Chemical Vapor Deposition for Atomically Dispersed and Nitrogen Coordinated Single Metal Site Catalysts

Article abstract of DOI:10.1002/anie.202009331

Atomically dispersed and nitrogen coordinated single metal sites (M-N-C, M=Fe, Co, Ni, Mn) are the popular platinum group-metal (PGM)-free catalysts for many electrochemical reactions. Traditional wet-chemistry catalyst synthesis often requires complex procedures with unsatisfied reproducibility and scalability. Here, we report a facile chemical vapor deposition (CVD) strategy to synthesize the promising M-N-C catalysts. The deposition of gaseous 2-methylimidazole onto M-doped ZnO substrates, followed by an in situ thermal activation, effectively generated single metal sites well dispersed into porous carbon. In particular, an optimal CVD-derived Fe-N-C catalyst exclusively contains atomically dispersed FeN₄ sites with increased Fe loading relative to other catalysts from wet-chemistry synthesis. The catalyst exhibited outstanding oxygen-reduction activity in acidic electrolytes, which was further studied in proton-exchange membrane fuel cells with encouraging performance.

Full text of DOI:10.1002/anie.202009331

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Chemical Vapor Deposition for Atomically Dispersed and
Nitrogen Coordinated Single Metal Site Catalysts
Authors: Shengwen Liu, Maoyu Wang, Xiaoxuan Yang, Qiurong Shi,
Qiao Zhi, Marcos Lucero, Qing Ma, Karren L. More, David A.
Cullen, Zhenxing Feng, and Gang Wu
This manuscript has been accepted after peer review and appears as an
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202009331
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
Chemical Vapor Deposition for Atomically Dispersed and
Nitrogen Coordinated Single Metal Site Catalysts
Shengwen Liu,†[a] Maoyu Wang,†[b] Xiaoxuan Yang,† [a] Qiurong Shi,[a] Zhi Qiao,[a] Marcos Lucero, Qing
[b]
Ma, Karren L. More, David A. Cullen,* Zhenxing Feng,*[b] and Gang Wu*[a]
[
c]
[d]
[d]
Abstract: Atomically dispersed and nitrogen coordinated single metal
sites (M-N-C, M=Fe, Co, Ni, or Mn) are the popular platinum group-
metal (PGM)-free catalysts for many electrochemical reactions.
Traditional wet-chemistry catalyst synthesis often requires complex
procedures with unsatisfied reproducibility and scalability. Here, we
report a chemical vapor deposition (CVD) strategy to synthesize the
promising single metal site (M-N-C) catalysts. The deposition of
gaseous 2-methylimidazole onto ZnO substrates doped with M,
followed by an in-situ thermal activation, was proved effective in
generating single metal sites well dispersed into porous carbon. In
particular, an optimal CVD-derived Fe-N-C catalyst is featured with
Among them, atomically dispersed and nitrogen-coordinated
single iron site catalysts hosted in porous carbon (Fe-N-C)
exhibited superior ORR activity and encouraging stability.[13-14]
They have been considered as the most promising candidate to
4
replace PGM catalysts. In Fe-N-C catalysts, atomic FeN moieties
were theoretically predicted and experimentally verified as active
sites for the ORR in acidic electrolytes.[15-19] Recently, substantial
endeavors have been devoted to developing Fe-N-C catalysts
with enhanced intrinsic activity and increased density of FeN
4
[
20-24]
active sites to improve overall ORR activity.
Compared to
traditional Fe-N-C catalysts often containing inactive Fe
aggregate species,[25-26] zeolite imidazole frameworks (ZIF-8s)
and their derived microporous carbon, which was firstly studied
by Proietti et al.,[27] have been identified as ideal precursors to
4
atomically dispersed FeN sites with increased Fe loading relative to
other catalysts from wet-chemistry synthesis. The catalyst exhibited
outstanding oxygen-reduction activity in acidic electrolytes, which was
further studied in proton-exchange membrane fuel cells with
encouraging performance. The CVD synthesis sheds some light on
the mass production of single metal site catalysts towards advanced
electrocatalysis.
generate exclusive FeN
4
active sites, thus exhibiting remarkably
variety of
enhanced ORR activity.[15,27-29] Subsequently,
a
strategies based on the ZIF-8, including coordination effect,
chemical bonding, and spatial confinement, have been developed
to increase the density of FeN
4
active sites.[22,29-30] However, the
further increment of site density remains a significant challenge
due to the agglomeration/migration of single iron sites into inactive
clusters or nanoparticles during the synthesis under high-
temperature. Also, most of Fe-N-C catalysts derived from ZIF-8
Introduction
Proton exchange membrane fuel cells (PEMFCs) are a promising
sustainable and clean energy conversion technology for
transportation.[1-2] Although current platinum-group metals (PGM)
cathode catalysts can provide good activity and stability for the
kinetically sluggish oxygen reduction reaction (ORR) in acidic
media, their high-cost and scarce remain grand challenges to limit
wide applications of PEMFCs.[3-6] In the last decade, extraordinary
achievements have been made in the development of PGM-free
electrocatalysts from earth-abundant materials.[7-12]
precursors, which were prepared by using traditional wet-
[8,31]
chemistry synthesis, contain dominant micropores.
FeN
Although
4
active sites are hosted in micropores (1-2 nm), dominant
micropores in catalysts might render most of the interior active
sites “buried” and unavailable,[8,19,32-33] because the ionomer used
for proton conductors in cathodes hardly penetrates these
[34]
micropores to build robust three-phase interfaces for the ORR.
Besides, the micropore structure is tortuous, which results in
[35-36]
unfavorable mass transport and poor water management.
Therefore, the porosity of carbon structures in catalysts is one of
the crucial factors that affect fuel cell performance. Template-
directed methods were studied to create significant meso- and
macropores in Fe-N-C catalysts. However, template-removal
procedures are complicated, which is challenging for scale-up
production.[37] Thus, all of the current methods for preparing Fe-
N-C catalysts still face grand challenges of scale-up synthesis for
Dr. S. Liu,† X. Yang,† Dr. Q. Shi, Z. Qiao, Prof. G. Wu
[
[
a]
b]
Department of Chemical and Biological Engineering
University at Buffalo, The State University of New York,
Buffalo, NY 14260 (USA) E-mail: gangwu@buffalo.edu
†
M. Wang, M. Lucero, Prof. Z. Feng
School of Chemical Biological, and Environmental Engineering, Oregon
State University, Corvallis, OR 97331 (USA) E-mail:
zhenxing.feng@oregonstate.edu
[19,24]
practical fuel cell applications.
