Author
Emiliano Fonda
Other affiliations: University of Wuppertal
Bio: Emiliano Fonda is an academic researcher from University of Trieste. The author has contributed to research in topics: Nanowire & Extended X-ray absorption fine structure. The author has an hindex of 27, co-authored 60 publications receiving 3308 citations. Previous affiliations of Emiliano Fonda include University of Wuppertal.
Papers published on a yearly basis
Papers
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TL;DR: Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis are synthesized, demonstrating that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support.
Abstract: While platinum has hitherto been the element of choice for catalysing oxygen electroreduction in acidic polymer fuel cells, tremendous progress has been reported for pyrolysed Fe-N-C materials. However, the structure of their active sites has remained elusive, delaying further advance. Here, we synthesized Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis. These materials exhibit nearly identical Mossbauer spectra and identical X-ray absorption near-edge spectroscopy (XANES) spectra, revealing the same Fe-centred moieties. However, the much higher activity and basicity of NH3-pyrolysed Fe-N-C materials demonstrates that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support. Following a thorough XANES analysis, the detailed structures of two FeN4 porphyrinic architectures with different O2 adsorption modes were then identified. These porphyrinic moieties are not easily integrated in graphene sheets, in contrast with Fe-centred moieties assumed hitherto for pyrolysed Fe-N-C materials. These new insights open the path to bottom-up synthesis approaches and studies on site-support interactions.
1,561 citations
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TL;DR: It is concluded that cobalt-based moieties bind O2 too weakly for efficient O2 reduction, and nitrogen-doped carbon materials with atomically dispersed iron or cobalt are promising for catalytic use.
Abstract: Single-atom catalysts with full utilization of metal centers can bridge the gap between molecular and solid-state catalysis. Metal-nitrogen-carbon materials prepared via pyrolysis are promising single-atom catalysts but often also comprise metallic particles. Here, we pyrolytically synthesize a Co–N–C material only comprising atomically dispersed cobalt ions and identify with X-ray absorption spectroscopy, magnetic susceptibility measurements and density functional theory the structure and electronic state of three porphyrinic moieties, CoN4C12, CoN3C10,porp and CoN2C5. The O2 electro-reduction and operando X-ray absorption response are measured in acidic medium on Co–N–C and compared to those of a Fe–N–C catalyst prepared similarly. We show that cobalt moieties are unmodified from 0.0 to 1.0 V versus a reversible hydrogen electrode, while Fe-based moieties experience structural and electronic-state changes. On the basis of density functional theory analysis and established relationships between redox potential and O2-adsorption strength, we conclude that cobalt-based moieties bind O2 too weakly for efficient O2 reduction. Nitrogen-doped carbon materials with atomically dispersed iron or cobalt are promising for catalytic use. Here, the authors show that cobalt moieties have a higher redox potential, bind oxygen more weakly and are less active toward oxygen reduction than their iron counterpart, despite similar coordination.
399 citations
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TL;DR: In this article, a Ru-doped ZnIn2S4 catalyst was used to photocatalyse the dehydrogenative C−C coupling of methylfurans, forming both hydrogen and diesel fuel precursors.
Abstract: Photocatalytic hydrogen production from biomass is a promising alternative to water splitting thanks to the oxidation half-reaction being more facile and its ability to simultaneously produce solar fuels and value-added chemicals. Here, we demonstrate the coproduction of H2 and diesel fuel precursors from lignocellulose-derived methylfurans via acceptorless dehydrogenative C−C coupling, using a Ru-doped ZnIn2S4 catalyst and driven by visible light. With this chemistry, up to 1.04 g gcatalyst−1 h−1 of diesel fuel precursors (~41% of which are precursors of branched-chain alkanes) are produced with selectivity higher than 96%, together with 6.0 mmol gcatalyst−1 h−1 of H2. Subsequent hydrodeoxygenation reactions yield the desired diesel fuels comprising straight- and branched-chain alkanes. We suggest that Ru dopants, substituted in the position of indium ions in the ZnIn2S4 matrix, improve charge separation efficiency, thereby accelerating C−H activation for the coproduction of H2 and diesel fuel precursors. Biomass can be used to scavenge photogenerated holes in photocatalytic hydrogen production, but the oxidized molecules that form are not always useful products. Here, the authors use Ru-ZnIn2S4 to photocatalyse the dehydrogenative C−C coupling of lignocellulose-derived methylfurans, forming both hydrogen and diesel fuel precursors.
