Identification of chemicals resulted in selective glycerol conversion as sustainable fuel on Pd-based anode nanocatalysts

Article abstract of DOI:10.1039/c4ra09822f

Palladium-based nanoparticles were prepared using mild microwave-assisted heating. The activity of carbon supported PdM (M = Mn and Fe) toward glycerol oxidation in alkaline medium was studied by coupling electrochemical, analytical and in situ spectroscopic techniques. The complementary findings showed that glycerol was converted into oxalate, tartronate, glycerate, glycolate and formate. The ex situ analytical methods (liquid chromatography and mass spectrometry) were helpful to reveal glycerate as the major reaction product on PdM/C anodes, while from in situ infrared spectroscopy measurements no irreversible adsorbed poisoning species was detected in glycerol or intermediate oxidation to carbonate at the prepared electrodes. The correlation of the analytical and physicochemical (XRD, EDX and TEM) results concerned the shift of the onset potential toward lower values and the high Faradaic currents due to electronic structures provided by the Mn and Fe contents to the Pd based materials. Accordingly, glycerol is a sustainable raw material, which can be used in cogeneration processes for renewable energy sources and selective production of added-value molecules.

Full text of DOI:10.1039/c4ra09822f

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PAPER
Identification of chemicals resulted in selective
glycerol conversion as sustainable fuel on Pd-based
anode nanocatalysts
Cite this: RSC Adv., 2014, 4, 64476
L. M. Palma,a T. S. Almeida,a V. L. Oliveira,b G. Tremiliosi-Filho,b E. R. Gonzalez,b
a
c
c
c
c
*
A. R. de Andrade, K. Servat, C. Morais, T. W. Napporn and K. B. Kokoh
Palladium-based nanoparticles were prepared using mild microwave-assisted heating. The activity of
carbon supported PdM (M ¼ Mn and Fe) toward glycerol oxidation in alkaline medium was studied by
coupling electrochemical, analytical and in situ spectroscopic techniques. The complementary findings
showed that glycerol was converted into oxalate, tartronate, glycerate, glycolate and formate. The ex situ
analytical methods (liquid chromatography and mass spectrometry) were helpful to reveal glycerate as
the major reaction product on PdM/C anodes, while from in situ infrared spectroscopy measurements
no irreversible adsorbed poisoning species was detected in glycerol or intermediate oxidation to
carbonate at the prepared electrodes. The correlation of the analytical and physicochemical (XRD, EDX
and TEM) results concerned the shift of the onset potential toward lower values and the high Faradaic
currents due to electronic structures provided by the Mn and Fe contents to the Pd based materials.
Accordingly, glycerol is a sustainable raw material, which can be used in cogeneration processes for
renewable energy sources and selective production of added-value molecules.
Received 4th September 2014
Accepted 10th November 2014
DOI: 10.1039/c4ra09822f
www.rsc.org/advances
glycerol molecule) when converted thoroughly into CO2, and an
excellent source of production of added-value molecules in a
selective oxidative conversion.7 It was reported that glycerol
1. Introduction
Glycerol is expected to play an important role in a CO2-decou-
pled scenario, as it is recognized to be one of the promising
sustainable organic compounds capable of supplying fuel direct
alcohol fuel cell (DAFC) devices.1–3 Indeed, to face the scarcity of
fossil energy sources, the use of alternative fuels from renew-
able sources should be envisaged as an environmentally
friendly approach. Glycerol is already used as raw material in
various industrial applications.4,5 But, as it represents 10% of
the amount of the biodiesel production that is increasing
because of the growing global energy demand,6 the surplus
glycerol can be used as fuel in solid polymer electrolyte fuel cell
applications to make the increase economically viable.7 Beyond
the fact that it is a non-toxic liquid and easy to transport
oxidation led to dihydroxyacetone,9–13 lactic,14 mesoxalic,15
glyceric,16,17 glycolic,18,19 tartronic9 acids. From these previous
reports, the distribution of the glycerol reaction products
strongly depends on the material surface and can be associated
with a cogenerating approach, which consists in both convert-
ing directly chemical energy to electrical energy, and recovering
added-value chemicals from glycerol selective electrooxidation.
