From a Molecular 2Fe-2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting

Article abstract of DOI:10.1002/anie.201706196

A highly active FeSe₂ electrocatalyst for durable overall water splitting was prepared from a molecular 2Fe-2Se precursor. The as-synthesized FeSe₂ was electrophoretically deposited on nickel foam and applied to the oxygen and hydrogen evolution reactions (OER and HER, respectively) in alkaline media. When used as an oxygen-evolution electrode, a low 245 mV overpotential was achieved at a current density of 10 mA cm^?2, representing outstanding catalytic activity and stability because of Fe(OH)₂/FeOOH active sites formed at the surface of FeSe₂. Remarkably, the system is also favorable for the HER. Moreover, an overall water-splitting setup was fabricated using a two-electrode cell, which displayed a low cell voltage and high stability. In summary, the first iron selenide material is reported that can be used as a bifunctional electrocatalyst for the OER and HER, as well as overall water splitting.

Full text of DOI:10.1002/anie.201706196

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Accepted Article
Title: From Molecular 2Fe-2Se Precursor to FeSe2 Acting as Highly
Efficient Electrocatalyst for Overall Water-Splitting
Authors: Matthias Driess, Chakadola Panda, Prashanth Wilfried
Menezes, Carsten Walter, Shenglai Yao, Matthias Miehlich,
Vitaly Gutkin, and Karsten Meyer
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201706196
Angew. Chem. 10.1002/ange.201706196
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10.1002/anie.201706196
Angewandte Chemie International Edition
COMMUNICATION
From Molecular 2Fe-2Se Precursor to FeSe2 Acting as Highly Efficient
Electrocatalyst for Overall Water-Splitting
Chakadola Panda,[a]+ Prashanth W. Menezes,[a]+ Carsten Walter,[a] Shenglai Yao,[a] Matthias E.
Miehlich,[b] Vitaly Gutkin,[c] Karsten Meyer,[b] and Matthias Driess[a]*
Abstract: A highly active FeSe2 electrocatalyst for durable overall
water-splitting has been prepared from molecular 2Fe-2Se
and overall water-splitting catalysts.
a
Although numerous transition-metal selenides are known
to be efficient for HER, high performance OER catalysts based
on selenides were discovered only very recently.[6] Early 2017,
Gao et al. reported on using FeSe2 for OER with considerable
low overpotential of 330 mV at a current density of 10 mAcm-2.[8]
In accordance with previous observations, however, the same
catalyst seems unsuitable for HER.[6b] While there is one iron
sulfide that has been identified with moderate activity for OER
and HER,[6c] there is – as of now and to the best of our
knowledge – no report on an iron selenide material that has
been utilized for overall water-splitting catalysis. This prompted
us to investigate whether the size, structural, morphological, and
the electronic properties of FeSe2 can be fine-tuned to achieve
not only high performance for bifunctional OER and HER but
also for overall water-splitting.
precursor. The as-synthesized FeSe2 was electrophoretically
deposited on nickel foam and applied for both oxygen (OER) and
hydrogen evolution reaction (HER) in alkaline media. When used as
an oxygen-evolution electrode, merely 245 mV of overpotential was
achieved at
a
current density of 10 mAcm-2, representing
outstanding catalytic activity and stability due to the formation of
Fe(OH)2/FeOOH active sites at the surface of FeSe2. Remarkably,
the system is also favorable for HER. Moreover, an overall water-
splitting set up was fabricated using a two-electrode cell displaying
low cell voltage and high stability. In summary, the first iron selenide
material is reported which can be used as superiorly active
bifunctional electrocatalyst for OER and HER as well as overall
water-splitting.
