Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals for High-Performance Electrocatalytic Overall Water-Splitting

Article abstract of DOI:10.1002/anie.201809787

The synthesis of structurally ordered non-noble intermetallic cobalt stannide (CoSn₂) nanocrystals and their utilization for high-performance electrocatalytic overall water-splitting is presented. The structurally and electronically beneficial properties of the tetragonal CoSn₂ exhibit a considerably low overpotential for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) on fluorine-doped tin oxide (FTO) and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation of Co under strongly alkaline conditions furnishes highly disordered amorphous active CoO_x(H), the catalytically active structure for OER. The Co⁰ atoms in the CoSn₂ act as active sites for HER and the presence of Sn provides efficient electrical conductivity. This intermetallic phase is a novel type of cost-effective and competitive bifunctional electrocatalysts and predestinated for overall water-splitting devices: A two-electrode electrolyzer with CoSn₂ on NF delivers a cell voltage of merely 1.55 V at 10 mA cm^?2 maintaining long-term stability.

Full text of DOI:10.1002/anie.201809787

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Accepted Article
Title: Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals
for High-Performance Electrocatalytic Overall Water-Splitting
Authors: Matthias Driess, Prashanth Menezes, Chakadola Panda,
Somenath Garai, Amandine Guiet, and Carsten Walter
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201809787
Angew. Chem. 10.1002/ange.201809787
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10.1002/anie.201809787
Angewandte Chemie International Edition
COMMUNICATION
Structurally Ordered Intermetallic Cobalt Stannide Nanocrystals
for High-Performance Electrocatalytic Overall Water-Splitting
Prashanth W. Menezes,[a]+* Chakadola Panda,[a]+ Somenath Garai,[a] Carsten Walter,[a] Amandine
Guiet,[b] and Matthias Driess[a]*
Abstract: The synthesis of structurally ordered non-noble
intermetallic cobalt stannide (CoSn2) nanocrystals and their
utilization for high-performance electrocatalytic overall water-splitting
in alkaline media is presented. The structurally and electronically
beneficial properties of the tetragonal CoSn2 exhibit a considerably
low overpotential for the oxygen evolution reaction (OER) and
hydrogen evolution reaction (HER) on fluorine-doped tin oxide (FTO)
and Ni foam (NF). Loss of Sn from the crystal lattices and oxidation
of Co under strongly alkaline conditions furnishes highly disordered
amorphous active CoOx(H) which is the catalytically active structure
for OER. On the other hand, the Co0 atoms in the CoSn2 act as
active sites for HER and the presence of Sn provides efficient
electrical conductivity. This intermetallic phase is a novel type of
cost-effective and competitive bifunctional electrocatalysts and
predestinated for overall water-splitting devices: A two-electrode
electrolyzer with CoSn2 on NF delivers a cell voltage of merely 1.55
V at 10 mAcm-2 maintaining long-term stability.
As a central part for a sustainable realization of renewable
energy conversion, the development of inexpensive materials for
technologies capable of electrochemical water-splitting into
hydrogen and oxygen in an economically viable way is highly
desired.[4] Currently, noble-metal-based materials (Pt, RuO2, and
IrO2) have been considered as the state-of-the-art
electrocatalysts for HER and OER; however, relatively high
costs and scarcity of the materials greatly stint their widespread
industrial applications.[5] Recently, high-performance bifunctional
OER and HER electrocatalysts based on non-noble transition
metal
oxides/hydroxides,[6]
carbonate/hydroxides,[7]
chalcogenides,[8] phosphides,[9] borides,[10] phosphates,[11] and
phosphite[12] functioning in a common electrolyte have been
designed. Nonetheless, their catalytic performances are still far
away from commercialization and therefore, extensive efforts
are required to further increase their activity and search for new
classes of suitable catalysts based on the non-noble metals. In
search of suitable bifunctional electrocatalysts for efficient
overall water-splitting, we investigated the enormously large
materials space of nanodimensional intermetallic phases
consisting of non-noble first-row and main-group metals with
distinct structural and electronic properties to attain significant
improvement of dual electrocatalytic performance along with
lasting stability. We discovered that intermetallic phases of Co
and Sn can act as highly competent electrocatalysts for overall
water-splitting with outstanding performance.