Various materials based on platinum and gold20–24 have been
used as electrocatalysts in the glycerol oxidation in alkaline
medium where many organics are very electroreactive because
of the active metal hydroxide or oxide sites at the electrode
surface. To some extent, bimetallic materials have the potential
to enhance reaction rate, alter product selectivity, and/or help or
prevent catalyst deactivation. The remarkable activity of palla-
dium, which is close to that of platinum, makes it a promising
material in catalysis and particularly in electrocatalysis7,15,25–28
because it is 200 times more abundant on earth than plat-
inum.8,29,30 It was reported that the high activity and stability of
palladium were due to its good poisoning resistance.31 Platinum
group metals (PGM) based multimetallic nanostructures with
well-controlled size, shape, structure chemical composition and
morphology can effectively enhance the catalytic reaction
kinetics through modifying surface compositions, optimizing
highly active crystalline facets, and tuning electronic struc-
tures.30,32–34 Indeed, the addition of a co-catalyst such as nickel,
and handle, glycerol has
a theoretical energy density
(6.4 kWh Lꢀ1).3,8 In comparison with other fuels such as
methanol and ethanol, glycerol has two major strengths: a high
theoretical number of exchanged electrons (14 electrons per
a
´
ˆ
˜
Departamento de Quımica da Faculdade de Filosoa Ciencias e Letras de Ribeirao
˜
˜
Preto, Universidade de Sao Paulo, Av. Bandeirantes, 3900, 14040-901, Ribeirao
Preto, SP, Brazil
b
´
˜
˜
Instituto de Quımica de Sao Carlos, Universidade de Sao Paulo, C.P. 780, 13560-970
˜
Sao Carlos, SP, Brazil
c
´
Universite de Poitiers, UMR CNRS 7285, « Equipe SAMCat », 4, rue Michel Brunet,
B27, TSA 51106, 86073 Poitiers Cedex 09, France. E-mail: boniface.kokoh@
univ-poitiers.fr
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silver, etc., to Pd-based anodes results in a benecial electronic crystallized, but under amorphous form, because of the
effect evidenced by an onset potential shied toward lower microwave-assisted approach undertaken without ultimate
values, high current densities, and CO removal from the heat-treatment stage.
electrode surface at lower potentials.35–42 In this work we show
Crystallite sizes estimated by the Scherrer equation on the
an oxidative transformation of glycerol when the Pd electrode well-dened (200) peak are lying between 3 and 7 nm. These size
surface is modied by Mn and Fe elements. Investigations were values are similar to those of other catalysts prepared by
focused on the identication of the main reaction products with microwave-assisted heating.45,46 EDX analysis conrmed the
an analytical setup composed of in situ infrared reectance presence of bimetallic catalysts in each sample and Table 1
spectroscopy, liquid chromatography (LC) and LC-Mass shows that the average atomic compositions of the different
Spectrometry.
materials are close to the nominal ones. Their lattice parame-
˚
ters are also close to that of the Pd crystallite (aPd ¼ 3.89 A),
indicating a priori no substantial deformation of the initial
structure, with the insertion of another metal in the Pd crys-
talline structure.
2. Results and discussion
2.1 Physicochemical characterization of the nanomaterials
Fig. 2 shows representative TEM images and histograms
obtained for the PdM/C materials. The Pd/C material present
clusters of particles from 10 to several hundred nanometers in
diameter (DTEM), and small particles ranging from 3–40 nm in
diameter. The distribution of the metallic phase and particle
size is heterogeneous on the carbon support, and the average
particle size is 4.2 nm. Pd53Mn47/C catalysts are distributed in
two forms: particles of pure Pd with diameter between 2 to 4
nm, and rods of MnxOy. Pd particles appear either onto the
carbon or MnxOy, and the average particle size is 3.8 nm.
Pd54Fe46/C catalysts also show two different distinct structures
on TEM images: spheres of Pd with diameter between 2 to 4 nm,
and clusters constituted mainly of Fe2O3 with 4 to 10 nm of
diameter. Both metals can also be found in the same cluster,
and the metallic phase is well distributed on the carbon
support; the average particle size is 4.8 nm (Table 1), indicating
a fair line with the crystallite sizes obtained from XRD analysis.