Usually metal chalcogenide materials are synthesized by
conventional synthetic routes (e.g. precipitation method) leading
to a random distribution of aggregates and an infinite number of
nanostructures among which only few are catalytically active.[9a-b]
To overcome this, the “low-temperature molecular precursor”
approach is a convenient method to control the composition and
size distribution of nanomaterials and to enable high catalytic
activity.[9c-g] Applying this concept, the synthesis of FeSe2 from a
molecular 2Fe-2Se precursor that shows superior catalytic
activity for both OER and HER is promising. The 2Fe-2Se
cluster core in the latter represents a heavy analog of 2Fe-2S
clusters in iron-sulfur proteins responsible for multi-electron
transfer processes in Nature.[10] Unlike isolable 2Fe-2S
clusters,[11] related 2Fe-2Se clusters are still scarce. By the
seminal work of Holm and co-workers, several Fe-Se clusters
could be synthesized with a range of iron nuclearities (2, 3, 4
and 6); thus, aiming at the development of an understanding of
electronic effects exerted by a heavy element, such as selenium,
in these clusters and the elucidation of their functionality in
biological systems.[11c,11d,11g,12]
Today’s one of the most fundamental scientific and
technological challenge remains in the development of
alternative clean energy sources to the current fossil based
fuels.[1] Large scale production of H2 through splitting of water is
the key to generate chemical fuels that are clean and
sustainable.[2] While several efficient catalysts are accessible for
the hydrogen evolution reaction (HER),[3] the oxygen evolution
reaction (OER) is considered to be the bottle-neck to water-
splitting as it comprises of multiple proton coupled electron
transfer (PCET) steps involving high energy intermediates.[2] The
current state of-the-art catalysts that perform both OER and
HER are based on noble metals, which are unsuitable for
practical large-scale applications owing to their scarcity and high
cost.[4] Tremendous research efforts have been devoted in this
direction to design inexpensive catalysts based on earth-
abundant transition metals that can perform OER and HER with
very high efficiency.[5] This includes cheap transition-metal
based materials, including oxides,[2a,2c-f] chalcogenides[6] and
pnictides[6b,7] that have been explored as alternative OER, HER
Here, we present (i) the synthesis of a bioinspired
molecular 2Fe-2Se cluster core supported by a β-diketiminato
ligand, (ii) the fabrication of FeSe2 nanomaterials from the
molecular 2Fe-2Se clusters via a versatile thermolytic approach,
(iii) the utilization of immobilized FeSe2 as an outstanding
electrocatalytic material for bifunctional OER and HER, and for
overall water-splitting catalysis, and (iv) the elucidation of
surface-structural phenomena, the nature of the active species,
and structure-activity relationships. In comparison to known iron
selenide systems, the catalytic activity of FeSe2 attained here
renders them to be one of the highly active catalysts so far.
The β-diketiminato supported all ferric molecular 2Fe-2Se
cluster 2, and its one electron reduced form 3 were prepared as
similar to the related 2Fe-2S clusters (Scheme 1, Supporting
Information).[11a] Both 2 and the anion in 3 displayed similar
geometrical features (Figure 1) as the analogous 2Fe-2S
clusters.[11a] Detailed spectroscopic investigations were
undertaken to ascertain that 2 consists of high spin FeIII/FeIII,
[a]
Dr. C. Panda, Dr. P. W. Menezes, M. Sc. C. Walter, Dr. S. Yao,
Prof. Dr. M. Driess
Department of Chemistry, Metalorganics and Inorganic Materials
Technische Universität Berlin
Strasse des 17. Juni 135, Sekr. C2, 10623 Berlin (Germany)
E-mail: matthias.driess@tu-berlin.de
[b]
[c]
[+]
M. Sc. M. E. Miehlich, Prof. Dr. K. Meyer
Department of Chemistry and Pharmacy, Inorganic
Chemistry, Friedrich-Alexander University Erlangen - Nürnberg
(FAU), Egerlandstr. 1, 91058 Erlangen, Germany
Dr. V. Gutkin
The Harvey M. Krueger Family Center for Nanoscience and
Nanotechnology, The Hebrew University of Jerusalem, Edmond J.
