arXiv subjects

Emiliano Fonda

Publications and source records attributed to Emiliano Fonda.

6 recordsLinked to original sources

arXiv2026

Photocatalytic methanol dehydrogenation promoted synergistically by atomically dispersed Pd and clustered Pd

Supported metal in the form of single atoms, clusters, and particles can individually or jointly affect the activity of supported heterogeneous catalysts. While the individual contribution of supported metal to the overall activity of supported photocatalysts has been identified, the joint activity of mixed metal species is overlooked because of their different photoelectric properties. Here, atomically dispersed Pd (Pd1) and Pd clusters are loaded onto CdS, serving as oxidation and reduction sites, respectively, for methanol dehydrogenation. The Pd1 substitutes Cd2+, forming hole-trapping states for methanol oxidation and assisting the dispersion of photo-deposited Pd clusters. Therefore, methanol dehydrogenation on CdS with supported Pd1 and Pd clusters exhibits the highest turnover frequency of 1.14 s-1 based on Pd content, and affords H2 and HCHO with a similar apparent quantum yield of 87 +/- 1% at 452 nm under optimized reaction conditions. This work highlights the synergistic catalysis of supported metal for improved photocatalytic activity.

cond-mat.mtrl-sci↗

arXiv2023

A Novel Electrochemical Flow-Cell for Operando XAS Investigations On X-ray Opaque Supports

Improvement of electrochemical technologies is one of the most popular topics in the field of renewable energy. However, this process requires a deep understanding of the electrode electrolyte interface behavior under operando conditions. X-ray absorption spectroscopy (XAS) is widely employed to characterize electrode materials, providing element-selective oxidation state and local structure. Several existing cells allow studies as close as possible to realistic operating conditions, but most of them rely on the deposition of the electrodes on conductive and X-ray transparent materials, from where the radiation impinges the sample. In this work, we present a new electrochemical flow-cell for operando XAS that can be used with X-ray opaque substrates, since the signal is effectively detected from the electrode surface, as the radiation passes through a thin layer of electrolyte. The electrolyte can flow over the electrode, reducing bubble formation and avoiding strong reactant concentration gradients. We show that high-quality data can be obtained under operando conditions, thanks to the high efficiency of the cell from the hard X-ray regime down to 4 keV. We report as a case study the operando XAS investigation at the Fe and Ni K-edges on Ni-doped maghemite films, epitaxially grown on Pt substrates. The effect of the Ni content on the catalytic performances for the oxygen evolution reaction is discussed.

physics.chem-ph↗

arXiv2022

Experimental investigation of the local environment and lattice distortion in refractory medium entropy alloys

EXAFS analysis of pure elements, binary and ternary equiatomic refractory alloys within the Nb-Zr-Ti-Hf-Ta system is performed at the Nb and Zr K-edges to analyze the evolution of the chemical local environment and the lattice distortion. A good mixing of the elements is found at the atomic scale. For some compounds, a distribution of distances between the central atom and its neighbors suggests a distortion of the structure. Finally, analysis of the Debye-Waller parameters show some correlation with the lattice distortion parameter $δ^2$, and allows to quantify experimentally the static disorder in medium entropy alloys.

cond-mat.mtrl-sci↗

arXiv2020

Iodine molecule modifications with high pressure

Metallization and dissociation are key transformations in diatomic molecules at high densities particularly significant for modeling giant planets. Using X-ray absorption spectroscopy and atomistic modeling, we demonstrate that in halogens, the formation of a \textit{connected} molecular structure takes place at pressures well below metallization. Here we show that the iodine diatomic molecule first elongates of $\sim$0.007 Å~up to a critical pressure of $P_c$ $\backsim$7~GPa developing bonds between molecules. Then its length continuously decreases with pressure up to 15-20~GPa. Universal trends in halogens are shown and allow to predict for chlorine a pressure of 42$\pm$8~GPa for molecular bond-length reversal. Our findings tackle the molecule invariability paradigm in diatomic molecular phases at high pressures and may be generalized to other abundant diatomic molecules in the universe, including hydrogen.

physics.chem-ph↗

arXiv2020

Mechanism of pressure induced amorphization of SnI4: a combined X-ray diffraction -- X-ray absorption spectroscopy study

We have studied the amorphization process of SnI4 up to 26.8GPa with unprecedented experimental details by combining Sn and I K edge X-ray absorption spectroscopy and powder X-ray diffraction. Standards and reverse Monte Carlo extended X-ray absorption fine structure (EXAFS) refinements confirm that the SnI4 tetrahedron is a fundamental structural unit that is preserved through the crystalline phase-I to crystalline phase-II transition about 7 to 10GPa and then in the amorphous phase that appears above 20GPa. Up to now unexploited Iodine EXAFS reveals to be extremely informative and confirms the formation of iodine iodine short bonds close to 2.85Å in the amorphous phase at 26.8 GPa. A coordination number increase of Sn in the crystalline phase-II appears to be excluded, while the deformation of the tetrahedral units proceeds through a flattening that keeps the average I-Sn-I angle close to 109.5°. Moreover, we put in evidence the impact of pressure on the Sn near edge structure under competing geometrical and electronic effects.

cond-mat.mtrl-sci↗

arXiv2020

Spectroscopies and electron microscopies unravel the origin of the first colour photographs

The first colours photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the 19th century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and size distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.

physics.app-ph↗