Fe-N-doped hierarchical mesoporous carbon nanomaterials as efficient catalysts for oxygen reduction in both acidic and alkaline media

Article abstract of DOI:10.1039/c9ta01807g

Fe-based electrocatalysts are known as one of the best alternatives to replace platinum in polymer electrolyte membrane fuel cells (PEMFCs) for their future application in small portable or automotive power sources. However, one key obstacle for the application of Fe-based catalysts is their dissatisfactory activity toward the oxygen reduction reaction (ORR). Herein, we demonstrate that agglomerated Fe₂O₃ nanoparticles are capable of improving the performance of Fe-based catalysts. The impact of the shape, size, and microstructure of Fe₂O₃ nanoparticles on the ORR activity of Fe-based catalysts is well discussed. All the results indicate that the Fe₂O₃ nanoparticles bound by high-index (110) facets may involve in the formation of numerous active sites for the ORR. The best Fe-based catalyst in this study exhibited superior ORR catalytic activity with its half-wave potential (E_1/2) only negatively shifting by 32 mV compared to that of commercial Pt/C in 0.1 M HClO₄ solution. Based on this catalyst, the peak power density of an air-breathing PEMFC reached approximately 63% of that of Pt/C (91 mW cm^-2) in an air-conditioned room with a temperature of 20 °C.

Full text of DOI:10.1039/c9ta01807g

View Article Online
View Journal
Journal of
M at erials Chemistry A
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: R. Dun, M. Hao, Y.
Su and W. Li, J. Mater. Chem. A, 2019, DOI: 10.1039/C9TA01807G.
Volume
4
Number
1
7
January 2016 Pages 1–330
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry A
Accepted Manuscripts are published online shortly after
Materials for energy and sustainability
www.rsc.org/MaterialsA
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

Page 1 of 9
J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
View Article Online
DOI: 10.1039/C9TA01807G
ARTICLE
Fe-N-Doped Hierarchical Mesoporous Carbon Nanomaterials as
Efficient Catalysts for Oxygen Reduction in Both Acidic and
Alkaline Media
Received 00th January 20xx,
Accepted 00th January 20xx
Rongmin Dun, a,b Menggeng Hao, a,b Yumiao Su and Wenmu Li *
a
a
DOI: 10.1039/x0xx00000x
Fe-based electrocatalysts are known as the one of best options to replace the platinum in the polymer electrolyte membrane
fuel cells (PEMFCs) for the future application in small portable or automotive power sources. One key obstacle for the
application of Fe-based catalysts is their dissatisfactory activity toward the oxygen reduction reaction (ORR). Here, it is
demonstrated that the agglomerate Fe
The impacts of the shape, size, and microstructure of Fe
discussed. All results point out that the Fe nanoparticles bound by high-index (110) facets might involve in the formation
of more active sites for ORR. The best Fe-based catalysts in this study exhibits a superior ORR catalytical activity with the
half-wave potential (E1/2) only 32 mV negative shifts than that of commercial Pt/C in 0.1 M HClO solution. Based on this
2
O
3
nanoparticles are capable of improving the performance of Fe-based catalysts.
2 3
O
nanoparticles on the ORR activity of Fe-based catalysts are well
2 3
O
4
-2
catalyst, the peak power density of air-breathing PEMFCs reaches approximately 63% to that of the Pt/C (91 mW cm ) in an
air-conditioned room with temperature of 20 °C.
-1
reported Fe-N
X
-C catalysts (turnover frequency, TOF = 0.4 s )
Introduction
The emergence of polymer electrolyte membrane fuel cells
are generally difficult to achieve better catalytic activity than
that of Pt/C (TOF = 25 s ) for ORR in acidic media. Therefore,
many efforts should be focused on fabricating the efficient M-
-1
16
(PEMFCs) is essential to solve the global energy shortage and
N
X
-C catalysts with plenty of active sites and the high surface
area.
In this regard, porous carbon materials are of significance for
the design and synthesis of high-performance M-N -C catalysts,
environmental pollution problems due to their high energy
conversion efficiency and environmentally friendly features.
However, in practice, the oxygen reduction reaction (ORR) of
the cathodic is relatively sluggish, which is a bottleneck for the
commercialization of PEMFCs.
catalysts have been recognized as the most efficient catalysts
toward ORR, the high cost, low abundance, poor stability, as
well as the intolerance to fuel crossover (e.g., methanol, CO,
etc.) of Pt/C significantly limit their widespread application,
which leads to enormous efforts devoted to investigating
1
,2
X
in which the microporous can create the catalytic active sites
and the mesoporous can offer better channels for mass
3
-5
Although Pt or Pt-based
1
7
transportation.
nanostructure of M-N
methods, soft-templating methods and liquid phase methods.
Although the M-N -C catalysts with silica colloid, ordered
There are various methods to tune
X
-C catalysts, such as the hard-templating
X
mesoporous silica SBA-15 or montmorillonite as template have
the well-controlled mesoporous structures and high catalytic
performance in acidic media, it is not economic and
environment friendly because of the additional methods and
the utilization of dangerous hydrofluoric acid or hot alkaline
6
-8
alternative cost-effective materials.
Therefore, rational
design of extremely stable non-precious metal (NPM) catalysts
with closing or even higher ORR activity than Pt is the core of
fuel-cell research.9 During the past decades, transition metal–
-13
X X
nitrogen–carbon (M–N –C) materials, especially for Fe-N -C,
1
8,19
liquor in removing the templates.
Therefore, searching a
which were generally prepared by heat-treating the Fe source,
N source with as-prepared carbon materials, have attracted
great interests because of the high reaction activity toward ORR
in both alkaline and acidic electrolytes.
poor intrinsic catalytic activity of a single active site, most of the
facile and effective strategy to synthesize high performance
mesoporous M-N
desirable.
X
-C nanomaterials toward ORR is highly
1
4,15
Whereas, due to the
Covalent triazine frameworks (CTFs) are microporous 1,3,5-
triazine units conjugated polymers with abundant nitrogen
atoms for transition metal coordination, which make them
potentially suitable as novel platforms for the synthesis of
a. Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian
Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, China E-mail: liwm@fjirsm.ac.cn
2
0-22
electrocatalysts.