Safra Campus, Givat Ram, Jerusalem 91904, Israel
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.201706196
Angewandte Chemie International Edition
COMMUNICATION
K+
N
FeII
N
N
FeIII
N
N
FeIII
N
N
N
N
N
N
N
H
H
Se
Se
Se
Se
1/4 Se8
-H2
K
FeII
FeIII
FeII
(1)
(2)
(3)
Scheme 1. Synthesis of the 2Fe-2Se clusters 2 and 3.
whereas 3 involves mixed valence FeII/FeIII centers,[13] such that
the electronic structures of both 2 and 3 (Table S5) are akin with
those observed for the 2Fe-2S analogue.[11a]
When 2 was subjected to thermal degradation under hot
injection conditions, FeSe2 was obtained in 72% yields. We
hypothesize that in the process of thermolysis, instant
dissociation of the weakly bound β-diketiminato ligand takes
place followed by Fe-Se core. As successful nucleation occurs;
a thermodynamically more stable orthorhombic FeSe2 phase is
obtained.[14] The as-prepared FeSe2 was characterized by
powder X-ray diffraction analysis (PXRD) and scanning electron
microscopy (SEM) (Figure S16-17). Transmission electron
microscopy (TEM) and high resolution (HR) TEM revealed that
the agglomerates consists of very small crystalline particles
ranging from 4-10 nm in diameter and the resulting lattice
spacing of 0.256 nm reflected the (111) plane of FeSe2 (Figure
2a, 2b and S18).[15] In addition, the rings in the selected area
diffraction pattern (SAED), extracted from the HR-TEM, revealed
the spacing of 0.302, 0.256, 0.201, 0.161, and 0.149 nm
Figure 1. Molecular structures of 2 and 3 (ion pair with potassium-crownether-
acetone).
M(OH)2/MOOH phase formation (Figure S21c).[19] In order to
gather more insights on the redox process, we compared bare
NF with the FeSe2/NF (Figure S21b) and found that, a slight
oxidation to Ni2+ in NF is unavoidable, however, the redox peaks
were gradually shifted during water oxidation in FeSe2/NF
indicating the oxidation of Fe2+. To entirely rule out whether the
redox peaks are from active Ni2+, we studied redox behavior of
FeSe2 on fluorine doped tin oxide (FTO) that exhibited a clear
redox couple and is solely ascribed to Fe2+/Fe3+.The catalytic
activity of FeSe2/NF outperformed that of the noble metal-based
RuO2/NF, IrO2/NF, Pt wire and bare NF catalysts, which were
corresponding to the (101), (111), (112), (211), and (023) planes, also measured under similar conditions (Figure 3). FeSe2
respectively (Figure 2c).[15] The as-prepared FeSe2 crystallizes in
the orthorhombic marcasite structure (space group Pnnm)
consisting of octahedrally surrounded FeII atoms coordinated to
six Se atoms; each tetrahedrally coordinated Se atom of the
displayed extremely high stability towards chronopotentiometric
(CP) analysis over 18 h with improving overpotentials of ~ 230
mV (Figure S22). After the CP measurements, a CV was
measured again for comparison (Figure S22) with the initial CV
and the difference was found to be marginal when compared at
100 mAcm-2. Similarly, the FeSe2 and other noble metal-based
materials were deposited on FTO and the linear sweep
voltammetry (LSV) in each case was measured and the details
are given in (Figure S23). The catalytic activities for both
FeSe2/NF and FeSe2/FTO are better than any iron selenide and
one of the best among both chalcogenides as well as other first-
row transition metal based materials (Tables S7 and S8 for
details).
HER was performed similar to the OER conditions in 1 M
KOH. Figure S24 shows the catalytic HER activity of FeSe2/NF
and those of commercial IrO2/NF and Pt catalysts. A strong
redox response was observed in the lower current density region
for FeSe2/NF indicating the reduction of Fe from mixed +2/+3 to
a more reduced state akin to what was reported for FeOx type
materials.[19b,20] Due to the interfering redox response at the
region of lower current densities (-10 mAcm-2), the
overpotentials were defined and compared at a current density
of -100 mAcm-2 (Table S10). The overpotential was determined
to be at 262 mV for FeSe2/NF, 334 mV for IrO2/NF, and Pt
showed the best with 135 mV. In addition, the influence of scan
rates on polarization current was also conducted where the
Se2 moieties is ligated to three Fe centers (Figure 2d).[14] The
2-
phase and composition of FeSe2 were confirmed by energy
dispersive X-ray analysis (EDX) and inductively coupled plasma
atomic emission spectroscopy (ICP-AES; Table S6, Figure S19).
