Stefano Fabris

• PhD
• Italian National Research Council

Methane is a valuable resource and its valorization is an important challenge in heterogeneous catalysis. Here it is shown that CeO2/CuO composite prepared by ball milling activates methane at a temperature as low as 250 °C. In contrast to conventionally prepared catalysts, the formation of partial oxidation products such as methanol and formaldehy...

Single atom catalysis (SAC) represents an emerging area of heterogeneous catalysis but faces challenges related to the low density of active sites and poor thermal stability. In this work, we...

The oxygen evolution reaction (OER) plays a crucial role in (photo)electrochemical devices that use renewable energy to produce synthetic fuels. Recent measurements on semiconducting oxides have found a power law dependence of the OER rate on surface hole density, suggesting a multihole mechanism. In this study, using transient photocurrent measure...

Single-atom catalysts represent an essential and ever-growing family of heterogeneous catalysts. Recent studies indicate that besides the valuable catalytic properties provided by single-atom active sites, the presence of single-atom sites on the catalyst substrates may significantly influence the population of supported metal nanoparticles coexist...

Heterogeneous catalysts based on Pt nanoparticles supported on oxides are used in a number of important catalytic processes, including oxidation of hydrocarbons and redox reactions in PEM fuel cells. The interaction with gas-phase oxygen is often a key component of the target chemistry and can affect the reactivity of the clusters because of their...

CuFeO2 is a p-type semiconductor that has been recently identified as a promising photocathode material for photoelectrochemical water splitting. CuFeO2 can absorb solar light and promote the hydrogen evolution reaction (HER), even though the photocurrents achieved so far are still well below the theoretical upper limit. While several experimental...

The cuprous delafossite, CuFeO2, has received significant attention in recent years as a potential photocathode material in photoelectrochemical water-splitting cells. Presented herein is an investigation of the electronic structure of CuFeO2 in the framework of density functional theory. We have benchmarked three of the most popular formulations f...

Materials based on regular π-stacks of planar organic radicals are intensively pursued by virtue of their technologically relevant properties. Yet, these π-stacks are commonly unstable against π-dimerization. In this computational study, we reveal that regular π-stacks of planar dithiazolyl radicals can be rendered stable, in some range of temperat...

CuFeO2 has been recently identified as a promising photocathode material for photoelectrochemical water splitting cells. In spite of the first encouraging results, improvements in the catalytic activity and charge separation are required and an adequate theoretical characterization is currently not available to complement experimental results. We p...

Quantitative assessment of the charge transfer phenomena in cobalt oxides and cobalt complexes is essential for the design of advanced catalytic materials. We propose a method for the evaluation of the oxidation state of cobalt oxides with mixed valence states using resonant photoemission spectroscopy. The method is based on the calculation of the...

Ceria represents a technologically indispensable reducible catalyst support. Besides the general impact on the surface chemistry, the oxygen content of the ceria surface directly influences the dispersion of ceria-supported metal nanoparticles, and the properties of ceria-supported metal catalysts. We investigate the role of oxygen atoms on a CeO2(...

Cu/CeO 2 catalysts are highly active for the low-temperature water–gas shift—a core reaction in syngas chemistry for tuning the H 2 /CO/CO 2 proportions in feed streams—but the direct identification and quantitative description of the active sites remain challenging. Here we report that the active copper clusters consist of a bottom layer of mainly...

Here, we show that the electronic properties of a surface-supported 2-dimensional (2D) layer structure can be self-texturized at the nanoscale. The local electronic properties are determined by structural relaxation processes through variable adsorption stacking configurations. We demonstrate that the spatially modulated layer-buckling, which arise...

Supported Pt nanoparticles are key components in heterogeneous catalysis for energy and environment applications that involve vapour and wet conditions. In the latter case, the reaction proceeds at the catalyst-water interface where the solvent actively participates in the reaction mechanism. In this work, ab initio molecular dynamics simulations s...