Developing a simple and
effective strategy at a large scale for preparing atomically
dispersed Fe-N-C catalysts with favorable hierarchical porosity is
particularly appealing.
[
[
c]
d]
Q. Ma
DND-CAT, Synchrotron Research Center, Northwestern University,
Evanston, IL 60208 (USA).
Dr. D. A. Cullen, Prof. K. L. More
Materials Science and Technology Division, Oak Ridge National
Laboratory, Oak Ridge, TN 37831 (USA) E-mail: cullenda@ornl.gov
These authors contributed equally to this work.
Here, we report a chemical vapor deposition (CVD) synthesis
strategy to prepare atomically dispersed Fe-N-C catalysts
exclusively containing FeN active sites. The synthesis only
4
[†
]
Supporting information for this article is given via a link at the end of the
document.
requires the gaseous deposition of 2-methyimidazolates (2-MeIm)
onto Fe-doped ZnO substrates. In particular, during the CVD
process at 350 C, the 2-MeIm reacts with ZnO to form a unique
o
2
topological structure of Zn(MeIm) intermediate, namely katsenite
1
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
o
(
kat-Zn(MeIm)
2
) phase.[38] Different from conventional ZIF-8 via
As the temperature increased from 220 to 350 C, the crystalline
[
39]
the wet-chemistry method, the kat-Zn(MeIm)
2
(kat) phase with
structure of the intermediates gradually evolved from zif towards
kat phase (Figures S2 to S3), denoted as CVD/Fe-zif and
CVD/Fe-kat, respectively. Thus, unlike traditional wet-chemistry
methods, the CVD strategy can generate a new topology of
narrower pore size could mitigate the Fe atoms diffusion and
agglomeration during the subsequent pyrolysis. Moreover, the
tunable morphologies and nanostructures of the Fe-ZnO
substrates provide great flexibility to engineer porosity in catalysts
and make it favorable for site accessibility and mass transport in
thick PGM-free cathodes. Also, the CVD method was further
demonstrated generally effective in preparing
atomically dispersed and nitrogen coordinated MN
and Mn) site catalysts.
2 2
Zn(MeIm) , namely kat-Zn(MeIm) phase, which is expected to
increase the number of active sites. The reason is that the formed
narrower pores, relative to the ZIF, could facilitate single Fe sites
to coordinate with N and mitigate the Fe atoms diffusion and
agglomeration. Fe doping into ZnO with a variety of content does
not change ZnO crystalline based on X-ray diffraction (XRD)
patterns (Figure S4a). Also, the crystalline structures of the Fe-
a
variety of
4
(M: Fe, Co,
doped katsenite (kat-Zn(MeIm)
2
with various Fe content are
Results and Discussion
identified similar to metastable polymorph of imidazolate
[
38]
frameworks (Figure S4b).
Synthesis principles and catalyst properties
o
The subsequent thermal treatment at 1000 C directly converts
these intermediates into Fe-N-C catalysts, which are labeled as
xCVD/Fe-N-C-kat catalyst. They represent two broad XRD peaks,
assignable to (002) and (004) planes of graphitized carbon,
respectively (Figure S4c). Regardless of the studied Fe content,
no apparent Fe-containing crystalline phase was detected. The
Fe-doped ZnO substrate was characterized by scanning electron
microscopy (SEM) (Figures 2a and S5a-b), showing a nanosheet
morphology with sizes of around 200-300 nm. However, after the
deposition, the CVD/Fe-kat intermediate displayed a granular
morphology with larger sizes of 300-400 nm (Figures 2b and S5c-
d). This confirmed the vapor-solid reaction occurred between the
contiguous Fe-ZnO nanosheets and 2-MeIm vapor during CVD
A scheme of the CVD process to prepare atomically dispersed
Fe-N-C catalysts is illuminated in Figure 1. A series of xCVD/Fe-
N-C-kat catalysts with different Fe content in ZnO substrates (x:
Fe content in ZnO) were synthesized via the CVD growth followed
by pyrolysis. Typically, Fe-doped ZnO substrates (Figure S1)
3 2 2 2
were prepared by mixing Fe(NO) ·9H O with Zn(Ac) ·2H O via a
sol-gel method. The preparation of ZnO templates is not the
limitation of the CVD synthesis in terms of its scalability. ZnO with
adjustable particle sizes and nanostructures can be easily
[
40-43]
synthesized by using a variety of well-established methods.
Then, 2-MeIm and the as-prepared Fe-ZnO nanosheets were
placed in two separate alumina combustion boats in a furnace
with two temperature zones, respectively. The temperatures for
o
o
the up and downstream zones are heated to 280 and 350 C,
growth. After pyrolysis at 1000 C, the morphology of the final
respectively. As a result, the evaporated gaseous 2-MeIm flows
with the argon gas and subsequently deposits onto Fe-ZnO
nanosheets. The gas-solid reaction leads to the formation of Fe-
0.17CVD/Fe-N-C-kat catalyst with optimal Fe precursor content
was presented in Figures 2c and S5e-f, showing connected
carbon particles with sizes reduced to 100-300 nm. The scanning
transmission electron microscopy (STEM) image (Figure 2d) and
aberration-corrected high angle annular dark-field (HAADF-
STEM) images (Figures 2e-g and S6) further validate the
absence of Fe-containing clusters in the 0.17CVD/Fe-N-C-kat
catalyst. Single Fe atoms (bright dots) are uniformly dispersed in
the carbon phase with randomly oriented graphitic domains.
Zn(MeIm)
mechanism:
2
intermediate according to the proposed reaction
[44]
2MeIm(g) + ZnO(s) → Zn(MeIm) (s) + H O(g) .
ꢀ
ꢀ
The CVD growth temperature of the downstream is crucial in
controlling the crystalline structure of the intermediates.
Figure 1. Schematic illustration of the one-pot synthesis process of atomically dispersed Fe-N-C catalysts via a CVD method.
2
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RESEARCH ARTICLE
Figure 2. SEM images of (a) 0.17Fe-ZnO nanosheet substrate, (b) 0.17CVD/Fe-kat intermediate, and (c) 0.17CVD/Fe-N-C-kat catalyst. (d-g) Morphology and
atomic structure of the 0.17CVD/Fe-N-C-kat catalyst. (d) Representative STEM images of the catalyst. (e-g) Aberration-corrected HAADF-STEM images along with
EEL point spectra. (h) EEL point spectrum from the atomic sites circled in green in (g) to determine the possible Fe-N coordination in the catalyst.