In our group, iron-modified CTFs catalysts
(Fe-CTFs) with comparable ORR activity to that of commercial
Pt/C were successfully prepared by simply one-pot ionothermal
b.
University of Chinese Academy of Sciences, Beijing 100049, China
Electronic Supplementary Information (ESI) available: XRD patterns, XPS spectrums,
EIS, SEM and electrochemical performances of control samples are listed in ESI. See
DOI: 10.1039/x0xx00000x
polymerization of aromatic nitrile monomers in molten ZnCl
2
23
containing FeBr
2
.
However, the repeatability of our method
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Page 2 of 9
ARTICLE
Journal Name
still needs further improvement. One possible explain is that the transparent solution. Then the solution was transVfieewrrAertdicleinOtnolinae
one-pot ionothermal preparation method cannot ensure the 50 mL Teflon-lined stainless-steel autoclavDeOfI:o1r0h.1y0d39ro/Cly9sTiAs0t1o80g7eGt
formation of large proportion of highly active sites in Fe-CTFs the Fe
materials. Therefore, more witty designs require further mg), m-Phthalodinitrile (200 mg) and anhydrous ZnCl
2
O
3
hollow microspheres. Fe
2
O
3
hollow microspheres (50
(1000 mg)
2
development of more effective Fe-CTFs catalysts. Recently, the were transferred into quartz tubes in a glovebox, then the
iron-based nanoparticles were proven to play a synergetic role quartz tubes were evacuated, sealed and heated at 700 °C for
2
4,25
in activating the catalytic activity of ORR.
that Fe/Fe C nanoparticles can potentially promote the activity was washed with 1 M HCl solution to remove ZnCl
of the neighboring Fe−N for catalyzing ORR. The roles that iron- iron compounds, and then washed with the deionized water
One explanation is 20 h. After cooling to room temperature, this carbon material
3
2
and possible
X
derived nanoparticles play on the formation of high ORR active and the tetrahydrofuran, dried in a vacuum overnight to get the
sites are not explored, though the theory on the indispensability catalyst. The other catalysts were also prepared via the similar
of iron in the formation of active structures of Fe-based process used p-Fe
2
O
3
,
r-Fe and commercial Fe
2
O
3
2 3
O
2
6,27
catalysts is well admitted.
Therefore, it is highly desirable to nanoparticles to replace the Fe O hollow microspheres
2 3
explore the impacts of iron-derived nanoparticles on the respectively.
development of Fe-based catalysts, simply utilizing one-pot
ionothermal polymerization Fe-CTFs method.
Materials Characterizations
The morphologies of these catalysts were characterized by
transmission electron microscopy (TEM) and scanning electron
microscope (SEM). The TEM images were obtained on a FEI
Tecnai F20 electron microscope diffractometer with a copper
target (λ = 0.154 nm) and the SEM images were obtained on a
Hitachi SU8010 under high vacuum with an acceleration voltage
of 5 kV. X-ray photoelectron spectroscopy (XPS) was performed
on a Thermo Scientific ESCALAB to test the element
composition of these samples. The Brunauer-Emmett-Teller
(
N
(
BET) method was performed by the adsorption/desorption of
using the ASAP2020 volumetric adsorption analyzer
Micromeritics, U.S.A.) to determine the specific surface area
2
and the pore size distribution. The structures of all samples
were examined by powder X-ray diffraction (XRD) with a
MiniFlex-II diffractometer (Rigaku, Japan) using a Cu Kα
radiation source. Raman spectra was collected on a Renishaw
Scheme 1 Illustration of synthetic process.
In this study, we demonstrate a one-pot ionothermal
polymerization method to synthesize carbon-encapsulated Fe-
2
000 with a 532 nm laser excitation.
doped mesoporous carbon nanomaterials, in which the Fe
hollow microspheres (h-Fe ) acted as multifunctional soft
template are encapsulated by a CTFs carbon shell (Scheme 1).
2 3
O
2 3
O
Electrochemical measurements
To evaluate the ORR activity, rotating disk electrode (RDE, disk
In order to verify the impacts of parameters of Fe
2
O
O
3
2
area: 0.196 cm ) and rotating ring-disk electrode (RRDE, disk
nanoparticles, Fe
O
2 3
2 3
hollow microspheres (h-Fe O ), Fe
2
3
2
2
area: 0.247cm , ring area: 0.1866 cm ) were utilized to do the
electrochemical tests. In the three-electrode electrochemical
cell, a glassy carbon RDE was used as the working electrode, a
Pt wire electrode was used as the counter electrode and an
Ag/AgCl electrode was used as the reference electrode. All the
potentials mentioned in this text were calibrated to the
reversible hydrogen electrode (RHE) potentials according to the
Nernst equation (ERHE = EAg/AgCl + 0.059×pH + 0.197, at 25°C).
In the test, 4 mg as-prepared catalysts were ultrasonically
mixed with 785 μL ethanol, 200 μL deionized water and 38 μL
polyhedrons (p-Fe
2
O
3
) and Fe nanorods (r-Fe
2
O
3
2
O
3
) with
different shape, size, and microstructure were deliberately
designed and prepared in this study. The physical and
electrochemical properties of these Fe-CTFs catalysts were
systematically characterized and discussed.
Experimental
Materials synthesis
All reagents are of analytical grade and used without further Nafion (5 wt.%) to get the electrocatalyst inks. Then, the RDE
purification. The anhydrous ZnCl
, aromatic nitrile and 20 wt% and RRDE were polished with alumina powder and sonicated
Pt/C were purchased from Alfa Aesar (China) Chemical Co., Ltd. with ethanol and deionized water for two minutes respectively,
Shanghai, China); the h-Fe , p-Fe and r-Fe
were dried at room temperature. The prepared catalyst ink was
prepared according to the reported literature.
