Electrocatalytic hydrogen evolution reaction with a supramolecular cobalt(II)phthalocyanine carrying four cobaloxime moieties

Article abstract of DOI:10.1016/j.ica.2017.07.024

A supramolecular cobalt phthalocyanine (CoPc) bearing four redox active cobaloxime (CoDMG) substituents ((CoDMG)₄-CoPc) was synthesized and electrochemically characterized in order to determine its functionalities for practical usages as effect

Full text of DOI:10.1016/j.ica.2017.07.024

Accepted Manuscript
Research paper
Electrocatalytic Hydrogen Evolution Reaction with a Supramolecular Co-
balt(II)phthalocyanine Carrying Four Cobaloxime Moieties
İbrahim Özçeşmeci, Aykut Demir, Duygu Akyüz, Atıf Koca, Ahmet Gül
PII:
S0020-1693(17)30425-5
http://dx.doi.org/10.1016/j.ica.2017.07.024
ICA 17747
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
21 March 2017
29 June 2017
12 July 2017
Please cite this article as: I. Özçeşmeci, A. Demir, D. Akyüz, A. Koca, A. Gül, Electrocatalytic Hydrogen Evolution
Reaction with a Supramolecular Cobalt(II)phthalocyanine Carrying Four Cobaloxime Moieties, Inorganica
Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.07.024
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Electrocatalytic Hydrogen Evolution Reaction with a Supramolecular
Cobalt(II)phthalocyanine Carrying Four Cobaloxime Moieties
a
a
b
b
a
İbrahim Özçeşmeci , Aykut Demir , Duygu Akyüz , Atıf Koca , Ahmet Gül *,
a
Department of Chemistry, Faculty of Science and Letters, Istanbul Technical University, 34469
Maslak, Istanbul, Turkey
b
Department of Chemical Engineering, Engineering Faculty, Marmara University,34722 Göztepe,
Istanbul- Turkey.
Abstract
A supramolecular cobalt phthalocyanine (CoPc) bearing four redox active cobaloxime
(
CoDMG) substituents ((CoDMG)
characterized in order to determine its functionalities for practical usages as effective
electrocatalysts. Voltammetric analyses of CoDMG, CoPc, and (CoDMG) -CoPc indicated
redox activity of each compounds and supported substitution of CoPc with CoDMG.
CoDMG) -CoPc showed three CoPc based reduction processes and two CoDMG based
4
-CoPc) was synthesized and electrochemically
4
(
4
reduction processes. While CoDMG showed two reduction and one oxidation processes,
CoPc illustrated three reduction and two oxidation processes. Binding of CoDMG to CoPc
increased the reduction processes to five. Multi-electron and metal and/or ring based redox
processes showed worthy of the (CoDMG) -CoPc for using as an electrocatalyst. Shifting of
4
the proton reduction reaction toward the positive potentials indicated electrocatalytic activities
of the complexes for the hydrogen evolution reaction (HER). Among CoDMG, CoPc, and
(
CoDMG)
highest electrocatalytic activity and it decreased the over-potential of the bare electrode about
60 mV and increased the current density of the electrode about 10 fold.
4
-CoPc, modified glassy carbon electrode with (CoDMG)
4
-CoPc illustrated the
3
Keywords: Supramolecule, Electrocatalyst, Hydrogen evolution reaction, Phthalocyanine
Corresponding authors Tel.: +90 212 285 68 27; Fax: +90 212 285 63 86
*
*E-mail address: ahmetg@itu.edu.tr (A. Gül)
1

