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Spectroscopic Studies of the Glycerol Electro-Oxidation
on Polycrystalline Au and Pt Surfaces in Acidic
and Alkaline Media
Janaina Fernandes Gomes & Germano Tremiliosi-Filho
Published online: 16 March 2011
# Springer Science+Business Media, LLC 2011
Abstract The electro-oxidation of glycerol on Au and Pt was
studied in acid and alkaline media. The reaction intermediates
and products formed were determined by in situ Fourier
transform infrared (FTIR) spectroscopy. The experimental
FTIR spectra measured on Au and Pt in acid and alkaline
media were compared with the standard ones for the
identification of the oxidation products. For Au, the oxidation
reaction is highly dependent on the solution pH. In alkaline
medium, dihydroxyacetone, tartronic acid, mesoxalic acid,
glyoxylic acid, and carbon dioxide are formed while in acidic
medium tartronic acid, formic acid, and carbon dioxide are
formed. However, the oxidation of glycerol on Pt leads to the
formation of tartronic acid, glycolic acid, glyoxylic acid,
formic acid, and carbon dioxide, independent of the solution
pH. For both electrode materials, Pt and Au, carbon dioxide is
detected indicating the possible breaking of the C–C–C bonds.
Clearly, the glycerol oxidation pathways can be controlled by
the nature of the electrode material and solution pH.
Furthermore, glycerol is a typical compound that has poten-
tiality to produce electricity when feed a fuel cell while many
chemicals with commercial interest are concomitantly formed.
Keywords Glycerol oxidation . Polycrystalline Au and Pt
electrodes . Acid medium . Alkaline medium . Reaction
intermediates and products formation
Introduction
Nowadays, in many countries, biodiesel is employed as an
alternative fuel to fossil diesel. Particularly, it is a reality in
Brazil. Biodiesel is produced by a transesterification
reaction. The process involves the catalytic reaction of
vegetable oils or animal fats with a short-chain aliphatic
alcohols, typically methanol or ethanol. In addition to
biodiesel, glycerol is also generated as a co-product of the
transesterification reaction. For each 9 kg of biodiesel, 1 kg
of glycerol is produced [1]. Glycerol is an organic
compound that nowadays, among other applications, is
used in pharmaceutical formulations and cosmetics manu-
facture. However, in a short timescale, the large volume of
glycerol that comes from the biodiesel production will
exceed the actual world demand. In this way, there is an
effort towards to find new applications to the glycerol. One
of the propositions is the utilization of glycerol in direct
glycerol fuel cells for electric energy generation [2]. Thus,
fundamental studies of the mechanism of the glycerol
oxidation are very important. This knowledge is essential to
develop efficient catalysts and to improve the electrochem-
ical process for the application of the glycerol to directly
feed fuel cells. The direct glycerol fuel cell is an alternative
device to hydrogen fuel cell. Theoretically, glycerol could
be employed in fuel cells and its use would have several
advantages in comparison with the use of hydrogen. In
particular, glycerol is a liquid fuel and, therefore, it is
relatively easier to handle, transport and storage than
gases, such as hydrogen. Considering the complete
oxidation of glycerol, which leads to the formation of
CO2 and liberation of 14 electrons/glycerol molecule; the
theoretical energy density of glycerol is comparable with
those of other alcohols, as methanol and ethanol. Specif-
ically, the theoretical energy density of glycerol corre-
sponds to 5.0 kWh kg−1 [3] while those of methanol,
ethanol, and hydrogen are 6.1, 8.1, and 32.8 kWh Kg−1,
respectively [4]. However, the viability of its use depends
on the improvement of the energetic yield of the oxidation
reaction. At the present time, some problems make
J. F. Gomes (*) :G. Tremiliosi-Filho
Instituto de Química de São Carlos, Universidade de São Paulo,
C.P. 780, 13560.970 São Carlos, SP, Brazil
e-mail: janainafg@iqsc.usp.br
Electrocatal (2011) 2:96–105
DOI 10.1007/s12678-011-0039-0
impracticable the application of glycerol in fuel cells. One
of the problems is that the glycerol oxidation occurs by
different reaction pathways some of which lead to partial
oxidation products due to the difficulty of breaking the C–
C–C bonds. This decreases the total efficiency of the
system. Another problem is the formation of adsorbed
intermediates that poison the catalyst surface at low
overpotentials.