Single atom catalysts represent the ultimate extreme in heterogeneous catalysis for maximum dispersion of mononuclear catalytic metal particles on supporting surfaces. Ultra-low Pt loading has been achieved on nanostructured ceria surfaces that allow for stabilizing metallic and ionic Pt sites that are anchored at surface defects. Here we assess th...

Reactions of reduced cerium oxide CeOx with water are fundamental processes omnipresent in ceria-based catalysis. Using thin epitaxial films of ordered CeOx, we investigate the influence of oxygen vacancy concentration and coordination on the oxidation of CeOx by water. Upon changing the CeOx stoichiometry from CeO2 to Ce2O3, we observe a transitio...

Here, we show that the electronic properties of a surface-supported 2-dimensional (2D) layer structure can be self-texturized at the nanoscale. The local electronic properties are determined by structural relaxation processes through variable adsorption stacking configurations. We demonstrate that the spatially modulated layer-buckling, which arise...

The concept of single atom catalysis offers maximum noble metal efficiency for the development of low-cost catalytic materials. Among possible applications are catalytic materials for proton exchange membrane fuel cells. In the present review, recent efforts towards the fabrication of single atom catalysts on nanostructured ceria and their reactivi...

The electronic properties and surface structures of K-doped graphene supported on Ir(111) are characterized as a function of temperature and coverage by combining low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory (DFT) calculations. Deposition of K on graphene at room temperature (RT) yields a...

Wet conditions in heterogeneous catalysis can substantially improve the rate of surface reactions by assisting the diffusion of reaction intermediates between surface reaction sites. The atomistic mechanisms under- pinning this accelerated mass transfer are however con- cealed by the complexity of the dynamic water/solid in- terface. Here we employ...

We conduct first principles calculations to study oxygen diffusion on the graphene surface as a function of temperature up to 3000K. The minimum energy migration path and the corresponding activation energy are determined by the nudged elastic band method with explicit inclusion of thermal electronic excitations. Below 1000K the activation energy f...

The reactivity of atomically dispersed Pt2+ species on the surface of nanostructured CeO2 films and the mechanism of H2 activation on these sites have been investigated by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy in combination with density functional calculations. Isolated Pt2+ sites are fou...

Single-atom catalysts maximize the utilization of supported precious metals by exposing every single metal atom to reactants. To avoid sintering and deactivation at realistic reaction conditions, single metal atoms are stabilized by specific adsorption sites on catalyst substrates. Here we show by combining photoelectron spectroscopy, scanning tunn...

Supplementary Figures 1-7, Supplementary Tables 1-2, Supplementary Note 1, Supplementary Discussion and Supplementary References

The electronic metal-substrate interaction plays an important role in the surface reactions on supported metal nanoparticles. We study the interaction between rhodium clusters and cerium oxide substrate having various stoichiometries, CeOx (2.00 > x > 1.67), by means of photoelectron spectroscopy. Our results show that rhodium deposited on substrat...

Electronic interactions between metal nanoparticles and oxide supports control the functionality of nanomaterials, for example, the stability, the activity and the selectivity of catalysts. Such interactions involve electron transfer across the metal/support interface. In this work we quantify this charge transfer on a well-defined platinum/ceria c...

Insulating hexagonal boron nitride monolayers (hBN) are best known for being resistant to chemical functionalization. This property makes hBN an excellent substrate for graphene heterostructures, but limits its application as an active element in nanoelectronics where tunable electronic properties are needed. Moreover, the two-dimensional-materials...

Water oxidation is efficiently catalyzed by several Ru-based polyoxometalate (POM) molecular catalysts differing in the number, local atomistic environment and oxidation state of the Ru sites. We employ density functional theory calculations to rationalize the dependency of the reaction overpotential on the main structural and electronic molecular...

The hydroxylation of oxide surfaces driven by molecular H2 dissociation plays a central role in a wide range of catalytic redox reactions. The high reducibility and oxygen storage capacity of ceria (CeO2) surfaces account for its extensive use as active catalyst support in these redox reactions. By means of ab initio molecular dynamics simulations,...

