Evaluating DNA Derived and Hydrothermally Aided Cobalt Selenide Catalysts for Electrocatalytic Water Oxidation

Article abstract of DOI:10.1021/acs.inorgchem.9b00354

Electrocatalysts with engaging oxygen evolution reaction (OER) activity with lesser overpotentials are highly desired to have increased cell efficiency. In this work, cobalt selenide catalysts were prepared utilizing both wet-chemical route (CoSe and CoSe-DNA) and hydrothermal route (Co_0.85Se-hyd). In wet-chemical route, cobalt selenide is prepared with DNA (CoSe-DNA) and without DNA (CoSe). The morphological results in the wet-chemical route had given a clear picture that, with the assistance of DNA, cobalt selenide had formed as nanochains with particle size below 5 nm, while it agglomerated in the absence of DNA. The morphology was nano networks in the hydrothermally assisted synthesis. These catalysts were analyzed for OER activity in 1 M KOH. The overpotentials required at a current density of 10 mA cm^-2 were 352, 382, and 383 mV for Co_0.85Se-hyd, CoSe, and CoSe-DNA catalysts, respectively. The Tafel slope value was lowest for Co_0.85Se-hyd (65 mV/dec) compared to CoSe-DNA (71 mV/dec) and CoSe (80 mV/dec). The chronoamperometry test was studied for 24 h at a potential of 394 mV for Co_0.85Se-hyd and was found to be stable with a smaller decrease in activity. From the OER study, it is clear that Co_0.85Se was found to be superior to others. This kind of related study can be useful to design the catalyst with increased efficiency by varying the method of preparation.

Full text of DOI:10.1021/acs.inorgchem.9b00354

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Evaluating DNA Derived and Hydrothermally Aided Cobalt Selenide
Catalysts for Electrocatalytic Water Oxidation
Kannimuthu Karthick,†,‡ Sathya Narayanan Jagadeesan,§ Piyush Kumar,§ Swathi Patchaiammal,§
and Subrata Kundu*,†,‡
†Academy of Scientific and Innovative Research (AcSIR), CSIR-Central Electrochemical Research Institute (CSIR-CECRI)
Campus, New Delhi, India
‡CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630003, Tamil Nadu, India
§Centre for Education (CFE), CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi-630003, Tamil Nadu, India
S
* Supporting Information
ABSTRACT: Electrocatalysts with engaging oxygen evolu-
tion reaction (OER) activity with lesser overpotentials are
highly desired to have increased cell efficiency. In this work,
cobalt selenide catalysts were prepared utilizing both wet-
chemical route (CoSe and CoSe-DNA) and hydrothermal
route (Co0.85Se-hyd). In wet-chemical route, cobalt selenide is
prepared with DNA (CoSe-DNA) and without DNA (CoSe).
The morphological results in the wet-chemical route had
given a clear picture that, with the assistance of DNA, cobalt
selenide had formed as nanochains with particle size below 5
nm, while it agglomerated in the absence of DNA. The
morphology was nano networks in the hydrothermally assisted
synthesis. These catalysts were analyzed for OER activity in 1 M KOH. The overpotentials required at a current density of 10
mA cm−2 were 352, 382, and 383 mV for Co0.85Se-hyd, CoSe, and CoSe-DNA catalysts, respectively. The Tafel slope value was
lowest for Co0.85Se-hyd (65 mV/dec) compared to CoSe-DNA (71 mV/dec) and CoSe (80 mV/dec). The
chronoamperometry test was studied for 24 h at a potential of 394 mV for Co0.85Se-hyd and was found to be stable with a
smaller decrease in activity. From the OER study, it is clear that Co0.85Se was found to be superior to others. This kind of related
study can be useful to design the catalyst with increased efficiency by varying the method of preparation.
Therefore, finding earth abundant based catalysts with better
activity and superior stability for long-term application with
continuous production remains a challenge till date.3
INTRODUCTION
■
The usage of fossil fuels with the increased demands for
harvesting energy has made catastrophic changes to the climate
and affected the environment much. To overcome this issue,
hydrogen is triggered to be a “future fuel” and currently
produced to the maximum by steam reforming of fossil fuels.1,2
For the greener production of energy, renewable energy
sources assisting hydrogen production is desired in large scale
to exclude the carbon emitting fuels to the environment.3 With
the electrolysis of water, hydrogen can be produced with ease
but lacks in the commercial scale due to the complex OER at
the anode.4,5 In electrolysis of water, the OER with four proton
and electron coupled reactions drag more overpotential to
drive the reaction.6 In HER, it involves electrochemical
adsorption of hydrogen ions and is followed by chemical or
electrochemical desorption of a hydrogen molecule from the
electrode surface.7 Finding a catalyst with increased efficiency
in OER is a bottleneck to the development of water
electrolysis. So far, IrO2 and RuO2 have been investigated as
better catalysts for OER, but fading of catalysts such as IrO3
and RuO4 to the electrolyte for long-term usage restricts its
commercial application, in addition to the material cost.8,9
The transition metals based catalysts have recently attracted
the researchers for their enhanced activity, notably, in alkaline
medium.10−14 Transition metals as oxides have been studied a
lot, and recently, chalcogenides have showed tremendous
activity with respect to the changes in stoichiometry.15−17 Also,
the effect of oxy-hydroxides and oxides of Co and Fe as
CoOOH, FeOOH, and CoFe2O4 are studied for OER.18−21 In
chalcogenides, among sulfides and selenides, selenides are
highly active for both OER and HER, respectively.22−24
Careful literature survey suggests that the selenides were
combined with Co, Ni, and Fe and studied as single and mixed
metallic selenides for enriched activity and stability.25−42
Recently, cobalt-based selenides were studied with different
stoichiometric ratios such as Co7Se8 and Co0.85Se and also with
