Employing iron and nickel to enhance ethanol oxidation of Pd-based anodes in alkaline medium

Article abstract of DOI:10.1016/j.electacta.2018.10.187

We report the addition of Fe or Ni to Pd:M electrocatalysts supported on Vulcan carbon XC-72 with 20 wt% metal loading to activate ethanol electrooxidation reaction in alkaline medium. Experimental bulk compositions of nanoparticles were very close to the nominal one. All the catalysts display the fcc crystalline structure of palladium with crystallite sizes ranging from 2.5 nm to 5.4 nm. Electrochemical tests in the presence of ethanol shows that the addition of Fe and Ni to Pd catalysts enhances ethanol electrooxidation. Ni-containing compositions such as Pd(56)Ni(44) and Pd(71)Ni(29) exhibit excellent catalytic mass activity (30 A g_Pd ^?1) at 0.5 V vs. RHE showing that they are promising anode electrocatalysts for direct ethanol alkaline fuel cells.

Full text of DOI:10.1016/j.electacta.2018.10.187

Accepted Manuscript
Employing iron and nickel to enhance ethanol oxidation of Pd-based anodes in
alkaline medium
T.S. Almeida, Y. Yu, A.R. de Andrade, H.D. Abruña
PII:
S0013-4686(18)32449-6
https://doi.org/10.1016/j.electacta.2018.10.187
EA 32986
DOI:
Reference:
To appear in: Electrochimica Acta
Received Date: 5 September 2018
Revised Date: 31 October 2018
Accepted Date: 31 October 2018
Please cite this article as: T.S. Almeida, Y. Yu, A.R. de Andrade, H.D. Abruña, Employing iron and nickel
to enhance ethanol oxidation of Pd-based anodes in alkaline medium, Electrochimica Acta (2018), doi:
https://doi.org/10.1016/j.electacta.2018.10.187.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Employing iron and nickel to enhance ethanol oxidation of Pd-based anodes in
alkaline medium
a,b,c
b
c*
b
T.S. Almeida , Y. Yu , A.R. de Andrade , H.D. Abruña
a
Departament of Chemistry and Chemical Biology, Cornell University, Ithaca, NY
4850,USA.
1
b
Universidade Federal do Triângulo Mineiro, Campus Universitário de Iturama.
Iturama, MG, 38280-000, Brazil
c
Departamento de Química, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto,
Universidade de São Paulo, Ribeirão Preto, SP, 14040-901, Brazil
*
Corresponding author: A. R. de Andrade (ardandra@ffclrp.usp.br)
Abstract: We report the addition of Fe or Ni to Pd:M electrocatalysts supported on
Vulcan carbon XC-72 with 20 wt.% metal loading to activate ethanol electrooxidation
reaction in alkaline medium. Experimental bulk compositions of nanoparticles were
very close to the nominal one. All the catalysts display the fcc crystalline structure of
palladium with crystallite sizes ranging from 2.5 nm to 5.4 nm. Electrochemical tests in
the presence of ethanol shows that the addition of Fe and Ni to Pd catalysts enhances
ethanol electrooxidation. Ni-containing compositions such as Pd(56)Ni(44) and
-1
Pd(71)Ni(29) exhibit excellent catalytic mass activity (30 A gPd ) at 0.5 V vs. RHE
showing that they are promising anode electrocatalysts for direct ethanol alkaline fuel
cells.
Keywords: Electrocatalysis, ethanol oxidation, Pd-based catalyst, iron and nickel
1

ACCEPTED MANUSCRIPT
1
. Introduction
Ethanol is an attractive potential fuel for low-temperature fuel cell systems [1]
due to its high theoretical energy density and production from biomass. However, it is a
difficult to release all 12 electrons from the ethanol molecule in order to achieve its full
energy density [2]. During the past years many researchers have investigated ethanol
electrooxidation in acidic media using the proton exchange membrane fuel cell (PEM-
FC) with different Pt-based materials as catalysts [3-6]. Also, a number of techniques
have been employed in an attempt to understand the phenomena occurring at the
interface and the electrooxidation mechanism. These include Fourier transform infrared
spectroscopy (FTIR) [7-8], differential electrochemical mass spectrometry (DEMS)
[
9,10], and high performance liquid chromatography (HPLC) [11,12]. So far, these
techniques have shown that ethanol electrooxidation affords acetaldehyde and acetic
acid as the major products, releasing between two and four electrons, respectively.
Scientists have gathered significant information about the phenomena occurring
at the electrode/solution interface and the reaction mechanism during ethanol
electrooxidation in acidic media. However, this same reaction still had been less
investigated in alkaline media due to difficulties inherent to alkaline fuel cells [13].
From a thermodynamic point of view, the alkaline exchange membrane direct
ethanol fuel cell (AEM-DEFC) system offers numerous advantages: (1) It presents a
global reaction potential of 1.24 V, which corresponds to a gain of 100 mV when
compared with the proton exchange membrane direct ethanol fuel cell (PEM-DEFC),
reaction potential of 1.14V. (2) In addition electrocatalytic reactions in alkaline media
can be more efficient than in acidic media [14]. (3) At an anion exchange membrane
-
(
AEM), the OH species that conducts ions in the system, presents a reverse ionic flow
2

ACCEPTED MANUSCRIPT
and corresponding electroosmotic flow; i.e., from the cathode side to the anode side,
largely inhibiting ethanol crossover [15].
Ethanol electrooxidation in alkaline media opens the possibility of using new
catalytic materials and lower the production cost of noble-based catalysts. The use of
alkaline electrolytes is of interest because alcohol oxidation generally does not strongly
depend on catalyst composition in this medium, enabling the use of non-platinum based
materials, such as Pd, Ag, Ni, and perovskite-type oxides [16-19]. While most of the Pt-
based catalysts used in acidic media could find application in alkaline media, Pd
displays the best performance due its higher oxophilicity and relatively inert nature [20].
Among Pd-based catalysts, PdFe and PdNi perform well in ORR [21-23] and could
catalyze alcohol electrooxidation in alkaline media. Shen and Xu [18,24] studied the
oxidation of alcohols such as methanol, ethanol, glycerol, and ethylene glycol on Pd-
based catalysts containing Ce, Ni, Mn, or Co oxides and showed that transition metal
oxides affect the activity of the catalyst. These authors observed that the Pd-NiO/C
catalyst presented the highest catalytic activity and the lowest rate of poisoning by
intermediates, because -OHads species could be readily generated on the oxide surface.
Indeed, the generation of OHads species at lower potentials can convert CO-like
poisoning species on Pt and Pd to CO or other products that dissolve in water,
2
liberating the Pt and Pd active sites for further electrochemical reaction. Fe O also
3
4
improved the catalytic performance of Pt and Pd based materials towards organic
reactions [25].
In this context, we report how the addition of different amounts of Fe and Ni to a
Pd/C catalyst enhances ethanol electrooxidation activity.
3

