Through a gelation–solvothermal method without heteroadditives, Cu–Sn–S composites self-assemble to form nanotubes, sub-nanotubes, and nanoparticles. The nanotubes with a Cu3–4SnS4 core and Cu2SnS3 shell can tolerate long cycles of expansion/contraction upon lithiation/delithiation, retaining a charge capacity of 774 mAh g–1 after 200 cycles with a high initial Coulombic efficiency of 82.5%. The importance of the Cu component for mitigation of the volume expansion and structural evolution upon lithiation is informed by density functional theory calculations. The self-generated template and calculated results can inspire the design of analogous Cu–M–S (M = metal) nanotubes for lithium batteries or other energy storage systems.Keywords: copper tin sulfide; core−shell; density functional theory; gelation−solvothermal; lithium battery; nanotube;

Well-defined palladium–gold nanoparticles (PdAuNPs) with randomly alloyed structures and broadly tunable compositions were studied in catalytic nitrite (NO2–) reduction. The catalysts were synthesized using a microwave-assisted polyol coreduction method. PdxAu100–xNPs with systematically varied compositions (x = 18–83) were supported on amorphous silica (SiO2) and studied as model catalysts for aqueous NO2– reduction in a batch reactor, using H2 as the electron donor. The reactions followed pseudo-first-order kinetics for ≥80% NO2– conversion. The PdxAu100–xNP-SiO2 catalysts showed a volcano-like correlation between NO2– reduction activity and x; the highest activity was observed for Pd53Au47, with an associated first-order rate constant of 5.12 L min–1 gmetal–1. Alloy NPs with greater proportions of Au were found to reduce the loss in catalytic activity due to sulfide fouling. Density functional theory calculations indicate that this is because Au weakens sulfur binding at PdAuNP surfaces due to atomic ensemble, electronic, and strain effects and thus reduces sulfur poisoning. The environmental relevance of the most active supported catalyst was evaluated by subjecting it to five cycles of catalytic NO2– reduction. The catalytic activity decreased over multiple cycles, but analysis of the postreaction PdxAu100–xNP-SiO2 materials using complementary techniques indicated that there were no significant structural changes. Most importantly, we show that PdxAu100–xNP-SiO2 alloys are significantly more active NO2– reduction catalysts in comparison to pure Pd catalysts.Keywords: density functional theory (DFT); heterogeneous catalysis; microwave synthesis; nitrite hydrogenation; palladium−gold alloys; sulfide poisoning; water treatment;

Ethanol (EtOH) decomposition has been widely studied in recent years. However, the initial dehydrogenation selectivity on catalytic surfaces, which plays a crucial role in EtOH partial oxidation and steam reforming, is not well understood. Here, density functional theory (DFT) was used to calculate the initial dehydrogenation selectivities of EtOH on monometallic and X/Au (X = Pd and Rh) close-packed surfaces. The energy for the initial bond scissions of O–H and α- and β-C–H were calculated on each surface. The binding energy of EtOH is found to be a good reactivity descriptor for the scission of O–H and β-C–H bonds, while the binding energy of CH3CHOH is a good reaction descriptor for α-C–H bond scission. The scaling relationships between the activation energy barriers and binding energies on Pd/Au and Rh/Au surface alloys are significantly different from those of monometallic surfaces. Additionally, the specific atomic ensembles on the Pd/Au and Rh/Au surfaces have different initial dehydrogenation selectivities of EtOH. Our calculated scaling relationships were used to construct contour plots that provide predictive trends for the selectivity of the initial EtOH dehydrogenation. We conclude that the presence of specific atomic ensembles on the surface of alloy catalysts can efficiently control the reaction products of EtOH dehydrogenation.

In this paper, we show that PtAu and PdAu random alloy dendrimer-encapsulated nanoparticles with an average size of ∼1.6 nm have different catalytic activity trends for allyl alcohol hydrogenation. Specifically, PtAu nanoparticles exhibit a linear increase in activity with increasing Pt content, whereas PdAu dendrimer-encapsulated nanoparticles show a maximum activity at a Pd content of ∼60%. Both experimental and theoretical results suggest that this contrasting behavior is caused by differences in the strength of H binding on the PtAu and PdAu alloy surfaces. The results have significant implications for predicting the catalytic performance of bimetallic nanoparticles on the basis of density functional theory calculations.