In general, the electro-oxidation reactions of alcohols
involve different steps: alcohol adsorption, breaking of the
inter-atomic bonds, electronic charge transfer, reaction
between oxygenated species and fragments from the
alcohol, and reaction products desorption. As a result, the
anode performance depends on the: (1) interaction between
the catalyst surface and the alcohol molecules, (2) interac-
tion between the catalyst surface and the resulting adsorbed
fragments from the original alcohol molecules, and (3)
surface oxides formation. In this context, from the
technological point of view, an efficient catalyst regarding
glycerol electro-oxidation would possibly contain multiple
elements with distinct roles allowing the formation of CO2 at
lower overpotentials and not a single element such as Au and
Pt. In particular, Pt is poisoned by CO at low overpotentials.
On the other hand, from the fundamental point of view, Au
and Pt may be good model catalysts for elementary studies
of the electrochemical oxidation of glycerol.
Previous results on the glycerol oxidation at the
heterogeneous liquid phase [5–10] as well as at the
electrochemical environment [3, 11–13] show that the
oxidation of glycerol can lead to the formation of different
reaction products, such as: glyceraldehyde, glyceric acid,
tartronic acid, glycolic acid, glyoxylic acid, dihydroxyace-
tone, hydroxypyruvic acid, mesoxalic acid, oxalic acid, and
carbon dioxide. There are evidences that the pH [12, 14],
the nature of the catalyst [3, 15], and the presence of a
support [10, 16] influences the catalyst activity and the
reaction selectivity. Furthermore, it is shown that the
selectivity of this reaction also depends on the electrode
potential [3, 12].
Although there are some fundamental studies about
the glycerol electro-oxidation, data regarding the reac-
tion mechanism are still scarce. The electro-oxidation
of glycerol on Pt and Au in alkaline medium has been
very recently investigated by combining voltammetry
with HPLC [17]. This approach provided an interesting
insight into the different mechanisms of the glycerol
oxidation on the two electrodes. With basis on this study,
it is proposed that glyceric acid, glycolic acid, and formic
acid are formed on both Au and Pt. In addition, oxalic
acid and tartronic acid are formed only on the Pt surface.
The glycerol electro-oxidation on Au in alkaline medium
was also recently investigated by in situ Fourier transform
Fig. 1 Cyclic voltammograms
of a polished polycrystalline
gold electrode in 0.1 mol L−1
NaOH (a) and 0.1 mol L−1
glycerol+0.1 mol L−1 NaOH
(b); scan rate 0.050 Vs−1. c In
situ FTIR spectra (P polariza-
tion) of the 0.1 mol L−1 glycerol
+0.1 mol L−1 NaOH/Au inter-
face as a function of the applied
potential. Spectra were
computed from the average of
128 interferograms. The
corresponding potentials are
indicated in the FTIR spectra.
The spectra are offset along the
y-axis for clarity
Electrocatal (2011) 2:96–105 97
infrared (FTIR) spectroscopy [18]. In this study, a
collection of FTIR spectra shows many features related
to the formation of the reaction products. However, only
carbon dioxide is unambiguously identified.
In the present work, the electro-oxidation of glycerol
on polycrystalline Au and Pt surfaces in acidic and
alkaline medium is investigated using in situFTIR
spectroscopy. We explore here the effects of the nature
of the electrode material and the electrolyte solution pH
on the formation of possible different reaction intermedi-
ates and final products. We have performed this funda-
mental spectroelectrochemical study on model Au and Pt
electrodes in acid and alkaline medium in order to
contribute to the understanding of the mechanistic
aspects of the glycerol oxidation on different electrode
materials and solution pH. A better understanding of this
reaction is of considerable importance. One of the
purposes of the research into the glycerol electro-
oxidation is to reach an atomic level understanding of
this reaction for an efficient design of the catalyst and,
consequently, an improvement of this electrochemical
process for fuel cell application in association to
chemicals generation.
Experimental
All the experiments were performed at room temperature
(25 °C±1 °C). The chemicals used for solution preparations
were high-purity sulfuric acid (Merck suprapur®), sodium
hydroxide (99.99% metals basis, Sigma Aldrich), glycerol (J.