ACCEPTED MANUSCRIPT
2
. Experimental
2
.1 Catalyst Preparation
Pd and Pd-M (M = Fe or Ni) containing 50, 30 or 10 wt. % of M were prepared
by the microwave assisted method. 50.0 mg of each catalysts with 20 wt. % metal
loading and different Pd:M metal ratios were obtained by mixing a calculated volume of
PdCl (Aldrich); NiCl .6H O (Mallinckrodt) or FeCl .6H O (Mallinckrodt) aqueous
2
2
2
3
2
-1
solution 0.05 mol L with 20 mL of ethylene glycol in a 200 mL becker, and the pH
-1
was adjusted to 10, dropwise, with 3.0 mol L NaOH. The mixture was stirred in an
ultrasonic bath for 10 minutes, followed by the addition of 40.0 mg of Vulcan Carbon
XC-72 powder. After was added 80 µL of hydrazine (Aldrich) as reducing agent and the
mixture was kept under magnetic stirring for 30 min to obtain a homogeneous
suspension. This suspension was placed in a common household microwave oven
(Sonny Caroussell R-220 BW, 2450 Hz) operating at a power of 100 W for 5 min. The
suspension was centrifuged and washed with water and the resulting solid product was
dried in a vacuum oven at 50ºC overnight.
2
.2 Physical Characterization
Diffraction patterns were acquired on a Rigaku diffractometer operating with Cu
Kα radiation (λ =1.5406 Å) generated at 40 kV and 40 mA. Scans were recorded at 5°
-1
min for 2θ values between 20 and 90°. Particle bulk and surface composition were
analyzed by energy dispersive X-ray spectroscopy (EDX) using a Leica microscope
Zeiss LEO 440 model SEM coupled to an Oxford 7060 model analyzer and X-ray
Photoelectron Spectroscopy (XPS) using Surface Science Instrument SSX-100,
respectively. Catalyst morphology was also investigated by electron microscopy
imaging using a Schottky-field-emission-gun Tecnai F20 scanning transmission
4

ACCEPTED MANUSCRIPT
electron microscope (STEM) operating at 200 keV. The STEM image was acquired
with a high angle annular dark field detector (HAADF. Energy dispersive x-ray (EDX)
analysis was performed on the F20 using an Oxford detector, at a beam current of about
1
nA; an EDX resolution of 1-5 nm was achieved with this setup. The Pd-L, Fe-K, Ni-K
edges were used to represent the EDX mapping or line scan data.
2
.3 Electrochemical characterization
The cyclic voltammetric (CV) profile of the catalysts was obtained in N -purged
2
1
.0 M NaOH (Mallinckrodt) solution. CVs were acquired on a PAR model 273
potentiostat. A conventional electrochemical cell was employed with a reversible
hydrogen electrode (RHE) and a platinum wire as the reference and counter electrodes,
respectively. To perform the electrochemical measurements, calculated amount of the
catalyst powder were dispersed into a solution (100 µL) consisting of isopropanol (95
µL) and Nafion® (5 µL). The mixture was homogenized in ultrasonic bath for 10
minutes. After homogenization, 10 µL of the catalysts ink were deposited onto a
2
previously polished glassy carbon disk electrode (0.196 cm ). In all cases, the catalyst
-2
layer had a metal loading of 0.1 mg cm . Activity and stability tests were carried out
Pd
by cyclic voltammetry in the range of +0.05 V to 0.80 V vs. RHE and
chronoamperometry in the presence of 1.0 M ethanol in 1.0 M NaOH at 0.5 V vs. RHE.
Electrochemical Active Surface Area (EASA) was determined as described in
[
48,49] by recording cyclic voltammogram in 1.0 M NaOH in the range of +0.05 V to
.2V vs RHE and integrating the cathodic peak for Pd(II)-oxide reduction.
1
5

ACCEPTED MANUSCRIPT
3
. Results and Discussion
3
.1 Physical characterization
EDX analysis yielded the bulk composition of the nanoparticles. Table I
summarizes the results for the Pd:M (M= Fe and Ni) catalysts. While the Pd(50)M(50)
and Pd(70)M(30) catalysts had experimental molar compositions near their nominal
values, Pd(90)M(10) presented much lower Ni (1%) and Fe (3%) percentages.
Nevertheless, it should be noted that EDX just provides semi-quantitative data, and
sometimes comparing metal compositions can lead to erroneous conclusions.
Table 1. Physical characteristics of Pd:M/C catalysts
Lattice
Constant
Crystallite
Size
Particle
Size
(nm)
Pd:M
(EDX)
Pd:M
(XPS)
Catalyst
a
b
(Å)
(nm)
Pd
3.888
3.895
3.884
3.915
3.920
3.880
3.886
3.8
5.4
2.6
2.5
3.1
2.6
2.8
-
-
-
-
Pd(90)Fe(10)
Pd(70)Fe(30)
Pd(50)Fe(50)
Pd(90)Ni(10)
Pd(70)Ni(30)
97:03
71:29
59:41
99:01
71:29
56:44
-
-
69:31
53:47
-
1.8
-
-
71:29
54:46
Pd(50)Ni(50)
2.4
a
b
from XRD analysis; from TEM analysis
Fig.1 presents the diffraction patterns of the catalysts. We calculated the
crystallite size using the Scherrer´s equation and using the (220) reflection. We
employed equation (1) to obtain the lattice parameter using the (220) reflection as well
(Table 1).
ꢀ
= √2ꢁλ⁄sin ꢂ
(1)
6

ACCEPTED MANUSCRIPT
Single Column
(111)
Pd(59)Fe(41)
Pd(71)Fe(29)
Pd(97)Fe(03)
Pd
A
(200)
(220)
(311)
20
30
40
50
60
70
80
90
2θ
(111)
Pd(56)Ni(44)
Pd(71)Ni(29)
Pd(99)Ni(01)
Pd
B
(200)
(220)
(311)
20
30
40
50
60
70
80
90
2θ
Fig. 1. XRD patterns of the carbon supported Pd-based materials prepared by the
microwave method. (A) Pd:Fe and (B) Pd:Ni catalysts.
7

