The Role of Ruthenium on Carbon-Supported PtRu Catalysts for Electrocatalytic Glycerol Oxidation under Acidic Conditions

Article abstract of DOI:10.1002/cctc.201601325

A series of binary PtRu catalysts with different Pt/Ru atomic ratios (from 7:3 to 3:7) were synthesized on a carbon support using the colloidal method; they were then used for electrooxidation of glycerol in acid media. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses were used to investigate particle size, size distribution, and structural and electronic properties of the prepared catalysts. Ru added to the Pt-based catalysts caused structural and electronic modifications over the PtRu alloy catalyst formation. The electrocatalytic activities of PtRu/C series catalysts were investigated using cyclic voltammetry. The Pt₅Ru₅/C catalyst shows enhanced catalytic activity at least 40 % higher than that of the Pt/C catalyst, with improved stability for glycerol electrooxidation; these improvements are attributed to structural and electronic modifications of the Pt catalysts. Using an electrocatalytic batch reactor, product analysis after the oxidation reaction was performed by high-performance liquid chromatography to determine and compare the reaction pathways on the Pt/C and PtRu/C catalysts. To understand different catalytic activities of glycerol oxidation on the PtRu alloy surfaces, density functional calculations were performed.

Full text of DOI:10.1002/cctc.201601325

Accepted Article
Title: Role of Ru on Carbon-supported PtRu Catalysts for Electro-
catalytic Glycerol Oxidation in Acidic Condition
Authors: Youngmin Kim, Hyun Woo Kim, Seonhwa Lee, Jisu Han,
Daewon Lee, Jeong-Rang Kim, Tae-Wan Kim, Chul-Ung Kim,
Soon-Yong Jeong, Ho-Jeong Chae, Beom-Sik Kim, Hyunju
Chang, Won Bae Kim, Sung Mook Choi, and Hyung Ju Kim
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the VoR from the journal website shown below when it is published
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To be cited as: ChemCatChem 10.1002/cctc.201601325
Link to VoR: http://dx.doi.org/10.1002/cctc.201601325
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10.1002/cctc.201601325
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Role of Ru on Carbon-supported PtRu Catalysts for Electro-
catalytic Glycerol Oxidation in Acidic Condition
Youngmin Kim,[a] Hyun Woo Kim,[b] Seonhwa Lee,[c] Jisu Han,[a] Daewon Lee,[a] Jeong-Rang Kim,[a]
Tae-Wan Kim,[d,e] Chul-Ung Kim,[d,e] Soon-Yong Jeong,[a,e] Ho-Jeong Chae,[a,e] Beom-Sik Kim,[a] Hyunju
Chang,[b] Won Bae Kim,[f] Sung Mook Choi,*[g] and Hyung Ju Kim*[a,e]
Abstract: A series of binary PtRu catalysts with different Pt:Ru atomic
ratios in a range from 7:3 to 3:7 are synthesized on carbon support
using the colloidal method; they are then used for electrooxidation of
glycerol in acidic media. X-ray diffraction (XRD), transmission electron
microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and X-
ray absorption spectroscopy (XAS) analyses are used to investigate
the particle size, size distribution, and structural and electronic
properties of the prepared catalysts. The addition of Ru content to the
Pt-based catalysts caused structural and electronic modifications over
the PtRu alloy catalyst formation. The electrocatalytic activities of
PtRu/C series catalysts are investigated by using the cyclic
voltammetry (CV) technique. Among the prepared catalysts, the
Pt5Ru5/C catalyst shows enhanced catalytic activity at least 40%
higher than that of the Pt/C catalyst, with improved stability for glycerol
electrooxidation; these improvements can be attributed to the
structural and electronic modifications of the Pt catalysts. Using an
electrocatalytic batch reactor, product analysis after the oxidation
reaction is performed by high-performance liquid chromatography
(HPLC) to determine and compare the reaction pathways on the Pt/C
and PtRu/C catalysts. To understand different catalytic activities of
glycerol oxidation on the PtRu alloy surfaces, density functional theory
(DFT) calculations have been performed and discussed with the
experimental results.
Introduction
Glycerol is a valuable byproduct in the production of biodiesel and
fatty acids.[1-4] Recently, efforts have been devoted to developing
efficient electrochemical conversion technologies to produce
value-added chemicals and/or energy from biomass-derived
oxygenates such as glycerol.[5-13] The electrocatalytic conversion
process of glycerol is a promising technology that can produce
valuable chemicals such as dihydroxyacetone, glyceraldehyde,
and glyceric acid by selective oxidation reaction[14-16] and
electrical energy by a full oxidization reaction[17-19]. In particular,
full glycerol oxidation has been considered a promising reaction
for direct alcohol fuel cells (DAFC), because glycerol is non-
flammable and has environment-friendly properties; it also
possesses high theoretical energy density, with relatively low
price and simple purification steps.[5,20] It has also been reported
that glycerol can be used as fuel for a DAFC in alkaline condition
over Pt and Pd-based catalysts.[5,21-27]
[a]
Dr. Y. Kim, Dr. S. Lee, J. Han, D. Lee, Dr. J. -R. Kim, Prof. Dr. S. -Y.