As shown in Figures 2g and 2h, both Fe and N were detected
simultaneously at the atomic level, indicating that these single Fe
sites are likely coordinated by nitrogen. The original EELS at
different atomic spots are also provided in Figure S6, further
confirming the generation of the atomically dispersed and
nitrogen coordinated single Fe sites throughout the carbon phase.
STEM-EELS analysis also determined that the N and Fe content
in the 0.17CVD/Fe-N-C-kat catalyst were 3.78 and 0.15 at%,
respectively (Table S1). When the Fe-free ZnO nanosheets (0Fe-
ZnO) was used as the substrate for the CVD, the resulting sample
(i.e., CVD/N-C-kat ) does not contain any atomic sites located at
the carbon phase according to the HAADF-STEM image (Figure
S7).
The X-ray absorption spectroscopy (XAS) further validates the
atomic dispersion of Fe sites and quantifies the local coordination
number.[45] The Fe K-edge X-ray absorption near edge structure
(
XANES) and extended X-ray absorption fine structure (EXAFS)
show that Fe in the 0.17CVD/Fe-N-C-kat catalyst has the same
oxidization state and local structures to the standard FePc
3
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RESEARCH ARTICLE
containing the well-defined FeN
4
coordination structure (Figures
of Fe-N coordination at the atomic level from the EELS and the
3
a and 3c). Only a peak around 1.3 Å is observed, but no peak is
4
very similar spectra to FeN containing FePc, the model-based
around 2.1Å associated with the metallic Fe-Fe scattering path in
the Fourier transforms of the EXAFS (FT-EXAFS) (Figure 3b).
The similarity further suggests the atomic dispersion of Fe sites in
the Fe-N-C catalyst with negligible or few Fe nanoclusters.
However, the scattering peak around 1.3 Å could stand for either
Fe-C, Fe-N, or Fe-O coordinations. Considering the confirmation
EXAFS fitting was carried out, which shows that Fe is primarily
coordinated with 4 N atoms with reasonable errors (Tables S2 and
S3). This agrees with the results of the atomic-level spectroscopic
analysis and further verifies that well-dispersed atomic Fe sites
are coordinated with N.
2 3
Figure 3. (a) The experimental XANES spectrum of the 0.17 CVD/Fe-N-C-kat catalyst and reference samples (Fe, FeO, Fe O , and FePc). (b, c) Fourier transform
EXAFS spectra in R-space for the 0.17CVD/Fe-N-C-kat catalyst. (d) Raman spectra, (e) XPS N 1s, and (f) C 1s spectra of the CVD/Fe-N-C-kat catalysts with
different Fe doping content into ZnO substrates.
Raman spectra can directly convey the carbon structure
information in these CVD/Fe-N-C-kat catalysts. Gaussian function
was used for the fitting of the spectra, and different fitting peaks
for each material stem from different resonance process involving
spectroscopy (XPS) (Figures 3e, 3f, and S8). Tables S4 to S6
summarize the elemental composition of different CVD/Fe-N-C-
kat catalysts. With an increase of Fe content in ZnO substrates
from 0.06 to 0.20
3 2
g in the form of Fe(NO) ·9H O, the
[
46-
phonons and defects, which refers to different carbon structure.
corresponding content of Fe in CVD/Fe-N-C-kat catalysts is
proportionally increased from 0.04 to 0.30 at%. The N content in
the Fe-free CVD/N-C-kat is 6.3 at% (Table S4), in which N 1s
spectrum shows three individual peaks (Figure 3e),
corresponding to the dominant pyridinic-N (~ 398.5 eV), graphitic-
N (~ 401.1 eV), and oxidized-N (403.5-406 eV). After Fe doping
into the ZnO, the peak at low binding energy becomes broader. A
new peak at ~ 399.4 eV appears, which is likely associated with
4
8]
D G
The intensity ratios of I /I can be used to estimate the
[
3]
graphitization degree of carbon in catalysts (Table S4). As
shown in Figure 3d, these CVD/Fe-N-C-kat catalysts with
different Fe doping amounts have similar carbon structures due
to the insignificant difference in their
D
I /I
G
ratios.[18] The
composition and chemical state of N and Fe in these CVD/Fe-N-
C-kat catalysts were analyzed by using X-ray photoelectron
4
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
the possible Fe-N configuration and nitrile.[28,32,49] With an
increase of Fe doping content, the derived catalysts present
increased Fe-N content. The catalyst with optimal Fe content (i.e.,
methods. For example, Kucernak et al. reported a Fe-N-C catalyst
by using a wet-chemistry method with a density of active sites of
-1 [50]
12±2 μmol g . Meanwhile, according to the ICP analysis, the
content of Zn in the 0.17CVD/Fe-N-C-kat catalyst is lower (~1.0
wt%) than that of most other similar catalysts from traditional wet-
chemistry (2-3 wt%) (Table S4). Thus, unlike traditional Fe-N-C
catalysts derived from ZIF-8 through wet-chemistry methods, the
CVD method can facilitate Zn removal from the catalyst. More
defects and vacancies could be available to host more active
0
.17CVD/Fe-N-C-kat) in terms of best activity contains Fe and N
at 0.28 and 5.45 at%, respectively (Table S4). The trend of
elemental composition is consistent with the results from STEM-
EELS measurement (Table S1). ICP and XPS analysis have
verified the increased Fe content in the CVD-derived catalyst,
relative to other Fe-N-C catalysts (Table S4). Also, we have
quantified the FeN
4
active site density by using in situ
4
FeN sites. Also, reduced Zn would enrich the porosity of catalysts
electrochemical measurements through the nitrite absorption
followed by reductive stripping (Figure S9).[ The active site
density of 0.17CVD/Fe-N-C-kat catalyst is about 26 μmol g ,
which is higher than most Fe-N-C catalysts prepared by other
and minimize the possible contamination to membrane and
ionomer.