other metals like Ni and Fe as CoOx-CoSe, Co1−xFexSe2, and
Ni0.33Co0.67Se2, respectively, for enriched water oxidation
Received: February 6, 2019
© XXXX American Chemical Society
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applications with better results.25−42 These kinds of transition
metals based catalysts had delivered superior stability in
alkaline medium.43,44 In addition to this, there are also reports
highlighted the formation of Ni, Fe and Cu based selenides
prepared in different experimental conditions for both
electrocatalytic OER and HER applications in different
media.37,42,45
was nano networks in the hydrothermally assisted formation of
Co0.85Se-hyd. These catalysts were analyzed for OER activity in
1 M KOH to prove their potentiality. The overpotentials
required at a current density of 10 mA cm−2 were 352, 382,
and 383 mV for Co0.85Se-hyd, CoSe, and CoSe-DNA catalysts,
respectively. Presence of phosphate groups in DNA enhanced
the activity of the CoSe catalyst, specifically at higher
overpotentials during OER. The Tafel slope value was lowest
for Co0.85Se-hyd (65 mV/dec) compared to CoSe-DNA (71
mV/dec) and CoSe (80 mV/dec), respectively, that showed
that the charge transfer kinetics was facile in Co0.85Se-hyd. The
potentiostatic analysis further confirmed that Co0.85Se-hyd,
CoSe-DNA, and CoSe were stable, with a minimal decrease in
activity for 24 h. The combined study clearly reveals that
Co0.85Se-hyd showed better activity and stability compared to
the others.
With different methods of synthesis of cobalt selenide
catalysts, namely, hydrothermal, electrodeposition, and wet
chemical synthesis, the wet-chemical route is easy to prepare
within a short span of time. The utilization of bioscaffolds like
DNA in the synthesis of cobalt selenide catalysts was not
explored yet. DNA with the aromatic base pairs and A−T and
G−C pairing give a perfect assembly to anchor the metal-based
nanoparticles (NPs) over the surface of DNA.46,47 This kind of
report has already been well explored. From the previous
literature survey, it has been found that DNA with negative
charges along with nucleobases provides a great platform for
anchoring positive metal ions via a simple electrostatic
interaction.48 From the DNA-templated synthesis, it is the
interaction of positive metal ions with the polyanionic
backbone of DNA is the initial step. Therefore, it is possible
to design different inorganic materials by adding reducing
agents or others to this assembly. Based on this, there are
different reports highlighting the DNA-assisted formation of
metal NPs by chemical reduction, photoreduction, and
electrodeposition methods.48 Different sources of DNA can
be exploited for the formation of inorganic materials by fine-
tuning the concentration of DNA.48 Recently, sulfides of Co
and Ni have also been prepared with the assistance of DNA
and applied in OER studies. The use of DNA assists the
anchoring of Co2+ over the DNA assembly and forms as
sulfides of CoS and NiS over DNA.22,49 The use of DNA has
been reported as a binder and as scaffold from earlier studies.22
In general, the presence of phosphate moieties are found to
enhance the OER kinetics, as observed from the literature
studies.50,51 In CoS-DNA work also, the presence of
phosphates with high concentration of DNA ensured better
activity at higher anodic overpotentials. At lower over-
potentials, CoS-DNA with a lower concentration of DNA
(0.036 M) showed better activity, and at higher overpotentials,
the CoS-DNA with high concentration (0.084 M) out-
performed it. This gives a clue that with a high concentration
of DNA with phosphates, at higher overpotentials, the activity
may be enhanced.22 Here, the presence of phosphate groups
from DNA could also tend to synergistically enhance the
electron transfer kinetics at the interface. Previously, metal-
based NPs have successfully anchored over the DNA by our
group.22,52 Hence, use of DNA in the synthesis of cobalt
selenide based catalysts will be interesting and also will tend to
improvise the activity at higher overpotentials in OER.
EXPERIMENTAL SECTION
■
Synthesis of CoSe-DNA, CoSe, and Co0.85Se-hyd. To prepare
CoSe-DNA, 0.13 g of selenium is added to the solution of H2O that
contains 0.048 M of DNA. Simultaneously, 0.25 g of NaBH4 is added
and stirred vigorously to form a clear solution of NaHSe in DNA.
Once the colorless solution is formed, 0.54 g of CoAc2 is added to the
solution, and immediately, the solution turns dark black, inferring the
nucleation of CoSe over DNA. The stirring continued for 30 min to
ensure complete formation of CoSe, and the settled CoSe is washed
with DI water several times to exclude sodium ions and was dried in
the oven for 60 °C for 12 h.
From Scheme 1, we can see that, at first, when Co2+ ions are added
to the DNA, there is a binding of Co2+ ions that occur by means of
Scheme 1. Schematic Representation of Anchoring of Co2+
Ions over DNA and Subsequent Formation of CoSe-DNA
electrostatic interactions with negative base pairs and nucleobases
present in DNA. After forming an assembly of Co2+-DNA by simple
stirring, the subsequent addition of NaHSe resulted in the formation
of CoSe-DNA nanochains. This kind of related study is well observed
by us and others previously.22,46,47,49,52 Following a similar strategy,
only CoSe is prepared, excluding the addition of DNA. For Co0.85Se-
hyd, 0.54 g of CoAc2 is added to the solution of ascorbic acid (1.4 g)
in 30 mL of H2O. The whole solution is added to 0.13 g of selenium
and 0.25 g of NaBH4 in 50 mL of H2O and kept in an autoclave at
200 °C for 24 h. After this, the collected Co0.85Se-hyd was washed
with DI water several times and it is dried in the oven for 60 °C for 12
h. The reagents used during the synthesis, the sample preparation
techniques for different characterizations, and details about the
instrument specifications for electrochemical studies have been
provided in the Supporting Information (SI).
