confirms the successful
synthesis of the polyamide network. Additionally, the carboxylic
acid C=O absorption at 1688 cm-1 is strongly attenuated in all
samples, also suggesting a high degree of conversion of
monomers to amide linked polymers.[6]
Figure 3. SEM image of (a) FeTAPP-NiTCPP-POP; (b) NiTAPP-FeTCPP-POP;
(c) NiTAPP-NiTCPP-POP and (d) FeTAPP-FeTCPP-POP.
Powder X-ray diffraction spectra indicated broad bands for
all POPs (Figure S1), consistent with poor crystallinity.
Thermogravimetric analysis indicated good thermal stability for all
four POPs. Weight loss observed below 100 ℃ is attributed to the
loss of solvent, followed by degradation of the polymer framework
at temperatures around 200 ℃ (Figure S1).
The porosities of the four POPs were measured by N2
adsorption and desorption at 77 K (Figure 2). All curves exhibited
typical type - I isotherms, consistent with a microporous polymeric
network. The Brunauer−Emmett−Teller (BET) surface areas of
FeTAPP-NiTCPP-POP was 261 m2 g−1 and quite similar in the
other three POPs (227 m2 g−1 for NiTAPP-FeTCPP-POP, 230 m2
g−1 for FeTAPP-FeTCPP-POP and 313 m2 g−1 for NiTAPP-
NiTCPP-POP). Pore sizes for all POPs were approximately 1 nm.
Polymer morphology was investigated by scanning electron
microscopy (SEM) and transmission electron microscopy (TEM)
(Figs.3 and 4, respectively). The SEM images indicated
agglomerated particles while the TEM images revealed layered
structures. X-ray photoelectron spectroscopy (XPS) spectra and
Figure 1. FTIR spectra of (a) FeTAPP-NiTCPP-POP; (b) NiTAPP-FeTCPP-
POP; (c) NiTAPP-NiTCPP-POP and (d) FeTAPP-FeTCPP-POP.
elemental mapping of FeTAPP-NiTCPP-POP revealed
a
homogeneous distribution of carbon, nitrogen, oxygen, iron and
nickel elements over the framework (Figs. S2-7). Inductively
Coupled Plasma (ICP) was used to confirm the stoichiometric
ratio of Fe/Ni in the bimetallic POPs (Table S1).
Figure 2. N2 adsorption – desorption isotherms of (a) FeTAPP-NiTCPP-POP;
(b) NiTAPP-FeTCPP-POP; (c) NiTAPP-NiTCPP-POP and (d) FeTAPP-
FeTCPP-POP. Pore size distributions inset.
2
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
slightly higher Tafel slope (75 mV dec-1) than FeTAPP-NiTCPP-
POP. Both bimetallic POPs possessed lower Tafel slopes than
that of commercial RuO2 (98 mV dec-1). Likewise, monometallic
POPs exhibited higher Tafel slopes of 99 mV dec-1 for NiTAPP-
NiTCPP-POP and 147 mV dec-1 for FeTAPP-FeTCPP-POP. The
Tafel slope is an indication of charger transfer ability. The lower
Tafel slope for bimetallic POPs indicates faster reaction kinetics.
These electrochemical measurements indicated that the
nickel-containing monometallic POP had superior OER activity
than its Fe counterpart, and that both bimetallic porphyrin
polymers exhibited better OER activity than the monometallic
polymers. These results can be attributed to synergistic
interactions between Fe and Ni atoms in the bimetallic species.
For comparison, we also investigated the catalytic activity of
monomers Fe(TAPP), Ni(TAPP), Fe(TCPP) and Ni(TCPP)
(Figure S8). The catalytic activity of Ni(TAPP) was low, while that
of Fe(TAPP) gradually decreased with the change of the number
of scans. Ni(TCPP) and Fe(TCPP) are soluble in aqueous KOH
and so their performance as heterogeneous OER catalysts
couldn’t be determined. These results further confirm that the
polymeric structures of these POPs are crucial for their superior
OER performance.
Figure 4. TEM image of (a) FeTAPP-NiTCPP-POP; (b) NiTAPP-FeTCPP-POP;
(c) NiTAPP-NiTCPP-POP and (d) FeTAPP-FeTCPP-POP.