Typically, transferred onto the surface of the working electrode (RDE: 20
2
(
O
2 3
O
2 3
2 3
O
2
8-31
-2
glycerol (5 mL) is first mixed with deionized water (35 mL) to μL: RRDE: 25 μL) with a loading of 0.4 mg cm and dried at room
form a uniform quasi-emulsion, followed by the addition of 120 temperature for 30 min. Meanwhile, the commercial 20 wt%
mg FeSO ·7H O with continued vigorously stirring to get a
4 2
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Journal Name
ARTICLE
Pt/C was also coated onto the RDE and RRDE in the same way as cathode, a piece of Zinc plate was used as anode and 6 M
View Article Online
-2
DOI: 10.1039/C9TA01807G
KOH was used as electrolyte. The Zn-air batteries were tested
with a loading of 20 μg Pt cm for comparison.
All the ORR measurements of prepared catalysts were at room temperature, and the polarization curves were
determined by using a VHI Electrochemical Station (Model calculated by LSV technique from 1.5 V to 0 V at the scan rate
-
1
7
4
60e) in 0.1 M HClO and 0.1 M KOH solution as the acidic and of 5 mV s on the CHI 760E electrochemical workstation. For
-2
alkaline electrolyte at room temperature. In the RDE tests, the comparison, 20% Pt/C with a loading of 1 mg cm was used as
cyclic voltammetry (CV) measurements were carried out in cathode.
−1
N
2
/O
2
-saturated electrolyte with a scan rate of 10 mV s . The
linear sweep voltammetry (LSV) measurements were
performed in electrolyte with a scan rate of 10 mV s at various
rotating speed from 400 to 2500 rpm, and the curve recorded
−1
Results and discussion
All these Fe
were synthesized by a simple hydrothermal method. The
morphologies of the obtained Fe nanoparticles were
2 3 2 3 2 3 2 3
O nanoparticles (h-Fe O , p-Fe O and r-Fe O )
in N
recorded in O
2
-saturated electrolyte was subtracted from the curve
-saturated electrolyte. The electron transfer
2
2 3
O
number (n) and kinetic current density (J
the Koutecky-Levich equation:
K
) were calculated from
characterized by scanning electron microscope (SEM),
transmission electron microscopy (TEM) and high-resolution
transmission electron microscopy (HRTEM). As shown in Fig. 1a-
1
1
1
1
1
b, the h-Fe
around 700 nm, and these spherical particles have relatively
thin shells (100-200 nm). The shells of h-Fe have the similar
size to p-Fe and r-Fe (Fig. 1d-e and Fig. 1g-h).
2 3
O retain its microsphere structure with a diameter
=
+
=
+
(1)
Bω1/2
퐽
퐽퐿 퐽퐾
퐽퐾
2 3
O
퐵 = 0.62푛퐹C 퐷 /3푉―1/6 (2)
2
0
0
O
2 3
2 3
O
Furthermore, the images shown in Fig. 1c, f and i reveal that h-
Where J is the measured current density; J
L
and J
K
are the Fe O have the crystal plane spacing of about 2.53 Å and 3.7 Å,
2
3
limiting and kinetic current density, respectively; ω is the indexed to be (110) and (012) planes; p-Fe O and r-Fe O have
2
3
2 3
rotation rate of electrode; n is the electron transfer number; F the crystal plane spacing of about 3.7 Å, indexed to be (012)
−1
is the Faraday constant (96485 C mol ), C
0
is the concentration plane.
is the diffusion coefficient of
oxygen (1.90 × 10−5 cm s ), and V is the kinematic viscosity of
−6
−3
of oxygen (1.2 × 10 mol cm ); D
0
2
−1
2
−1
the electrolyte (0.01 cm s ).
2 2
The hydrogen peroxide yield (H O %) and the electron
transfer number (n) were implemented by the RRDE, which
values were calculated via the following equations:
2
IR
퐻 푂 =
× 100 (3)
2
2
N ID
| |
+ IR
퐻 푂 (%)
2
2
푛 = 4 ― 2
(4)
(
)
1
00
Where N = 0.37 is the current collection efficiency of Pt ring, I
D
R
represents the disk current, and I represents the ring current.
Cell measurements
2 3 2 3 2 3
Fig. 1 SEM, TEM and HRTEM of h-Fe O (a-c), p-Fe O (d-f) and r-Fe O (g-i),
Air-breathing PEMFCs: To evaluate the performance of the
proton exchange membrane fuel cell, a homemade battery was
built. The battery was carried in an air-condition room with
respectively.
temperature of 20 °C, the flow of H
2
was not humidified and the
2 3
These Fe O -doped Fe-CTF catalysts were prepared by one-
cathode obtained O
2
directly from atmosphere. The h-FeNC ink pot ionothermal polymerization of m-Phthalodinitrile in molten
-
was coated onto carbon paper with a loading mass of 1 mg cm ZnCl at the presence of different Fe O nanoparticles, followed
2
2 3
2
as the cathode and the 70% Pt/C ink was coated onto carbon by acid etching to remove ZnCl and iron products. These
2
-2
paper with a loading mass of 0.5 mg cm as anode. The fuel cell catalysts doped with h-Fe O , p-Fe O , r-Fe O and
2
3
2
3
2 3
performance was measured by LSV technique with CHI 760E commercially available Fe O were labelled as h-FeNC, p-FeNC,
2
3
electrochemical working station. For comparison, 70% Pt/C with r-FeNC, and c-FeNC, respectively. The crystal structure and the
-2
a loading of 0.5 mg cm was used as cathode.
natures of these samples were characterized by powder X-ray
Zinc-air battery: To prepare Zn-air batteries, the h-FeNC loading diffraction (XRD) patterns and Raman spectroscopy. Fig. 2a
-2
on the carbon paper with a loading mass of 1 mg cm was used shows the XRD patterns of these samples. Two broad peaks at
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Page 4 of 9
ARTICLE
Journal Name
3
-1
3 -1
2
θ = 25° and 2θ = 43.5° can be indexed to the (002) and (101) bigger than p-FeNC (1.7 cm g ), r-FeNC (1.6 cm g ) and c-FeNC
View Article Online
3
2,33
3
-1
DOI: 10.1039/C9TA01807G
diffractions of graphitic carbons, respectively.