Li2MnSiO4 is a promising high capacity cathode material due to the potential to extract two Li ions per formula unit. In practice, however, the use of Li2MnSiO4 is restricted by a low discharge capacity, which has been attributed to an irreversible structural change in the first charge cycle. In this work, we use density functional theory calculations to explore the details of this structural change, and our results reveal that the structural change during delithiation has two components. First, we find that the material undergoes a structural collapse upon partial delithiation, which is characterized by distortion of the MnO4 tetrahedron. Remarkably, while this transformation results in a disordered structure, our calculations show that it is reversible upon relithiation and that the transformation does not strongly impede Li de/intercalation. The calculated reversibility of the phase change is consistent with recent experimental X-ray diffraction measurements showing that peaks associated with the crystalline MnO4 order, which disappear upon delithiation, are restored upon lithiation. Additional experiments are conducted showing the reversibility of the material during cycling as a function of charging cutoff voltages. Second, we argue that, the irreversible structural degradation is primarily caused by oxygen evolution in the highly delithiated state; the oxygen deficient structure can only reincorporate half of the total Li when discharged to 1.5 V. Experimentally observed voltage profile shifts of Li2MnSiO4 during the first few cycles as well as the different electrochemical behavior exhibited by Li2FeSiO4 can be explained by this two-component structural change model.

Density functional theory calculations reveal that the work function of Au supported on MgO(001) is substantially reduced because of an interfacial dipole moment formed at the Au/MgO interface. Consequently, the Au/MgO interface plays an active role in the activation of O2 molecules by promoting charge transfer to the O2 2π* orbital. The presence of F-centers in the MgO substrate can further promote the charge transfer and bonding of O2 at the interface boundary. However, O2 dissociation is kinetically hindered. The system is then able to catalyze CO oxidation at low temperature as adsorbed CO and O2 readily react to form CO2 with a low energy barrier.

Engineering a bimetallic system with complementary chemical properties can be an effective way of tuning catalytic activity. In this work, CO oxidation on CeO2(111)-supported Pd-based bimetallic nanorods was investigated using density functional theory calculations corrected by on-site Coulomb interactions. We studied a series of CeO2(111)-supported Pd-based bimetallic nanorods (Pd–X, where X = Ag, Au, Cu, Pt, Rh, Ru) and found that Pd–Ag/CeO2 and Pd–Cu/CeO2 are the two systems where the binding sites of CO and O2 are distinct; that is, in these two systems, CO and O2 do not compete for the same binding sites. An analysis of the CO oxidation mechanisms suggests that the Pd–Ag/CeO2 system is more effective for catalyzing CO oxidation as compared to Pd–Cu/CeO2 because both CeO2 lattice oxygen atoms and adsorbed oxygen molecules at Ag sites can oxidize CO with low energy barriers. Both the Pd–Ag and Pd–CeO2 interfaces in Pd–Ag/CeO2 were found to play important roles in CO oxidation. The Pd–Ag interface, which combines the different chemical nature of the two metals, not only separates the binding sites of CO and O2 but also opens up active reaction pathways for CO oxidation. The strong metal–support interaction at the Pd–CeO2 interface facilitates CO oxidation by the Mars–van Krevelen mechanism. Our study provides theoretical guidance for designing highly active metal/oxide catalysts for CO oxidation.

In this paper, we show that the onset potential for CO oxidation electrocatalyzed by ∼2 nm dendrimer-encapsulated Pt nanoparticles (Pt DENs) is shifted negative by ∼300 mV in the presence of a small percentage (<2%) of Cu surface atoms. Theory and experiments suggest that the catalytic enhancement arises from a cocatalytic Langmuir–Hinshelwood mechanism in which the small number of Cu atoms selectively adsorb OH, thereby facilitating reaction with CO adsorbed to the dominant Pt surface. Theory suggests that these Cu atoms are present primarily on the (100) facets of the Pt DENs.Keywords: bimetallic nanoparticle; CO electro-oxidation; density functional theory; isolated Cu

Density functional theory is used to determine the reaction mechanisms of CO oxidation and the active oxygen species on a Au/TiO2 model catalyst. The model consists of a Au rod supported along the TiO2 [11̅0] direction of the TiO2(110) surface. An interfacial Au/Ti5c site at the interface boundary is identified to be particularly active toward O2 adsorption and dissociation. At this site, O2 dissociation has an energy barrier of 0.5 eV, which is facile at room temperature. The resulting adsorbed Au/O/Ti5c oxygen species are shown to be stable and active for CO oxidation under relevant reaction conditions with an activation energy of 0.24 eV. Furthermore, the adsorbed Au/O/Ti5c oxygen species functions as an electron reservoir, and it lowers the oxygen vacancy formation energy of a surface lattice oxygen (Obri), as well as the Ti interstitial formation energy, due to electron transfer from high-energy defect states to low-energy p-states of the adsorbed Au/O/Ti5c oxygen species. Hence, the Obri species is activated at the oxidized Au/TiO2 interface boundary and the energy barrier of CO oxidation with Obri is calculated to be 0.55 eV. Thus, the CO oxidation reaction can proceed at room temperature either via a Langmuir–Hinshelwood mechanism with an adsorbed Au/O/Ti5c oxygen species or via a Au-assisted Mars–van Krevelen mechanism with Obri.Keywords: Au/TiO2; CO oxidation; density functional theory; gold catalysis; heterogeneous catalysis