Electrochemical Characterizations. The prepared CoSe-DNA,
CoSe, and Co0.85Se-hyd catalysts were subjected for electrocatalytic
OER studies in 1 M KOH. The working electrodes for electrocatalytic
studies prepared using 3 mg samples with H2O, nafion, and ethanol
were taken in a ratio (7.5:2:0.5) and sonicated to form a slurry
solution and are coated on a carbon fiber cloth (CC) substrate that
In this present work, the comparative OER study on the
cobalt selenide catalysts prepared in both wet-chemical and
hydrothermal conditions were analyzed. Moreover, the
influence of DNA as a scaffold and synergetic enhancement
in OER activity has also been observed at higher overpotentials
compared to only CoSe prepared in the wet-chemical route,
which was in accordance with the previous report on the DNA-
based CoS catalysts.22 The morphology was varied with
respect to the method adopted for the synthesis of cobalt
selenides. With the assistance of DNA, cobalt selenide had
formed as nanochains with a particle size below 5 nm and
agglomerated when prepared without DNA. The morphology
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Figure 1. (a) X-ray diffraction pattern of CoSe-DNA and (b) the XRD pattern of CoSe-hyd.
had dimensions of 4 × 0.5 cm and dried at 60 °C for 2 h. An Hg/
HgO reference electrode, Pt counter electrode, and cobalt selenide
working electrodes were used in 1 M KOH, and the corresponding
loading of the catalyst is 0.205 mg cm−2. Polarization curves were
acquired at a sweep rate of 5 mV s−1 and 100% iR compensation were
done manually from the Rs, as observed from EIS. To ensure the
stability of the as-prepared catalyst, continuous potentiostatic
electrolysis was done at a potential of 394 mV for 24 h and also by
accelerated degradation (AD) studies at a very high sweep rate of 200
mV s−1 for 500 cycles in 1 M KOH. The electrochemical impedance
spectroscopic (EIS) analysis was carried out in the frequency range of
1 Hz to 100 kHz with an amplitude potential of 0.05 V. The potential
scale of all the observed electrochemical results were converted into
reversible hydrogen electrode scale (RHE) following earlier literature
reports.53
RESULTS AND DISCUSSION
■
Figure 2. (a−c) Low and high magnified TEM images of CoSe-DNA;
(d) HRTEM image at high magnification; (e) HRTEM image with
lattice fringes; and (f) SAED pattern.
Characterization of CoSe-DNA and Co0.85Se-hyd
Catalysts. Various advanced characterization tools were
used to analyze the confirmation of the samples prepared.
Figure 1 showed the X-ray diffraction analysis for both
CoSe-DNA and Co0.85Se-hyd. Figure 1a shows no character-
istic information since there is no identifiable peak observed.
This gives information that the DNA-aided formation of CoSe
can be either amorphous in nature or the particle size would be
too small to diffract the incident X-ray beam. From Figure 1b,
which is for Co0.85Se-hyd, shows three humps at 33.3, 44.7, and
51.6° that exactly matched with Co0.85Se with ICDD No. 00-
052-1008.29
Likewise, XRD pattern of only CoSe that was prepared in
the wet-chemical route, showed a peak near 37.5° that
matched with CoSe in accordance with the ICDD No. 00-
015-0464 (shown in Figure S1 in the SI). After this, to have
information on the morphology, transmission electron
microscopy (TEM) was carried out and shown here as Figure
2 for CoSe-DNA and as Figure 3 for Co0.85Se-hyd. From
Figure 2a−c, the DNA with a chain-like structure can be seen
with increasing magnification and CoSe NPs decorated over it
with the size around 5 nm. Similar kinds of DNA-based metal
NPs and metal sulfides were prepared earlier from our
group.22,48 Figure 2d is the high resolution transmission
electron microscopy image that showed clear assembly of CoSe
NPs decorated over the surface of DNA chain. Figure 2e is the
lattice fringes observed at higher magnifications and from the
d-spacing, plane was observed to be (002) that was related to
the JCPDS file No. 01-089-2004 as seen from the inset of the
Figure 3. (a−d) Low and high magnified TEM images of Co0.85Se-
hyd and (e) the corresponding SAED pattern.
figure. The selected area diffraction (SAED) from Figure 2f
shows diffused ring pattern as the particle size is too small to
diffract the electron beam. The plane corresponding to CoSe
has been calculated from the radius of ring that was compared
with the JCPDS file No. 01-089-2004. From the micro-
structural study, it is clear that the formed CoSe has grown
over the DNA chain and the size was below 5 nm.22 Similarly,
for Co0.85Se-hyd, TEM images were analyzed, and from Figure
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3a−d, we can see low and high magnified images of Co0.85Se.
They show agglomerated particles with a size varying around
20 nm and has formed as nanonetworks with particles being
agglomerated. The SAED pattern shows polycrystalline nature
(Figure 3e).
presence of a heteroatom N from base pairs of DNA. Similarly,
from Figure 5e, P 2p is present as P 2p3/2 and P 2p1/2, further
confirming the components of DNA in CoSe. C 1s from Figure
5f showed peaks for C−O, C−OH, and C−C bonds from
DNA at different binding energies. These results clearly
confirm the presence of DNA along with CoSe and forms
assembly of CoSe-DNA.22 Similarly, for Co0.85Se-hyd also, XPS
analysis was performed and is provided as Figure S3 in the SI.