Intermetallic nanocrystals are considered to be an important
class of nanomaterials in the field of superconductivity,
ferromagnetism, thermoelectricity, shape-memory effects, and
catalysis owing to their intriguing chemical and physical
properties.[1] Recently, intermetallic compounds have gained
enormous attention in heterogeneous catalysis by virtue of their
unusual and attractive crystallographic and electronic
properties.[2] It has been shown that the extent of atomic
ordering and the relative concentration of both metals drastically
influence the overall reactivity efficiency. The recent
development of structurally ordered intermetallic materials based
on noble metals (Pt, Pd) and early transition-metals (Fe, Co, Ni)
have been successfully used for efficient oxygen reduction
reaction (ORR) and HER. Intermetallic compounds containing
non-noble metals (main group and transition-metals) have also
shown to be potential candidates for application in data storage,
magnetic materials, electronic and sensors to electrodes in
rechargeable batteries.[3] However, the geometric and electronic
influence of such materials for the energy conversion and
storage applications are still scarcely investigated.
Herein, we demonstrate a controllable synthesis of CoSn2
nanocrystals using a solution chemistry technique, which has
the potential of accessing more nanostructured complex
intermetallic materials. The CoSn2 nanocrystals provide
synergetic advantages of being cost-effective and superior
electrically conductive with sufficient density of active sites that
are a structural requirement in enhancing overall catalytic
activity. The electrocatalytic performances of CoSn2 achieved
here were notably higher than the precious metal-based
catalysts (RuO2, IrO2 and Pt) as well as single metallic Co and
Sn attained via the same method. As anticipated, CoSn2
underwent a complete structural transformation during OER
leading to structurally disordered amorphous active CoOx with
vacancies and defects by severe loss (leaching) of Sn from the
CoSn2 crystal lattices (Scheme 1). Conversely, only a slight
amount of Sn atoms was released without allowing much
structural reorganization during HER in strongly alkaline
conditions. Depending on the exceptional activity, an alkaline
electrolyzer using CoSn2 as cathode and anode material for
overall water-splitting was assembled, that demonstrated
considerable current density, notable cell potential, and high
stability. To the best of our knowledge, this is the first
intermetallic crystalline stannide that has been explored for OER,
HER and overall electrochemical water-splitting, and this work
specially provides a rational strategy to design new intermetallic
or alloy nanocrystals to boost bifunctional hydrogen and oxygen
evolution reaction catalysis towards technologically relevant
water-splitting devices.
[a]
Dr. P. W. Menezes, Dr. C. Panda, Dr. S. Garai, C. Walter, 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: prashanth.menezes@mailbox.tu-berlin.de,
matthias.driess@tu-berlin.de
[b]
[+]
Dr. A. Guiet
Université du Maine, CNRS UMR 6283, Institut des Molécules et
Matériaux du Mans (IMMM), Avenue Olivier Messiaen, 72085 Le
Mans Cedex 9, France
These authors have contributed equally
Supporting information for this article is given via a link at the end of
the document. ((Please delete this text if not appropriate))
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10.1002/anie.201809787
Angewandte Chemie International Edition
COMMUNICATION
three-dimensional network structure.[14] The as-synthesized
elemental Co crystallizes in the hexagonal close-packed system
(space group P63/mmc), while elemental Sn belongs to the
body-centered tetragonal lattice (space group I41/amd).
Interestingly, the structure of elemental Sn is highly anisotropic
and known to diffuse various metal atoms along its crystal axes
depending upon the diffusing rate of the metal (Scheme 1).[15]
Here, it is more likely a diffusion-based process that occurs
where Co and Sn are integrated simultaneously under the
reducing environment of the synthesis and the hexagonal Co
diffuses slowly into tetragonal Sn lattice by stabilizing the
formation of tetragonal CoSn2 phase.