Jeong, Prof. Dr. H. –J. Chae, Dr. B. –S. Kim, Prof. Dr. H. J. Kim
Carbon Resources Institute
Korea Research Institute of Chemical Technology (KRICT)
141 Gajeong-ro, Yuseong-gu, Daejeon 34114, South Korea
E-mail: hjkim@krict.re.kr
[b]
[c]
[d]
[e]
Dr. H. W. Kim, Dr. H. Chang
The electrooxidation reaction of glycerol can be represented as
below; this electrooxidation reaction can take place in a Pt-based
Center for Molecular Modeling and Simulation
Korea Research Institute of Chemical Technology (KRICT)
141 Gajeong-ro, Yuseong-gu, Daejeon 34114, South Korea
Dr. S. Lee
Department of Physics and Photon Science
Gwangju Institute of Science and Technology (GIST)
123 Cheomdangwagi-ro, Buk-gu, Gwangju 61005, South Korea
Prof. Dr. T. –W. Kim, Prof. Dr. C. –W. Kim
Center for Convergent Chemical Process
Korea Research Institute of Chemical Technology (KRICT)
141 Gajeong-ro, Yuseong-gu, Daejeon 34114, South Korea
Prof. Dr. T. –W. Kim, Prof. Dr. C. –W. Kim, Prof. Dr. S. -Y. Jeong,
Prof. Dr. H. –J. Chae, Prof. Dr. H. J. Kim
catalyst electrode in acidic media[17,28]
:
C3H8O3 + 3H2O → 3CO2 + 14H+ + 14e- at anode
(1)
Compared to the electrooxidation of methanol (CH3OH + H2O
→ CO2 + 6 H+ + 6 e-), the oxidation process of glycerol (Reaction
1) involves additional complicated reaction steps due to the
scission of more C–C and C-H bonds, especially at low
temperatures (20 - 120 °C). It also leads to the necessity of
additional activation energy for the reaction.[28,29] Therefore,
glycerol oxidation depends on the ability to break the C-C and C-
H bonds. Recently, we reported that PtRu-based catalysts
showed improved catalytic activity and stability for glycerol
electrooxidation in acidic condition.[17,18] However, more scientific
investigation is required to understand why the PtRu combination
is so active for glycerol electrooxidation in acidic condition.
Department of Green Chemistry & Biotechnology
University of Science and Technology (UST)
113 Gwahangno, Yuseong, Daejeon 34113, South Korea
Prof. Dr. W. B. Kim
[f]
Department of Chemical Engineering
Pohang University of Science and Technology (POSTECH)
77 Cheongnam-Ro, Nam-gu, Pohang 37673, South Korea
Dr. S. M. Choi
[g]
Surface Technology Division
Korea Institute of Materials Science (KIMS)
797 Changwondae-ro, Seongsan-gu, Changwon 51508, South
Korea
We report here an experimental and computational
investigation of PtRu/C catalysts used for electrocatalytic glycerol
oxidation in acidic electrolyte. PtRu/C catalysts with different
E-mail: akyzaky@kims.re.kr
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Pt:Ru atomic ratios are synthesized by the colloidal method and
characterized by using various physicochemical analyses such as
transmission electron microscopy (TEM), X-ray diffraction (XRD),
X-ray photoelectron spectroscopy (XPS), and X-ray absorption
spectroscopy (XAS). The electrocatalytic activities of the PtRu/C
catalysts are investigated using the cyclic voltammetry (CV)
technique and the chronoamperometry (CA) method; results are
analyzed and discussed along with the reaction product analysis
by employing high-performance liquid chromatography (HPLC).
With the help of density functional theory (DFT) calculations, we
also explore the correlation between the catalyst activity for
glycerol electrooxidation and the glycerol binding energy in order
to gain further insight into the promoting mechanism of Ru to Pt.
To the best of our knowledge, this is the first work to demonstrate
a glycerol electrooxidation mechanism in acidic condition with
reaction product analysis and DFT calculations over Pt-based
catalysts.
Figure 2. XRD patterns of the Pt/C and PtRu/C catalysts with different Pt:Ru
atomic ratios and the selected scan range of the Pt (111) reflection peaks.
respectively, with relatively narrow particle size distribution (see
Table 1).
XRD patterns of Pt/C and PtRu/C catalysts with different Pt:Ru
atomic ratios are displayed in Figure 2. In the XRD pattern of Pt/C,
the characteristic peaks at ca. 39°, 46°, 67°, and 81° exhibit a Pt
face-centered cubic (fcc) lattice structure corresponding to the
(111), (200), (220), and (311) planes, respectively. The diffraction
peaks of the PtRu/C catalysts with different Pt:Ru atomic ratios
are similar to those of the Pt/C, except that the 2θ values of the
Pt diffraction peaks are gradually shifted to higher values with
increasing Ru content, as summarized in Table 1. No
distinguishable diffraction peaks for Ru or RuO2 crystal peaks
appeared, suggesting an alloy formation between Pt and Ru
through incorporation of Ru atoms into the fcc crystal lattice of
Pt.[30-32] The lattice parameters of the prepared catalysts were
calculated using the following equation:
Results and Discussion
Structural properties of PtRu/C catalyst
Figure 1 presents the TEM images and the corresponding
histograms of the particle size distribution of carbon supported
Pt7Ru3, Pt5Ru5, and Pt3Ru7 nanoparticles with the ETEK
commercial Pt/C catalysts, showing the morphology and average
particle size distribution. Based on the TEM images, Pt and PtRu
nanoparticles can be seen to be finely and uniformly dispersed on
the surface of the carbon support, with a uniform metal particle
size. The average particle size was estimated with the following
equation using the more than 150 different particles visible on the
micrographs:
∑
∑
nidi
ni
λ
d =
2
2
2
√
h + k + l
a =
×
2 sin θ
where ni is the number of particles having a diameter of size di.[25]
The particle sizes of carbon supported Pt, Pt7Ru3, Pt5Ru5, and
Pt3Ru7 are estimated to be ca. 2.3, 2.0, 2.0, and 1.7 nm,
where a is the lattice parameter, (hkl) are the (220) Miller indices,
λ is the wavelength of the X-rays (1.54056 Å), and θ is the
diffraction peak position at the (220) plane. The values of the
lattice parameters of the PtRu/C catalysts were found to
consistently decrease with increasing of the Ru content due to the
smaller atomic radius of Ru relative to that of Pt (see Table 1).
