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Funding: J.L.P. thanks the University of St Andrews for funding and the Carnegie Trust for a Research Incentive Grant (RIG008653). The authors also thank EPSRC for funding (EP/T019298/1, EP/R023751/1 and EP/V034138/1). L.K.J. thanks UKRI for a Future Leaders Fellowship (MR/T022094/1). One of the great advantages of organic–inorganic metal halides is that their structures and properties are highly tuneable and this is important when optimizing materials for photovoltaics or other optoelectronic devices. One of the most common and effective ways of tuning the electronic structure is through anion substitution. Here, we report the inclusion of bromine into the layered perovskite [H3N(CH2)6NH3]PbBr4 to form [H3N(CH2)6NH3]PbBr4·Br2, which contains molecular bromine (Br2) intercalated between the layers of corner-sharing PbBr6 octahedra. Bromine intercalation in [H3N(CH2)6NH3]PbBr4·Br2 results in a decrease in the band gap of 0.85 eV and induces a structural transition from a Ruddlesden–Popper-like to Dion–Jacobson-like phase, while also changing the conformation of the amine. Electronic structure calculations show that Br2 intercalation is accompanied by the formation of a new band in the electronic structure and a significant decrease in the effective masses of around two orders of magnitude. This is backed up by our resistivity measurements that show that [H3N(CH2)6NH3]PbBr4·Br2 has a resistivity value of one order of magnitude lower than [H3N(CH2)6NH3]PbBr4, suggesting that bromine inclusion significantly increases the mobility and/or carrier concentration in the material. This work highlights the possibility of using molecular inclusion as an alternative tool to tune the electronic properties of layered organic–inorganic perovskites, while also being the first example of molecular bromine inclusion in a layered lead halide perovskite. By using a combination of crystallography and computation, we show that the key to this manipulation of the electronic structure is the formation of halogen bonds between the Br2 and Br in the [PbBr4]∞ layers, which is likely to have important effects in a range of organic–inorganic metal halides. Publisher PDF

Ni-containing heteropolyvanadate, Na

Surface diffusion is intimately correlated with crystal orientation and surface structure. Fast surface diffusion accelerates phase transformation and structural evolution of materials. Here, through in situ transmission electron microscopy observation, we show that a copper nanowire with dense nanoscale coherent twin-boundary (CTB) defects evolves into a zigzag configuration under electric-current driven surface diffusion. The hindrance at the CTB-intercepted concave triple junctions decreases the effective surface diffusivity by almost 1 order of magnitude. The energy barriers for atomic migration at the concave junctions and different faceted surfaces are computed using density functional theory. We proposed that such a stable zigzag surface is shaped not only by the high-diffusivity facets but also by the stalled atomic diffusion at the concave junctions. This finding provides a defect-engineering route to develop robust interconnect materials against electromigration-induced failures for nanoelectronic devices.

High-entropy-alloy (HEA) nanocrystals consisting of a minimum of five elements have recently emerged as a versatile family of catalysts due to immense chemical space and tunability1-3. However, there are no effective strategies for synthesizing libraries of HEA nanocrystals with controlled surface atomic structures of exposed facets for boosting catalytic performance4-19. Due to the distinct nucleation and growth kinetics of constituent metals and their distinctive crystal structures, it is incredibly challenging to confine five or more different metal species situated on the nanocrystal surface with a specific arrangement but also in a high-entropy random mixing state. Here we present a straightforward strategy to craft a library of facet-controlled HEA nanocrystals with up to ten dissimilar metallic elements (Pt, Pd, Ir, Ru, Rh, Os, Au, Fe, Co, and Ni) by solution-phase layer-by-layer epitaxial growth, enabling the design of 638 distinct catalysts with 5 to 10 elements in equimolar ratios. The subnanometer-thick solid-solution HEA atomic layers can be deposited epitaxially on nanocrystal seeds with {100} and {111} facets, thus achieving HEA shells with square and hexagonal atomic arrangements, respectively. The hollow HEA nanocages with ultrathin walls along a specific direction can be further fabricated via post-synthetic chemical etching. Three facet-dependent catalytic actives of HEA nanocrystals are discovered in electrocatalysis and photocatalysis, and their catalytic facets with real active sites are also identified by in situ synchrotron X-ray absorption spectroscopy and density-functional theory calculations. Our work enables facet engineering in the multi-elemental space and unveils the critical needs for their future development toward catalysis.

