Co–Pt and Co–Au core–shell nanoparticles were heated by molecular dynamics simulations to investigate their thermal stability. Two core structures, that is, hcp Co and fcc Co, have been addressed. The results demonstrate that the hcp–fcc phase transition happens in the hcp-Co-core/fcc-Pt-shell nanoparticle, while it is absent in the hcp-Co-core/fcc-Au-shell one. The stacking faults appear in both Pt and Au shells despite different structures of the Co core. The Co core and Pt shell concurrently melt and present an identical melting point in both Co–Pt core–shell nanoparticles. However, typical two-stage melting occurs in both Co–Au core–shell nanoparticles. Furthermore, the Au shell in the hcp-Co-core/fcc-Au-shell nanoparticle exhibits a lower melting point than that in the fcc-Co-core/fcc-Au-shell one, while the melting points are closely equal for both hcp and fcc Co cores. All of these observations suggest that their thermal stability strongly depends on the structure of the core and the element of the shell.

Pt–Co bimetallic nanoparticles are promising candidates for Pt-based nanocatalysts and magnetic-storage materials. By using molecular dynamics simulations, we here present a detailed examination on the thermal stabilities of Pt–Co bimetallic nanoparticles with three configurations including chemically disordered alloy, ordered intermetallics, and core–shell structures. It has been revealed that ordered intermetallic nanoparticles possess better structural and thermal stability than disordered alloyed ones for both Pt3Co and PtCo systems, and Pt3Co–Pt core–shell nanoparticles exhibit the highest melting points and the best thermal stability among Pt–Co bimetallic nanoparticles, although their meltings all initiate at the surface and evolve inward with increasing temperatures. In contrast, Co–Pt core–shell nanoparticles display the worst thermal stability compared with the aforementioned nanoparticles. Furthermore, their melting initiates in the core and extends outward surface, showing a typical two-stage melting mode. The solid–solid phase transition is discovered in Co core before its melting. This work demonstrates the importance of composition distribution to tuning the properties of binary nanoparticles.Keywords: alloy; core−shell structure; metallic nanoparticle; molecular dynamics; thermal stability;

Atomic-scale understanding of structures and thermodynamic stability of core–shell nanoparticles is important for both their synthesis and application. In this study, we systematically investigated the structural stability and thermodynamic evolution of core–shell structured Pd–Ni nanoparticles by molecular dynamics simulations. It has been revealed that dislocations and stacking faults occur in the shell and their amounts are strongly dependent on the core/shell ratio. The presence of these defects lowers the structural and thermal stability of these nanoparticles, resulting in even lower melting points than both Pd and Ni monometallic nanoparticles. Furthermore, different melting behaviors have been disclosed in Pd-core/Ni-shell and Ni-core/Pd-shell nanoparticles. These diverse behaviors cause different relationships between the melting temperature and the amount of stacking faults. Our results display direct evidence for the tunable stability of bimetallic nanoparticles. This study provides a fundamental perspective on core–shell structured nanoparticles and has important implications for further tailoring their structural and thermodynamic stability by core/shell ratio or composition controlling.

Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt–Fe alloy and core–shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt–Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure–property relationships of Pt–Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts.

Nanosized noble metallic particles enclosed by high-index facets exhibit superior catalytic activity because of their high density of low-coordinated step atoms at the surface, and thus have attracted growing interest over the past decade. In this article, we employed molecular dynamics simulations to investigate the thermodynamic evolution of tetrahexahedral Rh nanoparticles respectively covered by {210}, {310}, and {830} facets during the heating process. Our results reveal that the {210} faceted nanoparticle exhibits better thermal and shape stability than the {310} and {830} faceted ones. Meanwhile, because the {830} facet consists of {210} and {310} subfacets, the stability of the {830} faceted Rh nanoparticle is dominated by the {310} subfacet, which possesses a relatively poor stability. Furthermore, the shape transformation of these nanoparticles occurs much earlier than their melting. Further analyses indicate that surface atoms with higher coordination numbers display lower surface diffusivity, and are thus more helpful for stabilizing the particle shape. This study offers an atomistic understanding of the thermodynamic behaviors of high-index-faceted Rh nanoparticles.