Double layer capacitance (Cdl) was measured to evaluate
the electrochemical surfaces areas (ECSA) of the various
catalysts. Electrochemical performance could be indirectly
detected by cyclic voltammograms (CVs) at different scan rates
with the slope equal to the Cdl (Figure S9).[7] FeTAPP-NiTCPP-
POP had the largest Cdl value of 2.08 mF cm-2. The corresponding
value was 0.548 mF cm-2 for FeTAPP-FeTCPP-POP, 1.46 mF cm-
2
for NiTAPP-NiTCPP-POP and 1.55 mF cm-2 for NiTAPP-
FeTCPP-POP (Figure 6a). These results indicate the high
exposure of the catalytic active sites of FeTAPP-NiTCPP-POP,
which is presumably a major factor in the good electrocatalytic
activity of this POP. The bimetallic porphyrin polymers possessed
higher ECSAs, correlating with the ordering of overpotential
values and Tafel slopes, and consistent with synergetic
interactions between Ni and Fe centers.
Figure 5. (a) Linear sweep voltammograms (LSVs) of the catalysts in 1.0 M
KOH with iR (95%) at RT, scan rate: 10 mV s-1, glass carbon (GC) electrode
(diameter=5 mm, 0.196 cm2); (b) Tafel plots; (c) overpotential at 10 mA cm-2; (d)
FeTAPP-NiTCPP-POP LSV stability after 1000 CV cycles.
The polarization curves of FeTAPP-NiTCPP-POP, NiTAPP-
FeTCPP-POP, NiTAPP-NiTCPP-POP, FeTAPP-FeTCPP-POP,
pure glassy carbon electrode (GC) and commercial RuO2 were
obtained by linear sweep voltammetry (LSV) with iR-
compensation (95%) (Figure 5). Not surprisingly, pure GC had no
OER activity. Both bimetallic FeTAPP-NiTCPP-POP and
NiTAPP-FeTCPP-POP exhibited excellent OER activity with an
overpotential of 338 mV at a current density of 10 mA cm-2, which
is comparable with commercial RuO2 (320 mV). This value was
much smaller than that of NiTAPP-NiTCPP-POP (384 mV) and
FeTAPP-FeTCPP-POP (520 mV).
Figure 6. (a) Capacitive current densities plotted against scan rates and (b)
Nyquist plots obtained by EIS at 1.52V vs. RHE; (c) chronopotentiometric curves
of FeTAPP-NiTCPP-POP at a current density of 10 mA cm-2; (d) amperometric
i-t curve of FeTAPP-NiTCPP-POP (at 1.58 V vs. RHE) for 10000 s.
FeTAPP-NiTCPP-POP also exhibited the lowest Tafel slope
(52 mV dec-1) among these POPs. NiTAPP-FeTCPP-POP had a
3
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
Electrochemical impedance spectroscopy (EIS) was
FeNi-based catalysts are the active center for oxygen evolution.
Incorporation of Fe modulates the Ni electronic environment,
improving OER performance.[3b, 10] In our case, the Ni 2p peak of
FeTAPP-NiTCPP-POP (Ni 2p3/2 = 855.4 eV, Ni 2p1/2 = 872.7 eV)
and NiTAPP-FeTCPP-POP (Ni 2p3/2 = 855.0 eV, Ni 2p1/2 = 872.2
eV) shifted to lower binding energies compared with NiTAPP-
NiTCPP-POP (Ni 2p3/2 = 855.8 eV, Ni 2p1/2 = 873.1 eV), which
suggests the electron density at the Ni center increases. [11]
Amide-linked porphyrins are conjugated systems and a
change of the metal ions can adjust the electronic structure of the
whole system. Besides the XPS results, calculations of the
Mulliken charges can also provide evidences. We calculated the
Mulliken charges of Ni and Fe in the model complexes, FeP1-
NiP2, NiP1-FeP2, NiP1-NiP2 and FeP1-FeP2 (Figure S12).
These calculations were performed at the level of B3LYP/3-21G.