50]
-1
(
a)
(b)10
(c)1.25
xCVD/Fe-N-C-kat
0
xCVD/Fe-N-C-kat
0
0
1
2
3
4
Pt/C
0
0
.06
.09
0
0
.06
.09
8
6
4
2
0
1.00
-
-
-
-
0.13
0.13
0
0
.17
.20
0
0
.17
.20
0.75
Pt/C
xCVD/Fe-N-C-kat
Pt/C
0.50
0.17
0.13
0.09
0.25
0.00
0.06
0.20
0
.5 M H
0.8
Potential (V vs. RHE)
2
SO
4
0
0
.0
0.2
0.4
0.6
1.0
0.0
0.2
0.4
0.6
0.8
Catalysts
Potential (V vs. RHE)
(d)
(e)
(f)
Initial
0
1
2
3
4
0
-1
-2
-3
-4
0
-1
-2
1
2
3
4
5
0,000 cycles
80 mg
282 mg
549 mg
0.20CVD/Co-N-C-kat
0.12CVD/Mn-N-C-kat
0,000 cycles
0,000 cycles
0,000 cycles
0,000 cycles
-
-
-
-
3
5 mV
-
3
4
-
0
.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Potential (V vs. RHE)
Potential (V vs. RHE)
Potential (V vs. RHE)
o
Figure 4. ORR activity studies by using RRDE in O
2
saturated 0.5ꢀM H
yields, and (c) kinetic mass activity at 0.9 V (Ag ) current density for CVD/Fe-N-C-kat catalysts obtained from ZnO substrates with different Fe doping content. (d)
AST by cycling the potential (0.6-1.0 V) in O -saturated 0.5 M H SO for 50,000 cycles to study the stability of the best performing 0.17CVD/Fe-N-C-kat catalyst. (e)
2 4 2 2
SO electrolytes at 25 C and 900 rpm. (a) Steady-state ORR polarization plots, (b) H O
-
1
2
2
4
ORR activities of 0.17CVD/Fe-N-C-kat catalysts obtained from one-pot CVD synthesis at different scales to demonstrate the possible scalability. (f) Steady-state
ORR polarization plots of 0.20CVD/Co-N-C-kat and 0.12CVD/Mn-N-C-kat catalysts to validate the flexibility of the CVD synthesis to prepare other single metal site
catalysts.
XPS further investigated the effect of heating temperature on
the chemical state and content of N and Fe in these CVD/Fe-N-
C-kat catalysts (Figure S10 and Table S7-S9). The content of N
is declined from 12.47 to 2.18 at% when the temperature was
plots of CVD/Fe-N-C-kat catalysts as a function of Fe content in
ZnO substrates. The Fe-free kat(Zn) intermediate derived CVD/N-
C-kat catalyst exhibited poor activity, similar to N-doped carbon
catalysts.[51] The ORR activity was improved with an increase in
Fe content doped into ZnO substrates. The 0.17CVD/Fe-N-C-kat
catalyst exhibited the best ORR activity, with an onset potential
(Eonset) of 0.963 V and a half-wave potential (E1/2) of 0.835 V vs.
RHE (0.6 mg cm catalyst loading; 25 C; 900 rpm), representing
one of Fe-N-C catalysts with the highest RDE activity (Table S10).
However, further increasing Fe doping to 0.20 decreased the
activity with a negative E1/2 shift to 0.785 V. Traditional wet
chemistry methods to prepare Fe-doped ZIF-8 are challenging in
accurately controlling Fe-doping content in the precursor because
a portion of Fe ions always remained in the solvent. In contrast,
o
increased from 900 to 1100 C. Among studied heating
temperature, FeN
4
active sites reach the highest density at
o
1
000 C (discussed later). The identical C1s spectra (Figure 3f) of
-2
o
CVD/Fe-N-C-kat catalysts suggest no noticeable change in the
o
carbon structure from 900 to 1100 C.
Catalytic performance for the ORR
The ORR activity of CVD/Fe-N-C-kat catalysts was evaluated
by using a rotating ring disk electrode (RRDE) in 0.5 M H
2 4
SO .
Figures 4a and S11a show the ORR steady-state polarization
5
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
o
the CVD method enables accurate Fe doping into the ZnO
substrate, which allows all of Fe to participate in the formation of
(Figure S12). The catalyst from 1000 C exhibited the best ORR
activity. This is probably due to the optimal balance of the
FeN
4
active sites. The fine regulating Fe content is beneficial for
4
increased density of FeN sites and enhanced intrinsic activity
achieving the maximum density of FeN
4
active sites in the catalyst. associated with the shortening Fe-N bond length at higher heating
thermal temperature.[32] The activity of the catalyst from 1100 C is
slightly declined due to the loss of nitrogen dopants and single Fe
sites as well as the possible reconstruction of carbon structures
(Table S7).[32] Also, catalyst stability was studied by using an
accelerated stress test (AST) protocol. After 50,000 AST potential
o
H
2
O
2
yields were also calculated in Figures 4b and S11b to
evaluate the four-electron pathway selectivity. The 0.17CVD/Fe-
N-C-kat catalyst yielded the lowest H yields < 1%, indicating a
2 2
O
complete four-electron ORR pathway. The kinetic current density
at 0.9 V is also used for evaluating catalyst activity. The
0
.17CVD/Fe-N-C-kat catalyst generated the highest mass activity
cycles (0.6–1.0 V) in O
2
saturated 0.5 M H
2
SO
4
, the 0.17CVD/Fe-
-1
-1
(Ag ) at 0.9 V, indicating the highest kinetic activity among
N-C-kat catalyst lost 35 mV in E1/2 (Figure 4d) and 0.25 Ag in
kinetic current density at 0.9 V (Figure S13). When compared to
other Fe-N-C catalysts tested under the identical protocol (Table
studied Fe-N-C catalysts, but much lower than Pt/C due to the low
FeN
effect of pyrolysis temperature ranging from 900 to 1100 C on the
ORR activity by using the optimal Fe doping content of 0.17
4
active site loading (Figure 4c). We also investigated the
o
S11),
the
0.17CVD/Fe-N-C-kat
catalyst
demonstrated
[
8,28]
comparable stability improvement.