Electronic properties of PtRu/C catalyst
XPS was employed to explain the surface oxidation states of the
prepared catalysts. Figure 3 shows the Pt 4f and Ru 3p regions in
the XPS spectra of the Pt/C and PtRu/C series. The core-level
binding energies (BEs) and their relative amounts of oxidation
states for the Pt 4f and Ru 3p are reported in Table 1. It was found
that the predominant surface species in the prepared catalysts is
the metallic state of zero-valent Pt (Pt0); a relatively small amount
of the oxidized Pt (Pt2+) is present. Also, the BEs of Pt (Pt0) 4f7/2
for the PtRu/C series were positively shifted compared with that
of Pt/C, indicating that the vacancies in the Pt valence band
Figure 1. TEM images of carbon-supported Pt and PtRu catalysts with different
Pt:Ru atomic ratios, together with corresponding histograms of particle size.
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Figure 4. Pt L3 edge XANES spectra for the Pt/C and PtRu/C catalysts with
different Pt:Ru atomic ratios together with Pt foil as the reference. The inset is
a magnified image for the white line intensity.
with different BE values. More than 72% of the surface
composition is in metallic state in the PtRu/C series catalysts. The
XPS results suggest that on the surface of the binary PtRu/C
catalysts the dominant surface phase of Pt and Ru is the metallic
state.
Figure 4 shows the normalized XANES spectra obtained at the
Pt L3 edge for the prepared catalysts. Overall XANES shapes of
the Pt/C and PtRu/C series are similar to that of the Pt foil, except
for the white line (WL) intensity. WL, which is a strong peak above
the edge energy position, corresponds to the 2p3/2 → 5d transition
at the Pt L3 edge and is closely related to the density of vacant d
orbital states.[34,35] The WL intensities for all of the carbon-
supported catalysts show greater values than that of the Pt foil.
And, in case of the PtRu/C catalysts, the WL intensities appear to
increase in the order of Pt7Ru3/C < Pt5Ru5/C < Pt3Ru7/C (inset of
Figure 4). The increased WL intensities for the PtRu bimetallic
catalysts can be attributed to the 5d electron loss of the Pt in the
PtRu alloys.[36,37] The quantitative WL values, with the edge
energy analysis, are summarized in Table 1.
Figure 3. XPS of Pt 4f and Ru 3p for the Pt/C and PtRu/C catalysts with
different Pt:Ru atomic ratios.
increase due to Ru, leading to more tightly bound electrons in the
Pt core levels.[33] This implies that the Pt electronic structure in
PtRu/C was significantly modified by the presence of Ru. It was
possible to deconvoluted the Ru 3p3/2 spectra to the metallic
phase (Ru0) and to the oxidation states (Ru4+) in forms of RuO2
Table 1. Structural and electronic parameters of the catalysts characterized by XRD, TEM, XPS, and XANES analyses.
XRD
TEM
XPS
XANES
Lattice
parameter[b]
Mean particle
size[c]
WL
intensity[g]
[a]
[f]
Catalysts
2θmax
Pt 4f7/2
Ru 3p3/2
E0
(°)
(eV)
(eV)
( eV )
(Å )
(nm)
(a.u.)
Pt foil
Pt/C
-
-
-
-
-
-
11564.0
11564.0
1.26
1.42
67.8
68.7
68.9
70.3
3.905
2.3 ± 0.42
71.05 (60.2)[d]
74.38 (39.8)[d]
71.34 (59.3)
74.67 (40.7)
71.30 (60.5)
74.63 (39.5)
71.29 (61.0)
74.62 (39.0)
Pt7Ru3/C
Pt5Ru5/C
Pt3Ru7/C
3.880
3.850
3.826
2.0 ± 0.39
2.0 ± 0.43
1.7 ± 0.45
461.94 (83.3)[e]
464.90 (16.7)[e]
462.49 (75.2)
465.51 (24.8)
462.01 (72.0)
464.84 (28.0)
11564.0
11564.4
11564.4
1.42
1.52
1.56
[a] The angular position of Pt(220) reflection peak. [b] Lattice parameter calculated from XRD measurement. [c] Mean particle diameter of the samples from TEM
images. [d] Relative % of the Pt0 and Pt2+ species. [e] Relative % of the Ru0 and Ru4+ species. [f] Pt L3 edge energy. [g] White line intensity.
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Table 2. Comparison of the electrocatalytic activity of the catalysts for
glycerol oxidation.
[a]
[b]
[c]
Eonset
Ef
If
Catalysts
(V vs. SHE)
(V vs. SHE)
(mA cm-2)
Pt/C
0.635
0.480
0.448
0.498
0.893
0.862
0.854
0.825
27.5
33.7
38.6
21.9
Pt7Ru3/C
Pt5Ru5/C
Pt3Ru7/C
[a] Onset potential. [b] Forward anodic peak potential at 50 mV s-1. [c]
Forward anodic peak current density at 50 mV s-1.
most prominent electrochemical performance in terms of the
largest forward peak current density and the lowest onset
potential. It should be noted that the peak current density of the
Pt3Ru7/C catalyst is the lowest among the tested catalysts, which
may be due to a substantial reduction of available surface Pt
active sites by large amounts of Ru.
