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Molecular metal clusters based on Pt-CO complexes, with different CO/metal ratios, are synthetized and electrochemically characterized for ORR in alkaline media. The carbonyl complexes have been used to both control the resulting metallic nanoparticles size and shape, in order to mix them with other metal particles to prepare bimetallic electrocatalysts, and fix them on a suitable carbon support

È un errore frequente, fra stimatori del caravaggismo incuranti della realtà storica, interpretare la Negazione di Pietro come un soggetto anticattolico – una denunzia di un tradimento commesso dal fondatore della Chiesa di Roma e rinnovato dai pontefici romani – ignorando il suo nesso con quei cardini della fede cattolica che sono la contrizione e la remissione del peccato. Siccome Nicolas Tournier affronta quel soggetto ripetutamente, e in modo personalissimo, conviene chiarire molti equivo...

Nicolas Tournier est un des peintres dont le nom est indissociable de la ville de Toulouse, où il a exercé son métier durant les années 1630. Originaire de Franche-Comté, il a séjourné à Rome dans les années 1620, puis s’est établi en Languedoc, à Narbonne, Carcassonne et Toulouse. Durant les douze dernières années de sa vie, il y a exécuté des tableaux sur lesquels les historiens d’art se sont appuyés pour reconstituer son œuvre peint. « Redécouvert » par Charles Sterling (1934), qui avait révélé ce que l’on pensait alors être la production languedocienne de Tournier (c’est-à-dire trois tableaux), ce sui­veur de Caravage est un peintre dont la vie et la carrière reposent sur de rares documents. Les travaux entrepris, ceux de R. Longhi en premier, ont eu pour principal objectif d’établir le catalogue de ses tableaux (une quarantaine de toiles aujourd’hui), aboutissant à un résultat para­doxal : un œuvre italien conséquent, qui repose entièrement sur l’attribution ; un œuvre languedocien qui a peu évolué. Or, chacun sait que toute étude mono­graphique, aussi utile soit-elle, atteint les limites de l’exercice même qui tend à enfermer le peintre dans sa vie et son œuvre. À l’occasion de la première expo­sition rétrospective du peintre présentée au Musée des Augustins, il a paru opportun de proposer une approche complémentaire à la reconstitution de l’œuvre qui touche à des problématiques plus larges qui se posent aujourd’hui à l’historien d’art : replacer Tournier et sa peinture dans le cadre du mouvement international du caravagisme, reprenant ainsi le débat précédemment engagé sur le sujet, dans le cadre de la peinture en Europe du premier XVIIe siècle. On a donc privilégié deux axes : premièrement, Tournier et l’Italie, car le peintre y a séjourné au moins sept ou huit ans, de 1619 à 1626 si l’on se réfère aux Stati d’anime ; deuxièmement, la diffusion du caravagisme : en France car Tournier, qui travaille en Languedoc, est un des principaux acteurs de la diffusion du cara­vagisme en France, avec Finson, Bigot et les François ; et en Espagne, d’une part parce que ce pays a aussi été touché par la mode du caravagisme et d’autre part car une vieille hypothèse, bien ébranlée mais tenace, veut que la peinture tou­lousaine ait des rapports avec l’art espagnol.

Sn-modification of TiO2 photocatalysts has been recently proposed as a suitable strategy to improve pollutant degradation as well as hydrogen production. In particular, visible light activity could be promoted by doping with Sn2+ species, which are, however, thermally unstable. Co-promotion with N and Sn has been shown to lead to synergistic effects in terms of visible light activity, but the underlying mechanism has, so far, been poorly understood due to the system complexity. Here, the structural, optical, and electronic properties of N,Sn-copromoted, nanostructured TiO2 from sol-gel synthesis were investigated: the Sn/Ti molar content was varied in the 0&ndash, 20% range and different post-treatments (calcination and low temperature hydrothermal treatment) were adopted in order to promote the sample crystallinity. Depending on the adopted post-treatment, the optical properties present notable differences, which supports a combined role of Sn dopants and N-induced defects in visible light absorption. X-ray absorption spectroscopy at the Ti K-edge and Sn L2,3-edges shed light onto the electronic properties and structure of both Ti and Sn species, evidencing a marked difference at the Sn L2,3-edges between the samples with 20% and 5% Sn/Ti ratio, showing, in the latter case, the presence of tin in a partially reduced state.

Chlorine dioxide (ClO2) has been widely used as a disinfectant in drinking water in the past but its effects on water pipes have not been investigated deeply, mainly due to the difficult experimental set-up required to simulate real-life water pipe conditions. In the present paper, four different kinds of water pipes, two based on plastics, namely random polypropylene (PPR) and polyethylene of raised temperature (PERT/aluminum multilayer), and two made of metals, i.e., copper and galvanized steel, were put in a semi-closed system where ClO2 was dosed continuously. The semi-closed system allowed for the simulation of real ClO2 concentrations in common water distribution systems and to simulate the presence of pipes made with different materials from the source of water to the tap. Results show that ClO2 has a deep effect on all the materials tested (plastics and metals) and that severe damage occurs due to its strong oxidizing power in terms of surface chemical modification of metals and progressive cracking of plastics. These phenomena could in turn become an issue for the health and safety of drinking water due to progressive leakage of degraded products in the water.