Scheme 1. Unit cell structures of Co (orange), Sn (green) and CoSn2 (mixed
orange and green) and schematic representation of a structural modification of
CoSn2 during electrochemical OER and HER in strongly alkaline media.
The synthesis of intermetallic CoSn2 nanocrystals involved
a one-pot reduction of cobalt and tin salts using sodium
borohydride in the presence of polyethylene glycol (PEG) in
ethylene glycol (EG) at 170 °C (Supporting Information). The
powder X-ray diffraction (PXRD) analysis (Supporting
Information, Fig. S1) displayed reflections corresponding to
CoSn2 (JCPDS 25-256) affirming the phase-purity of the product.
Figure 1a and Figure S2a (Supporting Information) show the
morphological feature of the as-prepared CoSn2 by scanning
electron microscopy (SEM) with uniformly distributed network
type nanoparticles. The transmission electron microscopy (TEM)
and high-resolution (HR) TEM images exhibited very small
nanocrystalline particles of a diameter in the range of ~10 nm
that were assembled to form nanonets (Figure 1b). The lattice
spacing (Figure 1c) and the corresponding rings (Figure 1d) in
the selected area electron diffraction (SAED) pattern also
displayed characteristics of CoSn2 (Fig. 1d, Fig. S4, Supporting
Information). The presence of Co and Sn, as well as the
chemical composition, was additionally carried out by energy
dispersive X-ray (EDX) and inductively coupled plasma atomic
emission spectroscopic (ICP-AES) analysis (Figure S3 and
Table S1). The BET (Brunauer–Emmett–Teller (BET) surface
area of CoSn2 was found to be 24.2 m2g−1. The chemical states
of the elements and the composition was investigated by the X-
ray photoelectron spectroscopy (XPS) and the details of Co 2p
Sn 3d and O1s spectra are given in Figure S5-S6 (Supporting
Information). The single metallic Co (BET: 8 m2g−1) and Sn
(BET: 3.1 m2g−1) phases were also synthesized separately with
the same procedure from the respective metal salts and
thoroughly characterized (Supporting Information; Figs. S1-S2,
S7-S10 and Table S1) to establish a direct electrochemical and
structure-activity correlation with that of CoSn2.
Figure 1. (a) SEM, (b) TEM image exhibiting the net-type structure of
nanoparticles, (c) HR-TEM image displaying well-resolved lattice fringes with a
spacing of 0.25 nm indicative of (211) plane and, (d) The rings in the SAED
pattern also confirm the phase purity of the as-synthesized CoSn2.
For the electrocatalytic performance of CoSn2, Co and Sn
toward OER, the precatalysts were electrophoretically deposited
(EPD) on FTO and measured in aqueous 1 M KOH. Figure S11a
presents the polarization curves attained by the linear sweep
voltammetry (LSV) on blank FTO, CoSn2/FTO, Co/FTO, Sn/FTO,
RuO2/FTO, IrO2/FTO and Pt wire. Strikingly, CoSn2/FTO exhibits
high-performance OER with a low overpotential of 299 mV
whereas Co/FTO displayed overpotential of 368 mV to drive the
current density of 10 mAcm-2. As expected, Sn/FTO remained
inactive. Notably, CoSn2/FTO illustrated enhanced catalytic
activity in comparison to the state-of-the-art benchmark
RuO2/FTO (344 mV), IrO2/FTO (398 mV) and Pt electrocatalysts
and the performance achieved is one of the best compared to
other nonprecious-metal OER electrocatalysts on FTO
(Supporting Information, Table S2,).[4a,7,10,16] Figure S12 shows
an anodic peak at ~1.1 V prior to the onset of the OER,
suggesting the oxidation of Co to higher-valence states. The
redox peaks are virtually reversible, consistent with previously
reported Co based nanoparticles.[17] The corresponding Tafel
slopes displayed a value of 89 mVdec-1 for CoSn2/FTO, 135
