The oxidation of palladium nanoparticles causes the performance degradation of alkaline direct ethanol fuel cells. Quantifying this oxidation is a task of tremendous importance to design mitigation strategies that extend the service life of catalysts and devices. Here, we show that the Fixed Energy X-ray Absorption Voltammetry (FEXRAV) can provide this information with an in-situ approach. To do so, we have developed a quantification method that assumes the linear response at fixed energy. With this method, we have investigated the oxidation of carbon black-supported palladium electrocatalysts during cyclic voltammetry in the same solution employed as a fuel in the direct ethanol fuel cells. We have shown that up to 38% of the palladium is oxidised at 1.2 V vs. RHE and that such oxidation also happens at lower potentials that the catalyst can experience in real direct ethanol fuel cells. The result of this study is a proof of concept of quantitative FEXRAV.

Alkaline membrane fuel cells (AMFCs) have started to become more attractive in recent years due to the development of polymeric membranes with good anionic conductivity and durability. However, few studies investigating the performance of H-2/O-2 fueled AMFCs and alkaline direct ethanol fuel cells (DEFCs) with membrane electrode assemblies (MEAs) fabricated with Pt-group metal (PGM)-free catalysts are available in the literature. In this paper, we synthesized and fully characterized a Fe-Co-N-C electrocatalyst for the oxygen reduction reaction ORR) by a sacrificial method, using pyrrole as a unique and inexpensive precursor for N-doped carbonaceous materials. Very good ORR activity and stability were obtained in alkaline conditions, most likely due to the presence of Co-Fe@C nanoparticles. We achieved a very high performance in an AMFC, 420 mWcm(-2) at 60 degrees C, among the highest in the literature for PGM-free catalysts, and a good performance in a passive DEFC, 28 mW cm(-2) at room temperature.

Two different synthetic approaches to carbon nanotube N-decoration/doping are used to foster the hypothesis of a unique N-configuration (N-pyridinic) at work in the ORR.

Manganese(II) sulfide (MnS) is a candidate component for a window or buffer material in solar cells; the ability to synthesize this compound by electrodeposition may open novel routes toward the low-cost, large-scale production of multicomponent chalcogenides with continuously tunable properties. We show here that underpotential codeposition enables formation of MnS films with precise stoichiometry and hexagonal structure. Film morphology consists of polycrystalline polygonal features. The films exhibit a bandgap of 3.9 eV, sometimes together with other, lower bandgaps due to secondary phases; these materials are also photoactive, with an observed photon-to-current conversion efficiency of similar to 10%. (C) 2016 The Electrochemical Society. All rights reserved.

Deactivation is one the main causes still preventing the full exploitation of palladium electrocatalysts in alkaline direct alcohol fuel cells and the electrochemical reforming of alcohols. While often attributed to the adsorption of poisoning species generated in the alcohols oxidation, in the present work we demonstrate that deactivation is provoked by the formation of palladium oxides. A combined approach including i) fuel cell runs, ii) cyclic voltammetry and iii) near edge X-ray absorption spectroscopy has enabled us to draw the conclusions reported in the paper. (C) 2015 Elsevier Ltd. All rights reserved.

The combination of two different metals, each of them acting on different steps of the oxygen reduction reaction (ORR), yields synergic catalytic effects. In this respect, the electrocatalytic effect of silver is enhanced by the addition of cobalt, which is able to break the O–O bond of molecular oxygen, thus accelerating the first step of the reduction mechanism. At the same time, research is to further reduce the catalyst’s cost, reducing the amount of Ag, which, even though being much less expensive than Pt, is still a noble metal. From this point of view, using a small amount of Ag together with an inexpensive material, such as graphite, represents a good compromise. The aim of this work was to verify if the synergic effects are still operating when very small amounts of cobalt (2–10 μg·cm−2) are added to the microparticles of silver electrodeposited on glassy carbon, described in a preceding paper from us. To better stress the different behaviour observed when cobalt and silver are contemporarily present in the deposit, the catalytic properties of cobalt alone were investigated. The analysis was completed by the Levich plots to evaluate the number of electrons involved and by Tafel plots to show the effects on the reaction mechanism.