1
.
Introduction
Supramolecular chemistry interests on well organized, synthetically built up molecular
receptors for effecting molecular recognition, catalysis, light harvesting, transport processes
and for setting up molecular devices. The use of macrocyclic structures like tetrapyrole was
pushed by the need to achieve better control over the geometry of molecular receptors [1, 2].
Despite the great interest in terms of synthesis and reactivity of oximes and their metal
complexes in medicinal and materials chemistry, there are very few studies with tetrapyrole/
cobaltdioxime combined systems on the production of H in the literature [3, 4].
2
Metallophthalocyanines (MPcs) were used as functional materials in different
electrochemical technologies due to their rich redox activities [5-7]. Redox activities of MPcs
can be enhanced by incorporating redox active metal ions into the cavity of the Pc ring and/or
by substituting with redox active moieties [8, 9].
MPcs having metal based electron transfer reaction generally behave as active species,
thus a supramolecular cobalt phthalocyanine bearing four redox active cobaloxime
II
substituents (CoDMG)
4
-CoPc bearing redox active Co ions in both the Pc ring and four
redox active CoDMG moieties was synthesized and tested as possible electrocatalyst for
hydrogen evolution reaction (HER). Transition metal complexes with various ligands were
extremely studied as homogeneous and/or heterogeneous electrocatalysts for HER, due to
their rich redox properties [10-14]. In this context the complexes having metal-based
reduction processes generally showed good electrocatalytic activity for HER [5, 6].
2
2
. Experimental
.1 Materials and equipment
FT-IR spectra were recorded on a Perkin-Elmer Spectrum One FT-IR (ATR sampling
accessory) spectrometer and electronic spectra was obtained on a Scinco S-3100
spectrophotometer using 1cm path length cuvettes at room temperature. Mass spectra were
2

performed on a Bruker Microflex LT MALDI-TOF MS spectrometer. All reagents and
solvents were of reagent grade quality obtained from commercial suppliers. Anhydrous metal
o
salts were finely ground and dried at 100 C. The purity of the products was tested in each
step by thin-layer chromatography (TLC). The solvents were stored over molecular sieves. 4-
(
4-pyridyloxy)phthalonitrile (1) was prepared according to the literature [15] and
chloro(pyridine)cobaloxime (CoDMG) complex was prepared according to reported
procedures [16-17].
2
2
.2 Synthesis
.2.1. 2,9,16,23-tetrakis(4-pyridyloxy)phthalocyaninatocobalt (II) (CoPc)
A mixture of 4-(4-pyridyloxy)phthalonitrile (0.200 g, 0.900 mmol) and cobalt (II) chloride
0.039 g, 0.300 mmol) in N,N-(dimethylamino)ethanol (2 mL) was heated and stirred at 140
C for 24 h under nitrogen atmosphere. After cooling to room temperature the crude product
(
°
was precipitated by addition of hexane. The solid was washed several times with ethanol,
chloroform, acetone, hexane, and diethyl ether and then dried in vacuo. Yield: 0.109 g
(
51.4%). Anal. calcd. for C52
H28CoN12
O
4
C, 66.18; H, 2.99; N, 17.81;%. Found: C, 66.24; H,
-1
3
.03; N, 17.78%. IR: max, cm 3060 (Ar–H), 1633, 1547, 1257 (C–O–C), 1189, 842. UV-Vis
(
DMF): λmax nm (log ε) 295 (4.20), 340 (3.96), 678 (4.26). (MALDI-TOF): m/z 944.84
+
[
M+1]
2
.2.2. Pentanuclear supramolecular phthalocyanine (CoDMG)
4
-CoPc)
(0.156 g, 1.200 mmol) and
A mixture of dimethylglyoxime (0.278 g, 2.400 mmol), dry CoCl
2
CoPc (0.189 g, 0.200 mmol) was stirred in ethanol (20 mL) at reflux temperature and a very
gentle stream of air is bubbled through the solution. After 24 h, the solvent was evaporated at
reduced pressure. The solid was washed several times with chloroform, acetone, hexane, and
diethyl ether and then dried in vacuo. Yield: 0.285 g (63.6%). Anal. calcd. for
C
84
H
84Cl
4
Co
5
N
28
O20 C, 45.00; H, 3.78; N, 17.49 %. Found: C, 45.14; H, 3.83; N, 17.54%. IR:
3