ACCEPTED MANUSCRIPT
All the compositions displayed the typical face-centered cubic (fcc) structure of
Pd (space group Fm-3m) corresponding to the (111), (200), (220), (311), and (222)
reflections (PDF Card No.: 04-001-0111) with crystallite sizes around 3.0 nm for the
binary compositions. Only Pd(97)Fe(03) presented crystallite size (5.4 nm) larger than
pure Pd (3.8 nm). Despite being low, the amounts of Ni and Fe on the Pd(90)M(10)
catalysts modified the diffraction patterns (Fig. 1A-B) and caused peaks shift to lower
2
θ values, resulting in larger apparent lattice parameters than that of pure Pd (3.898 Å)
(Table I). Such behavior has been reported before for Pd:M (M = Co, Ni and Fe)
catalysts and the increased of the lattice parameter is explained due the addition of the
second metal to an interstitial position in the cell eliciting an isotropic expansion [26].
Increasing the molar ratio of the second metal (70:30 and 50:50) displaced 2θ to slightly
higher values, yielding smaller lattice parameters when compared with pure Pd. This
behavior can be attributed to the atomic radii of Fe (126 pm) and Ni (124 pm), which
have smaller atomic radii than Pd (137 pm), so the lattice contracted when a nickel or
iron replaced Pd. Particle and crystallite size are equal for the catalysts investigated, the
difference observed are within the experimental error (Table 1).
XPS analyses were used to estimate the surface atomic composition and to
analyze the electronic structure of the components in the synthesized catalysts.
Palladium, carbon and oxygen were the main elements in all cases.
We were able to detect iron and nickel only for the compositions containing higher
amounts of these metals (30 and 50 at. %). It was not possible to determine the surface
compositions of Pd(97)Fe(03) and Pd(99)Ni(01) because the concentration of the
second metal on the surface was too low to yield reliable results. Table 1 presents the
XPS compositions of the different materials. In the case of nanoparticles of 2-3 nm in
diameter, as found in this work, XPS is between bulk and surface technique, so the
8

ACCEPTED MANUSCRIPT
same compositions obtained by XPS and EDS only suggest that there is no great
inhomogeneity of the compositions between bulk and catalyst surface.
By recording XPS over narrow energy ranges corresponding to the Pd 3d, Fe 2p,
and Ni 2p core levels, we obtained the electronic structure of the catalyst particles (Fig.
2
). For this analysis, we corrected all the spectra to the carbon 1s peak at a binding
energy (BE) of 284.8 eV. Fig. 2A shows a representative spectrum of the Pd 3d core
levels obtained from a pure Pd sample. We resolved the Pd 3d5/2 and 3d3/2 peaks into
three sets of spin–orbit doublets fitted by constraining the 5.2 eV spin–orbit separation.
The Pd (3d , ) peaks at 335.7 and 340.9 eV corresponded to metallic Pd only,
5
/2 3/2
whereas the peaks at 336.7 and 342.1 eV and the peaks at 338.0 and 344.0 in the
2
+
4+
deconvolved spectrum referred to Pd(3d , ) peaks of Pd (PdO) and Pd (PdO2)
5
/2 3/2
2
+
4+
species, respectively. The values obtained for Pd metal, and the Pd and Pd species
0
2+
4+
were close to reported values [27]. We detected Pd , Pd , and Pd for pure Pd and
Pd(97)Fe(03) and Pd(99)Ni(01) compositions. As for the materials containing 30% and
0
2+
5
0 at.% of Fe and Ni, only Pd and Pd were present in the samples. Hence, increasing
the atomic ratio of the second metal inhibited the formation of Pd at higher oxidation
4
+
states; like Pd . Table 2 presents the binding energies for the Pd 3d , levels, the
5
/2 3/2
palladium species observed on the catalyst surface, and the relative intensity of the
species. Metallic Pd is the major specie in all the compositions; the binding energy from
the Pd 3d , shifts slightly when Ni or Fe is added indicating a possible and moderate
5
/2 3/2
electronic effect of these metals over the d-band of palladium induced by the electron
transfer between Pd and Ni or Fe [28,29]. Such electronic effect may be responsible to
decrease the adsorption strength of the intermediate compounds over Pd catalyst sites
speeding up ethanol oxidation [30,31].
9

ACCEPTED MANUSCRIPT
Double Column
Fig. 2. Spectra of the core levels of (A) Pd 3d, (B) Fe 2p, (C) Ni 2p of the Pd/C,
Pd(59)Fe(41), and Pd(56)Ni(44) catalysts, respectively.
Table 2. Distribution of Pd species in the Pd:M/C catalysts as determined by XPS
Binding Energy (eV)
Pd
3d
Pd
3d
5/2
Rel.
intensity
(%)
Pd
Species
Catalyst
3
/2
0
Pd
340.9 335.6
342.1 336.6
344.0 338.0
341,0 335.7
342.2 336.3
344.2 338.5
341.2 335.8
342.9 337.1
65.9
23.9
10.2
67.2
26.5
6.3
2
+
+
Pd
Pd
Pd
4
0
Pd
2
+
+
Pd(97)Fe(03)
Pd(70)Fe(30)
Pd
Pd
4
0
Pd
78.9
21.1
-
2
+
+
Pd
Pd
4
-
-
1
0

ACCEPTED MANUSCRIPT
0
Pd
340.6 335.3
342.2 337.5
79.3
20.7
-
2
+
+
Pd(59)Fe(41)
Pd(99)Ni(01)
Pd(71)Ni(29)
Pd(56)Ni(44)
Pd
Pd
4
-
-
0
Pd
341.1 335.7
342.2 336.2
343.7 338.7
341.1 335.8
342.3 337.1
54.2
32.8
13.0
67.0
33.0
-
2
+
+
Pd
Pd
4
0
Pd
2
+
+
Pd
Pd
4
-
-
0
Pd
341.0 335.6
342.1 336.7
69.7
30.3
-
2
+
+
Pd
Pd
4
-
-
We refined the chemical state of iron in the catalysts using the Fe 2p spectra
(
Fig. 2B). The XPS spectra can be split in two parts Fe 2p3/2 and Fe 2p ; where each
1/2
part consists of a main line and a satellite. The Fe 2p3/2 main line is located at 711.3 eV
with a satellite peak at 716.7 eV; and the Fe 2p main line is located at 724.5 eV with a
1
/2
satellite peak at 731.0 eV. The presence of a main line together with a satellite peak
results from a ligand-to-metal charge transfer during the photoemission process [32].
This profile allowed us to conclude that the iron on the surface had a +3 formal
oxidation state, indicating the presence of Fe O [33]. Catalysts containing Ni had the
2
3
same profile. The Ni 2p and Ni 2p spectrum presented two pairs of prominent peaks
3
/2
1/2
at 855.9 and 861.9 eV and 873.7 and 879.9 eV (Fig. 2C). We attributed the peaks at
55.9 and 873.7 eV to NiO and identified the peaks at 861.9 and 879.9 eV as a multi-
8
electron excitation satellite peak [34].
As we will discuss later, the Pd(59)Fe(41) and Pd(56)Ni(44) catalysts exhibited
the best electrocatalytic activity towards ethanol oxidation. Hence, we analyzed these
materials by TEM (Fig. 3 and Fig. 4). The TEM micrograph of Pd(59)Fe(41) (Fig. 3A)
revealed well-distributed catalyst nanoparticles on the carbon support and an average
particle size of 1.8 ± 0.8 nm (Fig. 3B). Particle distribution maps provided more
1
1