The carbon supported Pd-based nanomaterials obtained
through microwave-assisted heating (MW) were rst charac-
terized physicochemically by XRD and TEM techniques.
The XRD patterns of PdM/C (M ¼ Fe, Mn) are displayed in
Fig. 1. As can be seen, all the XRD patterns have similar char-
acteristic peak positions attributed to a face-centred-cubic (fcc/
Fm3ꢀm) palladium structure. Indeed, the peaks at 40.25, 46.5 and
68.08 and 83.02ꢁ represent respectively the (111), (200), (220)
and (311) reection planes of a Pd crystallite.
All the samples also show a broad peak at 25.1ꢁ, which is
assigned to the (002) plane of carbon graphite issued from the
support used to disperse the metal loading. The diffractogram
of Pd containing the iron element displays other peaks at 35, 57
and 63ꢁ which can be attributed to the Fe2O3 phases. Although
the diffractogram of the PdMn/C material does not exhibit any
peak related to the Mn element, as already described in the
literature,19,43,44 TEM and EDX analyses provided evidences of
the presence of Mn oxides. They are probably not well
2.2 Electrochemical and analytical measurements
Glycerol oxidation was conducted in a two-compartment cell
separated with a Fumatech anion exchange membrane. Prior to
long-term chronoamperometric tests, a cyclic voltammogram of
each anode catalyst was recorded for evaluating the electro-
chemical behaviour of the molecule at the material surface. As
shown in Fig. 3, one intense oxidation peak is observed during
the forward potential scan. This peak takes place at ca. 0.9 V vs.
RHE on the Pd/C electrode. When the latter material is modied
by either Mn or Fe elements the onset potential shis towards
lower values, indicating its benecial effect on Pd towards
glycerol electrooxidation. The presence of the Mn element in
the catalyst composition increases the current densities and
leads to a larger potential domain of the glycerol oxidation.
Although the increase in the current density is lower for the
Table 1 XRD and EDX results for the prepared nanomaterials
Material
˚
Nominal
Experimental Phase a/A
DDRX (200)/nm DTEM/nm
Pd/C
Pd50Fe50/C
Pd50Mn50/C Pd53Mn47/C
Pd/C
Pd54Fe46/C
Pd
Pd
Pd
3.89 6.87
3.89 3.12
3.89 4.90
6.16
4.82
3.81
Fig. 1 XRD patterns of the PdM (M ¼ Mn and Fe) nanomaterials
prepared by MW process and dispersed on Vulcan XC-72 carbon; (C)
Fe2O3 phase.
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Fig.
3
Cyclic voltammograms of the PdM/C (M ¼ Mn and Fe)
electrocatalysts in 0.1 M NaOH containing 0.1 M glycerol, recorded at
5 mV sꢀ1
.
bare Pd; hence this facilitates the initial molecule and inter-
mediates oxidative removal from the electrode surface.30,47
During the negative going-scan the second glycerol oxidation
peak takes place earlier and/or has higher current densities on
PdM/C than on Pd/C. This is probably due to the presence of
active Mn and Fe oxide/hydroxide species at the Pd-based
electrode surface in this potential domain. Song et al.48 have
shown that PdFe/C catalysts were not active to the oxidation of
alcohols such as methanol and ethanol in acidic medium.
Taking into account that glycerol contains similar primary
alcohol groups and the current densities obtained herein, it can
be concluded that the alkaline electrolyte does have a contri-
bution in the activation of the molecule in the presence of
oxygenated species at the PdM (M ¼ Mn and Fe) electrode
surface.
Regarding these different electroreactivities of glycerol at the
Pd-based anodes, chronoamperometry experiments were per-
formed at 0.8 V vs. RHE during 4 h. These long-term electrolyses
provide helpful information on the durability of the catalyst in
direct glycerol fuel cell, and also permit to determine the main
resulted reaction products in a cogeneration glycerol process on
such PdM/C anode catalysts. Accordingly, at the end of each
electrolysis the bulk solution of the anodic compartment was
recovered and divided in two parts.
The rst volume was sampled in liquid chromatography to
determine the amounts of the reaction products by comparison
with commercial standards. Fig. 4 shows the results of the
chromatograms in terms of the products obtained in the glyc-
erol oxidation on the different Pd-based electrode materials.