α-FeOOH (goethite) and γ-FeOOH (lepidocrocite) were found to be the main corrosion products of the steel cathode in the sodium chlorate process; the identification of the phases formed under reducing potentials, along with the study of the electrodes during the reoxidation, is fundamental to understanding their role in this process. In this work, FeOOH-based electrodes were investigated through in situ and in operando X-ray absorption spectroscopy (XAS), combined to electrochemical measurements (e.g., voltammetry and chronoamperometry). At sufficiently negative potentials (below −0.4 V vs RHE ca.) and under hydrogen evolution conditions an unknown iron(II)-containing phase is formed. A comprehensive analysis of the whole XAS spectrum allowed proposing a structure bearing a relation with that of green rust (space group P31m). This phase occurs independently of the nature of the starting electrode (α- or γ-FeOOH). During electrochemical reoxidation, however, the original phase is restored, meaning that the...

In this work we studied the kinetics of oxide formation and reduction on Pt nanoparticles in HClO4 in the absence and in the presence of Br− and Cl− ions. The study combines potential step methods (i.e. chronoamperometry and choronocoulometry) with energy dispersive X-ray absorption spectroscopy (ED-XAS), which in principle allows to record a complete XAS spectrum in the timescale of milliseconds. Here, the information on the charge state and on the atomic surrounding of the considered element provided by XAS was exploited to monitor the degree of occupancy of 5d states of Pt in the course of oxide formation and growth, and to elucidate the competing halide adsorption/desorption phenomena. Electrochemical methods and XAS agree on the validity of a log(t) depending growth of Pt oxide, that is significantly delayed in the presence of Cl− and Br− anions. In the proximity of formation of one monolayer, the growth is further slowed down.

The development of efficient, sustainable, cheap and safe methods for the synthesis of hydrogen peroxide is a very important challenge from the environmental viewpoint, since H 2 O 2 can be used as a solar fuel or for degradation of organic, inorganic and biologic pollutants from wastewater. Efficient photocatalytic or photoelectrochemical formation of hydrogen peroxide from water and/or oxygen in an acidic medium has been obtained using nickel or cobalt titanates under visible light illumination. The concentration of H 2 O 2 achieved in the photoreaction reached 2.5 mM when nickel titanate was irradiated for 1 h in oxygen saturated suspension. In such conditions, NiTiO 3 provide active sides for both, oxygen reduction and water oxidation leading to H 2 O 2 formation.

Metal-air batteries are one of the most promising electrochemical systems for energy storage and conversion. Herein we report promising results by exploiting manganese dioxide nanoparticles as ORR electrocatalysts. MnO2 nanorods were prepared through a hydrothermal synthesis, i.e. by varying both the salt precursors (i.e. manganese sulphate or chloride) and the oxidizing agents (i.e. ammonium persulfate or potassium permanganate). All the nanopowders were finely characterized on structural, morphological and surface points of view. Then, their electrocatalytic power was tested either in aqueous 0.1 M potassium hydroxide or in Tetra Ethylene Glycol Dimethyl Ether (TEGDME)/LiNO3 0.5 M electrolytes, by using Gas Diffusion Electrodes (GDEs) and Glassy Carbon (GC) as cathodes, respectively. All the nanoparticles promoted the ORR by causing a shift of the onset potential up to 100 mV in both solvents. Nevertheless, this shift was different according to the solvent/electrolyte used: in the case of the ether-based solvent, different values are obtained by adopting the synthesized MnO2 powders. Thus, we hypothesized that the structural/surface properties of MnO2 samples are leveled in the aqueous medium (i.e. in a OH rich solvent, the hydroxyls can interact with the homologs on the MnO2 surface), contrary to what occurs in the organic solvent. Furthermore, a different behavior was observed also on the kinetic point of view thus leading to diverse interpretations of the oxygen reduction mechanism, especially in TEGDME.

Funding Information: This research was funded by the Jane and Aatos Erkko Foundation, grant: ?Renewable energy storage to high value chemicals?; the Italian Ministry of University, grant number Prot. 2017YH9MRK; the Universit? degli Studi di Milano, grant number PSR 2020. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This work aims at reviewing the most impactful results obtained on the development of Cu-based photocathodes. The need of a sustainable exploitation of renewable energy sources and the parallel request of reducing pollutant emissions in airborne streams and in waters call for new technologies based on the use of efficient, abundant, low-toxicity and low-cost materials. Photoelectrochemical devices that adopts abundant element-based photoelectrodes might respond to these requests being an enabling technology for the direct use of sunlight to the production of energy fuels form water electrolysis (H2) and CO2 reduction (to alcohols, light hydrocarbons), as well as for the degradation of pollutants. This review analyses the physical chemical properties of Cu2O (and CuO) and the possible strategies to tune them (doping, lattice strain). Combining Cu with other elements in multinary oxides or in composite photoelectrodes is also discussed in detail. Finally, a short overview on the possible applications of these materials is presented.