T. Baker), and ultrapure water from Millipore system. A
Pt foil and a reversible hydrogen electrode (RHE) were
used as counter and reference electrode, respectively. The
working electrodes were polycrystalline Au and Pt discs
of 0.78 cm2 geometric surface area. They were mechan-
ically polished to a mirror-like finish with alumina powder
(0.05 μm) and chemically cleaned by overnight immersion
in concentrated sulfuric acid and abundant rinsing with
purified water. Prior each experiment, the working electro-
des were heated in a butane–oxygen flame, cooled down
in a reductive H2+N2 atmosphere and quenched in
ultrapure water in equilibrium with this atmosphere.
Electrode surfaces were heated in a flame and cooled in
a controlled atmosphere in order to have a clean surface
and, in addition, they were protected with a waterdroplet
during the transfer to the electrochemical or spectro-
electrochemical cells in order to prevent the contamination
of the surfaces. The working electrode was then
introduced to the cell containing deaerated electrolyte
solution at the open circuit potential and subsequently
was polarized at 0.05 V vs. RHE. In the sequence, cyclic
voltammetry or FTIR spectroscopy experiments were
performed. The cleanliness of the electrolyte solutions
was tested by the stability of the characteristic voltam-
metric features of Au and Pt electrodes.
The FTIR instrument was a Nicolet Nexus 670
spectrometer equipped with a liquid nitrogen cooled
MCT detector. In situ FTIR experiments were performed
in a three-electrode spectro-electrochemical cell with an
IR transparent window (ZnSe) attached to the bottom of
the cell. Details concerning the cell are described
elsewhere [19]. Briefly, a movable piston supports the
working electrode. A platinum or a gold wire connected
to the working electrode passes through the piston and
keeps the electric contact. The ZnSe window functions as
a transparent cover for the cell and, also, as a wall
against which the working electrode is pressed to obtain
a thin film of electrolytic solution. In such a way, during
the FTIR measurements, the absorption of the infrared
beam by the solution is minimized. FTIR spectra were
taken in the wavenumber region between 740 and
4,000 cm−1, and between 0.05 and 1.5 V for Pt, and 0.05
and 1.7 V for Au in 0.05 V steps. Spectra were computed
from the average of 128 interferograms. The spectral
Fig. 2 The 800 to 2,000 cm−1 and 2,300 to 2,400 cm−1 expanded
scale spectral regions of the spectra of the Fig. 1c
98 Electrocatal (2011) 2:96–105
resolution was set to 8 cm−1. Reflectance spectra were
calculated as the ratio (R/Ro) where R represents a spectrum
at the sample potential and Ro is the spectrum collected at
0.05 V. Positive and negative bands represents the consump-
tion and the production of substances at the sample potential,
respectively.
In order to compare the activity of Au and Pt for the
glycerol oxidation in acidic and alkaline media, the
faradaic currents were normalized by the Au- and Pt-
active surface areas. These areas were determined with
basis on the cyclic voltammograms of Au and Pt in the
supporting electrolyte (0.1 M sulfuric acid or 0.1 M
sodium hydroxide). For Pt, the active surface area was
calculated by integrating the faradaic current related to
the hydrogen desorption. The faradaic charge of a
hydrogen monolayer on Pt is assumed to be
210 μC cm−2. For Au, the active surface area was
estimated by integrating the faradaic current referred to
the reduction of the gold oxides formed up to 1.7 V vs.
RHE in the positive-going scan. The faradaic charge
corresponding to the reduction of an AuO monolayer is
assumed as 386 μC cm−2 ([20] and references therein).
Results and Discussion
Figure 1a shows the typical cyclic voltammogram of Au in
alkaline medium. In the positive-going scan, the oxidation
of the gold surface starts close to 1.2 V and in the negative-
going scan the reduction of the gold oxides begins at
approximately 1.3 V. Figure 1b presents the cyclic
voltammogram corresponding to the electro-oxidation of
0.1 M glycerol on Au in alkaline medium. In the positive-
going scan, the oxidation of glycerol begins ca. 0.65 V and
the peak current occurs at 1.4 V. The maximum current
density is about 14 mA cm−2. In the negative-going scan,
gold oxides formed in the positive-going scan are reduced.
