Surface Segregation of Fe in Pt–Fe Alloy Nanoparticles: Its Precedence and Effect on the Ordered‐Phase Evolution during Thermal Annealing

Prabhudev, Sagar; Bugnet, Matthieu; Zhu, Guo‐zhen; Bock, Christina; Botton, Gianluigi A.

doi:10.1002/cctc.201500380

Cited by 27 publications

(17 citation statements)

References 58 publications

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“…3 (a) where such contrast extends out 0.6 nm or more. Most likely this is Fe-rich material as reported by Prabhudev et al [22]. The possibility that the Fe is oxidized cannot be excluded.…”

Section: Annealing At 500°csupporting

confidence: 51%

In situ investigation of ordering phase transformations in FePt magnetic nanoparticles

2017

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In situ high-resolution electron microscopy was used to reveal information at the atomic level for the disordered-to-ordered phase transformation of equiatomic FePt nanoparticles that can exhibit outstanding magnetic properties after transforming from disordered face-centered-cubic into the tetragonal L1 ordered structure. High-angle annular dark-field imaging in the scanning transmission electron microscope provided sufficient contrast between the Fe and Pt atoms to readily monitor the ordering of the atoms during in situ heating experiments. However, during continuous high-magnification imaging the electron beam influenced the kinetics of the transformation so annealing had to be performed with the electron beam blanked. At 500°C where the reaction rate was relatively slow, observation of the transformation mechanisms using this sequential imaging protocol revealed that ordering proceeded from (002) surface facets but was incomplete and multiple-domain particles were formed that contained anti-phase domain boundaries and anti-site defects. At 600 and 700°C, the limitations of sequential imaging were revealed as a consequence of increased transformation kinetics. Annealing for only 5min at 700°C produced complete single-domain L1 order; such single-domain particles were more spherical in shape with (002) facets. The in situ experiments also provided information concerning nanoparticle sintering, coalescence, and consolidation. Although there was resistance to complete sintering due to the crystallography of L1 order, the driving force from the large surface-area-to-volume ratio resulted in considerable nanoparticle coalescence, which would render such FePt nanoparticles unsuitable for use as magnetic recording media. Comparison of the in situ data acquired using the protocol described above with parallel ex situ annealing experiments showed that identical behavior resulted in all cases.

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“…3 (a) where such contrast extends out 0.6 nm or more. Most likely this is Fe-rich material as reported by Prabhudev et al [22]. The possibility that the Fe is oxidized cannot be excluded.…”

Section: Annealing At 500°csupporting

confidence: 51%

In situ investigation of ordering phase transformations in FePt magnetic nanoparticles

2017

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“…[65] By controlling the H 2 reduction temperature and time, core-shell structured Pt-Pt 3 Co nanoparticles with 2-3 atomic-layer Pt shells (Pt 3 Co@Pt) could be obtained, [66] even Pt-skin on Pt 3 Co (or Pt 3 Ni) bimetallic materials. [69][70][71] Pt has negative segregation energy, and Ni (or Co) has positive segregation energy; hence, Pt tends toward surface segregation. [68] The precursor mixtures (containing Pt precursor and Ni precursor) usually are dispersed into solvents, and then these mixtures are ultrasonicated before the solvents evaporate.…”

Section: Chemical Methodsmentioning

confidence: 99%

“…Finally, by controlling the thermal treatment, Pt‐skin on well‐dispersed Pt 3 Ni bimetallic nanoparticles can be obtained. The reason why CTTM could tune the surface composition is that there is a general trend in the surface segregation phenomena in the bimetallic nanomaterials . Pt has negative segregation energy, and Ni (or Co) has positive segregation energy; hence, Pt tends toward surface segregation .…”

Section: Controlling the Surface Composition Of Ptm Bimetallicsmentioning

confidence: 99%

A Comprehensive Review on Controlling Surface Composition of Pt‐Based Bimetallic Electrocatalysts

