Single Co-Atoms as Electrocatalysts for Efficient Hydrazine Oxidation Reaction

Article abstract of DOI:10.1002/smll.202006477

Single-atom catalysts (SACs) have aroused great attention due to their high atom efficiency and unprecedented catalytic properties. A remaining challenge is to anchor the single atoms individually on support materials via strong interactions. Herein, single atom Co sites have been developed on functionalized graphene by taking advantage of the strong interaction between Co²⁺ ions and the nitrile group of cyanographene. The potential of the material, which is named G(CN)-Co, as a SAC is demonstrated using the electrocatalytic hydrazine oxidation reaction (HzOR). The material exhibits excellent catalytic activity for HzOR, driving the reaction with low overpotential and high current density while remaining stable during long reaction times. Thus, this material can be a promising alternative to conventional noble metal-based catalysts that are currently widely used in HzOR-based fuel cells. Density functional theory calculations of the reaction mechanism over the material reveal that the Co(II) sites on G(CN)-Co can efficiently interact with hydrazine molecules and promote the N-H bond-dissociation steps involved in the HzOR.

Full text of DOI:10.1002/smll.202006477

Full PaPer
www.small-journal.com
Single Co-Atoms as Electrocatalysts for Efficient Hydrazine
Oxidation Reaction
Ravishankar G. Kadam, Tao Zhang, Dagmar Zaoralová, Miroslav Medveď,
Aristides Bakandritsos, Ondřej Tomanec, Martin Petr, Johnny Zhu Chen, Jeffrey T. Miller,
Michal Otyepka, Radek Zbořil,* Tewodros Asefa,* and Manoj B. Gawande*
the extensive use of fossil fuels not only
Single-atom catalysts (SACs) have aroused great attention due to their
high atom efficiency and unprecedented catalytic properties. A remaining
challenge is to anchor the single atoms individually on support materials
via strong interactions. Herein, single atom Co sites have been developed
on functionalized graphene by taking advantage of the strong interaction
between Co2+ ions and the nitrile group of cyanographene. The potential of
causes severe environmental issues but
also compromises efforts to attain a sus-
tainable energy future.[1,2] This has made
researchers to investigate cost-effective
and non-polluting alternatives to produce
energy in a greener manner, through
such systems as photovoltaic cells, elec-
trolyzers, and fuel cells. Among them,
fuel cells have attracted great attention
over the past few years.[1] These devices
can convert the chemical energy in fuels
such as hydrogen, alcohols, organic acids,
and hydrazine into electricity, with high
efficiency and minimal greenhouse gas
emissions. Among the fuels used in fuel
cells, hydrazine is of particular interest for
the following three reasons: 1) It produces
only N2 and H2O and it does not release
the greenhouse gas CO2 or other harmful
byproducts as fossil fuels do; 2) Hydrazine
is relatively easy to store and transport

the material, which is named G(CN) Co, as a SAC is demonstrated using the
electrocatalytic hydrazine oxidation reaction (HzOR). The material exhibits
excellent catalytic activity for HzOR, driving the reaction with low overpo-
tential and high current density while remaining stable during long reaction
times. Thus, this material can be a promising alternative to conventional
noble metal-based catalysts that are currently widely used in HzOR-based fuel
cells. Density functional theory calculations of the reaction mechanism over