Consequently, gold sites become free for reacting with
glycerol molecules close to the surface and the gold
electrode is reactivated. The reactivation of the Au starts
at 1.2 V and the peak current appears at 1.1 V. A set of
FTIR spectra in the wavenumber range from 740 to
4,000 cm−1 is shown in Fig. 1c. These spectra were
obtained during the series of increasing potential steps
from 0.05 to 1.65 V. In general, different bands can be
observed in the FTIR spectra. The occurrence of these
Fig. 3 Cyclic voltammograms of a polished polycrystalline gold
electrode in 0.1 mol L−1 H2SO4 (dashed line) and 0.1 mol L
−1
glycerol+0.1 mol L−1 H2SO4 (solid line) (a); scan rate 0.050 Vs
−1.
Inset expanded scale region of the cyclic voltammograms. In situ
FTIR spectra (P polarization) of the 0.1 mol L−1 glycerol+0.1 mol L−1
H2SO4/Au interface as a function of the applied potential. Spectra
were computed from the average of 128 interferograms. The
corresponding potentials are indicated in the FTIR spectra. The
spectra are offset along the y-axis for clarity
Electrocatal (2011) 2:96–105 99
bands depends on the applied potential. The majority of the
observed signals are associated with the reaction intermedi-
ates and products formed/consumed during the glycerol
oxidation, excepting the bands related to water in the thin
layer. The bands corresponding to the OH bending and OH
stretching vibration modes of water appear at around 1,630
and 3,000 to 4,000 cm−1, respectively. As mentioned
before, in the present work, we performed the FTIR
measurements in a thin layer configuration. It means that
a thin layer of working solution was intentionally formed
between the working electrode and the ZnSe window in
order to minimize the absorption of the IR beam by the
solution. This layer of solution is not absolutely stable
along the FTIR experiments. Solution (55 M water!) can go
in and go out the thin layer and very often the thin layer can
significantly modify. As a result, the FTIR spectra
measured at different potentials usually present strong
variation of intensity of the broad band between 3,000
and 4,000 cm−1 that corresponds at most to the entrance/
exit of water in the thin layer and not to the formation/
consumption of species related to the glycerol oxidation.
The huge variation of intensity of the broad band between
3,000 and 4,000 cm−1 can mask other bands appearing in
this wavenumber region. So, it is difficult to analyze the
bands in this specific region. For this reason, the bands
between 3,000 and 4,000 cm−1 will not be considered in the
analysis of the results. Attention will be focused in two
regions of the FTIR spectra ranging between 800 and
2,000 cm−1 and between 2,300 and 2,400 cm−1. Figure 2
presents an expanded view of the FTIR spectra showed in
Fig. 1c.
Figure 2 shows that the first FTIR bands start to appear
at 0.65 V. This potential coincides with the onset potential
of the electro-oxidation of glycerol on Au, according to the
cyclic voltammogram presented in Fig. 1b. At potentials
higher than 0.65 V, other bands appear. In general, with the
increase of the applied potential, the intensity of the bands
increases. The FTIR spectra taken at 1.55 and 1.65 V
clearly present some bands less evident in the spectra taken
at relatively less-positive potentials. Particularly, in the
wavenumber region between 800 and 2,000 cm−1, FTIR
bands are observed at: 821, 890, 957, 1,006, 1,087, 1,137,
1,308, 1,338, 1,592, and 1,730 cm−1. In the wavenumber
region between 2,300 and 2,400 cm−1, we observe a strong
Fig. 4 Cyclic voltammograms of a polished polycrystalline platinum
electrode in 0.1 mol L−1 NaOH (a) and 0.1 mol L−1 glycerol+
0.1 mol L−1 NaOH (b); scan rate 0.050 Vs−1. c In situ FTIR spectra
(P polarization) of the 0.1 mol L−1 glycerol+0.1 mol L−1 NaOH/Pt
interface as a function of the applied potential. Spectra were computed
from the average of 128 interferograms. The corresponding potentials
are indicated in the FTIR spectra. The spectra are offset along the y-
axis for clarity
100 Electrocatal (2011) 2:96–105
band at 2,340 cm−1 that appears at 1.2 V. This band has been
widely reported in the literature and is assigned to the O–C–O
asymmetric stretching mode of CO2 molecule [18]. The onset
potential of the CO2 formation corresponds to the onset
potential of the gold oxides formation (see cyclic voltammo-
gram presented in Fig. 1a). Therefore, the presence of
oxygenated species on the gold surface promotes the CO2
formation. Furthermore, since we did not observe a detectable
signal corresponding to adsorbed CO species (between 1,870
and 2,050 cm−1), the pathway leading to the formation of CO2
possibly does not involve the formation of adsorbed CO as a
reaction intermediate. Previously, Jeffery and Camara [18]
reported that CO is not formed on gold surfaces in alkaline
medium and they suggest that the formation of CO2 can result
from either the oxidation of the intact glycerol molecule or the
oxidation of formate radicals. The assignment of the other
bands presented in Fig. 2 will be discussed later.