mVdec-1 for Co/FTO, 128 mVdec-1 for RuO2/FTO and 151
mVdec-1 for IrO2/FTO and a smaller Tafel slope of CoSn2/FTO
indicates more favorable reaction kinetics in the OER process
(Supporting Information, Fig. S11c). The electrochemical
Perhaps, the most notable feature of CoSn2 is the crystal
structure but the classification of this material within the known
bonding concepts according to Zintl–Klemm, Hume-Rothery or
Laves is rather difficult and complicates the interpretation of the
nature of atomic interactions in CoSn2.[13] CoSn2 crystallizes in
the CuAl2 structure type and belongs to the tetragonal system
(space group I4/mcm; Co in 4a, Sn in 8h).[13] Taking into account
the heteroatomic Co−Sn interactions, the crystal structure
comprises of Co atoms surrounded by eight Sn atoms forming a
quadratic antiprism. Thus formed antiprisms are stacked along
the four-fold axis, possessing common edges by constructing a
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10.1002/anie.201809787
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stability of CoSn2/FTO and Co/FTO at a constant potential of
strongly alkaline medium.[20] Figure S17b depicts the Sn 3d
spectra of both after OER CA and HER CA showing two peaks
at the 3d5/2 and 3d3/2 attributed to the metallic state of Sn (Sn0)
and oxidized Sn2+ (SnO).[21] It should be noted that during OER
1.54 and 1.61
V Vs RHE were conducted. Figure S13
(Supporting Information) shows the chronoamperometric (CA)
curves over 14 hours with initial enhanced current density with a
fairly stable performance for CoSn2/FTO, while Co/FTO
displayed ~20% decrease in current.
CA,
a large amount of loss of Sn was observed with
simultaneous oxidation of the remaining Sn0.[21b] However, only a
minor amount of Sn leaching at the surface occurred during
HER (Supporting Information, Fig. S19; Tab. S4). The
deconvoluted O 1s XPS spectra of CoSn2 after electrochemical
OER CA and HER CA exhibited peaks corresponding to metal–
oxygen bonds in the metal oxide (CoOx), hydroxylation
(Co(OH)2/CoOOH) and adsorbed water molecules on the
materials (Supporting Information, Fig. S20).[19,22]
The electrocatalytic HER performance of CoSn2/FTO,
Co/FTO, and Sn/FTO was also measured similarly and
compared with that of RuO2/FTO, IrO2/FTO, and Pt wire. As
anticipated, the Pt wire showed the best HER activity and
reaches a current density of -10 mAcm-2 at an overpotential of 50
mV. The CoSn2/FTO exhibited the overpotential of merely 196
mV that is significantly lower than Co/FTO (428 mV) and
IrO2/FTO (437 mV). RuO2/FTO and Sn/FTO were found to be
barely active (Supporting Information, Fig. S11b). The resulted
HER activity of CoSn2/FTO was also superior to many prominent
first-row transition metal catalysts on FTO (Table S3, Supporting
Information).[4a,16b,16c,18] The corresponding Tafel slope
What is the role of Sn in the intermetallic CoSn2 precursor
catalyst with respect to the electrocatalytic OER and HER
activities? The post characterization of CoSn2 after OER clearly
showed that a large amount of Sn leached from the CoSn2
crystal lattices converting the precursor into a disordered,
(Supporting Information, Fig. S11d) of CoSn2/FTO is 78 mVdec-1, defected and vacant amorphous active material with
a
A
is slightly higher than Pt wire (42 mVdec-1) but clearly lower than
Co/FTO (95 mVdec-1), IrO2/FTO (235 mVdec-1) and RuO2/FTO
(276 mVdec-1) rendering favorable kinetics. In addition, the long-
term stability experiments revealed that the HER performance of
CoSn2/FTO was stable at a potential of -0.2 V vs RHE and at -
0.41 V, a slight deactivation of Co/FTO was attained (Supporting
Information, Fig. S14).