-1

max, cm 3045 (Ar–H), 1635, 1552, 1260 (C–O–C), 1232, 1189, 842. UV-Vis (DMF): λmax
+
nm (log ε) 293 (4.40), 333(4.26), 675 (4.18). (MALDI-TOF): m/z 2242.31 [M+1]
2
.3 Chemicals and solutions
The experimental studies were carried on with high purity chemicals. Extra pure
dichloromethane (DCM), and ultra-pure water (≥18 M_, Milli-Q, Millipore) were used as
solvents. Electrochemical grade tetrabutylammonium perchlorate (TBAP), NaOH, NaCl,
H
3
PO
4
, KH
2
PO
4
, LiClO
4
, HCl, and other reagents were purchased from Aldrich and used
3
without further purification. The buffer solutions were prepared by using 0.1 mol/dm H
3
PO ,
4
3
and 0.1 mol/dm KH
2
PO . The desired pH was obtained by addition of conjugate acids or 0.1
4
3
mol/dm NaOH solution.
2
.4 Electrode modification
Glassy carbon working electrodes (GCE) were coated with CoDMG, CoPc, and
CoDMG) -CoPc by using the cast film coating technique. During this modification process,
(
4
-5
-3
1
00 µL of 5.0 10 moldm each complexes dissolved in DMSO was dropped on the active
surface of GCE and then it was dried under vacuum at room temperature. Finally, the
modified electrodes (GCE/CoDMG, GCE/CoPc, and GCE/(CoDMG) -CoPc) were washed
with water and used as modified working electrode for HER in the phosphate buffer solution.
4
2
.5 Electrochemical measurements
The electrochemical measurements were performed with a GAMRY reference
00Potentiostat/Galvanostat/ZRA utilizing a three-electrode cell configuration at 25°C. For
6
cyclic voltammetry (CV), linear sweep voltammetry (LSV), square wave voltammetry
(
SWV), controlled potential coulometry (CPC), chronoamperometry (CA), and
4

chronocoulometry (CC) measurements, the working electrode was a bare or modified
GCE/CoDMG, GCE/CoPc, and GCE/(CoDMG) -CoPc electrodes with a surface area of
4
2
0
.071 cm . A Pt wire was used as the counter electrode. Ag/AgCl electrode was employed as
the reference electrode. Both of the reference and counter electrodes were separated from the
electrolyte with salt bridges. High purity N was used to remove dissolved O for at least 15
2
2
min prior to each run and to maintain a nitrogen atmosphere over the solution during the
measurements. UV–vis absorption spectrum of the electrodes was measured with an Ocean
Optics QE65000 diode array spectrophotometer.
3
. Result and Discussion
3
.1 Synthesis and characterization
Scheme 1 showed the synthetic route of pentanuclear supramolecular phthalocyanine
(
CoDMG)
pyridyloxy substituent was achieved by base-catalyzed nucleophilic aromatic displacement of
-nitrophtalonitrile and with 4-hydroxypyridine according to the literature [15]. Cobaloxime
4
-CoPc). The synthesis of a new supramolecular phthalocyanine precursor bearing
4
(
CoDMG) complex was prepared according to reported procedures [16, 17]. Conversion of 4-
4-pyridyloxy)phthalonitrile into the corresponding cobalt (II) phthalocyanines (CoPc) was
(
accomplished in a high-boiling N-donor solvent (N,N-(dimethylamino)ethanol ) in the
presence of the metal salt (CoCl ).
2
The primary goal of this study was the construction of a supramolecular structure
starting with a phthalocyanine molecule. Taking into account the ready coordination of
CoDMG with four pyridine donors, these penta-coordinated complexes were preferred as the
capping agents for tetra pyridine end-groups on each molecule to reach the penta nuclear
supramolecular structure. The blue solid pentanuclear supramolecular product
was obtained in powder form. All of these new compounds were characterized by
5

elemental analysis, IR, UV–Vis and Mass spectroscopy techniques. The spectroscopic data of
the new compounds were in accordance with the structures.
Scheme 1
Naturally, the phthalocyanine products synthesized during this work are a mixture of
positional isomers while 4-(4-pyridyloxy)phthalonitrile carry a single substituent [18, 19].
The FT-IR spectra of CoPc and (CoDMG)
4
-CoPc) confirmed the structures of target
-1
compounds by exhibiting the disappearance of C≡N band at 2238 cm and the presence of
-
1
aromatic CH stretching bands at 3060 and 3045 cm , respectively. The IR spectra of these
-1
compounds showed aromatic C=C and C–O–C peaks around at 1635, 1260 cm , respectively.
CoPc and (CoDMG) -CoPc) show typical electronic spectra with two strong
4
absorption regions, one of them in the UV region at about 300-400 nm (B band) arising from
the deeper  - levels → LUMO transition and the other in the visible part of the spectrum
around 600-700 nm (Q band) attributed to the -* transition from the highest occupied
-2
molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of the Pc
ring [20-22]. In the UV-Vis spectra of CoPc and (CoDMG) -CoPc) in DMF, the absorption
4
peaks belonging to Q bands were observed at 678 and 675 nm and B bands at 340 and 333
nm, respectively (Fig. 1). The outcome of the presence of the CoDMG was an absorption
band with a maximum at about 295 nm comparable in intensity with the B-bands of the
(
CoDMG)
4
-CoPc). MALDI-TOF mass spectra of CoPc and (CoDMG) -CoPc) show the
4
+
presence of the characteristic peaks at m/z = 944.84 [M+1] (CoPc) (Fig. S1) and 2242.31
+
[
M+1] (CoDMG)
4
-CoPc) (Fig. S2) confirming the proposed structures.
Figure 1
6