Direct alkaline ethanol fuel cells (DEFCs) are usually run with Pd anodic catalysts, but their performance can be improved by utilizing alloys of Pd and Co. The oxyphilic Co serves to supply ample OH to the ethanol oxidation reaction, accelerating the rate limiting step at low overpotential under alkaline conditions. Pd Co films with compositions between 20 and 80 at% Co can be prepared by electrodeposition from a NH3 complexing electrolyte. Cyclic voltammetry studies show that the ethanol oxidation peak exhibits increasing current density with increasing Co content, reaching a maximum at 77% Co. In contrast, potentiostatic measurements under conditions closer to fuel cell operating conditions show that a 50 at% Co alloy has the highest performance. Importantly, the Co Pd film is also found to undergo phase and morphological transformations during ethanol oxidation, resulting in a change from a compact film to high surface area flake-like structures containing Co3O4 and CoOOH; such a transformation instead is not observed when operating at a constant potential of 0.7 V-RHE. (C) 2015 Elsevier B.V. All rights reserved.

We report on the N-decoration of multiwalled carbon nanotubes (MWCNTs) via chemical functionalization under mild reaction conditions. The introduction of tailored pyridinic functionalities as N-containing edge-type group mimics generates effective catalysts for the oxygen reduction reaction (ORR) in an alkaline environment. The adopted methodology lists a number of remarkable technical advantages, among which is an easy tuning of the electronic properties of N-containing groups. The latter aspect further increases the level of complexity for the rationalization of the role of the N-functionalities on the ultimate electrochemical performance of the as-prepared metal-free catalysts. Electrochemical outcomes crossed with the computed electronic charge density distributions on each scrutinized pyridine group have evidenced the central role played by the N-chemical environment on the final catalyst performance. Notably, small variations of the atomic charges on the N-proximal carbon atoms of the chemically grafted heterocycles change the overpotential values at which the oxygen reduction reaction starts. The protocol described hereafter offers an excellent basis for the development of more active metal-free electrocatalysts for the ORR. Finally, the as-prepared catalytically active materials represent a unique model for the in-depth understanding of the underlying ORR mechanism.

The electrocatalytic properties of small amounts of silver (3-17 mu g cm(-2)) electrodeposited on glassy carbon can be sensibly increased by an activation protocol based on pretreatment oxidation/reduction Cycles that produces significant changes in particle's morphology. The catalytic effects on both Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR) are evaluated by the onset potentials of the voltammetric curves, and the number of electrons involved in ORR is evaluated by the Levich plot. Tafel plots of both OER and ORR curves obtained after the activation protocol show significant changes that rule out the hypothesis that the catalytic effect could only be attributed to an increased roughness of the samples. Furthermore, the electrochemically active surface area of silver, as measured by the charge involved in Pb underpotential deposition, was found to increase linearly with the amount of depositing silver. On the contrary, the Tafel plots of increasing amounts of silver show that the increase of the catalytic effect with silver loading is not linear as expected in a mere increase of the roughness factor. Levich-Koutecky and Tafel plots evidenced that the highest silver loading showed a catalytic effect greater than that expected on the basis of the electrochemically active surface area. (C) 2014 The Electrochemical Society. All rights reserved.

