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10.1002/anie.202109058
Angewandte Chemie International Edition
COMMUNICATION
Compressive Strain Modulation of Single Iron Sites on Helical
Carbon Support Boosts Electrocatalytic Oxygen Reduction
Jia Yang,[a,b,§] Zhiyuan Wang,[b,§] Chun-Xiang Huang,[c,§] Yida Zhang,[d] Qinghua Zhang,[e] Cai Chen,[b]
Junyi Du,[b] Xiao Zhou,[b] Ying Zhang,[b] Huang Zhou,[b] Lingxiao Wang,[b] Xusheng Zheng,*[d] Lin Gu,[e]
Li-Ming Yang,*[c] Yuen Wu*[b]
[a]
[b]
Dr. J. Yang
Institutes of Physical Science and Information Technology, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of
Education, Anhui Graphene Engineering Laboratory
Anhui University
Hefei, Anhui 230601, China
Dr. J. Yang, Dr. Z. Wang, C. Chen, Dr. J. Du, Dr. X. Zhou, Dr. Y. Zhang, Dr. H. Zhou, L. Wang, Prof. Y. Wu
Hefei National Laboratory for Physical Sciences at the Microscale, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), School of
Chemistry and Materials Science
University of Science and Technology of China
Hefei, Anhui 230026, China
E-mail: yuenwu@ustc.edu.cn
[c]
[d]
C.-X. Huang, Prof. L.-M. Yang
Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica, Key Laboratory of Material Chemistry for Energy Conversion and Storage of Ministry
of Education, Hubei Key Laboratory of Materials Chemistry and Service Failure, Hubei Engineering Research Center for Biomaterials and Medical
Protective Materials, School of Chemistry and Chemical Engineering
Huazhong University of Science and Technology
Wuhan, Hubei 430074, China
E-mail: Lmyang.uio@gmail.com, Lmyang@hust.edu.cn
Y. Zhang, Prof. X. Zheng
National Synchrotron Radiation Laboratory (NSRL)
University of Science and Technology of China
Hefei, Anhui 230029, China
E-mail: zxs@ustc.edu.cn
[e]
[§]
Dr. Q. Zhang, Prof. L. Gu
Beijing National Laboratory for Condensed Matter Physics
Institute of Physics, Chinese Academy of Sciences
Beijing 100190, China
J. Yang, Z. Wang, C. Huang contribute equally
Abstract: Designing and modulating the local structure of metal
sites is the key to gain the unique selectivity and high activity of
single metal site catalysts. Herein, we report strain engineering of
curved single atomic iron-nitrogen sites to boost electrocatalytic
activity. First, a helical carbon structure with abundant high-curvature
surface is realized by carbonization of helical polypyrrole that is
templated from self-assembled chiral surfactants. The high-curvature
surface introduces compressive strain on the supported Fe-N4 sites.
Consequently, the curved Fe-N4 sites with 1.5% compressed Fe-N
bonds exhibit downshifted d-band center than the planar sites. Such
a change can weaken the bonding strength between the oxygenated
intermediates and metal sites, resulting a much smaller energy
barrier for oxygen reduction. Catalytic tests further demonstrate that
a kinetic current density of 7.922 mA/cm2 at 0.9 V vs. RHE is
obtained in alkaline media for curved Fe-N4 sites, which is 31 times
higher than that for planar ones. Our findings shed light on
modulating the local three-dimensional structure of single metal sites
and boosting the catalytic activity via strain engineering.
To further improve or regulate the catalytic activity of carbon
supported single metal site catalysts (M-Nx/C), various strategies
have been developed.[14] Considering that the catalytic activity of
the metal sites is closely related with the coordination structure,
numerous efforts are devoted to engineering the coordination
numbers, coordinated atoms, environmental atoms, axial guest
groups and etc. to tune the intrinsic activity and selectivity of the
metal sites for desired applications.[15] However, the above
strategies are mainly focused on the in-plane structure of metal-
nitrogen sites. The local three-dimensionally structural
modulation on the metal sites, which could mediate the catalytic
activity by strain effect, still remains challenging and has rarely
been discussed.[16] The local three-dimensional structure of
metal sites is highly correlated with the surface morphology and
geometric structure of support.[17] Compared with the flat surface,
high-curvature surface tends to create nonplanar curved
structure and introduce strain effect, which may be benificial to
improving the catalytic activity.[18] Single metal sites could also
be immobilized stronger on high-curvature support, affecting the
catalytic activity.[19-22]
Single metal site catalysts, with isolated single metal sites
dispersed on proper supports, have been emerging as a new
frontier in material and catalysis science.[1,2] They integrate the
advantages of homogeneous and heterogeneous catalysts such
as maximum atomic utilization efficiency, quantum-size effect
and tunable electronic environment, thus exhibiting ultra high
activity and unique selectivity in various catalytic reactions.[3-13]
Among which, carbon support single metal site catalysts with
atomic metal-nitrogen sites are promising candidates for energy
related catalytic reactions.[4,10]
Herein, we report strain engineering of curved single atomic
iron-nitrogen sites to boost electrocatalytic activity for oxygen
reduction reaction (ORR). Helical polypyrrole is firstly obtained
by using self-assembled chiral surfactants as the polymerization
template. After pyrolysis, right-handed helical single atomic iron
catalyst (D-Fe SAC) is obtained, featuring with isolated Fe-N4
sites on helical high-curvature hollow carbon nanofibers. The
high-curvature surface introduces compressive strain effect on
the supported Fe-N4 sites. As a result, the D-Fe SAC delivers
1
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