CoOx/CoOOH phase (with Co3+ centered active species).[23]
similar situation has recently been described for CoSn(OH)6 and
SnNiFe hydroxide perovskite.[23] The leaching and corrosion
process is likely to go on beyond the nanoparticle surface during
prolonged electrolysis and may completely transform CoSn2
structure into CoOx(H). The latter enables a stronger electronic
interaction and optimal adsorption of -O species (Oad), thus
facilitating the formation of adsorbed -OOH species (OOHad) via
nucleophilic attack, thereby promoting the deprotonation of
OOHad to produce O2. In stark contrast, during electrocatalytic
HER, only a slight loss of Sn from the surface occurs, exposing
the resulting Co0 to protons for adsorption and reduction to form
H2; a related mechanism has been reported for numerous
phosphide- and oxide-based materials.[24] The retained metallic
CoSn2 core assists the transport of electrons throughout the bulk
material thereby making CoSn2 a superior HER catalyst. The
fate of single metallic Co after the applied electrochemical OER
and HER conditions was also investigated by means of
microscopic and spectroscopic techniques. HR-TEM confirmed
the changes on the surface through CoCoOx oxidation and the
presence of a crystalline core under OER conditions. Similar to
CoSn2, the single metallic Co is unchanged under strongly
alkaline HER conditions apart from minor surface passivation.
The deconvoluted Co 2p and O 1s XPS studies further
substantiated the results obtained from TEM. The detailed
description of TEM, HR-TEM, SAED, EDX and XPS analysis are
given in Figure S21-S24.
After the successful electrocatalytic testing of CoSn2/FTO,
we were encouraged to investigate the electrochemical OER
and HER activity of CoSn2 on NF electrode which is well-known
for its 3D porous structure, higher surface area, and electrical
conductivity.[25] The OER and HER activities of the CoSn2/NF,
Co/NF, and Sn/NF were measured exactly similar to that of FTO
along with RuO2/NF, IrO2/NF, and Pt wire (Figure 2a and 2b). In
the reaction of OER, as low as 230 mV of overpotential resulted
for CoSn2/NF at a current density of 10 mAcm-2, which was
remarkably lower than that of Co/NF (283 mV), Sn/NF (396 mV)
and commercial benchmark RuO2/NF (278 mV) and IrO2/NF
(298 mV) catalysts (Supporting Information, Fig. S25 and Table
S2). The CA studies also evidenced the superior stability of
As discussed previously, the behavior of structurally
ordered intermetallic materials with complex bonding situations
and unique electronic structure under strongly alkaline OER and
HER conditions, and the subsequent associated reaction
processes to uncover the active species that are responsible for
intrinsic electrochemical activity was one of the prime goals of
the present work. Hence, we investigated CoSn2/FTO and
Co/FTO systematically by all possible analytical, microscopic
and spectroscopic techniques. The first clue on the modifications
on the surface of CoSn2 was obtained by the redox process
occurring just prior to OER suggesting that the oxidation of Co to
its higher valence state that could be instantly correlated to the
formation of CoOx(H) phase of cobalt.[19] The TEM and HR-TEM
images conducted on the surface of the thin films of CoSn2 after
the OER CA clearly showed loss of Sn transforming
nanoparticles into an amorphous structure that was also
apparent from the SAED pattern of the catalyst (Supporting
Information, Fig. S15; Table S4). The ICP-AES analysis
evidenced the considerable amount of Sn leaching into the
electrolyte under OER conditions and the concomitant
appearance of oxygen in the EDX pattern also formulated the
formation of the amorphous CoOx(H). On the other hand, TEM
and SAED of the thin films of CoSn2 after HER CA confirmed
only a slight corrosion of Sn (as seen by ICP) accompanied by
surface oxidation (Supporting Information, Fig. S16; Table S4).