Our density functional theory calculations reveals a N2 activation mechanism that explains the different dissociation barriers of N2 on models of unsupported Ru(0001) terraces, Ru B5 sites, and polar MgO(111)-supported Ru B5 homologues.

The lead halide perovskite material has recently drawn significant attention from the scientific community and has been employed as an active layer material for optoelectronic devices with a wide range of applications. Notably, in recent years, organic inorganic lead halide perovskite solar cell devices have reached power conversion efficiencies rivaling those of silicon-based ones. However, to this date environmental stability of these active layer materials has not yet been fully resolved, thereby hindering their commercialization. Recently, the 2D layered Ruddlesden–Popper type perovskite, has emerged as a possible alternative owing to its enhanced stability against the elements. However, despite of this advantage, devices employing this material have not yet matched the efficiency of their 3D counterparts, which can be explained by the possible presence of structural defects. The intertwined defects of 2D perovskites have been reported from experiments; however, there have been no detailed studies on the impacts of these intertwined defects on 2D perovskite. In this work, we performed series of large-scale ab-initio calculations of the intertwined structures and computed the formation energies of n = 1, n = 2 and n = 3 members. Decreasing intertwined structure formation energy with increasing 2D perovskite principle number implies higher stability of intertwined structures with increasing number of inorganic layers, which is consistent with experimental observations. Band structure calculations reveal flat dispersion curves along the a and c directions in the real space, indicating that the exciton transfer is confined to one direction. Hence, the present study revealed the stability of the intertwined defects and their potential impacts to the device performance, suggesting that careful control of the number of principle members is critical for preventing the formation of intertwined structures.

In this study, electronic structure calculations and Bader charge analysis have been completed on the inverse, intermediate, and normal spinel structures of NiCo2O4 in both primitive and conventional cells, using density functional theory with Hubbard U correction. Three spinel structures have been computed in the primitive cell, where the fully inverse spinel, 50% intermediate spinel, and normal spinel can be acquired by swapping Ni and Co atoms on tetrahedral and octahedral sites. Furthermore, NiCo2O4 with different degrees of inversion in the conventional cells was also investigated, along with their doping energies. Confirmed by the assigned formal charges, magnetic moments, and decomposed density of state, our results suggest that the electronic properties of Ni and Co on the tetrahedral site can be altered by swapping Ni and Co atoms, whereas both Ni and Co on the octahedral site are uninfluenced. A simple and widely used model, crystal field theory, is also compared with our calculations and shows a consistent prediction about the cation distribution in NiCo2O4. This study analyzes the correlation between cation arrangements and formal charges, which could potentially be used to predict the desired electronic properties of NiCo2O4 for various applications.

White and gray Ta2O5 powders were fabricated by sol-gel and then annealed at 850 °C in air and vacuum, respectively. Analyses by Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, electron paramagnetic resonance spectroscopy, UV-visible reflectance spectroscopy, photoluminescence spectroscopy, and density functional theory calculations indicated that oxygen vacancies are formed on the surface of gray Ta2O5, resulting in a disordered shell and more absorption of visible light. Its surface concentration ratio of oxygen to tantalum was determined to be 2.31. It generated 48% higher photocatalytic hydrogen than that of the white one, and cycling test indicated that it remained stable during 12 h irradiation. It also exhibited higher incident photon-to-current conversion efficiency than that of white Ta2O5 in the wavelength range of 300–600 nm.

A comparative study of the hydrogen spillover phenomenon on pristine graphene and anatase (101)-supported Pt4 catalysts has been carried out by using density functional theory with Hubbard correcti...

Scanning tunneling microscopy and spectroscopy experiments under ultrahigh vacuum and low-temperature conditions have been performed on water-intercalated graphene on Pt(111). We find that the confined water layer, with a thickness around 0.35 nm, induces a strong hole doping in graphene, i.e., the Dirac point locates at round 0.64 eV above the Fermi level. This can be explained by the presence of a single "puckered bilayer" of ice-Ih, which has not been experimentally found on bare Pt(111), being confined in between graphene and Pt(111) surface. Moreover, the water intercalation makes graphene highly decoupled from the substrate, allowing us to reveal the intrinsic graphene phonons and double Rydberg series of even and odd symmetry image-potential states. Our work not only demonstrates that the electronic properties of graphene can be tuned by the confined water layer between graphene and the substrate, but also provides a generally applicable method to study the intrinsic properties of graphene as well as of other supported two-dimensional materials.