ACCEPTED MANUSCRIPT
information about metal distribution on the nanoparticle (Fig. 3C). Images evidenced
regions rich in Fe (green) and Pd (red) indicating segregation of the nanoparticle.
Pd(56)Ni(44) also displayed a homogeneous particle distribution on the support, with an
average particle size equal to 2.4 ± 0.7 nm (Fig. 4A-B). For EDX analysis, we selected a
line through the nanoparticle instead of choosing an area as in the case of Pd(59)Fe(41).
We analyzed metal distribution as a function of position (Fig. 4C-D). Both Pd and Ni
appeared homogenous distributed on the nanoparticle.
Single Column
Fig. 3. (A) TEM micrograph of the Pd(59)Fe(41)/C catalyst. (B) Particle size
distribution (count: 60 nanoparticles) (C) Composition map for Pd and Fe.
1
2

ACCEPTED MANUSCRIPT
Single Column
Fig. 4. (A) TEM micrograph of the Pd(56)Ni(44)/C catalyst. (B) Particles size
distribution (count: 116 nanoparticles) (C) and (D) composition of the PdNi
nanoparticle.
In summary, TEM indicated the presence of small particles well distributed on
the carbon support, but with some aggregates for both Pd(59)Fe(41) and Pd(56)Fe(44).
Particle sizes were comparable with those obtained by XRD. The composition map
confirmed a good homogenous mixture of the metals (Ni and Fe) with Pd, as suggested
by EDX analysis.
3
.2 Electrochemical characterization
Figure 5A presents the cyclic voltammograms (CVs) of different Pd:Fe anode
catalysts recorded in 1.0 M NaOH over the potential range from +0.05 to +0.8 V vs
1
3

ACCEPTED MANUSCRIPT
RHE. Three peaks were observed during the positive sweep corresponding to different
electrochemical processes at the Pd electrode surface. Peak I, between +0.05 and +0.15
V, is ascribed to absorbed and adsorbed hydrogen oxidation [35]:
−
−
Pd-H / + OH → Pd + H O + e
(3)
(4)
abs ads
2
-
-
Pd + OH ↔ Pd-OH + e
ads
-
Peak II, attributed to OH adsorption (Eq. (4)), appeared in different potential ranges for
each Pd:Fe catalyst: between +0.38 and +0.72 V for Pd(59)Fe(41) and Pd(71)Fe(29),
and between +0.18 to +0.43V for Pd(97)Fe(03) and Pd. This shift resulted from the high
Fe concentration and the presence of Fe O in the Pd(59)Fe(41) and Pd(71)Fe(29)
2
3
compositions, as evidenced by XPS analysis. Therefore, electron transfer from Fe to Pd
-
may have modified the adsorption energy of OH ions and the concentration of this
species on the catalyst surface [25].
Peaks III/III´ were ascribed to redox process of Fe [36] and appeared just for
Pd(59)Fe(41). PdO formation was not evident since its formation only arises at
potentials higher than +0.8 V vs ERH [35].
When Ni was the co-catalyst, the behavior was similar (Fig. 6A). However,
-
contrary to the Pd:Fe compositions, all the Pd:Ni catalysts displayed lower OH
adsorption potentials (+0.3V vs RHE). This resulted in the formation of PdO at lower
potentials as evidenced by peak IV. Due to high amount of Ni at this composition peak
II can be ascribed not only due Pd-OHads formation (Eq. 4) but also by the transition
between Ni and α-Ni(OH) as described by Obradovic et al. [37]. Although XPS
2
analysis indicated the presence of nickel oxides, the transition between Ni and α-
1
4

ACCEPTED MANUSCRIPT
-
Ni(OH) is convoluted with the OH adsorption over Pd (peak II) and makes the
2
voltammetric profile not clear.
double Column
-
1
Fig. 5. (A) Cyclic voltammograms of the Pd:Fe catalysts recorded in NaOH 1.0 mol L
-1
at 10 mV s ; (B) Cyclic voltammograms of the Pd:Fe catalysts recorded in NaOH 1.0
mol L + EtOH 1.0 mol L at 10 mV s ; (C) Mass activities of Pd:Fe catalysts from
their corresponding current-time curves and (D) Polarization curve of the Pd:Fe
-1
-1
-1
-1
-1
catalysts recorded in NaOH 1.0 mol L + EtOH 1.0 mol L at 0.5 V for 30 min.
1
5

ACCEPTED MANUSCRIPT
double Column
-
1
Fig. 6. (A) Cyclic voltammograms of the Pd:Ni catalysts recorded in NaOH 1.0 mol L
-1
at 10 mV s ; (B) Cyclic voltammograms of the Pd:Ni catalysts recorded in NaOH 1.0
mol L + EtOH 1.0 mol L at 10 mV s ; (C) Mass activities of Pd:Ni catalysts from
their corresponding current-time curves and (D) Polarization curve of the Pd:Ni
-1
-1
-1
-1
-1
catalysts recorded in NaOH 1.0 mol L + EtOH 1.0 mol L at 0.5 V for 30 min.
The Electrochemical Active Surface Area (EASA) was determined by
integrating the cathodic peak for PdO reduction when cyclic voltammetry was record at
higher potential as 1.2 V vs. RHE. To determine the EASA we take as parameter the
-2
charge of 424 ꢀC per cm , which correspond to the charge of two electrons to reduce
the PdO to Pd [38]. The results listed in Table 3 show that the EASA of the catalysts
2
-1
remain between 7.0 to 12.0 m gPd
.
We examined the electrocatalytic activity of Pd:M electrocatalysts for ethanol
electrooxidation in alkaline media. Fig. 5B and 6B present the cyclic voltammograms of
the Pd:Fe and Pd:Ni catalysts in 1.0 M NaOH and 1.0 M ethanol solution at a sweep
1
6