More details on the surface of the catalysts were attained by
XPS spectroscopy. The Co 2p XPS spectra of CoSn2 after OER
CA indicated the rise in the overall oxidation state of Co0/2+ to
Co3+(Figs. S17a and S18, Supporting Information).[20] This
evidence major changes in the near-surface region during OER
CA forming
a CoOx(H) phase. On the contrary, peaks
corresponding largely to Co2+ were attained suggesting the
surface structure was also affected by HER conditions in the
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10.1002/anie.201809787
Angewandte Chemie International Edition
COMMUNICATION
CoSn2/NF while the stability of Co/NF and Sn/NF dropped
Based on the above results on NF, we further fabricated an
alkaline water electrolyzer with its anode and cathode prepared
by CoSn2/NF║CoSn2/NF which was then compared with
Co/NF║Co/NF and Sn/NF║Sn/NF (Supporting Information, Fig.
S32). Figure 2c shows the LSV of water electrolysis in aqueous
largely over 14
h (Supporting Information, Fig. S26). A
significant enhancement in the catalytic activity was also
observed when CoSn2/NF was treated for the reaction of HER. A
merely 103 mV of overpotential was achieved for CoSn2/NF at a
current density of -10 mAcm-2 (Supporting Information, Fig. S27). 1 M KOH. The CoSn2/NF electrodes displayed exceptional
At a similar current density, Co/NF attains an overpotential of
179 mV but unexpectedly overpotential of only 141 mV was
obtained for Sn/NF. It seems that under a strongly alkaline
media at highly reductive potentials, the NF most likely forms a
hybrid adduct of Sn that enormously contributes to the resultant
reactivity and such phenomena have been already established
for Ni-LDH and Ni(OH)2 type materials.[26] The electrocatalytic
active surface area (ECSA) was deduced from the Cdl values
that converted into ECSA using the specific capacitance value
(Supporting Information, Fig. S28). The calculated active ECSA
of CoSn2 was 1.88 cm2 which was higher than Co and Sn
indicating a greater number of exposed active sites. The ECSA
normalized current density plot has been shown in Figure S29
(Supporting Information).[27] The Nyquist plots obtained from
electrochemical impedance spectroscopy (EIS) displayed a
small charge transfer resistance (Rct) for CoSn2 compared to Co
and Sn that signified faster charge transport to exhibit higher
activity, reaching a water-splitting current density of 10 mAcm-2
by applying a bias of just 1.55 V that is marginally lower than
Co/NF (1.56 V) and Sn/NF (1.58 V,) and the values ascribed
here are superior to most of the other reported bifunctional
electrocatalysts.[28] Moreover, to evaluate the limiting electrodes
for overall water-splitting, the experiments on variation of CoSn2
anode with Co or Sn cathode (and vice versa) were conducted
displaying excellent activity only when bifunctional CoSn2
electrodes were used as both anode and cathode (Supporting
Information, Fig. S33). The bare NF and NF under EPD
condition (without catalyst) were also measured to rule out the
possible influence of Ni in NF (Supporting Information, Fig. S34).
To compare the electrochemical stability of CoSn2/NF with that
of Co/NF, Sn/NF and bare NF, CA experiments were conducted
at fixed potentials to deliver a current density of 10 mAcm-2 that
showed CoSn2/NF (Faradaic efficiency ~100%; see Supporting
Information) was highly stable over a period of 16 h in contrast
catalytic activity (Supporting Information, Fig. S30). Furthermore, to Co/NF, Sn/NF and bare NF (lost their activity within a few
RuO2/NF (231 mV) and IrO2/NF (211 mV) were also found to be
active for HER but with much lower activity compared to
CoSn2/NF. The CA produced greater stability curves for all
CoSn2/NF and Co/NF and Co/NF (Supporting Information, Fig.
S31). Most interestingly, the described overpotentials for the half
reactions of OER and HER of CoSn2/NF were found to be highly
competent with the presently best active first-row transition
metal phosphide/chalcogenide/oxide-based materials in alkaline
conditions making it one of the versatile catalysts for water-
splitting (Supporting Information, Table S2-S3).[6-7,10-11,16,18]
hours of operation, Fig. 2d). Additionally, a CA experiment was
performed at an applied potential of 1.75 V by maintaining the
current of 100 mAcm-2 (Supporting Information, Fig. S35), where
CoSn2/NF was exceptionally stable for at least over 100 h.