3
.2. Electrochemistry of (CoDMG)
In order to decide possible usage of a functional material, its redox behaviors should be
investigated in detail [23-26]. Therefore, electrochemical behaviors of CoDMG, CoPc, and
CoDMG) -CoPc were determined with CV, SWV and in situ spectroelectrochemistry. The
4
-CoPc
(
4
results were compared with each other in order to understand effects of each groups to the
redox responses. Fig.2 shows CV and SWV responses of CoDMG in DMSO/TBAP
electrolyte system. CoDMG illustrates two irreversible reduction processes at -0.47 V (E
Red1S) and at -0.75 V (E1/2 of Red2S) and an oxidation at 1.24 V (E of Oxd1S). Fig.3
c
of
a
illustrates CV and SWV responses of CoPc in DMSO/TBAP electrolyte system. CoPc gives a
metal based reduction at -0.23 V (E1/2 of Red1P) and two Pc based reductions at -1.07 V (E1/2
of Red2P) and at -1.63 V (E1/2 of Red3P) respectively. Moreover, two oxidation processes are
also observed at 0.61 V (E1/2 of Oxd1P) and 1.18 V (E1/2 of Oxd2P).
Figure 2
Figure 3
Binding of CoDMG to CoPc extends the redox processes from five to seven processes as
shown in Fig.4. (CoDMG) -CoPc shows five reduction and two oxidation processes. The
4
CoPc and CoDMG based processes are observed clearly as shown in this figure. While the
peaks at -0.22 V (E1/2 of Red1P), -1,06 V (E1/2 of Red2P), -1.66 (E1/2 of Red3P), and -1.83 V
(
E
1/2 of Red3P) are easily assigned to the reduction of CoPc part of (CoDMG)
wave at -0.71 V (E1/2 of Red1S) and -1.19 V (E1/2 of Red2S) are assigned to the reduction of
CoDMG groups of (CoDMG) -CoPc complex. During the oxidation reactions, (CoDMG) -
4
-CoPc, the
4
4
CoPc illustrates two oxidations. When compared with the voltammetric responses of CoDMG
7

and CoPc , the first oxidation process at 0.27 V (E1/2 of Oxd1P) can be easily assigned to the
oxidation of CoPc center of the complex. The wave at 1.18 V is most propably due to the
overlap of the oxidation of CoDMG and CoPc groups of the complex. When compared with
the similar complexes in the literature, it can be easily stated that the first oxidation (Oxd1P
)
and the first reduction processes (Red1P and Red1S) of (CoDMG) -CoPc should be metal
4
II
III
III
based processes. Since MPcs having Co , Mn , Fe and etc. gives metal-based reduction and
oxidation reactions firstly in polar coordination solvents due to the d orbital positions between
the HOMO and LUMO orbital of Pc ring [1, 27]. Peak assignments of (CoDMG) -CoPc were
4
also performed with in situ spectroelectrochemical measurements discussed below.
Figure 4
3
.3. in situ Spectroelectrochemistry of (CoDMG)
In order to decide the redox assignments, in situ spectroelectrochemical measurements
of CoPc and (CoDMG) -CoPc were performed and compared with each other. As shown in
Fig. 5 and 6 there are very slight differences between the spectral changes of CoPc and
CoDMG) -CoPc. During the spectral changes of CoPc under -0.50 V applied potential
application, while the Q band shifts from 662 to 704 nm, anew band is observed at 488 nm
4
-CoPc
4
(
4
II
2-
I
2- 1-
(
Fig. 5a). These spectral changes are characteristic changes for [Co Pc ]/[Co Pc ] process.
The spectral changes given in Fig. 5b are the characteristic changes for a Pc based reduction,
I
2- 1-
I
3- 2-
thus this process is assigned to [Co Pc ] /[Co Pc ] process. During the oxidation reaction,
the Q band shift to longer wavelengths with increase in absorption intensity. These changes
II
2-
III
2- 1+
are characteristic for [Co Pc ] /[Co Pc ] process (Fig. 5c). (CoDMG)
4
-CoPc shows
similar spectral changes with slight differences. (CoDMG) -CoPc shows a metal based
4
II
II
2-
II
I
2- 1-
reduction reaction for [(Co -DMG)
4
-Co Pc ]/[(Co -DMG) -Co Pc ] process under -0.50 V
4
8