ACCEPTED MANUSCRIPT
-1
rate of 10 mV s (Table 3). We normalized by the equivalent mass of Pd deposited on
the glassy carbon support electrode and by the electrochemical surface-active area
(EASA).
Addition of different amounts of Fe to the Pd catalyst did not enhance
significantly the ethanol oxidation current values nevertheless; the onset oxidation
potential (Eonset) is shifted towards lower values when compared with pure Pd (Fig. 5B,
inset). The double layer charges increase as a function of the iron content. Pd(59)Fe(41)
and Pd(71)Fe(29) exhibited more positive Eonset values when compared with
Pd(97)Fe(03). The addition of increasing amounts of Ni enhanced the ethanol
electrooxidation current (Fig. 6B). The only exception was Pd(99)Ni(01), which was
less active than pure Pd. Regarding Eonset, Pd(99)Ni(01) presented the most positive
value, which resulted in its lower activity toward ethanol oxidation. The Eonset of the
other catalysts shifted negatively (by 50 mV) when compared with pure Pd (+0.30 V).
Table 3. Initial onset potential and catalytic activity for ethanol oxidation on Pd:M
catalysts
EASA
Mass Activity
Intrinsic Activity*
(A m )
@ 0.5 V vs RHE
2
-1
E
onset
-1
-2
Catalyst
(m g
)
(A gPd
)
Pd
(
V vs RHE)
@
0.5 V vs RHE
7
7
8
9
.0
.1
0.28
Pd
0.30
0.20
0.25
0.29
0.38
0.25
0.25
2
3
0.42
1.36
2.15
0.14
2.43
2.48
Pd(97)Fe(03)
Pd(71)Fe(29)
Pd(59)Fe(41)
Pd(99)Ni(01)
Pd(71)Ni(29)
Pd(56)Ni(44)
.1
.3
11
20
1.5
26
30
1
1
1
0.7
0.7
2.1
*
Intrinsic activity = mass activity/EASA
1
7

ACCEPTED MANUSCRIPT
Chronoamperometric experiments at a fixed potential (+0.5 V) in the presence of
1
.0 M NaOH and 1.0 M ethanol (Fig. 5D and 6D) showed sharply drop of the current
until achieve a steady state thereafter. At the beginning of the experiment, the active
sites are free of adsorbed/oxidized ethanol molecules, but the rate at which new ethanol
molecules are adsorbed depends on the availability of active catalyst sites as the
-1
reaction proceeds [11]. Table 3 and Fig. 5C and 6C presents the mass activities (A gPd
obtained from the current of the chronoamperometric curve at the end of the experiment
30 min). Pd(59)Fe(41) had the highest catalytic activity among all the investigated
)
(
iron-containing compositions. It is also worth noting that this composition contained the
lowest amount of Pd. The combination of Pd nanoparticles with metal oxides increased
catalyst activity towards alcohol oxidation in alkaline media, accounting for the better
results.
The generally accepted mechanism of the EOR on Pd surfaces in alkaline
environments for DEFC applications has been reported by many authors [37,39,40].
Pd + CH CH OH ⇄ Pd–(CH CH OH)
(5)
(6)
(7)
(8)
3
2
3
2
ads
−
–
Pd–(CH CH OH) + 3OH → Pd–(CH CO) + 3H O + 3e
3
2
ads
3
ads
2
Pd−(CH CO) + PdOHads → Pd−CH COOH + Pd
3
ads
3
−
−
Pd–CH COOH + OH → Pd + CH COO + H O
3
3
2
Initially, the ethanol molecules are adsorbed in the Pd surface by a dissociative
process (Eq. 5) that leads to molecule dehydrogenation and formation of ethoxy
intermediate (CH CO)ads (Eq. 6). This intermediate is removed from Pd surface by the
3
-OH species (Eq. 4), also adsorbed on Pd sites, forming acetic acid (Eq. 7) that is
quickly converted in acetate ions by simple acid-base equilibrium (Eq. 8). Different
1
8

ACCEPTED MANUSCRIPT
from ethanol oxidation in acidic media where the mechanism passes through the -CO
formation on the catalyst sites of Pt [11,20]. In alkaline media the mechanism predicts
the formation of the Pd–(CH CO)ads intermediate, not CO . In this mechanism the rate
3
ads
determining step represents the oxidative removal of (CH CO)ads by adsorbed -OH
3
species leading to acetate formation as the major product.
-1
Addition of Ni to Pd presents higher catalytic activity (30 A gPd ) than when Fe
-1
is introduced (20 A gPd ). This is in line with the intrinsic activity of PtNi and PtFe
compositions. Moreover, Ni is claimed to be a good co-catalyst for Pt and Pd in alkaline
-
media [41,42] since can generate surplus OH through the auto-catalytic reaction (Eq. 9
-
and 10). Promoting, the increase of local OH concentration around the catalyst [29].
ꢃꢄꢅꢆꢇꢈ → ꢃꢄꢆ + ꢇ ꢆꢁ
(9)
ꢉ
ꢉ
ꢊ
ꢌ
ꢃꢄꢅꢆꢇꢈ → ꢃꢄꢆꢆꢇ +ꢁꢇ +ꢁꢋ
(10)
ꢉ
The effect of iron addition over Pd or Pt towards small organics molecules
oxidations in alkaline media still unclear. Nevertheless, it is claimed the beneficial
effect of iron to improve ORR due to a significant electronic effect of iron over Pd or Pt
d-band [43,44]. This effect was also observed for PtFe alloy on methanol oxidation
[
45,46]. Our XPS-data have shown a very fair electronic effect of iron addition on Pd-
catalyst.
4
. Conclusion
We have investigated the activity activity of Pd:M (M = Fe or Ni) catalysts
towards ethanol electrooxidation in alkaline media. All the compositions investigated
10, 30 and 50 at. % M loading) displayed the Pd face centered cubic (fcc) structure and
the experimentally determined compositions were close to the nominal ones. The only
(
1
9