Figure S3a, which is for the Co 2p high resolution spectrum,
shows peaks for 780.5 and 796.3 eV, which are for Co 2p3/2
and Co 2p1/2, respectively, along with characteristic satellite
peaks.29 For the Se 3p high resolution spectrum (Figure S3a),
peaks observed for 164.4 and 170.2 eV confirmed the presence
of selenium with surface oxides. For the O 1s spectrum (Figure
S3c), it showed peaks for H2O, OH, and SeO2 functionalities
at binding energy values of 530.3, 531.1, and 534.5 eV,
respectively. These results together confirm the formation of
CoSe catalysts prepared at different conditions with concurrent
observation.
For comparison, TEM images of only CoSe prepared in wet-
chemical route have been provided as Figure S2 in the SI.
From the images of Figure S2a−d, it is clear that the formed
CoSe NPs get agglomerated and formed as nanoburls. The
SAED pattern observed was diffused ring pattern similar to
that of CoSe-DNA (Figure S2e). From these micrographs, it is
proved that with the absence of DNA, CoSe formed is
agglomerated whereas in the presence of DNA, it is assembled
over the surface of DNA to form nanochain assemblies of
CoSe-DNA. The comparative microstructural analysis revealed
that, with the method of preparation, the resulting morphology
was also varied, and particularly, in the wet-chemical route,
DNA has exclusively formed chain-like morphology and,
without DNA, it is agglomerated.
To further ascertain the presence of DNA along with CoSe
in CoSe-DNA, high angle annular dark field (HAADF)
mapping was carried out in the HR-TEM mode and is given
here as Figure 4. From Figure 4a, the image clearly shows the
Electrocatalytic Water Oxidation Studies of CoSe-
DNA, CoSe, and Co0.85Se-hyd Catalysts. The electro-
catalytic water oxidation studies were carried out in a
conventional three electrode system in 1 M KOH where
cobalt selenide was used as a working electrode, Hg/HgO as
reference, and Pt as counter electrodes.
The LSV curves were iR corrected 100% manually and have
been shown here as Figure 6. The LSV curves from Figure 6a
show that for attaining a current density of 10 mA cm−2,
Co0.85Se-hyd had required an overpotential of 354 mV, while
CoSe-DNA and only CoSe had required 382 and 383 mV,
respectively. A closer look at the figure shows that, at higher
overpotentials, the activity of CoSe-DNA was enhanced much
due to the presence of phosphate groups from DNA that could
synergistically enhance the OER performance, similar to the
previous reports.22 The Tafel slopes (Figure 6b) extracted
from the LSV curves were lowest for Co0.85Se-hyd that shows
65 mV/dec, while CoSe-DNA and CoSe show 71 and 80 mV/
dec, respectively. From LSV and Tafel slopes, it has been
observed that the OER activity was superior in the case of
Co0.85Se-hyd, however, at higher overpotentials, the activity of
CoSe-DNA was enhanced, indicating the influence of DNA in
the CoSe catalyst. The accelerated degradation (AD) study
was carried out at a high scan rate of 200 mV/s for 500 cycles
in all three catalysts, and the LSV curves acquired after AD test
have been given here as Figure 6c. The increase in
overpotentials at a same current density of 10 mA cm−2 was
62, 50, and 39 for CoSe-DNA, CoSe, and Co0.85Se-hyd. This
shows the better stability of the prepared catalysts even at
higher scan rates for more cycles. These kinds of selenium-
based catalysts were reported earlier and showed promising
stability.43,44 Hence, from the AD test it is clear that the
stability was comparatively high, even at such a rapid scan rate
of 200 mV/s. Moreover, as an important tool to test the real-
time stability of a catalyst, potentiostatic analysis was carried
out for all three catalysts for 24 h and were found to be stable,
with very less degradation in activity from a current density of
10 mA cm−2 (Figure 6d). In addition to this, electrochemical
impedance study was carried out at an overpotential of 424 mV
and is provided as Figure S4. In general, at higher
overpotentials, the electron transfer rate will be too fast and
therefore the observed Rct changes will be less. Here, the
charge transfer resistance values as can be seen from the image
were in between 8 and 12 Ω (Figure S4a) in all the cases that
Figure 4. (a) Area taken for HAADF mapping and (b−f) the
mapping of Co, Se, N, P, and O (K shells), respectively.
CoSe-DNA nanochains where HAADF mapping was carried
out. From Figure 4b−f, the presence of Co, Se, N, P, and O K
shells further ascertain the CoSe-DNA assemblies.22 From
these analyses it is clear that CoSe is assembled over DNA to
form CoSe-DNA nanochains. After the morphological studies,
the chemical nature of both CoSe-DNA and Co0.85Se-hyd were
analyzed by X-ray photoelectron spectroscopy (XPS). The
XPS study of CoSe-DNA has been provided here as Figure 5.