The global environmental concerns and the escalating demand for energy, coupled with a steady progress in renewable energy technologies, are opening up new opportunities for the utilization of renewable energy resources. Electrodeposition is well known for depositing metals and metallic alloys at the industrial level, with a wide range of applications from large area surface treatments to most advanced electronic industries. Electrodeposition of semiconducting materials represents a new challenge, not only from the academic point of view, but also from the economic point of view, since this method presents interesting characteristics for large area, low cost and generally low temperature and soft processing of materials. In this presentation, we exploited alternated electrodeposition of some metals by E-ALD (Electrochemical Atomic Layer Deposition) to obtain thin films, controlling the growth of the structures at the nanometric level. Selective Electrodesorption Based Atomic Layer Deposition (SEBALD [1]) was used to prepare new bimetallic electrodes for fuel cells. This new method of Electrodeposition, recently pointed out in Florence on the base of ECALE method [2], allows to deposit under morphological and compositional control those metals that cannot be deposited at underpotential. We have recently reported the use of nanostructured palladium in the realization of a new “green” and energetically self-sustainable paradigm for the chemical industry based on the electro-oxidation of renewable alcohols [3]. The exploitation of the catalytic properties of palladium toward the oxidation of alcohols strongly depends on the availability of methods capable of generating supported metal nanoparticles with high index facets, as well as selecting size and metal loading. The concomitant control of all these aspects is a major challenge for nanotechnology oriented to catalysis and electrocatalysis. To achieve these targets we developed a method (Electrochemical Milling and Faceting – ECMF [4]), consisting of an electrochemical post-deposition treatment. Ultimately the purpose of the method is to perform a milling and faceting of the palladium nanoparticles deposited by virtually any known deposition method. [1] M. Innocenti, S. Bellandi, E. Lastraioli, F. Loglio, and M. L. Foresti, Langmuir, 2011. [2] Gregory, B. W.; Stickney, J. L. J. Electronanal. Chem. 1991, 300, 543. [3] V. Bambagioni, M. Bevilacqua, C. Bianchini, J. Filippi, A. Lavacchi, A. Marchionni, F. Vizza and P. K. Shen, ChemSusChem, 3 (2010) 851. [4] Y.X. Chen, A. Lavacchi, S.P Chen, F. Di Benedetto, M. Bevilacqua, C. Bianchini, P. Fornasiero, M. Innocenti, M. Marelli, W. Oberhauser, .S.G. Sun, F. Vizza. Angew. Chem. Int. Ed. 2012, 51, 8500 –8504.

The increasing attention addressed toward the synergic effect of various metals on the catalysis of one of the most important electrocatalytic reaction, such as the Oxygen Reduction Reaction (ORR), led us to study the effect of monolayers of Fe and of mixed Fe and Co on Ag(111), whose catalytic activity is already known and well characterized. Fe and Co/Fe clusters were obtained by the Selective Electrodesorption Based Atomic Layer Deposition (SEBALD) method, which is a novel electrochemical route to deposit metal clusters on a foreign substrate recently proposed by our group. SEBALD of Fe or Co/Fe resulted in an enhanced catalytic activity; Co/Fe in particular was demonstrated to assemble in small clusters, providing access of the electrolyte to Ag and enabling a bimetallic catalytic effect. (C) 2013 Elsevier B.V. All rights reserved.

Tin sulfides present electrical and optical properties, which give them high potential use in opto-electronic devices and photoconductive cells, i.e. photovoltaic applications. In this paper we report an electrochemical study of a tin solution, carried out by cyclic and stripping voltammetry. These techniques allow to establish the presence of surface limited processes and, hence, to define the experimental conditions for the Underpotential Deposition of Sn on Ag(111) previously covered by a S monolayer. Moreover, we studied the growth of the first layers of tin sulfides.

A straightforward, energy- and atom-saving process to the production of tailored N-doped and catalytically active metal-free carbon nanostructures, has been set up. Our ex situ approach to the N-decoration of the carbon nanotube sidewalls contributes to elucidate the complex structure–reactivity relationship of N-doped carbon nanomaterials in oxygen reduction reactions, providing fundamental insights on the nature of the N-active sites as well as on the role of neighboring carbons.

Department of Chemistry, University of Florence, Via della Lastruccia 3-13, 50019 Sesto Fiorentino (Florence), Italy Dept. Earth Sciences, Univ. Florence (Italy), Via La Pira 4, 50121 Firenze, Italy Institute of Chemistry of OrganoMetallic Compounds, ICCOM-CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, (Florence) Italy. ESRF, 6, Rue Horowitz, F-BP 220, 38043, Grenoble, Cedex, France 5 Chemistry Department, University of Bari “Aldo Moro”, Bari, Italy