ACCEPTED MANUSCRIPT
exceptions were compositions containing 10 at. % of M, for which the second metal
was actually presented at less than 5 at. %. XPS analysis revealed that the nanoparticle
surface composition was close to the bulk composition found by EDX. Also, a more
detailed analysis showed that while Pd existed in its oxidized form PdO and PdO2,
metallic Pd prevailed. XPS also detected Fe O and Ni oxides for the compositions
2
3
containing 30 and 50 at. % Fe and Ni, respectively. TEM analysis demonstrated that the
nanoparticles as well as Pd and the added metals (Fe and Ni) were homogeneously
distributed on the carbon support. Addition of Fe or Ni enhanced the catalytic activity of
Pd nanoparticles. The current increased and the Eonset for ethanol oxidation shifts to less
positive potential when compared with pure Pd, except for Pd(99)Ni(01). Pd(50)M(50)
compositions yielded the highest catalytic activity, and Ni addition affected the activity
towards ethanol electrooxidation more markedly than Fe. In conclusion, Pd(50)M(50)
catalysts are easy and fast to prepare by microwave methods. The resulting catalyst
represent a potential option for DAFCs.
Acknowledgements
T.S. Almeida acknowledges the PhD fellowship under the contract number FAPESP
2
8
011/15034-2. Y.Yu is supported by the Department of Energy though grant DE-FG02-
7ER45298, by the Energy Materials Center at Cornell (EMC2), an Energy Frontier
Research Center funded by the U.S. Department of Energy, Office of Basic Energy
Sciences under Award Number DE-SC0001086. This work made use of the electron
microscopy and XPS facility of the Cornell Center for Materials Research (CCMR)
with support from the National Science Foundation Materials Research Science and
Engineering Centers (MRSEC) program (DMR 1120296). A. R. De Andrade
acknowledge CNPq (Proc. 305085/2014-0).
2
0

ACCEPTED MANUSCRIPT
[
1] J.R. Mielenz, Ethanol production from biomass: technology and
commercialization status, Curr. Opin. Microbiol.
doi:10.1016/S1369-5274(00)00211-3.
4
(2001) 324–329.
[
[
2] E.H. Yu, U. Krewer, K. Scott, Principles and Materials Aspects of Direct Alkaline
Alcohol Fuel Cells, Energies. 3 (2010) 1499–1528. doi:10.3390/en3081499.
3] E. Antolini, F. Colmati, E.R. Gonzalez, Ethanol oxidation on carbon supported
(
PtSn)alloy/SnO2 and (PtSnPd)alloy/SnO2 catalysts with a fixed Pt/SnO2 atomic
ratio: Effect of the alloy phase characteristics, J. Power Sources. 193 (2009) 555–
61. doi:10.1016/j.jpowsour.2009.04.039.
5
[
[
4] K. Zhang, H. Xu, B. Yan, J. Wang, Z. Gu, Y. Du, Rapid synthesis of dendritic
Pt/Pb nanoparticles and their electrocatalytic performance toward ethanol
oxidation, Appl. Surf. Sci. 425 (2017) 77–82. doi:10.1016/j.apsusc.2017.06.270.
5] R.M. Antoniassi, J.C.M. Silva, T. Lopes, A. Oliveira Neto, E.V. Spinacé, Carbon-
supported Pt nanoparticles with (100) preferential orientation with enhanced
electrocatalytic properties for carbon monoxide, methanol and ethanol oxidation in
acidic medium, Int. J. Hydrog. Energy. 42 (2017) 28786–28796.
doi:10.1016/j.ijhydene.2017.10.036.
[
6] M. Sedighi, A.A. Rostami, E. Alizadeh, Enhanced electro-oxidation of ethanol
using Pt–CeO2 electrocatalyst prepared by electrodeposition technique, Int. J.
Hydrog. Energy. 42 (2017) 4998–5005. doi:10.1016/j.ijhydene.2016.12.014.
[
7] S. García-Rodríguez, S. Rojas, M.A. Peña, J.L.G. Fierro, S. Baranton, J.M. Léger,
An FTIR study of Rh-PtSn/C catalysts for ethanol electrooxidation: Effect of
surface composition, Appl. Catal. B Environ. 106 (2011) 520–528.
doi:10.1016/j.apcatb.2011.06.011.
[
8] W.J. Pech-Rodríguez, D. González-Quijano, G. Vargas-Gutiérrez, C. Morais, T.W.
Napporn, F.J. Rodríguez-Varela, Electrochemical and in situ FTIR study of the
ethanol oxidation reaction on PtMo/C nanomaterials in alkaline media, Appl.
Catal. B Environ. Complete (2017) 654–662. doi:10.1016/j.apcatb.2016.10.058.
[
[
[
9] A. Bach Delpeuch, F. Maillard, M. Chatenet, P. Soudant, C. Cremers, Ethanol
oxidation reaction (EOR) investigation on Pt/C, Rh/C, and Pt-based bi- and tri-
metallic electrocatalysts: A DEMS and in situ FTIR study, Appl. Catal. B Environ.
1
81 (2016) 672–680. doi:10.1016/j.apcatb.2015.08.041.
10] Y.-H. Hong, Z.-Y. Zhou, M. Zhan, Y.-C. Wang, Y. Chen, S.-C. Lin, M. Rauf, S.-
G. Sun, Liquid-inlet online electrochemical mass spectrometry for the in operando
monitoring of direct ethanol fuel cells, Electrochem. Commun. 87 (2018) 91–95.
doi:10.1016/j.elecom.2017.12.028.
11] J. Ribeiro, D.M. dos Anjos, J.-M. Léger, F. Hahn, P. Olivi, A.R. de Andrade, G.
Tremiliosi-Filho, K.B. Kokoh, Effect of W on PtSn/C catalysts for ethanol
electrooxidation, J. Appl. Electrochem. 38 (2008) 653–662. doi:10.1007/s10800-
0
08-9484-8.
2
1