We study alkali-metal adsorption on supported graphene by means of density-functional-theory calculations that include dispersion corrections. Graphene supported by the Au/Ni(111) surface is an important system for fundamental studies because this surface allows one to support graphene, preserving the electronic properties of freestanding graphene....

The chemistry of several catalytic processes can be controlled by tuning metal-oxide interfaces, as demonstrated by fundamental studies on inverse model catalysts. We investigate the effects of the metal-oxide interface on the surface reactivity of ceria (CeO2) thin films supported by a copper metal surface. Our density functional theory (DFT+U) ca...

We study subnanometer (sub-nm) Pt clusters supported by highly reducible oxide surfaces and establish the role of cluster morphology in the thermodynamics and kinetics of surface processes relevant for reactivity, namely cluster mobility, reverse oxygen spillover, and oxygen vacancy formation. The relationships between cluster morphology and reacti...

This work assesses the predictive power and capabilities of classical interatomic potentials for describing the atomistic structure of a fully inorganic water-oxidation catalyst in the gas phase and in solution. We address a Ru-polyoxometalate molecule (Ru-POM) that is presently one of the most promising catalysts for water oxidation due to its eff...

We combine classical empirical potentials and density functional theory (DFT) calculations to characterize the catalyst/electrode interface of a promising device for artificial photosynthesis. This system consists of inorganic Ru-polyoxometalate (Ru-POM) molecules that are supported by a graphitic substrate functionalized with organic dendrimers. T...

Some of the most promising catalysts for water oxidation rely on crystalline and amorphous cobalt oxide nanoparticles. Density functional theory (DFT) calculations are routinely used to study the electronic and atomic structures of these materials as well as the thermodynamics and mechanisms of the electrochemical oxygen evolution reaction. The acc...

We investigate, with high-resolution angle-resolved photoemission spectroscopy, the spectral function of potassium-doped quasi-free-standing graphene on Au. Angle-dependent x-ray photoemission and density functional theory calculations demonstrate that potassium intercalates into the graphene/Au interface, leading to an upshift of the K-derived ele...

Density functional theory (DFT) calculations are used to identify correlations among reactivity, structural stability, cohesion, size, and morphology of small Au clusters supported on stoichiometric and defective CeO2(111) surfaces. Molecular adsorption significantly affects the cluster morphology and in some cases induces cluster dissociation into...

The spin and orbital configuration of magnetic metal phthalocyanines (MPcs) deposited on metallic substrates are strongly influenced by the rehybridization of the molecular states with the underlying metal. FePc, CoPc, and CuPc isolated molecules are archetypal systems to investigate the interrelationship between magnetic moments and orbital symmet...

Solar-to-fuel energy conversion relies on the invention of efficient catalysts enabling water oxidation through low-energy pathways. Our aerobic life is based on this strategy, mastered by the natural Photosystem II enzyme, using a tetranuclear Mn-oxo complex as oxygen evolving center. Within artificial devices, water can be oxidized efficiently on...

Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0 0 0 1) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-r...

ABSTRACT: Supramolecular nanostructures with tunable dimensionalities are fabricated by deposition of benzene−carboxylic acids on the Cu(110) surface. By tailoring the number and position of the functional moieties, the structure of the final molecular assemblies can be rationally modified ranging from isolated one-dimensional chains to compact two...

We adopt fringe counting from classical moiré interferometry on moiré patterns observed in scanning tunneling microscopy of strained thin films on single crystalline substrates. We analyze inhomogeneous strain distribution in islands of CeO_{2}(111) on Cu(111) and identify a generic source of strain in heteroepitaxy-a thickness-dependent lattice co...

Solar-driven water splitting is a key photochemical reaction that underpins the feasible and sustainable production of solar fuels. An amorphous cobalt-phosphate catalyst (Co-Pi) based on earth-abundant elements has been recently reported to efficiently promote water oxidation to protons and dioxygen, a main bottleneck for the overall process. The...