From Figure 5a, which is for a Co 2p high resolution spectrum,
two characteristic peaks are shown that are due to the spin−
orbit coupling and observed as Co 2p3/2 and Co 2p1/2
,
respectively. It shows peaks at 781 and 796.2 eV that
corresponded to the +2 oxidation state of Co from CoSe-
DNA.44 The peaks arrived at the higher binding energy values,
which were the respective satellite peaks of the same. Similarly,
for Se 3d high resolution spectrum (Figure 5b), Se 3d5/2 and
Se 3d3/2 were observed at binding energy values of 54.4 and
57.6 eV, respectively. The O 1s spectrum (Figure 5c) shows
two peaks at binding energy values of 530.1 and 533.2 eV that
correspond to the moisture and some oxides of Se over the
surface.44 Figure 5d is for N 1s that is observed from the
D
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Figure 5. (a) Co 2p high resolution spectra; (b) high resolution spectra of Se 3d; and (c) O 1s, (d) N 1s, (e) P 2p, and (f) C 1s high resolution
spectra, respectively.
showed the increased activity of CoSe catalysts at a high
anodic potential. After the AD test also, the Rct values were in
the range of 12−20 Ω (Figure S4b) for CoSe-DNA, CoSe, and
Co0.85Se-hyd catalysts, respectively. From an EIS study, it is
clear that Co0.85Se was found to be superior to the other two
catalysts. Moreover, electrochemical surface area (ECSA) was
measured by double layer capacitance method (Cdl). The plot
between Δj(ja − jc) versus scan rate is portrayed as Figure S5
in the SI. Among three catalysts, the Cdl value was higher for
Co0.85Se-hyd, with a value of 0.92 μF, while comparing the
other two CoSe-DNA (0.5 μF) and CoSe (0.3 μF),
respectively. From the electrochemical studies, it has been
observed that the Co0.85Se-hyd catalyst has shown better
activity than the other two catalysts. However, CoSe-DNA at
higher overpotentials could deliver better activity that stresses
the role of DNA in enhancing the electrocatalytic activity while
comparing other catalysts. After the OER studies, the structural
changes have been monitored by XRD and Raman spectral
studies first and is given in the SI as Figures S6 and S7. From
Figure S6a, the peak observed at 37.5° was attributed to the
CoO phase formed during OER and well matches with the
ICDD file No. 042-1300. The peak at 31.7° was due to the Se
and O2 formed after OER that matched with the ICDD file
No. 01-083-2439. Figure S6b was again confirming the peaks
of carbon cloth used as a substrate for the electrochemical
studies. The formation of CoO phase during OER is again
confirmed with Raman spectra and showed peaks for the
Co0.85Se and CoO after OER.54,55 The peaks observed at 117
and 674 cm−1 were corresponded to the Co0.85Se and CoO and
is in accordance with the earlier reports (Figure S7). The
morphological robustness of Co0.85Se-hyd was monitored with
HR-TEM analysis and shown as Figure S8a−d in the SI. As
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Figure 6. (a) iR corrected LSV at a scan rate of 5 mV/s, (b) Tafel slope extracted from LSV, (c) LSV after accelerated degradation test, and (d) the
chronoamperometry study for 24 h at 394 (Co0.85Se-hyd) and 444 mV (CoSe-DNA and CoSe).
observed from Figure S8a−c, the morphology was still like
agglomerates of Co0.85Se with a sheet-like structure. This could
be attributed to the electrode preparation method, oxide phase
formed during OER, and also, the sample preparation method
for HR-TEM analysis (sonication) that deliberately resulted in
the agglomerated sheets of Co0.85Se. Figure S8d showed the
polycrystalline nature of the catalyst after OER. To further
ensure the presence of elements after the OER studies,
HAADF color mapping was carried out for Co0.85Se and has
been given as Figure S9a−d in the SI. Figure S9a and b are the
images of area taken and the mixture of mapping of Co, Se,
and O, respectively. Moreover, the presence of Co, Se, and O
is well observed from the individual K shell mappings of Co,
Se, and O from Figure S9c−e, respectively. These findings
clearly stress that, even though selenium is leached as SeO2
during anodization, even after 24 h of PSTAT analysis, still the
presence of Co and Se is observed that showed the material
robustness at harsh anodic conditions.43,44
that Co0.85Se-hyd was the most active one compared to the
other two. Between CoSe-DNA and only CoSe, the activity
was enhanced in the former one because of the influence of
DNA. With our present synthesis methods, CoSe-DNA proved
to be more advantageous compared to Co0.85Se-hyd and is
found to be the most optimal catalyst, with a significant
increase in efficiency. From OER studies, it is the Co0.85Se-hyd
catalyst that was found to be better than other catalysts in
terms of activity and stability. In the future, similar
chalcogenide-based catalysts can be derived from DNA for
increased OER activity.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00354.
■
S
Information on the materials used and the sample
preparation for various characterization techniques and
figures related to electrochemical studies (PDF)
CONCLUSION
■
To summarize, cobalt selenide is prepared in three methods,
namely, with and without DNA in wet-chemical route and
without DNA in hydrothermal route. All three catalysts have
shown different morphological features. The potentiality of
three catalysts was analyzed for electrocatalytic OER in 1 M
KOH. From OER study, at a current density of 10 mA cm−2,
the Co0.85Se-hyd required a very low overpotential of 354 mV.
The CoSe-DNA and CoSe required 382 and 383 mV,
respectively, at the same current density. The Tafel slope,
AD test, and potentiostatic analyses clearly gave information
AUTHOR INFORMATION
Corresponding Author
*E-mail: kundu.subrata@gmail.com; skundu@cecri.res.in.
■
ORCID
Kannimuthu Karthick: 0000-0003-2689-0657
Subrata Kundu: 0000-0002-1992-9659
Notes
The authors declare no competing financial interest.
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(17) Tian, T.; Jiang, J.; Ai, L. In situ electrochemically generated
composite-type CoOx/WOx in self-activated cobalt tungstate nano-
structures: implication for highly enhanced electrocatalytic oxygen
evolution. Electrochim. Acta 2017, 224, 551−560.