the material reveal that the Co(II) sites on G(CN) Co can efficiently interact

with hydrazine molecules and promote the N H bond-dissociation steps
involved in the HzOR.
with existing infrastructures, as it is liquid at room tempera-
ture; and 3) Direct hydrazine fuel cells (DHFCs) have a large
theoretical cell voltage (+1.61 V) and higher energy/power den-
sity than many other fuel cells (e.g., compared with H2/O2 fuel
cell, which is considered one of the best fuel cells).[1] However,
1. Introduction
The rapidly growing global energy demand has led to the con-
sumption of increased amounts of non-renewable fossil fuel
resources, including coal, petroleum, and natural gas. However,
Dr. R. G. Kadam, D. Zaoralová, Dr. M. Medved’, Dr. A. Bakandritsos,
M. Petr, Dr. M. B. Gawande
Regional Centre of Advanced Technologies and Materials
Palacký University
Olomouc Šlechtitelů 27, Olomouc 783 71, Czech Republic
E-mail: manoj.gawande@upol.cz, mb.gawande@marj.ictmumbai.edu.in
Dr. T. Zhang, Prof. T. Asefa
Department of Chemical and Biochemical Engineering
Rutgers, The State University of New Jersey
98 Brett Road, Piscataway, NJ 08854, USA
E-mail: tasefa@rci.rutgers.edu
O. Tomanec, Prof. M. Otyepka, Prof. R. Zbořil
Regional Centre of Advanced Technologies and Materials
Czech Advanced Technology and Research Institute
Palacký University
Dr. A. Bakandritsos, Prof. R. Zbořil
Nanotechnology Centre
CEET
VŠB-Technical University of Ostrava
17. Listopadu 2172/15, Ostrava-Poruba 708 00, Czech Republic
Dr. J. Zhu Chen, Prof. J. T. Miller
Davidson School of Chemical Engineering
Purdue University
480 Stadium Mall Drive, West Lafayette, IN 47906, USA
Prof. T. Asefa
Department of Chemistry and Chemical Biology
Rutgers, The State University of New Jersey
610 Taylor Road, Piscataway, NJ 08854, USA
Prof. M. B. Gawande
Department of Industrial and Engineering Chemistry
Institute of Chemical Technology
Olomouc 779 00, Czech Republic
E-mail: radek.zboril@upol.cz
Marathwada Campus, Jalna, Mumbai 431203, India
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.202006477.
DOI: 10.1002/smll.202006477
2006477 (1 of 7)
Small 2021, 17, 2006477
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.small-journal.com

Scheme 1. Synthesis of G(CN) Co catalyst. In the structural model, C, F, N, and Co atoms are represented by grey, cyan, blue, and green balls.
in order to enable DHFCs to work effectively and find large-
scale practical applications, the rational design and synthesis
2. Results and Discussion

2.1. Synthesis and Structural Characterization of G(CN) Co Catalyst
of advanced, efficient, and sustainable electrocatalysts that can
replace noble metal-based electrocatalysts (such as Pt, Pd, Ir,
Au, and their alloys), which are currently widely used in them,
is required.[3]

The procedure applied to synthesize G(CN) Co is illustrated
in Scheme 1 (see Supporting Information for more details). It
follows similar steps as those used to produce various function-
alized graphene.[28] Powder X-ray diffraction pattern (Figure 1a;
Figure S1, Supporting Information) confirmed the absence of
distinctive peaks associated with Co or Co-based inorganic par-
ticles. This indirectly suggests the dispersion of Co in isolated
forms on the structures of the material. The representative
In recent years, single-atom catalysts (SACs) have attracted
increased research attention in heterogeneous catalysis since
they offer an ultimate atom economy and allow for the full
exposure of active sites, resulting in greater catalytic activity
in comparison to nanocatalysts.[4–9] Some SACs have also been
reported to catalyze various electrochemical reactions with
excellent efficiency. However, there are also challenges when
applying SACs in practical systems, due to the tendency of
single atoms to cluster and leach during the reactions. One
effective strategy to address these challenges entails the use of
2D materials as substrates to anchor the single atoms.[8,10–20]
Graphene, a 2D material, which has large surface area, high
electrical conductivity, and good stability, has received signifi-
cant interest as a support material for making SACs. Graphene
is of interest also because of its ability to tune the electronic
properties of the guest atoms. Surface-functionalized graphene
derivatives, in particular, can render strong interactions with
the single atoms, and thereby stabilize SACs and prevent their
aggregation and transformation into nanoparticles during cata-
lytic reactions.[17,19–27]

TEM image revealed the presence of G CN sheets (Figure 1b)
without any heavy element-associated inorganic particles.
Furthermore, high-angle annular dark-field scanning TEM
(HAADF-STEM) (Figure 1c) showed that individual Co atoms

are uniformly dispersed on the G CN sheets. The Co atoms
are the bright spots marked with yellow circles in the magnified
HAADF-STEM images shown in Figure 1d. In the literature,
advance detectors had been used for HAADF-STEM images to
probe Co SACs on N-doped carbon.[25,29,30]
Elemental mapping performed with HAADF-STEM image
(Figure 1e–j) confirmed a homogenous dispersion of Co single

atoms on the G CN sheets, besides O, N, and C atoms. How-
ever, as precise identification of the lighter elements with
HAADF-STEM is challenging,[31,32] we had to resort to XANES
and EXAFS to indirectly determine them (see below).
To this end, herein we present a novel approach to anchor

single Co(II) ions on cyanographene (G CN) sheets to obtain
X-ray photoelectron spectroscopy (XPS) was applied to inves-