Hydrogen spillover is the phenomenon where a hydrogen atom, generated from the dissociative chemisorption of dihydrogen on the surface of a metal species, migrates from the metal to the catalytic support. This phenomenon is regarded as a promising avenue for hydrogen storage, yet the atomic mechanism for how the hydrogen atom can be transferred to the support has remained controversial for decades. As a result, the development of catalytic support for such a purpose is only limited to typical reducible oxide materials. Herein, by using a combination of in situ spectroscopic and imaging technique, we are able to visualize and observe the atomic pathway for which hydrogen travels via a frustrated Lewis pair that has been constructed on a nonreducible metal oxide. The interchangeable status between the hydrogen, proton, and hydride is carefully characterized and demonstrated. It is envisaged that this study has opened up new design criteria for hydrogen storage material.

The structural, energetic and electronic structure properties of stoichiometric and nonstoichiometric slab models of bare MgO(111) and Ru/MgO(111) with different coverages of 1 monolayer (ML), 1/4 ML and 1/16 ML have been investigated using spin-polarized density functional theory. Calculated results show that the structural, energetic properties and charge transfer of both bare MgO(111) and Ru/MgO(111) are independent of the stoichiometric and nonstoichiometric models. In contrast, their density of state (DOS) profiles demonstrate metal and half-metal characters for the stoichiometric and nonstoichiometric bare MgO(111) surfaces, respectively. The Ru–O orbital coupling characters of these two types of Ru/MgO(111) models are also different. This work indicates that for a polar surface model, the calculated features and trends of the structural and energetic properties, charge distributions and magnetic structures might not be affected by their stoichiometric and nonstoichiometric models; however, the detailed features of their DOS features would strongly depend on the models constructed.

In this paper, a modified Cyclotriveratrylene was synthesized and linked to a branched Polyethylenimine, and this unique polymeric material was subsequently examined as a potential supramolecular carrier for Doxorubicin. Spectroscopic analysis in different solvents had shown that Doxorubicin was coordinated within the hollow-shaped unit of the armed Cyclotriveratrylene, and the nature of the host&ndash, guest complex revealed intrinsic Van der Waals interactions and hydrogen bonding between the host and guest. The strongest interaction was detected in water because of the hydrophobic effect shared between the aromatic groups of the Doxorubicin and Cyclotriveratrylene unit. Density functional theory calculations had also confirmed that in the most stable coordination of Doxorubicin with the cross-linked polymer, the aromatic rings of the Doxorubicin were localized toward the Cyclotriveratrylene core, while its aliphatic chains aligned closer with amino groups, thus forming a compact supramolecular assembly that may confer a shielding effect on Doxorubicin. These observations had emphasized the importance of supramolecular considerations when designing a novel drug delivery platform.

The free-standing Au20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au20 clusters are obtained. We demonstrate that individual size-selected Au20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au20n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size. ispartof: SCIENCE ADVANCES vol:6 issue:1 ispartof: location:United States status: published

The high cost of oxygen reduction reaction (ORR) catalysts is a critical hurdle to fuel cell commercialization. In an effort to develop low-cost ORR catalysts with low noble-metal loading but high activity and stability, we designed model catalysts of small Pt3 clusters-decorated core–shell structures (e.g. Co or Ni as the core, Pd as the shell) by tuning the shell thickness, calculated by density functional theory (DFT). We found that incorporation of Pt3 into the bimetallic surface is more stable than adsorption of Pt3 on the surface. Additionally, the magnitude of atomic oxygen adsorption of our model catalysts depends on their adsorption sites and Pd thickness. Small Pt3-decorated Co@Pd and Ni@Pd model core–shell catalysts with exact monolayers of Pd are expected to exhibit high ORR activity based on their moderate atomic oxygen adsorption energies on various stable active sites, −0.57 to −0.93 and −0.53 to −0.96 eV, and moderate O2 dissociation reaction barriers, 0.74 to 0.87 and 0.59 to 0.72 eV. The d-band centers (ed) of selected model catalysts were computed; the outcomes reveal that the ed values of the optimum model catalysts are close to that of pure Pt(111) and fall around the top of the volcano plot, further demonstrating that high ORR activity should be expected.

