Synergistic Effects between Atomically Dispersed Fe?N?C and C?S?C for the Oxygen Reduction Reaction in Acidic Media

Article abstract of DOI:10.1002/anie.201706602

Various advanced catalysts based on sulfur-doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur-doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template-sacrificing method. The incorporated sulfur gives a thiophene-like structure (C?S?C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e^? ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur-free variant (Fe/NC) in 0.5 m H₂SO₄.

Full text of DOI:10.1002/anie.201706602

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Synergistic Effect between the Atomically Dispersed Active Site
of Fe-N-C and C-S-C for ORR in Acidic Medium
Authors: Hangjia Shen, Eduardo Gracia-Espino, Jingyuan Ma, Ketao
Zang, Jun Luo, Le Wang, Sanshuang Gao, Xamxikamar
Mamat, Guangzhi Hu, Thomas Wagberg, and Shaojun Guo
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201706602
Angew. Chem. 10.1002/ange.201706602
Link to VoR: http://dx.doi.org/10.1002/anie.201706602
http://dx.doi.org/10.1002/ange.201706602

10.1002/anie.201706602
Angewandte Chemie International Edition
COMMUNICATION
Synergistic Effect between the Atomically Dispersed Active Site
of Fe-N-C and C-S-C for ORR in Acidic Medium
Hangjia Shen,‡ Eduardo Gracia-Espino,‡ Jingyuan Ma,‡ Ketao Zang, Jun Luo, Le Wang, Sanshuang
Gao, Xamxikamar Mamat, Guangzhi Hu*, Thomas Wagberg* and Shaojun Guo*
Abstract: Various advanced catalysts of sulfur doped Fe-N-C
materials have been recently designed for oxygen reduction reaction
(ORR), however, the enhanced activity is still controversial and
usually attributed to differences in surface area, improved
conductivity, or to uncertain synergistic effects. Here, a sulfur-doped
Fe-N-C catalyst (denoted as Fe/SNC) derived via a template
most promising non-precious metal catalysts with superior
methanol tolerance. Especially in alkaline medium, high activity
was achieved on Fe-N-C catalysts and the nature of the active
sites is progressively disclosed in recent works.[7] In acidic
medium, however, despite significant recent improvements, Fe-
N-C catalysts still exhibit higher overpotential and lower
stability.[8] This effect is attributed to a different state of the active
site under acidic and alkaline conditions. It has been suggested
that the iron center is not accessible as an active site in strongly
alkaline solutions.[9] The inner-Helmholtz plane of active sites in
alkaline conditions are all covered by adsorbed hydroxyl species
(OHads acting as an outer-sphere bridge), and the solvated O2 is
sacrificing method is presented. The incorporated
S gives a
thiophene-like structure (C-S-C), reduces the electron localization
around the Fe center, improves the interaction with oxygenated
species, and therefore facilitates the complete 4e- ORR in acid
solution. This synergistic effect makes the Fe/SNC catalyst exhibits
much better ORR activity than sulfur free catalyst (Fe/NC) in 0.5 M
H2SO4.
-
localized in outer-Helmholtz plane, but the intermediate of HO2
as the Lewis basic can be adsorbed and immediately reduced to
the 4e- product on Lewis acidic Fe2+ active sites.[10] Nonetheless,
in acidic medium, the ORR active site is directly accessible to
the reactant (O2, H+) and other intermediate products (i.e. H2O2).
