A novel fabrication of a polymeric ionic liquid hybrid film modified electrode and its successful application to the electrogeneration of a superoxide anion in aqueous media

Article abstract of DOI:10.1039/c4cc08410a

A novel polymeric ionic liquid hybrid film-modified electrode, in which the electrode surface is coated with a hydrophobic hybrid material composed of an ionene polymer with quaternary ammonium sites in its polymeric backbone and ionic liquids, was fabricated by electropolymerization of N,N-dimethylaniline in a hydrophobic ionic liquid, which can be applied for the electrogeneration of a superoxide anion via one-electron reduction of O₂ in aqueous media. This journal is

Full text of DOI:10.1039/c4cc08410a

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A novel fabrication of a polymeric ionic liquid
hybrid film modified electrode and its successful
application to the electrogeneration of a
superoxide anion in aqueous media†
Cite this:DOI: 10.1039/c4cc08410a
Received 24th October 2014,
Accepted 12th January 2015
a
b
b
a
Dilani Nilushika, Mohamed I. Awad, Mahmoud M. Saleh, Takeyoshi Okajima,
DOI: 10.1039/c4cc08410a
c
a
Lanqun Mao and Takeo Ohsaka*
www.rsc.org/chemcomm
A novel polymeric ionic liquid hybrid film-modified electrode, in applications for ion transfer across the IL/aqueous solution inter-
which the electrode surface is coated with a hydrophobic hybrid face, concentration of redox active anions from the aqueous
material composed of an ionene polymer with quaternary ammo- phase, electrochemical sensing, electrocatalysis, stable immobili-
3,4
nium sites in its polymeric backbone and ionic liquids, was fabricated zation of enzyme for biosensing, fuel cells, etc.
by electropolymerization of N,N-dimethylaniline in a hydrophobic In this communication, we report a novel, simple fabrication
ionic liquid, which can be applied for the electrogeneration of a of a polymeric ionic liquid hybrid (PILH)-modified electrode, in
superoxide anion via one-electron reduction of O
2
in aqueous media. which the electrode surface is coated with an ionene polymer with
quaternary ammonium sites in its polymeric backbone and ILs
Room Temperature Ionic Liquids (RTILs), being entirely composed are embedded into its matrix, via electropolymerization of
of cations and anions, have been receiving intense attention as a N,N-dimethylaniline in ILs. This PILH-modified electrode is
1
new class of solvents that offer alternatives to conventional applied successfully for electrogeneration of a superoxide anion
À
ꢀ
molecular solvents for numerous applications in the general field (O
of chemistry, because of their unique physicochemical properties conventional O
such as low volatility, nonflammability, electrochemical and and H O, respectively, depending on the electrocatalyst used). The
thermal stability and high ionic conductivity) which could be present idea for preparing the PILH film with a polymeric ionene
2
) via 1e-reduction of O
2
in aqueous media in contrast to the
2
reduction (i.e., 2e- and 4e-reductions of O
2
2 2
to H O
5
(
2
2
À
ꢀ
arbitrarily tailored by appropriately choosing cations and anions.
structure in which O2 is chemically stable is developed originally
Since the late 1990s, RTILs have been also deliberately used for from our previous studies on the preparation of such polymeric
electrode modifications by covering electrode surfaces typically ionone films by electropolymerization of dialkylanilines, which
with free-standing IL films, IL droplets, adsorbed ILs, mixtures of was carried out in acidic aqueous media, and recent studies on
ILs and other components (such as organic or inorganic polymers, the electrochemistry of the O
nanoparticles, nanotubes and other micro- or nano-objects) and The PILH film-modified electrode was prepared by an
polymeric ILs. By careful and appropriate choice of the cation oxidative electropolymerization of N,N-dimethylaniline (DMA)
and anions, we can introduce, for example, a hydrophobic IL in hydrophobic IL, typically N-methyl-N-propyl-pyrrolidinium
domain on electrode surfaces and the resulting IL-modified bis(trifluoromethanesulfonyl) imide ([MPP] [N(Tf) ] , Kanto
6
7
-
ꢀ
2
/O
2
redox couple in ILs.
