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A and B are HAADF-STEM micrographs of PtCu nanoparticles formed from using PtCl 4 and CuCl 2 (PtCu-Cl) as precursors and using PtBr 4 and CuBr 2 (PtCu-Br) as precursors, respectively. The red dashed boxes indicate the area in which the spectrum image was obtained. The EDS map of (A) is shown with (C) the HAADF-STEM signal, (D) the Cu Kα peak, (E) the Pt L peak, and (F) the overlap. The EDS map of (B) is shown with (G) the HAADF-STEM signal, (H) the Cu K peak, (I) the Pt L peak, and (J) the overlap. K and L are line profiles obtained from the white dashed box in C, D, and E and G, H, and I, respectively. The HAADF signal is in arbitrary units and is scaled to fit on the profile.
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The characteristics of bimetallic nanomaterials are dictated by their size, shape and elemental distribution. Solution synthesis is widely utilized to form nanomaterials, such as nanoparticles, with controlled size and shape. However, the effects of variables on the characteristics of bimetallic nanomaterials are not completely understood. In this...
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... particle edge length was determined by measuring along the {111} facet, and the composition was determined by energy dispersive X-ray spectroscopy (EDS). The PtNi alloy particles formed with Figure 1A and Supporting Information Figure S3). The particles formed with the chlorides with NiCl 2 ·6H 2 O and PtCl 2 were 6.2 ± 0.8 nm (∼Pt 40 Ni 60 ) nano-octahedra (Figure 1C and Supporting Information Table S1), and with NiCl 2 ·6H 2 O and PtCl 4 , the formed particles were 9 ± 1 nm (∼Pt 46 Ni 54 ) nano-octahedra (Figure 1 E). ...
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... understand the intensity differences in the HAADF- STEM images, the octahedra formed with PtCl 4 and CuCl 2 (PtCu-Cl) and with PtBr 4 and CuBr 2 (PtCu-Br) were investigated with STEM-EDS spectrum imaging. The elemental map of PtCu-Cl and PtCu-Br ( Figure 3A−L) shows platinum enrichment on the surface of the nanoparticle and copper enrichment in the center ( Figure 3C−J), which is in agreement with the HAADF-STEM images. From the intensity line profiles, it can be seen that the platinum surface enrichment occurs ∼2 nm before the nanoparticle edge in both of the samples ( Figure 3K,L). ...
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... understand the intensity differences in the HAADF- STEM images, the octahedra formed with PtCl 4 and CuCl 2 (PtCu-Cl) and with PtBr 4 and CuBr 2 (PtCu-Br) were investigated with STEM-EDS spectrum imaging. The elemental map of PtCu-Cl and PtCu-Br ( Figure 3A−L) shows platinum enrichment on the surface of the nanoparticle and copper enrichment in the center ( Figure 3C−J), which is in agreement with the HAADF-STEM images. From the intensity line profiles, it can be seen that the platinum surface enrichment occurs ∼2 nm before the nanoparticle edge in both of the samples ( Figure 3K,L). ...
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... elemental map of PtCu-Cl and PtCu-Br ( Figure 3A−L) shows platinum enrichment on the surface of the nanoparticle and copper enrichment in the center ( Figure 3C−J), which is in agreement with the HAADF-STEM images. From the intensity line profiles, it can be seen that the platinum surface enrichment occurs ∼2 nm before the nanoparticle edge in both of the samples ( Figure 3K,L). For PtCu-Br, the platinum intensity also shows an increase at the surface ( Figure 3L). ...
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... the intensity line profiles, it can be seen that the platinum surface enrichment occurs ∼2 nm before the nanoparticle edge in both of the samples ( Figure 3K,L). For PtCu-Br, the platinum intensity also shows an increase at the surface ( Figure 3L). The platinum-rich shell can be seen at all orientations (Supporting Information Figure S6). ...