In addition, the neutral H2O2 negates its Lewis basic character
and undermines its stabilization on Fe2+ active sites, facilitating
the 2e- ORR pathway and generating H2O2.[7a]
Proton exchange membrane fuel cells (PEMFCs) are
considered as promising clean and high efficient energy systems
to convert chemical energy directly into electrical energy.[1]
Technical limitation associated with the PEMFCs, in particular
the cathode catalyst for low oxygen reduction reaction (ORR)
activity in acidic solution, has proven to be a complicated
bottleneck to overcome.[2] Traditionally, platinum and its alloy
have been regarded as the best ORR catalysts,[3] however, the
scarcity, high costs and low methanol crossover tolerance of Pt
alloys have motivated the search to indetify cost-effective non-
noble metal electrocatalysts,[4] including earth-abundant
transition metal and nitrogen co-doped carbons (M-N-C),[5] and
metal-free heteroatom-doped carbons.[6]
To achieve a breakthrough in promoting the efficiency, one
viable strategy is to design and regulate the structure of
catalysts to improve the selectivity toward 4e- reduction of O2 by
suppressing the production of H2O2.[1] Attractively, S-doped Fe-
N-C catalyst exhibits better ORR activity than undoped Fe-N-C
in acidic electrolyte.[11] The enhanced ORR properties might be
ascribed to iron-containing active sites surrounded by sulfur
species,[12] however, the precise role of S during the ORR is still
unclear. Here, we design a novel S-doped Fe-N-C catalyst via a
template casting procedure (Scheme S1). Sublimed sulfur was
introduced as S precursor during the synthesis and finally doped
into the carbon skeleton to form thiophene-like structures (C-S-
C). Furthermore, different from the previous reports that heating
the mixture of Fe and carbon precursors led to the Fe-N-C
Among them, Fe-N-C catalysts have emerged as one of the
[a]
H. Shen,‡ L. Wang, S. Gao, X. Mamat, G. Hu
Key Laboratory of Chemistry of Plant Resources in Arid Regions,
State Key Laboratory Basis of Xinjiang indigenous medicinal plants
resource utilization, Xinjiang Technical Institute of Physics and
Chemistry, Chinese Academy of Sciences, 830011, Urumqi (China)
E-mail: guangzhihu@ms.xjb.ac.cn
[13]
catalyst containing Fe/Fe3C (hard to be removed by acid),
herein our new strategy of pre-anchoring Fe precursor on the
template (SBA-15) surface can only produce the acid-resistant
Fe-N-C catalyst after acid treatment. In acidic medium, although
the site C-S-C is less-active for ORR, it plays an important role
in reducing the electron localization around the Fe center, and
thereby lowering the ORR activation barriers on Fe-N-C. The
observed synergistic effects between C-S-C and Fe-N-C sites
boost the ORR activity manifested by a positive shift of the half-
wave potential by 30 mV when compared with the sulfur-free
Fe/NC counterpart.
N2 adsorption-desorption isotherm curves (Figure S2a)
for S-doped samples exhibit absorbed volumes that are
significantly larger than that of sulfur-free samples, and
decrease with Fe incorporation. The specific surface areas
are also increased after S doping. As listed in Table S1,
SNC and Fe/SNC show specific surface areas of 1062 and
1031 m2 g-1, respectively, while the sulfur-free N-doped
carbon (NC) and Fe/NC samples exhibit the surface area of
S. Guo
Department of Materials Science and Engineering, College of
Engineering, Peking University, 100871, Beijing (Chna)
E-mail: guosj@pku.edu.cn
E. Gracia-Espino,‡ G. Hu, T. Wagberg
Department of Physics, Umeå University, 901 87, Umeå (Sweden)
E-mail: thomas.wagberg@physics.umu.se
H. Shen,‡ L. Wang
[b]
University of Chinese Academy of Sciences, 100049, Beijing
(China)
J. Ma‡
Shanghai Synchrotron Radiation Facility, Shanghai Institute of
Applied Physics, Chinese Academy of Sciences, 201204, Shanghai
(China)
K. Zang, J. Luo
Center for Electron Microscopy, Tianjin Key Laboratory of Advanced
Functional Porous Materials, Institute for New Energy Materials &
Low-Carbon Technologies, School of Materials, Tianjin University of
Technology, Tianjin 300384 (China)
‡ These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201706602
Angewandte Chemie International Edition
COMMUNICATION
only 705 and 525 m2 g-1. The type IV isotherm curves
shown in Figure S2a present a clear hysteresis implying the
existence of mesopores.[14] The relative pore size
distribution (PSD) in Figure S2b is calculated with the
Barrett-Joyner-Halenda (BJH) method based on the
desorption branches, confirming the existance of
mesopores with the diameters centered at ~3.8 nm, in
accordance with the wall thickness of SBA-15[15] as a result
of template replication.