Figure 5. MEA studies of various Fe-N-C catalysts from CVD synthesis: cathode loading ~4.0 mg cm–2; anode: Pt/C, 0.20 mgPt cm ; 100% RH; 1.0 bar gas pressure;
-2
o
2
Nafion 212 membrane; cell temperature: 80 C; MEA area: 5.0 cm . I-V polarization (solid symbols and lines) and power density (hollow symbols and lines) plots of
a) H -O and (b) H -air cell using 0.17CVD/Fe-N-C-kat, 0.17CVD/Fe-N-C-zif, and 0.13CVD/Fe-N-C-zif cathodes. The flow rates of O /air and H are 500 and 300
mL min , respectively. (c) Fuel cell performance comparison between the 0.17CVD/Fe-N-C-kat catalyst and other Fe-N-C catalysts reported in the literature,
(
2
2
1
2
2
2
–
[8,19,32-
3
3,52-54]
2
including the area metric current density at 0.9 ViR-free under 1.0ꢀbar O (X-axis) and area metric current density at 0.8 V under 1.0ꢀbar air (Y-axis). (d) Fuel
–
1
cell durability test at a constant potential of 0.70 V at a flow rate of air at 200 mL min . (e) Recorded polarization plots of the 0.17CVD/Fe-N-C-kat cathode during
the 100-hour durability test at 0.70 V. (f) Recorded polarization plots of the 0.17CVD/Fe-N-C-kat cathode at different cycle number during the 30,000-cycle durability
AST (0.60 to 0.95 V).
As previously described, when the CVD growth temperature
was reduced to 220 C, the obtained intermediate was assigned
to CVD/Fe-zif. The corresponding 0.17CVD/Fe-N-C-zif catalyst
exhibited inferior ORR activity with a decreased E1/2 of 0.78 V
exhibited slightly improved activity, with an E1/2 of 0.80 V (Figure
S14). Regardless of Fe doping content, all CVD/Fe-N-C-
zif catalysts are inferior to the best performing 0.17CVD/Fe-N-C-
kat catalyst (Figure S17). Thus, the Fe-kat(Zn) phase is more
o
(
Figure S14). XPS analysis (Figure S15 and Table S12-14)
indicated that the 0.17CVD/Fe-N-C-zif catalyst contains a lower
content of FeN active sites compared to the 0.17CVD/Fe-N-C-
kat catalyst. Raman spectrum of 0.17CVD/Fe-N-C-zif also
presents a lower value of I /I ratio (Figure S16), indicating a
4
effective for generating a higher density of FeN active site than
traditional ZIF-8. More importantly, the scale-up synthesis of Fe-
N-C catalysts via the CVD method in one batch, including 80, 282,
and 549 mg were also successfully achieved (Figures S18-20).
Although the differences of ORR activity (Figures 4e and S21)
and fuel cell performance (Figure S22) for these catalysts are
noticeable, the scalable synthesis effort validated the feasibility to
engineer further the CVD method for mass production of active
4
D
G
higher degree of graphitization structure relative to the CVD/Fe-
N-C-kat catalyst. When we slightly reduced the Fe doping from
0
.17 to 0.13, the corresponding 0.13CVD/Fe-N-C-zif catalyst
6
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
Fe-N-C catalysts. Notably, by using larger quartz tubes and
alumina combustion boats along with innovative designs of CVD
set-up to mitigate the diffusion resistance of gaseous precursor,
the scale-up synthesis of such single metal site catalysts in a
gram-scale with sufficient ORR activity is very likely. Also, the
unique CVD method is versatile in synthesizing other M-N-C
catalysts (M: Co, Mn) by doping corresponding metal precursors
into ZnO substrates. Figures 4f and S23-24 present ORR steady-
state polarization plots of CVD/Co-N-C-kat and CVD/Mn-N-C-kat
catalysts, showing similar ORR activity to corresponding
atomically dispersed M-N-C catalysts synthesized from wet-
chemistry methods.[
only losing a total of 50 mA cm-2 during the overall 100 hours test.
In a different AST protocol, voltage cycling from 0.6 and 0.95 V
2
for 30,000 cycles under H /air was conducted. Polarization plots
were also recorded at different cycles during the stability test
(Figure 5f). The loss of current density at a relatively high voltage
of 0.8 V is 40% after the first 5000 cycles. The accumulated loss
is 55% after 30,000 cycles. Using both stability testing protocols,
the decline of current density at low voltage ranges (<0.45 V) is
insignificant. For example, at 0.4 V, only 9.2% and 9.6% losses in
current density occurred during the prolonged potential cycling
(0.6~0.95 V for 30,000 cycles) and the potentiostatic test (0.7 V
for 100 hours), respectively. The well retained current density in
7,55]
low voltage implied the MEA did not suffer severe mass transport
loss or water flooding,[8,10] possibly due to the favorable
Fuel cell performance
The best performing 0.17CVD/Fe-N-C-kat catalyst was mixed
with the Nafion ionomer solution to prepare membrane electrode
mesoporous structure (Figure S24 and Table S15). The
performance degradation in MEAs is complicated than that in
aqueous acidic electrolytes. Demetallation of active sites, attack
assemblies (MEAs) for fuel cell performance evaluation. The H
2
-
O
2
cell was first measured to study catalyst activity in MEAs with
2 2
of the carbon/active sites by H O /radicals, micropore flooding,
minimized mass transport resistance. Figure 5a exhibited an
open-circuit voltage (OCV) of 0.984 V and a current density of 27
mA cm–2 at 0.9 V under 1.0 bar pressure of O2. This value is
approaching to the DOE 2025 target (44 mA cm–2 at 0.9 ViR-free).
In contrast, the 0.17CVD/Fe-N-C-zif based MEAs delivered a
significantly decreased current density of 5.8 mA cm-2 at 0.9 ViR-
free under identical conditions. The Brunauer-Emmett-Teller (BET)
and degradation of three-phase (gas, liquid, solid) interfaces were
[36,58-60]
proposed as four primary degradation mechanisms.
Among others, the carbon corrosion in the Fe-N-C catalysts due
to the attacks from the ORR byproducts, i.e., H and/or reactive
radical species, is the root cause of a significant loss of the FeN
2 2
O
4
active sites.[61] In this work, the CVD-derived Fe-N-C catalyst has
demonstrated promising stability in MEAs, relative to other
reported catalysts.[57] Engineering carbon structures with
enhanced corrosion resistance and optimized electrode
structures are imperative to address further the stability challenge
of the Fe-N-C catalyst in MEAs.[62-63]
2
-1
surface area (Figure S25) of the 0.17CVD/Fe-N-C-zif (296 m g )
2
-1
is higher than that of 0.17CVD/Fe-N-C-kat (216 m g ). Thus, the
increased activity and MEA performance of the 0.17CVD/Fe-N-C-
kat catalyst is due to the optimized mesoporous structures for
promoting the mass transfer and exposing more accessible active
sites. Jaouen et al., pointed out that the Fe-N-C catalysts could
be performing better in MEAs relative to their activity measured
by using RDE.[51] In some cases, highly active catalysts also
cannot generate expected MEA performance due to that their
morphologies and porosity are not favorable for establishing
efficient three-phase interfaces within 3D electrodes for the
ORR.[56-57] Here, the improved MEA performance of the
Conclusion
In summary, we developed a CVD strategy to prepare atomically
dispersed and nitrogen coordinated FeN
reduction. Gaseous deposition of 2-MeIm onto a Fe-doped ZnO
substrate can generate kat-Zn(MeIm) (kat) phase intermediate
4
site catalysts for oxygen
2
1
7CVD/Fe-N-C-kat catalyst may be attributed to the narrowed
by appropriately controlling the CVD temperature. The
subsequent in-situ thermal activation at 1000 C yielded well-
pore size of kat(Zn) phase, which can mitigate the Fe atom
o
diffusion and agglomeration. MEA performance was evaluated
defined FeN
4
sites uniformly dispersing into a mesopore-
further by using more practical H
The OCV value only dropped 22 mV relative to that measured in
, i.e., 0.962 V. The critical current densities at 0.80 and 0.65 V
2
-air cells at 1.0 bar air pressure.