(18) Feng, J.; Xu, H.; Dong, Y.; Ye, S.; Tong, Y.; Li, G. FeOOH/Co/
FeOOH Hybrid Nanotube Arrays as High-Performance Electro-
catalysts for the Oxygen Evolution Reaction. Angew. Chem. 2016, 128,
3758−3762.
ACKNOWLEDGMENTS
■
K.K. wishes to acknowledge UGC for SRF award. S.K. wishes
to acknowledge the Department of Science and Technology
(DST) for EMR research funding by #EMR/2017/000860 on
May 11th, 2018 and Institute OM Number 18-29-03/(27/
2018)-TTBD-CSIR-CECRI on October 29th, 2018.
(19) Feng, J.; Ye, S.; Xu, H.; Tong, Y.; Li, G. Design and Synthesis of
FeOOH/CeO 2 Heterolayered Nanotube Electrocatalysts for the
Oxygen Evolution Reaction. Adv. Mater. 2016, 28, 4698−4703.
(20) Lu, X.; Gu, L.; Wang, J.; Wu, J.; Liao, P.; Li, G. Bimetal-Organic
Framework Derived CoFe2O4/C Porous Hybrid Nanorod Arrays as
High-Performance Electrocatalysts for Oxygen Evolution Reaction.
Adv. Mater. 2017, 29, 1604437.
(21) Ye, S.; Shi, Z.; Feng, J.; Tong, Y.; Li, G. Activating CoOOH
Porous Nanosheet Arrays by Partial Iron Substitution for Efficient
Oxygen Evolution Reaction. Angew. Chem., Int. Ed. 2018, 57, 2672−
2676.
(22) Karthick, K.; Anantharaj, S.; Karthik, P. E.; Subramanian, B.;
Kundu, S. Self-Assembled Molecular Hybrids of CoS-DNA for
Enhanced Water Oxidation with Low Cobalt Content. Inorg. Chem.
2017, 56, 6734−6745.
(23) Chen, J. S.; Ren, J.; Shalom, M.; Fellinger, T.; Antonietti, M.
Stainless steel mesh-supported NiS nanosheet array as highly efficient
catalyst for oxygen evolution reaction. ACS Appl. Mater. Interfaces
2016, 8, 5509−5516.
(24) Wang, D. Y.; Gong, M.; Chou, H. L.; Pan, C. J.; Chen, H. A.;
Wu, Y.; Lin, M. C.; Guan, M.; Yang, J.; Chen, C. W.; Wang, Y. L.;
Hwang, B. J.; Chen, C. C.; Dai, H. Highly Active and Stable Hybrid
Catalyst of Cobalt-Doped FeS2 Nanosheets−Carbon Nanotubes for
Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2015, 137, 1587−
1592.
(25) Zhao, X.; Zhang, H.; Yan, Y.; Cao, J.; Li, X.; Zhou, S.; Peng, Z.;
Zeng, J. Engineering the Electrical Conductivity of Lamellar Silver-
Doped Cobalt (II) Selenide Nanobelts for Enhanced Oxygen
Evolution. Angew. Chem., Int. Ed. 2017, 56, 328−332.
(26) Zhang, C.; Xin, B.; Duan, S.; Jiang, A.; Zhang, B.; Li, Z.; Hao, J.
Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide
Nanostructures as Highly Efficient Electrocatalysts for the Oxygen
Evolution Reaction. Chem. - Asian J. 2018, 13, 2700−2707.
(27) Carim, A. I.; Saadi, F. H.; Soriaga, M. P.; Lewis, N. S.
Electrocatalysis of the hydrogen-evolution reaction by electro-
deposited amorphous cobalt selenide films. J. Mater. Chem. A 2014,
2, 13835−13839.
REFERENCES
■
(1) Garland, N. L.; Papageorgopoulos, D. C.; Stanford, J. M.
Hydrogen and fuel cell technology: Progress, challenges, and future
directions. Energy Procedia 2012, 28, 2−11.
(2) Edwards, P. P.; Kuznetsov, V. L.; David, W. I. F.; Brandon, N. P.
ydrogen and fuel cells: towards a sustainable energy future. Energy
Policy 2008, 36 (12), 4356−4362.
(3) Wendt, H.; Imarisio, G. Nine years of research and development
on advanced water electrolysis. A review of the research programme
of the Commission of the European Communities. J. Appl.
Electrochem. 1988, 18, 1−14.
(4) Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser,
P. The mechanism of water oxidation: from electrolysis via
homogeneous to biological catalysis. ChemCatChem 2010, 2 (7),
724−761.
(5) Yan, Y.; Xia, B. Y.; Zhao, B.; Wang, X. A review on noble-metal-
free bifunctional heterogeneous catalysts for overall electrochemical
water splitting. J. Mater. Chem. A 2016, 4 (45), 17587−17603.
(6) McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F.
Benchmarking heterogeneous electrocatalysts for the oxygen
evolution reaction. J. Am. Chem. Soc. 2013, 135, 16977−16987.
(7) You, B.; Jiang, N.; Sheng, M.; Sun, Y. Microwave vs solvothermal
synthesis of hollow cobalt sulfide nanoprisms for electrocatalytic
hydrogen evolution and supercapacitors. Chem. Commun. 2015, 51,
4252−4255.
(8) Yagi, M.; Tomita, E.; Sakita, S.; Kuwabara, T.; Nagai, K. Self-
Assembly of Active IrO2 Colloid Catalyst on an ITO Electrode for
Efficient Electrochemical Water Oxidation. J. Phys. Chem. B 2005, 109
(46), 21489.
(9) Anantharaj, S.; Kundu, S. Self-Assembly of Active IrO2 Colloid
Catalyst on an ITO Electrode for Efficient Electrochemical Water
Oxidation. Curr. Nanosci. 2017, 13 (4), 333−341.