Two broad peaks at ~25o and ~44o were observed in the
X-ray diffraction (XRD) patterns of the as-prepared four
catalysts (Figure S3). Additionally, Fe-containing samples
of Fe/NC and Fe/SNC exhibit one more defined diffraction
peak at 26.8o, assigned to the (002) plane of graphitic
range were observed under high-angle annular dark field
(HAADF) mode (Figure 1b), which are assigned to the iron
atoms. The EDS mappings (Figure 1c-h) disclose that the
elements C, N, Fe, O, and S are homogeneously distributed
on the surface of Fe/SNC.
The surface chemical state of these samples is further
confirmed by X-ray photoelectron spectroscopic (XPS)
(Figure S4). The wide-range spectrum (Figure S4a) portrays
the presence of C, N, O, and F for all the synthesized catalysts,
where the signal of fluorine originates from residuals of the HF
etching process. After introducing Fe, a weak peak centered at
around 711 eV is observed for both Fe/NC and Fe/SNC (Figure
S4b), attributed to Fe2p in Fe-N-C configuration.[18] Along with S
doping, the high resolution S 2p spectra in Figure S4c highlight
two peaks at the binding energies of 163.9 and 165 eV,
assigned to S 2p3/2 and S 2p1/2 of thiophene-like structure (C-S-
C) between carbon and sulfur atoms, respectively.[11a]
Correspondingly, no peaks of SOx-C with higher binding energy
are observed.[19] Moreover, contrary to the composite before
carbonization (Figure S5), no metal-S bonds are detected for
Fe/SNC in either Fe 2p or S 2p spectra since Fe-based sulfides,
carbides, and oxides can be removed by the HF leaching.[20]
Thus, the sulfur is only incorporated into aromatic carbon
structures, and the residual Fe is therefore only coordinated by
N,[17] verified by the N 1s spectra in Figure S4d. The peaks at
398.3, 399.9, 401.0, and 403.0 eV in the deconvoluted N 1s
XPS spectra are attributed to pyridinic (Py-N), pyrrolic (Pyr-N),
graphitic-like (G-like) and oxidized type (Py-N-O) nitrogen,
respectively.[18,21] For both Fe/NC and Fe/SNC incorporated with
iron, a peak centered at around 399.1 eV is observed, attributed
to iron-coordinated nitrogen (Fe-N)[22] as the pyridinic and
pyrrolic nitrogen atoms can associate with Fe to form the
catalytically active Fe-N-C sites.[23] The detail elemental
analyses by XPS are summarized in Table S2. The amount of N
coordinated to Fe on Fe/SNC samples is 0.34 at.%, which is
comparable to Fe/NC (0.35 at.%).
carbon.
[16] It is noteworthy that there are no diffraction peaks
related to Fe-based compounds, suggesting that Fe
species are highly dispersed on the carbon framework
without any large nanoparticle.[5a,17]
Figure 1. (a) TEM image of Fe/SNC; (b) and (c) HAADF STEM image of
Fe/SNC; (d-h) EDS mapping of carbon, oxygen, nitrogen, iron, and sulfur over
the area in (c) of Fe/SNC.
Figure 2. (a) 57Fe Mössbauer spectroscopy of Fe57/SNC and (b) Fourier
transforms of the EXAFS spectra of Fe/SNC.
