22 Search Results

X-ray absorption spectroscopy is utilized to study the distribution of Au and Ag within the metal core of the Au ₁₀₄ Ag ₄₀ (PET) ₆₀ nanocluster, revealing a Ag single-atom alloy structure associated with unique bonding properties.

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Nanoscale multi-principal element intermetallics (MPEIs) may provide a broad and tunable compositional space of active, high–surface area materials with potential applications such as catalysis and magnetics. However, MPEI nanoparticles are challenging to fabricate because of the tendency of the particles to grow/agglomerate or phase-separated during annealing. Here, we demonstrate a disorder-to-order phase transition approach that enables the synthesis of ultrasmall (4 to 5 nm) and stable MPEI nanoparticles (up to eight elements). We apply just 5 min of Joule heating to promote the phase transition of the nanoparticles into L1₀ intermetallic structure, which is then preserved by rapidly cooling. Thismore » disorder-to-order transition results in phase-stable nanoscale MPEIs with compositions (e.g., PtPdAuFeCoNiCuSn), which have not been previously attained by traditional synthetic methods. This synthesis strategy offers a new paradigm for developing previously unexplored MPEI nanoparticles by accessing a nanoscale-size regime and novel compositions with potentially broad applications.« less

Carbon-supported nanocomposites are attracting particular attention as high-performance, low-cost electrocatalysts for electrochemical water splitting. These are mostly prepared by pyrolysis and hydrothermal procedures that are time-consuming (from hours to days) and typically difficult to produce a nonequilibrium phase. Herein, for the first time ever, we exploit magnetic induction heating-quenching for ultrafast production of carbon-FeNi spinel oxide nanocomposites (within seconds), which exhibit an unprecedentedly high performance towards oxygen evolution reaction (OER), with an ultralow overpotential of only +260 mV to reach the high current density of 100 mA cm ^-2 . Experimental and theoretical studies show that the rapid heating and quenching process (ca.more » 10 ³ K s ^-1 ) impedes the Ni and Fe phase segregation and produces a Cl-rich surface, both contributing to the remarkable catalytic activity. Results from this study highlight the unique advantage of ultrafast heating/quenching in the structural engineering of functional nanocomposites to achieve high electrocatalytic performance towards important electrochemical reactions.« less

Abstract Silver nanoclusters (NCs) are of significant interest owing to their interesting structural, electronic, and catalytic properties. Among these NCs, Ag ₂₅ (SR) ₁₈ is particularly attractive due to its identical geometry as its Au counterpart, Au ₂₅ (SR) ₁₈ . Herein, the site‐specific electronic properties of Ag ₂₅ (SR) ₁₈ and Au ₂₅ (SR) ₁₈ using X‐ray spectroscopy experiments and quantum simulations are presented. To overcome the final state effect observed in X‐ray photoelectron spectroscopy (XPS), a unique method is developed to reliably analyze the charge transfer behavior of the NCs. Density functional theory calculations are combined with XPSmore » to provide more insight into the electronic properties of the NCs. The differences in the XPS valence bands of these two NCs are further compared and interpreted using the relativistic effect. The first derivative of the X‐ray absorption near‐edge structure (XANES) spectrum is further used as a tool to sensitively probe the bonding properties of Ag ₂₅ (SR) ₁₈ . By combining the experimental XANES data and their site‐specific quantum simulations, the large impact of the staple motif on the bonding properties of the NC is demonstrated. These findings highlight the unique electronic properties of each atomic site in Ag ₂₅ (SR) ₁₈ ; the effective X‐ray analysis techniques developed here can offer new opportunities for the site‐specific study of other NCs.« less

Activation of O₂ is a critical step in heterogeneous catalytic oxidation. Here, the concept of increased electron donors induced by nitrogen vacancy is adopted to propose an efficient strategy to develop highly active and stable catalysts for molecular O₂ activation. Carbon nitride with nitrogen vacancies is prepared to serve as a support as well as electron sink to construct a synergistic catalyst with Pt nanoparticles. Extensive characterizations combined with the first-principles calculations reveal that nitrogen vacancies with excess electrons could effectively stabilize metallic Pt nanoparticles by strong p-d coupling. The Pt atoms and the dangling carbon atoms surround the vacancymore » can synergistically donate electrons to the antibonding orbital of the adsorbed O₂. This synergistic catalyst shows great enhancement of catalytic performance and durability in toluene oxidation. The introduction of electron-rich non-oxide substrate is an innovative strategy to develop active Pt-based oxidation catalysts, which could be conceivably extended to a variety of metal-based catalysts for catalytic oxidation.« less

Abstract Due to their interesting chemical and optical properties, metal nanoclusters are used in various catalytic reactions and in energy conversion. By incorporating thiolate‐protecting ligands, their size and composition can be tuned. Doping these nanoclusters to form single‐atom alloy (SAA) nanoclusters is shown to further enhance these properties as a result from the synergy between the dopant and host atoms. In addition to their optical and chemical properties, SAA nanoclusters also have interesting electronic properties. However, these properties are often underdiscussed when studying SAA nanoclusters. This review provides an overview of representative studies done on the in‐depth understanding of themore » electronic properties and catalytic activities of Ag‐based and Au‐based thiolate‐protected SAA nanoclusters. The use of density functional theory (DFT), X‐ray absorption spectroscopy, and X‐ray photoelectron spectroscopy are employed to correlate the changes in charge states of thiolate‐protected SAA nanoclusters with their superior catalytic activity versus monometallic nanoclusters. DFT, UV–vis spectroscopy, and voltammetric methods link the changes in molecular energy levels of thiolate‐protected SAA nanoclusters to their enhanced catalytic performance over monometallic nanoclusters.« less

The structure–property relationship of single-atom alloy catalysts is reviewed from the perspective of atomic structure analysis, electronic properties, and catalytic activities.

Recent progress has been made on the synthesis and characterization of metal halide perovskite magic-sized clusters (PMSCs) with ABX ₃ composition ( $A=\text{C}{\text{H}}_3\text{N}{{\text{H}}_3}^{+}$ or Cs ⁺ , $B=\text{P}{\text{b}}^{2+}$ , and $X=\text{C}{\text{l}}^{-}$ , Br ^- , or I ^- ). However, their mechanism of growth and structure ismore » still not well understood. In our effort to understand their structure and growth, we discovered that a new species can be formed without the CH ₃ NH ₃ ⁺ component, which we name as molecular clusters (MCs). Specifically, CH ₃ NH ₃ PbBr ₃ PMSCs, with a characteristic absorption peak at 424 nm, are synthesized using PbBr ₂ and CH ₃ NH ₃ Br as precursors and butylamine (BTYA) and valeric acid (VA) as ligands, while MCs, with an absorption peak at 402 nm, are synthesized using solely PbBr ₂ and BTYA, without CH ₃ NH ₃ Br. Interestingly, PMSCs are converted spontaneously overtime into MCs. An isosbestic point in their electronic absorption spectra indicates a direct interplay between the PMSCs and MCs. Therefore, we suggest that the MCs are precursors to the PMSCs. From spectroscopic and extended X-ray absorption fine structure (EXAFS) results, we propose some tentative structural models for the MCs. The discovery of the MCs is critical to understanding the growth of PMSCs as well as larger perovskite quantum dots (PQDs) or nanocrystals (PNCs).« less