Co-based single atom catalysts (G(CN) Co SACs). The syn-
tigate the chemical composition of G(CN) Co. The survey
thetic process is schematically described in Scheme 1. The
amounts of Co(II) ions on G CN could easily be varied
by changing the relative amount of Co(II) ions mixed with
G CN. The materials showed efficient electrocatalytic activity
toward the hydrazine oxidation reaction (HzOR). Comple-
mentary experiments and density functional theory (DFT)
calculations corroborated the anchoring of atomically isolated
cobalt sites on G CN. The successful binding of Co(II) ions
to G CN was verified with inductively coupled plasma mass
spectrometry, high-resolution transmission electron micro-
scopy (TEM), extended X-ray absorption fine structure (EXAFS)
and X-ray absorption near edge structure spectra (XANES).
The resulting materials exhibited among the highest electro-
catalytic activities for HzOR as well as better activities than
many noble metal-based catalytic systems reported in the lit-
erature. The stability of the materials was also investigated,
spectra (Figure 2a) confirmed the presence of C (85.7%), N
(8.8%), O (4.8%), and Co (0.7%). The deconvolution of the
C 1s spectrum (Figure S2a, Supporting Information) dis-
played distinct peaks with binding energies (BEs) of 284.82


and 286.01 eV that can be assigned to sp2 C and sp3 C atoms
[9,33]

bound to CN groups.
Deconvolution of the N 1s spec-
trum (Figure S2b, Supporting Information) gave three peaks
at 398.77, 400.00, and 401.31 eV corresponding to different
nitrogen functional groups, respectively (see further details
in the Supporting Information). The peak at BE of 781.87 eV
(Figure 2b), with the corresponding satellite peaks at 785.19
and 788.77 eV, was assigned to Co2+ 2p species.[34] The charge
transfer and the interaction between Co(II) cations and N-atoms



in G CN was analyzed by high-resolution (HR)-XPS of N 1s
envelope (Figure S3, Supporting Information).
The oxidation state and coordination environment of cobalt


and the results suggested that both G CN and the strong bond
species in G(CN) Co were further determined by XANES and
EXAFS. The pre-edge XANES peak can be used to identify
between its CN groups and Co(II) ions were crucial in pre-
venting single Co sites from leaching during the electrocatalytic
reaction.
the oxidation state of the catalyst (Figure 2c).[35] The pre-edge

energy of G(CN) Co SACs (7708.1 eV) was very similar to that
Small 2021, 17, 2006477
2006477 (2 of 7)
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.small-journal.com



Figure 1. Characterization of G(CN) Co (3.4 wt%): a) Powder X-ray diffraction (XRD) patterns of G CN and G(CN) Co; b) TEM image; c) repre-
sentative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image; d) magnified HAADF-STEM image showing

the presence of single Co atoms (highlighted by yellow circles); and e) another HAADF image of G(CN) Co along with the corresponding elemental
mapping images of f) Co, g) O, h) N, i) Co and N, and j) Co, N, and C.

of CoO (7708.3 eV) and single site Co(II) on SiO2. The result
we obtained for the latter is similar to one reported before.[36]
The k2-weighted magnitude of the first shell peak of EXAFS
The EXAFS of G(CN) Co shows only the first shell Co-X scat-

tering, also with 6 Co N (or O), at 2.07 Å with no scattering
from Co atoms at longer distance, which is consistent with
single Co2+ ions. In EXAFS, the scattering is proportional to
the number of electrons; thus, it is not easy to distinguish
the type of scattering from C, O, and N atoms. The first shell

spectrum for G(CN) Co (black) and CoO (blue) are very sim-

ilar to each other (Figure 2d). CoO has 6 Co O bonds at 2.06 Å
(about 1.7 Å phase uncorrected distance in Figure 2d), as can
be seen from the fitting results given in Table S1, Supporting
Information. In the case of CoO, there is a large second shell

coordination number of Co/SiO2 is 4 Co O at 1.98 Å, which
is similar to the result previously reported for this material.[36]


 
peak due to the scattering by Co (O) Co at about 2.8 Å. This
higher shell peak is characteristic of Co-oxide nanoparticles.
The absence of a higher shell Co O Co (in Co/SiO2) is sim-

ilar to that of G(CN) Co, which is a SAC containing Co(II)
2006477 (3 of 7)
© 2021 Wiley-VCH GmbH
Small 2021, 17, 2006477

www.advancedsciencenews.com
www.small-journal.com


Figure 2. a) Survey X-ray photoelectron spectra of G(CN) Co. b) High-resolution X-ray photoelectron spectra of G(CN) Co showing the Co 2p region.