Figure 5. CVs for the electrooxidation of glycerol over the Pt/C and PtRu/C
catalysts in 0.5 M H2SO4 + 2 M C3H5(OH)3 with a scan rate of 50 mV s-1 at
room temperature.
Figure 6 shows the long term cycle test results for the Pt5Ru5/C
and Pt/C catalysts in 0.5 M H2SO4 with 2 M glycerol at a scan rate
of 50 mV s-1. To compare the decay rate, the current density was
normalized by the initial current. After 500 cycles, Pt5Ru5/C
presents a normalized current density ratio of 0.635, which is
much higher than that of Pt/C (0.465). This result indicates that
the Pt5Ru5/C catalyst has stability better than that of the Pt/C
catalyst.
Electrocatalytic activity and stability of PtRu/C catalyst
The electrocatalytic activity of the Pt/C and PtRu/C series
catalysts was investigated by the cyclic voltammetry (CV)
technique in 0.5 M H2SO4 with 2 M glycerol at a scan rate of 50
mV s-1, as shown in Figure 5. The current densities were
normalized to the geometric area of the electrode. The
electrocatalytic test results are summarized in Table 2. By
comparing the characteristics of the CVs, the addition of Ru to Pt
was found to substantially enhance the catalytic activity for
glycerol electrooxidation. First, the onset potentials (indicative of
the catalytic activity) of glycerol oxidation in the case of alloyed
catalysts showed relatively lower values than that of only the Pt
catalyst. The positions of the onset potentials follow the order of
Pt5Ru5/C < Pt7Ru3/C < Pt3Ru7/C < Pt/C. Second, the forward peak
current densities (showing the maximum catalyst performance) of
the binary catalysts toward glycerol oxidation are in the order of
Pt5Ru5/C > Pt7Ru3/C > Pt/C > Pt3Ru7/C. In particular, the peak
current density of the Pt5Ru5/C catalyst is 1.4 times higher than
that of the Pt/C catalyst. Thus, the Pt5Ru5/C catalyst exhibited the
Reaction pathways for glycerol electrooxidation over PtRu/C
catalyst
In order to understand how the reaction path differs for the Pt/C
and Pt5Ru5/C catalysts, we conducted electrocatalytic glycerol
oxidation using an electrochemical batch reactor featuring a
three-electrode system with catalyst-coated carbon paper as the
working electrode. Liquid samples after the reaction were
analyzed by HPLC. Table 3 shows the glycerol conversion,
product selectivity, and mass balance for the electrocatalytic
oxidation of glycerol using the batch reactor over the Pt/C and
Figure 6. Long-term cycle stability for the electrooxidation of glycerol over the Figure 7. Chronoamperometry results at the reaction temperature of 60 oC for the
Pt/C and Pt5Ru5/C catalysts in 0.5 M H2SO4 + 2 M C3H5(OH)3 with a scan rate of electrooxidation of 0.1 M glycerol in 0.5 M H2SO4, collected at the anode applied
50 mV s−1 at room temperature.
potential of 1.1 V (vs. SHE).
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Table 3 Glycerol conversion and product selectivity for electrocatalytic glycerol oxidation using a batch reactor at 60 oC over Pt/C and Pt5Ru5/C catalysts.
Glycerol
Conv.[d]
[%]
Product Selec.[d] [%]
Catalyst
System
Mass Bal.[c]
[%]
Feed Solution[a]
Applied Potential[b]
DHA
GAD
GLA
GCA
Pt/C
0.1M Glycerol
0.1M Glycerol
1.1 V
1.1 V
100.4
80.4
20.3
31.5
0
42.1
17.1
57.8
11.1
0.5
Pt5Ru5/C
35.0
17.2
[a] The 0.1 M glycerol in 0.5 M H2SO4 was used as feed solution. [b] The anode applied potential for the electrocatalytic glycerol oxidation was 1.1 V (vs. SHE).
[c] Mass balance (bal.) was determined on basis of observed C2 and C3 products. [d] Glycerol conversion (conv.) and product selectivity (selec.) were calculated
after 7 hours reaction and identified in liquid C2 and C3 products; Liquid samples after the reaction were analyzed by HPLC; DHA = dihydroxyacetone, GAD =
glyceraldehyde, GLA = glyceric acid, GCA = glycolic acid
Pt5Ru5/C catalysts. Results for the electrooxidation of glycerol
were obtained at a reaction temperature of 60 °C and 0.1 M
glycerol in 0.5 M H2SO4 at a fixed potential of 1.1 V (vs. SHE) for
7 hours reaction. Figure 7 exhibits the current–time plots of the
Pt5Ru5/C and Pt/C catalysts in 0.5 M H2SO4 with 0.1 M glycerol.
Similar to the CV results (Figure 5 and Table 2), the current
density of Pt5Ru5/C, determined from chronoamperometry
measurement, is much higher than that of Pt/C. As can be seen
in Table 3, the glycerol conversion of PtRu/C achieved a value of
31.5 %, which was higher than the value of 20.3 % of Pt/C. As
Table 3 indicates, the glycerol oxidation on Pt/C catalyst mainly
leads to the formation of glyceraldehyde and glyceric acid. In the
case of the Pt5Ru5/C catalyst, dihydroxyacetone of 35.0 % was
observed, indicating that the production of dihydroxyacetone is
favored on the PtRu surface. More oxidized products such as
glycolic acid were produced over the PtRu/C catalyst. The mass
balance of detectable products decreased from 100.4 % for Pt/C
to 80.4 % for PtRu/C. The undetectable carbon was probably C1
molecules (formic acid or CO2) produced by C-C cleavage
reactions over the PtRu/C. These results demonstrate how the
PtRu surface can increase the rate of C-C bond cleavage as well
as that of C–H and O–H bond breakage compared to only the Pt
surface. It has been reported by several authors[17,19,38-40] that the
modified structural and electronic properties of the Pt may
promote the C-C and C-H bond cleavage, thus enhancing the
catalytic activity for the alcohol electrooxidation.