Figure 3a shows the cyclic voltammograms of polycrys-
talline Au in acidic medium in the absence and in the
presence of glycerol. It can be seen that, in acidic medium,
the voltammetric profile of Au in the presence of glycerol is
very close to that of Au in glycerol-free solution. This
indicates that the catalytic activity of gold towards the
glycerol electro-oxidation in acidic medium is very low.
Figure 3b presents a set of FTIR spectra for the electro-
oxidation of glycerol on Au in acidic medium. Concerning
the occurrence of the FTIR bands and the variation of their
intensity as function of the increasing applied potential, we
observe the same tendency as that observed in the FTIR
spectra related to the glycerol oxidation on gold in alkaline
medium. In the wavenumber region ranging between 800
and 2,000 cm−1, the spectra taken at 1.6 and 1.7 V clearly
show FTIR bands at 900, 970, 1,030, 1,050, 1,100, 1,130,
1,207, and 1,730 cm−1. In the wavenumber range from
2,300 to 2,400 cm−1, there is a pronounced band at
2,345 cm−1. In general, the FTIR bands in acid medium
are relatively less intense than those observed for glycerol
oxidation on Au in alkaline medium.
The cyclic voltammograms of the polycrystalline Pt in
alkaline medium in the absence and in the presence of
Fig. 5 Cyclic voltammograms of a polished polycrystalline platinum
electrode in 0.1 mol L−1 H2SO4 (a) and 0.1 mol L
−1 glycerol+
0.1 mol L−1 H2SO4 (b); scan rate 0.050 V s
−1. c In situ FTIR spectra
(P polarization) of the 0.1 mol L−1 glycerol+0.1 mol L−1 H2SO4/Pt
interface as a function of the applied potential. Spectra were computed
from the average of 128 interferograms. The corresponding potentials
are indicated in the FTIR spectra. The spectra are offset along the y-
axis for clarity
Electrocatal (2011) 2:96–105 101
glycerol are displayed in Fig. 4a and b, respectively. The
profile of the cyclic voltammogram of the Pt in alkaline
medium agrees with those previously found in similar
experimental conditions [21]. This attests the quality of the
surface and cleanliness of the solution. In the positive-going
scan, the oxidation of glycerol starts ca. 0.5 V and the peak
current appears at 0.95 V. The maximum current density is
about 8 mA cm−2. In the negative-going scan, the platinum
oxides are reduced. Like this, Pt sites become available for
reacting with glycerol molecules and the Pt electrode is
reactivated. The reactivation of the Pt starts at 0.8 V and the
peak current occurs at 0.7 V. The set of FTIR spectra
(Fig. 4c) shows that the first bands start to appear at 0.5 V.
This potential corresponds to the onset potential of the
glycerol oxidation. At potentials higher than 0.5 V,
different signals appear between 800 and 2,000 cm−1
and between 2,300 and 2,400 cm−1. The intensity of these
signals depends on the applied potential. With the increase
of the applied potential, the intensity of the bands
increases. The spectra taken at 1.4 and 1.5 V clearly show
FTIR bands at: 820, 945, 1,003, 1,065, 1,123, 1,240,
1,620, 1,725, and 2,340 cm−1.