The Mulliken charge of Fe and Ni was 1.170 and 1.027e in FeP1-
NiP2, 1.172 and 1.025e in NiP1-FeP2. (Table S3) Compared with
the average 1.190e for Fe in FeP1-FeP2 and 1.111e for Ni in
NiP1-NiP2, these lower Mulliken charges in the mixed-metal
models suggest higher electron densities at metal centers which
is consistent with the XPS results.
performed at a potential of 1.52 V vs. RHE. As shown in the
Nyquist plots of the catalysts and corresponding equivalent circuit
model (Figure 6b), the charge transfer resistances (Rct) were
52.28 Ω for FeTAPP-NiTCPP-POP, 63.75 Ω for NiTAPP-
FeTCPP-POP, 207.6 Ω for NiTAPP-NiTCPP-POP and 1475 Ω for
FeTAPP-FeTCPP-POP. The bimetallic species had obviously
smaller Rct values, indicating a lower charge-transfer impedance
and smaller resistance values, consistent with better electrode
conductivity and faster electron transfer rate, ultimately resulting
in the better electrocatalytic performance of these catalysts for
OER.
We also measured turnover frequencies (TOFs) to evaluate
the intrinsic activity of the POPs.[8] TOF values were calculated at
a current density of 10 mA cm-2 (Table S2). The TOF value for
FeTAPP-NiTCPP-POP (0.110 s-1) was the highest among these
polymers. The value of NiTAPP-FeTCPP-POP (0.108 s-1) was
higher than that for NiTAPP-NiTCPP-POP (0.103 s-1) and
FeTAPP-FeTCPP-POP (0.079 s-1), confirming the superior OER
performance of the bimetallic POPs. The electrocatalytic
properties of FeTAPP-NiTCPP-POP and NiTAPP-FeTCPP-POP
were similar, suggesting that the small structural difference
between these two species made little difference to their catalytic
activity.
Stability is another important parameter for evaluating
electrochemical catalyst performance and so we investigated the
stability of the best performing catalyst, FeTAPP-NiTCPP-POP.
The LSV curves of FeTAPP-NiTCPP-POP before and after 1000
CV cycles (Figure 5d) indicated only a small change in current
density. The chronopotentiometric curve (Figure 6c) indicated that
the potential of the FeTAPP-NiTCPP-POP remained unchanged
at a current density of 10 mA cm-2 for a duration of 10000 s. The
i-t curve of the FeTAPP-NiTCPP-POP in Figure 6d also showed
negligible loss in the static current. These results demonstrate the
high stability of FeTAPP-NiTCPP-POP for OER catalysis.
The microstructure of FeTAPP-NiTCPP-POP after the OER
stability test was investigated by SEM and TEM. The SEM and
TEM images in Figure S10 suggested that morphology was
retained after 1000 CV cycles.
Both experimental results and theoretical analysis reveal
there are synergetic interactions between the Fe/Ni centers which
could facilitate the formation of oxygenated intermediates and
improve the catalytic OER activity of the bimetallic POPs. [3a, 3i, 11-
12]
XPS spectra of used FeTAPP-NiTCPP-POP revealed new
peaks for Ni 2p3/2 and Ni 2p1/2 at 857.1 eV and 874.7 eV (Figure
S11) correspond to Ni3+, demonstrating the formation of high
valence Ni during the oxygen evolution process under alkaline
conditions. In the high-resolution O 1s spectrum (Fig. S11c), a
new signal at 530.8 eV is ascribed to metal-O (M-O) bonding.[15]
These results indicate that during the oxygen evolution reaction,
the oxidation state of the metal changes and active intermediates
such as metal oxides or peroxides are formed, resulting in
favorable reaction kinetics.
Conclusion
Porphyrin-based NiFe POPs exhibit RuO2-like OER activity.
FeTAPP-NiTCPP-POP reached a current density of 10 mA cm-2
at a low overpotential of 338 mV with a small Tafel slope of 52 mV
dec-1, which is significantly better than the corresponding catalytic
performance of the monometallic POPs. Experimental results and
theoretical calculations indicate that the electronic structures of
the metal ions are modulated by each other in the conjugated
bimetallic POPs, leading to electron rich Ni centers that facilitate
the formation of oxygenated intermediates and improve the
catalytic OER activity of the bimetallic POPs. Our work presents
one useful example for the development of porphyrin-based
POPs as OER catalysts.
Figure 7. (a) Fe 2p and (b) Ni 2p XPS spectra of these POPs.
In order to better understand the synergetic interactions
between Fe and Ni atoms for OER catalysis, we investigated the
XPS data more closely.(Figure 7) The high-resolution XPS
spectrum of FeTAPP-FeTCPP-POP possessed two diagnostic
Iron peaks, Fe 2p3/2 and Fe 2p1/2 at 712.2 eV and 725.1 eV,
respectively, while the corresponding values for FeTAPP-
NiTCPP-POP were 711.8 eV and 724.2 eV, 711.6 eV and 724.1
eV for NiTAPP-FeTCPP-POP, unveiling the Fe(Ⅲ) nature in the
POPs.[9] These lower Fe 2p binding energies for the bimetallic
catalysts by 0.4-1 eV may help explain the improved catalytic
performance of the mixed-metal POP catalysts. The Ni centers of
Experimental Section
General Information.
