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He et al. Sci China Chem June (2020) Vol.63 No.6
[20] used tetrakis(triphenylphosphine)palladium (Pd(PPh3)4)
catalysed Suzuki-Miyaura reaction to obtain the bromo-
porphyrin-based Fe-N-C catalyst. However, besides the tar-
get atomically dispersed metal species, most of them in-
volves other metal species as additives, which would cause
the tedious pre- and/or post-treatment to remove the ad-
ditives [21]. Moreover, the trace residue may mislead the
mechanistic investigations and active-site identification
[22,23]. Therefore, it is a great challenge to rationally design
and facilely synthesize the porphyrin-based SACs with un-
ambiguous identification the active sites at the atomic/mo-
lecular level.
Herein, we propose a facile precursor-dilution strategy to
prepare Fe-N-C-type SACs through the Schiff-based reac-
tion via co-polycondensation of amino-porphyrin materials,
followed by pyrolysis at high temperature. The obtained Fe
SACs show much higher ORR performance than those of Fe
nanoclusters (NCs) or Fe nanoparticles (NPs). Besides, it is
superior to commercial 20 wt% Pt/C in terms of ORR ac-
tivities, stability, and methanol resistance in alkaline condi-
tion. Additionally, it gives moderate ORR activities under the
acidic condition. This work provides an ideal model for
understanding the structure-activity relationship of the cat-
alyst and promising candidate for ORR research.
freshly distilled pyrrole (50 mmol). After refluxing for 3 h,
the solution was cooled to room temperature naturally and
250 mL absolute ethanol was added. Subsequently, the as-
obtained precipitate was filtered and washed with DMF,
CH3OH, respectively. The product was dried at 80 °C in
vacuum for 12 h, giving the atropurpureus powder with the
yield of 22% [24].
Synthesis of tetra(4-aminophenyl)porphyrin (TAPP). Un-
der the N2 atmosphere, the as-synthesized TNPP (2.0 mmol),
tin chloride anhydrous (SnCl2, 20 mmol) were dissolved in
the concentrated hydrochloric acid (100 mL) in a three-
necked round-bottomed flask (250 mL) under magnetic
stirring and refluxed at 80 °C for 3 h. The solution was
cooled to room temperature naturally and 500 mL deionized
water was added. After the system was cooled to 0 °C, 5 wt%
sodium hydroxide solution was used to adjust the pH value to
8. The as-obtained precipitate was filtered and dried at 80 °C
in vacuum for 12 h and purified by Soxhlet extraction with
chloroform. Finally, the solvent was removed under vacuum
1
and gave the nut-brown powder with the yield of 66%. H
NMR (500 MHz, CDCl3): δ 8.90 (s, 8H, pyrrole β–H), 8.00–
7.99 (d, J=7.99 Hz, 8H, Ar–H), 7.08–7.06 (d, J=7.07 Hz, 8H,
Ar–H), 4.04 (s, 8H, –NH2). ESI-MS (m/z): [M+H]+ calcd.,
675.30; found, 675.15 [24].
Synthesis of tetra(4-aminophenyl)porphyrin iron (Fe-
TAPP). Under the N2 atmosphere, the TAPP (2.0 mmol), iron
(II) chloride (FeCl2, 10.0 mmol), methanol (30 mL), N,N-
dimethylformamide (30 mL) and chloroform (90 mL) were
charged in a three-necked round-bottomed flask (250 mL)
under magnetic stirring, followed by refluxing for 3 h at
150 °C. Subsequently, system was cooled to room tempera-
ture, transferred into a separatory funnel and washed with
water three times. The organic layer was collected and dried
over Na2SO4. Finally, the solvent was removed under va-
cuum, producing the khaki powder with the yield of 68%.
MALDI-TOF MS ([M-Cl]+): m/z calcd., 728.21; found,
727.73.
Synthesis of poly-FeTAPP(20). Under the N2 atmosphere,
the FeTAPP (0.075 mmol), TAPP (1.5 mmol; FeTAPP:
TAPP=1:20, mmol:mmol), p-phthalaldehyde (3.15 mmol),
1,2-dichlorobenzeneand (40 mL), n-butanol (40 mL) and
6 M acetic acid solution were charged in a three-necked
round-bottomed flask (250 mL), the mixture was stirred and
refluxed for 24 h at 100 °C. Subsequently, system was cooled
to room temperature, the as-obtained precipitate was filtered
and purified by Soxhlet extraction with dioxane and acetone,
respectively. And the product was dried at 80 °C in vacuum
for 12 h and gave the khaki powder with the yield of 81%.
Synthesis of Fe-N-C-T (T represent the pyrolysis tem-
perature). The above resulting material poly-FeTAPP(20)
was placed in a programmable tube furnace and subjected to
the following thermal treatments in a flow of N2 at a rate of
100 mL/min. The furnace temperature was firstly increased
2 Experimental
2.1 Chemicals and materials
Pyrrole (99%), 4-nitrobenzaldehyde (97%), nitrobenzene
(99.5%), lactic acid (85%), ethanol (99.5%), N,N-
dimethylformamide (DMF, 99.9%), 1,2-dichlorobenzeneand
(99.5%), n-butanol (99.5%), acetic acid (99.5%), methanol
(CH3OH, 99.9%), p-phthalaldehyde (99.5%), and tin chloride
anhydrous (SnCl2, 99%) were purchased from Aladdin.
Chloroform (99.5%) and hydrochloric acid (AR) were ob-
tained from Guangzhou Chemical Reagent Factory (China).
Iron oxide (Fe2O3, 99.9%), sodium hydroxide (98%), iron(II)
chloride (FeCl2, 99.9%) and tetraphenylporphyrin iron(III)
chloride (FeTPPCl, 98%) were obtained from Huaweiruike
Chemical. Platinum on activated carbon (20 wt% Pt/C) and
Nafion solution (5 wt%) were bought from Johnson Matthey
and DuPont company, respectively. Pyrrole was distilled un-
der the N2 atmosphere before used. Other chemical or mate-
rials were used as received without any further purification.
2.2 Preparation procedures
Synthesis of tetra(4-nitrophenyl)porphyrin (TNPP). Typi-
cally, 4-nitrobenzaldehyde (50 mmol), nitrobenzene
(200 mL) and lactic acid (50 mL) were added into a two-
necked round-bottomed flask (500 mL) under magnetic
stirring and heated to 120 °C, followed by the addition of