Figure 5a shows the typical cyclic voltammogram of Pt in
acidic medium. Figure 5b presents the cyclic voltammogram
correlated to the electro-oxidation of 0.1 M glycerol over Pt in
acidic medium. In the positive-going scan, the oxidation of
glycerol begins close to 0.5 Vand two peaks appear at ca. 0.75
and 0.8 V. The platinum electrode is reactivated at 1.1 V. In the
negative-going scan, the reactivation of the Pt starts at 0.8 V
and the peak current is observed at 0.6 V. The causes of the
reactivation processes in the positive- and negative-going
scans are different. As discussed before, in the negative-going
scan, the reduction of platinum oxides leads to the formation
of free platinum sites that are then available for reacting with
glycerol molecules. Thus, the platinum electrode is reacti-
vated. In a different way, in the positive-going scan, the
reactivation of the platinum electrode is probably favored by
the oxidation of strongly adsorbed reaction intermediates that
block the platinum surface at low potentials. Because it is
difficult to oxidize these species at low potentials, they form
the so-called catalyst poison. At high potentials, strongly
adsorbed reaction intermediates are oxidized and Pt sites
become free for reacting with glycerol molecules. So, the
platinum electrode is reactivated.
Table 1 Assignment of the main bands observed in the FTIR spectra shown in Figs. 2–5
Au/NaOH
(cm-1) 
Au/H2SO4
(cm-1)
Pt/NaOH
(cm-1) 
Pt/H2SO4
(cm-1) Assignment
821 820 
890 900 906
957 945 952 δ(CH) of 
aldehydes
970
1,006 1,003 1,010
1,030
1,050
1,065 1,072
1,087 
1,100
1,137 1,130 1,123 1,126
ν(C-O) of alcohols
1,207 1,207
1,240
1,308 
ν(C-O) of 
carboxylic acids;
ν(C-C) of aliphatic
ketones
1,338 
δ(OH) of alcohols;
ν(C-C) of aliphatic
ketones
1,408 ν(O-C-O) ofglyceratead
1,592 
1,620 1,640 δS(OH) of water 
1,730 1,730 1,725 1,730
ν(C=O) of
carboxylic acids,
ketones and
aldehydes
2,340 2,345 2,340 2,345 νA(O=C=O) 
102 Electrocatal (2011) 2:96–105
Fig. 7 Comparison between the in situ FTIR spectra of the glycerolelectro-oxidation on Au and Pt surfaces in acidic and alkaline media
and the standard FTIR spectra of the reaction products: a in situ FTIR
spectrum of the glycerol on Au in alkaline medium at 1.55 V and
standard FTIR spectra of dihydroxyacetone, tartronic acid, mesoxalic
acid, and glyoxylic acid; b in situ FTIR spectrum of the glycerol on
Au in acidic medium at 1.7 V and standard FTIR spectra of tartronic
acid and formic acid; c in situ FTIR spectrum of the glycerol on Pt in
alkaline medium at 1.5 V and the standard FTIR spectra of tartronic
acid, glycolic acid, glyoxylic acid, and formic acid; d in situ FTIR
spectrum of the glycerol on Pt in acidic medium at 1.2 V and the
standard FTIR spectra of tartronic acid, glycolic acid, glyoxylic acid,
and formic acid
Fig. 6 Standard FTIR spectra of
glycerol, dihydroxyacetone,
tartronic acid, mesoxalic acid,
glycolic acid, oxalic acid,
glyoxylic acid, and formic acid.
The spectra are offset along the
y-axis for clarity
Electrocatal (2011) 2:96–105 103
The faradaic current densities related to the glycerol
electro-oxidation on Pt in acidic medium are lower than those
referred to the electro-oxidation of glycerol on Pt in alkaline
medium. In the FTIR spectrum taken at 1.2 V (Fig. 5c),
different bands clearly appear at 906, 952, 1,010, 1,072,
1,126, 1,207, 1,640, 1,730, and 2,345 cm−1. Despite the
difference concerning the faradaic current density, the FTIR
spectra are very close to those associated with the same
reaction on Pt in alkaline medium.