The h-FeNC (1.6 cm g ), and the detailed pore properties of these catalysts
has a relatively strong (101) diffraction peak, indicating a higher are summarized in Table S1. The favorable pore structure and
graphitization degree than the other three catalysts. Also, no surface area of h-FeNC can significantly provide better mass
impurity phase peak can be found in those XRD patterns, transfer and more active sites for ORR.
suggesting that iron atoms were incorporated well into carbon
The morphologies of the h-FeNC are shown in Fig. 3. The SEM
framework, while the ZnCl and possible iron-derived images in Fig. 3a indicate that numerous loosely agglomerated
2
nanoparticles were removed completely through the acid particles with a size of around 10 nm are homogeneously
leaching. To further confirm this assumption, we performed the distributed on the surface of h-FeNC, and there are abundant
XRD test of the h-FeNC with and without acid leaching, pore structures (50-100 nm) inside the h-FeNC. The SEM images
respectively. The catalyst before acid leaching shows the of p-FeNC, r-FeNC and c-FeNC also reveal that these catalysts
obvious peaks for ZnCl (16.61°, 25.5°) and the iron oxide consist of loosely agglomerated particles, and there is no
2
hydrate (14.01°, 21.29°), while these peaks were removed after obvious difference in the structure of these catalysts (Fig. S2).
acid leaching (Fig. S1). In the Raman spectrum, all these The TEM and HRTEM images of h-FeNC illustrate the existence
-1
catalysts display two typical D band (about 1360 cm ) and G of graphite structure (Fig. 3b-c), in consistence with the XRD
-1
band (about 1585 cm ), wherein the ratio of the D and G band results. The selected-area electron diffraction (SAED) pattern of
intensities (I /I ) is used to evaluate the amounts of defects and h-FeNC further confirms the existence of graphitic structure
disorder. As shown in Fig. 2b, the corresponding I /I ratios in (Fig. 3d). We further investigate the elemental distribution of h-
D
G
D
G
Raman spectra decrease from 2.68 to 2.48 for h-FeNC, p-FeNC, FeNC using high-angle annular dark-field scanning transmission
r-FeNC, and c-FeNC. The obtained results demonstrate that the electron microscopy (HAADF-STEM). The energy dispersive X-
h-FeNC could provide more structure defects to serve as active ray spectroscopy (EDS) mapping images reveal that the N and
3
4-36
sites, and then promote the activity for electrocatalysis.
Fe atoms can be homogeneously distributed in the architecture
of the h-FeNC (Fig. 3e). Meanwhile, the Fe atoms are adjacent
to N atoms at atomic level, which are believed to contribute to
2
5,37
X
the formation of highly active Fe-N sites.
Fig. 2 (a) XRD patterns, (b) Raman spectrums, (c) Nitrogen adsorption-desorption
isotherms and (d) Pore size distributions of h-FeNC, p-FeNC, r-FeNC and c-FeNC. Fig. 3 (a) SEM, (b) TEM, (c) HRTEM, (d) SAED, (e) HAADF-STEM and EDS
mapping images of h-FeNC.
The porous structures of these samples were determined by
X-ray photoelectron spectroscopy (XPS) measurement was
2
the N adsorption/desorption method. As shown in Fig. 2c, all
used to reveal the elemental compositions of the catalysts. As
shown in Fig. S3a, h-FeNC contains more Fe element than p-
FeNC, r-FeNC and c-FeNC, mainly composed of C (85.72 at.%), O
the samples display a fast uptake at the low relative pressure
P/P < 0.1) and a distinct hysteresis loop between the
(
0
adsorption and desorption branches, indicating the coexistence
of both micropores and mesoporous. The BET surface areas of
(8.21 at.%), N (5.86 at.%), Fe (0.21 at.%), which may be
2
-1
2
-1
2
attributed to the fact that high surface area of h-FeNC can
expose more Fe for the XPS detection. Meanwhile, no Zn ions
were found in the XPS spectrum, which was consistent with the
XRD results (Fig. S3b and S1). The high-resolution N 1s XPS
spectrums (Fig. S4) were used to analyze the nitrogen type of
these catalysts, which were deconvoluted into four types of
common nitrogen, corresponding to pyridinic N (N1 398.3 eV),
pyrrolic N (N2 399.65 eV), graphitic N (N3 400.8 eV) and oxidized
h-FeNC (2454 m g ), p-FeNC (2248 m g ) and r-FeNC (1934 m
-1
2
-1
g ) are significantly larger than that of c-FeNC (1864 m g ).
Also, the average pore diameter of these catalysts was
calculated by the Barrett-Joyner-Halenda (BJH) model. As
shown in Fig. 2d, the average pore diameter of h-FeNC, p-FeNC,
r-FeNC, and c-FeNC decrease from 3.4 to 3.2 nm, which further
demonstrates the existence of mesoporous structure of h-
3
-1
FeNC. Similarly, the total pore volume of h-FeNC (1.9 cm g ) is
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 9
J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Journal Name
ARTICLE
N (N4 402.2 eV), respectively. As shown in Fig. S3c and Table S2, reported non-noble catalysts (Table S3). MeVainewwAhrtiiclele,Onwlinee
the total ratio of pyridinic N and pyrrolic N of h-FeNC is higher compared the ORR activity of this catalDyOstIs: 10w.1i0th39d/Cif9fTeAr0e1n8t07hG-
than that of the other three samples. It has been reported that Fe O contents (40mg, 50 mg, 60 mg), the content of h-Fe O
2 3 2 3
the total content of pyridinic N and pyrrolic N are related with (50 mg) we used in this work has the best ORR activity of the
the activity of ORR, because their locating at the edge of catalyst (Fig. S7). The half-wave potential (E1/2) of h-FeNC is 25
graphite are capable of coordinating with Fe to form Fe-N
X
and 33 mV more positive shift than that of p-FeNC and r-FeNC,
3
8,39
active sites for ORR in acid solution.