dominant carbon. Compared to other Fe-N-C catalysts derived
from ZIF-8 through wet-chemistry synthesis, the CVD method can
O
2
yield a higher density of FeN
pore size of kat-Zn(MeIm)
4
active sites due to that the narrow
(kat) phase could mitigate the
-2
reached 117 and 448 mA cm , respectively, (Figure 5b), which
is higher than most of the reported Fe-N-C catalysts (Figures 5c,
S26, and Table S13). Notably, the performance at 0.8 V
2
formation of inactive metal aggregates. The catalyst derived from
optimal Fe doping, heating temperature, and ZnO template,
exhibited encouraging catalytic activity and stability toward the
ORR in challenging acidic electrolytes. Importantly, MEA studies
further verified its high active site density and favorable mass
transfer, which can deliver outstanding performance (e.g., 27
-2
approaches to the DOE target (150 mA cm at 1.0 bar air).
The performance durability is the most significant challenge of
viable Fe-N-C catalysts for PEMFC applications.[58-59] Two
stability testing protocols were employed to evaluate the durability
of the CVD-derived Fe-N-C catalyst. At first, MEA performance
mAꢀcm-2 at 0.9 V under 1.0ꢀbar H
-O
2
and 117ꢀmAꢀcm-2 at 0.8 V
2
under 1.0ꢀbar H -air) approaching the U.S. DOE targets. We also
2
2
was assessed by holding at a constant voltage of 0.70 V in an H –
demonstrated that the CVD method provided a possibility to
realize the challenging scale-up synthesis of single metal site
catalysts. Besides, the CVD can be modified to prepare a variety
of catalysts, including Fe, Co, and Mn by using corresponding
metal-doped ZnO substrates. Therefore, this CVD synthesis
air cell for 100 hours (Figure 5d). Although overall performance
loss at the continuous 0.7 V test is significant, the corresponding
polarization plots recorded at different time intervals during the
durability test demonstrated encouraging stability enhancement
(
Figure 5e) when compared to other similar catalysts.[8-9] After the
approach may open
a new avenue for the continuous
-
first 20 hours, the current density loss at 0.80 V is ca. 28 mA cm
2.
development of versatile and highly efficient single metal sites
However, the subsequent degradation rates are much slower,
7
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Angewandte Chemie International Edition
10.1002/anie.202009331
RESEARCH ARTICLE
catalysts for fuel cells and other electrocatalysis applications. In
this work, by modifying the morphologies and nanostructures of
employed ZnO substrates, there is still much room for further
improving the ORR catalytic activity and MEA performance. For
example, the studied CVD-derived Fe-N-C catalyst still has
relatively low surface areas (216 m2 g-1), which should be
significantly increased for hosting more active sites. Also,
graphitized carbon structure with enhanced corrosion resistance
in the CVD catalysts is highly desirable to improve stability.
[10] V. Goellner, V. Armel, A. Zitolo, E. Fonda, F. Jaouen, J.
Electrochem. Soc. 2015, 162, H403-H414.
11] J. Wang, Z. Huang, W. Liu, C. Chang, H. Tang, Z. Li, W. Chen,
C. Jia, T. Yao, S. Wei, Y. Wu, Y. Li, J. Am. Chem. Soc. 2017,
139, 17281-17284.
[
[12] M. Chen, Y. He, J. S. Spendelow, G. Wu, ACS Energy Lett.
2019, 4, 1619-1633.
[
13] Q. Shi, S. Hwang, H. Yang, F. Ismail, D. Su, D. Higgins, G. Wu,
Mater. Today 2020,
https://doi.org/10.1016/j.mattod.2020.1002.1019.
[14] Y. Zhu, J. Sokolowski, X. Song, Y. He, Y. Mei, G. Wu, Adv.
Energy Mater. 2020, 10, 1902844.
[
15] A. Zitolo, V. Goellner, V. Armel, M. T. Sougrati, T. Mineva, L.
Stievano, E. Fonda, F. Jaouen, Nat. Mater. 2015, 14, 937-942.
Acknowledgments
[16] K. Liu, G. Wu, G. Wang, J. Phys. Chem. C 2017, 121, 11319-
1324.
1
[
17] Z. K. Yang, Y. Wang, M. Z. Zhu, Z. J. Li, W. X. Chen, W. C.
Wei, T. W. Yuan, Y. T. Qu, Q. Xu, C. M. Zhao, X. Wang, P. Li,
Y. F. Li, Y. Wu, Y. D. Li, ACS Catal. 2019, 9, 2158-2163.
The authors acknowledge the financial support from the U.S.
Department of Energy, Office of Energy Efficiency and
Renewable Energy (EERE), Fuel Cell Technology Office (DE-
EE0008075, DE-EE0008076, and DE-EE0008417) along with
National Science Foundation (CBET-1604392, 1804326). Z. F.
thanks for the startup funding from Oregon State University. This
X-ray absorption spectroscopy research used resources of the
beamline 5-BM, DND-CAT at the Advanced Photon Source (APS)
that is a U.S. Department of Energy (DOE) Office of Science User
Facility operated for the DOE Office of Science by Argonne
National Laboratory under Contract DE-AC02-06CH11357. DND-
CAT is supported through E. I. duPont de Nemours & Co.,
Northwestern University, and The Dow Chemical Company.
[18] V. Armel, S. Hindocha, F. Salles, S. Bennett, D. Jones, F.
Jaouen, J. Am. Chem. Soc. 2017, 139, 453-464.