X-ray absorption spectra of G(CN) Co (black curve), CoO reference (blue curve), and Co(II)/SiO2 (another reference material, which we prepared for
comparative study (red curve). c) Co K-edge XANES and d) k2 weighted magnitude of Fourier transformation of EXAFS (inset: the proposed model

for G(CN) Co.




sites with 6 Co N (or Co O) bonds, each with a bond dis-
tance of 2.07 Å.
G(CN) Co (1.2 wt%) and G(CN) Co (1.5 wt%), with values of
2.7 and 3.0 mA cm−2, respectively. These results showed that

G(CN) Co (3.4 wt%) required a lower overpotential to catalyze


HzOR compared with G(CN) Co (1.2 wt%) and G(CN) Co
(1.5 wt%), indicating that the electrocatalytic activity of these
materials increases with the amount of Co. The result also indi-

2.2. Electrocatalytic Performance of G(CN) Co for HzOR

The electrocatalytic performances of the as-prepared materials
cated that G(CN) Co’s electrocatalytic activity for HzOR was
related to the Co(II) single sites. In addition, the support mate-

containing different amounts of Co (i.e., G(CN) Co (1.2 wt%),



G(CN) Co (1.5 wt%), and G(CN) Co (3.4 wt%)) for HzOR
were studied. First, cyclic voltammetry (CV) curves for the
catalysts in the presence of 50 mmol L−1 hydrazine solution
in phosphate buffered saline (PBS) (pH 7.4) at a scan rate of
10 mV∙s−1 from −0.5 to 0.3 V (vs SCE) were recorded (Figure 3a).
The anodic peaks, which were observed in the CV curves of all
three catalysts, could be attributed to the oxidation of hydrazine,
demonstrating that all samples had catalytic activity toward
rial, G CN, showed negligible activity toward HzOR, indirectly
corroborating that the anchored Co(II) cations were the active
sites. It is also worth adding that the catalytic performance of

G(CN) Co (3.4 wt%) for HzOR was higher than that of many
other transition and noble-metal based nanocatalysts that were
recently reported (see Table S2, Supporting Information). The
mass activities of the three materials for HzOR were com-
pared by normalizing the current densities to the mass of Co


HzOR. Among the catalysts, G(CN) Co (3.4 wt%) displayed
atoms in the materials. The results indicated that G(CN) Co
the best electrocatalytic activity for the reaction, with a relatively
large negative onset potential (which means a low overpoten-
tial), with a value of ≈−0.28 V (vs SCE). The corresponding
(1.2 wt%) gave the highest catalytic activity for HzOR per mass
of Co (Figure 3b). This means, although higher loading of Co
could enhance the overall HzOR activity in terms of current
density, their relationship was not linear. Therefore, the loading
of metals could be optimized to further lower the cost of such
catalysts while achieving optimal electrocatalytic activity or cur-
rent density.


values for G(CN) Co (1.2 wt%) and G(CN) Co (1.5 wt%) were

−0.25 and −0.26 V, respectively. G(CN) Co (3.4 wt%) also gave
a large negative peak potential of −0.1 V (vs SCE) while the cor-


responding values for G(CN) Co (1.2 wt%) and G(CN) Co

(1.5 wt%) were −0.07 and −0.09 V, respectively. Additionally,
The CV curves of HzOR obtained over G(CN) Co materials

the peak current density during the HzOR over G(CN) Co
using different concentrations of hydrazine solution (ranging
(3.4 wt%) was ≈3.5 mA cm−2, which was higher than those of
from 10 to 50 mmol L−1) are shown in Figure S4a–c, Supporting
Small 2021, 17, 2006477
2006477 (4 of 7)
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.small-journal.com