Iron-phthalocyanine molecules deposited on the Au(110) reconstructed channels assemble into one-dimensional molecular chains, whose spatial distribution evolves into different structural phases at increasing molecular density. The plasticity of the Au channels first induces an ordered phase with a 5×5 symmetry, followed by a second long-range order...

Water splitting is at the basis of artificial photosynthesis for solar energy conversion into chemical fuels. While the oxidation of water to molecular oxygen and the reduction of protons to molecular hydrogen are typically promoted by different catalysts, the Ru(II)-pincer complex recently synthesized by Kohl et al. [Science2009, 324, 74] has been...

The quasi-particle energy levels of the Zn-Phthalocyanine (ZnPc) molecule calculated with the GW approximation are shown to depend sensitively on the explicit description of the metal-center semicore states. We find that the calculated GW energy levels are in good agreement with the measured experimental photoemission spectra only when explicitly i...

Iron-phthalocyanine (FePc) molecules deposited on the Au(110) surface self-organize in ordered chains driven by the reconstructed Au channels. The interaction process induces a rehybridization of the electronic states localized on the central metal atom, breaking the 4-fold symmetry of the molecular orbitals of the FePc molecules. The molecular ads...

Discontinuous ceria layers on Cu(111) represent heterogeneous catalysts with notable activities in water–gas shift and CO oxidation reactions. Ultrathin ceria islands in these catalysts are composed of monolayers of ceria exhibiting CeO2(111) surface ordering and bulklike vertical stacking (O–Ce–O) down to a single ceria monolayer representing the...

The structural patterns formed by molecular self-assembly at surfaces are usually controlled by the relative strengths of the intermolecular and molecule–substrate interactions. An additional steering effect is present when the substrate can easily reconstruct upon molecular adsorption, which therefore drives a self-templating effect on the metal s...

The high chemical reactivity of unsaturated metal sites is a key factor for the development of novel devices with applications in sensor engineering and catalysis. It is also central in the research for sustainable energy concepts, e.g., the efficient production and conversion of chemical fuels. Here, we study the process of oxygen dissociation by...

We identify mechanisms and surface precursors for the nucleation and growth of extended defects on oxidized graphene. Density functional theory calculations show that the formation of surface structures capable to initiate the unzipping and cracking of the oxidized C network is strongly influenced by the constraint of the graphitic lattice on the s...

The possibility of modifying the intermolecular interactions of absorbed benzene-carboxylic acids from coordination to hydrogen bonding by changing their surface coverage is demonstrated through a combination of scanning tunnelling microscopy, X-ray photoemission spectroscopy and density functional theory calculations.

Graphene is easily produced by thermally reducing graphene oxide. However, defect formation in the C network during deoxygenation compromises the charge carrier mobility in the reduced material. Understanding the mechanisms of the thermal reactions is essential for defining alternative routes able to limit the density of defects generated by carbon...

We present a combined experimental and theoretical study of the ultrathin film of Co-octaethylporphyrin (Co-OEP) molecules deposited on the Ag(110) surface. The morphological and electronic properties of this heterogeneous metallorganic interface were studied by means of scanning tunneling microscopy (STM), near-edge X-ray adsorption fine structure...

The reduction of graphene oxide surfaces yielding molecular CO/CO2 is studied from first principles using density functional theory. We find that this reaction can proceed exothermically only from surface precursors containing more oxygen atoms than strictly needed to produce CO/CO2 in the gas phase. The calculations show that the lowest-energy con...

We present a computational study addressing the catalytic cycle of a recently-synthesized all-inorganic homogeneous catalyst capable to promote water oxidation with low overpotential and high turnover frequency [Sartorel et al., J. Am. Chem. Soc., 2008, 130, 5006; Geletii et al., Angew. Chem., Int. Ed., 2008, 47, 3896]. This catalyst consists of a...

The thermodynamic, structural and electronic properties of Cu-CeO(2) (ceria) surfaces and interfaces are investigated by means of density functional theory (DFT+U) calculations. We focus on model systems consisting of Cu atoms (i) supported by stoichiometric and reduced CeO(2) (111) surfaces, (ii) dispersed as substitutional solid solution at the s...