Figure 8 shows the possible reaction pathway over the Pt-
based catalysts for glycerol electrooxidation in acidic media. The
glycerol molecule is primarily oxidized to glyceraldehyde and/or
dihydroxyacetone, which are further oxidized to glyceric acid. The
glyceric acid is subsequently oxidized to glycolic acid,
hydroxypyruvic acid, and tartronic acid. It has been reported that
low levels of hydroxypyruvic acid and tartronic acid were detected
for the oxidation of glyceric acid over Pt-based catalysts,
indicating that the oxidation of glyceric acid to glycolic acid under
acidic media may be favored by C–C bond cleavage.[15] This is
consistent with the reaction mechanism on the PtRu/C catalyst,
discussed above and shown in Table 3.
Figure 8. Proposed reaction pathways over the PtRu catalyst for electrocatalytic glycerol oxidation in acidic condition. (DHA:
dihydroxyacetone, GAD: glyceraldehyde, GLA: glyceric acid, HPA: hydroxypyruvic acid, TTA: tartronic acid, GCA: glycolic acid, OXA: oxalic
acid)
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Figure 10. Relation between glycerol binding energy and onset potential (vs.
SHE) for glycerol electrooxidation over PtRu/C catalysts.
Figure 9. Binding modes and energies of glycerol on Pt, Ru, and Pt mixed with
Ru surfaces. (a) Glycerol binding on Pt, Pt5Ru5, and Ru surfaces (from left to
right). Pt atoms are shown in blue and Ru atoms are in pink. (b) Glycerol
binding energies and (c) average partial charges of surface atoms with respect
to Ru contents.
obtained when the catalytic activity for a reaction is correlated to
the ability of the catalyst surface to form chemical bonds with
reactants, reaction intermediates, or products.[41,42] Considering
that the Pt5Ru5 surface acts as the most active catalyst (see Table
2 and Figure 5), we suggest that the optimal glycerol binding
energy is ~1.75 eV for oxidizing glycerol molecules with mixed
metal surfaces. This result highlights the idea that the glycerol
molecules on the modified PtRu surface can be efficiently
oxidized by controlling the adsorption/desorption properties of
glycerol and of the other reaction products.
Correlation between catalyst activity and binding energy
First principle DFT calculations were carried out to understand the
interactions between glycerol molecules and the metal surface. In
Figure 9a, we have drawn optimized structures of the glycerol
molecules and metal surfaces for three cases: Pt, Pt5Ru5, and the
Ru surfaces. Two oxygen atoms of glycerol are close to the
surface, indicating that oxygen-metal interaction holds the
glycerol to the surface. In addition, as oxygen atoms are bound to
the surface, hydrogen atoms in C-H and O-H bonds are also close
to the surface. This binding mode will surely be the same for all
other oxidized intermediates containing oxygen atoms and
implies several chemical bonds are affected by the catalyst.
Although the binding modes are the same, binding energies show
different behavior. For the mixed surfaces, the binding energies
of glycerol decrease as the Ru content increases (Figure 9b). The
pure Pt and Ru surfaces also interact with the glycerol molecules.
However, their interaction is weaker compared to the case of the
mixed surfaces. This can be well-explained based on electrostatic
interactions between oxygen and the surface atoms. From Bader
analysis of all the atoms on the surfaces, we estimated the
average partial charges of the atoms on the top-most layer, with
results shown in Figure 9c. If the Pt and Ru atoms are mixed, Ru
atoms become partially positive, while Pt atoms are partially
negative. The more positive Ru atoms show stronger electrostatic
interactions with the electronegative oxygen atoms of glycerol,
and thus exhibit higher binding energies. The highest binding
energy is observed for the Pt7Ru3 surface, where the average
charge of Ru atoms is the most positive. As can be seen in Figure
10, there seems to exist a volcano-type relation between the
theoretically calculated values of glycerol binding energy and the
experimentally obtained values of onset potential for glycerol
electrooxidation. It has been reported that a volcano-shaped
curve generated from the Brønsted–Evans–Polanyi relation is
Conclusions
In this work, the electrooxidation of glycerol was investigated on
a series of Ru-modified Pt/C catalysts. The XRD and TEM results
indicate that bimetallic PtRu nanoparticles with different atomic
ratios (Pt:Ru = 7:3, 5:5, 3:7) are well alloyed and uniformly
dispersed on the carbon support, with an average particle size of
about 2 nm. XPS and XANES analyses revealed that the Pt
electronic structure was significantly modified through the
formation of the PtRu alloy. The electrochemical measurements
showed more enhanced catalytic activities for the glycerol
electrooxidation on the bimetallic PtRu/C catalysts than for the
Pt/C catalyst in acidic media. In the electrocatalytic batch reactor,
the PtRu/C catalyst produced more oxidized products, such as
glycolic acid, at higher glycerol conversion compared to the Pt/C
catalyst. DFT calculations revealed that there exists a volcano-
type relation between the glycerol binding energy and the catalytic
activity for glycerol electrooxidation. This study thus highlights
that glycerol molecules on the structurally and electronically-
modified PtRu surface can be efficiently oxidized by controlling
the adsorption/desorption properties of glycerol and by breaking
more C-C, C-H, and O-H bonds. Further systematic studies
including theoretical calculations are required to better
understand
the
C-C,
C-H,
and
O-H
bond
cleavage/adsorption/desorption during glycerol electrooxidation
over PtRu/C catalyst.