Oxalate, tartronate, glycerate, glycolate and formate are detec-
ted in the bulk solution aer 4 h glycerol oxidation. Although
the same products are formed on Pd-based catalysts, glycerate
remains, whatever the electrode, the main organic compound.
It is worthy of note that the chromatographic peak of oxalate
overlaps partially the injection peak, preventing under these
analytical conditions the accurate quantication of its amount.
Under similar mild conditions, these reaction products were
also found on Au/C catalysts, except for the presence in small
Fig. 2 TEM images of the PdM/C (M ¼ Mn and Fe) nanomaterials
prepared by the MW method. The insets represent the histograms of
the particle size distribution.
Fe-containing material the glycerol oxidation domain remains
still larger, ranging from 0.6 to ca. 1.3 V vs. RHE. Addition of the
oxophilic metal to a catalyst composition is of great interest not
only to decrease the noble metal content, but also to nucleate
adsorbed hydroxides at potentials less positive than those on
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2.3 Spectroelectrochemical identication of the products
To get further insights on how glycerol is electrooxidized in
alkaline medium on these nanoscale PdM/C materials, in situ
Fourier Transform Infrared Spectroscopy (FTIRS) experiments
were undertaken. These in situ spectroelectrochemical
measurements allow detection of intermediates and reaction
products in very small amounts and will hopefully provide
supplementary insights to LC-MS ndings on the glycerol
oxidation. In Fig. 6 are depicted the single potential alteration
infrared (SPAIR) spectra obtained for the different Pd-based/C
catalysts. Reectivities were recorded at 50 second intervals
during the glycerol electrooxidation in alkaline medium (0.1 M
NaOH) at a sweep rate of 1 mV sꢀ1. These spectra will allow
correlating the appearance and/or disappearance of certain
characteristic vibration bands to the potential applied to the
working electrode.
Fig. 4 Distribution of the glycerol oxidation products after 4 h elec-
trolysis performed at 0.8 V vs. RHE on PdM/C (M ¼ Mn and Fe) elec-
trocatalysts in 0.1 M NaOH.
The rst important outcome is the evidence of CO2 (asym-
metric stretching band at 2343 cmꢀ1) production on the Pd/C
and PdFe/C nanocatalysts at about 1.0 V vs. RHE. Indeed, CO2
appears as soon as carbonate (1390–1420 cmꢀ1) could not be
further formed due to the lack of OHꢀ indicating therefore an
acidication of the medium. It has been shown by simple
calculation that the depletion of OHꢀ in the thin layer (window-
electrode interface) is enough to justify a pH change during
glycerol electrooxidation in alkaline medium.50 The acidica-
tion of the thin layer between the working electrode and the
CaF2 window is therefore clearly shown. Another point is that
no vibration band indicating the presence of corresponding
linear or bridged CO was observed.
Based on the obtained spectra an attempt to identify the
reaction intermediates will be now undertaken. The positive
bands at 1050, 1900 and 2700 cmꢀ1 observed in the different
FTIR spectra are attributed to glycerol and OHꢀ consumption,
whereas the positive band appearing at ca. 1640 cmꢀ1 corre-
sponds to water bending vibration. The characteristic FTIR
spectra of the different possible products or intermediates
recorded in alkaline medium have been published elsewhere51
and will be used herein to conclude on their presence in the
electrolytic solution. So, for the Pd/C catalyst several
amounts of mesoxalate and lactate reported on Au/C
materials.22,49
The second volume of electrolytic solution was rst
neutralized on an ion exchange resin (Dowex). It consists briey
in regenerating the as-received resin with 0.5 M H2SO4 and then
washing it until obtaining a neutral pH. Aerwards the elec-
trolytic solution was passed through the resin to neutralize the
supporting electrolyte (NaOH) and thereby the carboxylate ions
become carboxylic acids. To be sure to recover all the
compounds an equivalent volume of water was added on the
resin. The pretreated solution was injected on an Aminex
column (HPX-87H) connected to the mass spectrometer as
detector. The samples obtained from glycerol electrooxidation
on Pd/C, PdMn/C and PdFe/C gave qualitatively the same
spectrograms; the representative one PdMn/C is shown in
Fig. 5.