We report on the formation of chiral domains self-assembled from terephthalic acid (TPA) and iron on a Cu(110) surface. Using scanning tunnelling microscopy, we observe that the supramolecular structures are organized on successive hierarchical levels. Chirality develops only at the latest assembly step, with the primary TPA constituents and the se...

The electronic structure of single and multiple layers of C60 molecules deposited on a Rh(100) surface is investigated by means of valence photoemission spectroscopy and density functional theory calculations. The binding of the fullerene monolayer to the metal surface yields the appearance of a new state in the valence band spectrum crossing the F...

The defect chemistry and electronic structure of NiO/CeO2 solid solutions are studied by means of DFT+U calculations in the limit of low Ni doping. We consider four representative solid solutions in which the Ni atoms are present as substitutional and interstitial point defects in bulk crystalline CeO2, both in its stoichiometric form and in the pr...

The parameters controlling the catalytic activity of oxide-supported Au atoms and clusters are studied by means of density functional theory calculations. CeO2(111) surfaces containing positively charged Au ions, either as supported Au^+ or as substitutional Au^3+ ions, are shown to activate molecular CO and to catalyze its oxidation to CO2 via par...

Water oxidation has been recognized as the key bottleneck toward the development of artificial photosynthesis, where the goal is to use solar energy to produce chemicals for energy conversion and storage. This reaction requires the loss of four electrons and four protons and has a standard reduction potential of 1.23 V (pH=0, NHE). The recent devel...

Aufgelockerte Überstruktur: Ein durch Hocherhitzen einer Lösung synthetisierter Pd/CeO2-Katalysator ist drei- bis fünfmal aktiver bei der CH4-Verbrennung als die besten herkömmlichen Palladiumsysteme. Der Katalysator trägt eine geordnete Pd-O-Ce-Überstruktur auf seiner Oberfläche (siehe Bild; der türkise Pfeil verweist auf ein quadratisch-planar ko...

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation...

Density functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U) reveal the mechanisms for the oxidation of CO catalyzed by isolated Au atoms as well as small clusters in Au/CeO(2) catalysts. Ceria (111) surfaces containing positively charged Au ions, either as supported Au(+) adatoms or as substitu...

The initial oxidation stages of perfect and defective graphitic surfaces exposed to atomic oxygen have been studied with a combined high-resolution photoemission spectroscopy (HR-PES) and density functional theory (DFT) computational approach. The resulting oxygen-containing surface functional groups are identified by analyzing the multicornponent...

QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation...

The electronic structure of isolated bis(phthalocyaninato) terbium(III) molecules, a novel single-molecular-magnet (SMM), supported on the Cu(111) surface has been characterized by density functional theory and scanning tunneling spectroscopy. These studies reveal that the interaction with the metal surface preserves both the molecular structure an...

The electronic, structural, and magnetic properties of Co-based low-dimensional nanostructures supported by Pt surfaces are investigated using computer simulations based on density functional theory. The effects of the local orientation of the magnetization, including the magnetic anisotropy energy, are accounted for within a noncollinear spin-dens...

The limiting steps of CO oxidation catalyzed by ceria via the Mars-van Krevelen reaction mechanism are identified and investigated by means of density functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U). We address the adsorption of CO on the (111) and (110) surfaces, and its oxidation via part...

The adsorption of organic molecules on metal surfaces can lead to complex nanostructuration of the supporting substrate. The precise atomistic and electronic structures of the C60/Au(110) interface are unveiled by combining synchrotron-based diffraction and spectroscopic techniques with density functional theory calculations. We show that the inter...

The adsorption of trimesic acid (TMA) on Cu(110) has been studied in the temperature range between 130 and 550 K and for coverages up to one monolayer. We combine scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), reflection absorption infrared spectroscopy (RAIRS), X-ray photoemission spectroscopy (XPS), and density funct...