To obtain further insight respectively. The p-FeNC shows only 8 mV slightly more positive
of these catalysts, the high-resolution Fe 2p XPS spectrums of half wave shifts comparing to that of r-FeNC. It is well known
these catalysts were deconvoluted into five peaks. Fig. S5 shows that the activity of Fe-based catalysts is closely related to BET
that the peaks at 710.8 eV and 713.2 eV are assignable to the surface area, the content and form of iron atoms and nitrogen
2
+
3+
2
p
3/2 orbitals of the N-coordinated Fe and Fe species, while atoms. To verify their impacts, the ORR activities of our Fe-
the peaks at 721.2 ,724.6 and 718.1 eV are respectively assigned based catalysts were normalized according to the surface area,
2
+
3+
to Fe 2p1/2, Fe 2p1/2 and the satellite peaks. The Fe 2p around Fe and N content. As shown in Fig. 4d-f, the area-specified
11 eV are favorable for the formation of Fe-N species, which kinetic current densities (Jarea), Fe and N mass-specified kinetic
further suggests the existence of Fe-N
configuration.38,40
7
X
X
current densities (Jmass) at 0.85 V were calculated by using the
Koutecky-Levich equation. The h-FeNC has the highest Jarea and
J
mass among these catalysts, which suggests that h-FeNC has the
4
2
most optimal composition for catalyzing the ORR. Therefore,
it is of significance to explore the factors affecting the highest
intrinsic activity of h-FeNC. As described in previous sections, all
of our catalysts were obtained by the same procedure except
for the use of different Fe
2 3
O nanoparticles. This means that
Fe nanoparticles play an important role on the formation of
2 3
O
high activity Fe-based catalysts. The iron species were
speculated to serve as catalysts (catalyzing the formation of a
special type of ORR active carbon), active sites center
(
generating the M–N species), auxiliary (promoting a reaction
4
3
between chelate and subjacent carbon). The shapes and sizes
of Fe nanoparticles are very important when they are
2 3
O
considered as catalysts to catalyze the formation of highly
intrinsic ORR active carbon during high temperature treatment.
To identify the impacts of Fe
2 3
O nanoparticles’ size, the p-
Fig. 4 (a) RDE polarization curves of Pt/C, h-FeNC, p-FeNC, r-FeNC and c-FeNC
-1
Fe with different sizes ranges from 50 nm, 150 nm, and 250
2 3
O
2 4
in O -saturated 0.1 M HClO solution at 1600 rpm, with a scan rate of 10 mV s .
-1
(
b) Voltammograms of h-FeNC at various speeds with a scan rate of 10 mV s ; nm were synthesized respectively. However, the ORR activity
inset is the corresponding K–L plots at different potentials. (c) H
2 2
O yield (bottom)
test clearly demonstrated that the activity of p-FeNC type
catalysts were not sensitive to the sized of p-Fe (Fig. S8 and
solution at a scan rate of 10 mV s-1 (Fe mass S9). We further explored the microstructure of Fe
and electron-transfer number (top) of Pt/C, h-FeNC, p-FeNC, r-FeNC and c-FeNC.
2 3
O
(d-f) Area and mass-specific ORR kinetic current densities of h-FeNC, p-FeNC, r-
FeNC and c-FeNC in 0.1 M HClO
4
O
2 3
for (e) and N mass for (f)). (g) Tafel plots of Pt/C, h-FeNC, p-FeNC, r-FeNC and
c-FeNC in 0.1 M HClO . (h) Methanol tolerance test of h-FeNC and Pt/C in O
saturated 0.1 M HClO solution and (i) RDE results of h-FeNC and Pt/C before
and after 10000 potential cycles in O -saturated 0.1 M HClO solution.
nanoparticles by HRTEM after excluded the impacts of the size
and shape of Fe nanoparticles (Fig. 1c, f and i). The h-Fe
have not only the crystal plane spacing of about 3.70 Å
assignable to (012) planes but also the crystal plane spacing of
about 2.53 Å assignable to the high-index (110) planes, while
4
2
-
O
2 3
2 3
O
4
2
4
The ORR activity of the series of samples as well as the the p-Fe O and r-Fe O have only the (012) plane. It’s well
2
3
2 3
commercial Pt/C were systematically studied by using RDE in documented that high-index facets can endow nanocrystals
-saturated 0.1 M HClO . Cycle voltammetry measurements with high surface energy, which can endow nanocrystals with
CVs) were firstly carried out to investigate the catalysts high activity.29,44,45 Therefore, h-Fe O with high-index facets
O
2
4
(
2
3
2 2 4
activities in N - and O -saturated 0.1 M HClO solution (Fig. S6). would be more conducive to catalyze the formation of highly
The typical catholic ORR peaks of these catalysts were found in intrinsic ORR active sites during high temperature treatment.
2
O -saturated electrolyte while no peaks were observed under
In addition, the ORR kinetics of these samples were carried
N
2
-saturated electrolyte. The h-FeNC exhibits a cathodic peak at out by RDE measurements at different rotating speeds from 400
-1
around 785 mV, which suggests the efficient catalyst ORR to 2500 rpm with a scan rate of 10 mV s . We can see that the
4
1
activity of h-FeNC in acidic electrolyte. RDE measurements current density enhances with the increase of rotating speed
were carried out to further evaluate the catalytic performance (Fig. 4b and Fig. S10). Koutecky–Levich (K–L) equations were
of these samples. As shown in Fig. 4a, h-FeNC exhibits much used to analyze the kinetic parameters. The K–L plots show
higher ORR activity compared with the other three catalysts in excellent linearity and are parallel for all these catalysts at
0
4
.1M HClO , whose half-wave potential (E1/2) is only 32 mV various potentials, suggesting the first-order reaction kinetics
more negative than that of Pt/C, exceeding most of the towards the ORR and the similar electron transfer number for
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Page 6 of 9
ARTICLE
Journal Name
the ORR at different potentials. The electron transfer number
n) of h-FeNC was thus calculated to be an average value of 3.91
View Article Online
DOI: 10.1039/C9TA01807G
(
at potentials ranging from 0.2–0.7 V, indicating a four-electron
transfer pathway for the ORR. Besides, the RRDE tests of these
catalysts (the potential of Pt ring electrode was set to 1.2 V vs.
RHE) were conducted in 0.1 M HClO
yields and the corresponding electron transfer numbers
Fig. 4c). Similar to the catalytic behavior of Pt/C, the peroxide
4
solution to calculate the
2 2
H O
(
species yield of h-FeNC is less than 3.41% over the potential
range from 0.2 to 0.8 V, and the electron transfer number is
higher than 3.93. This result confirms that the h-FeNC is
beneficial to reduce the intermediate yield of two-electron-
transfer pathway to promote the reduction of oxygen to water
4
6,47
through four-electron-transfer process.