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Citations
... A few researchers have reported that the choice of organic ligands (e.g., acetylacetonate) has a significant impact on the catalyst when used as a metal complex in thermal decomposition synthesis [32][33][34][35]. This led us to speculate that the carbon source for the carbon shell originates from the precursor ligand. ...
Proton exchange membrane fuel cells (PEMFCs) face technical issues of performance degradation due to catalyst dissolution and agglomeration in real-world operations. To address these challenges, intensive research has been recently conducted to introduce additional structural units on the catalyst surface. Among various concepts for surface modification, carbon shell encapsulation is known to be a promising strategy since the carbon shell can act as a protective layer for metal nanoparticles. As an interesting approach to form carbon shells on catalyst surfaces, the precursor ligand-induced formation is preferred due to its facile synthesis and tunable control over the carbon shell porosity. However, the origin of the carbon source and the carbon shell formation mechanism have not been studied in depth yet. Herein, this study aims to investigate carbon sources through the use of different precursors and the introduction of new methodologies related to the ligand exchange phenomenon. Subsequently, we provide new insights into the carbon shell formation mechanism using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Finally, the thermal stability and electrochemical durability of carbon shells are thoroughly investigated through in situ transmission electron microscopy (in situ TEM) and accelerated durability tests.
... Unfortunately, X-ray powder diffraction (XRD) fails to provide any information on the nature of the metals' distribution in twocomponent NPs. Moreover, the calculation of the crystallite size according to the Scherrer formula, undertaken using the half-width of the characteristic reflection in the X-ray diffraction pattern, may provide incorrect results for NPs with a core-shell architecture, which is due to the complexity in separating the phase reflections based on platinum and nickel d-metal [44][45][46]. ...
Within this research, we studied the structural–morphological and electrochemical characteristics of the PtNi/C catalysts synthesized via the two-stage sequential reduction of precursors. We also carried out a comparative study of the obtained bimetallic catalysts and their commercial Pt/C analog. The use of triethylamine as a surfactant as well as the acid treatment as an additional synthesis stage, were shown to have a positive effect on the functional parameters of the bimetallic electrocatalysts. The resulting PtNi/C electrocatalyst demonstrates a mass activity value of 389 A gPt−1, which is 1.6 times higher than this parameter for a commercial analog.
... It is well known from the literature that the nanoparticle shapes can be efficiently controlled by varying the ratios of ligand to metal precursor [50], the ligands [81,82], and the metal salts [83,84]. In this respect, the morphologies of PtNPs can be controlled by stabilizing agents. ...
Here, the controlled formation of platinum nanoparticles (PtNPs) and silver nanoparticles (AgNPs) using amine-functionalized multivalent ligands are reported. The effects of reaction temperature and ligand multivalency on the growth kinetics, size, and shape of PtNPs and AgNPs were systematically studied by performing a stepwise and a one-step process. PtNPs and AgNPs were prepared in the presence of amine ligands using platinum (II) acetylacetonate and silver (I) acetylacetonate, respectively. The effects of ligands and temperature on the formation of PtNPs were studied using a transmission electron microscope (TEM). For the characterization of AgNPs, additionally, ultraviolet-visible (UV-Vis) absorption was employed. The TEM measurements revealed that PtNPs prepared at different temperatures (160–200 °C, in a stepwise process) are monodispersed and of spherical shape regardless of the ligand multivalency or reaction temperature. In the preparation of PtNPs by the one-step process, ligands affect the shape of the PtNPs, which can be explained by the affinity of the ligands. The TEM and UV-Vis absorption studies on the formation of AgNPs with mono-, di-, and trivalent ligands showed narrower size distributions, while increasing the temperature from 80 °C to 120 °C and with a trivalent ligand in a one-step process.