Nanocatalysts (NCs) with Co core–Pd shell structures and surface decoration of atomic scale Pt clusters (namely Co@Pd–Pt) are synthesized by using a self-aligned wet chemical reduction method in carbon nanotube supports. The Co@Pd–Pt contains ∼2.48 at% Pt metal. It shows a 30.2-fold mass activity (2056.3 mA mg−1) of the Pt metal as compared to that of commercial Pt catalysts (67.1 mA mg−1) at 0.85 volt (vs. RHE) and shows an exceptional stability of retained current density of ∼100% vs. the initial ones in an accelerated degradation test (ADT) for over 310k cycles in an alkaline electrolyte. The results of structural characterization and electrochemical analyses reveal that the high current density with substantial stability in the ORR is attributed to a strong electronic coupling and interface lattice that extract electrons from Co and Pd atoms in the presence of atomic Pt clusters in the Pd shell. A worth noticing finding is that such exceptional electrochemical performances are developed in a novel composition window in which Pt atoms are mostly positioned in defect sites of the Pd–Co interface in the shell region.

Single-atom catalysts have attracted attention in the past decade since they maximize the utilization of active sites and facilitate the understanding of product distribution in some catalytic reactions. Recently, this idea has been extended to single-atom nanozymes (SAzymes) for the mimicking of natural enzymes such as horseradish peroxidase (HRP) often used in bioanalytical applications. Herein, it is demonstrated that those SAzymes without constructing the reaction pocket of HRP still undergo the OH radical-mediated pathway like most of the reported nanozymes. Their positively charged single-atom centers resulting from support electronegative oxygen/nitrogen hinder the reductive conversion of H2 O2 to OH radicals and hence display low activity per site. In contrast, it is found that this step can be facilitated over their metallic counterparts on cluster nanozymes with much higher site activity and atom efficiency (cf. SAzymes with 100% atom utilization). Besides the mimicking of HRP in glucose detection, cluster nanozymes are also demonstrated as a better oxidase mimetic for glutathione detection.

Using DFT+U calculations with inclusion of van-der-Waals (vdW) forces, we studied CO2 activation and the initial steps of CO2 hydrogenation over Cu10 and Ru10 clusters supported on the TiO2 anatase (101) surface. CO2 is readily adsorbed and activated on the Ru cluster where direct CO2 dissociation proceeds with a barrier of 0.8eV. When H atoms are co-adsorbed on the Ru cluster, H-addition to CO2 becomes preferred, as the best Ru sites for CO2 dissociation are blocked. A H atom is added to the CO2 molecule with formation of a formate [HCOO] species and an activation barrier of 1.2eV. On Cu10/TiO2, only weak adsorption modes of the CO2 molecule are found, whereas H2 readily adsorbs on the Cu cluster. A reduction of the titania support does not significantly change this picture. Therefore, the only viable pathway for the CO2 hydrogenation over Cu10/TiO2 is the addition of a pre-adsorbed H atom to CO2 coming from the gas phase. This corresponds to an Eley–Rideal mechanism for the H-association to CO2. The work shows the importance to consider the hydrogen coverage on the metal cluster as an important variable in modeling the CO2 hydrogenation reaction. Graphical Abstract: [Figure not available: see fulltext.].

In this report, the substitution of the oxygen group (=O) of Tetraphenylcyclopentadienone with =CR2 group (R = methyl ester or nitrile) was found to have tuned the electro-optical properties of the molecule. Although both groups are electrons withdrawing in nature, their absorption from UV-vis spectra analysis was observed to have been blue-shifted by methyl ester substitution and red-shifted by nitrile substitution. Interestingly, these substitutions helped to enhance the overall intensity of emission, especially in the context of methyl ester substitution whereby the emission was significantly boosted at higher concentrations due to hypothesized restrictions of intramolecular motions. These observations were explained through detailed descriptions of the electron withdrawing capability and steric properties of the substituents on the basis of density functional theory calculations.

Pyramidal Au20 clusters are intactly deposited and visualized at the single cluster level., The free-standing Au20 cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital–lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The “magic” Au20 has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au20 clusters are obtained. We demonstrate that individual size-selected Au20 on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au20n agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size.