The morphology and structure of Fe/SNC were further
examined by aberration-corrected scanning transmission
electron microscopy (AC-STEM) equipped with an energy
dispersive X-ray spectrometer (EDS). TEM image of Fe/SNC
in Figure 1a indicates the inverse replicate of the rod-like
framework of SBA-15 with a highly ordered mesoporous
structure, similar to Fe/NC (labelled as FeN2/NOMC-3 in
previous work[17]). A number of bright spots in the atomic
Mössbauer spectroscopy was carried out to gain a deeper
insight into the structure of Fe/SNC, and the results are shown
in Figure 2a. Similar to our previous work,[17] the Mössbauer
spectrum of Fe/SNC was fitted with three doublets assigned to
Fe-N species, while no other Fe related phases (Fe, FexC, FeXO,
FexS, etc) were observed, indicating that Fe are only
coordinated by N atoms. The corresponding fitting parameters,
and the relative peak area for the catalysts were summarized in
This article is protected by copyright. All rights reserved.

10.1002/anie.201706602
Angewandte Chemie International Edition
COMMUNICATION
1
Table S3. As
a
sensitive characterization to identify
at low over-potentials, close to the 58 mV per decade of Pt/C
noncrystalline species, extended X-ray absorption fine structure
(EXAFS) at Fe k-edge X-ray absorption spectroscopy was
conducted to further explore the coordination environment of
iron (Figure 2b). The Fe/SNC shows a single well-resolved peak
at 1.7 Å, assigned to Fe-N distance. After fitting the profile using
the IFEFFIT package, an average coordination number (N) of ~
2.0 is obtained (Table S4), similar to that of Fe/NC sample.
These results confirm the consistent environment of the
atomically dispersed FeN2 sites, and demonstrate that the sulfur
doping has minimal or no effect towards Fe-N-C structure. With
advances of the pristine configuration, it’s possible to
understand the effect of different ORR active site between Fe-N-
C and C-S-C without interference of Fe/FexC.
First, the ORR activity of the as-synthesized materials is
investigated by linear sweep voltammetry (LSV) in alkaline
meida (0.1 M KOH). Compared with NC in Figure S6a, the
steady-state diffusion current density and half-wave potential
(E1/2) both increase for SNC and Fe/CN samples due to larger
amount of active sites (C-S-C and FeN2).[11b,24] The SNC
exhibits a half-wave potential (E1/2) of 0.79 V, and the E1/2 of
Fe/NC is about 0.86 V, 30 mV positive shift compared to that of
commercial Pt/C (0.83 V). In comparison to Fe/NC, the Fe/SNC
shows an enhanced steady-state diffusion current density with a
similar E1/2. The kinetic currents at different potentials are
calculated by the equation Jk=JL⋅J/(JL-J), as presented in Figure
S6b. In terms of that the ORR is more efficient on Fe-N-C than
on C-S-C, the Jk of Fe/NC is an order of magnitude higher than
that of SNC. After co-doped with Fe and S, the Jk of Fe/SNC is a
little bit larger than that of Fe/NC, and equal to the sum Jk of
SNC and Fe/NC. It is suggested that each active site of C-S-C
and Fe-N-C in Fe/SNC hybrid works separately, and no
synergistic effect is observed in alkaline solution, since the
active center is not directly accessible[9] as their inner-Helmholtz
plane are all covered by adsorbed hydroxyl species (OHads does
not block the charge transfer but acts as the bridge to facilitate
the charge transfer) in strongly alkaline.[7a,25]
catalyst, and much smaller than that over NC (102 mV decade-1)
or SNC (84 mV decade-1). To quantitatively compare the intrinsic
activity, the kinetic current was calculated through the Koutecky-
Levich equation and the results are depicted in Figure 3c. Unlike
the kinetic current in 0.1 M KOH, the Jk of Fe/SNC in acidic
condition is much larger than the sum of the Fe/NC and SNC
samples, implying the existence of synergistic effects between
Fe-N-C and C-S-C sites.