Metallic nanoparticles with high-index facets exhibit exceptional electrocatalytic activity owing to the high density of low coordination sites at the surface, thus they have attracted intense interest over the past few years. Alloying could further improve their catalytic activity by the synergy effects of high-index facets and electronic structures of components. Using atomistic simulations, we have investigated thermodynamic and shape stabilities of tetrahexahedral Pt–Pd alloy nanoparticles respectively bound by {210} and {310} facets. Energy minimization through Monte Carlo simulations has indicated that the outermost layer is predominated by Pd atoms while Pt atoms preferentially occupy the sub-outermost layer of nanoparticles. Molecular dynamics simulations of the heating process have shown that the {210} faceted nanoparticles possess better thermodynamic and shape stabilities than the {310} faceted ones. The coordination numbers of surface atoms were used to explore the potential origin of the different stabilities. Furthermore, a high Pt ratio will help enhance their stabilities. For both faceted nanoparticles, the melting has homogeneously developed from the surface into the core, and the tetrahexahedra have finally evolved into sphere-like shape prior to the overall melting. These results are helpful for understanding the composition and thermodynamic properties of high-index faceted nanoparticles, and are also of practical importance to the development of alloy nanocatalysts.

High-index-faceted Pt nanoparticles exhibit exceptional electrocatalytic activity owing to the high density of low coordinated sites on their surface, and thus have attracted extensive studies over the past few years. In this study, we have employed atomistic simulations to systematically investigate the structural and thermal stabilities and shape evolution of Pt nanoparticles with different high-index facets, that is, tetrahexahedra enclosed by {hk0} facets, trapezohedra by {hkk} ones, and trisoctahedra by {hhk} ones. The results show that {221} faceted trisoctahedral nanoparticles display the best structural and thermal stabilities while {410} faceted tetrahexahedral ones display the worst. The shape stability of these nanoparticles generally decreases in the order from trapezohedron to tetrahexahedron to trisoctahedron. For the same type of polyhedron, the structural, thermal and shape stabilities of the nanoparticles all decrease according to the order of {2kl}, {3kl} and {4kl} facets. Further analyses have discovered that a large proportion of high-coordinated surface atoms are beneficial for enhancing both the thermal and shape stabilities. This work provides an in-depth understanding of surface structures and thermodynamic evolution of high-index-faceted metallic nanoparticles.

A microscopic understanding of the thermal stability of metallic core–shell nanoparticles is of importance for their synthesis and ultimately application in catalysis. In this article, molecular dynamics simulations have been employed to investigate the thermodynamic evolution of Au–CuPt core–shell trimetallic nanoparticles with various Cu/Pt ratios during heating processes. Our results show that the thermodynamic stability of these nanoparticles is remarkably enhanced upon rising Pt compositions in the CuPt shell. The melting of all the nanoparticles initiates at surface and gradually spreads into the core. Due to the lattice mismatch among Au, Cu and Pt, stacking faults have been observed in the shell and their numbers are associated with the Cu/Pt ratios. With the increasing temperature, they have reduced continuously for the Cu-dominated shell while more stacking faults have been produced for the Pt-dominated shell because of the significantly different thermal expansion coefficients of the three metals. Beyond the overall melting, all nanoparticles transform into a trimetallic mixing alloy coated by an Au-dominated surface. This work provides a fundamental perspective on the thermodynamic behaviors of trimetallic, even multimetallic, nanoparticles at the atomistic level, indicating that controlling the alloy composition is an effective strategy to realize tunable thermal stability of metallic nanocatalysts.

