Ab Initio Insights into the Formation Mechanisms of 55-Atom Pt-Based Core–Shell Nanoalloys

Abstract

Platinum-based nanoalloys can yield unique properties due to synergistic effects derived from the combination of Pt with one or more transition-metal (TM) species, as well as from the chemical ordering within the particles such as the formation of core–shell PtTM structures. Although several studies have been reported, our atomistic understanding of the key physical and chemical descriptors that lead to the formation and stability of the core–shell structures are not completely understood. Here, we discuss such descriptors to understand the formation and stability of 11 platinum-based nanoalloys through ab initio density functional theory calculations employing 55-atom PtTM model systems. Studying several properties and using the Spearman correlation analysis, we found that the core–shell PtTM nanoalloys are energetically more stable if the surface region is populated by the chemical species with larger atomic radius and lower surface energy, which helps to reduce strain and forms stable structures. For nanoalloys of chemical species with large difference in the electronegativity, the energetic stability is enhanced by the Coulomb attraction between the cationic core and anionic surface derived from charge transfer, which increases the strain on the core and contributes to increase the segregation of large species to the surface region. Thus, the atomic radii, surface energies, and charge transfer play a crucial role in the formation and stability of core–shell PtTM nanoalloys.

Nanometal Thermocatalysts: Transformations, Deactivation, and Mitigation

“…Figure 5c [ 95 ] presents an example of DFT analysis of the complex influence chemical composition, atomic size, and surface energy on the stability of core–shell configurations. As can be seen, smaller atoms and atoms with lower surface energy tend to segregate in the particle surface to minimize the excess energy.…”

>i<Ab Initio>/i< investigation of the adsorption of molecules, involved in carbon dioxide and glycerol utilization, on transition-metal substrates

“…For the subsequent chapters of this thesis and articles published while developing this thesis, 145,146,159 all relevant bulk and clean surface properties were recalculated using the conditions established for each self-contained study; for example, using the D3 correction and respecting the specific POTCAR files, cutoff energies and convergence criteria defined for each chapter. Hence, small differences in the properties are possible, but all variations are within expected errors from DFT calculations (order of meV), considering that the computational parameters satisfy the convergence of the properties.…”

“…The different convergence criteria for Chapter 5 were made to manage the computational cost, because of the large number of adsorption configurations optimized and only a small impact is expected for the results, according to convergence tests and the literature, such as previous studies with TM nanoclusters. 35,146 Regarding spin polarization and the local magnetic moments, the electronic optimizations were not constrained and the self-consistent lowest energy solution was employed for each system.…”

“…35,217 For the nanoalloys, the number of possible configurations increase dramatically, then, our group performed a systematic study to investigate the formation of several types of Pt 13 TM 42 and Pt 42 TM 13 nanoalloys, including core-shell, homogeneously distributed and segregated side by side. 146 The aforementioned investigation initiated with a Master degree study that explored some trends driving the formation of core-shell arrangements. 136 The study was published later, after a meticulous review, normalization of the calculations to improve the consistency of computational parameters, further exploration of the possible local magnetic moments for each nanoparticle, evaluation of all properties and additional analyses of the correlations between such properties and the stability of the nanoalloys; in total, 330 nanoalloys were investigated.…”

“…136 The study was published later, after a meticulous review, normalization of the calculations to improve the consistency of computational parameters, further exploration of the possible local magnetic moments for each nanoparticle, evaluation of all properties and additional analyses of the correlations between such properties and the stability of the nanoalloys; in total, 330 nanoalloys were investigated. 146 Here, we employed the lowest energy configuration, from the referred previous study, 146 for each PtTM system to study CO 2 adsorption. Additionally, all cluster morphologies observed for the nanoalloys were also studied for Pt 55 to demonstrate the influence of particle morphology on the adsorption.…”