... W 0 can then be used as a reductant, rapidly reducing Pt 2+ to Pt 0 (atoms/ seeds). This leads to fast Pt nucleation (Zhang and Fang, 2009;LaGrow et al., 2015). However, W 0 does not alloy with Pt 0 under the reaction conditions and thus remains as an ionic species (W n+ or W 6+ ) in the organic synthesis mixture (Zhang and Fang, 2009), but facilitates growth of the nanoparticles (Zhang et al., 2010). ...
SYNOPSIS Optimizing the catalytic performance of multimetallic nanoparticle (NP) catalysts demands a concrete understanding of their design, while preferentially deploying wet chemical synthesis procedures to precisely control surface structural properties. Here we report the influence of reductants such as hydrogen-rich tetrabutylammonium borohydride (TBAB) and carbon monoxide-rich molybdenum carbonyl (Mo(CO)6) on the shape and morphological evolution of Pt-based binary (PtNi and PtCo) and ternary (PtNiAu and PtCoAu) nanostructures derived from a homogeneous solution of amine-based surface active agents (surfactants) in a high boiling point solvent. We successfully synthesized nanostructures exhibiting well-defined and composition-controlled surfaces deploying a one-pot synthetic approach. The development of the surface properties was, however, observed to be alloy-specific. The resultant highly monodisperse alloy NP with narrow size distributions and facet-oriented surfaces are expected to display enhanced functionality as catalysts for utilization in specific chemical reactions. Keywords: catalyst. platinum alloy, nanoparticles, synthesis, mixed-metal nanostructure.
... shape-directing agents such as CTAB, 38 CTAC, 39 I -, 40 and CO gas. 41 The effect of different precursor-ligand couples has been investigated 41 and ternary CuPtM (M=Pd and Ni) has been synthesized as well. 42,43 Here, we report a highly efficient strategy for a one-pot synthesis of well-defined PtCu octahedral nanocrystals dispersed on carbon in which the size is tunable. ...
... The XRD results are in agreement with the EDX results and suggest the interplay between particle size, and the number of Pt layers on the surface in our case study. Comparable asymmetry has been described for dealloyed PtCu 3 films by Yang et al. 11 and for octahedral MPt (M = Cu or Ni) by LaGrow et al. 41 We performed precisely the same reaction but, in the absence of CTAB. The PtCu octahedral NPs could not be formed and only spherical NPs with the smallest particle size of 4.6 ± 0.6 nm and a pure Pt composition according to the EDX results ( Figure 4). ...
The synthetic control through colloidal synthesis led to a remarkable increase in platinum mass activity in octahedral nanocrystals with Pt-rich surface. In this manuscript, we demonstrate that the ratio of surfactant can tune the size of Pt surface enriched PtCu nano-octahedra from 8 to 18 nm with homogeneous size and shape on carbon support. For the nano-octahedra, the Pt-rich surface has been determined by high-angle annular dark field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. The Pt-rich surface exhibits an increasing compressive strain with increasing surface of the {111} facets. With increasing surface, the PtCu nano-octahedra display higher oxygen reduction reaction (ORR) activity but, leads to higher onset over-potentials in methanol oxidation reaction (MOR) and CO-stripping. This observed trends for a series of size-selected nano-octahedra demonstrates the benefits of controlling the strained {111} Pt surface for the ORR and MOR activity.
... The decomposition kinetics is greatly affected by the binding strength between the cation and the anion within the specific reaction mixture. 33,38 Therefore, we changed the types of the Fe(acac) 3 precursor to FeCl 3 , Fe(acac) 2 , and Fe(OAc) 2 to investigate the correlation between the decomposition kinetics of precursors and the morphology of synthesized nanoparticles, as shown in Figure S10. Although the average size of nanoparticles is varied because the anion complex of Fe precursors could affect the formation kinetics of Cu 29 S 16 , the sandwich-like structural morphology was still found. ...