Figure 3. a) Cyclic voltammetry (CV) curves of HzOR obtained over G(CN) Co (1.2 wt%), G (CN)-Co(1.5 wt%), G(CN) Co (3.4 wt%), and G(CN) using
50 mmol∙L−1 hydrazine in PBS (pH 7.4) at a scan rate of 10 mV∙s−1 and b) the corresponding current density normalized to the total mass of Co atoms.
Information. The current density in the CV curves was found to
be proportional to the hydrazine concentration (see Figure S4d–f,
Supporting Information). The shapes of the CV curves revealed
only oxidation peaks and no cathodic peaks during the reverse
By using Equations (1–3), the total number of electrons
involved in the HzOR for the tested catalysts was calculated
to be close to 4. This indicated that the reaction would pro-
ceed through a 4-electron process to complete the oxidation
(Figure S5, Supporting Information), and the net reaction could
be written as: N2H4 + 4OH− → N2 + 4H2O + 4e−.
The long-term stability of electrocatalysts is important for
their practical application in DHFCs. Thus, the stability of the
three materials during electrocatalysis was evaluated by moni-
toring the change in current density near their respective peak
potentials in 50 mmol L−1 hydrazine for 10 000 s (Figure S6,
Supporting Information). The results showed that there was
only a minimal change in the residual current density during
the reaction, suggesting that the materials remained reasonably
stable during the HzOR. All the above electrochemical results

scans, confirming that the oxidation (or HzOR) over G(CN) Co
was an irreversible process. On the other hand, kinetic studies
revealed that increasing electrochemical scan rates resulted in a
slight shift toward positive peak potential in the catalytic HzOR
(Figure S5a–c, Supporting Information). This is related to the
mass diffusion-controlled electrochemical processes involved
in HzOR and the occupation of active sites by the reacting spe-
cies, as reported in our previous works.[36,39] The oxidation cur-
rent density was found to be linearly proportional to the square
root of scan rate (Figure S5d–f, Supporting Information), once
again indicating that the HzOR over the materials was diffu-
sion-controlled.[1,37–41] The electron transfer number (n) involved
in HzOR over the catalysts was determined based on the slope
of the current density (I/A) versus square root of the scan rate
(v1/2) using equation:[37–41]

clearly demonstrated that G(CN) Co materials could serve as
efficient noble metal-free electrocatalysts for HzOR. This also
means that these materials have a potential to serve as sustain-
able electrocatalysts at the anode side of DHFC, given their
excellent activity as well as good atom economy and non-noble
elemental composition.
I/A = 3.01×10−5n[ 1−α n ]1/2 cD−1/2v1/2
(1)
(
)
α
where I is the current produced by the electrocatalytic reaction,
A is the surface area of the working electrode (A = 0.071 cm2), n
is the total number of electrons involved in the HzOR, α is
the electron transfer coefficient, nα is the number of electrons
involved in the rate-determining step (nα = 1), D is the diffusion
coefficient, c is the concentration of hydrazine (c = 50 mmol L−1),
and v is the scan rate. The values of α and D are determined
based on the linear relationship between the peak potential (Ep)
and the natural logarithm of scan rate (log v) (Equation (2)) as
well as on the linear correlation between the current density
(I/A) and the inverse square root of time (t−1/2) as expressed by
the Cottrell equation (Equation (3)):
2.3. Density Functional Theory Studies of the Reaction
Mechanism of HzOR on the Catalysts
The mechanism of HzOR over the electrocatalyst was studied
step-by-step by geometry optimizations of N2H4, N2, and all

intermediates with and without G(CN) Co catalyst using
DFT in combination with the implicit solvation model[42] to
account for the aqueous environment. Theoretical models

of the G(CN) Co catalyst were derived from a trans-14f,14k-

dicyanoovalene molecule representing the G CN substrate
by anchoring either a single Co2+ cation (model A, Figure S7a,
Supporting Information) or a Co2+ cation coordinated with five
water molecules (model B, Figure S7b, Supporting Informa-
tion) to one of the cyano groups. The positive binding affinity
(2)
E = k + 0.03/αn log v
[
]
p
α
of Co2+ cations to G CN was recently rationalized in terms of

where k is a constant and nα = 1
I/A = nFCD1/2 −1/2t−1/2
efficient charge transfer from the substrate to metal cations.[43]
The reaction mechanism consists of four deprotonation steps
(in basic environment) and four electrochemical oxidation steps
(Figure 4). In total, four electrons are released. The HzOR may
(3)
π
where F is Faraday constant (F = 96 496 C mol−1).
2006477 (5 of 7)
© 2021 Wiley-VCH GmbH
Small 2021, 17, 2006477

www.advancedsciencenews.com
www.small-journal.com
synthetic method. The material showed efficient and selec-
tive electrocatalytic activity toward HzOR with low onset/peak
potential, high current density, and good stability. The electro-