3
+
À
2
electrodes are expected to allow for electrochemical experiments Chemicals Co. Japan) with a purity of 499% and less than
in aqueous media with fundamental and practical prospective 0.005% water (Scheme 1). The anodic peak corresponding to
a
Department of Electronic Chemistry, Interdisciplinary Graduate School of Science
and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-Ku,
Yokohama 226-8502, Japan. E-mail: ohsaka@echem.titech.ac.jp;
Fax: + 81-45-924-5489; Tel: + 81-45-924-5404
b
Chemistry Department, Faculty of Science, Cairo University, Cairo 12613, Egypt
c
Beijing National Laboratory for Molecular Science, Institute of Chemistry,
Chinese Academy of Science, 2 Zhongguancum North First Street, Beijing 100190,
P. R. China
†
Electronic supplementary information (ESI) available: Preparation of PDMA
+
À
from aqueous solution, surface image, surface profiles. See DOI: 10.1039/
c4cc08410a
Scheme 1 Electro-oxidative polymerization of DMA in [MPP] [N(Tf) ] ,
2
+
À
resulting in a PILH film impregnated with [MPP] [N(Tf) ] .
2
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+
À
Fig. 1 Consecutive CVs (100 cycles) at GC electrode in IL [MPP] [N(Tf)
2
]
À1
containing 0.2 M DMA at 50 mV s under Ar atmosphere. The inset shows
an LSM image of the PILH-modified GC electrode.
Fig. 2 Deconvoluted N1s spectra of PILH of PDMA film.
+
ꢀ
+
the formation of the monocation radical (DMA ) of DMA was the quaternary ammonium sites of [MPP] , respectively. The
observed at ca. 0.8 V and on successive potential cycling this comparison of each area of these three peaks indicates that the
anodic peak current continuously decreased and actually ratio of the total area of two cationic N moieties to the peak area
completely disappeared after the 100th scan (Fig. 1), suggesting of the anionic N moiety is almost close to unity and at the same
the formation of an electroinactive polymer film (poly(N,N- time confirms that the obtained PILH film is composed of a
+
ꢀ
À
2
dimethylaniline), PDMA) through the polymerization of DMA
on the electrode surface and that new DMA monomers from the anion and the neat IL, [MPP] [N(Tf)
cationic ionene polymer, PDMA with [N(Tf)
]
as a counter
(Scheme 1).
into the PILH film of PDMA
reach the electrode surface and then they are oxidized to was used to confirm its polycationic ionene property and
+
À
2
]
+
À
3À
6
bulk of the [MPP] [N(Tf)
2
]
must diffuse through this film to
Immobilization of [Fe(CN) ]
+
ꢀ
DMA , i.e., the film becomes more compact as the electrolysis further to examine the anion-exchange capability. Incorpora-
+
ꢀ
3À/4À
6
proceeds and the diffusion of DMA and DMA through the tion of the [Fe(CN)
]
redox couple into the PDMA film was
formed film is retarded accordingly and thus a limiting film examined by consecutively recording a series of cyclic voltam-
thickness is finally reached. Actually, the thickness of the mograms (CVs) obtained with the PDMA film-modified GC
PDMA film obtained by the potential scan for 100 times was electrode in 0.1 M phosphate buffer solution (PBS) containing
3
À
ca. 16 mm and further scan did not increase it (Fig. S3, ESI†). 0.1 mM [Fe(CN)
6
]
(Fig. 3A). At a glance, we can see that the
This maximum thickness is much larger than that (ca. 1 mm) of redox response corresponding to the redox reaction of the
6
3À/4À
the PDMA film prepared in aqueous media (Fig. S1–S3, ESI†).
[Fe(CN)
6
]
couple increases with increasing potential scan
The obtained cyclic voltammetric behaviour (Fig. 1) is essentially duration and the response reaches a constant after a potential
almost the same as that obtained for the electropolymerization of scan of ca. 90 min and the peak height is about 20 times larger
N,N-dialkylanilines in acidic aqueous media (Fig. S1, ESI†), but than that (the dashed line in Fig. 3A) at the bare GC electrode in
3
À
formation of the dimer, tetramethylbenzidine (TMB), the redox the same solution, indicating the incorporation of [Fe(CN) ]
6
3
À/4À
response of which is faintly observed at ca. 0.4 V only in the initial into the PDMA film via anion exchange. The thus [Fe(CN)
]
6
-
+
ꢀ
several scans, by a tail–tail coupling of DMA is considerably less incorporated PDMA modified electrode was transferred into the
3À
and the decrement in the main anodic peak current upon the [Fe(CN)
potential cycling is larger. These facts indicate that the electro-
polymerization of DMA is more feasible under the present IL
6
] -free supporting electrolyte (0.1 M PBS) and the CV
6,8
condition compared with that in aqueous media. The PILH film
exhibits a uniform microporous structure (inset in Fig. 1) being
different from the PDMA films (prepared in aqueous media) with
slightly compact microstructure and poor porosity (Fig. S2, ESI†)
and the films of aniline and its derivatives, which have irregular
9
grains, slice or rod-like structures.