We have performed a comparative study of the acid–base characteristics of the surfaces of anatase TiO2 and tetragonal ZrO2. To this end we performed DFT + U calculations on CO and CO2 probe molecules adsorbed both on terraces and steps of the two oxides. For titania, CO adsorption results in a moderate adsorption energy (about − 0.3 eV) and in a positive shift of the [Formula presented] stretching frequency (about + 40 cm− 1), typical of Lewis acid sites, with no clear difference in the acidity between terraces or steps. For zirconia we found a similar CO binding energy as for titania, and a CO vibrational shift that depends on the location of the Zr cation: negligible on terraces, similar to TiO2 on steps. We conclude that the acidic properties are similar in the two oxide surfaces. Things are different for CO2 adsorption. On titania the interaction is weak and surface carbonates compete with physisorbed CO2, indicating a weak basic character. On the contrary, on zirconia three types of stable carbonates have been identified. Their vibrational frequencies are consistent with IR measurements reported in the literature. The most stable species forms on steps of the t-ZrO2 surface and consists of a CO32 − unit which lies flat on the surface with the O atoms pointing towards three Zr ions. The species forms spontaneously by extraction of a lattice oxygen by an incoming CO2 molecule. The different reactivity points towards a much more pronounced basic character of zirconia compared to titania, at least if measured by CO2 adsorption.

The deoxygenation of phenol on stoichiometric and reduced Ru10/TiO2 anatase (1 0 1) surfaces has been studied by using DFT with the Hubbard correction (DFT+U). If the molecule orients with the OH group towards the metal–oxide interface, the direct deoxygenation of phenol can occur. However, on the stoichiometric TiO2 surface, the reaction is thermodynamically unfavorable. Two kinds of reduced surfaces have been considered: one in which Ti3+ centers are generated by hydrogen addition, and a second one in which a water molecule is removed from a hydroxylated surface with the formation of O vacancies and Ti3+ centers. On the surface reduced by hydrogen addition (Ti3+ ions), the phenol molecular and dissociative adsorptions (C6H5+OH fragments) become isoenergetic; the barrier to dissociate the C−OH bond is 1.19 eV, which indicates a possible channel for the deoxygenation of phenol. On the surface reduced by O vacancies, the dissociative adsorption is 0.22 eV more stable than the molecular adsorption, which indicates a thermodynamically favorable process; however, the C−OH activation energy is higher, 1.50 eV. The results show that the C−O scission can be an important step towards the direct deoxygenation. The reduction of the surface facilitates the direct deoxygenation of phenol significantly.

Membranes and their size-selective filtering properties are universal in nature and their behavior is exploited to design artificial membranes suited for, e.g., molecule or nanoparticle filtering and separation. Exploring and understanding penetration and transmission mechanisms of nanoparticles in thin-film systems may provide new opportunities for size selective deposition or embedding of the nanoparticles. Here, we demonstrate an unexpected finding that the sieving of metal nanoparticles through atomically thin nonporous alkali halide films on a metal support is size dependent and that this sieving effect can be tuned via the film thickness. Specifically, relying on scanning tunneling microscopy and spectroscopy techniques, combined with density functional theory calculations, we find that defect-free NaCl films on a Au(111) support act as size-dependent membranes for deposited Au nanoclusters. The observed sieving ability is found to originate from a driving force toward the metal support and from the dynamics of both the nanoparticles and the alkali halide films.

Stable and low-cost carbon dots (C-dots) were prepared from polyethylenimine (PEI) by a hydrothermal method. It is found that the fluorescence of the C-dots (best measured at excitation/emission wavelengths of 365/473 nm) is quenched by selective oxidation of surface PEI by periodate but recovers in the presence of uric acid (UA). It is assumed that this is due to the selective reduction of the nitrone groups to hydroxylamine groups by UA. The findings were used to design a fluorometric method for determination of UA that has a 2.3 nM detection limit. This is lower than that of reported fluorometric and enzymatic assays. The performance of the method has been validated by determination of UA in samples of human saliva. It is found that the results agree well with those obtained by a commercial UA assay. Graphical abstract Schematic presentation of the polyethylenimine (PEI) carbon nanodots (C-dots) as a fluorescent probe for uric acid. Their fluorescence is quenched by periodate (IO