Structurally well-defined heteronanoparticles have received a great attention because their distinct structural features can be altered to achieve unprecedented properties. The cation exchange reaction, one of the most powerful techniques to synthesize heteronanoparticles, can tune the regiospecific composition of nanoparticles, while maintaining the overall morphology of the template. Herein, we demonstrate that the nascent interface between the cation-exchanged region and the unchanged template can induce a significant tensile or compressive strain on the lattice of the template so that the cation exchange process at the interface can be greatly facilitated. The fate of the overall cation exchange reaction can be dictated by placing the initial cation exchange sites on the template regioselectively. Via a careful kinetic and thermodynamic control of the cation exchange, we could prepare two completely different nanostructures of Cu5FeS4/Cu2-xS/Cu5FeS4 nanosandwich and Cu5FeS4/Cu2-xS Janus nanoparticle. The synthetic concept described in this study could be further extended to the synthesis of various rationally de-signed multiphasic nanoparticles with exciting physicochemical properties.
... Size differences of the obtained NPs from these two sources could be due to the difference in selenium oxidation. This is also in agreement with the findings of LaGrow et al. who demonstrated that the precursor oxidation state affects the nanoparticles size [24]. Given the equal amount of salt and other test conditions, it appeared that the number of nuclei initially formed at S 1 was greater than S 2 . ...
Selenium sulfide is a well-known bioactive chemical whose biosynthesis as a nanoparticle (NP) is a controversial issue. In the present study, we employed Saccharomyces cerevisiae to generate a novel synthetic process of selenium sulfide NPs. The addition of selenium/sulfur precursors to S. cerevisiae culture produced NPs, which we isolated and characterized the physicochemical properties, toxicity, and antifungal activity. Transmission electron microscopy indicated the presence of the NPs inside the cells. Selenium sulfide NPs were successfully synthesized with average size of 6.0 and 153 nm with scanning electron micrographs and 360 and 289 nm in Zeta sizer using different precursors. The presence of sulfur/selenium in the particles was confirmed by energy-dispersive X-ray spectroscopy and elemental mapping. Fourier-transform infrared spectroscopy supported the production of selenium sulfide NPs. X-ray diffractograms showed the presence of characteristic peaks of selenium sulfide NPs which were further confirmed by mass spectrometry. The obtained NPs strongly inhibited the growth of pathogenic fungi that belonged to the genera Aspergillus, Candida, Alternaria and the dermatophytes, while no cytotoxicity was observed in MTT assay. In conclusion, efficient green synthesis of selenium sulfide NPs with appropriate physicochemical properties is possible in bio-systems like S. cerevisiae.
... Furthermore, the peaks were shifted to a high angle with the increasing Cu content because of the incorporation of Cu atoms into the Pt fcc lattice. 14,42,43 The alloy structure is further confirmed by the EDX line scanning (Fig. 2B) and elemental analysis mapping (Fig. 2C-F). Fig. 2B-F displayed the line-scan EDX spectra and elemental analysis mapping of the as-synthesized Pt 34.5 Cu 65.5 octahedra. ...
... The enhancement of catalytic performance of the octahedral Pt 34.5 Cu 65.5 nanoalloys may be ascribed to the ensemble effect including the octahedral shape effect that exhibits eight {111} facets, twelve edges and six corners, composition effect that resulted in a synergic effect between Pt and Cu atoms and the downshift of the d-band center of Pt (Fig. 3A). 24,[42][43][44][45][46]49 Impressively, our Pt 34.5 Cu 65.5 octahedron had a competitively high mass activity achieved in an acid medium in comparison with previously reported PtCu nanocrystals (Tables S2 and S3, ESI †). The stability of the Pt 34.5 Cu 65.5 octahedron toward MOR was tested using current-time curves recorded at 0.6 V for 3600 s (Fig. 5A), and the current density on Pt 34.5 Cu 65.5 octahedra is much larger than those on Pt cubes and commercial Pt black over the entire time. ...