Morphologies of gold nanoparticles play an important role in determining their chemical and physical (catalytic, electronic, optical, etc.) properties. Therefore, a fundamental understanding of the morphological stability is of crucial importance to their applications. In this article, we employed atomistic simulations to systematically investigate the structural and thermal stabilities of gold particles with eight representative nanoshapes, including single-crystalline and multiple-twinned structures. Our investigation has revealed that the truncated octahedron and the octahedron possessed the best structural stability, while the tetrahedron and the icosahedron did the worst. Further analyses have discovered different thermal stabilities and diverse melting behaviors in these particles. Especially, an inhomogeneous melting of the icosahedron was disclosed, and the relevant mechanism was elucidated. This study provides significant insight not only into the experimental preparation of gold nanoparticles but also into the design of gold nanostructures with both high catalytic activity and excellent stability.

Nanosized metallic particles with high-index facets have exhibited excellent electrocatalytic activity and thus attracted intense interests over the past few years. Moreover, bimetallic particles with high-index facets could further enhance the catalytic activity by the synergy effects of high-index facets and electronic structures of the alloy. In this article, we employed atomistic simulations to investigate the thermal stability and shape evolution of tetrahexahedral Au–Pd core–shell nanoparticles respectively enclosed by {210} and {310} facets. The ground-state energy calculations indicated that the {210} faceted nanoparticles are more structurally stable than the {310} faceted ones. More importantly, it has been discovered that the former possess better thermal and shape stabilities than the latter. The Lindemann index was introduced to shed light on the melting mechanism, and the atomic distribution function was adopted to describe the diffusion tendency. For these two high-index terminated Au–Pd bimetallic nanoparticles, the core and the shell exhibit different thermal evolution as they are heated to melting, though the melting generally proceeds from the shell into the core. Beyond the overall melting, Au atoms prefer to aggregate near the surface to favor the minimization of the total energy. These results are helpful for understanding the composition, shape, and thermodynamic properties of high-index faceted nanoparticles and therefore could be of great importance to the development of bimetallic core–shell nanocatalysts with both high reactivity and excellent stability.

Comprehensive understanding of thermodynamic properties of metallic nanoparticles is of significance for their utility in catalysis. In this article, we have employed molecular dynamics simulations with quantum Sutton–Chen many-body potentials to examine the thermal stability of Au–Pt core–shell nanoparticles with different sizes during continuous heating. Our study shows that, for fixed particle size, the melting temperature is independent of core size for a small core while it is linearly decreased with a rising core radius for a large core. Diverse melting mechanisms have been discovered for different-core-sized nanoparticles. For a small core, the melting is progressively developed from the surface into the core, similar to that of monometallic nanoparticles. For a moderate or large core, an inhomogeneous melting has been found in these nanoparticles. The nucleation and activity of Shockley partial dislocations have initialized the local structural instability of the core–shell interface, leading to the inhomogeneous premelting of the Au core and the Pt shell for the moderate core. Nevertheless, when the core is large enough (resulting superthin shell), the diffusion of Au atoms from the core into the shell plays a dominant role in the destruction of the core–shell interface. This study provides a fundamental perspective on the melting behaviors of bimetallic (even multimetallic) nanoparticles at the atomistic level.

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.

We present a systematic investigation on the mechanical properties of platinum nanowires with single-crystalline and fivefold twinned structures by means of atomistic simulations. The results show that the Young’s moduli of both types of nanowires are significantly higher than that of bulk counterpart. Furthermore, the fivefold twinned nanowire generally exhibits a higher elastic modulus than the single-crystalline one. The introduction of the twinned structures enhances the yielding strength of the nanowires but remarkably lowers their ductility. The initiation of the yielding mechanism of the two types of nanowires is through a nucleation process and the activity of Shockley partial dislocations under external stress. However, due to the obstacle to partial dislocations, the twin boundaries have been found to be simultaneously destructive, initiating the fracture of twinned nanowire. A comparison of the results with those of other fcc nanowires has indicated that the nonlinear elasticity and the yielding strain should also be responsible for the yielding strength of the nanowires.Highlights► Fivefold twinned nanowire exhibits higher Young’s modulus than the single-crystalline one. ► Fivefold twinned nanowire has higher yielding strength but lower ductility than the single-crystalline one. ► The destructive twin boundaries initiates the fracture of twinned nanowire.