The obtained PDMA film is a composite impregnated with the
IL used, as can be seen from the deconvoluted N1s XPS spectra
10
(
Fig. 2). That is, three different peaks were obtained; the peak at
03.5 eV corresponds to the quaternary ammonium sites in the
PDMA backbone and the remaining two peaks at 399.6 and
02.7 eV, which were also observed for the IL used itself
Fig. 3 (A) Continuous potential cycling at the PILH film-modified GC electrode
solid line) and the bare GC electrode (dashed line) in 0.1 M PBS solution (pH 7)
4
(
3À
3À/4À
containing 0.1 mM [Fe(CN)
6
]
. (B) CV response of [Fe(CN)
6
]
immobilized
4
3À
PILH film-modified GC electrode in [Fe(CN)
6
]
-free 0.1 M PBS. (C) Variation of
À
À
3À
À1
(Fig. S4, ESI†), correspond to the –N -group of [N(Tf)
2
]
and G([Fe(CN)
6
]
) with pH. Potential scan rate: 10 mV s
.
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response was examined (Fig. 3B). A small decrease in the current
response was observed only for the initial few scans and after
that, a stable response was obtained. In addition, we found that
3À
the surface coverage (G([Fe(CN)6] )) of the incorporated
3
À
3À
[
Fe(CN)6]
does not change with pH when the [Fe(CN)6]
-
-
3
À
incorporated PDMA electrode was transferred into the [Fe(CN)
6
]
free electrolyte solutions of various pHs (Fig. 3C). In this case,
3
À
À9
À2
G([Fe(CN)
(
6
]
) = 2.0 Â 10 mol cm , corresponding to ca. 1.3 mM
2À
ꢀ
2
Scheme 2 (A) O
at the PILH modified electrode in aqueous media and (B) O
catalyzed by SOD enzyme at the PILH film/aqueous interface.
electrogeneration via one-electron reduction of O
based on the thickness of 16 mm) which is 13 times the concen-
tration (0.1 mM) of the [Fe(CN)
À
ꢀ
2
dismutation
3
À
6
]
solution into which the PDMA-
modified electrode was soaked. These facts demonstrate that the
3À/4À
[Fe(CN)6]
couple is electrostatically incorporated, concentrated
1
3
highly and immobilized stably in the PDMA film. In other words, such as DMSO, DMF, and AN as well as those (ca. 115 and
the present PDMA is a polycationic ionene polymer with positively 170 mV, respectively) obtained at the bare GC electrode in
+
À
+
À
charged ammonium sites in its backbone and thus has a pH- [MPP] [N(Tf)
2
]
and [TMPA] [N(Tf)
2
]
(Fig. 4B(b) and (c)). The
independent anion-exchange property (eqn (1)).
large DE in Fig. 4A(b) may be due to the retarded diffusion of O
p
ꢀ
2
À
+
À
and O2 and the electrolyte ions ([MPP] and [N(Tf) ] ) through
2
the coating of insulating PDMA. The results in Fig. 4 demonstrate
that the present PILH modified electrode can be successfully
À
ꢀ
applied for the electrogeneration of O
2
via 1e-reduction of O
2
in
(1)
aqueous media (Scheme 2(A)), in which the PILH film is only an
electrolyte layer, while the electrochemical reaction takes place
on the GC substrate surface, in contrast to the conventional O
2
5
reductions, i.e., 2e- and 4e-reductions of O
2 2 2 2
to H O and H O,
respectively, depending on the electrode used.
Fig. 4A(b) shows a typical CV obtained at the PILH film-
modified GC electrode in O -saturated 0.1 M PBS (pH 10.0). A
couple of well-defined redox peaks were obtained at around
À
ꢀ
The formation of O2 in aqueous media was also confirmed
2
ꢀ
by examining the O
2
/O
2À
redox reaction in the presence of
superoxide dismutase (SOD), which effectively catalyzes the
À0.6 V vs. Ag/AgCl/KCl (sat.) and the redox behaviour (eqn (2))
À
ꢀ
14
À
ꢀ
2 2
is almost the same as those (Fig. 4B(b) and (c)) for the O /O
dismutation of O
Interestingly, the anodic peak for the oxidation of O
appears completely, while the cathodic one corresponding to the
reduction of O is almost doubled as expected for a fast dismuta-
. The overall O reduction is expressed by eqn (3).