19] X. Wan, X. Liu, Y. Li, R. Yu, L. Zheng, W. Yan, H. Wang, M.
Xu, J. Shui, Nat. Catal. 2019, 2, 259-268.
20] L. Yang, D. Cheng, H. Xu, X. Zeng, X. Wan, J. Shui, Z. Xiang,
D. Cao, Proc. Natl. Acad. Sci. U S A 2018, 115, 6626-6631.
21] J. D. Yi, R. Xu, Q. Wu, T. Zhang, K. T. Zang, J. Luo, Y. L.
Liang, Y. B. Huang, R. Cao, ACS Energy Lett. 2018, 3, 883-
[
[
[
8
89.
[
[
22] Y. Lin, P. Liu, E. Velasco, G. Yao, Z. Tian, L. Zhang, L. Chen,
Adv. Mater. 2019, 31, e1808193.
23] Z. Miao, X. Wang, M.-C. Tsai, Q. Jin, J. Liang, F. Ma, T. Wang,
S. Zheng, B.-J. Hwang, Y. Huang, S. Guo, Q. Li, Adv. Energy
Mater. 2018, 8, 1801226.
[
[
[
[
[
24] Y. Chen, Z. Li, Y. Zhu, D. Sun, X. Liu, L. Xu, Y. Tang, Adv.
Mater. 2019, 31, e1806312.
25] M. Lefevre, E. Proietti, F. Jaouen, J. P. Dodelet, Science 2009,
Conflict of interest
3
24, 71-74.
26] G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science 2011,
The authors declare no conflict of interest.
332, 443-447.
27] E. Proietti, F. Jaouen, M. Lefevre, N. Larouche, J. Tian, J.
Herranz, J. P. Dodelet, Nat. Commun. 2011, 2, 416.
28] H. Zhang, S. Hwang, M. Wang, Z. Feng, S. Karakalos, L. Luo,
Z. Qiao, X. Xie, C. Wang, D. Su, Y. Shao, G. Wu, J. Am. Chem.
Soc. 2017, 139, 14143-14149.
Keywords: Single metal sites; chemical vapor deposition; Fe-N-
C; oxygen reduction reaction; electrocatalysis.
[
29] Y. Chen, S. Ji, Y. Wang, J. Dong, W. Chen, Z. Li, R. Shen, L.
Zheng, Z. Zhuang, D. Wang, Y. Li, Angew. Chem. Int. Ed.
2
017, 56, 6937-6941.
[
[
[
1] X. X. Wang, M. T. Swihart, G. Wu, Nat. Catal. 2019, 2, 578-
89.
2] Y. Li, H. Wang, C. Priest, S. Li, P. Xu, G. Wu, Adv. Mater.
020, https://doi.org/10.1002/adma.202000381, 2000381.
3] Z. Qiao, S. Hwang, X. Li, C. Wang, W. Samarakoon, S.
Karakalos, D. Li, M. Chen, Y. He, M. Wang, Z. Liu, G. Wang, H.
Zhou, Z. Feng, D. Su, J. S. Spendelow, G. Wu, Energy.
Environ. Sci. 2019, 12, 2830-2841.
[30] B. C. Hu, Z. Y. Wu, S. Q. Chu, H. W. Zhu, H. W. Liang, J.
Zhang, S. H. Yu, Energy. Environ. Sci. 2018, 11, 2208-2215.
[31] M. M. Wu, K. Wang, M. Yi, Y. X. Tong, Y. Wang, S. Q. Song,
ACS Catal. 2017, 7, 6082-6088.
[32] J. Li, H. Zhang, W. Samarakoon, W. Shan, D. A. Cullen, S.
Karakalos, M. Chen, D. Gu, K. L. More, G. Wang, Z. Feng, Z.
Wang, G. Wu, Angew. Chem. Int. Ed. 2019, 58, 18971-18980.
[33] J. Li, L. Jiao, E. Wegener, L. L. Richard, E. Liu, A. Zitolo, M. T.
Sougrati, S. Mukerjee, Z. Zhao, Y. Huang, F. Yang, S. Zhong,
H. Xu, A. J. Kropf, F. Jaouen, D. J. Myers, Q. Jia, J. Am. Chem.
Soc. 2020, 142, 1417-1423.
5
2
[
4] S. Ott, A. Orfanidi, H. Schmies, B. Anke, H. N. Nong, J.
Hubner, U. Gernert, M. Gliech, M. Lerch, P. Strasser, Nat.
Mater. 2020, 19, 77-85.
[
[
[
5] J. Hou, M. Yang, C. Ke, G. Wei, C. Priest, Z. Qiao, G. Wu, J.
Zhang, EnergyChem 2020, 2, 100023.
6] X. Ren, Q. Lv, L. Liu, B. Liu, Y. Wang, A. Liu, G. Wu, Sustain.
Energy Fuels 2020, 4, 15-30.
7] J. Z. Li, M. J. Chen, D. A. Cullen, S. Hwang, M. Y. Wang, B. Y.
Li, K. X. Liu, S. Karakalos, M. Lucero, H. G. Zhang, C. Lei, H.
Xu, G. E. Sterbinsky, Z. X. Feng, D. Su, K. L. More, G. F.
Wang, Z. B. Wang, G. Wu, Nat. Catal. 2018, 1, 935-945.
8] H. Zhang, H. T. Chung, D. A. Cullen, S. Wagner, U. I. Kramm,
K. L. More, P. Zelenay, G. Wu, Energy. Environ. Sci. 2019, 12,
[34] V. Yarlagadda, M. K. Carpenter, T. E. Moylan, R. S. Kukreja, R.
Koestner, W. Gu, L. Thompson, A. Kongkanand, ACS Energy
Lett. 2018, 3, 618-621.
[35] A. Kongkanand, V. Yarlagadda, T. R. Garrick, T. E. Moylan, W.
Gu, ECS Trans. 2016, 75, 25-34.
[36] J.-Y. Choi, L. Yang, T. Kishimoto, X. Fu, S. Ye, Z. Chen, D.
Banham, Energy. Environ. Sci. 2017, 10, 296-305.
[37] S. Lee, D.-H. Kwak, S.-B. Han, Y.-W. Lee, J.-Y. Lee, I.-A. Choi,
H.-S. Park, J.-Y. Park, K.-W. Park, ACS Catal. 2016, 6, 5095-
5102.