Glyceric acid is the main reaction product well identied
with m/z ¼ 105, which corresponds to the molecular weight
without a proton. Oxalic acid is also determined by its mass
spectrum (m/z ¼ 89), as depicted in Fig. 5. The same molecules
were found on spectrograms recorded with the electrolytic
solution issued from the glycerol oxidation on Pd/C and PdFe/C.
Fig. 5 Representative mass spectra of the main molecules resulting
from the glycerol oxidation performed at 0.8 V vs. RHE on PdMn/C Fig. 6 SPAIR spectra recorded during glycerol (0.1 M) oxidation on Pd/
electrocatalyst.
C (a), PdFe/C (b) and PdMn/C (c) electrocatalysts in 0.1 M NaOH.
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compounds could be evidenced at potential values above 0.8 V 0.1 mol Lꢀ1 glycerol in alkaline medium. The spectra obtained
vs. RHE,ꢀn1 amely glycerate (characteristic bands at 1111 and aer 30 minutes are plotted in Fig. 7 for the three studied
1409 cm ), glycolate (characteristic bands at 1073, 1324 and catalysts. The absence of the band at 2343 cmꢀ1 conrms the
1409 cmꢀ1) oxalate (sharp band at 1308 cmꢀ1) and formate hypothesis that carbon dioxide is produced from the oxidation
(1354, 1383 cmꢀ1). No band characteristic of tartronate and/or of adsorbed species at high potential values. Another point is
mesoxalate ions (characteristic IR bands at 1100, 1338 and the enhancement of some vibration bands that might be
1438 cmꢀ1) was observed but their presence in very little assigned to adsorbed species, conrming therefore the
amounts in the thin layer electrolyte solution cannot be progressive poisoning of the catalysts. Indeed, the band at 1680
excluded. It should be stated that the intense band at 1576 cmꢀ1 cmꢀ1 has been assigned to adsorbed glyceraldehyde and
is characteristic of different carboxylate ions and there also carbonyl species whereas the band at ca. 1380 cmꢀ1 has been
might be a contribution of the water bending vibration to this shown to be characteristic of adsorbed glycerate.
band. For potential values higher than 1.0 V vs. RHE CO2
Chronoamperometry experiments coupled with in situ FTIR
formation takes place while the amounts of formate, glycolate measurements conrm therefore the glyceraldehyde pathway
and oxalate (region from 1308 to 1410 cmꢀ1) increase. This for the glycerol electrooxidation in alkaline medium on Pd-
indicates therefore the transformation at high potential values based materials bringing to light adsorbed glyceraldehyde and
of glycerate into glycolate and/or formate with the formation of glycerate as main intermediates.
adsorbed CO that is immediately oxidized to carbonate or CO2,
depending on the pH, according to the mechanism proposed in
ref. 51. Finally, a broad vibration band is also clearly visible at
3. Experimental
ca. 1666 cmꢀ1 that might be attributed to adsorbed glyceral-
Electrocatalysts with nominal composition PdM/C (50 : 50),
M ¼ Fe, and Mn, were prepared by microwave-assisted heating
(MW).52 The nanocatalysts were obtained by mixing PdCl2
(Aldrich) aqueous solution with the appropriate amount of
FeCl3$6H2O (Sigma Aldrich) or MnCl2$4H2O (Sigma Aldrich)
alcoholic solution in 30 mL of propylene glycol. Sodium
hydroxide was added to the mixture, to increase the pH
approximately to 10; it also acts as stabilizing agent. The
mixture was stirred for 10 min in an ultrasonic bath. Next,
enough pre-treated Vulcan XC-72 carbon powder was added, to
obtain electrocatalysts with 40 wt% metal loading. Ultrasound
irradiation for 50 min provided a homogeneous suspension,
which was placed in a common commercial microwave oven
(Panasonic NN-ST568WRU, 2450 Hz, 800 W) for 1 min on, 10 s
off, 1 min on. Finally, the suspension was ltered and washed
with acetone (Merck), and the solid product was dried in an
dehyde or carbonyl species. The same reaction intermediates
were identied when using bimetallic materials as electro-
catalysts. The major differences occur at high potential values.