Synergetic effect between Pt and cheap metal, downshift of the d-band center of Pt and the shape can boost the catalytic performance of Pt-based nanocrystals. Therefore, tailoring the shape and composition within the nanoscale is the key to designing robust electrocatalyst in electrochemical energy conversion. Here, Cu-rich PtCu octahedral alloys achieved by composition-driven shape evolution route have been used as outstanding bifunctional electrocatalysts for both methanol oxidation (MOR) and oxygen reduction reaction (ORR) in acid medium. When benchmarks against commercial Pt black or Pt/C, for MOR, the specific activity/mass activity on Pt34.5Cu65.5 octahedrons is 4.74/7.53 times higher than that on commercial Pt black; for ORR, the specific activity/ mass activity on Pt34.5Cu65.5 octahedrons is 7.7/4.2 times higher than that on commercial Pt/C. After current-time test for 3600s, the remaining mass activity on Pt34.5Cu65.5 octahedrons is 35.5 times higher than that on commercial Pt black for MOR. And undergoing 5000 cycles for ORR, the remaining mass activity on Pt34.5Cu65.5 octahedrons is 4.2 times higher than that on commercial Pt/C.
... The nanoparticles were grown continuously via a millifluidic reaction system [24][25] run with toluene as the solvent, oleylamine as the surfactant and metal carbonyls supplying carbon monoxide (CO) as the reducing agent. 9,[26][27][28] The metal carbonyls were observed to control the proportion of the crystal structures in the nanoparticles formed, and the morphology of the particles with W(CO) 6 , or Re 2 (CO) 10 as the reducing agent formed branched or faceted nanoparticles respectively. Without the carbonyl spherical Ru nanoparticles were formed. ...
... [40][41] The increased size of the particles using a chloride precursor instead of an acetylacetonate has been reported previously with platinum alloys. 27 The particles 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 19 formed without the carbonyl are generally spherical, lacking a distinct shape, which is indicative of only having a single surfactant in solution which is not interacting strongly with any particular surface facet of the particles. The work with metal carbonyls demonstrated that the carbonyl had a distinct effect on the particle size, and the occurrence of the branched particles. ...
Several systems have shown the ability to stabilize uncommon crystal structures during the synthesis of metallic nanoparticles. By tailoring the nanoparticle crystal structure, the physical and chemical properties of the particles can also be controlled. Herein, we first synthesized branched nanoparticles of mixed hcp/fcc ruthenium, which were formed using tungsten carbonyl [W(CO)6] as both a reducing agent and a source of carbon monoxide. The branched particles were formed from multiple particulates off a central core. High-resolution transmission electron microscopy (HRTEM) clearly showed that the branched structures consisted of aligned hcp crystal domains, a mixture of fcc and hcp crystal domains with several defects and misalignments, and particles that contained multiple cores and branches. Branched particles were also formed with molybdenum carbonyl [Mo(CO)6], and faceted particles of hcp and fcc particles were formed with Re2(CO)10 as a carbon monoxide source. Without metal carbonyls, small particles of spherical hcp ruthenium were produced, and their size could be controlled by the selection of the precursor. The ruthenium nanoparticles were tested for ammonia borane hydrolysis; the branched nanoparticles were more reactive for catalytic hydrogen evolution than the faceted hcp/fcc nanoparticles or the spherical hcp nanoparticles. This work showcases the potential of crystal phase engineering of transition metal nanoparticles by different carbon monoxide precursors for tailoring their catalytic reactivity.
... This framework structural feature has originated from the sequential decomposition of Ni precursor, followed by decomposition of Pt precursor. The reduction potential of Pt is higher than that of Ni, however, the Cl − ion from the CTAC might form the [PtCl 4 ] 2− complex and impede the reduction kinetics of Pt. 40 This inverse reduction sequence makes it possible to synthesize an ultrathin PtNi nanoframework. Similarly, PC@PCN nanocrystals could be observed in the presence of 0.5 equiv of Cu precursor (Figure 4e) due to the sequential decomposition of Cu and Pt, followed by Ni with residual Cu and Pt. ...