catalytic performances of G(CN) Co for HzOR were also found
to be better than many metal-based catalysts reported in the lit-
erature. DFT calculations of the reaction mechanism indicated
that single Co active sites would readily interact with the hydra-

zine molecules and significantly foster the N H bond disso-
ciation steps. The presented simple synthetic strategy used to

produce G(CN) Co SAC and their efficient catalytic properties
can encourage further research into other SACs with improved
catalytic activity for HzOR and other reactions.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Figure 4. Reaction mechanism of hydrazine oxidation reaction (repre-

sented with yellow bubble) with and without the G(CN) Co catalyst (in
the center). The numbers marked in red and green correspond to reac-
tion energies (in eV) obtained without and with the catalyst (model A),
respectively.
Acknowledgements
R.G.K. and T.Z. contributed equally to this work. The authors gratefully
acknowledge the support of the Operational Program Research,
Development and Education—European Regional Development Fund
(ERDF) (project no. CZ.02.1.01/0.0/0.0/16_019/0000754) and the ERDF
project “Development of pre-applied research in nanotechnology and
biotechnology” (project no. CZ.02.1.01/0.0/0.0/17_048/0007323) of the
Ministry of Education, Youth and Sports of the Czech Republic. R.Z. and
A.B. acknowledge the support of the Czech Science Foundation, project
No. 19-27454X. M.O. acknowledges ERC project (No. 683024) from the
European Union’s Horizon 2020. T.A. gratefully acknowledges the financial
assistance of the US National Science Foundation (Grant No.: NSF DMR-
1508611). Use of the Advanced Photon Source by JTM was supported by
the U.S. Department of Energy Office of Basic Energy Sciences under
contract no. DE-AC02-06CH11357. MRCAT operations, beamline 10-BM,
were supported by the Department of Energy and the MRCAT member
institutions.
proceed via two routes differing in steps 3–5 by dissociation of

N H bonds, which are however energetically comparable (see
detailed mechanisms in Figures S8 and S9, Supporting Infor-
mation). Without the catalyst, all reaction steps (except step
7) are energetically demanding (the values marked in red in

Figure 4). The presence of G(CN) Co catalyst significantly pro-
motes the deprotonation steps 1, 3, 5, and 7 (the values marked

in green in Figure 4) due to lowering of the N H bond polarity
(see Tables S3 and S4, Supporting Information). In addition,

the negatively charged intermediates (i.e., the N H bond dis-
sociation products) are stabilized owing to charge transfer from
N2Hx (x = 1–4) to the catalyst (see qtot values in Tables S3 and S4,
Supporting Information), which further decreases the reaction
energies of these steps. The electrochemical steps (i.e., electron
releasing steps 2, 4, 6, and 8 in Figure 4) are energetically more
demanding in the presence of the catalyst.
The coordination of Co2+ ion in G(CN) Co with water mole-

Conflict of Interest
The authors declare no conflict of interest.
cules lowers the positive charge on Co2+ and thus decreases

the binding affinity of hydrazine molecule to G(CN) Co
catalyst, from −1.3 to −0.6 eV (step 0 in Figures S8 and S10,
Supporting Information). However, the reaction energies and
ionization potentials do not substantially change compared to
those attained by the simpler model, which does not explicitly
take into account water molecules. For example, the reaction
energies of steps 1 and 2 decrease from −0.4 to −0.3 eV and
from 3.7 to 3.0 eV, respectively (Figures S8 and S10, Supporting
Information). Interestingly, a deprotonation step involving
coordinatively bound water molecules was also found feasible
(path b in Figure S10, Supporting Information). Although, this
process can face competition with one involving a direct attack
of OH− on hydrazine, the deprotonation steps appear to be
energetically more favorable in the presence of the catalyst.
Data Availability Statement
Research data are not shared.
Keywords
electrocatalysis, hydrazine oxidation reaction, renewable energy, single
atom catalyst, single Co atom catalyst
Received: October 16, 2020
Revised: February 24, 2021
Published online: March 30, 2021
3. Conclusions
[1] T. Zhang, T. Asefa, Adv. Mater. 2019, 31, 1804394.
[2] T. Zhang, J. Low, K. Koh, J. Yu, T. Asefa, ACS Sustainable Chem. Eng.
2018, 6, 531.
In summary, we have successfully developed Co-based SAC,