Indeed, the spectra obtained at high potential values for the
PdFe/C material indicate that the oxidation of glycerate occurs
preferentially following the glycolate pathway with the forma-
tion of large amounts of carbonyl species (1666 cmꢀ1) and
subsequently high amounts of carbonate (1390–1420 cmꢀ1
)
and/or CO2 (2343 cmꢀ1). For the PdMn/C material the oxidation
into formate (1354 and 1383 cmꢀ1) is predominant. Based on
these results we can therefore state that the pathway for the
electrooxidation of glycerol on PdM/C materials in alkaline
medium is the glyceraldehyde one and the major reaction
products are glycerate, glycolate and formate.
An in situ IR study coupled with chronoamperometry exper-
iments has also been performed. Chronoamperometry was
carried out during one hour at 0.8 V vs. RHE in the presence of
ꢁ
oven at 120 C for 2 h, under N2 atmosphere.
3.1 Physical characterization
The diffraction patterns of the electrocatalysts were obtained on
an X-ray diffractometer (D5005 Siemens) operating with Cu Ka
˚
radiation (l ¼ 1.5406 A) generated at 40 kV and 40 mA. The
following parameters were kept constant during the analysis: 2q
range ¼ 20–90ꢁ, step ¼ 0.03ꢁ, and total analysis time ¼ 1.97 h.
Catalyst phase composition and analysis of the position relative
to the Ka1 monochromatic radiation were achieved by tting
the experimental angular range of interest to the pseudo-Voigt
function per crystalline peak with the aid of the Prole Plus
program (Siemens AG). The crystallite size values were obtained
using the Debye–Scherrer equation.53 Details of the procedure
have been described previously.54 The unit cell parameters were
determined by a computer program (U-Fit.exe v1.3-1992) using
the least-squares method. The 2q experimental values and the
reection planes (h k l) were employed, to calculate the unit cell.
Energy dispersive X-ray (EDX) analysis using a Leica micro-
scope Zeiss LEO 440 model TEM coupled to an Oxford 7060
Fig. 7 FTIR spectra of the species recorded after 30 minutes of
chronoamperometry measurements performed at 0.8 V vs. RHE on
Pd/C (a), PdFe (b) and PdMn (c) electrocatalysts in 0.1 M NaOH con-
taining 0.1 M glycerol.
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model analyzer was used to determine the chemical composi- glassy carbon slab, the working electrode consisted on the
tion and homogeneity of the nanomaterials. catalytic powder deposited over a glassy carbon disk (7 mm
The morphology of the electrocatalysts was also investigated diameter) and a Reversible Hydrogen Electrode (RHE) was used
by Transmission Electron Microscopy (TEM) using a TEM/STEM as reference electrode. For the measurements 5 mL of the cata-
JEOL 2100 UHR microscope (200 kV) equipped with a LaB6 lytic ink were deposited onto the glassy carbon substrate
lament. The mean particle size and size distribution were previously polished with alumina. To minimize the absorption
determined by measuring the diameter of an average of 200 of the infrared beam by the solution, the working electrode was
isolated particles using ImageJ soware.
pressed against the CaF2 window during the acquisition and a
thin layer of electrolytic solution was obtained. Two methods
were used. The rst one was the SPAIRS (Single Potential
Alteration IR Spectroscopy), carried out in the potential range of
0.3–1.40 V vs. RHE at 1 mV sꢀ1 and spectra were recorded every
0.05 V. The second one was a chronoamperometry/FTIRS study,
performed at 0.8 V vs. RHE during 1 h with acquisition of
spectra every 3 min. For each spectrum, 532 interferograms
were co-added. The reectance spectra were calculated for the
different potential values as changes in the reectivity (Ri)
relative to a reference single-beam spectrum (R0), as follows: DR/
R ¼ (Ri ꢀ R0)/R0. The positive and negative bands represent a
decrease and an increase in the number of species, respectively.
3.2 Electrochemical measurements
Chronoamperometry measurements were carried out in a Pyrex
two-compartment cell. The compartments were separated with
an anion-exchange membrane (35 mm thickness, from Fuma-
tech) and were deaerated by ultrapure N2 (U Quality, from l’Air
Liquide). A Reversible Hydrogen Electrode (RHE) and slab of
vitreous carbon were used as reference and counter electrode,
respectively. The reference electrode was separated from the
solution by a Luggin–Haber capillary tip.