2
to O and H O (Fig. 4A(c) Scheme 2(B)).
2 2 2
À
ꢀ
2
dis-
couple in a hydrophobic IL, N,N,N-trimethyl-N-propylammonium
+
À
bis(trifluoromethanesulfonyl)imide ([TMPA] [N(Tf) ] ) in which
2
+
2
is [TMPA] has a quaternary ammonium group similar to the
N,N-dimethyl ammonium moieties of PDMA and [MPP] [N(Tf)
À
+
À 11 tion of O
2
2
2
] .
2
O + e $ O
2À
ꢀ
(2)
The cathodic peak can be assigned to the one-electron reduction
(3)
À
ꢀ
of O
2
2À
to O
2
, while the anodic one corresponds to the oxidation
ꢀ
a
of O
cathodic one (I
about 350 mV, too large compared with the DE
theoretically expected for a one-electron reversible redox reac-
to O
2
. The ratio of the anodic peak current (I
p
) to the
) is close to unity and the peak separation (DE ) is
of 59 mV
c
p
p
2À
ꢀ
Again, such a fact confirms the O
reduction of O
generation via the 1e-
at the present PILH-modified electrode in aqueous
solution and at the same time demonstrates that this modified
electrode could be applied for electrochemically clarifying various
chemical and biochemical reactions of unstable O2 , typically at
a hydrophilic/hydrophobic interface similar to biological circum-
p
2
1
2
tion and the DE values obtained in conventional aprotic media
p
À
ꢀ
À
ꢀ
15
stances where O
2
plays various physiological roles.
In conclusion, we have fabricated a novel polymeric ionic
liquid composite film-modified electrode by electro-oxidative
polymerization of DMA in a hydrophobic ionic liquid, typically
+
À
[
MPP] [N(Tf) ] . The electrode surface is coated with a hydro-
2
phobic composite composed of an ionene polymer, PDMA, with
quaternary ammonium sites in its polymeric backbone and ionic
Fig. 4 (A) CVs at the PILH film-modified GC electrode in the absence
+
À
liquids [MPP] [N(Tf) ] and thus its use in aqueous media inevitably
2
(
a, b) and the presence (c) of 12 mM SOD in 0.1 M PBS (pH 10.0) under (a) Ar
establishes a hydrophobic ionic liquid layer/hydrophilic water inter-
face on the electrode surface. This modified electrode actually
allowed us to electrogenerate a superoxide anion in aqueous media
and (b, c) O
2
atmosphere and (B) CVs at the bare GC electrode in (b)
+
À
À
+
À
[
[
TMPA] [N(Tf)
TMPA] [N(Tf)
2
]
]
and (c) [MPP] [N(Tf)
under Ar atmosphere at 100 mV s
2
]
under O
2
atmosphere and in (a)
.
+
À1
2
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via 1e-reduction of O
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2
(which is usually possible in conventional
6 (a) N. Oyama, T. Ohsaka and T. Shimizu, Anal. Chem., 1985,
57, 1526; (b) T. Oshaka, T. Okajima and N. Oyama, J. Electroanal.
Chem., 1986, 200, 159.
(a) X. J. Huang, E. I. Rogers, C. Hardacre and R. G. Compton, J. Phys.
Chem. B, 2009, 113, 8953; (b) M. Hayyan, F. S. Mjalli, M. A. Hashim,
I. M. AlNashef, S. M. Alzahrani and K. L. Chooi, J. Electroanal. Chem.,
012, 664, 26; (c) M. M. Islam and T. Ohsaka, J. Phys. Chem. C, 2008,
12, 1269; (d) C. Pozo-Gonzalo, P. C. Howlett, J. L. Hodgson,
L. A. Madsen, D. R. MacFarlane and M. Forsyth, Phys. Chem. Chem.
Phys., 2014, 16, 25062; (e) S. K. Praneshwar, J. R. Monnier,
M. A. Matthews and J. W. Weidner, Anal. Bioanal. Electrochem.,
1
3
7
aprotic organic media and some ILs, but not in protic media (e.g.,
5
water) ), opening a new avenue for electrochemically studying
7
various chemical and biochemical reactions and reactivities of
À
ꢀ
O2 at a hydrophobic layer/hydrophilic liquid interface, similar
2
1
À
ꢀ
to biological circumstances where O
logical roles.