To further
understand the inherent electrochemical catalytic processes for
ORR, Tafel slope was calculated. Fig. 4g illustrates that the h-
FeNC has a smallest Tafel slope of 52 mV per decade at low Fig. 5 (a) RDE polarization curves of Pt/C, h-FeNC, p-FeNC, r-FeNC and c-FeNC
-1
in O2-saturated 0.1 M KOH solution at 1600 rpm, with a scan rate of 10 mV s .
b) Voltammograms of h-FeNC at various speeds with a scan rate of 10 mV s−1
inset is the corresponding K–L plots at different potentials. (c) H yield (bottom)
over-potentials, which is close to 59 mV per decade for the Pt/C
catalyst. Similar to the Pt/C catalyst, the transfer of the first
(
;
2
O
2
electron is probably the rate-determining step of the ORR for and electron-transfer number (top) of Pt/C, h-FeNC, p-FeNC, r-FeNC and c-FeNC
2
in 0.1 M KOH. (d) Methanol tolerance test of h-FeNC and Pt/C in O -saturated 0.1
M KOH solution.
4
8-50
the h-FeNC catalyst in acidic media.
Compared with p-FeNC, r-FeNC, c-FeNC and Pt/C catalysts,
the h-FeNC catalyst has a lower charge-transfer resistance as
evidenced by the smaller semicircle, further demonstrating the
Besides the efficient catalytic activity in acidic electrolyte, h-
FeNC also put up a competitive electrocatalytic performance for
ORR in 0.1 M KOH solution. Fig. S14 displays the CV curves of
relatively high catalytic activity of h-FeNC in acidic electrolyte
1,52
(
Fig. S11).5 Apart from the high catalytic activity, h-FeNC also
exhibits better methanol tolerance and stability than
commercial Pt/C catalyst in the acidic electrolyte. The tolerance
to methanol crossover was performed by the method of
current-time (I-T) at 0.677 V vs RHE with an RDE rotation of 1600
these samples in N
well-defined cathodic peak of h-FeNC appears at around 900
mV in O -saturated electrolyte. The RDE measurements show
that h-FeNC displays a comparable onset potential (Eonset = 996
mV) and half-wave potential (E1/2 = 883 mV) to that of Pt/C
2 2
- and O -saturated 0.1 M KOH solution. A
2
2
rpm upon the addition of 1 M methanol into the O -saturated
electrolyte after 300 s. It can be seen that the ORR current
density of h-FeNC only slightly decrease while the Pt/C suffers a
sharp decrease (Fig. 4h). Meanwhile, the stability test was
carried out by RDE in the potential window of 0.6 to 1.0 V vs
(Eonset= 954 mV, E1/2 = 843 mV) in 0.1 M KOH solution with a
rotating speed of 1600 rpm (Fig. 5a). It indicates that the ORR
activity of h-FeNC exceeds most of the other nonprecious
2 2
catalysts (Table S5). Furthermore, the H O yield of h-FeNC
ranges from 0.42% to 6.40% at all potentials and the electron
transfer number ranges from 4 to 3.88 respectively, revealing a
four-electron-pathway dominated ORR process, which is almost
in keeping with the results from the K–L plots (Fig. 5b, c and
S15). And then we carried out the methanol-tolerance test of
Pt/C and h-FeNC by adding 1M methanol to 0.1 M KOH, h-FeNC
exhibits a much better methanol-tolerance ability than Pt/C
-1
2 4
RHE at the scan rate of 50 mV s in O -saturated 0.1 M HClO .
After 10000 continuous cycles, the E1/2 of the h-FeNC exhibits
only a 30 mV negative shifts, which is lower than that of the
commercial Pt/C (77 mV negative shifts) (Fig. 4i). XPS survey
spectra and SEM showed that the composition and structure of
h-FeNC did not change significantly before and after the stability
test (Fig. S12, S13 and Table S4). All these results indicate that
the h-FeNC has high stability.
(Fig. 5d).
To further understand the nature of the active sites, the
electrochemical poisoning tests of h-FeNC were conducted by
-
-
-
adding 5 mM SCN , Cl , Br ions into the 0.1 M HClO
4
electrode,
-
respectively. As shows in Fig. S16a, after adding 5 mM SCN into
the electrode, the diffusion current density of h-FeNC
significantly decreased at 0.75 V. Fig. S16b-d show that the E1/2
of h-FeNC negatively shifted by 103 mV after adding 5 mM SCN
into the electrolyte, which is bigger than the effect of Cl and Br
-
-
-
ions on ORR activity (the potential are negatively shift by only
-
2
3 and 16 mV, respectively). It is well known that SCN
coordinate strongly to iron and poison the iron-centered
catalytic sites for ORR. The result strongly illustrated that the Fe
ions combined with nitrogen to form Fe-N species active sites
X
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Journal Name
ARTICLE
in h-FeNC, which can greatly improve the ORR catalytic Zn-air batteries, and the performance outperformed most of
View Article Online
activity.5
3,54
DOI: 10.1039/C9TA01807G
the reported nonprecious metal catalysts. This work opens a
new way to prepare highly efficient and cost-effective ORR
catalysts for advanced energy conversion and storage.
Acknowledgements
The authors gratefully acknowledge the financial support of the
high-level talents for entrepreneurship and innovation of Fujian
Province, Key project of the Chinese academy of sciences
(Project Nos. ZDRW-CN-2016-1), and technique support from
the Prof. Xiaochun Zhou at Suzhou Institute of Nano-tech and
Nanobionics, CAS.
Notes and references
1
2
3
L. Dai, Y. Xue, L. Qu, H. J. Choi and J. B. Baek, Chem. Rev., 2015,
115, 4823-4892.
W. Xia, A. Mahmood, Z. Liang, R. Zou and S. Guo, Angew.
Chem. Int. Ed., 2016, 55, 2650-2676.
Fig. 6 (a) Air-breathing proton exchange membrane fuel cells polarization plots.
b) Zn-air fuel cells polarization plots. (c, d) Photographic images of two series of
h-FeNC-based Zn-air fuel cell lighting green (c) and blue LED (d).