[38] A. D. Katsenis, A. Puskaric, V. Strukil, C. Mottillo, P. A. Julien,
K. Uzarevic, M. H. Pham, T. O. Do, S. A. Kimber, P. Lazic, O.
Magdysyuk, R. E. Dinnebier, I. Halasz, T. Friscic, Nat.
Commun. 2015, 6, 6662.
[
[
2
548-2558.
9] Y. He, S. Hwang, D. A. Cullen, M. A. Uddin, L. Langhorst, B. Li,
S. Karakalos, A. J. Kropf, E. C. Wegener, J. Sokolowski, M.
Chen, D. Myers, D. Su, K. L. More, G. Wang, S. Litster, G. Wu,
Energy. Environ. Sci. 2019, 12, 250-260.
8
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202009331
RESEARCH ARTICLE
[
[
[
[
[
[
[
39] Q. Liu, X. Liu, L. Zheng, J. Shui, Angew. Chem. Int. Ed. 2018,
7, 1204-1208.
40] M. Monge, M. L. Kahn, A. Maisonnat, B. Chaudret, Angew.
5
Chem. Int. Ed. 2003, 42, 5321-5324.
41] Y. T. Chung, M. M. Ba-Abbad, A. W. Mohammad, N. H. H.
Hairom, A. Benamor, Mater. Des. 2015, 87, 780-787.
42] Y. Z. Mao, S. Y. Ma, W. Q. Li, J. Luo, L. Cheng, D. J.
Gengzang, X. L. Xu, Mater. Lett. 2015, 157, 151-154.
43] J. Zhang, B. Zhao, Z. Pan, M. Gu, A. Punnoose, Cryst. Growth
Des. 2015, 15, 3144-3149.
44] J. B. Lin, R. B. Lin, X. N. Cheng, J. P. Zhang, X. M. Chen,
Chem. Commun. 2011, 47, 9185-9187.
45] M. Wang, L. Árnadóttir, Z. J. Xu, Z. Feng, Nano-Micro Lett.
2
019, 11, 47.
[
[
46] A. C. Ferrari, D. M. Basko, Nat. Nanotech. 2013, 8, 235-246.
47] Y. Zhou, S. L. Candelaria, Q. Liu, E. Uchaker, G. Cao, Nano
Energy 2015, 12, 567-577.
[
[
48] J.-M. Vallerot, X. Bourrat, A. Mouchon, G. Chollon, Carbon
2
006, 44, 1833-1844.
49] F. Jaouen, J. Herranz, M. Lefevre, J. P. Dodelet, U. I. Kramm, I.
Herrmann, P. Bogdanoff, J. Maruyama, T. Nagaoka, A.
Garsuch, J. R. Dahn, T. Olson, S. Pylypenko, P. Atanassov, E.
A. Ustinov, ACS Appl. Mater. Interfaces 2009, 1, 1623-1639.
50] D. Malko, A. Kucernak, T. Lopes, Nat. Commun. 2016, 7,
[
[
[
[
1
3285.
51] G. Wu, A. Santandreu, W. Kellogg, S. Gupta, O. Ogoke, H.
Zhang, H.-L. Wang, L. Dai, Nano Energy 2016, 29, 83-110.
52] H. T. Chung, D. A. Cullen, D. Higgins, B. T. Sneed, E. F. Holby,
K. L. More, P. Zelenay, Science 2017, 357, 479-484.
53] J. Tian, A. Morozan, M. T. Sougrati, M. Lefevre, R. Chenitz, J.
P. Dodelet, D. Jones, F. Jaouen, Angew. Chem. Int. Ed. 2013,
5
2, 6867-6870.
[
[
54] X. Fu, N. Li, B. Ren, G. Jiang, Y. Liu, F. M. Hassan, D. Su, J.
Zhu, L. Yang, Z. Bai, Z. P. Cano, A. Yu, Z. Chen, Adv. Energy
Mater. 2019, 9, 1803737.
55] X. X. Wang, D. A. Cullen, Y. T. Pan, S. Hwang, M. Wang, Z.
Feng, J. Wang, M. H. Engelhard, H. Zhang, Y. He, Y. Shao, D.
Su, K. L. More, J. S. Spendelow, G. Wu, Adv. Mater. 2018, 30,
2
01706758.
[
[
[
[
[
[
56] F. Jaouen, V. Goellner, M. Lefèvre, J. Herranz, E. Proietti, J. P.
Dodelet, Electrochim. Acta 2013, 87, 619-628.
57] Y. He, S. Liu, C. Priest, Q. Shi, G. Wu, Chem. Soc. Rev. 2020,
4
9, 3484-3524.
58] U. Martinez, S. K. Babu, E. F. Holby, P. Zelenay, Curr. Opin.
Electrochem. 2018, 9, 224-232.
59] Y. Shao, J. P. Dodelet, G. Wu, P. Zelenay, Adv. Mater. 2019,
e1807615.
60] R. Chenitz, U. I. Kramm, M. Lefevre, V. Glibin, G. X. Zhang, S.
H. Sun, J. P. Dodelet, Energy Environ. Sci. 2018, 11, 365-382.
61] K. Kumar, L. Dubau, M. Mermoux, J. Li, A. Zitolo, J. Nelayah,
F. Jaouen, F. Maillard, Angew. Chem. Int. Ed. 2020, 59, 3235-
3
243.
[
[
62] X. Zhao, X. Yang, M. Wang, S. Hwang, S. Karakalos, M. Chen,
Z. Qiao, L. Wang, B. Liu, Q. Ma, D. A. Cullen, D. Su, H. Yang,
H.-Y. Zang, Z. Feng, G. Wu, Appl. Catal. B Environ. 2020,
1
19400.
63] G. Chen, P. Liu, Z. Liao, F. Sun, Y. He, H. Zhong, T. Zhang, E.
Zschech, M. Chen, G. Wu, J. Zhang, X. Feng, Adv. Mater.
2
020, 32, 1907399.
9
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Table of Contents
Atomically dispersed and nitrogen coordinated iron (Fe-N-C) catalysts are prepared by using the chemical vapor deposition method.
The resultant catalyst exhibits outstanding oxygen-reduction activity in acidic electrolytes, which can further transfer into membrane
electrode assemblies (MEAs) for fuel cell applications. The achieved MEA performance and durability are encouraging, capable of
generating compelling current densities: 27 mAcm-2 at 0.9 V (1.0 bar O
targets.
) and 117 mAcm-2 at 0.8 V (1.0ꢀbar air), close to the U.S. DOE
2
10
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