2
plays various physio-
The present work was financially supported by Grant-in-Aid
for Scientific Research (A) to T. O. from the Ministry of Educa-
tion, Culture, Sports, Science, and Technology (MEXT), Japan
and to D. N. from Tokyo Institute of Technology Global COE
program for Energy Science.
2
013, 5, 711; ( f ) T. Nakagawa, Y. Katayama and T. Miura, ECS
Trans., 2012, 50, 159; (g) A. Rene, D. Hauchard, C. Lagrost and
P. Hapiot, J. Phys. Chem. B, 2009, 113, 2826.
8
9
O. Ocon and P. Herrasti, J. Mater. Sci., 1991, 26, 6487.
(a) S. Golczak, A. Kanciurzewaks, M. Faheman, K. Langer and
S. S. Langer, Solid State Ionics, 2008, 179, 2234; (b) M. H. Pournaghi-
Aazar and B. Habibi, Electrochim. Acta, 2007, 52, 4222; (c) M. C. Li,
C. A. Ma, B. Y. Liu and Z. M. Jim, Electrochem. Commun., 2005, 7, 209.
Notes and references
1
0 M. Shigeyasu, H. Murayama and H. Tanaka, Chem. Phys. Lett., 2008,
1
(a) Ionic Liquids in Synthesis, ed. P. Wassersheid and T. Welton,
Wiley-VCH, Weinheim, 2003; (b) Ionic Liquids: Industrial Applications 11 Here note that, in Fig. 4B, Ag, wire was used as quasi-reference electrode
463, 373.
À
ꢀ
for Green Chemistry, ed. R. Rogers and K. R. Seddon, ACS Symp.Ser.,
002, p. 818; (c) Electrochemical Aspects of Ionic Liquids, ed. H. Ohno,
to avoid any contamination of water to which O
chemically. The difference in the formal potentials of the O
couple in [TMPA] N(Tf)
À
in the solvation energies of O and/or O
2 2
2
is very sensitive
À
ꢀ
2
2
2
/O
reflects the difference
ꢀ
in both ionic liquids.
+[
À
+[
À
2
John Wiley and Sons, New Jersey, 2005; (d) B. Kirchner, Ionic Liquids,
2
] and [MPP] N(Tf) ]
Topics in Current Chemistry, Springer, 2009.
2
3
4
(a) T. Welton, Chem. Rev., 1999, 99, 2071; (b) P. Wassercheid and 12 A. J. Bard and L. R. Faulkner, Electrochemical Methods: Fundamentals
W. Keim, Angew. Chem., Int. Ed., 2009, 39, 3772. and Applications, John Wiley and Sons, inc., New York, 2nd edn, 2001.
M. Opallo and A. Lesniewski, J. Electroanal. Chem., 2011, 656, 2 and 13 T. D. T. Sawyer, Oxygen Chemistry, Oxford Univ. Press, New York,
references therein. 1991.
(a) J. D. Wadhawan, U. Schroder, A. Neudeck, S. J. Wilkins, R. G. 14 (a) T. Ohsaka, Y. Tian, M. Shioda, S. Kasahara and T. Okajima, Chem.
compton, F. Marken, C. S. Consorti, R. F. de Souza and J. Dupont,
J. Electroanal. Chem., 2000, 493, 75; (b) V. A. Hernandez and F. Scholz,
Electrochem. Commun., 2006, 8, 967; (c) Y. Shen, Y. Zhang, X. Qiu,
H. Guo, L. Niu and A. Ivaska, Green Chem., 2007, 9, 746; (d) Y. Liu,
L. Huang and S. Dong, Biosens. Bioelectron., 2007, 23, 35.
K. Kinoshita, Electrochemical Oxygen Technology, John Wiley & Sons,
Inc, New Jersey, 1992.
Commun., 2002, 990; (b) Y. Tian, L. Mao, T. Okajima and T. Ohsaka, Anal.
Chem., 2002, 74, 2428; (c) Y. Tian, T. Ariga, N. Takashima, T. Okajima,
L. Mao and T. Ohsaka, Electrochem. Commun., 2004, 6, 609; (d) Y. Tian,
L. Mao, T. Okajima and T. Ohsaka, Anal. Chem., 2004, 76, 4162.
15 Reactive Oxygen Species in Biological Systems: An Interdisciplinary
Approach, ed. D. L. Gilbert and C. A. Colton, Kluwer Academic/
Plenum Publishers, New York, 1999.
5
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