Nafion (5%, Sigma-Aldrich), tetrahydrofuran (THF, 3A Dry) and
triethylamine (TEA, 3A Dry) were purchased from 3 A Chemicals. Carbon,
mesopor (cabot Vulcan xc-72) was purchased from Macklin. Pyrrole used
4
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
freshly distilled under vacuum. Solvents, acids, bases and metal salts were
used as received. 5,10,15,20-Tetrakis(4-aminophenyl)-21H,23H porphyrin
(TAPP) was prepared according to literature reports.[13,14] Metallation of
To a solution of Fe(TMCPP)Cl (80 mg, 0.086 mmol) in a mixed solvent of
THF (8 mL) and MeOH (8 mL) was added 2 mol L-1 KOH (3.2 mL), and the
reaction was refluxed for 12 h. After cooling to room temperature, the
organic solvent was evaporated, and water added. The resulting slurry was
heated until the solid was fully dissolved and the resulting homogeneous
solution was acidified with 1M HCl until a precipitate stopped forming. This
brown solid was collected by filtration, washed with water and dried under
vacuum, yield 95%. FTIR (ATR): v= 3444 (m), 2921 (w), 2515 (w), 1687
(s), 1604 (s), 1582 (m), 1404 (s), 1311 (m), 1238 (s), 1202 (m), 1174 (m),
1100 (m), 999 (s), 867 (m), 799 (s), 784 (s), 719 (m) cm-1.
TCPP (TCPP
= 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin) was
performed according to a literature report.[16]
Preparation of Fe(TAPP)
TAPP (0.50 g, 0.74 mmol) and anhydrous FeCl2 (0.50 g,3.94 mmol) were
mixed in a 100 mL Schlenk flask, which was then evacuated and filled with
nitrogen for three cycles. Anhydrous THF (50 mL) and pyridine (0.3 mL)
were added and the resulting mixture was refluxed for 3h. After cooling to
room temperature, the solution was evaporated to dryness and the solid
was washed with CH2Cl2 (50 mL×2) and distilled water until the filtrate was
colourless. The solid was then washed with CH3OH, again until the filtrate
was colourless. The methanol filtrate was collected and evaporated to
dryness. The resulting solid was dried under vacuum and 0.26 g of dark
purple solid was obtained, yield 47.0%. UV-vis (CH3OH, λmax, nm): 425,
658. FTIR (ATR): v= 3355 (m), 3207 (w), 3028 (w), 1601 (s), 1512 (s),
1491 (w), 1387 (m), 1335 (m), 1176 (s), 996 (s), 847 (m), 802 (s), 715 (w)
cm-1.
[5,10,15,20-Tetrakis(4-carboxyphenyl) porphyrinato]-nickel(
(Ni(TCPP))
Ⅱ )
To a solution of Ni(TMCPP) (0.77 g, 0.85 mmol) in the mixed solvent of
THF (77 mL) and MeOH (77 mL) was added 2 mol L-1 KOH (30.8 mL), and
the reaction was refluxed for 12 h. After this period, the organic solvent
was evaporated and water added. The resulting mixture was heated until
the solid was fully dissolved, then the homogeneous solution was acidified
with HCl to pH=2-3. Cooling in ice water produced a red solid that was
filtered under vacuum. This red solid was collected, washed with water and
dried under vacuum, yield 93%. FTIR (ATR): v= 3405 (w), 2922 (w), 2519
(w), 1687 (s), 1604 (s), 1565 (m), 1403(s), 1350(m), 1311 (m), 1237 (s),
1175 (m), 1100 (m), 1002 (s), 865 (m), 826 (m), 790 (s), 711 (m) cm-1. 1H
NMR (400MHz, DMSO): δ13.28(s,4H), 8.73(s, 8H), 8.29(s, 8H), 8.12(d,
8H).
Preparation of Ni(TAPP)
A solution of TAPP (0.50 g, 0.74 mmol) and Ni(OAc)2·4H2O (1.84 g, 7.4
mmol) in 45 mL of mixed solvent (DMF/CH2Cl2=2:1) was refluxed overnight.