Zhang

Yang

Wang

et al. 2018

Advanced Energy Materials

133

104

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version efficiency. [12][13][14][15] Among these metal electrocatalysts, platinum (Pt) exhibits the best activity for formic acid electrooxidation, ethanol electrooxidation, and oxygen reduction. However, pure Pt electrocatalyst faces several severe shortages, which limit its wide application in fuel cells. First, for formic acid and ethanol electrooxidation on pure Pt, the poisoning phenomenon (poison intermediates adsorption) usually happens on the surface of Pt, which will significantly decrease its electrocatalytic performance. [16][17][18][19][20] Second, for cathodic reaction, the oxygen reduction on pure Pt is sluggish. [21][22][23][24] Third, Pt is noble metal, which is limited reserve in nature. Therefore, how to reduce the Pt content and at the same time maintain its electrochemical performance are critical to achieve the commercialization of fuel cell.Bimetallic nanomaterials play an essential role in electrochemical energy conversion and storage, such as in fuel cells and metal-air batteries. [25][26][27] Unlike their monometallic counterparts, bimetallic nanomaterials ordinarily present better performance beneficial from synergistic effects, which means that the electrochemical performance of the whole will be superior than the sum of its parts. [28][29][30] In the case of the noble metals (especially Pt), their high cost and scarcity are obstructing the commercial viability of fuel cells. [31][32][33][34] Reducing the Pt loading without compromising its performance is the target of electrocatalytic investigations. [35][36][37] The typical approach is to incorporate with another metal, which could obtain better performance with much prolonged duration than the traditional commercial Pt/C. There are a great quantity of works on Ptbased bimetallic electrocatalysts, such as alloying Pt with 3d-transition metals, including Fe, [38,39] Co, [40][41][42] Ni, [43,44] and Cu. [45,46] PtM (M = Fe, Co, Ni, etc.) bimetallic nanomaterials have been demonstrated to be promising electrocatalysts, which strategic enhancement and development of the performance of commercial Pt/C electrocatalyst; and fundamental researches have shown that the enhanced catalytic activity originates from the modified electronic structures and geometric structures of Pt in these alloy catalysts. [47][48][49] It is a remarkable fact that these electrocatalytic reactions merely occur on the surface of the electrocatalysts. [28,50] Thus, the surface constituents of electrocatalysts determine the adsorption/desorption behaviors of the reactants and intermediates during the electrochemical reaction. Therefore, the catalytic reactions mechanisms and efficiencies strongly rely on the With increasing energy demands worldwide, significant efforts have been made to develop superior electrocatalysts for efficient energy conversion systems. Among all the electrocatalysts exploited, Pt-based bimetallic nanomaterials stand out by virtue of their high catalytic activity and relatively low cost due to the introduction of a nonprecious metal component. I...

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“…With high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and EELS, we have studied the evolution of alloy catalysts following in-situ and ex-situ annealing procedures. Starting with a disordered PtFe nanoparticle, we captured the ordering transformation, showing evidence of ordered Pt and Fe rich planes formation, and evidence of both Pt and Fe-rich shells over a Pt-Fe ordered core ( Figure 1) [2]. We also showed that the Pt surface segregation induces local strain and atomic displacements [2] ( Figure 2) that can be further correlated to the enhanced catalytic activity of the material, in addition to the enhanced durability shown previously [3,4].…”

mentioning

confidence: 99%

“…Starting with a disordered PtFe nanoparticle, we captured the ordering transformation, showing evidence of ordered Pt and Fe rich planes formation, and evidence of both Pt and Fe-rich shells over a Pt-Fe ordered core ( Figure 1) [2]. We also showed that the Pt surface segregation induces local strain and atomic displacements [2] ( Figure 2) that can be further correlated to the enhanced catalytic activity of the material, in addition to the enhanced durability shown previously [3,4]. Using in-situ heating, and taking advantage of fast acquisition capabilities with EELS, it has also been possible to study the alloying phenomena of AuPt nanoparticles showing evidence of full miscibility starting at 200ºC (Figure 3), well below the thermodynamically expected temperature, due to the reduced scale of the system.…”

mentioning

confidence: 99%

Microscopy and Spectroscopy of Catalysts and Energy Storage Materials

et al. 2016

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Electron microscopy has always played an important role in the development and the understanding of new materials. In the last ten years there have been significant advancements in instrumentation, enabling improved studies of materials at the nanoscale. In the area of catalysts and energy storage materials, detailed microscopy of material structure, composition and bonding at the nanometer length scale are needed to optimize material properties and performance. Here we summarize recent examples of work related to the study of nano-alloy catalysts used in proton exchange membrane fuel cells and commercial Li ion battery materials, illustrating the crucial role of imaging and spectroscopy for the characterization of these materials.

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Surface Segregation of Fe in Pt–Fe Alloy Nanoparticles: Its Precedence and Effect on the Ordered‐Phase Evolution during Thermal Annealing

Cited by 27 publications

References 58 publications

In situ investigation of ordering phase transformations in FePt magnetic nanoparticles

In situ investigation of ordering phase transformations in FePt magnetic nanoparticles

A Comprehensive Review on Controlling Surface Composition of Pt‐Based Bimetallic Electrocatalysts

Microscopy and Spectroscopy of Catalysts and Energy Storage Materials

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