potential application (Fig. 6a) [28-31]. Similarly, spectral changes assigned to a Pc based
reduction are observed at -1.25 V applied potential. The main difference is the changes on the
band at around 488 nm. While the bad at 488 nm shift towards the longer wavelength with
slight decrease in intensity for CoPc, this band increases with shift to 503 nm for (CoDMG)
CoPc during the second reduction reaction. Moreover, the band at 805 nm is only observed
during the second reduction reaction of CoPc. These spectral differences may be resulted
4
-
from the electron transfer reactions of CoDMG groups of (CoDMG)
electron transfer reactions of CoPc center. Distinctive color changes are observed during the
redox reactions for both complexes as shown in the chromaticity diagram of the complex (Fig.
d and 6d). The color changes of these complexes have same trend. The cyan color (of the
4
-CoPc in addition to the
5
neutral species turns to yellow and then to orange during the reduction reactions and a light
blue color is observed for the monocationic species.
Figure 5
Figure 6
3
.4. Electrocatalytic hydrogen evolution on GCE/(CoDMG)
It is well known that for practical application, an electrocatalyst should be coated on
an electrode, and this catalyst should behave as heterogeneous active catalyst for HER [32,
3]. GCE/CoDMG, GCE/CoPc and GCE/(CoDMG) -CoPc electrodes were constructed with
4
-CoPc electrode
3
4
cast film coating technique and used as electrocatalyst for HER. Electrocatalytic activities of
the electrode are examined with different LSV technique. LSV is performed for the bare Pt
and GCE and GCE/CoDMG, GCE/CoPc and GCE/(CoDMG) -CoPc modified electrode in
4
order to compare catalytic activities of the electrodes (Fig. 7). While onset potential of HER
on GCE is observed at -0.72 V, it is shifted to -0.22 V on Pt working electrode. If the onset
potential closes to that on Pt electrode, it has possibilities to be used as practical catalyst for
9

HER. As shown in Fig. 7, onset potential of HER shifts up to -0.65 V on GCE/CoPc -0.62 V
on GCE/CoDMG and -0.36 V on GCE/(CoDMG) -CoPc modified electrode. These results
indicated that binding of CoDMG to CoPc enhance the electrocatalytic activity of CoPc and
the highest catalytic activity is observed with GCE/(CoDMG) -CoPc modified electrode.
Onset potential of HER on GCE/(CoDMG) -CoPc electrode closes to that of Pt electrode,
which shows GCE/(CoDMG) -CoPc electrode can be used instead of Pt electrode in the water
electrolyzers. Under -0.50 V constant applied potential hydrogen gas evolving can be seen
easily on the surface of GCE/ (CoDMG) -CoPc electrode with naked eyes. As shown in the
figure, positive potential shifts of HER onset potentials and enhancing in the current density
of HER process and overpotentials of HER decrease about 360 mV on GCE/(CoDMG) -CoPc
4
4
4
4
4
4
modified electrode with respect to those on bare GCE at pH 3.40. In addition to the small
overpotential of these electrodes, approximately 77-fold enchantment of the current density of
HER indicates superior catalytic activities of the electrode.
Figure 7
Tafel plots are used to determine mechanism of the catalytic reaction [34]. During
HER in acidic media, an initial step involves the reduction of a proton in solution followed by
adsorption of intermediate Hads to the electrode surface as follows (Eq. 1):
ꢁꢂꢃꢃꢃꢄꢃꢃꢅ ꢃꢃꢄꢇꢈꢃꢃꢉꢃꢃꢇꢈꢊ ꢋꢌꢍꢃꢃꢃꢃꢄꢃꢃ ꢎꢁꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢏꢐꢑꢃꢃꢏꢒꢓꢔꢕꢅꢖꢃꢖꢅꢗꢘꢙꢚꢓꢛꢑ
ꢆ
ꢀ
−
1
A Tafel slope of approximately 120 mV dec is associated with this reaction step.
This is followed by desorption of H by either of the following reactions (Eq. 2 and 3):
2
ꢂ
ꢆ
ꢇꢈꢊ ꢋꢌꢍꢃꢃꢃꢄꢃꢃꢃ ꢁ ꢃꢃꢃꢄꢃꢃꢅ ꢃꢃꢉꢃꢃꢇꢈꢃꢃꢃꢄꢃꢃ ꢎꢃꢃꢃꢃꢄꢃꢃ ꢎꢁꢃꢃꢃꢃꢃꢃꢃꢃꢏꢜꢑ(Heyrovsky reaction)
ꢀ
ꢇꢈꢊ ꢋꢌꢍꢃꢃꢃꢄꢃꢃꢃꢇꢈꢊ ꢋꢌꢍꢃꢉꢃꢃꢜꢇꢈꢃꢃꢃꢄꢃꢃ ꢎꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢃꢏꢝꢑ(Tafel reaction)
−
1
The latter reaction has a Tafel slope of approximately 30 mV dec . While Tafel slope
−
1
of Pt electrode is around 130 mV dec at higher overpotentials, these values are around 200
10