The working electrode consisted of catalytic powders
deposited on a Carbon Toray used as conductive carrier with a
geometric surface area of 3 cm2. The electrical connection of the
carbon Toray substrate was established with a gold wire using a
carbon paste. A catalytic ink was prepared from the metal/C
powder (2 mg) added in a mixture of 425 mL of Naon®
suspension (Aldrich) and 75 mL of water. 50 mL of the catalytic
ink was nally deposited onto each face of the carbon Toray
sheet and the solvent was evaporated at room temperature; this
amount represents 133 mg cmꢀ2 of metal loading.
3.4 Chromatography and mass spectrometry measurements
Analytical investigations on glycerol conversion at the Pd-based
electrode surface during long-term electrolysis were performed
with high performance liquid chromatography (HPLC) with a
semi-preparative ion exclusion column (Aminex HPX-87H). This
liquid chromatography is also equipped with an UV-vis detector
followed by a refractive index detector. At the end of long-term
electrolysis in a two-compartment cell separated by anion
exchange membrane, the recovered reaction products were
neutralized on anion resin to remove the supporting electrolyte,
and nally identied by LC-MS (Mass Spectrometry, Xevo Q-
ToF, Waters) in negative ionization mode with an eluent that
was water slightly acidied with formic acid (0.2%).
A conventional three-electrode electrochemical cell (50 mL)
was used for the CV electrochemical measurements conducted
on an Autolab (PGSTAT-30) Potentiostat. The ink consisting of
an appropriate amount of the electrocatalyst powder, isopropyl
alcohol (99 mL), and Naon® (1 mL) (5 wt% in aliphatic alcohols,
Aldrich) was homogenized in ultrasonic bath for 60 min. A mass
density of 0.32 mgPd cmꢀ2 was deposited onto a previously
polished glassy carbon electrode (area ¼ 0.07 cm2).
4. Conclusions
All the catalysts were characterized in alkaline medium (0.1
mol Lꢀ1 NaOH – Merck), and in the presence of glycerol
(0.1 mol Lꢀ1 – Sigma-Aldrich). Cyclic voltammetry in the
potential range 0.1 to 1.40 V vs. RHE and chronoamperometry at
0.8 V vs. RHE for four hours, was performed in order to deter-
mine the products formed.
The identication of glycerol electrooxidation reaction products
was performed using ex situ (LC-MS) and in situ (FTIR spec-
troscopy) complementary techniques. This provided evidence
that this sustainable molecule can be used in a cogeneration
process as fuel for renewable energy sources and as environ-
mentally friendly raw material to produce added-value
compounds. The results obtained show that palladium, 200
3.3 Fourier transform infrared spectroscopy measurements
In situ FTIR experiments were carried out under external times more abundant that platinum on earth, when the distri-
reection conditions in a Bruker IFS 66v spectrometer which bution size is well controlled by microwave-assisted DPP
was modied for beam reection on the electrode surface at a synthesis method, can catalyse as well as other PGM electrode
65ꢁ incidence angle. The detector was a MCT (HgCdTe), nanomaterials the glycerol oxidation in alkaline medium.
beforehand cooled by liquid nitrogen. To avoid the presence of Furthermore, the Mn and Fe content in the Pd catalyst
IR bands due to atmospheric CO2 and H2O, the system was composition effectively enhance the electrocatalytic glycerol
maintained under vacuum. The spectral resolution was of 4 reaction kinetics through tuning electronic structures and
cmꢀ1 and the FTIR spectra were recorded in the MIR wave- modifying highly active crystalline facets of palladium. This is
number region going from 1000 to 4000 cmꢀ1. A three-electrode supported by the high current densities and the shi of the
spectroelectrochemical cell, tted with an MIR transparent at onset potential toward lower values on PdM (M ¼ Mn and Fe)
window (CaF2) at the bottom was used. The potentiostat was the electrodes. The oxidative glycerol conversion leads selectively to
same as used in CV experiments. The counter electrode was a glycerate. Moreover and according to FTIRS measurements, the
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preferential facets of the prepared Pd-based nanocrystals are 20 G. L. Brett, Q. He, C. Hammond, P. J. Miedziak,
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