denoted G(CN) Co, with well-defined Co(II) sites by a simple
Small 2021, 17, 2006477
2006477 (6 of 7)
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.small-journal.com
[3] J. Sanabria-Chinchilla, K. Asazawa, T. Sakamoto, K. Yamada,
H. Tanaka, P. Strasser, J. Am. Chem. Soc. 2011, 133, 5425.
[4] A. Wang, J. Li, T. Zhang, Nat. Rev. Chem. 2018, 2, 65.
[5] X. Li, X. Yang, Y. Huang, T. Zhang, B. Liu, Adv. Mater. 2019, 31,
1902031.
[23] K. Jiang, S. Siahrostami, T. Zheng, Y. Hu, S. Hwang, E. Stavitski,
Y. Peng, J. Dynes, M. Gangisetty, D. Su, K. Attenkofer, H. Wang,
Energy Environ. Sci. 2018, 11, 893.
[24] S. Zhou, L. Shang, Y. Zhao, R. Shi, G. I. N. Waterhouse, Y.-C. Huang,
L. Zheng, T. Zhang, Adv. Mater. 2019, 31, 1900509.
[6] B. Singh, V. Sharma, R. P. Gaikwad, P. Fornasiero, R. Zbořil,
M. B. Gawande, Small 2020, 2006473, https://doi.org/10.1002/
smll.202006473.
[7] X. F. Yang, A. Wang, B. Qiao, J. Li, J. Liu, T. Zhang, Acc. Chem. Res.
2013, 46, 1740.
[8] M. B. Gawande, P. Fornasiero, R. Zbořil, ACS Catal. 2020, 10,
2231.
[9] A. Bakandritsos, R. G. Kadam, P. Kumar, G. Zoppellaro, M. Medved,
J. Tuček, T. Montini, O. Tomanec, P. Andrýsková, B. Drahoš,
R. S. Varma, M. Otyepka, M. B. Gawande, P. Fornasiero, R. Zbořil,
Adv. Mater. 2019, 31, 1900323.
[25] Z. Du, X. Chen, W. Hu, C. Chuang, S. Xie, A. Hu, W. Yan, X. Kong,
X. Wu, H. Ji, L.-J. Wan, J. Am. Chem. Soc. 2019, 141, 3977.
[26] H.-J. Qiu, Y. Ito, W. Cong, Y. Tan, P. Liu, A. Hirata, T. Fujita, Z. Tang,
M. Chen, Angew. Chem., Int. Ed. 2015, 54, 14031.
[27] H. Zhang, J. Li, S. Xi, Y. Du, X. Hai, J. Wang, H. Xu, G. Wu, J. Zhang,
J. Lu, J. Wang, Angew. Chem., Int. Ed. 2019, 58, 14871.
[28] D. D. Chronopoulos, A. Bakandritsos, M. Pykal, R. Zbořil,
M. Otyepka, Appl. Mater. Today 2017, 9, 60.
[29] X. Wei, D. Zheng, M. Zhao, H. Chen, X. Fan, B. Gao, L. Gu, Y. Guo,
J. Qin, J. Wei, Y. Zhao, G. Zhang, Angew. Chem., Int. Ed. 2020, 59,
14639.
[10] H. Fei, J. Dong, D. Chen, T. Hu, X. Duan, I. Shakir, Y. Huang,
X. Duan, Chem. Soc. Rev. 2019, 48, 5207.
[11] Y. Wang, J. Mao, X. Meng, L. Yu, D. Deng, X. Bao, Chem. Rev. 2019,
119, 1806.
[12] C. Zhang, J. Sha, H. Fei, M. Liu, S. Yazdi, J. Zhang, Q. Zhong,
X. Zou, N. Zhao, H. Yu, Z. Jiang, E. Ringe, B. I. Yakobson, J. Dong,
D. Chen, J. M. Tour, ACS Nano 2017, 11, 6930.
[13] X. Zhang, J. Guo, P. Guan, C. Liu, H. Huang, F. Xue, X. Dong,
S. J. Pennycook, M. F. Chisholm, Nat. Commun. 2013, 4,
1924.
[30] Y. Pan, R. Lin, Y. J. Chen, S. J. Liu, W. Zhu, X. Cao, W. X. Chen,
K. L. Wu, W. C. Cheong, Y. Wang, L. R. Zheng, J. Luo, Y. Lin,
Y. Q. Liu, C. G. Liu, J. Li, Q. Lu, X. Chen, D. S. Wang, Q. Peng,