(
J. Li, S. Ghoshal, W. Liang, M. T. Sougrati, F. Jaouen, B. Halevi,
S. McKinney, G. McCool, C. Ma, X. Yuan, Z. Ma, S. Mukerjee
and Q. Jia, Energy Environ. Sci., 2016, 9, 2418-2432.
Q. Peng, J. Chen, H. Ji, A. Morita and S. Ye, J. Am. Chem. Soc.,
2018, 140, 15568-15571
To corroborate the excellent catalytic activities under real
fuel cell operation conditions, air-breathing proton exchange
membrane fuel cell (AB-FEMFC) and zinc-air battery were
assembled using either h-FeNC or Pt/C as cathodic catalyst. Fig.
4
5
6
7
8
9
M. Shao, Q. Chang, J. P. Dodelet and R. Chenitz, Chem. Rev.,
2
016, 116, 3594-3657.
6
a shows the polarization and power density of air-breathing
D. Malko, A. Kucernak and T. Lopes, J. Am. Chem. Soc., 2016,
38, 16056-16068.
proton exchange membrane fuel cell (AB-FEMFC) on h-FeNC
1
-2
and Pt/C (0.5 mg Pt cm ), which was carried in an air-
conditioned room with temperature of 20 °C. The open-circuit
voltage of h-FeNC is 0.96 V, higher than that of Pt/C (0.92 V),
Y. Chen, R. Gokhale, A. Serov, K. Artyushkova and P.
Atanassov, Nano Energy, 2017, 38, 201-209.
L. Lin, Q. Zhu and A. Xu, J. Am. Chem. Soc., 2014, 136, 11027-
11033.
K. Strickland, E. Miner, Q. Jia, U. Tylus, N. Ramaswamy, W.
Liang, M. T. Sougrati, F. Jaouen and S. Mukerjee, Nat.
Commun., 2015, 6, 7343-7350.
-2
and the peak power density is 57 mW cm , which reachs
-2
approximately 63% of commercial Pt/C (91 mW cm ) under
identical test conditions. To our knowledge, this performance is
better than most of the reported Fe-N
X
-C catalysts. In the zinc- 10 M. Wang, W. Yang, H. Wang, C. Chen, Z. Zhou and S. Sun, ACS
air battery, the open-circuit voltage of h-FeNC is 1.6 V with a
Catal., 2014, 4, 3928-3936.
−2
11 X. Li, G. Liu and B. N. Popov, J. Power Sources, 2010, 195, 6373-
peak power density of 215 mW cm , which is higher than that
6
378.
−2
of 1.5 V and 135 mW cm for the Pt/C (Fig. 6b). As exemplified
1
2 Z. Chen, D. Higgins, A. Yu, L. Zhang and J. Zhang, Energy
Environ. Sci., 2011, 4, 3167-3192.
in Fig. 6c and 6d, two series of h-FeNC-based Zn-air batteries
were applied to power various light-emitting diode (LED) to 13 D. Malko, T. Lopes, E. Symianakis and A. R. Kucernak, J. Mater.
demonstrate the potential application for the device. All these
results demonstrate that the h-FeNC exhibits excellent
electrocatalytic activity in both alkaline and acidic conditions,
and the h-FeNC can be successfully employed as a promising
cathode catalyst in fuel cells.
Chem. A, 2016, 4, 142-152.
1
1
4 E. Proietti, F. Jaouen, M. Lefèvre, N. Larouche, J. Tian, J.
Herranz and J. P. Dodelet, Nat. Commun., 2011, 2, 416-424.
5 G. Yang, W. Choi, X. Pu and C. Yu, Energy Environ. Sci., 2015,
8
, 1799-1807.
16 A. Kong, X. Zhu, Z. Han, Y. Yu, Y. Zhang, B. Dong and Y. Shan,
ACS Catal., 2014, 4, 1793-1800.
1
1
7 Y. Wang, A. Kong, X. Chen, Q. Lin and P. Feng, ACS Catal., 2015,
5
, 3887-3893.
Conclusions
8 X. Zheng, X. Cao, X. Li, J. Tian, C. Jin and R. Yang, Nanoscale,
2017, 9, 1059-1067.
In conclusion, we have demonstrated a reliable strategy for the
synthesis of high-performance Fe-CTF ORR catalysts by direct 19 H. Liang, W. Wei, Z. Wu, X. Feng and K. Müllen, J. Am. Chem.
Soc., 2013, 135, 16002-16005.
0 C. E. Chan-Thaw, A. Villa, P. Katekomol, D. Su, A. Thomas and
L. Prati, Nano Lett., 2010, 10, 537-541.
1 K. Kamiya, R. Kamai, K. Hashimoto and S. Nakanishi, Nat.
Commun., 2014, 5, 5040-5045.
2 2 3
heating the dry mixture of ZnCl , dinitrile monomer and Fe O
nanomaterials. The Fe O nanomaterials were proven not only
2 3
to be an eco-friend multifunctional template but also play an
important part in improving the ORR activity of Fe-CTF catalysts.
2
2
It is noteworthy that the catalyst we got exhibits higher stability 22 K. Iwase, T. Yoshioka, S. Nakanishi, K. Hashimoto and K.
Kamiya, Angew. Chem. Int. Ed., 2015, 54, 11068-11072.
and superior methanol tolerance to commercial 20 wt% Pt/C for
ORR in both acidic and alkaline conditions. Furthermore, the h-
FeNC can be a promising cathode catalyst in both PEMFCs and
2
3 L. Tong, Z. Shao, Y. Qian and W. Li, J. Mater. Chem. A, 2017, 5,
3
832-3838.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

J Po lue ran sael od fo Mn aot te rai ad l js u Cs ht emm ai rs gt ri yn sA
Page 8 of 9
ARTICLE
Journal Name
2
2
4 Y. Hu, J. O. Jensen, W. Zhang, L. N. Cleemann, W. Xing, N. J. 53 Q. Wang, Z. Zhou, Y. Lai, Y. You, J. Liu, X. Wu,ViEew. TAretircelefOen,liCne.
Bjerrum and Q. Li, Angew. Chem. Int. Ed., 2014, 53, 3675-
679.