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0.2 to 1.0 V (vs. Ag/AgCl) at room temperature with a scan rate of 50 mV
s−1 in N2 saturated 2 M glycerol in a 0.5 M H2SO4 electrolyte solution. All
potentials were referenced to the standard hydrogen electrode (SHE).
Experimental Section
Chemicals
Electrocatalytic batch reaction and product analysis
Chloroplatinic acid hexahydrate (H2PtCl6·6H2O, ACS reagent, Sigma-
Aldrich), ruthenium(III) chloride hydrate (RuCl3·xH2O, 99.98%, Sigma-
Aldrich), ethylene glycol (99.8%, Sigma-Aldrich), de-ionized water (DI
water, 18 MΩ cm, Millipore), sodium hydroxide solution (NaOH, 50%
solution in water, Aldrich), Nafion® ionomer solution (5 wt.%, Sigma-
Aldrich), carbon black powder (Vulcan® XC72R, Cabot Corp.), Pt/C (20
wt.%, ETEK), hydrochloric acid (HCl, 37%, Sigma-Aldrich), carbon paper
(TGP-H090, Toray), and glycerol (≥99.5%, Sigma-Aldrich) were
purchased and used as received without further purification.
Carbon paper was used as the working electrode for the electrocatalytic
glycerol batch reaction. A Pt wire and Ag/AgCl (in sat. KCl) were used as
the counter electrode and the reference electrode, respectively. For the
catalyst coated carbon paper, the prepared Pt/C and PtRu/C catalysts
were suspended in isopropyl alcohol, which contained a 5 wt.% Nafion®
ionomer solution; mixture was then sonicated for 3 h. Next, catalyst ink
was deposited on the surface of the carbon paper electrodes (with a 2 cm2
geometric area and 1 mg cm-2 metal loading) using a spray method; this
was followed by drying in an oven at 70 °C for 1 h. Using the
chronoamperometry technique, oxidation of glycerol was carried out in a 7
ml mixture consisting of 0.1 M glycerol in a 0.5 M H2SO4 solution. The
reaction temperature of 60 °C was controlled by directly heating the
electrochemical reactor using a temperature regulator. Prior to any
electrochemical measurements, the mixture was completely purged with
pure N2 to eliminate the dissolved dioxygen gas. The pH values of the
mixture were nearly the same during the reaction and were invariant under
all conditions of pH variation of 0.4 - 0.6.
Synthesis of carbon-supported PtRu electrocatalysts
Prior to its use as a catalyst support, carbon black powder was pretreated
with 6 M HCl solution for 12 h and then washed with DI water until the
solution pH was around 5.5; this was followed by filtering and drying for 5
h in air at 120 °C. For a typical synthesis of 20 wt.% PtRu/C, the pre-
calculated amounts of Pt and Ru salts (atomic ratios of Pt:Ru = 7:3, 5:5, or
3:7) were first dissolved in 50 ml of ethylene glycol. Then, the solution was
adjusted to pH 12 by adding NaOH solution; mixture was then aged for 30
min at room temperature. Subsequently, the solution was heated at 160 °C
for 3 h with stirring under reflux condition and then cooled to room
temperature. The acid pretreated carbon powders were then added to the
resulting solution and stirred for 24 h. The final solution was filtered and
washed with DI water and was dried using a vacuum freeze dryer. Finally,
the dried PtRu/C catalysts were heat treated under N2 atmosphere at
100 °C for 2 h.
The reaction products formed during glycerol electrooxidation were
collected and examined by analyzing each phase of the reaction mixture
using high-performance liquid chromatography (HPLC, Waters 2535) with
an RI detector and a UV–Vis detector (220 nm). A Biorad Aminex HPX-
87H sugar column was used with 0.005 M H2SO4 (at a flow rate of 0.3 ml
min-1) as the eluent at 60 °C. 1 μl liquid samples were injected after
filtration through a 0.2 μm filter. The amount of consumed glycerol and the
reaction product yields were quantified with an external calibration method.
Materials characterization
Computational details
The XRD patterns of the as-produced samples were obtained using a
Rigaku Rotalflex (RU-200B) X-ray diffractometer equipped with a Cu Kα (λ
= 1.5405 Å) source and an Ni filter at 40 mA, 40 kV, and a scan rate of 5˚
min−1. The TEM analysis was performed with a JEOL JEM-2100EX
microscope operating at an accelerating voltage of 200 kV. The XPS
(ESCALAB 250, UK) was carried out using a monochromic Al Kα X-ray
source (E = 1486.6 eV); the data processing was performed with the
XPSPEAK software. The binding energy of the C 1s peak at 284.5 eV was
taken as an internal standard and the background was fitted by the Shirley
method. The XAS measurement was conducted on the 7D beamline of the
Pohang Accelerator Laboratory (PLS-II, 3.0 GeV, Korea) using a Si (111)
double crystal monochromator. The spectra were taken at room
temperature in transmission mode for the L3-edge of Pt (11,564 eV) under
ambient conditions; energy calibration was performed using standard
metal foil. The X-ray absorption near edge structure (XANES) spectra were
processed and analyzed with the ATHENA program.[43]
All density functional theory (DFT) computations were carried out with the
Vienna ab initio simulation package (VASP).[44,45] We employed the
optB86b-vdW density functional[46,47] because noncovalent interactions
between glycerol molecules and the metal surface were reasonably
explained with this functional.[48] A Pt (111) surface with four layers was
generated from the bulk platinum. To avoid non-physical interactions
among atoms in different periodic cells, the surfaces were prepared with a
size of 16.3 × 14.1 × 25.9 Å 3. Other surfaces were prepared by randomly
substituting Pt atoms with Ru atoms on the Pt (111) surface. For all metal
surfaces, both the cell parameter and the ionic positions were properly
relaxed without any constraints. We also optimized the glycerol molecule
to its most probable conformation and then placed the molecule on the
metal surfaces in such a way that two oxygen atoms pointed towards the
surfaces. We relaxed all atoms of the two top layers; we also relaxed the
glycerol molecule while fixing two bottom layers of the surface. The kinetic
energy cutoff was set at 400 eV for all DFT calculations. The Brillouin zone
was sampled with 3 × 3 × 1 Monkhorst-pack k-point grids. All reported
structures were optimized until all forces were smaller than 0.05 eV Å -1.