Microscopic understanding of thermodynamic behaviors of metallic nanoparticles is of significance for their applications in nanoscale catalysis and thermal energy storage. In this article, molecular dynamics simulations are used to investigate the thermal stabilities of Pt–Pd core–shell nanoparticles with different core sizes and shell thicknesses. Our study shows that a distinct two-stage melting occurs during the continuous heating of bimetallic nanoparticles. It has experienced a much broader temperature range compared with the melting of monometallic nanoparticles, although they have both developed from surface into interior. The temperature width for the two-stage melting is dependent not only on the bulk melting points of two component metals but also on the ratio of the shell thickness and core size. Furthermore, due to the melting of the Pd shell beforehand, the melting point of the Pt core is lower than that of the same size Pt nanoparticle not encapsulated by the Pd shell. This study provides a fundamental perspective on the melting behavior of bimetallic (even multimetallic) nanoparticles at the atomic level.

Atomic-level understanding of structural characteristics and thermal behaviors of nanocatalysts is important for their syntheses and applications. In this article, we present a systematic study on structural and thermal stabilities of Pt–Pd bimetallic nanoparticles with core–shell and alloyed structures by using atomistic simulations. It was revealed that the Pd-core/Pt-shell structures are the least structurally stable, while the inverted Pt-core/Pd-shell nanoparticles are more stable than the alloyed ones when the Pt percentage exceeds 42% or so. The origin for this order was clarified through analysis of atomic energy distribution in these structures. Furthermore, the core–shell structures exhibit enhanced thermal stability as compared to the alloyed ones for Pt composition more than about 30%. The diverse melting behaviors of bimetallic nanoparticles, associating with their thermally driven structural evolutions under the heating process, were characterized by the measurement of the Lindemann index. In addition, the analyses of diffusion behavior and atomic distribution suggest that the minimization of surface energy tends to form Pd surface segregation. This study is of considerable importance not only to experimental preparation of Pt–Pd nanocatalysts but also to design of bimetallic (even multimetallic) nanostructures of high catalytic activity and excellent stability.

Platinum is the most active and one of most commonly used catalytic metals. In this article, atomistic simulations have been employed to systematically investigate the thermal stability of platinum nanowires with single-crystalline and fivefold twinned structures. It has been revealed that the single-crystalline nanowires possess better structural stabilities than the twinned ones. Furthermore, when subjected to continuous heating, the twinned nanowires exhibit an inhomogeneous melting, essentially different from what happens in the single-crystalline ones, and hence the lower melting point. By analyses of the microstructural evolution and dynamics behavior during the heating process, the structural transition of the nanowire is discussed and the inhomogeneity in the twinned nanowire is identified to originate from the dislocation-induced destruction of twin boundaries.

High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

The energetic and structural evolutions of fcc Fe nanoparticles under heating process have been investigated by molecular dynamics simulations, and the phase transition between fcc and bcc phases is addressed. It is found that the solid–solid transition from fcc to bcc phase happens prior to the melting, accompanied with the particle shape from initial sphere into ellipsoid. The critical temperatures of phase transition and melting are inversely proportional to the particle diameters. It is demonstrated that high percentage of surface atoms may be beneficial to the phase transition of fcc Fe nanoparticles.Graphical abstractSnapshots of Fe nanocrystal taken at five temperatures during continuous heating.Research highlights► The solid–solid phase transition happens in fcc Fe nanoparticles prior to the melting. ► The temperatures of phase transition and melting are inversely proportional to the particle size.

Using molecular dynamics simulations with the quantum corrected Sutton–Chen type many-body potential, we have investigated the mechanical responses of Au nanowires along the [1 0 0], [1 1 0], and [1 1 1] crystallographic orientations under compression and tension. The main focus of this work is the orientation-dependent effects on the mechanical properties. The common neighbor analysis method is used to investigate the structural evolution and deformation mechanism of Au nanowires. The simulation results show that the Young’s modulus is strongly dependent on nanowire’s orientation. Under tension, all the oriented nanowires yield via the activities of Shockley partial dislocations, and their plastic deformation is accommodated by partial dislocation activities without twining. Under compression, the [1 0 0] nanowire presents the same yield mechanism together with the deformation twins occurring in its plastic deformation, however, for the [1 1 0] and [1 1 1] nanowires, the buckling instability preferentially occurs, followed by full dislocation activities to carry the plastic deformation without partial dislocations involved. The deformation behaviors indicate that the predication of the Schmidt factor based on bulk single crystal is valid for Au nanowires under compression but not under tension. Our study also shows that the [1 1 0] Au nanowire exhibits a better ductibility, while the [1 1 1] Au nanowire possesses excellent overall mechanical properties.