In X-ray photoelectron spectroscopy (XPS), it is known that the
binding energy of Fe2p3/2 is about 709 eV for FeII, and 711 eV for
FeIII.[15] The peak of the Fe2p3/2 regions, obtained at 710.4 eV
indicate that both FeII and FeIII are present at the surface of
FeSe2.[16] Similarly, the peak corresponding to 2p1/2 was located
at 723.8 eV confirming the FeII/III character originating from
partial corrosion of Fe at the surface, which is in agreement with
previously reported analyses of FeSe2.[9b] Further details on the
Fe2p and Se3d XPS are given in supporting information (Figure
S20).[17,18] The attained Fe:Se ratio on the surface is about 1:2
which is in accordance with the ICP-AES and EDX analyses.
The electrocatalytic OER was examined by depositing
FeSe2 on nickel foam (NF) using a three electrode set-up (SI)
and the overpotential exhibited at 10 mAcm-2 was merely 245
mV, while at 100 mAcm-2, the overpotential was only 308 mV
(Figure S21a, b). The resulting overpotentials are not only one of
the lowest in the series of chalcogenides but also lower than
most of the high-performance transition-metal based catalysts
(Tables S7, S8). While cycling between 1.22 and 1.44 V vs RHE, current was slightly decreased with decrease in scan rates from
a small reversible redox couple was attained (prior to the OER)
for FeSe2/NF. This is attributed to the presence of FeII/FeIII, and
is typical for first-row transition-metal based materials with
20 mV/s to 1 mV/s (Figure S24b) and the overpotential at -10
mAcm-2 was 178 mV. The activity comparison with existing
materials indicates the moderate efficiency of FeSe2 (Tables S9,
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10.1002/anie.201706196
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Figure 3. Current-potential curves of FeSe2 and commercial noble metal-
based catalysts deposited on nickel-foam (NF) with a scan rate of 20 mV/s in
1M KOH.
Figure 2. TEM images (a), HR-TEM (b) SAED (c) images and the
orthorhombic marcasite crystal structure (d) of FeSe2.
was oxidized from mixed Fe2+/Fe3+ to Fe3+, consistent with
literature-reported examples.[17,22] The Se3d peaks were slightly
shifted from the initial spectrum and a minor peak at ~ 58.3 eV
suggests oxidation of the selenium surface (Figure S31).[23] In
addition, the XPS analysis revealed the loss of surface Se
(~ 40%) supporting the results of ICP-AES. The O1s XPS
spectra of both CV OER and CP OER of FeSe2 could be
deconvoluted into small O1 and broad O2 peaks (Figure S32).
The O1 peak ~ 529.2 eV (O1) could be assigned to the
formation of iron-oxygen bonds on the surface, due to the
surface passivation of FeSe2 to form FeOx species. The peak at
~ 531.7 eV (O2) is due to large dominance of oxyhydroxide/-
hydroxides.[2b,2c,2d,2e,7]
S10). The CP was recorded for FeSe2/NF maintaining constant
current of -10 mAcm-2 (Figure S25). Although
a good
overpotential was achieved initially (176 mV), the long-time
stability was further decreased and the resulting overpotential
increased to ~ 260 mV. The CV after the CP showed a decrease
in the current density (-640 to -440 mAcm-2) as well as slight
increase in the overpotential at -100 mAcm-2 (260 mV to 320
mV). The LSVs of FeSe2 and the commercially available noble
metal-based catalysts deposited on FTO were carried out and
compared (Figure S26, Tables S9, S10).