The solvent was then evaporated to dryness and the resulting solid was
washed with water and dried under vacuum. A purple solid (0.43 g) was
obtained, yield 85%. 1H NMR (DMSO, 400MHz, ppm): δ5.51(s, 8H), 6.91(s,
8H), 7.63(s, 8H), 8.76(s, 8H). UV-vis (CH3OH, λmax, nm): 422, 531.
Synthesis of POP materials
POP materials were synthesized by an amidation reaction between acyl
chlorides and amines at room temperature. Ni(TCPP) (33.9 mg, 0.04
mmol) was refluxed in SOCl2 (5 mL) overnight. The solvent was then
removed and the resulting solid dissolved in anhydrous THF. This solution
was then added dropwise to a solution of Fe(TAPP) (29.8 mg, 0.04 mmol)
and TEA (0.0223 mL, 0.16 mmol) in anhydrous THF (5 mL) under N2. The
temperature was maintained at 0 ℃ for 1 h, then raised to room
temperature. The mixture was stirred for 72 h and the resulting precipitate
was separated by centrifugation, washed several times with water,
acetone, methanol and ethanol, and finally dried at 70℃ under vacuum.
The product, FeTAPP-NiTCPP-POP, was obtained in 80 % yield. NiTAPP-
FeTCPP-POP, FeTAPP-FeTCPP-POP and NiTAPP-NiTCPP-POP were
prepared using similar procedures.
Preparation
of
5,10,15,20-tetrakis(4-methoxycarbonylphenyl)
porphyrin (TMCPP)
To propionic acid (100 mL) in a 500 mL three-neck flask were added
pyrrole (3.0 mL, 0.043 mol) and methyl p-formylbenzoate (6.9 g, 0.042
mol). The solution was refluxed for 12 h in darkness. After the reaction
mixture was cooled to room temperature, crystals were collected by
suction-filtration. (1.9 g, 2.24 mmol, 21.3% yield). 1H NMR (300MHz,
CDCl3): δ8.81(s, 8H), 8.43(s, 8H), 8.28(d, 8H), 4.11(s, 12H), -2.83(s, 2H).
[5,10,15,20-Tetrakis(4-methoxycarbonylphenyl)
porphyrinato]-
iron(Ⅲ) chloride (Fe(TMCPP)Cl).
Catalyst Characterization.
A solution of TMCPP (0.25 g, 0.3 mmol), and FeCl2·4H2O (0.76 g, 3.84
mmol) in 30 mL of DMF was refluxed for 6h. After the mixture was cooled
to room temperature, 45 mL of H2O was added. The resulting precipitate
was filtered and washed with 15 mL of H2O twice. The resulting solid was
dissolved in CHCl3 washed three times with 1 M HCl and twice with water.
The organic layer was dried over anhydrous magnesium sulfate and
evaporated to afford quantitative dark brown crystals.
1H NMR spectra were recorded using an INOVA-400 NMR spectrometer.
The samples were examined by powder X-ray diffraction (PXRD), which
was conducted on
PANalytical) with
a
X’Pert-Pro MPD diffractometer (Netherlands
Cu Kα X-ray source (λ 1.540598 Å).
a
=
Thermogravimetry analysis (TGA) of the samples were conducted using a
Mettler Toledo Star System under a nitrogen atmosphere at a heating rate
of 10 ℃ /min. FT-IR spectra were acquired with a Bruker VERTEX
70+HYPERION 2000. XPS measurements were conducted on a Thermo
Scientific EXCALAB 250 XI spectrometer. Energy dispersive X-ray
spectroscopy (EDS) was performed using a Carl Zeiss EVO18 scanning
electron microscope. Scanning electron microscopy (SEM) images were
taken with a HITACHI S-4700 cold field-emission scanning electron
microscope. The morphology of the materials was studied by transmission
electron microscopy (TEM, HITACHI HT7700). ICP (inductively coupled
plasma) was used to analyse metal content and performed using a 710-
ES inductively coupled plasma spectrometer. N2 gas adsorption
experiments were carried out on a BELSORP-max (BEL, Japan).