Chen, L. Song, M. Rauf, N. Tian and S. Sun, J. Am. Chem. Soc.,
DOI: 10.1039/C9TA01807G
3
2014, 136, 10882-10885.
5 W. Jiang, L. Gu, L. Li, Y. Zhang, X. Zhang, L. Zhang, J. Wang, J. 54 L. Song, Z. Wu, F. Zhou, H. Liang, Z. Yu and S. Yu, Small, 2016,
Hu, Z. Wei and L. Wan, J. Am. Chem. Soc., 2016, 138, 3570-
578.
12, 6398-6406.
3
2
2
2
2
3
3
3
6 J. Masa, W, Xia, M. Muhler and W. Schuhmann, Angew. Chem.
Int. Ed., 2015, 54, 10102-10120.
7 D. Deng, L. Yu, X. Chen, G. Wang, L. Jin, X. Pan, J. Deng, G. Sun
and X. Bao, Angew. Chem. Int. Ed., 2013, 52, 371-375.
8 B. Wang, J. Chen, H. Wu, Z. Wang and X. Lou, J. Am. Chem. Soc.,
2
011, 133, 17146-17148.
9 F. Gao, R. Liu, J. Yin and Q. Lu, Sci. China Chem., 2014, 57, 114-
21.
1
0 J. Ouyang, J. Pei, Q. Kuang, Z. Xie and L. Zheng, ACS Appl.
Mater. Interfaces, 2014, 6, 12505-12514.
1 Z. Fu, T. Jiang, Z. Liu, D. Wang, L. Wang and T. F. Xie,
Electrochim. Acta, 2014, 129, 358-363.
2 Y. J. Sa, D. J. Seo, J. Woo, J. T. Lim, J. Y. Cheon, S. Y. Yang, J. M.
Lee, D. Kang, T. J. Shin, H. S. Shin, H. Y. Jeong, C. S. Kim, M. G.
Kim, T. Y. Kim and S. H. Joo, J. Am. Chem. Soc., 2016, 138,
1
5046-15056.
3 Y. Qian, T. An, K. E. Birgersson, Z. Liu and D. Zhao, Small, 2018,
4, 1704169.
4 H. Hu, H. Cheng, J. Zhou, Q. Zhu and Y. Yu, Mater. Today Phys.,
017, 3, 7-15.
5 B. Huang, Y. Liu and Z. Xie, J. Mater. Chem. A, 2017, 5, 23481-
3488.
3
3
3
3
3
3
3
4
1
2
2
6 T. Zhou, Y. Zhou, R. Ma, Z. Zhou, G. Liu, Q. Liu, Y. Zhu and J.
Wang, Carbon, 2017, 114, 177-186.
7 W. Zhong, J. Chen, P. Zhang, L. Deng, L. Yao, X. Ren, Y. Li, H. Mi
and L. Sun, J. Mater. Chem. A, 2017, 5, 16605-16610.
8 Y. Zhao, K. Watanabe and K. Hashimoto, J. Am. Chem. Soc.,
2
012, 134, 19528-19531.
9 X. Cui, S. Yang, X. Yan, J. Leng, S. Shuang, P. M. Ajayan and Z.
Zhang, Adv. Funct. Mater., 2016, 26, 5708-5717.
0 Z. Tan, H. Li, Q. Feng, L. Jiang, H. Pan, Z. Huang, Q. Zhou, H.
Zhou, S. Ma and Y. Kuang, J. Mater. Chem. A, 2019, 7, 1607-
1
615.
4
4
4
4
4
4
1 W. Niu, L. Li, X. Liu, N. Wang, J. Liu, W. Zhou, Z. Tang and S.
Chen, J. Am. Chem. Soc., 2015, 137, 5555-5562.
2 C. Zhang, S. Y. Hwang, A. Trout and Z. Peng, J. Am. Chem. Soc.,
2
014, 136, 7805-7808.
3 J. A. R. van Veen, H. A. Colijn and J. F. van Baar, Electrochim.
Acta, 1988, 33, 801-804.
4 J. Yin, Z. Yu, F. Gao, J. Wang, H. Pang and Q. Lu, Angew. Chem.
Int. Ed., 2010, 49, 6328-6332.
5 N. Tian, Z. Zhou, S. Sun, Y. Ding and Z. Wang, Science, 2007,
3
16, 732-735.
6 J. Wang, Z. Huang, W. Liu, C. Chang, H. Tang, Z. Li, W. Chen, C.
Jia, T. Yao, S. Wei, Y. Wu and Y. Li, J. Am. Chem. Soc., 2017,
1
39, 17281-17284.
4
4
7 R. Du, N. Zhang, J. Zhu, Y. Wang, C. Xu, Y. Hu, N. Mao, H. Xu,
W. Duan, L. Zhuang, L. Qu, Y. Hou and J. Zhang, Small, 2015,
1
1, 3903-3908.
8 J. Sun, S. E. Lowe, L. Zhang, Y. Wang, K. Pang, Y. Wang, Y.
Zhong, P. Liu, K. Zhao, Z. Tang and H. Zhao, Angew. Chem. Int.
Ed., 2018, 57, 16511-16515.
4
5
5
5
9 Y. Li, W. Zhou, H. Wang, L. Xie, Y. Liang, F. Wei, J. C. Idrobo, S.
J. Pennycook and H. Dai, Nat Nanotechnol., 2012, 7, 394-400.
0 F. Yu, L. Yu, I. K. Mishra, Y. Yu, Z. Ren and H. Zhou, Mater.
Today Phys., 2018, 7, 121-138.
1 Y. Liu, G. Li, Z. Chen and X. Peng, J. Mater. Chem. A, 2017, 5,
9
775-9784.
2 L. Yu, H. Zhou, J. Sun, F. Qin, F. Yu, J. Bao, Y. Yu, S. Chen and Z.
Ren, Energy Environ. Sci., 2017, 10, 1820-1827.
8
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Journal of Materials Chemistry A
View Article Online
DOI: 10.1039/C9TA01807G
The hierarchical mesoporous carbon nanomaterials synthesized by using
Fe hollow microspheres as multifunctional template exhibits efficient
catalytic performance for oxygen reduction in both acidic and alkaline media.
2 3
O