To gather insights on the nature of the active species as
well as the structural and morphological transformations
occurring at the near-surface zone during electro-catalysis, the
FeSe2 was characterized after the electrochemical OER and
HER, i.e., post CV (CV OER and CV HER) as well as post CP
(CP OER and CP HER). In the case of CV OER, the TEM and
HR-TEM images revealed a thin amorphous shell, which
appeared to be started growing on the surface of the particles
confirming the immediate changes on the surface at applied
potentials (Figure S27), while the thickness of the amorphous
shell was further increased after CP OER (Figure S28). This
observation suggests the formation of Fe(OH)2/FeOOH on the
surface, which could also be observed from CV cycling during
OER measurements (Figure S21), and is consistent with
respective literature reported data for iron based catalysts.[19]
Both HRTEM and SAED pattern showed that the core of the
particle was intact (Figure S28).[15] Clearly, the Fourier transform
infrared (FT-IR) spectra exhibited broad bands that are
indicative for hydroxylation in comparison to the FeSe2, where
such bands were absent (Figure S29). Interestingly, ICP-AES
disclosed a tiny loss of Se during CV OER but the amount of Se
loss increased after CP OER suggesting corrosion of FeSe2.
This surface change for selenides has already been reported for
the Ni0.8Fe0.2Se2 catalyst.[21] In the XPS spectra (Figure S30), the
Fe2p3/2 of CV OER showed a peak at 710.7 eV, while CP OER
exhibits a peak at 711 eV evidencing an increase in the
oxidation state of Fe from mixed Fe2+/Fe3+ to Fe3+.[15] Similarly,
the 2p1/2 for CV OER and CP OER were found to be at the
binding energy of 724.7 eV and 724.9 eV, respectively. The
values obtained clearly indicate, that the surface of the catalysts
In case of CV HER and CP HER, no indication for the
formation of amorphous shell was observed in the HR-TEM
(Figure S33). The SAED pattern displayed rings corresponding
to FeSe2 phase (Figure S33). Unlike post-OER, only a negligible
amount of Se was detached from the particles as observed from
ICP-AES. In the XPS spectra (Figure S34), the Fe2p3/2 of CV
HER and CP HER, also exhibited a peak at ~ 710.7 eV (similar
to OER) indicative of a slight increase in the oxidation state;
presumably because of surface passivation when exposed to
oxygen in the atmosphere and/or placing the electrode in strong
alkaline media.[17,24] Similarly, the 2p1/2 for CV HER and CP HER
were found to be close to 724.4 eV. Interestingly, the satellite
peak at ~ 719 eV completely disappeared and a new peak
appeared at ~ 716 eV, which corresponds to the Fe2p3/2 satellite
for FeII.[17,22] The Se3d peak of FeSe2 located at 55.5 eV
matched well to that of CV HER and CP HER (Figure S35).
However, the minor peak at ~ 58.3 eV, implicating the surface
oxidation of Se species, was increased strongly from CV to
CP.[23] The O1s XPS spectra of both CV HER and CP HER of
FeSe2 could be deconvoluted into small O1 and broad O2 peaks
and could be described akin to the OER CP (Figure S36).[2b,2c,2d,
2e,7]
Based on the aforementioned results, the outstanding
OER activity of FeSe2 can be attributed to the (i) advantageous
use of 2 as molecular precursor enabling very small and defined
particle size and enrichment of significantly higher active sites
(ii) formation of Fe-rich amorphous shell consisting of Fe(OH)2/
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10.1002/anie.201706196
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COMMUNICATION
Alexander von Humboldt Foundation for
a
postdoctoral
fellowship (2015–2017). We thank Dr. Mathias Wiechen and Dr.
Somenath Garai for help. KM acknowledges financial support
from the Friedrich-Alexander-University Erlangen-Nürnberg
(FAU).
Keywords: bioinspired complexes • mixed valence • hydrogen
evolution • oxygen evolution • energy conversion
[1] H. B. Gray, Nat. Chem. 2009, 1, 7-7.
[2] a) A. Indra, P. W. Menezes, I. Zaharieva, E. Baktash, J. Pfrommer, M.
Schwarze, H. Dau, M. Driess, Angew. Chem., Int. Ed. 2013, 52, 13206-
13210; b) P. W. Menezes, A. Indra, N. R. Sahraie, A. Bergmann, P.