The alloy-core@shell nanoparticle structure combines the advantages of a robust noble-metal shell and a tunable alloy-core composition. In this study we demonstrate a set of linear correlations between the binding of adsorbates to the shell and the alloy-core composition, which are general across a range of nanoparticle compositions, size, and adsorbate molecules. This systematic tunability allows for a simple approach to the design of such catalysts. Calculations of candidate structures for the hydrogen evolution reaction predict a high activity for the PtRu@Pd structure, in good agreement with what has been reported previously. Calculations of alloy-core@Pt 140-atom nanoparticles reveal new candidate structures for CO oxidation at high temperature, including Au0.65Pd0.35@Pt and Au0.73Pt0.27@Pt, which are predicted to have reaction rates 200 times higher than that of Pt(111).Keywords: alloy-core/shell; binding energy; catalyst design; CO oxidation; hydrogen evolution; nanoparticles

The Prussian Blue analog, NaxFeMn(CN)6, is a potential new cathode material for Na-ion batteries. During Na intercalation, the dehydrated material exhibits a monoclinic to rhombohedral phase transition, while the hydrated material remains in the monoclinic phase. With density functional theory calculations, the phase transition is explained in terms of a competition between Coulomb attraction, Pauli repulsion, and d–π covalent bonding. The interstitial Na cations have a strong Coulomb attraction to the N anions in the host material, which tend to bend the Mn–N bonds and reduce the volume of the structure. The presence of lattice H2O enhances the Pauli repulsion so that the volume reduction is suppressed. The calculated volume change, as it depends upon the presence of lattice H2O, is consistent with experimental measurements. Additionally, a new LiFeMn(CN)6 phase is predicted where MnN6 octahedra decompose into LiN4 and MnN4 edge-sharing tetrahedra.

We present a method for quantifying the accuracy of extended X-ray absorption fine structure (EXAFS) fitting models. As a test system, we consider the structure of bare Au147 nanoparticles as well as particles bound with thiol ligands, which are used to systematically vary disorder in the atomic structure of the nanoparticles. The accuracy of the fitting model is determined by comparing two distributions of bond lengths: (1) a direct average over a molecular dynamics (MD) trajectory using forces and energies from density functional theory (DFT) and (2) a fit to the theoretical EXAFS spectra generated from that same trajectory. Both harmonic and quasi-harmonic EXAFS fitting models are used to characterize the first-shell Au–Au bond length distribution. The harmonic model is found to significantly underestimate the coordination number, disorder, and bond length. The quasi-harmonic model, which includes the third cumulant of the first-shell bond length distribution, yields accurate bond lengths, but incorrectly predicts a decrease in particle size and little change in the disorder with increasing thiol ligands. A direct analysis of the MD data shows that the particle surfaces become much more disordered with ligand binding, and the high disorder is incorrectly interpreted by the EXAFS fitting models. Our DFT calculations compare well with experimental EXAFS measurements of Au nanoparticles, synthesized using a dendrimer encapsulation technique, showing that systematic errors in EXAFS fitting models apply to nanoparticles 1–2 nm in size. Finally we show that a combination of experimental EXAFS analysis with candidate models from DFT is a promising strategy for a more accurate determination of nanoparticle structures.Keywords: Au nanoparticles; density functional theory; extended X-ray absorption fine structure; structural disorder;

A set of benchmark systems is defined to compare different computational approaches for characterizing local minima, transition states, and pathways in atomic, molecular, and condensed matter systems. Comparisons between several commonly used methods are presented. The strengths and weaknesses are discussed, as well as implementation details that are important for achieving good performance. All of the benchmarks and methods are provided in an online database to make the implementation details available and the results reproducible. While this paper provides a snapshot of the benchmark results, the online framework is structured to be dynamic and incorporate new methods and codes as they are developed.

Density functional theory calculations reveal that the work function of Au supported on MgO(001) is substantially reduced because of an interfacial dipole moment formed at the Au/MgO interface. Consequently, the Au/MgO interface plays an active role in the activation of O2 molecules by promoting charge transfer to the O2 2π* orbital. The presence of F-centers in the MgO substrate can further promote the charge transfer and bonding of O2 at the interface boundary. However, O2 dissociation is kinetically hindered. The system is then able to catalyze CO oxidation at low temperature as adsorbed CO and O2 readily react to form CO2 with a low energy barrier.

In this study, we present a framework for characterizing the structural and thermal properties of small nanoparticle catalysts by combining precise synthesis, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) calculations. We demonstrate the capability of this approach by characterizing the atomic structure and vibrational dynamics of Au147. With the combination of EXAFS spectroscopy and DFT, the synthesized Au147 nanoparticles are determined to have an icosahedral structure. A decrease in the Einstein temperature of the Au147 particles compared to their bulk value was observed and interpreted in terms of softer vibration modes of surface bonds.