By means of atomistic simulations, we have investigated the energetics and stability of Fe nanocrystals with different crystal structures and shapes. It has been found that structural stability of Fe nanocrystals depends strongly on the size of nanocrystals. Furthermore, twinned fcc nanocrystals are energetically more stable than bcc single nanocrystals at very small sizes. Investigation on dynamics evolution of fcc Fe nanocrystals under heating reveals that the solid−solid phase transition from fcc to bcc occurs prior to the melting. The temperature of phase transformation depends on the shape of Fe nanocrystals. The bcc phase preferentially nucleates in apes of fcc Fe nanocrystals and spreads through entire ones with increased temperature. Twin structures suppress the propagation of the nucleated bcc phase, thereby, enhancing the thermal stability of twinned fcc Fe nanocrystals.

Using molecular dynamics simulations with the quantum corrected Sutton−Chen type many-body potential, we have studied the thermal stability of Au nanowires along the [100], [110], and [111] crystallographic orientations during continuous heating. The bond pair analysis and Lindemann index are used to characterize the structural and thermal evolution of these nanowires. The results show that the critical temperatures of structural transition, melting, and fracture are dependent on the crystallographic orientation of Au nanowires. It is found that all the Au nanowires exhibit an inhomogeneous melting behavior from the surface into the interior. The structural transition from a fcc to hcp structure prior to surface premelting is closely associated with the activities of Shockley partial dislocations driven by the internal stress because of the thermal expansion of the nanowires with increased temperature. A comparison of the results of three types of nanowires indicates that the [110] nanowire possesses a better thermal and structural stability compared with other oriented nanowires, which helps to explain why Au nanowires possess a [110] preferred orientation during the experimental growth procedure.

We present the analysis of uniaxial deformation of nickel nanowires using molecular dynamics simulations, and address the strain rate effects on mechanical responses and deformation behavior. The applied strain rate is ranging from 1 × 108 s−1 to 1.4 × 1011 s−1. The results show that two critical strain rates, i.e., 5 × 109 s−1 and 8 × 1010 s−1, are observed to play a pivotal role in switching between plastic deformation modes. At strain rate below 5 × 109 s−1, Ni nanowire maintains its crystalline structure with neck occurring at the end of loading, and the plastic deformation is characterized by {1 1 1} slippages associated with Shockley partial dislocations and rearrangements of atoms close to necking region. At strain rate above 8 × 1010 s−1, Ni nanowire transforms from a fcc crystal into a completely amorphous state once beyond the yield point, and hereafter it deforms uniformly without obvious necking until the end of simulation. For strain rate between 5 × 109 s−1 and 8 × 1010 s−1, only part of the nanowire exhibits amorphous state after yielding while the other part remains crystalline state. Both the {1 1 1} slippages in ordered region and homogenous deformation in amorphous region contribute to the plastic deformation.

Using a molecular static approach with a many-body force field, we have simulated the elastic responses of a nickel monocrystal subjected to uniaxial tensile and compressive loadings in the [001], [011] and [111] directions. The main focus of this work is the nonlinear effects on the elastic modulus and Poisson’s ratio. The study shows that the elastic behavior exhibits strongest nonlinear effects for [011] loading, and, for [001] and [111] loadings, the lateral deformation is isotropic. Further, the dependence of the Young’s moduli and Poisson’s ratios on strain are discussed in detail. A comparison of the results with those of ab initio calculations is also presented, which shows a fair consistency.