A series of iron-doped nickel cobalt oxide/activated carbon (Fe0.1Ni0.9Co2O4/AC) composites with various ratios of activated carbon were synthesised via a microwave-assisted hydrothermal method. The introduction of activated carbon significantly promotes the catalytic activity of Fe0.1Ni0.9Co2O4 for the oxygen evolution reaction (OER); meanwhile the complete coverage of nanoparticulate Fe0.1Ni0.9Co2O4 onto activated carbon particles prevents the carbon oxidation, leading to improved cycling durability of a zinc-air cell. Scanning electron microscopy images shows a good protective coverage of the nanoparticulate Fe0.1Ni0.9Co2O4 onto the activated carbon particles. Rotating disk electrode voltammetry and electrochemical impedance spectroscopic results reveal that the OER overpotential and charge-transfer resistance of the Fe0.1Ni0.9Co2O4 electrocatalyst are substantially lowered by the introduction of activated carbon. With respect to the cycling stability, Fe0.1Ni0.9Co2O4/1.0 wt%AC and Fe0.1Ni0.9Co2O4/1.5 wt%AC composites maintain excellent activity for 80 h in a rechargeable zinc-air battery, due to the uniformly protective coverage of metal oxide on activated carbon. Furthermore, the Fe0.1Ni0.9Co2O4/3.7 wt%AC composite was examined in a prolonged rechargeable zinc-air battery test for 120 h and the charge-discharge voltage gap was negligibly enlarged (0.02 V increment after 120 h), which showed their potential as electrocatalysts for long-term energy storage systems.

It is generally assumed that low-coordinated sites at extended defects of oxide surfaces like steps or edges are more reactive than the regular, fully coordinated sites at the flat terraces. In this work we have considered the properties of stepped surfaces of anatase TiO2 and tetragonal ZrO2 by means of periodic DFT+U calculations. For both oxides, the stability of oxygen vacancies located near the step edges is compared to that of the same defects at the regular terraces. The capability of the steps to induce nucleation of metal nanoparticles on the surface has been evaluated by simulating the adsorption of a single ruthenium adatom. We conclude that, for anatase, step edges have no particular role in favouring the reduction of the oxide by reducing the cost for oxygen abstraction; in the same way, there is no special role of the stepped anatase surface in stabilizing adsorbed Ru atoms. On the contrary, step edges on zirconia display some capability to stabilise oxygen vacancies and ruthenium adatoms.

Dehydroxylated, hydroxylated and hydrated anatase TiO2 samples have been exposed to acetylene at room temperature. The interaction leads to the formation of polycyclic aromatic hydrocarbons (PAHs) and is accompanied by the appearance of Ti3+ ions, as shown by electron paramagnetic resonance (EPR) spectra. Fully or partly dehydroxylated samples show higher reactivity, whereas the hydrated samples are chemically inert. The experimental results point towards a crucial role of the more reactive (001) facets of anatase nanoparticles. Density functional theory calculations show that acetylene physisorbs on the anatase (101) surface without activation of the C-H bond. The reduced (101) surface (O vacancies) leads to acetylene activation but not to dissociative adsorption. In contrast, the dehydroxylated (001) anatase surface is very active and leads to the spontaneous splitting of the C-H bond with formation of Ti-C2H and OH groups. This is followed by subsequent additions of C2H2 molecules with formation of PAHs. During the dissociation of C2H2, radical species do not form and electrons are not transferred to the surface because direct Ti-C covalent bonds form on the surface. However, the ring closure in the formation of the aromatic compounds leaves behind hydrogen atoms that donate their valence electrons to the oxide. This results in the appearance of EPR-active Ti3+ centres. On the surface of things: Acetylene oligomerisation occurs on the surface of anatase TiO2 leading to the formation of polycyclic aromatic hydrocarbons and a reduced titania surface. The mechanism of the reaction has been elucidated by EPR measurements and DFT calculations (see figure).