ACCEPTED MANUSCRIPT
[
12] S. Rousseau, C. Coutanceau, C. Lamy, J.-M. Léger, Direct ethanol fuel cell
(
DEFC): Electrical performances and reaction products distribution under
operating conditions with different platinum-based anodes, J. Power Sources. 158
2006) 18–24. doi:10.1016/j.jpowsour.2005.08.027.
(
[
[
13] S.C.S. Lai, M.T.M. Koper, Ethanol electro-oxidation on platinum in alkaline
media, Phys. Chem. Chem. Phys. 11 (2009) 10446–10456.
doi:10.1039/B913170A.
14] J.S. Spendelow, A. Wieckowski, Electrocatalysis of oxygen reduction and small
alcohol oxidation in alkaline media, Phys. Chem. Chem. Phys. 9 (2007) 2654–
2
675. doi:10.1039/B703315J.
[
[
15] D.R. Dekel, Review of cell performance in anion exchange membrane fuel cells, J.
Power Sources. 375 (2018) 158–169. doi:10.1016/j.jpowsour.2017.07.117.
16] J. Cai, Y. Huang, Y. Guo, Bi-modified Pd/C catalyst via irreversible adsorption
and its catalytic activity for ethanol oxidation in alkaline medium, Electrochimica
Acta. 99 (2013) 22–29. doi:10.1016/j.electacta.2013.03.059.
[
[
17] F. Hu, C. Chen, Z. Wang, G. Wei, P.K. Shen, Mechanistic study of ethanol
oxidation on Pd–NiO/C electrocatalyst, Electrochimica Acta. 52 (2006) 1087–
1
091. doi:10.1016/j.electacta.2006.07.008.
18] C. Xu, Z. Tian, P. Shen, S.P. Jiang, Oxide (CeO2, NiO, Co3O4 and Mn3O4)-
promoted Pd/C electrocatalysts for alcohol electrooxidation in alkaline media,
Electrochimica Acta. 53 (2008) 2610–2618. doi:10.1016/j.electacta.2007.10.036.
[
19] Z. Nodehi, A.A. Rafati, A. Ghaffarinejad, Palladium-silver polyaniline composite
as an efficient catalyst for ethanol oxidation, Appl. Catal. Gen. 554 (2018) 24–34.
doi:10.1016/j.apcata.2018.01.018.
[
20] Y. Wang, S. Zou, W.-B. Cai, Recent Advances on Electro-Oxidation of Ethanol on
Pt- and Pd-Based Catalysts: From Reaction Mechanisms to Catalytic Materials,
Catalysts. 5 (2015) 1507–1534. doi:10.3390/catal5031507.
[
21] W. Wang, R. Wang, S. Ji, H. Feng, H. Wang, Z. Lei, Pt overgrowth on carbon
supported PdFe seeds in the preparation of core–shell electrocatalysts for the
oxygen reduction reaction, J. Power Sources. 195 (2010) 3498–3503.
doi:10.1016/j.jpowsour.2009.12.015.
[
[
22] M. Neergat, V. Gunasekar, R. Rahul, Carbon-supported Pd–Fe electrocatalysts for
oxygen reduction reaction (ORR) and their methanol tolerance, J. Electroanal.
Chem. 658 (2011) 25–32. doi:10.1016/j.jelechem.2011.04.016.
23] Y. Pan, F. Zhang, K. Wu, Z. Lu, Y. Chen, Y. Zhou, Y. Tang, T. Lu, Carbon
supported Palladium–Iron nanoparticles with uniform alloy structure as methanol-
tolerant electrocatalyst for oxygen reduction reaction, Int. J. Hydrog. Energy. 37
(2012) 2993–3000. doi:10.1016/j.ijhydene.2011.11.042.
2
2

ACCEPTED MANUSCRIPT
[
[
24] P.K. Shen, C. Xu, Alcohol oxidation on nanocrystalline oxide Pd/C promoted
electrocatalysts,
Electrochem.
Commun.
8
(2006)
184–188.
doi:10.1016/j.elecom.2005.11.013.
25] Z. Zhang, C. Zhang, J. Sun, T. Kou, Q. Bai, Y. Wang, Y. Ding, Ultrafine
nanoporous PdFe/Fe3O4 catalysts with doubly enhanced activities towards electro-
oxidation of methanol and ethanol in alkaline media, J. Mater. Chem. A. 1 (2013)
3
620–3628. doi:10.1039/C3TA01464A.
[
[
26] F.I. Pires, H.M. Villullas, Pd-based catalysts: Influence of the second metal on
their stability and oxygen reduction activity, Int. J. Hydrog. Energy. 37 (2012)
1
7052–17059. doi:10.1016/j.ijhydene.2012.08.102.
27] S. Santra, K. Dhara, P. Ranjan, P. Bera, J. Dash, S.K. Mandal, A supported
Palladium nanocatalyst for copper free acyl Sonogashira reactions: One-pot
multicomponent synthesis of N-containing heterocycles, Green Chem. 13 (2011)
3
238–3247. doi:10.1039/C1GC15869D.
[
28] Y. Feng, D. Bin, B. Yan, Y. Du, T. Majima, W. Zhou, Porous bimetallic PdNi
catalyst with high electrocatalytic activity for ethanol electrooxidation, J. Colloid
Interface Sci. 493 (2017) 190–197. doi:10.1016/j.jcis.2017.01.035.
[
[
29] A. Dutta, J. Datta, Energy efficient role of Ni/NiO in PdNi nano catalyst used in
alkaline DEFC, J. Mater. Chem. A. 2 (2014) 3237. doi:10.1039/c3ta12708g.
30] G.M. Alvarenga, I.B. Coutinho Gallo, H.M. Villullas, Enhancement of ethanol
oxidation on Pd nanoparticles supported on carbon-antimony tin oxide hybrids
unveils the relevance of electronic effects, J. Catal. 348 (2017) 1–8.
doi:10.1016/j.jcat.2017.02.002.
[
31] A. Calderón-Cárdenas, J.E. Ortiz-Restrepo, N.D. Mancilla-Valencia, G.A. Torres-
Rodriguez, F.H.B. Lima, A. Bolaños-Rivera, E.R. Gonzalez, W.H. Lizcano-
Valbuena, CO and ethanol electro-oxidation on Pt-Rh/C, J. Braz. Chem. Soc. 25
(2014) 1391–1398. doi:10.5935/0103-5053.20140121.
[
[
[
[
32] J. Malherbe, H. Martinez, B. Fernández, C. Pécheyran, O.F.X. Donard, The effect
of glow discharge sputtering on the analysis of metal oxide films, Spectrochim.
Acta Part B At. Spectrosc. 64 (2009) 155–166. doi:10.1016/j.sab.2008.11.009.
33] M. Aronniemi, J. Sainio, J. Lahtinen, Chemical state quantification of iron and
chromium oxides using XPS: the effect of the background subtraction method,
Surf. Sci. 578 (2005) 108–123. doi:10.1016/j.susc.2005.01.019.
34] N.H.H. Abu Bakar, M.M. Bettahar, M. Abu Bakar, S. Monteverdi, J. Ismail, M.
Alnot, PtNi catalysts prepared via borohydride reduction for hydrogenation of
benzene, J. Catal. 265 (2009) 63–71. doi:10.1016/j.jcat.2009.04.011.
35] Z.X. Liang, T.S. Zhao, J.B. Xu, L.D. Zhu, Mechanism study of the ethanol
oxidation reaction on palladium in alkaline media, Electrochimica Acta. 54 (2009)
2
203–2208. doi:10.1016/j.electacta.2008.10.034.
2
3