(10) Ganesan, P.; Sivanantham, A.; Shanmugam, S. Inexpensive
electrochemical synthesis of nickel iron sulphides on nickel foam:
super active and ultra-durable electrocatalysts for alkaline electrolyte
membrane water electrolysis. J. Mater. Chem. A 2016, 4 (42), 16394−
16402.
(11) Yeo, B. S.; Bell, A. T. Enhanced activity of gold-supported
cobalt oxide for the electrochemical evolution of oxygen. J. Am. Chem.
Soc. 2011, 133 (14), 5587−5593.
(28) Zhang, J. Y.; Lv, L.; Tian, Y.; Li, Z.; Ao, X.; Lan, Y.; Jiang, J.;
Wang, C. Rational Design of Cobalt-Iron Selenides for Highly
Efficient Electrochemical Water Oxidation. ACS Appl. Mater. Interfaces
2017, 9, 33833−33840.
(12) Tran, P. D.; Chiam, S. Y.; Boix, P. P.; Ren, Y.; Pramana, S. S.;
Fize, J.; Artero, V.; Barber, J. Novel cobalt/nickel−tungsten-sulfide
catalysts for electrocatalytic hydrogen generation from water. Energy
Environ. Sci. 2013, 6 (8), 2452.
(13) Zhang, Y.; Gao, T.; Jin, Z.; Chen, X.; Xiao, D. A robust water
oxidation electrocatalyst from amorphous cobalt−iron bimetallic
phytate nanostructures. J. Mater. Chem. A 2016, 4 (41), 15888−
15895.
(29) Li, S.; Peng, S.; Huang, L.; Cui, X.; Al-Enizi, A. M.; Zheng, G.
Carbon-Coated Co3+-Rich Cobalt Selenide Derived from ZIF-67 for
Efficient Electrochemical Water Oxidation. ACS Appl. Mater. Interfaces
2016, 8, 20534−20539.
(30) Masud, J.; Swesi, A. T.; Liyanage, W. P. R.; Nath, M. Cobalt
Selenide Nanostructures: An Efficient Bifunctional Catalyst with High
Current Density at Low Coverage. ACS Appl. Mater. Interfaces 2016,
8, 17292−17302.
(14) Yang, L.; Xie, L.; Ge, R.; Kong, R.; Liu, Z.; Du, G.; Asiri, A. M.;
Yao, Y.; Luo, Y. Core−Shell NiFe-LDH@ NiFe-Bi Nanoarray: In Situ
Electrochemical Surface Derivation Preparation toward Efficient
Water Oxidation Electrocatalysis in near-Neutral Media. ACS Appl.
Mater. Interfaces 2017, 9 (23), 19502−19506.
(15) Liu, P.-F.; Zhou, J.-J.; Li, G.-C.; Wu, M.-K.; Tao, K.; Yi, F.-Y.;
Zhao, W.-N.; Han, L. A hierarchical NiO/NiMn-layered double
hydroxide nanosheet array on Ni foam for high performance
supercapacitors. Dalt. Trans. 2017, 46 (23), 7388−7391.
(16) Stern, L.-A.; Hu, X. Enhanced oxygen evolution activity by
NiOx and Ni (OH)2 nanoparticles. Faraday Discuss. 2014, 176, 363−
379.
(31) Wang, Z.; Li, J.; Tian, X.; Wang, X.; Yu, Y.; Owusu, K. A.; He,
L.; Mai, L. Porous Nickel-Iron Selenide Nanosheets as Highly
Efficient Electrocatalysts for Oxygen Evolution Reaction. ACS Appl.
Mater. Interfaces 2016, 8, 19386−19392.
(32) Swesi, A. T.; Masud, J.; Liyanage, W. P. R.; Umapathi, S.;
Bohannan, E.; Medvedeva, J.; Nath, M. Textured NiSe2 Film:
Bifunctional Electrocatalyst for Full Water Splitting at Remarkably
Low Overpotential with High Energy Efficiency. Sci. Rep. 2017, 7, 1−
11.
(33) Liu, B.; Zhao, Y. F.; Peng, H. Q.; Zhang, Z. Y.; Sit, C. K.; Yuen,
M. F.; Zhang, T. R.; Lee, C. S.; Zhang, W. J. Nickel−Cobalt
Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni
G
DOI: 10.1021/acs.inorgchem.9b00354
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Foam: An All-pH Highly Efficient Integrated Electrocatalyst for
Hydrogen Evolution. Adv. Mater. 2017, 29, 1606521.
(34) Liao, M.; Zeng, G.; Luo, T.; Jin, Z.; Wang, Y.; Kou, X.; Xiao, D.
Three-dimensional coral-like cobalt selenide as an advanced electro-
catalyst for highly efficient oxygen evolution reaction. Electrochim.
Acta 2016, 194, 59−66.
(52) Anantharaj, S.; Karthik, P. E.; Kundu, S. Self-assembled IrO2
nanoparticles on a DNA scaffold with enhanced catalytic and oxygen
evolution reaction (OER) activities. J. Mater. Chem. A 2015, 3,
24463−24478.
(53) Anantharaj, S.; Ede, S. R.; Karthick, K.; Sam Sankar, S.;
Sangeetha, K.; Karthik, P. E.; Kundu, S. Precision and Correctness in
the Evaluation of Electrocatalytic Water Splitting: Revisiting Activity
Parameters with a Critical Assessment. Energy Environ. Sci. 2018, 11,
744−771.