High index surfaces are introduced into Pt nanocrystals because they are expected to exhibit higher catalytic activity than low index planes such as {111}, {100}, and even {110}. This article presents a systematic investigation on the structure and stability of polyhedral Pt nanocrystals with both low-index and high-index facets by means of atomistic simulations. It has been found that the stability of Pt nanocrystals depends strongly on the particle shape and surface structures. Those nanocrystals, enclosed by high-index facets of {310}, {311}, and {331}, possess better stability and higher dangling bond density of surface compared with those ones with low-index facets, such as {100} and {110}, suggesting that they should become preferential candidates for nanocatalysts. The octahedral nanocrystals with {111} facets, though they have excellent structural and thermal stabilities, present the lowest dangling bond density of surface.

Platinum is the most active and one of most commonly used catalytic metals. In this article, atomistic simulations have been employed to systematically investigate the thermal stability of platinum nanowires with single-crystalline and fivefold twinned structures. It has been revealed that the single-crystalline nanowires possess better structural stabilities than the twinned ones. Furthermore, when subjected to continuous heating, the twinned nanowires exhibit an inhomogeneous melting, essentially different from what happens in the single-crystalline ones, and hence the lower melting point. By analyses of the microstructural evolution and dynamics behavior during the heating process, the structural transition of the nanowire is discussed and the inhomogeneity in the twinned nanowire is identified to originate from the dislocation-induced destruction of twin boundaries.

Development of core–shell bimetallic nanoparticles with bifunctional catalytic activity and excellent stability is a challenging issue in nanocatalyst synthesis. Here we present a detailed study of thermal stabilities of Au-core/Pt-shell nanoparticles with different core sizes and shell thicknesses. Molecular dynamics simulations are used to provide insights into the melting and diffusive behavior at atomic-level. It is found that the thermal stabilities of core-shell nanoparticles are significantly enhanced with increasing thickness of Pt shell. Meanwhile, the melting mechanism is strongly dependent on the shell thickness. When the core size or shell thickness is very small, the melting is initiated in the shell and gradually spreads into the core, similar to that of monometallic nanoparticles. As the core increases up to moderate size, an inhomogeneous melting has been observed. Due to the relatively weak confinement of thin shell, local lattice instability preferentially takes place in the core, leading to the inhomogeneous premelting of Au core ahead of the overall melting of Pt shell. The diffusion coefficients of both Au and Pt are decreased with the increasing thickness of shell, and the difference in their diffusions favors the formation of inhomogeneous atomic distributions of Au and Pt. The study is of considerable importance for improving the stability of Pt-based nanocatalysts by tuning the shell thickness and core size.

Metallic nanoparticles with high-index facets exhibit exceptional electrocatalytic activity owing to the high density of low coordination sites at the surface, thus they have attracted intense interest over the past few years. Alloying could further improve their catalytic activity by the synergy effects of high-index facets and electronic structures of components. Using atomistic simulations, we have investigated thermodynamic and shape stabilities of tetrahexahedral Pt–Pd alloy nanoparticles respectively bound by {210} and {310} facets. Energy minimization through Monte Carlo simulations has indicated that the outermost layer is predominated by Pd atoms while Pt atoms preferentially occupy the sub-outermost layer of nanoparticles. Molecular dynamics simulations of the heating process have shown that the {210} faceted nanoparticles possess better thermodynamic and shape stabilities than the {310} faceted ones. The coordination numbers of surface atoms were used to explore the potential origin of the different stabilities. Furthermore, a high Pt ratio will help enhance their stabilities. For both faceted nanoparticles, the melting has homogeneously developed from the surface into the core, and the tetrahexahedra have finally evolved into sphere-like shape prior to the overall melting. These results are helpful for understanding the composition and thermodynamic properties of high-index faceted nanoparticles, and are also of practical importance to the development of alloy nanocatalysts.