Further, the remnant of Sn with respect to Co after water
electrolysis was measured by ICP-AES analysis (Supporting
Information, Fig. S36). An inverted electrochemical cell
(graduated) was constructed to collect the evolved H2 and O2
separately at atmospheric pressure and their ratios (~2:1) were
quantified (Supporting Information, Figs. S37-S38).
In summary, we have demonstrated that atomically ordered
intermetallic
CoSn2
acts
as
versatile
bifunctional
electro(pre)catalyst for OER, HER and overall water-splitting
with excellent activity and long-term stability in strongly alkaline
media for the first time. Its higher catalytic performance and
long-term stability in comparison to the single metallic Co and
Sn components is explained by the co-existence of Co (as
catalytically active center) and Sn (superior electrical conductor).
The massive loss of Sn and oxidation of Co during OER
transforms the crystalline CoSn2 into a highly disordered, and
vacancy induced amorphous CoOx(H) material as an active
phase that facilitates O2 evolution. However, relatively minimal
structural reorganization and loss of Sn occurs under HER
conditions. Finally, we ambitiously designed the alkaline water-
splitting device leading to highly efficient, functional and stable
electrodes with low overpotentials. Our approach to bifunctional
electrocatalysts with tunable properties using intermetallic
materials may open new avenues for electrocatalytic
applications beyond water-splitting.
Figure 2. LSV’s of (a) OER (a) and (b) HER of CoSn2 to that of Co, Sn and
other commercial noble metal-based catalysts deposited on NF in aqueous 1
M KOH solution with a sweep rate of 1 mVs-1. (c) LSV curves of water
electrolysis for CoSn2∥CoSn2, Co∥Co, and Sn∥Sn on NF as anode and
cathode in a two-electrode cell and (d) stability of corresponding electrolysis at
a potential of 1.55, 1.56, 1.58 and 1.8 V, for CoSn2, Co, Sn and NF,
respectively. The inset in (d) is the schematic view of a water electrolyzer.
Experimental Section
The detailed synthetic procedure, characterisation and electrocatalytic
applications can be obtained in the Supporting Information.
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10.1002/anie.201809787
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COMMUNICATION
[13] M. Armbruster, W. Schnelle, R. Cardoso-Gil, Y. Grin, Chem. Eur. J. 2010,
16, 10357-10365.
Acknowledgements
[14] M. Armbruster, M. Schmidt, R. Cardoso-Gil, H. Borrmann, Y. Grin, Z.
Krist.-New Cryst. Struct. 2007, 222, 83-84.
Financial support by the Deutsche Forschungsgemeinschaft
(UniCat, EXC 314-2) is gratefully acknowledged. The authors
are also indebted to Dr. Vitaly Gutkin (HU Jerusalem, Israel) and
Dr. Johannes Schmidt for XPS, Mr. Christoph Fahrenson for
SEM and Caren Göbel (TU Berlin) for TEM measurements.
[15] N. H. Chou, R. E. Schaak, J. Am. Chem. Soc. 2007, 129, 7339-7345.
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Keywords: renewable energy • intermetallic • cobalt stannide •
oxygen and hydrogen evolution • water-splitting electrocatalyst
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10.1002/anie.201809787
Angewandte Chemie International Edition
COMMUNICATION
COMMUNICATION
When Two Become One: The
first tetragonal intermetallic cobalt
stannide electrocatalyst produced
through diffusion of Co and Sn
acts as a superiorly active material
for the electrocatalytic oxygen
evolution and hydrogen evolution
reaction as well as for overall
water-splitting in strongly alkaline
Prashanth W. Menezes,* Chakadola
Panda, Somenath Garai, Carsten
Walter, Amandine Guiet, and
Matthias Driess*
Page No. – Page No.
Structurally Ordered Intermetallic
Cobalt Stannide Nanocrystals for
High-Performance Electrocatalytic
Overall Water-Splitting
media.
The
self-supporting
structural and electronic factors of
Co and Sn enable enhanced net
catalytic activities and long-lasting
stability.
This article is protected by copyright. All rights reserved.