Commonly, Damjanovic model is used for the evaluation of
ORR, which contains the following pathways: (1) Direct pathway
involving 4e-, (2) sequential or peroxide pathway involving 2e-
reduction of O2 to H2O2, and further H2O2 reduction by another
2e- process, and (3) parallel pathway of 1 and 2.[10,26] The doped
S in carbon framwork is suggested to improve the selectivity
toward 4e- reduction of O2 to H2O on Fe-N-C, which is further
supported by rotating ring-disk electrode (RRDE) test in Figure
S8. Based on the recorded data of the disk - (Figure S8a) and
ring current (Figure S8b), the yield of H2O2 over the potential
range from 0.7 to 0.4 V on Fe/SNC is below 6% (Figure S8c),
giving an electron transfer number of ∼3.9 (Figure S8d).
Whereas, on sulfur free Fe/NC catalyst, the yield of H2O2
increases to 8% along with the electron transfer number
downwards to 3.85. The structure and density of Fe-N-C active
sites on both Fe/SNC and Fe/NC are similar, as confirmed by
Mössbauer spectroscopy, EXAFS and XPS. Therefore, the
declinling yield of H2O2 can be ascribed to the enhanced
adsorption and further reduction of H2O2 on Fe/SNC caused by
synergistic effects of the doped sulfur.
The ORR activity in acidic medium is significantly more
attractive due to the application in acidic proton exchange
membrane fuel cells (PEMFCs).[1] The as-prepared catalysts and
benchmark Pt/C were measured by cyclic voltammetry (CV) in
0.5 M H2SO4 (Figure S7). In contrast to the featureless CV
curves collected in a N2-saturated electrolyte, the CV curves
show maximum peak potentials of 0.62 V, 0.68 V and 0.78 V on
Fe/NC, Fe/SNC and Pt/C in O2-saturated electrolyte,
respectively. Their ORR activity is further compared by
polarization curves in O2-saturated 0.5 M H2SO4. From Figure 3a,
it is clearly observed that S-doping enhances the catalytic
activity for ORR as the JL and E1/2 on SNC are 4.8 mA cm-2 and
0.65 V, much higher than those observed on NC. The Fe/SNC
exhibits a half-wave potential of 0.77 V, ~30 mV more positive
than that on sulfur-free Fe/NC (0.74 V) ， and only 50 mV
negative than that on commercial Pt/C (0.82 V). These results
indicate that the prepared Fe/SNC is one of the most active Fe-
based electrocatalysts for ORR in acidic conditions in
comparison with recent state-of-the-art non-noble metal
catalysts listed in Table S5. The high ORR activity of Fe
incorporated catalysts is also supported by Tafel slope in Figure
3b. Fe/SNC and Fe/NC display the Tafel slope of 57 mV decade-
Figure 3. ORR polarization curves (a), Tafel plots (b) and kinetic current
density (c) of the as-synthesized catalysts in O2-saturated 0.5 M H2SO4 at a
scan rate of 10 mV s-1. (d) Tendency chart of relative current-time (top) and
chronoamperometric responses of different catalysts in 0.5 M H2SO4 before
and after adding 0.5 M methanol (bottom).
Ab initio theoretical computations are performed to investigate
the synergistic effects observed on our Fe/SNC electrocatalyst.
Spin-polarized DFT is used to investigate how the addition of
sulfur reduces the H2O2 production and favors the 4e- ORR
pathway. According to our experimental results, the iron atoms
This article is protected by copyright. All rights reserved.

10.1002/anie.201706602
Angewandte Chemie International Edition
COMMUNICATION
adsorption energy (Table S7), indicating its capability to
complete the H2O2 reduction if necessary. The trend observed
theoretically agrees with our experimental observations where
the Fe/SNC exhibits enhanced ORR performance. However, the
discrepancy with the experimental observations under alkaline
and acidic conditions must arise from changes in oxygen
coverage, solvent reorganization, and electrical double layer
effects, factors not considered in our theoretical model.