[5,10,15,20-Tetrakis(4-methoxycarbonylphenyl)
porphyrinato]-
nickel(Ⅱ) (Ni(TMCPP))
A solution of TMCPP (0.254 g, 0.3 mmol) and NiCl2·6H2O (0.913 g, 3.84
mmol) in 30 mL of DMF was refluxed for 6 h. After cooling to room
temperature, 45 mL of H2O was added and the resulting precipitate was
filtered and washed with 15 mL of H2O twice. The solid was dissolved in
CHCl3 and washed three times with 1 M HCl and twice with water. The
organic layer was dried over anhydrous magnesium sulfate and
evaporated to afford crimson crystals quantitatively.
Electrochemical Studies.
[5,10,15,20-Tetrakis(4-carboxyphenyl)
chloride (Fe(TCPP)Cl)
porphyrinato]-iron(
Ⅲ
)
The electrochemical performance of the POPs materials was evaluated on
a CHI760E electrochemical workstation using a three electrode system,
5
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
with Pt wire as the counter electrode, a glass carbon (GC) electrode (5 mm
in diameter) as the working electrode, and Ag/AgCl (3 M KCl) as the
reference electrode. The catalytic ink was prepared by dispersing 2.5 mg
of the material and 2.5 mg of the cabot Vulcan xc-72 in 500 μL solution
containing 485 μL isopropanol and 15 μL 5% Nafion solution followed by
ultrasonication for 1 h. The above suspension (10 μL) was dropped on to
the GC electrode and dried at room temperature. All potentials were
Sang, Q. Wu, H. Liu, K. Liu, Int. J. Hydrogen Energy 2019, 44, 2656-
2663; h) M. Gong, H. Dai, Nano Research 2015, 8, 23-39; i) W. Li, F. Li,
H. Yang, X. Wu, P. Zhang, Y. Shan, L. Sun, Nat. Commun. 2019, 10,
5074; j) W. Cheng, X. Zhao, H. Su, F. Tang, W. Che, H. Zhang, Q. Liu,
Nat. Energy 2019, 4, 115-122; k) M. P. Browne, Z. Sofer, M. Pumera,
Energ. Environ. Sci. 2019, 12, 41-58; l) D. A. Kuznetsov, B. Han, Y. Yu,
R. R. Rao, J. Hwang, Y. Roman-Leshkov, Y. Shao-Horn, Joule 2018, 2,
225-244; m) V. Vij, S. Sultan, A. M. Harzandi, A. Meena, J. N. Tiwari, W.-
G. Lee, T. Yoon, K. S. Kim, ACS Catal. 2017, 7, 7196-7225; n) J. Qi, W.
Zhang, R. Cao, Chemcatchem 2018, 10, 1206-1220.
referred to the reversible hydrogen electrode (RHE): ERHE = EAg/AgCl
+
0.197 + 0.059 × pH. Linear sweep voltammetry (LSV) was recorded in an
O2-saturated 1.0 M KOH at a scan rate of 10 mV· s-1 to obtain the
polarization curves. The overpotential (η) was calculated according to the
following formula: η = ERHE - 1.23 V. The Tafel slope was obtained from
the LSV curves and Tafel equation. LSV and Tafel data were corrected
for iR compensation. Electrochemical impedance spectroscopy (EIS) was
performed at a frequency ranging from 100 kHz to 0.1 Hz at 1.52 V vs.
RHE with the three-electrode cell system in 1.0 M KOH solution. The
chronopotentiometry was measured at a current density of 10 mA cm-2. To
estimate the electrochemical active surface area (ECSA) of the catalysts,
the electrochemical double layer capacitance (Cdl) was measured via CV
in the non-Faradaic potential range of 0.076 to 0.176 V versus Ag/AgCl
with scan rates from 10-100 mV s-1. The current differences at 0.126 V
against scan rates were fitted to obtain the Cdl: Cdl = Δj / ΔV, where Cdl, Δj
and ΔV are the double-layer capacitance (mF cm-2) of the electroactive
materials, charging current (mA cm-2) and scan rate (mV s-1), respectively.
ESCA = Cdl / Cs, (Cs is the specific capacitance, and the measured value
in the 1.0 M KOH electrolyte solution is 0.040 mF cm-2). Turnover
frequency (TOF) values of catalysts were calculated according to the
following equation: TOF = (J×A)/(4×F×m), where j (mA cm-2) is the current
density during the LSV measurement in 1.0 M KOH, A is the surface area
of the glass carbon electrode (GC, 0.196 cm2), F is the Faraday constant
(96485 C mol-1) and 4 is because the OER is a four electron transfer step,
m is the moles of active sites on the electrode (the value of m can be
calculated from the weight and the molecular weight of the coated
catalysts).