−
1
mV dec for other electrodes except GCE/(Co-DMG)
DMG) -CoPc electrode shows two linear ranges. At small overpotential, it gives Tafel slope
of approximately 79 mVdec and at higher overpotentials, Tafel slope of approximately 137
4
-CoPc. Tafel plot of GCE/(Co-
4
−
1
−
1
mVdec is observed. These data indicate that HER occurs via Volmer–Heyrovsky equation
with different efficiency at small and higher over potentials respectively. Although only one
linear range were reported with electrocatalytic HERs with MPcs [35]. LSV and Tafel plot of
GCE/(Co-DMG) -CoPc electrode is different than the previous once. This difference may be
4
resulted from the presence of redox active Co-DMG groups on (Co-DMG) -CoPc complex.
4
II
Most probable both of the Co-DMG groups and Co metal center of the Pc ring of (Co-
DMG) -CoPc complex catalyze the HER. Protonation of Co-DMG groups catalyzes HER at
4
small overpotentials (between -0.36 and -0.57 V). After that potential current response of the
electrode reach to a steady state and then it starts to change its trend due to the catalyzing
II
HER with Co metal center of the Pc ring at higher overpotentials (after -0.57 V).
Stability of the (CoDMG)
4
-CoPc electrode was tested with consecutive 50 LSVs and only
1
7.8% current losses was observed, which showed suitable stability of the electrode for
practical usage. During the repetitive LSV measurement, LSV intensely changed and reach to
th
a steady state after the 10 LSV. During the first LSV, the current increases at -0.32 V and
reaches to a steady state at around -0.42 V. Then after -0.60 V the current sharply increases
again. However, during the consecutive LSVs the current linearly increases after the onset
potential of -0.36 V (Fig. 7). After this point it gives a stable response. it loses 17.8% of its
th
current response until the 50 LSV.
Conclusions
In this study, CoPc bearing redox active four CoDMG groups ((CoDMG) -CoPc) was
4
synthesized and electrochemically characterized in order to determine its functionalities for
practical usages as effective electrocatalysts. Electrochemical and spectroelectrochemical
11

characterization of CoPc and (CoDMG)
groups and CoPc center of (CoDMG) -CoPc complex were redox active. Multi-electron
transfer reactions of the complex showed possible usage of the complex as electrocatalysts for
HER reactions. Coating of GCE electrode with (CoDMG) -CoPc decreased the over potential
up to 360 mV when compared with the bare GCE. Observation of the onset potential of HER
on GCE/(CoDMG) -CoPc electrode very close to that of Pt and enhanced current density of
HER on GCE/(CoDMG) -CoPc electrode indicated usability of this complex as active
4
-CoPc complexes showed that both (CoDMG)
4
4
4
4
electrocatalyst for water splitting reactions.
Acknowledgments
This work was supported by the Research Funds of the TÜBİTAK (Project No: 113M991)
and Technical University of Istanbul. AG and AK thank Turkish Academy of Sciences
(
TUBA) for partial support.
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14