The resistance to methanol crossover and life cycle are of
particular importance for PEMFCs. Here, the durability of the
catalysts was assessed by chronoamperometric measurement
in the O2-saturated 0.5 M H2SO4 solution at the potential of 0.68
V. After 3000 s, the commercial Pt/C catalyst suffers a 12% loss
of its initial current density, whereas the Fe/SNC exhibits a
decrease of 14% (Figure 3d, top), demonstrating a Pt/C
comparable stability in acidic solution. Whereas, having the
crossover effects in mind,[1] methanol tolerance was investigated
by instantaneously adding 0.5
M
methanol during the
chronoamperometric measurement (Figure 3d, bottom). After
the addition of methanol, due to oxygen preferentially adsorbs
on Fe-N-C sites,[30] only a slight oscillation in the ORR current is
observed, implying a great tolerance to methanol. In contrast,
the ORR current of the commercial Pt/C catalyst significantly
decreases to 75% after the methanol injection.
Figure 4. (a) Optimized geometry of the Fe/SNC-7.3 system, the dashed circle
indicates the reactive site. (b) Free energy diagram for the Fe/NC and Fe/SNC
systems during the ORR in acidic conditions at the equilibrium potential of U0
= 1.23 V. The largest change in free energy determines the limiting step and
overpotential.
In summary, we synthesized S-doped Fe-N-C electrocatalyst
(Fe/SNC) using a template casting methodology to produce a
high-density atomically dispersed Fe-N-C sites that outperform
commercial Pt/C for ORR in alkaline solutions. Synergistic effect
between C-S-C and Fe-N-C sites remarkably boosts its ORR
activity in acidic medium because the active site C-S-C assists
the reduction of intermediate H2O2. The obtained Fe/SNC has a
high half-wave potential of 0.77 V towards ORR with superior
methanol tolerance and Pt/C-comparable stability. This study
paves a profound understanding on the effect of different ORR
active sites in alkaline and acidic medium. The outstanding
characteristics of our earth-abundant transition metals Fe/SNC
catalyst make it a promising candidate for PEMFCs applications.
are coordinated with two nitrogens by forming
a Fe-N2
configuration mostly located at the graphene edges. In this way,
the Fe/CN moiety is collocated at the edge of a zig-zag
graphene nanoribbon, and the iron coordination sphere is
completed with hydroxyl groups. The optimized structures are
shown in Figure 4a,b and S9. The position of the sulfur atom is
varied along the zig-zag edge, resulting in 3 systems labeled
Fe/SNC-2.4, Fe/SNC-4.9, and Fe/SNC-7.3, where the number
indicates the Fe-S distance in Å. The ORR is studied using the
associative mechanism at the Fe atom in acidic condition. The
free energy and ORR overpotential are determined using the
CHE model,[27] see supporting information for further details in
Figure 4b, Table S6 and S8. The theoretical results indicate that
the presence of sulfur does not directly benefit the ORR on
systems of Fe/SNC-2.4 and Fe/SNC-4.9 that exhibit similar or
larger overpotential than that of sulfur-free Fe/CN, which is seen
as larger change in free energy in Figure 4b. However, its truly
beneficial effect is observed when sulfur is located at least 7.3 Å
away from the iron center, Fe/SNC-7.3, causing a reduction of
~40% in the overpotential compared with the Fe/CN system
(Table S6). The enhanced ORR performance for the Fe/SNC-
7.3 is attributed to the spatial distribution of sulfur, which
reduces the electron localization around the Fe center and
improves the interaction with oxygenated species due to larger
availability of electronic states around the Fermi level (Figure
S10). Similar results have been observed for phosphorous-
nitrogen co-doped graphene.[28] In particular, the strong
interaction with *O2 and the *OOH intermediates, and therefore
lower activation barriers due to the Brønsted-Evans-Polanyi
relationship,[29] facilitate the complete 4e- ORR and reduces the
H2O2 production. Moreover, the adsorption energy of H2O2
exhibit a similar trend, and the Fe/SNC-7.3 has the largest
Acknowledgements
This work was supported by National Natural Science Foun-
dation of China (21677171, 21505154 and 51671003), Xinjiang
International Science and Technology Cooperation Project
(20166010), National Key Research and Development Program
of China (No. 2016YFB0100201), 1000-Talent Program
(Recruitment Program of Global Expert, In Chinese: Qian-Ren-
Ji-Hua). The theoretical simulations were performed on
resources provided by the Swedish National Infrastructure for
Computing (SNIC) at the High Performance Computing Center
North (HPC2N).
