Electrochimica Acta 55 (2010) 3118–3122
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
[As
8
W
48
O
184
]
40-
, a new crown-shaped heteropolyanion: Electrochemistry and
electrocatalytic properties towards reduction of nitrite
Malika Ammam
a,b,∗
, Israel-Martyr Mbomekalle
a
, Bineta Keita
a
, Louis Nadjo
a
, Jan Fransaer
b
a
Laboratoire de Chimie Physique, UMR 8000, CNRS, Université Paris-Sud, Bâtiment 350, 91405 Orsay Cedex, France
b
Department of Metallurgy and Materials Engineering (MTM), K.U.Leuven, Kasteelpark Arenberg 44, B-3001, Heverlee, Belgium
article info
Article history:
Received 1 December 2009
Received in revised form 16 January 2010
Accepted 18 January 2010
Available online 25 January 2010
Keywords:
Polyoxometalates
Crown-shaped heteropolyanion
Cyclic voltammetry
Acid–base properties
Electrocatalysis
abstract
The electrochemical behavior of the new crown-shaped heteropolyanion [As
8
W
48
O
184
]
40-
was investi-
gated. Compared to the analogous complex [P
8
W
48
O
184
]
40-
, [As
8
W
48
O
184
]
40-
displayed a close similar
behavior. As previously reported for [P
8
W
48
O
184
]
40-
, [As
8
W
48
O
184
]
40-
is found to be stable in a large
range of pH, roughly from 0 to 8 and found to be slightly more soluble than [P
8
W
48
O
184
]
40-
. Comparison
between the cyclic voltammetry curves of the two complexes reveals that the potentials of the redox
waves of [As
8
W
48
O
184
]
40-
are slightly shifted towards the positive values. Contrary to the high depen-
dence of [P
8
W
48
O
184
]
40-
to buffer capacity of the supporting electrolyte, interestingly, [As
8
W
48
O
184
]
40-
displays less sensitivity. The numerous possibilities for chemical applications opened up by the electro-
chemistry of this new complex are exemplified here by the good linear relationship between the peak
potentials of the redox waves as a function of pH and, by the electrocatalytic reduction of nitrite.
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Polyoxometalates (POMs), as early transition-metal clusters,
attract extensive interest in fields such as catalysis, ion exchange,
electrochemistry, electrochromism, magnetism, and in medicine
[1–7]. Recently, much work was devoted to the synthesis of large
and giants POMs possessing unique structures and properties with
potential applications in catalysis and electrochemistry [8–11].
Among these, crown-shaped heteropolyanion [P
8
W
48
O
184
]
40-
has
been reported by Contant and Tézé [9]. Its synthesis and its for-
mula qualify it as a cyclo-tetramer derived from the lacunary
type-Dawson [P
2
W
12
O
48
]
14-
. Several characteristics attract our
attention for this particular crown-shaped anion more particularly
its stability over a large range of pH (from 0 to 8) and the large
number of electrons involved in its redox processes [12].
The exploration of arsenic (As
V
) as a central heteroatom for
POMs has been reported recently for Dawson-type POMs [13–18].
The initiation of these unprecedented arsenic based POMs aroused
our interest, in view of the possibilities offered to manipulate the
acid–base and redox properties of the new compounds. In addition,
the nature of the central heteroatom was found to influence the
potential locations of the first several waves [15]. A comparison of
∗
Corresponding author at: Department of Metallurgy and Materials Engineering
(MTM), K.U.Leuven, Kasteelpark Arenberg 44, B-3001, Heverlee, Belgium.
Tel.: +32 16 321260; fax: +32 16 321991.
E-mail address: Malika.Ammam@mtm.kuleuven.be (M. Ammam).
a series of monosubstituted Wells–Dawson tungstodiphosphates
and tungstodiarsenates revealed that the presence of the arsenic
heteroatom shift the first several voltammetric waves towards
the positive potential [15]. In the present communication, we
report a new crown-shaped heteropolyanion based on arsenic as
a central heteroatom [As
8
W
48
O
184
]
40-
synthesized following the
procedure reported by Cantant and Tézé [9] for the analogous
complex [P
8
W
48
O
184
]
40-
. The electrochemical behavior of the new
complex is studied as a function of pH and nature of the support-
ing electrolyte. The electrocatalytic properties of the new complex
towards the reduction of nitrite were investigated.
2. Experimental
2.1. Materials
[As
2
W
12
O
48
]
14-
(abbreviated as As
2
W
12
) and [As
8
W
48
O
184
]
40-
(abbreviated as As
8
W
48
) were obtained by the procedure analo-
gous to that used for the synthesis of [P
2
W
12
O
48
]
14-
(abbreviated
as P
2
W
12
) and [P
8
W
48
O
184
]
40-
(abbreviated as P
8
W
48
) [9]. As a key
difference between synthesis of As
8
W
48
and P
8
W
48
, we found that
the yield of As
8
W
48
(∼7%) is largely inferior to the yield of P
8
W
48
(∼50%). Briefly, the synthesis of As
8
W
48
is carried out as follows:
under constant stirring, 28 g (7 mM) of As
2
W
12
were dissolved in
950 mL ultrapure water containing 60 mL (1 M) CH
3
COOH, 21 g
(0.5 M) LiOH and 21 g (0.5 M) LiCl. The solution was left under con-
stant stirring for 15 min. Afterword, the solution was covered with
parafilm and, after 2–3 days fine white radiating needles appeared,
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.01.067