[4]
[5]
Y. Wang, B. Kong, D. Zhao, H. Wang, C. Selomulya, Nano Today 2017,
15, 26-55.
a) D. D. Qi, X. Chen, W. P. Liu, C. X. Liu, W. B. Liu, K. Wang, J. Z. Jiang,
Inorg. Chem. Front. 2020, 7, 642-646; b) Z. Liao, Y. Wang, Q. Wang, Y.
Cheng, Z. Xiang, Appl. Catal. B-Environ. 2019, 243, 204-211. c) Y. Li, X.
Tao, J. Wei, X. Lv, H.-G. Wang, Chem. Asian J. 2020, 15,1970-1975; d)
A. Wang, L. Cheng, W. Zhao, X. Shen, W. Zhu, J. Colloid Interface Sci.
2020, 579, 598-606; e) A. Singh, S. Roy, C. Das, D. Samanta, T. K. Maji,
Chem Commun (Camb) 2018, 54, 4465-4468; f) S. Bhunia, K. Bhunia, B.
C. Patra, S. K. Das, D. Pradhan, A. Bhaumik, A. Pradhan, S.
Bhattacharya, ACS Appl Mater Interfaces 2019, 11, 1520-1528; g) A.
Wang, L. Cheng, X. Shen, W. Zhu, L. Li, Dyes Pigments 2020, 181; h) H.
Li, Z. Sui, New J. Chem. 2019, 43, 17963-17973.
[6]
[7]
a) N. Manoranjan, D. H. Won, J. Kim, S. I. Woo, J. CO2 Util. 2016, 16,
486-491; b) A. Rehman, S.-J. Park, Bull. Korean Chem. Soc. 2017, 38,
1285-1292; c) Z. Liu, J. Ou, H. Wang, X. You, M. Ye, ACS Appl. Mater.
Inter. 2016, 8, 32060-32067; d) B.-J. Yao, J.-T. Li, N. Huang, J.-L. Kan,
L. Qiao, L.-G. Ding, F. Li, Y.-B. Dong, ACS Appl. Mater. Inter. 2018, 10,
20448-20457.
a) J. Meng, Y. Zhou, H. Chi, K. Li, J. Wan, Z. Hu, Chemistryselect 2019,
4, 8661-8670; b) F.-L. Li, P. Wang, X. Huang, D. J. Young, H.-F. Wang,
P. Braunstein, J.-P. Lang, Angew. Chem. Int. Edit. 2019, 58, 7051-7056;
c) G. Liu, K. Wang, X. Gao, D. He, J. Li, Electrochim. Acta 2016, 211,
871-878.
[8]
[9]
a) G. Cai, L. Zeng, L. He, S. Sun, Y. Tong, J. Zhang, Chemistry – An
Asian Journal 2020, 15, 1963-1969; b) X. L. Wang, L. Z. Dong, M. Qiao,
Y. J. Tang, J. Liu, Y. Li, S. L. Li, J. X. Su, Y. Q. Lan, Angew. Chem. Int.
Ed. Engl. 2018, 57, 9660-9664.
Acknowledgements
a) F. Zheng, D. Xiang, P. Li, Z. Zhang, C. Du, Z. Zhuang, X. Li, W. Chen,
ACS Sustain. Chem. Eng. 2019, 7, 9743-9749; b) S. Yuan, L. Cui, X. He,
W. Zhang, T. Asefa, Int. J. Hydrogen Energy 2020, 45, 28860-28869; c)
Z. Liao, Y. Wang, Q. Wang, Y. Cheng, Z. Xiang, Appl. Catal. B-Environ.
2019, 243, 204-211.
We thank the National Nature Science Foundation of China for
financial support (Nos 22071169 and 51673141), as well as the
Local Joint Engineering Laboratory for Novel Functional
Polymeric Materials, the Priority Academic Program Development
of Jiangsu Higher Education Institutions (PAPD) and the Project
of Scientific and Technologic Infrastructure of Suzhou
(SZS201905).
