Local magnetic properties and electronic structures of 3d and 4d impurities in Cu clusters

Design of Atomically Dispersed CoN4 Sites and Co Clusters for Synergistically Enhanced Oxygen Reduction Electrocatalysis

Constructing dual-site catalysts consisting of atomically dispersed metal single atoms and metal atomic clusters (MACs) is a promising approach to further boost the catalytic activity for oxygen reduction reaction (ORR). Herein, a porous CoSA-AC@SNC featuring the coexistence of Co single-atom sites (CoN4) and S-coordinated Co atomic clusters (SCo6) in S, N co-doped carbon substrate is successfully synthesized by using porphyrinic metal-organic framework (Co-TPyP MOF) as the precursor. The introduction of the sulfur source creates abundant microstructural defects to anchor Co metal clusters, thus modulating the electronic structure of its surrounding carbon substrate. The synergistic effect between the two types of active sites and structural advantages, in turn, results in high ORR performance of CoSA-AC@SNC with half-wave potential (E1/2) of 0.86 V and Tafel slope of 50.17 mV dec-1. Density functional theory (DFT) calculations also support the synergistic effect between CoN4 and SCo6 by detailing the catalytic mechanism for the improved ORR performance. The as-fabricated Zn-air battery (ZAB) using CoSA-AC@SNC demonstrates impressive peak power density of 174.1 mW cm-2 and charge/discharge durability for 148 h. This work provides a facile synthesis route for dual-site catalysts and can be extended to the development of other efficient atomically dispersed metal-based electrocatalysts.

Electron counting in cationic and anionic silver clusters doped with a 3d transition-metal atom: endo- vs. exohedral geometry

Cationic and anionic AgNM+/− (M = Sc–Ni) clusters are explored to examine the electron-counting rule. Among 18-valence-electron clusters, endohedrally doped ones are stable due to superatomic electron-shell closure involving delocalized 3d electrons.

A Systematic Investigation on CrCun Clusters with n = 9-16: Noble Gas and Tunable Magnetic Property

A systematic investigation on structure, dissociation behavior, chemical bonding, and magnetic property of Cr-doped Cun clusters (n = 9-16) is carried out using the mean of density functional theory calculations. It is found that CrCu12 is a crucial size, preferring an icosahedral Cu12 cage with the central Cr dopant. Smaller cluster sizes appear as on the way to form the CrCu12 icosahedron while larger ones are produced by attaching additional Cu atoms to the CrCu12 core. The presence of Cr dopant obviously enhances the stability of CrCun clusters in comparison to that of pure counterparts. Exceptionally stable CrCu12 has an 18-electron closed-shell electronic structure, mimicking a noble gas in the viewpoint of superatom concept. Analysis on cluster electronic structure shows that the interplay between 3d orbitals of Cr and 4s orbitals of Cu has a vital role on the magnetic properties of CrCun clusters.

Structural and electronic properties of uranium-encapsulated Au₁₄ cage

The structural properties of the uranium-encapsulated nano-cage U@Au₁₄ are predicted using density functional theory. The presence of the uranium atom makes the Au₁₄ structure more stable than the empty Au₁₄-cage, with a triplet ground electronic state for U@Au₁₄. Analysis of the electronic structure shows that the two frontier single-occupied molecular orbital electrons of U@Au₁₄ mainly originate from the 5f shell of the U atom after charge transfer. Meanwhile, the bonding orbitals and charge population indicate that the designed U@Au₁₄ nano-cage structure is stabilized by ionocovalent interactions. The current findings provide theoretical basis for future syntheses and further study of actinide doped gold nanoclusters, which might subsequently facilitate applications of such structure in radio-labeling, nanodrug carrier and other biomedical applications.

Low-energy isomer identification, structural evolution, and magnetic properties in manganese-doped gold clusters MnAu(n) (n = 1-16)

The size-dependent electronic, structural, and magnetic properties of Mn-doped gold clusters have been systematically investigated by using relativistic all-electron density functional theory with generalized gradient approximation. A number of new isomers are obtained for neutral MnAu(n) (n = 1-16) clusters to probe the structural evolution. The two-dimensional (2D) to three-dimensional (3D) transition occurs in the size range n = 7-10 with manifest structure competitions. From size n = 13 to n = 16, the MnAu(n) prefers a gold cage structure with Mn atom locating at the center. The relative stabilities of the ground-state MnAu(n) clusters show a pronounced odd-even oscillation with the number of Au atoms. The magnetic moments of MnAu(n) clusters vary from 3 μ(B) to 6 μ(B) with the different cluster size, suggesting that nonmagnetic Au(n) clusters can serve as a flexible host to tailor the dopant's magnetism, which has potential applications in new nanomaterials with tunable magnetic properties.

Magnetic properties in transition-metal-doped gold clusters: M@Au6 (M = Ti, V, Cr)

The electronic structure and magnetic properties in a series of transition-metal-doped Au clusters, MAu6- (M = Ti, V, Cr), are investigated experimentally using photoelectron spectroscopy (PES) and density functional calculations. PES features due to the impurity atoms and the host are clearly observed. It is found that all the MAu6- and MAu6 clusters possess a planar structure, in which the transition metal atom is located in the center of an Au6 ring and carries large magnetic moments (2, 3, and 4 muB for MAu6, M = Ti, V, and Cr, respectively).

Quenching of the magnetic moment of a transition metal dopant in silver clusters

Single magnetic atoms embedded in a nonmagnetic host exhibit the Kondo effect in the bulk limit, while in very small molecules the magnetic atom is hardly affected by the matrix. In a combined theoretical (density functional theory) and experimental (photofragmentation and mass spectrometry) study we consider the intermediate case of nanometer sized transition-metal-doped silver clusters. In particular, we provide experimental evidence for enhanced stability of the cobalt-doped silver cluster Ag10Co+ and show theoretically that it has a symmetric endohedral geometry with a closed 18-electron singlet electronic shell structure. This implies that the magnetic moment on the cobalt atom is quenched.

Element- and size-dependent electron delocalization in AuNX+ clusters (X = Sc, Ti, V, Cr, Mn, Fe, Co, Ni)

We investigated the stability of gold clusters doped with open 3d-shell atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Steps, peaks, and odd-even staggering in mass abundance spectra upon photofragmentation provide evidence for enhanced stability for specific cluster sizes. The observed magic numbers are explained in terms of size- and dopant-dependent modifications of the effective mean-field potential within a phenomenological shell-model approach. Element-dependent 3d electron delocalization and odd-even staggering amplitudes are related to the dopant-atom structure.