Strasser, M. Driess, ChemSusChem 2015, 8, 164-171; c) P. W. Menezes,
A. Indra, D. González-Flores, N. R. Sahraie, I. Zaharieva, M. Schwarze, P.
Strasser, H. Dau, M. Driess, ACS Catal. 2015, 5, 2017-2027; d) A. Indra, P.
W. Menezes, N. R. Sahraie, A. Bergmann, C. Das, M. Tallarida, D.
Schmeißer, P. Strasser, M. Driess, J. Am. Chem. Soc. 2014, 136, 17530-
17536; e) P. W. Menezes, A. Indra, O. Levy, K. Kailasam, V. Gutkin, J.
Pfrommer, M. Driess, Chem. Commun. 2015, 51, 5005-5008.
Figure 4. Current−potential curve for FeSe2║FeSe2 on NF in a two-electrode
set-up for overall water-splitting solution with a scan rate of 5 mV/s in alkaline
medium. The long-term stability of the catalysts is shown in the inset.
FeOOH species at the surface, and (iii) the formation of defect
structure with anionic vacancies due to the loss of Se from the
particle surface. The active species on the surface of the
catalysts can thus facilitate the adsorption of OH- ions and
stimulate transport of electrons to have simple recombination of
two oxygen atoms to promote efficient oxygen evolution.[25]
Activity of FeSe2 in HER can be correlated to the bond strength
of Se that plays a crucial role. In principle, HER electrocatalyst
should have neither too weak nor too strong bonding, but should
have moderate bonding state with the intermediates and
products. Interestingly, within chalcogenides, the bond strength
of Se−H (276 kJ mol-1) is much lower compared to S−H (363 kJ
mol-1) and it can trap protons by acting as bases and accelerates
deprotonation to release H2.[6b,7]
[3] D. Kong, J. J. Cha, H. Wang, H. R. Lee, Y. Cui, Energy Env. Sci. 2013, 6,
3553-3558.
[4] a) C. C. L. McCrory, S. Jung, J. C. Peters, T. F. Jaramillo, J. Am. Chem.
Soc. 2013, 135, 16977-16987; b) S. J. Kwon, F.-R. F. Fan, A. J. Bard, J.
Am. Chem. Soc. 2010, 132, 13165-13167; c) S. Anantharaj, M.
Jayachandran, S. Kundu, Chem. Sci. 2016, 7, 3188-3205.
[5] a) A. Singh, L. Spiccia, Coord. Chem. Rev. 2013, 257, 2607-2622; b) H.
Liu, Y. Zhou, R. Moré, R. Müller, T. Fox, G. R. Patzke, ACS Catal. 2015, 5,
3791-3800; c) M. Huynh, C. Shi, S. J. L. Billinge, D. G. Nocera, J. Am.
Chem. Soc. 2015, 137, 14887-14904; d) J. R. Galán-Mascarós,
ChemElectroChem 2015, 2, 37-50; e) D. K. Bediako, A. M. Ullman, D. G.
Nocera, in Solar Energy for Fuels (Eds.: H. Tüysüz, C. K. Chan), Springer
International Publishing, Cham, 2016, pp. 173-213.
[6] a) X. Xu, F. Song, X. Hu, Nat. Chem. 2016, 7, 12324; b) S. Anantharaj, S.
R. Ede, K. Sakthikumar, K. Karthick, S. Mishra, S. Kundu, ACS Catal. 2016,
6, 8069-8097; c) B. C. M. Martindale and E. Reisner, Adv. Energy Mater.
2016, 6, 1502095.
[7] P. W. Menezes, A. Indra, C. Das, C. Walter, C. Göbel, V. Gutkin, D.
Schmeiβer, M. Driess, ACS Catal. 2017, 7, 103-109.
An alkaline water electrolyzer was constructed (two-
electrode configuration) using FeSe2/NF as both anode and
cathode (FeSe2║FeSe2) where the water-splitting reaction
initiated at a potential of 1.52 V and reached 1.73 V at a current
density of 10 mAcm-2 (Figure 4, S37). The potential acquired
here are very much in the range of highly aspiring water-splitting
catalysts[6b,26] and stability test showed that the electrodes are
very stable over a period of 24 hours (Figure 4 inset).