Atomic partial charges were computed based on Bader analysis.[49,50]
Electrocatalytic activity and stability tests
The catalytic activity toward glycerol electrooxidation was investigated
from cyclic voltammetry (CV) results using a half-cell system made up of
well-polished glassy carbon (0.196 cm2) as a working electrode (WE), a
platinum wire as a counter electrode (CE), and an Ag/AgCl (in sat. KCl) as
a reference electrode (RE); all were connected to a Solartron Analytical
instrument (AMETEK model 1470E). To prepare the WE, each catalyst
was homogeneously suspended in a mixture of DI water and 5 wt.%
Nafion® ionomer solution and ultra-sonicated to obtain homogeneous inks.
Then, the catalyst ink (2.5 μl contains 6.42 μg of metal) was loaded onto
the WE and was dried in an oven at 70 °C for 30 min to prepare a thin film
of the catalyst electrode. The CV was carried out in the potential range of
Acknowledgements
This work was supported by the KRICT Flagship Research
Program. This work was also supported by the New & Renewable
Energy Core Technology Program of the Korea Institute of Energy
Technology Evaluation and Planning (KETEP), granted financial
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10.1002/cctc.201601325
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FULL PAPER
[24] X. Han, D. J. Chadderdon, J. Qi, L. Xin, W. Li, W. Zhou, Int. J. Hydrog.
Energy 2014, 39, 19767-19779.
resource from the Ministry of Trade, Industry & Energy, Republic
of Korea. (No. 20143010031770).
[25] J. Qi, L. Xin, D. J. Chadderdon, Y. Qiu, Y. Jiang, N. Benipal, C. Liang, W.
Li, Appl. Catal. B-Environ. 2014, 154–155, 360-368.
[26] J. Qi, L. Xin, Z. Zhang, K. Sun, H. He, F. Wang, D. Chadderdon, Y. Qiu,
C. Liang, W. Li, Green Chem. 2013, 15, 1133-1137.
[27] Z. Zhang, L. Xin, J. Qi, Z. Wang, W. Li, Green Chem. 2012, 14, 2150-
2152.
Keywords: PtRu alloy • Glycerol • Electrocatalysis • Fuel cells •
Energy conversion
[1]
[2]
G. W. Huber, S. Iborra, A. Corma, Chem. Rev. 2006, 106, 4044-4098.
A. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chem.
2008, 10, 13-30.
[28] J. H. Kim, S. M. Choi, S. H. Nam, M. H. Seo, S. H. Choi, W. B. Kim, Appl.
Catal. B-Environ. 2008, 82, 89-102.
[29] W. Vielstich, A. Lamm, H.A. Gasteiger, Handbook of Fuel Cells, John
Wiley & Sons, England, 2003.
[3]
[4]
[5]
[6]
[7]
P. Gallezot, Chem. Soc. Rev. 2012, 41, 1538-1558.
P. Gallezot, ChemSusChem 2008, 1, 734-737.
[30] X. Yu, P. G. Pickup, J. Power Sources 2011, 196, 7951-7956.
[31] V. Radmilovic, H. A. Gasteiger, P. N. Ross, J. Catal. 1995, 154, 98-106.
[32] C. Alegre, M. E. Galvez, R. Moliner, V. Baglio, A. Stassi, A. S. Arico, M.
J. Lazaro, ChemCatChem 2013, 5, 3770-3780.
Z. Zhang, L. Xin, W Li, Appl. Catal. B-Environ. 2012, 119-120, 40-48.
L. Xin, Z. Zhang, Z. Wang, W Li, ChemCatChem 2012, 4, 1105-1114.
Y. Kwon, Y. Birdja, I. Spanos, P. Rodriguez, M. T. M. Koper, ACS Catal.
2012, 2, 759-764.
[33] F. Bautie de Mongeot, M. Scherer, B. Gleich, E. Kopatzki, R. J. Behm,
Surf. Sci. 1998, 411, 249-262.
[8]
[9]
P. Nilges, T. R. dos Santos, F. Harnisch, U. Schroder, Energy Environ.
Sci. 2012, 5, 5231-5235.
[34] A. C. Garcia, V. A. Paganin, E. A. Ticianelli, Electrochim. Acta 2008, 53,
4309-4315.
S. K. Green, G. A. Tompsett, H. J. Kim, W. B. Kim, G. W. Huber,
ChemSusChem 2012, 5, 2410-2420.
[35] F. H. B. Lima, E. R. Gonzalez, Appl. Catal. B-Environ. 2008, 79, 341-346.