Figures and Scheme captions:
-5
Figure 1. Absorption spectra of the CoPc and (CoDMG) -CoPc (5x10 M) in DMF. (İnsert:
4
-4
Absorption spectrum of the CoDMG (1x10 M) in DMF.)
−4
−3
Figure 2. CV and SWV of CoDMG (5.0 × 10 mol dm ) at various scan rates on GCE in
DMSO/TBAP electrolyte system.
−
4
−3
Figure 3. CV and SWV of CoPc (5.0 × 10 mol dm ) at various scan rates on GCE in
DMSO/TBAP electrolyte system.
−
4
−3
Figure 4. CV and SWV of (CoDMG)
4
-CoPc (5.0 × 10 mol dm ) at various scan rates on
GCE in DMSO/TBAP electrolyte system.
−4
−3
Figure 5. In situ UV-Vis spectral changes of CoPc (5.0 × 10 mol dm ) in DMSO /TBAP.
a) Eapp = -0.50 V. b) Eapp = -1.25 V. c) Eapp= = 0.80 V. d) Chromaticity diagram (each symbol
II
−2
I
−2 −1
represents the color of electro-generated species; : [Co Pc ], :[Co Pc ] ;
:
I
−3 −2
II
−1 +1
[
Co Pc ] ; : [Co Pc ] .
−
4
−3
Figure 6. In situ UV-Vis spectral changes of (CoDMG)
4
-CoPc (5.0 × 10 mol dm ) in
DMSO /TBAP. a) Eapp = -0.50 V. b) Eapp = -1.25 V. c) Eapp= = 0.80 V. d) Chromaticity
II
−2
diagram (each symbol represents the color of electro-generated species; : [Co Pc ],
I
−2 −1
II
−1 +1
:
[Co Pc ] ; : [Co Pc ] .
Figure 7. a) LSVs and b) Tafel plots of Pt, GCE, and GCE/CoDMG, GCE/CoPc, and
−
1
GCE/(CoDMG)
4
-CoPc electrodes recorded at 10 mV s scan rate in PBS containing 0.1 M
LiClO at pH 3.40.
4
−
1
Figure 8. Repetitive LSVs of GCE/(CoDMG)
4
-CoPc electrode recorded at 10 mV s scan
rate in PBS containing 0.1 M LiClO at pH 3.40.
4
Scheme 1. The syntheses of CoPc and (CoDMG) -CoPc.
4
15

Figures and Scheme:
-5
Figure 1. Absorption spectra of the CoPc and (CoDMG) -CoPc (5x10 M) in DMF. (İnsert:
4
-4
Absorption spectrum of the CoDMG (1x10 M) in DMF.)
16

400
300
200
100
0
Oxd1S
-
1
2
5 mVs
0 mVs
-100
-200
-300
-400
-1
5
-
1
100 mVs
250 mVs
Red1S
-1
-1
5
00 mVs
Red2S
-1
1000 mVs
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
E / V vs. Ag/AgCl
−4
−3
Figure 2. CV and SWV of CoDMG (5.0 × 10 mol dm ) at various scan rates on GCE in
DMSO/TBAP electrolyte system.
17

7
5
2
5
0
5
0
-
-
1
1
2
5
1
2
5
1
5 mVs
0 mVs
Oxd2P
a)
-
-
-
1
1
1
00 mVs
50 mVs
00 mVs
-1
000 mVs
Oxd1P
Red1P
-25
Red2P
Red3P
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
E / V vs. Ag/AgCl
10.0
Oxd2P
b)
7
5
2
0
.5
.0
.5
.0
Oxd1P
Red3P
Red2P
Red1P
-
2.5
5.0
-
-
2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
E / V vs. Ag/AgCl
−
4
−3
Figure 3. CV and SWV of CoPc (5.0 × 10 mol dm ) at various scan rates on GCE in
DMSO/TBAP electrolyte system.
18

6
4
3
1
0
5
0
5
0
-
-
1
1
2
5
1
2
5
5 mVs
0 mVs
a)
Oxd2P
-
-
-
1
1
1
00 mVs
50 mVs
00 mVs
-
1
1000 mVs
Oxd1P
-
15
30
Red1S Red1P
Red2S Red2P
-
Red3P
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
E / V vs. Ag/AgCl
Oxd2P
5
.0
.5
.0
b)
2
0
Oxd1P
-
2.5
Red1S
Red1P
Red3P
-2.0 -1.5
Red2P
Red2S
-1.0
-
2.5
-0.5
0.0
0.5
1.0
1.5
E / V vs. Ag/AgCl
−
4
−3
Figure 4. CV and SWV of (CoDMG)
4
-CoPc (5.0 × 10 mol dm ) at various scan rates on
GCE in DMSO/TBAP electrolyte system.
19

