Chen et al.
Enhanced FAEO on PdIr Nanoparticles Prepared by Ethylene Glycol-Assisted NaBH4 Reduction Process
The Pd/C and Pd–Ir/C (20 wt.% of metals loading; the
mass ratio of Pd to Ir was 7:1, 5:1 and 3:1, respectively)
catalysts were synthesized by the following route. The
40 mg of pretreated carbon black and appropriate PdCl2
and H2IrCl6 aqueous solution were dispersed in 20 ml EG
with sonication for 30 min, and then stirred for 2 hours.
A freshly prepared NaBH4 in EG solution (the molar ratio
of NaBH4 to metal was 125:1) was added dropwise into
ꢀ
the above solution at 20 C and the resulting suspension
was stirred for 3 hours. The mixtureꢀwas filtered, washed,
and dried in a vacuum oven at 75 C for 10 hours. The
prepared PdIr/C catalysts with Pd:Ir mass ratio of 7:1, 5:1
and 3:1 were designated as PdIr/C-7, PdIr/C-5, PdIr/C-3,
respectively.
Fig. 1. XRD patterns of the (a) Pd/C, (b) PdIr/C-7, (c) PdIr/C-5 and
(d) PdIr/C-3 catalysts.
respectively. For all PdIr/C catalysts the diffraction signals
are slightly shifted toward smaller 2 theta values compared
to the Pd/C sample, indicating that Ir atoms entered into Pd
lattice and substituted Pd atoms forming PdIr solid solu-
tion. In addition, no peak related to IrO2 and Ir phases,
which indicated the absence of metallic Ir and the presence
of unalloyed Ir most probably in amorphous oxides states.
Figure 2 shows TEM images of the prepared PdIr/C-5
catalysts and its corresponding particle size distribution
histograms. The 20–30 nm spherical particles are carbon
blacks and the dark dots are PdIr-NPs supported on the
2.2. Characterization of the Catalysts
The X-ray diffraction (XRD) analyses were carried out on
a DX-2000 X-ray diffractometer (DX-2000, Dandong Ltd.,
China). TEM images were obtained using a FEI, TECNAI
G2 microscope (USA).
All electrochemical measurements were carried out in a
conventional three-electrode electrochemical cell at 25 C
using LSV and CV techniques on a CHI 760B. The
counter electrode was a graphite electrode and the refer-
ence electrode was a saturated calomel electrode (SCE).
ꢀ
All potentials reported in this paper were referred to the
Delivered by Publishing Technolcoagrbyotno:bMlaccMksa.sItterisUonbivseerrvseitdy from Figure 2(a) that the
SCE. A glassy-carbon working electrode (ꢁ3, surface area
IP: 190.90.44.40 On: Mon, 14 Mar 2016 10:35:30
PdIr NPs of the PdIr/C-5 catalyst prepared by the EG-
2
Copyright: American Scientific Publishers
7.0 mm ꢀ was used as substrate. A 5.0 mg sample of the
prepared catalyst was dispersed in a solution containing
1.0 mL of deionized water, 1.0 mL of isopropanol, and
50 ꢂL of a 5 wt% Nafion solution using 30 min of ultra-
sonification to form a uniform suspension. A 5 ꢂL sample
of the dispersed catalyst suspension was pipetted onto the
glassy-carbon substrate. The calculated loading of metal
was 35 ꢂg cm−2. The LSV and CV were carried out in
0.5 mol L−1 HCOOH+0.5 mol L−1 H2SO4 solution deaer-
ated by ultra-pure argon for 20 min before measurements.
assisted NaBH4 reduction method are highly dispersed on
the carbon support. According to distribution histogram of
catalysts, the PdIr NPs have a mean size of 2.6 nm with a
narrow size distribution. These features are consistent with
the results of XRD analyses.
Figure 3 presents the cyclic voltammograms of 0.5 mol
L−1 H2SO4 solution at different catalyst electrodes. It can
be observed that the peaks of the adsorption/desorption of
hydrogen around 0 V are obvious at the Pd/C catalyst elec-
trode, while there are not observed on PdIr/C catalysts.
This result also indicates the formation of PdIr solid solu-
tion, as Ir has poor ability for the adsorption/desorption
of hydrogen. Moreover, the onset potential of the Pd oxi-
dation for all the Pd/C and PdIr/C catalysts are at around
3. RESULTS AND DISCUSSION
The crystalline structure of the prepared catalysts is con-
firmed by the XRD technique and the results are shown
in Figure 1. All diffraction patterns show the typical sig-
nals of the face centered cubic (fcc) structure of Pd (PDF
87-0643). And the ratio of the diffraction peak intensity
of metal to that of carbon indicates that the relative crys-
tallinity of PdIr nanoparticles (NPs) is higher than that of
Pd NPs. Moreover, the mean crystallite size can be cal-
culated using Scherrer’s equation.21ꢃ22 For that, the (220)
peak of the Pd fcc structure was used because the broad
carbon peak does not interfere in this region. Although,
the lower diffraction peak intensity of Pd/C catalyst makes
it look broader, the crystallite sizes of Pd/C, PdIr/C-7,
PdIr/C-5, PdIr/C-3 catalysts are 3.3, 2.8, 2.7 and 2.5 nm,
Fig. 2. TEM images of the PdIr/C-5 catalyst and the corresponding his-
togram of size distribution of the PdIr nanoparticles.
J. Nanosci. Nanotechnol. 13, 7008–7011, 2013
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