Global warming and the huge production of the greenhouse gases are very actual concerns. A new paradigm for energy production must be followed, and in this context the possibility to increase the usage of renewable energies and the development and research on new technologies for efficiency energy production and storage are very actual issues. Fuel cells and metal air batteries are possible solutions to the worldwide energy requirements, but, to date, the Oxygen Reduction Reactions (ORR) still remain a bottleneck for a wide spread and use of these technologies. For this reason, in the last 50 years a huge amount of work has been done on this reaction, in term of understanding the possible reaction mechanisms of the process and of investigating new cathodic materials to reduce the overall overpotential To date, platinum metal group, finely dispersed on suitable carbon support, are the best materials commercial available[1,2]. However, some important drawbacks are connected with the use of Pt as catalytic metal: i) high cost; ii) scarcity; iii) stability of micro- and nano- particles on carbon support; iv) poisoning with CO[3 ]. Therefore, obtaining new catalytic materials able to improve the activity, selectivity, and durability of the ORR reactions is desirable. In this context, we have synthetized different carbonyl Pt clusters, either belonging to the [Pt3n(CO)6n] 2- series (Chini-type clusters), or based on fcc close packed metal cores, to prepare nanostructured electrocatalyst, supported on black carbon (Vulcan XC72R®) powder, to be employed as positive pole in fuel cells and metal air batteries. The synthesis and physico-chemical characterization will be briefly presented and discussed. The electrochemical characterization of composite electrocatalytic powders has been carried out using Rotating Ring Disk Electrode in order to investigate the reduction route: 4 or 2 electrons pathway. The values of ORR onset potentials and limiting currents for these new Atomically precise metal clusters are very interesting, especially for [Pt15(CO)30] 2- and [Pt24(CO)30] 2- which exhibits higher limiting currents than a commercial Pt-loaded carbon powder, despite the lower amount of noble metal. Moreover, these powder show a very low production of H2O2, thus indicating a preferential route for 4-electrons pathway reduction reaction. The results are presented in term of specific activity and mass activity.

Energy-dispersive X-ray absorption spectroscopy was applied, aimed at solving the problem of the structure and stability of a copper(II) lactate complex in alkaline solution, used as a precursor for the electrodeposition of Cu2O. The application of multiple scattering calculations to the simulation of the X-ray absorption near-edge structure part of the spectra allowed an accurate resolution of the structure: the copper(II) cation is surrounded by four lactate ions in a distorted tetrahedral environment, with the lactate anions acting as monodentate ligands. This results in an atomic arrangement where copper is surrounded by four oxygen atoms located at quite a short distance (ca. 1.87 A) and four oxygen atoms located quite far apart (ca. 3.1–3.2 A). The complex was finally found to be stable in a wide range of applied potentials.

Electrochemical devices for energy conversion and storage are central for a sustainable economy. The performance of electrodes is driven by charge transfer across different layer materials and an understanding of the mechanistics is pivotal to gain improved efficiency. Here, we directly observe the transfer of photogenerated charge carriers in a photoanode made of hematite (α-Fe2O3) and a hydrous iridium oxide (IrOx) overlayer, which plays a key role in photoelectrochemical water oxidation. Through the use of operando X-ray absorption spectroscopy (XAS), we probe the change in occupancy of the Ir 5d levels during optical band gap excitation of α-Fe2O3. At potentials where no photocurrent is observed, electrons flow from the α-Fe2O3 photoanode to the IrOx overlayer. In contrast, when the composite electrode produces a sustained photocurrent (i.e., 1.4 V vs. RHE), a significant transfer of holes from the illuminated α-Fe2O3 to the IrOx layer is clearly demonstrated. The analysis of the operando XAS spectra further suggests that oxygen evolution actually occurs both at the α-Fe2O3/electrolyte and α-Fe2O3/IrOx interfaces. These findings represent an important outcome for a better understanding of composite photoelectrodes and their use in photoelectrochemical systems, such as hydrogen generation or CO2 reduction from sunlight.

In this work we demonstrate the feasibility of hard X-rays operando XAS in photoelectrochemistry. WO3, one of the most studied photoanodes for water splitting and for environmental remediation, is here studied at the W LIII-edge. This guarantees the direct observation of the W 5d band. The material, that is preliminary fully characterized in terms of its photoelectrochemical features, is studied in a three-electrode spectroelectrochemical cell, while X-ray absorption is measured in the X-ray absorption near edge structure (XANES) region. The recording of differential spectra and the monitoring of X-ray absorption at constant energy are used to compensate for the little XANES differences expected in the dark and under visible light illumination, which otherwise risks to be masked by experimental errors and/or by signal manipulation for data analysis. The results point to the filling of the W t2g orbitals under illumination, that is followed by a structural rearrangement that compensates for the accumulation of electrons in the conduction band under open circuit (OC) conditions.