Assignment of the FTIR Bands
Table 1 summarizes the FTIR results for the glycerol
oxidation on Au and Pt in acidic and alkaline media. In
general, the observed features are assigned to bending and
stretching vibration modes of aldehydes, alcohols, carboxylic
acids, and ketones.
Some expected products of the glycerol oxidation
were independently analyzed by FTIR spectroscopy
(not in situ) in order to produce standard spectra at
liquid phase. The considered products were dihydroxy-
acetone, tartronic acid, mesoxalic acid, glycolic acid,
oxalic acid, glyoxylic acid, and formic acid. Addition-
ally, glycerol was also explored. The standard spectra
of these compounds at liquid phase are displayed in
Fig. 6.
Given the in situ FTIR results of the glycerol electro-
oxidation studies on Au and Pt surfaces in acidic and
alkaline media, in conjunction with the standard FTIR
spectra of some of the possible reaction products, we
suggest that the reaction on Pt in acidic as well as in
alkaline medium leads to the formation of tartronic acid,
glycolic acid, glyoxylic acid, and formic acid, in addition to
carbon dioxide. Over Au in acidic medium, the glycerol
oxidation forms tartronic acid, formic acid and, additional-
ly, carbon dioxide. Finally, we suggest that over Au in
alkaline medium, the reaction leads to the formation of
tartronic acid, mesoxalic acid, glyoxylic acid, and also
carbon dioxide. Additionally, we have evidences (FTIR
bands at 1,308 and 1,338 cm−1) that dihydroxyacetone is
also formed during the glycerol electro-oxidation on Au in
alkaline medium. The formation of other reaction products
(different from those products considered here) cannot be
excluded. Figure 7a–d shows the direct comparison
between the in situ FTIR spectra of the glycerol electro-
oxidation on Au and Pt surfaces in acidic and alkaline
Fig. 8 Suggested intermediates of the glycerol oxidation on platinum and gold electrodes in acidic and alkaline media
104 Electrocatal (2011) 2:96–105
media at high potentials and the standard FTIR spectra of
the reaction products suggested above.
Based on the evidences presented in the current work,
the probable products of the electro-oxidation of glycerol
on platinum and gold in acidic and alkaline solutions are
summarized in Fig. 8.
Conclusions
✓ Au in alkaline medium is more active for the glycerol
electro-oxidation than Au in acidic medium;
✓ The selectivity of the reaction over Au depends on
the pH. In alkaline medium, dihydroxyacetone,
tartronic acid, mesoxalic acid, glyoxylic acid, and
carbon dioxide are formed while in acidic medium
tartronic acid, formic acid and carbon dioxide are
formed.
✓ Pt in alkaline medium is more active for the glycerol
electro-oxidation than Pt in acidic medium but less active
than Au in alkaline medium (at high overpotentials).
✓ For the considered products, the selectivity of the
glycerol electro-oxidation over Pt does not depend on
the pH. In alkaline as well as in acidic medium
tartronic acid, glycolic acid, glyoxylic acid, formic
acid, and carbon dioxide are formed.
✓ Finally, the present work can be useful to consider
future studies on the glycerol oxidation. In general,
efforts should be done in order to reach an atomic
level understanding of this reaction. Specifically, the
identification of the adsorbed intermediates and final
products of the glycerol oxidation as well as their
relation with: (1) the geometric and electronic properties
of the electrodes, (2) the glycerol concentration, and (3)
the working conditions (electrolyte solution, tempera-
ture, etc.) are very important points for the understanding
of the reaction mechanism. This knowledge is absolutely
important for designing catalysts more tolerant with
respect to the poisoning adsorbed intermediates and, in
addition, more selective towards the CO2 formation.
Catalysts with these characteristics would allow us to
improve the glycerol electro-oxidation process for fuel
cell applications.
Acknowledgments The authors gratefully acknowledge CNPq,
Capes, and FAPESP for the financial support of this work. JFG thanks
FAPESP for a post doctoral fellowship (process number: 2009/08511-9).
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Electrocatal (2011) 2:96–105 105
	Spectroscopic Studies of the Glycerol Electro-Oxidation on Polycrystalline Au and Pt Surfaces in Acidic and Alkaline Media
	Abstract
	Introduction
	Experimental
	Results and Discussion
	Assignment of the FTIR Bands
	Conclusions
	References