[36] M. Wakisaka, S. Mitsui, Y. Hirose, K. Kawashima, H. Uchida, M
Watanabe, J. Phys. Chem. B 2006, 110, 23489-23496.
[37] S. Mukerjee, S. Srinivasan, M. P. Soriaga, J. Mcbreen J. Electrochem.
Soc. 1995, 142, 1409-1422.
[10] S. K. Green, J. Lee, H. J. Kim, G. A. Tompsett, W. B. Kim, G. W. Huber,
Green Chem. 2013, 15, 1869-1879.
[11] Z. Li, S. Kelkar, L. Raycraft, M. Garedew, J. E. Jackson, D. J. Miller, C.
M. Saffron, Green Chem. 2014, 16, 844-852.
[12] L. Thia, M. Xie, Z. Liu, X. Ge, Y. Lu, W. E. Fong, X. Wang,
ChemCatChem 2016, DOI: 10.1002/cctc.201600725.
[13] H. Tan, O. E. Tall, Z. Liu, N. Wei, T. Yapici, T. Zhan, M. N. Hedhill, Y.
Han, ChemCatChem 2016, 8, 1699-1707.
[38] I. De A. Rodrigues, J. P. I. De Souza, E. Pastor, F. C. Nart, Langmuir
1997, 13, 6829-6835.
[39] Q. Ding, W. Xu, P. Sang, J. Xu, L. Zhao, X. He, W. Guo, Appl. Surf. Sci.
2016, 369, 257-266.
[14] H. J. Kim, J. Lee, S. K. Green, G. W. Huber, W. B. Kim, ChemSusChem
2014, 7, 1051-1054.
[40] Q. Jiang, L. Jiang, H. Hou, J. Qi, S. Wang, G. Sun, J. Phys. Chem. C
2010, 114, 19714-19722.
[15] S. Lee, H. J. Kim, E. J. Lim, Y. Kim, Y. Noh, G. W. Huber, W. B. Kim,
Green Chem. 2016, 18, 2877-2887.
[41] J. A. Dumesic, D. F. Rudd, L. M. Aparicio, J. E. Rekoske, A. A. Treviño,
The Microkinetics of Heterogeneous Catalysis, Am. Chem. Soc.
Washington, DC, 1993.
[16] Y. Kwon, K. J. P. Schouten, M. T. M. Koper, ChemCatChem 2011, 3,
1176-1185
[42] T. Bligaard, J. K. Nørskov, S. Dahl, J. Matthiesen, C. H. Christensen, J.
Sehested, J. Catal. 2004, 224, 206-217.
[17] H. J. Kim, S. M. Choi, S. Green, G. A. Tompsett, S. H. Lee, G. W. Huber,
W. B. Kim, Appl. Catal. B-Environ. 2011, 101, 366-375.
[18] H. J. Kim, S. M. Choi, M. H. Seo, S. Green, G. W. Huber, W. B. Kim,
Electrochem. Commun. 2011, 13, 890-893.
[43] B. Ravel, M. Newville, J. Synchrotron Rad. 2005, 12, 537-541.
[44] G. Kresse, J. Furthmuller, Phys. Rev. B 1996, 54, 11169-11186.
[45] G. Kresse, D. Joubert, Phys. Rev. B 1999, 59, 1758-1775.
[46] J. Klimes, D. R. Bowler, A. Michaelides, J. Phys.: Condens. Matter 2010,
22, 022201-022205.
[19] S. Lee, H J. Kim, S. M. Choi, M. H. Seo, W. B. Kim, Appl. Catal. A-Gen.
2012, 429– 430, 39-47.
[20] M. Simoes, S. Baranton, C. Coutanceau, Appl. Catal. B-Environ. 2010,
93, 354-362.
[47] J. Klimes, D. R. Bowler, A. Michaelides, Phys. Rev. B 2011, 83, 195131-
195143.
[21] Y. Kim, H. Kim, W. B. Kim, Electrochem. Commun. 2014, 46, 36-39.
[22] J. Qi, N. Benipal, C. Liang, W. Li, Appl. Catal. B-Environ. 2016, 199, 494-
503.
[48] J. Baltrusaitis, M. Valter, A. Hellman, J. Phys. Chem. C 2016, 120, 1749-
1757.
[49] R. F. W. Bader, Acc. Chem. Res. 1985, 18, 9-15.
[50] G. Henkelman, A. Arnaldsson, H. Jonsson, Comput. Mater. Sci. 2006,
36, 354-360.
[23] Y. Qiu, J. Huo, F. Jia, B. H. Shanks, W. Li, J. Mater. Chem. A 2016, 4,
83-95.
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Entry for the Table of Contents
FULL PAPER
The promotional effects of Ru addition
to Pt/C catalysts for glycerol
Youngmin Kim, Hyun Woo Kim,
Seonhwa Lee, Jisu Han, Daewon Lee,
Jeong-Rang Kim, Tae-Wan Kim, Chul-
Ung Kim, Soon-Yong Jeong, Ho-Jeong
Chae, Beom-Sik Kim, Hyunju Chang,
Won Bae Kim, Sung Mook Choi,* and
Hyung Ju Kim*
electrooxidation in acid media were
investigated by reaction product
analysis and DFT calculations. The
glycerol molecules on the structurally
and electronically modified PtRu
surfaces can be efficiently oxidized by
controlling glycerol binding energy and
by breaking more C-C, C-H, and O-H
bonds.
Page No. – Page No.
Role of Ru on Carbon-supported
PtRu Catalysts for Electro-catalytic
Glycerol Oxidation in Acidic
Condition
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