The discontinuity in the lattice periodic potential at surfaces often leads to the creation of new electronic surface states. We developed a photoemission based Fermi surface tomography whose surface sensitivity allowed us to quantify the charge redistribution on the Be(0001) surface. The volume enclosed by the bulklike Fermi surface is significant...

The diffusion mechanism of indium atoms along multiwalled carbon nanotubes is studied by means of photoemission spectromicroscopy and density functional theory calculations. The unusually high activation temperature for diffusion (approximately 700 K), the complex C 1s and In 3d5/2 spectra, and the calculated adsorption energies and diffusion barri...

Reversible oxygen release makes ceria (CeO2) among the most efficient oxide supports for low-temperature oxidation reactions. A clear identification of the species responsible for this oxygen buffering is still missing since only indirect information is available. We present a systematic study of O adsorbates on the most stable ceria surfaces based...

The interaction of the (110) and (111) surfaces of ceria (CeO(2)) with atomic hydrogen is studied with ab initio calculations based on density functional theory. A Hubbard U term added to the standard density functional allows to accurately describe the electronic structure of the two surfaces. The minimum energy configuration for the adsorbed H on...

We report scanning tunneling microscopy observations on the formation of 2D Co-based coordination compounds on the reconstructed Au(111) surface. Preorganized arrays of Co bilayer islands are shown to be local reaction sites, which are consumed in the formation of Co-terephthalate aggregates and regular nanoporous grids. The latter exhibit a planar...

In the attempt to understand the structure-dependent characteristics of ceria (CeO2) surfaces with various morphologies (films, nanoparticles, single crystals), we focus on high-resolution scanning tunneling microscopy of a (111) single crystal surface. A new preparation procedure is described that generates one trilayer deep pits on the surface, e...

We address the issues raised in the preceding Comment by discussing the effects of an explicit account of the nonlinear core correction (NLCC) into the Ce pseudopotential employed in our previous calculations of reduced ceria [Phys. Rev. B 71, 041102(R) (2005)]. At the plain density-functional-theory (DFT) level, such an account brings our pseudopo...

The atomistic and electronic structures of oxygen vacancies on the (111) and (110) surfaces of ceria are studied by means of periodic density functional calculations. The removal of a neutral surface oxygen atom leaves back two excess electrons that are shown to localize on two cerium ions neighboring the defect. The resulting change of valency of...

Line them up: Metal-organic chains (see scanning tunneling microscopy image) have been created in situ by self-organized growth at a metal surface under ultrahigh vacuum. These 1D arrangements of metal centers (Fe, Cu), regularly spaced by organic linkers such as trimesitylic acid, open new possibilities for the study of low-dimensional magnetism....

The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subs...

Modeling multiple-valence compounds using density-functional theory has long been considered a formidable task due to the role that strong electronic correlations play in these systems. We show that, in the case of defective ceria, the main effect of these correlations is to produce a multitude of metastable low-energy states among which the one di...

The electronic and structural properties of pure and defective cerium oxide are investigated using a unified LDA+U approach which allows to treat the different valence states of Ce occurring for different stoichiometries on a same ground, without any {\it a priori} assumptions on the defect chemistry. The method correctly predicts the atomistic and...

The modifications in atomistic structure, chemical bonding, and energetics induced by substitutional cation impurities isolated in the bulk volume and segregated at grain boundaries of α-Al2O3 were investigated by combining empirical ionic-model and first-principles electronic-structure calculations. The dependency of these modifications on the bou...

The microscopic mechanism leading to stabilization of cubic and tetragonal forms of zirconia (ZrO$_2$) is analyzed by means of a self-consistent tight-binding model. Using this model, energies and structures of zirconia containing different vacancy concentrations are calculated, equivalent in concentration to the charge compensating vacancies assoc...

The microscopic structure of a prismatic Σ3(101¯0) twin boundary in α-Al2O3 is characterized by combining ab initio local-density-functional theory, electron energy-loss spectroscopy measuring energy-loss near-edge structures (ELNES) of the oxygen K-ionization edge, and high-resolution transmission electron microscopy (HRTEM). Theoretically, two di...