Journal of the American Chemical Society
Communication
The ultrafine PtIr alloy NWs were synthesized by a colloidal-
chemical approach, using platinum(II) acetylacetonate (Pt-
and Ir (PDF #06-0598) (Figure 1f). An atomistic observation
of randomly selected PtIr NWs (Figure 1g) demonstrates their
polycrystalline nature with abundant atomic steps and grain
boundaries. Besides, smaller-diameter NWs tend to be
defective/disordered. The corresponding energy-dispersive
spectroscopy (EDS) discloses the existence of element Pt and
Ir (Figure 1h).
To illustrate the growth mechanism and critical factors
during the formation process of ultrafine nanowires, a series of
products with various experimental conditions were inves-
tigated. The results revealed that PtIr nanoparticles were
formed at the initial stage. Then, the nanoparticle grew into
nanowires along the 1D direction and grew gradually with time
(
acac) ) and iridium(III) 2,4-pentanedionate (Ir(acac) ) as
2
3
metal precursors, CO in situ released from molybdenum
41
hexacarbonyl (Mo(CO) ) and (1-hexadecyl) trimethylammo-
6
nium bromide (CTAB) as structural directing agents, and
oleylamine as a reducing agent. The as-synthesized product
presents ultrafine 1D morphology with a diameter of 1.0 nm
(
Figure S3). During the synthetic process, the content of Ir in
at 5 h (Figure S4). Notably, there were no obvious changes in
the morphology and composition of PtIr nanowires with the
further extension of reaction time. In addition, when the
surfactant and reducing agent were replaced by (1-hexadecyl)
trimethylammonium chloride (CTAC) and tungsten carbonyl
(
6
synthesis was conducted without surfactant addition or using
reveal that the formation of PtIr nanowires is highly dependent
on the use of carbonyl salts and surfactants and mainly follows
the oriented attachment mechanism. As a comparison, Pt
nanowires were synthesized by a standard step without
introducing an Ir precursor (Figure S9).
The electrocatalytic properties of ultrafine PtIr nanowires
toward EOR and HER were assessed. Before the electro-
chemical tests, the catalysts were prepared by depositing the
nanowires onto the commercial carbon supports (Ketjen
Black-300J) and subsequently were washed with acetic acid to
nanowires (Figure S10). The resulting carbon supported
nanocrystal catalysts were denoted as PtIr NWs/C and Pt
NWs/C, respectively. To assess the EOR activity, all the
catalysts were first pretreated by applying the consecutive
cyclic potential cycles at a sweep rate of 500 mV s− until the
cyclic voltammograms (CVs) became stable. We found that
PtIr NWs/C exhibits excellent electrocatalytic performance for
NWs with various Pt−Ir atomic ratios (Pt68Ir32 NWs, Pt78Ir22
Figure 1. Morphology and structure characterization of PtIr NWs. (a)
Transmission electron microscopy (TEM) image, (b) scanning TEM
(
STEM) image and its corresponding STEM-energy-dispersive
spectroscopy (EDS) elemental mappings, (c and d) X-ray photo-
electron spectroscopy (XPS) spectra, (e) high-angle annular dark-field
scanning transmission electron microscopy (HAADF-STEM) image,
(f) power X-ray diffraction (PXRD) pattern, (g) HAADF-STEM
image, and (h) EDS pattern of PtIr NWs. Note that the Fourier
transform (FFT) images (e1 and e ) were taken from the
2
corresponding two dashed squares (areas e and e ) in e, and (e )
1
2
3
1
integrated pixel intensity of crystal phase was taken from the cyan
solid rectangle in e.
high-angle annular dark-field scanning transmission electron
microscopy (HAADF-STEM) element mappings confirm the
(
Figure 1b and Figure S2). The high-resolution X-ray
NWs, and Pt91Ir NWs) were synthesized (Figure S14). The
9
photoelectron spectroscopy (XPS) of Pt 4f and Ir 4f show
the binding energies of 75.1 and 71.8 eV, assigned to the
electrocatalytic tests revealed that Pt68Ir32 NWs/C exhibited
32−36
metallic Pt 4f5/2 and Pt 4f7/2 (Figure 1c),
energies of 64.5 and 61.5 eV, assigned to the metallic Ir 4f
and the binding
and Pt91Ir
9
SO ethanol electrolyte, the
4
In N -saturated 0.5 M H
5
/2
2
2
37−40
and Ir 4f7/2 (Figure 1d).
Furthermore, the atomic ratio of
optimal PtIr NWs/C shows the lowest onset potential with the
Pt/Ir was estimated to be 2.1:1 by XPS.
order of PtIr NWs/C < Pt NWs/C ≈ Pt/C (Figure 2a,b).
−
2
The crystal phase of the PtIr NWs was identified from the
atomic stacking sequence and the corresponding fast Fourier
transform (FFT) pattern. The FFT patterns, taken from
regions e and e , marked as white dashed squares in Figure
When the current density reaches 30 mA cm , the potential
for EOR of the PtIr NWs decreases by 480 and 470 mV
relative to those of commercial Pt/C and Pt NWs, respectively.
1
2
−
1
1
e ,e , show that the PtIr nanowires have fcc phase with two
mV dec in all the investigated catalysts (Figure S16a),
indicating the accelerated EOR kinetics on the ultrathin PtIr
NWs/C structure. In light of the noble metals, such as Pt and
Ir, applied for this catalytic system, we normalized the mass
activities at 0.3 V vs saturated calomel electrode (SCE) on the
basis of the mass of noble metal determined by inductively
1
2
typical characteristic diffraction patterns of [011] and [001]
zones, and the average lattice spacing of PtIr (200) facets on
one random PtIr NW is 0.18 nm (Figure 1e ). The powder X-
ray diffraction (PXRD) pattern of PtIr nanowires shows that
the diffraction peaks locate those between Pt (PDF #04-0802)
3
1
0823
J. Am. Chem. Soc. 2021, 143, 10822−10827