[8] R. Gao, H. Zhang, D. Yan, Nano Energy 2017, 31, 90-95.
[9] a) L. Chen, H. Zhan, X. Yang, Z. Sun, J. Zhang, D. Xu, C. Liang, M. Wu, J.
Fang, CrystEngComm 2010, 12, 4386-4391; b) L. Chen, X. Yang, X. Fu, C.
Wang, C. Liang, M. Wu, Eur. J. Inorg. Chem. 2011, 2098-2102; c) M.
Akhtar, M. A. Malik, J. Raftery, P. O'Brien, J. Mater. Chem. A 2014, 2,
20612-20620; d) P. W. Menezes, A. Indra, P. Littlewood, C. Göbel, R.
Schomäcker, M. Driess, ChemPlusChem 2016, 81, 370-377; e) K.
Samedov, Y. Aksu, and M. Driess, Chem. Mater. 2012, 24, 2078-2090; f) P.
W. Menezes, A. Indra, P. Littlewood, M. Schwarze, C. Go
Schomacker, M. Driess, ChemSusChem 2014, 7, 2202−2211; g) Y. Aksu,
M. Driess, Angew. Chem. Int. Ed. 2009, 48, 7778 – 7782.
̈bel, R.
̈
In conclusion, we have synthesized bioinspired molecular
2Fe-2Se compounds 2 and 3 analogous to 2Fe-2S clusters of
iron-sulphur proteins. Using 2 as low temperature molecular
precursor, FeSe2 can be produced that exhibits remarkable
catalytic activity towards both OER and HER with considerably
low overpotentials, exceedingly high current density and long-
term stability. Subsequently, insightful information on the nature
of active species, surface structural arrangement, and a
structure-activity relation in FeSe2 during OER and HER was
obtained. Finally, an overall water-splitting set-up was
constructed using a two-electrode cell, displaying low cell
voltage and remarkable durability. This is the first report on iron
selenide investigated for bifunctional OER, HER, and for overall
water-splitting catalysis
[10]a) H. Beinert, R. H. Holm, E. Münck, Science 1997, 277, 653-659; b) E. I.
Solomon, X. Xie, A. Dey, Chem. Soc. Rev. 2008, 37, 623-638.
[11] a) S. Yao, F. Meier, N. Lindenmaier, R. Rudolph, B. Blom, M. Adelhardt, J.
Sutter, S. Mebs, M. Haumann, K. Meyer, M. Kaupp, M. Driess, Angew.
Chem., Int. Ed. 2015, 54, 12506-12510; b) P. Venkateswara Rao, R. H.
Holm, Chem. Rev. 2004, 104, 527-560; c) H. Strasdeit, B. Krebs, G.
Henkel, Inorg. Chim. Acta 1984, 89, L11-L13; d) J. G. Reynolds, R. H.
Holm, Inorg. Chem. 1980, 19, 3257-3260; e) M. E. Reesbeck, M. M.
Rodriguez, W. W. Brennessel, B. Q. Mercado, D. Vinyard, P. L. Holland, J.
Biol. Inorg.Chem. 2015, 20, 875-883; f) R. H. Holm, W. Lo, Chem. Rev.
2016, 116, 13685-13713; g) L. Fohlmeister, K. R. Vignesh, F. Winter, B.
Moubaraki, G. Rajaraman, R. Pottgen, K. S. Murray, C. Jones, Dalt. Trans.
2015, 44, 1700-1708; h) J. Ballmann, A. Albers, S. Demeshko, S. Dechert,
E. Bill, E. Bothe, U. Ryde, F. Meyer, Angew. Chem., Int. Ed. 2008, 47,
9537-9541; i) A. Albers, S. Demeshko, K. Pröpper, S. Dechert, E. Bill, F.
Meyer, J. Am. Chem. Soc. 2013, 135, 1704-1707; j) A. Albers, S.