ACCEPTED MANUSCRIPT
[
[
36] O. Khaselev, J.M. Sykes, In-situ electrochemical scanning tunneling microscopy
studies on the oxidation of iron in alkaline solution, Electrochimica Acta. 42
(1997) 2333–2337. doi:10.1016/S0013-4686(96)00416-1.
37] M.D. Obradović, Z.M. Stančić, U.Č. Lačnjevac, V.V. Radmilović, A. Gavrilović-
Wohlmuther, V.R. Radmilović, S.L. Gojković, Electrochemical oxidation of
ethanol on palladium-nickel nanocatalyst in alkaline media, Appl. Catal. B
Environ. 189 (2016) 110–118. doi:10.1016/j.apcatb.2016.02.039.
[
[
38] D.A.J. Rand, R. Woods, The nature of adsorbed oxygen on rhodium, palladium
and gold electrodes, J. Electroanal. Chem. Interfacial Electrochem. 31 (1971) 29–
3
8. doi:10.1016/S0022-0728(71)80039-6.
39] M. Niu, W. Xu, S. Zhu, Y. Liang, Z. Cui, X. Yang, A. Inoue, Synthesis of
nanoporous CuO/TiO2/Pd-NiO composite catalysts by chemical dealloying and
their performance for methanol and ethanol electro-oxidation, J. Power Sources.
3
62 (2017) 10–19. doi:10.1016/j.jpowsour.2017.07.011.
[
[
40] L. Zhang, Q. Chang, H. Chen, M. Shao, Recent advances in palladium-based
electrocatalysts for fuel cell reactions and hydrogen evolution reaction, Nano
Energy. 29 (2016) 198–219. doi:10.1016/j.nanoen.2016.02.044.
41] S.Y. Shen, T.S. Zhao, J.B. Xu, Y.S. Li, Synthesis of PdNi catalysts for the
oxidation of ethanol in alkaline direct ethanol fuel cells, J. Power Sources. 195
(2010) 1001–1006. doi:10.1016/j.jpowsour.2009.08.079.
[
42] Z. Qi, H. Geng, X. Wang, C. Zhao, H. Ji, C. Zhang, J. Xu, Z. Zhang, Novel
nanocrystalline PdNi alloy catalyst for methanol and ethanol electro-oxidation in
alkaline
media,
J.
Power
Sources.
196
(2011)
5823–5828.
doi:10.1016/j.jpowsour.2011.02.083.
[
[
43] K. Maiti, J. Balamurugan, S.G. Peera, N.H. Kim, J.H. Lee, Highly Active and
Durable Core–Shell fct-PdFe@Pd Nanoparticles Encapsulated NG as an Efficient
Catalyst for Oxygen Reduction Reaction, ACS Appl. Mater. Interfaces. 10 (2018)
1
8734–18745. doi:10.1021/acsami.8b04060.
44] D.Y. Chung, S.W. Jun, G. Yoon, S.G. Kwon, D.Y. Shin, P. Seo, J.M. Yoo, H.
Shin, Y.-H. Chung, H. Kim, B.S. Mun, K.-S. Lee, N.-S. Lee, S.J. Yoo, D.-H. Lim,
K. Kang, Y.-E. Sung, T. Hyeon, Highly Durable and Active PtFe Nanocatalyst for
Electrochemical Oxygen Reduction Reaction, J. Am. Chem. Soc. 137 (2015)
1
5478–15485. doi:10.1021/jacs.5b09653.
[
[
45] Q. Lv, Y. Xiao, M. Yin, J. Ge, W. Xing, C. Liu, Reconstructed PtFe Alloy
Nanoparticles with Bulk-Surface Differential Structure for Methanol Oxidation,
Electrochimica Acta. 139 (2014) 61–68. doi:10.1016/j.electacta.2014.06.135.
46] C. Xu, Q. Li, Y. Liu, J. Wang, H. Geng, Hierarchical Nanoporous PtFe Alloy with
Multimodal Size Distributions and Its Catalytic Performance toward Methanol
Electrooxidation, Langmuir. 28 (2012) 1886–1892. doi:10.1021/la203835n.
2
4

ACCEPTED MANUSCRIPT
Figure Captions
Fig. 1. XRD patterns of the carbon supported Pd-based materials prepared by the
microwave method. (A) Pd:Fe and (B) Pd:Ni catalysts.
Fig. 2. Spectra of the core levels of (A) Pd 3d, (B) Fe 2p, (C) Ni 2p of the Pd/C,
Pd(59)Fe(41), and Pd(56)Ni(44) catalysts, respectively.
Fig. 3. (A) TEM micrograph of the Pd(59)Fe(41)/C catalyst. (B) Particle size
distribution (count: 60 nanoparticles) (C) Composition map for Pd and Fe.
Fig. 4. (A) TEM micrograph of the Pd(56)Ni(44)/C catalyst. (B) Particles size
distribution (count: 116 nanoparticles) (C) and (D) composition of the PdNi
nanoparticle.
-
1
Fig. 5. (A) Cyclic voltammograms of the Pd:Fe catalysts recorded in NaOH 1.0 mol L
-1
at 10 mV s ; (B) Cyclic voltammograms of the Pd:Fe catalysts recorded in NaOH 1.0
mol L + EtOH 1.0 mol L at 10 mV s ; (C) Mass activities of Pd:Fe catalysts from
their corresponding current-time curves and (D) Polarization curve of the Pd:Fe
-1
-1
-1
-1
-1
catalysts recorded in NaOH 1.0 mol L + EtOH 1.0 mol L at 0.5 V for 30 min.
-
1
Fig. 6. (A) Cyclic voltammograms of the Pd:Ni catalysts recorded in NaOH 1.0 mol L
-1
at 10 mV s ; (B) Cyclic voltammograms of the Pd:Ni catalysts recorded in NaOH 1.0
mol L + EtOH 1.0 mol L at 10 mV s ; (C) Mass activities of Pd:Ni catalysts from
their corresponding current-time curves and (D) Polarization curve of the Pd:Ni
-1
-1
-1
-1
-1
catalysts recorded in NaOH 1.0 mol L + EtOH 1.0 mol L at 0.5 V for 30 min.
2
5

ACCEPTED MANUSCRIPT
-
-
Pd-M/C (M = Ni or Fe) catalysts were prepared by the microwave method.
This method is advantageous because easy, fast and promotes small
nanoparticles.
-
-
Pd(50)M(50) compositions yielded the highest catalytic activity.
Ni addition affected the activity towards ethanol electrooxidation more markedly
than Fe.
We obtained catalytic activity 30 mA gPd for Pd(50)Ni(50) confirming the
beneficial effect of adding Ni.
-1
-