[10] a) F. L. Li, P. Wang, X. Huang, D. J. Young, H. F. Wang, P. Braunstein,
J. P. Lang, Angew. Chem. Int. Ed. Engl. 2019, 58, 7051-7056; b) F. L. Li,
Q. Shao, X. Huang, J. P. Lang, Angew. Chem. Int. Ed. Engl. 2018, 57,
1888-1892; c) M. W. Louie, A. T. Bell, J. Am. Chem. Soc. 2013, 135,
12329-12337; d) C. Tang, H. S. Wang, H. F. Wang, Q. Zhang, G. L. Tian,
J. Q. Nie, F. Wei, Adv. Mater. 2015, 27, 4516-4522; e) J. Chang, L. Chen,
S. Zang, Y. Wang, D. Wu, F. Xu, K. Jiang, Z. Gao, J. Colloid Interface
Sci. 2020, 569, 50-56; f) X. Zhang, H. Xu, X. Li, Y. Li, T. Yang, Y. Liang,
ACS Catal. 2015, 6, 580-588.
Keywords: Porous organic polymer • Porphyrin • Oxygen
evolution reaction • Electrocatalysis
[11] a) H. Dong, X. Zhang, X. C. Yan, Y. X. Wang, X. Sun, G. Zhang, Y. Feng,
F. M. Zhang, ACS Appl Mater Interfaces 2019, 11, 45080-45086; b) X.
Ling, F. Du, Y. Zhang, Y. Shen, T. Li, A. Alsaedi, T. Hayat, Y. Zhou, Z.
Zou, Rsc Advances 2019, 9, 33558-33562; c) Q. Zha, M. Li, Z. Liu, Y. Ni,
ACS Sustain. Chem. Eng. 2020, 8, 12025-12035.
[1]
a) S. Das, P. Heasman, T. Ben, S. Qiu, Chem. Rev. 2017, 117, 1515-
1563; b) D. Taylor, S. J. Dalgarno, Z. Xu, F. Vilela, Chem. Soc. Rev. 2020,
49, 3981-4042; c) T. Zhang, G. Xing, W. Chen, L. Chen, Mater. Chem.
Front. 2020, 4, 332-353; d) Y. Tian, G. Zhu, Chem. Rev. 2020, 120, 8934-
8986.
[12] X. Zhao, B. Pattengale, D. Fan, Z. Zou, Y. Zhao, J. Du, J. Huang, C. Xu,
ACS Energy Letters 2018, 3, 2520-2526.
[2]
[3]
T.-X. Wang, H.-P. Liang, D. A. Anito, X. Ding, B.-H. Han, J. Mater. Chem.
A 2020, 8, 7003-7034.
[13] M. Yuasa, K. Oyaizu, A. Yamaguchi, M. Kuwakado, J. Am. Chem. Soc.
2004, 126, 11128-11129.
a) J. Mohammed-Ibrahim, J. Power Sources 2020, 448, 227375; b) L.
Lei, D. Huang, C. Zhou, S. Chen, X. Yan, Z. Li, W. Wang, Coord. Chem.
Rev. 2020, 408, 213177; c) L. Gong, H. Yang, A. I. Douka, Y. Yan, B. Y.
Xia, Adv. Sustain. Syst. 2020, 2000136; d) R. Gao, D. Yan, Adv. Energy
Mater. 2019, 1900954; e) K. Zhu, X. Zhu, W. Yang, Angew. Chem. Int.
Edit. 2019, 58, 1252-1265; f) W. Zhang, D. Li, L. Zhang, X. She, D. Yang,
J. Energy Chem. 2019, 39, 39-53; g) C. Li, J. Chen, Y. Wu, W. Cao, S.
[14] Z. Tan, J. Zhu, W. Yang, Catal. Commun. 2017, 94, 60-64.
[15] J.-T. Ren, L. Chen, Y.-S. Wang, W.-W. Tian, L.-J. Gao, Z.-Y. Yuan, ACS
Sustain. Chem. Eng. 2019, 8, 223-237.
[16] D. Feng, Z. Y. Gu, J. R. Li, H. L. Jiang, Z. Wei, H. C. Zhou, Angew. Chem.
Int. Ed. Engl. 2012, 51, 10307-10310.
6
This article is protected by copyright. All rights reserved.

10.1002/cctc.202001876
ChemCatChem
FULL PAPER
Entry for the Table of Contents
Porphyrin-based NiFe porous organic polymers (POPs) exhibit RuO2-like OER activity. These bimetallic POPs show better catalytic
OER activity than their monometallic counterparts, which can be attributed to the synergetic interactions between the iron and nickel
centers.
7
This article is protected by copyright. All rights reserved.