(54) Li, Y.; Qiu, W.; Qin, F.; Fang, H.; Hadjiev, V. G.; Litvinov, D.;
Bao, J. Identification of Cobalt Oxides with Raman Scattering and
Fourier TransformTransform Infrared Spectroscopy. J. Phys. Chem. C
2016, 120, 4511−4516.
(55) Yu, B.; Qi, F.; Chen, Y.; Wang, X.; Zheng, B.; Zhang, W.; Li, Y.;
Zhang, L. C. Nanocrystalline Co0.85Se Anchored on Graphene
Nanosheets as a Highly Efficient and Stable Electrocatalyst for
Hydrogen Evolution Reaction. ACS Appl. Mater. Interfaces 2017, 9,
30703−30710.
̈
(35) Xia, C.; Liang, H.; Zhu, J.; Schwingenschlogl, U.; Alshareef, H.
N. Active Edge Sites Engineering in Nickel Cobalt Selenide Solid
Solutions for Highly Efficient Hydrogen Evolution. Adv. Energy Mater.
2017, 7, 1−9.
(36) Xia, C.; Jiang, Q.; Zhao, C.; Hedhili, M. N.; Alshareef, H. N.
Selenide-Based Electrocatalysts and Scaffolds for Water Oxidation
Applications. Adv. Mater. 2016, 28, 77−85.
(37) Panda, C.; Menezes, P. W.; Walter, C.; Yao, S.; Miehlich, M. E.;
Gutkin, V.; Meyer, K.; Driess, M. From aMolecular 2Fe-2SePrecursor
to aHighly EfficientIron Diselenide Electrocatalyst for Overall Water
Splitting. Angew. Chem., Int. Ed. 2017, 56, 10506−10510.
(38) Zhu, J.; Ni, Y. Phase-controlled synthesis and the phase-
dependent HER and OER performances of nickel selenide nanosheets
prepared by an electrochemical deposition route. CrystEngComm
2018, 20, 3344−3352.
(39) Li, X.; Zhang, L.; Huang, M.; Wang, S.; Li, X.; Zhu, H. Cobalt
and nickel selenide nanowalls anchored on graphene as bifunctional
electrocatalysts for overall water splitting. J. Mater. Chem. A 2016, 4,
14789−14795.
(40) Xu, X.; Du, P.; Chen, Z.; Huang, M. An electrodeposited
cobalt−selenide-based film as an efficient bifunctional electrocatalyst
for full water splitting. J. Mater. Chem. A 2016, 4, 10933−10939.
(41) Hou, Y.; Lohe, M. R.; Zhang, J.; Liu, S.; Zhuang, X.; Feng, X.
Vertically oriented cobalt selenide/NiFe layered- double-hydroxide
nanosheets supported on exfoliated graphene foil: an efficient 3D
electrode for overall water splitting. Energy Environ. Sci. 2016, 9, 478−
483.
(42) Swesi, A. T.; Masud, J.; Nath, M. Nickel selenide as a high-
efficiency catalyst for oxygen evolution reaction. Energy Environ. Sci.
2016, 9, 1771−1782.
(43) Kong, D.; Wang, H.; Lu, Z.; Cui, Y. CoSe2 Nanoparticles
Grown on Carbon Fiber Paper: An Efficient and Stable Electrocatalyst
for Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2014, 136,
4897−4900.
(44) Liu, T.; Liu, Q.; Asiri, A. M.; Luo, Y.; Sun, X. An amorphous
CoSe film behaves as an active and stable full water-splitting
electrocatalyst under strongly alkaline conditions. Chem. Commun.
2015, 51, 16683−16686.
(45) Anantharaj, S.; Amarnath, T. S.; Subhashini, E.; Chatterjee, S.;
Swaathini, K. C.; Karthick, K.; Kundu, S. Shrinking the Hydrogen
Overpotential of Cu by 1 V Imparting Ultralow Charge Transfer
Resistance for Enhanced H2 Evolution. ACS Catal. 2018, 8, 5686−
5697.
(46) Kuzuya, A.; Ohya, Y. DNA nanostructures as scaffolds for metal
nanoparticles. Polym. J. 2012, 44, 452−460.
(47) Goodman, C. M.; Chari, N. S.; Han, G.; Hong, R.; Ghosh, P.;
Rotello, V. M. DNA-binding by functionalized gold nanoparticles:
mechanism and structural requirements. Chem. Biol. Drug Des. 2006,
67, 297−304.
(48) Chen, Z.; Liu, C.; Cao, F.; Ren, J.; Qu, X. DNA metallization:
principles, methods, structures, and applications. Chem. Soc. Rev.
2018, 47, 4017−4072.
(49) Karthick, K.; Anantharaj, S.; Kundu, S. Nickelo-Sulfurization of
DNA Leads to an Efficient Alkaline Water Oxidation Electrocatalyst
with Low Ni Quantity. ACS Sustainable Chem. Eng. 2018, 6, 6802−
6810.
(50) Shi, Y.; Zhang, B. Recent advances in transition metal
phosphide nanomaterials: synthesis and applications in hydrogen
evolution reaction. Chem. Soc. Rev. 2016, 45, 1529−1541.
(51) Xu, J.; Li, J.; Xiong, D.; Zhang, B.; Liu, Y.; Wu, K. H.; Amorim,
I.; Li, W.; Liu, L. Trends in activity for the oxygen evolution reaction
on transition metal (M= Fe, Co, Ni) phosphide pre-catalysts. Chem.
Sci. 2018, 9, 3470−3476.
H
DOI: 10.1021/acs.inorgchem.9b00354
Inorg. Chem. XXXX, XXX, XXX−XXX