203 citations
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TL;DR: In this article, the local structure of the M-O bond in CeO2-ZrO2mixed oxides is investigated with the aim of finding a correlation between structural parameters and oxygen exchange properties.
185 citations
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TL;DR: In this paper, the degradation of catalysts induced by H 2 O 2 was investigated by contacting them ex situ with various amounts of H 2 o 2 and showed that the degradation increased with increasing amounts of HO 2 2.
Abstract: 7 8 Fe-N-C and CoN -C materials are promising catalysts for reducing oxygen in fuel cells. The degradation of such catalysts induced by H 2 O 2 was investigated by contacting them ex situ with various amounts of H 2 O 2. The degradation increased with increasing amounts of H 2 O 2. The effect was most severe for Cr-N-C followed by Fe-N-C and last by CoN -C. Treatment with H 2 O 2 leads to diminished oxygen reduction activity at high potential and/or reduced transport properties at high current density in fuel cell. From spectroscopic characterisation, it was found that 66 and 80% of the CoN x C y and FeN x C y moieties present in pristine catalysts survived the extensive H 2 O 2 treatment, respectively. In parallel, the activity for oxygen reduction was divided by ca 6–10 for Fe-N-C and by ca 3 for CoN -C. The results suggest that the main degradation mechanism in fuel cell for such catalysts is due to a chemical reaction with H 2 O 2 that is generated during operation. The super-proportional decrease of the oxygen reduction activity with loss of FeN x C y and CoN x C y moieties suggests either that only a small fraction of such moieties are initially located on the top surface, or that their turnover frequency for oxygen reduction was drastically reduced due to surface oxidation by H 2 O 2 .
144 citations
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01 May 1993
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.
Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.
29,323 citations
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TL;DR: The unique advances on ultrathin 2D nanomaterials are introduced, followed by the description of their composition and crystal structures, and the assortments of their synthetic methods are summarized.
Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...
3,628 citations
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TL;DR: This Review will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities in a unifying manner.
Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...
2,700 citations
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01 Jun 2018TL;DR: A review of single-atom catalysts can be found in this paper, where the authors discuss the utility of SACs in a broad scope of industrially important reactions and highlight the advantages these catalysts have over those presently used.
Abstract: Single-atom catalysis has arguably become the most active new frontier in heterogeneous catalysis. Aided by recent advances in practical synthetic methodologies, characterization techniques and computational modelling, we now have a large number of single-atom catalysts (SACs) that exhibit distinctive performances for a wide variety of chemical reactions. This Perspective summarizes recent experimental and computational efforts aimed at understanding the bonding in SACs and how this relates to catalytic performance. The examples described here illustrate the utility of SACs in a broad scope of industrially important reactions and highlight the advantages these catalysts have over those presently used. SACs have well-defined active centres, such that unique opportunities exist for the rational design of new catalysts with high activities, selectivities and stabilities. Indeed, given a certain practical application, we can often design a suitable SAC; thus, the field has developed very rapidly and afforded promising catalyst leads. Moreover, the control we have over certain SAC structures paves the way for designing base metal catalysts with the activities of noble metal catalysts. It appears that we are entering a new era of heterogeneous catalysis in which we have control over well-dispersed single-atom active sites whose properties we can readily tune. Single-atom catalysts are heterogeneous materials featuring active metals sites atomically dispersed on a surface. This Review describes methods by which we prepare and characterize these materials, as well as how we can tune their catalytic performance in a variety of important reactions.
2,306 citations
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TL;DR: Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C, which could facilitate new discoveries at the atomic scale in condensed materials.
Abstract: A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal–organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.
1,779 citations