Keywords: oxygen reduction reaction • Fe-N-C • C-S-C •
synergistic effect • atomic dispersion
[1] M. E. Scofield, H. Liu, S. S. Wong, Chemical Society reviews 2015, 44,
5836-5860.
[2] M. Shao, Q. Chang, J.-P. Dodelet, R. Chenitz, Chemical Reviews 2016,
This article is protected by copyright. All rights reserved.

10.1002/anie.201706602
Angewandte Chemie International Edition
COMMUNICATION
116, 3594-3657.
[14]M. Thommes, K. Kaneko, A. V. Neimark, J. P. Olivier, F. Rodriguez-
Reinoso, J. Rouquerol, K. S. W. Sing, Pure and Applied Chemistry 2015,
87.
[3] Y. J. Wang, N. Zhao, B. Fang, H. Li, X. T. Bi, H. Wang, Chemical reviews
2015, 115, 3433-3467.
[4] aL. Dai, Y. Xue, L. Qu, H. J. Choi, J. B. Baek, Chemical reviews 2015, 115,
4823-4892; bY. Nie, L. Li, Z. Wei, Chemical Society reviews 2015, 44,
2168-2201; cZ. Xia, L. An, P. Chen, D. Xia, Advanced Energy Materials
2016, 6, 1600458.
[15]Y. Ding, G. Yin, X. Liao, Z. Huang, X. Chen, Y. Yao, J. Li, Microporous and
Mesoporous Materials 2013, 170, 45-51.
[16]Y. Jiao, D. Han, L. Liu, L. Ji, G. Guo, J. Hu, D. Yang, A. Dong, Angewandte
Chemie 2015, 54, 5727-5731.
[5] aY. 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, S. H. Joo, Journal of the American Chemical Society 2016; bY. Liu,
H. Jiang, Y. Zhu, X. Yang, C. Li, Journal of Materials Chemistry A 2016, 4,
1694-1701.
[17]H. Shen, E. Gracia-Espino, J. Ma, H. Tang, X. Mamat, T. Wagberg, G. Hu,
S. Guo, Nano Energy 2017, 35, 9-16.
[18]W.-J. Jiang, L. Gu, L. Li, Y. Zhang, X. Zhang, L. Zhang, J. Wang, J.-S. Hu,
Z. Wei, L.-J. Wan, Journal of the American Chemical Society 2016, 138,
3570-3578.
[6] aJ.-C. Li, P.-X. Hou, S.-Y. Zhao, C. Liu, D.-M. Tang, M. Cheng, F. Zhang,
H.-M. Cheng, Energy & Environmental Science 2016, 9, 3079-3084; bJ.
Zhang, L. Dai, ACS Catalysis 2015; cC. Tang, Q. Zhang, Advanced
Materials 2017, 1604103.
[19]M. H. Naveen, K. Shim, M. S. A. Hossain, J. H. Kim, Y.-B. Shim, Advanced
Energy Materials 2016, 1602002.
[20]P. Chen, T. Zhou, L. Xing, K. Xu, Y. Tong, H. Xie, L. Zhang, W. Yan, W.
Chu, C. Wu, Y. Xie, Angewandte Chemie 2017, 56, 610-614.
[21]C. Zhu, S. Fu, J. Song, Q. Shi, D. Su, M. H. Engelhard, X. Li, D. Xiao, D.