C. Chen, Y. D. Li, J. Am. Chem. Soc. 2018, 140, 4218.
[31] H. Yang, L. Shang, Q. Zhang, R. Shi, G. I. N. Waterhouse, L. Gu,
T. Zhang, Nat. Commun. 2019, 10, 4585.
[32] K. Sohlberg, T. J. Pennycook, W. Zhou, S. J. Pennycook, Phys. Chem.
Chem. Phys. 2015, 17, 3982.
[33] A. Bakandritsos, M. Pykal, P. Błoński, P. Jakubec,
D. D. Chronopoulos, K. Poláková, V. Georgakilas, K. Čépe,
O. Tomanec, V. Ranc, A. B. Bourlinos, R. Zbořil, M. Otyepka, ACS
Nano 2017, 11, 2982.
[14] K. C. Kwon, J. M. Suh, R. S. Varma, M. Shokouhimehr, H. W. Jang,
Small Methods 2019, 3, 1800492.
[15] J. Guo, J. Huo, Y. Liu, W. Wu, Y. Wang, M. Wu, H. Liu, G. Wang,
Small Methods 2019, 3, 1900159.
[16] Y. Cheng, S. Zhao, B. Johannessen, J. P. Veder, M. Saunders,
M. R. Rowles, M. Cheng, C. Liu, M. F. Chisholm, R. De Marco,
H. M. Cheng, S. Z. Yang, S. P. Jiang, Adv. Mater. 2018, 30,
1706287.
[34] G. Zhang, C. Huang, X. Wang, Small 2015, 11, 1215.
[35] J. P. Krogman, J. R. Gallagher, G. Zhang, A. S. Hock, J. T. Miller,
C. M. Thomas, Dalton Trans. 2014, 43, 13852.
[36] B. Hu, A. B. Getsoian, N. M. Schweitzer, U. Das, H. Kim, J. Niklas,
O. Poluektov, L. A. Curtiss, P. C. Stair, J. T. Miller, A. S. Hock,
J. Catal. 2015, 322, 24.
[17] Y. Zhu, W. Peng, Y. Li, G. Zhang, F. Zhang, X. Fan, Small Methods
2019, 3, 1800438.
[18] W. H. Lai, Z. Miao, Y. X. Wang, J. Z. Wang, S. L. Chou, Adv. Energy
Mater. 2019, 9, 1900722.
[19] M. D. Hossain, Z. Liu, M. Zhuang, X. Yan, G. L. Xu, C. A. Gadre,
A. Tyagi, I. H. Abidi, C. J. Sun, H. Wong, A. Guda, Y. Hao, X. Pan,
K. Amine, Z. Luo, Adv. Energy Mater. 2019, 9, 1803689.
[20] Y. N. Chen, X. Zhang, Z. Zhou, Small Methods 2019, 3, 1900050.
[21] R. R. Amirov, J. Shayimova, Z. Nasirova, A. Solodov, A. M. Dimiev,
Phys. Chem. Chem. Phys. 2018, 20, 2320.
[22] V. Georgakilas, M. Otyepka, A. B. Bourlinos, V. Chandra, N. Kim,
K. C. Kemp, P. Hobza, R. Zbořil, K. S. Kim, Chem. Rev. 2012, 112,
6156.
[37] T. Zhang, T. Asefa, Front. Chem. Sci. Eng. 2018, 12, 329.
[38] B. Dong, B. L. He, J. Huang, G. Y. Gao, Z. Yang, H. L. Li, J. Power
Sources 2008, 175, 266.
[39] Y. Meng, X. Zou, X. Huang, A. Goswami, Z. Liu, T. Asefa, Adv.
Mater. 2014, 26, 6510.
[40] A. L. Cazetta, T. Zhang, T. L. Silva, V. C. Almeida, T. Asefa, Appl.
Catal., B 2018, 225, 30.
[41] A. C. Martins, X. Huang, A. Goswami, K. Koh, Y. Meng,
V. C. Almeida, T. Asefa, Carbon 2016, 102, 97.
[42] A. V. Marenich, C. J. Cramer, D. G. Truhlar, J. Phys. Chem. B 2009,
113, 6378.
[43] D. Zaoralová, R. Mach, P. Lazar, M. Medveď, M. Otyepka, Adv.
Mater. Interfaces 2020, 2001392.
2006477 (7 of 7)
© 2021 Wiley-VCH GmbH
Small 2021, 17, 2006477