The mechanism of imine reduction by formic acid with a single-site iridicycle catalyst has been investigated by density functional theory (DFT), NMR spectroscopy, and kinetic measurements. The NMR and kinetic studies suggest that the transfer hydrogenation is turnover-limited by the hydride formation step. The calculations reveal that, amongst a number of possibilities, hydride formation from the iridicycle and formate probably proceeds by an ion-pair mechanism, whereas the hydride transfer to the imino bond occurs in an outer-sphere manner. In the gas phase, in the most favourable pathway, the activation energies in the hydride formation and transfer steps are 26-28 and 7-8 kcal mol(-1) , respectively. Introducing one explicit methanol molecule into the modelling alters the energy barrier significantly, reducing the energies to around 18 and 2 kcal mol(-1) for the two steps, respectively. The DFT investigation further shows that methanol participates in the transition state of the turnover-limiting hydride formation step by hydrogen-bonding to the formate anion and thereby stabilising the ion pair.

The scope of this work is to study at atomistic level the mechanism of hydrogen spillover promoted by metal particles on oxide surfaces. By means of Density Functional Theory calculations with Hubbard correction (DFT+U) we have analyzed the adsorption and dissociation of molecular hydrogen on anatase titania, a-TiO2 (101), and tetragonal zirconia, t-ZrO2 (101), surfaces in the presence of a supported Ru10 nanocluster. The role of the supported metal particle is essential as it favors the spontaneous dissociation of H2, a process which does not occur on the bare oxide surface. At low hydrogen coverage, the H atoms prefer to stay on the Ru10 particle, charge accumulates on the metal cluster, and reduction of the oxide does not take place. On a hydroxylated surface, the presence of a Ru nanoparticle is expected to promote the reverse effect, i.e. hydrogen reverse spillover from the oxide to the supported metal. It is only at high hydrogen coverage, resulting in the adsorption of several H2 molecules on the metal cluster, that it becomes thermodynamically favorable to have hydrogen transfer from the metal to the O sites of the oxide surface. In both TiO2 and ZrO2 surfaces the migration of an H atom from the Ru cluster to the surface is accompanied by an electron transfer to the empty states of the support with reduction of the oxide surface.

During the last 20 years, using scanning tunneling microscopy (STM) and atomic force microscopy, scientists have successfully achieved vertical and lateral repositioning of individual atoms on and in different types of surfaces. Such atom manipulation allows the bottom-up assembly of novel nanostructures that can otherwise not be fabricated. It is therefore surprising that controlled repositioning of virtual atoms, i.e., atomic vacancies, across atomic lattices has not yet been achieved experimentally. Here we use STM at liquid helium temperature (4.5 K) to create individual Cl vacancies and subsequently to laterally manipulate them across the surface of ultrathin sodium chloride films. This allows monitoring the interactions between two neighboring vacancies with different separations. Our findings are corroborated by density functional theory calculations and STM image simulations. The lateral manipulation of atomic vacancies opens up a new playground for the investigation of fundamental physical properties of vacancy nanostructures of any size and shape and their coupling with the supporting substrate, and of the interaction of various deposits with charged vacancies.

A ternary metallic CuPdPt nanocatalyst (NC) is synthesized using a wet chemical reduction method, which is sequentially designed, in the presence of acid treated carbon nanotubes. This NC is a nanocrystal with a configuration of a Cu@Pd core and atomic Pt clusters (∼9 wt%) on the top (Cu@Pd/Pt). A residual current of 92.6%, 5.2 times higher than that of commercial Pt catalysts (at 0.85 V vs. RHE), is retained after 40 000 cycles of an accelerated degradation test (ADT). Atomic and electronic structure analyses show that such exclusive stability mainly results from electron localization at Pt clusters in heterogeneous interfaces of the Cu–Pd core. Most importantly, we develop a robust ternary NC, which shows outstanding MA, superior chemical durability, and ∼90 wt% lower Pt loading than commercial Pt NCs in the oxygen reduction reaction.

Mass-selected anionic cobalt clusters of two different sizes (Co2 and Co13) were deposited onto ultrathin NaCl films grown on an Au(111) substrate. Using scanning tunneling microscopy experiments and density functional theory simulations, we show that the deposited Co2 cluster dissociates and that the resulting Co atoms dope the NaCl surface by substituting Na ions. In contrast, the larger Co13 cluster does not dissociate and remains stable on top of the NaCl film. The size-dependent fragmentation of clusters is an important aspect in the understanding of the chemical interaction between size-selected small aggregates of atoms and supporting surfaces. [Figure not available: see fulltext.]