(a)
(b)
3
00 400 500 600 700 800 900
300 400 500 600 700 800 900
Wavelength / nm
Wavelength / nm
0
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
(
c)
5
20 nm
(d)
5
60 nm
5
00 nm
5
80 nm
00 nm
6
7
00 nm
.1 480 nm
3
80 nm
.0
3
00 400 500 600 700 800 900
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
x
Wavelength / nm
−4
−3
Figure 5. In situ UV-Vis spectral changes of CoPc (5.0 × 10 mol dm ) in DMSO /TBAP.
a) Eapp = -0.50 V. b) Eapp = -1.25 V. c) Eapp= = 0.80 V. d) Chromaticity diagram (each symbol
II
−2
I
−2 −1
represents the color of electro-generated species; : [Co Pc ], :[Co Pc ] ;
:
I
−3 −2
II
−1 +1
[
Co Pc ] ; : [Co Pc ] .
20

(b)
(a)
3
00 400 500 600 700 800 900
300 400 500 600 700 800 900
Wavelength / nm
Wavelength / nm
0
0
0
0
0
0
0
0
0
.8
.7
.6
.5
.4
.3
.2
(
c)
520 nm
(d)
5
60 nm
5
00 nm
5
80 nm
00 nm
6
7
00 nm
.1 480 nm
3
80 nm
.0
3
00 400 500 600 700 800 900
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
x
Wavelength / nm
−
4
−3
Figure 6. In situ UV-Vis spectral changes of (CoDMG)
4
-CoPc (5.0 × 10 mol dm ) in
DMSO /TBAP. a) Eapp = -0.50 V. b) Eapp = -1.25 V. c) Eapp= = 0.80 V. d) Chromaticity
II
−2
diagram (each symbol represents the color of electro-generated species; : [Co Pc ],
I
−2 −1
II
−1 +1
:
[Co Pc ] ; : [Co Pc ] .
21

GCE
GCE/CoPc
0.00
a)
-0.2
b)
GCE/CoCl -DMG
2
GCE/CoPc-DMG
Pt
-
-
-
-
0.25
0.50
0.75
-
0.4
GCE
GCE/CoPc
GCE/CoCl -DMG
2
-0.6
GCE/CoPc-DMG
Pt
1.00
-
-0.8
0.8
-0.6
-0.4
-0.2
0.0
-4.0
-3.5
-3.0
-2.5
-2.0
-2
E (V) vs. RHE
Log (J (mAcm ))
Figure 7. a) LSVs and b) Tafel plots of Pt, GCE, and GCE/CoDMG, GCE/CoPc, and
−
1
GCE/(CoDMG)
4
-CoPc electrodes recorded at 10 mV s scan rate in PBS containing 0.1 M
LiClO at pH 3.40.
4
0.0
-0.5
-1.0
-1.5
Repetitive LSVs of GCE/CoPc-DMG:
th
1
1
LSV
th
0 LSV
th
2
0 LSV
th
3
0 LSV
th
4
0 LSV
th
5
0 LSV
-0.75
-0.50
-0.25
0.00
E (V) vs. RHE
−
1
Figure 8. Repetitive LSVs of GCE/(CoDMG)
4
-CoPc electrode recorded at 10 mV s scan
rate in PBS containing 0.1 M LiClO at pH 3.40.
4
22

Scheme 1. The syntheses of CoPc and (CoDMG) -CoPc.
4
23

Graphical abstract Pictogram
Electrocatalytic Hydrogen Evolution Reaction with a Supramolecular
Cobalt(II)phthalocyanine Carrying Four Cobaloxime Moieties
İbrahim Özçeşmeci, Aykut Demir, Atıf Koca, Ahmet Gül*,
24

Research highlights



A symmetrical phthalocyanine with Pyridyl substituents has been prepared.
It is converted to pentanuclear supramolecule by interaction with CoDMG
Electrochemical properties of the supramolecule and the precursors have been
investigated.

Multi-electron transfer reactions of the supramolecule showed possible usage as
electrocatalysts for HER reactions.
25