Journal of Power Sources 196 (2011) 4193–4199
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Journal of Power Sources
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Homolytic cleavage C–C bond in the electrooxidation of ethanol and bioethanol
J. Barroso
a,∗
, A.R. Pierna
a,1
, T.C. Blanco
a
, E. Morallón
b
, F. Huerta
c
a
Dept. Ingeniería Química y del Medio Ambiente, Universidad del País Vasco, Plaza de Europa 1, CP 20018, San Sebastián, Spain
b
Dept. Química Física, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain
c
Dept. Ingeniería Textil y Papelera, Universidad Politécnica de Valencia, Plaza Ferrándiz y Carbonell 1, E-03801 Alcoy, Spain
article info
Article history:
Received 30 July 2010
Received in revised form
16 September 2010
Accepted 29 September 2010
Available online 7 October 2010
Keywords:
Bi-catalytic catalysts
Ethanol
Bioethanol
Electrooxidation
Acetic acid
CO
2
abstract
Nowadays, the studies are focused on the search of better electrocatalysts that promote the complete
oxidation of ethanol/bioethanol to CO
2
. To that end, amorphous bi-catalytic catalysts of composition
Ni
59
Nb
40
Pt
1−x
Y
x
(Y = Cu, Ru, x = 0.4% at.) have been developed, obtained by mechanical alloying, resulting
in higher current densities and an improvement in tolerance to adsorbed CO vs. Ni
59
Nb
40
Pt
1
catalyst. By
using voltammetric techniques, the appearance of three oxidation peaks can be observed. The first peak
could be associated with the electrooxidative process of ethanol/bioethanol to acetaldehyde, the second
peak could be the oxidation of acetaldehyde to acetic acid, and the last peak might be the final oxidation to
CO
2
. Chrono-amperometric experiments show qualitative poisoning of catalytic surfaces. However, the
in situ Fourier Transformed Infrared Spectroscopy, FTIR, is used for the quasi-quantitative determination
with which can be observed the appearance and evolution of different vibrational bands of carbonyl
and carboxylic groups of different species, as it moves towards anodic potential in the electrooxidative
process.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Nowadays, there is a wide interest in the development of fuel
cells of direct ethanol (DEFCs), and the employment of ethanol
and/or bioethanol as renewable and sustainable fuel with the
environment, is in its heyday. The completed electrooxidation of
ethanol/bioethanol to CO
2
[1,2] involves the transference of 12
electrons in the anodic reaction (1), as follows:
CH
3
CH
2
OH + 3H
2
O → 2CO
2
+ 12H
+
+ 12e
−
(1)
However, the homolytic cleavage of C–C bond is the determining
stage of electrooxidative process, limiting the electronic transfer to
4 electrons, as follow in reaction (2):
CH
3
CH
2
OH + H
2
O → CH
3
COOH + 4H
+
+ 4e
−
(2)
Considering working conditions, for a DEFC at 0.5 V at
50 mA cm
−2
with complete oxidation to CO
2
, the energy efficiency
(3) would be:
ε
C
2
H
5
OH/O
2
cell
=
Á
exp
FE(|j|)
−H
0
= ε
rev
eq
× ε
E
× ε
F
=
W
el
(−H
0
)
∗
Corresponding author. Tel.: +34 943 017 127, fax: +34 943 017 131.
E-mail addresses: jbarroso003@ikasle.ehu.es, javierbarrosolazaro@yahoo.es
(J. Barroso), iapropia@sp.ehu.es (A.R. Pierna).
1
Tel.: +34 943 017 183.
×
E
work
E
0
eq
×
Á
exp
Á
th
= 0.424 (3)
If the electrooxidative process stops at the acetic acid, which
involves 4 electrons instead of 12 electrons, the energy efficiency
will be reduced by one third, being only 0.14. Therefore, the real
electric efficiency obtained with the DEFCs, are below 50% [3]. The
cell voltage E (j) decreases greatly due to three limiting factors: the
charge transfer overvoltages at the anode and cathode, the ohmic
drop in the electrolyte and interface, and the mass transfer limita-
tions for reactants and products.
To get a higher conversion of chemical energy in electricity, the
search of better electrocatalysts is necessary [4]. The nature and
structure of these new electrodic materials affect the electroox-
idative process, controlling the formation of adsorbed species and
final products, and favouring the cleavage of C–C bond. Nowadays,
one of the most important research activities is the development
of Pt catalysts. Platinum is regarded as the most active material
for ethanol/bioethanol electrooxidation, especially in acid media,
which is the only active and stable noble metal. However, its global
shortage makes it very expensive. In addition, the platinum itself is
known for the fast poisoning of its surface, especially for CO. Previ-
ous electrochemical works have been carried out on metal–metal
glasses, but few studies have focused on Ni
60
Nb
40
based amorphous
alloys. These metals are alloyed with platinum, which are used as
anodic materials for electrochemical treatments of different toxic
compounds and for its application in fuel cells [5,6]. The amorphous
0378-7753/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2010.09.087