Demeshko, S. Dechert, E. Bill, E. Bothe, F. Meyer, Angew. Chem., Int. Ed.
2011, 50, 9191-9194.
[12] J. Meyer, J.-M. Moulis, J. Gaillard, M. Lutz, in Advances in Inorganic
Chemistry, Vol. Volume 38 (Ed.: C. Richard), Academic Press, 1992, pp.
73-115.
[13] C. Achim, E. L. Bominaar, J. Meyer, J. Peterson, E. Munck, J. Am. Chem.
Soc. 1999, 121, 3704-3714.
[14] B. G. Ganga, P. N. Santhosh, arXiv:1303.1381v1 2013.
Acknowledgements
[15] S. Tengner, Z. Anorg. Allg. Chem. 1938, 239, 126.
[16] S. S. Huang, Q. Q. He, W. L. Chen, Q. Q. Qiao, J. T. Zai, X. F. Qian,
Chem. Eur. J. 2015, 21, 4085-4091.
[17] J. S. Cho, J. S. Park, Y. C. Kang, Sci. Rep. 2016, 6, 38933.
We thank the Deutsche Forschungsgemeinschaft (UniCat; EXC
314-2) for financial support. C.P. gratefully acknowledges the
This article is protected by copyright. All rights reserved.

10.1002/anie.201706196
Angewandte Chemie International Edition
COMMUNICATION
[18] X. Chang, J. Jian, G. Cai, R. Wu, J. Li, Electr. Mater. Lett. 2016, 12, 237-
[23] a) X. Y. Chang, J. K. Jian, G. M. Cai, R. Wu, J. Li, Electron. Mater. Lett.
2016, 12, 237-242; b) Q. L. Zheng, X. Cheng, H. Y. Li, Catalysts 2015, 5,
1079-1091.
242.
[19] a) L. Trotochaud, S. L. Young, J. K. Ranney, S. W. Boettcher, J. Am.
Chem. Soc. 2014, 136, 6744-6753; b) L. C. C. Ferraz, W. M. Carvalho, D.
Criado, F. L. Souza, ACS Appl. Mater. Interfaces 2012, 4, 5515-5523.
[20] D. A. Salvatore, K. E. Dettelbach, R. H. Hudkins, P. B. Berlinguette, Sci.
Adv. 2015, 1, e1400215.
[24] P. Li, E. Y. Jiang, H. L. Bai, J. Phys. D: Appl. Phys. 2011, 44, 075003.
[25] P. W. Menezes, A. Indra, A. Bergmann, P. Chernev, C. Walter, H. Dau, P.
Strasser, M. Driess, J. Mater. Chem. A. 2016, 4, 10014-10022.
[26] a) Y. Yan, B. Y. Xia, B. Zhao, X. Wang, J. Mater. Chem. A. 2016, 4,
17587-17603; b) X. M. Li, X. G. Hao, A. Abudula, G. Q. Guan, J. Mater.
Chem. A. 2016, 4, 11973-12000.
[21] J.-X. Feng, S.-H. Ye, H. Xu, Y.-X. Tong, G.-R. Li, Adv. Mater. 2016, 28,
4698-4703.
[22] A. P. Grosvenor, B. A. Kobe, M. C. Biesinger, N. S. McIntyre, Sur. Inter.
Anal. 2004, 36, 1564-1574.
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Chakadola Panda, Prashanth W.
Menezes, Carsten Walter, Shenglai Yao,
Matthias E. Miehlich, Vitaly Gutkin,
Karsten Meyer and Matthias Driess*
Bridging the gap: For the first
time, a superiorly active iron
selenide electrocatalyst could be
prepared at low temperature
from
a
bioinspired 2Fe-2Se
Page No. – Page No.
molecular complex and applied
for bifunctional oxygen and
hydrogen evolution reactions as
well as for overall water-
splitting. The nature of active
sites and structure-activity
relationships were uncovered.
From Molecular 2Fe-2Se Precursor to
FeSe2 Acting as Highly Efficient
Electrocatalyst for Overall Water-
Splitting
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