Li, L. Estevez, D. Du, Y. Lin, Small 2017, 1603407.
[7] aN. Ramaswamy, U. Tylus, Q. Jia, S. Mukerjee, Journal of the American
Chemical Society 2013, 135, 15443-15449; bA. Zitolo, V. Goellner, V.
Armel, M.-T. Sougrati, T. Mineva, L. Stievano, E. Fonda, F. Jaouen, Nature
materials 2015, 14, 937-942.
[22]A. Serov, K. Artyushkova, P. Atanassov, Advanced Energy Materials 2014,
4, 919-926.
[8] J. Herranz, Journal of Physical Chemistry C 2011, 115, 16087-16097.
[9] D. Malko, A. R. J. Kucernak, T. Lopes, Journal of the American Chemical
Society 2016, 138, 16056-16068.
[23]Y. Zhao, K. Watanabe, K. Hashimoto, Journal of the American Chemical
Society 2012, 134, 19528-19531.
[24]Z. Yang, Z. Yao, G. Li, G. Fang, H. Nie, Z. Liu, X. Zhou, X. A. Chen, S.
Huang, Acs Nano 2012, 6, 205.
[10]A. Muthukrishnan, Y. Nabae, T. Okajima, T. Ohsaka, ACS Catalysis 2015,
5, 5194-5202.
[25]K. Wan, Z.-p. Yu, X.-h. Li, M.-y. Liu, G. Yang, J.-h. Piao, Z.-x. Liang, ACS
Catalysis 2015, 5, 4325-4332.
[11] aK. Hu, L. Tao, D. Liu, J. Huo, S. Wang, ACS Applied Materials &
Interfaces 2016; bY. C. Wang, Y. J. Lai, L. Song, Z. Y. Zhou, J. G. Liu, Q.
Wang, X. D. Yang, C. Chen, W. Shi, Y. P. Zheng, Angewandte Chemie
2015, 127, 10045-10048.
[26]A. Damjanovic, M. A. Genshaw, J. O. M. Bockris, Journal of Chemical
Physics 1966, 45, 4057-4059.
[27]J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. R. Kitchin, T.
Bligaard, H. Jónsson, The Journal of Physical Chemistry B 2004, 108,
17886-17892.
[12]D.-H. Kwak, S.-B. Han, Y.-W. Lee, H.-S. Park, I.-A. Choi, K.-B. Ma, M.-C.
Kim, S.-J. Kim, D.-H. Kim, J.-I. Sohn, K.-W. Park, Applied Catalysis B-
Environmental 2017, 203, 889-898.
[28]E. Gracia-Espino, The Journal of Physical Chemistry C 2016, 120, 27849-
27857.
[13] aH.-W. Liang, W. Wei, Z.-S. Wu, X. Feng, K. Müllen, Journal of the
American Chemical Society 2013, 135, 16002-16005; bL. Osmieri, A. H. A.
Monteverde Videla, M. Armandi, S. Specchia, International Journal of
Hydrogen Energy 2016, 41, 22570-22588; cJ. Y. Cheon, T. Kim, Y. Choi,
H. Y. Jeong, M. G. Kim, Y. J. Sa, J. Kim, Z. Lee, T. H. Yang, K. Kwon, O.
Terasaki, G. G. Park, R. R. Adzic, S. H. Joo, Scientific reports 2013, 3,
2715.
[29]aA. Michaelides, Z. P. Liu, C. J. Zhang, A. Alavi, D. A. King, P. Hu, Journal
of the American Chemical Society 2003, 125, 3704-3705; bE. Gracia-
Espino, X. Jia, T. Wågberg, The Journal of Physical Chemistry C 2014,
118, 2804-2811.
[30]D. Sebastián, A. Serov, I. Matanovic, K. Artyushkova, P. Atanassov, A. S.
Aricò, V. Baglio, Nano Energy 2017, 34, 195-204.
This article is protected by copyright. All rights reserved.