Nanosized noble metallic particles enclosed by high-index facets exhibit superior catalytic activity because of their high density of low-coordinated step atoms at the surface, and thus have attracted growing interest over the past decade. In this article, we employed molecular dynamics simulations to investigate the thermodynamic evolution of tetrahexahedral Rh nanoparticles respectively covered by {210}, {310}, and {830} facets during the heating process. Our results reveal that the {210} faceted nanoparticle exhibits better thermal and shape stability than the {310} and {830} faceted ones. Meanwhile, because the {830} facet consists of {210} and {310} subfacets, the stability of the {830} faceted Rh nanoparticle is dominated by the {310} subfacet, which possesses a relatively poor stability. Furthermore, the shape transformation of these nanoparticles occurs much earlier than their melting. Further analyses indicate that surface atoms with higher coordination numbers display lower surface diffusivity, and are thus more helpful for stabilizing the particle shape. This study offers an atomistic understanding of the thermodynamic behaviors of high-index-faceted Rh nanoparticles.

A microscopic understanding of the thermal stability of metallic core–shell nanoparticles is of importance for their synthesis and ultimately application in catalysis. In this article, molecular dynamics simulations have been employed to investigate the thermodynamic evolution of Au–CuPt core–shell trimetallic nanoparticles with various Cu/Pt ratios during heating processes. Our results show that the thermodynamic stability of these nanoparticles is remarkably enhanced upon rising Pt compositions in the CuPt shell. The melting of all the nanoparticles initiates at surface and gradually spreads into the core. Due to the lattice mismatch among Au, Cu and Pt, stacking faults have been observed in the shell and their numbers are associated with the Cu/Pt ratios. With the increasing temperature, they have reduced continuously for the Cu-dominated shell while more stacking faults have been produced for the Pt-dominated shell because of the significantly different thermal expansion coefficients of the three metals. Beyond the overall melting, all nanoparticles transform into a trimetallic mixing alloy coated by an Au-dominated surface. This work provides a fundamental perspective on the thermodynamic behaviors of trimetallic, even multimetallic, nanoparticles at the atomistic level, indicating that controlling the alloy composition is an effective strategy to realize tunable thermal stability of metallic nanocatalysts.

Atomic-scale understanding of structures and thermodynamic stability of core–shell nanoparticles is important for both their synthesis and application. In this study, we systematically investigated the structural stability and thermodynamic evolution of core–shell structured Pd–Ni nanoparticles by molecular dynamics simulations. It has been revealed that dislocations and stacking faults occur in the shell and their amounts are strongly dependent on the core/shell ratio. The presence of these defects lowers the structural and thermal stability of these nanoparticles, resulting in even lower melting points than both Pd and Ni monometallic nanoparticles. Furthermore, different melting behaviors have been disclosed in Pd-core/Ni-shell and Ni-core/Pd-shell nanoparticles. These diverse behaviors cause different relationships between the melting temperature and the amount of stacking faults. Our results display direct evidence for the tunable stability of bimetallic nanoparticles. This study provides a fundamental perspective on core–shell structured nanoparticles and has important implications for further tailoring their structural and thermodynamic stability by core/shell ratio or composition controlling.

High-index-faceted Pt nanoparticles exhibit exceptional electrocatalytic activity owing to the high density of low coordinated sites on their surface, and thus have attracted extensive studies over the past few years. In this study, we have employed atomistic simulations to systematically investigate the structural and thermal stabilities and shape evolution of Pt nanoparticles with different high-index facets, that is, tetrahexahedra enclosed by {hk0} facets, trapezohedra by {hkk} ones, and trisoctahedra by {hhk} ones. The results show that {221} faceted trisoctahedral nanoparticles display the best structural and thermal stabilities while {410} faceted tetrahexahedral ones display the worst. The shape stability of these nanoparticles generally decreases in the order from trapezohedron to tetrahexahedron to trisoctahedron. For the same type of polyhedron, the structural, thermal and shape stabilities of the nanoparticles all decrease according to the order of {2kl}, {3kl} and {4kl} facets. Further analyses have discovered that a large proportion of high-coordinated surface atoms are beneficial for enhancing both the thermal and shape stabilities. This work provides an in-depth understanding of surface structures and thermodynamic evolution of high-index-faceted metallic nanoparticles.

Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt–Fe alloy and core–shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt–Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure–property relationships of Pt–Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts.