1,721,346 research outputs found
Electroreductive dehalogenation: crossroads for waste detoxification and conversion to valued compounds
No full textThe environmental impact of halogenated organic compounds is bound to their present (and past) use in a wide variety of industrial and civil applications, thanks to the wide spectrum of their physical and chemical properties, which, in turn, are at the basis of the assessed risks connected with their persistency and rapid dissemination in soils, water- and air-streams.
An integrated approach for environmental remediation and protection requests both long-term activities devoted to eradicate the risks, and immediate actions to drastically abate the toxicity of the actual wastes while controlling the treatment costs.
In this complex context, the electrochemical technologies can play a key role in terms not only of detoxification efficiency, but also of energy/cost saving and earning potentialities.
The exploitation of these technologies for the electroreductive (hydro)dehalogenation of organic halides is discussed in terms of the recent advances [1-5] on the preparation of cathode materials, reactor design, and investigation tools/methodologies (e.g. C-ME and FEXRAV [3,6]) purportedly developed to characterize both the reaction pathways and the process performances.
[1] O. Lugaresi, H. Encontre, C. Locatelli, A. Minguzzi, A. Vertova, S. Rondinini, Ch.
Comninellis, Electrochem. Commun. submitted
[2] O. V. Klymenko, O. Buriez, E. Labbè, D.-P. Zhan, S. Rondinini, Z.-Q. Tian, I. Svir,
Ch. Amatore, ChemElectroChem 2014, 1, 227-240
[3] A. Minguzzi, C. Locatelli, O. Lugaresi, A. Vertova, S. Rondinini, Electrochim.
Acta 2013, 114, 637-642
[4] O. Lugaresi, A Minguzzi, C Locatelli, A. Vertova, S. Rondinini, Ch. Amatore,
Electrocatalysis 2013, 4, 353-357
[5] A. Minguzzi, O. Lugaresi, G. Aricci, S. Rondinini, A. Vertova, Electrochem.
Commun. 2012, 22, 25-28
[6] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. D’Acapito, E. Achilli, P.
Ghigna, Anal. Chem. 2013, 85, 7009−
Au-based electrochemically etched cavity microelectrodes as optimal tool for quantitative analyses of finely dispersed electrode materials
No full textThe cavity microelectrode (C-ME) is an innovative tool for the study of finely dispersed electrode materials to be adopted in several electrochemical systems. Beside the different advantages of C-MEs, there is the possibility to carry out a rapid screening of the electrochemical behaviour of different materials thanks of the possibility of a quick and reliable electrode preparation [1,2]. In addition, the precise knowledge of the cavity volume (and thus of the amount of loaded powder) implies that any analysis carried out by a C-ME can be considered as quantitative [3]. This in turn leads to a optimal use of the C-ME as a tool for accurate evaluation of the relevant physico-chemical “specific” quantities of the powder under investigation, i.e. normalized by the amount of sample. In turn, this allows the rapid and quantitative screening of different electrocatalytic powder materials and to extract their intrinsic (“per site”) activities. The use of gold as the cavity current collector allows to obtain a regular cylindrical recess, whose volume is easily determined with good accuracy and precision. In particular different preparation methods were examined and that allow to obtain a very regular cylinder-shaped C-MEs was individuate.
The features of Au/C-MEs is well demonstrated by the good linear correlation between the cavity volume (determined by electrochemical methods) and the quantity of charge related to the amount of electroactive powder inserted into the cavities. To further prove the point, we adopted two different test systems: Pt on carbon and an IrO2-based material. Finally, we proved the adequacy of Au/C-MEs in determining the electrocatalytic activity of Ag particles as electrocatalysts for the hydrodehalogenation of trichloromethane and the specific conductivity of different mixed oxide materials.
Acknowledgements: Financial supports from the Italian Ministry of Education, University and Research (PRIN 2008N7CYL5), Fondazione Cariplo (2010-0506) and Università degli Studi di Milano (PUR 2009 Funds) are gratefully acknowledged. C.L. is grateful to the University of Milan for a post-doc fellowship. The contribution of Chiara Marchiori to the electrochemical experimental tests is also acknowledged.
[1] A. Minguzzi, C. Locatelli, G. Cappelletti, M. Scavini, A. Vertova, P. Ghigna, S. Rondinini, J. Phys Chem 2012, 116, 6497.
[2] A. Minguzzi, C. Locatelli, G. Cappelletti, C.L. Bianchi, A. Vertova, S. Ardizzone, S. Rondinini, J. Mater. Chem. 2012, 22, 8896.
[3] C. Locatelli, A. Minguzzi, A. Vertova, C. Paola, S. Rondinini, Anal. Chem. 2011, 83, 2819
Electrocatalytic IrO2-SnO2 nanopowders:evaluation of pH effect on the kinetic of Oxygen Reduction Reaction by Rotating Ring Disk Electrode
No full textThe Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are currently considered promising high efficiency, low environmental impact power sources. One important aspect that hinders their rapid commercialization is the high cost of the materials used to prepare the electrodes, based on Pt and Pt alloys due to their high activity and chemical stability1. For this reason, the development of platinum free electrocatalysts, inexpensive, stable, and able to significantly reduce the overvoltage for Oxygen Reduction Reaction (ORR) represents a major challenge in the development of PEMFCs.
Moreover, the possibility of a large commercialization of PEMFC is strictly connected to the availability of hydrogen; for this reason the development of bifunctional fuel cell/water electrolysis systems, Unitized Reversible Fuel Cell URFC, are strategic and this can be accomplished by developing new materials able to catalyze both ORR and Oxygen Evolution Reaction (OER).The high catalytic activity of IrO2-based composite electrodes toward OER is well known2 and largely studied.
This contribution presents new results on electrochemical characterization of IrO2-SnO2 nanostructured powder, synthetized by sol-gel technique and containing 15% mol of iridium under ORR condition. The investigation is carried out using potentiodynamic techniques and the Rotating Ring Disk Electrode at different at different pH values.
Acknowledgements: The financial contributions of PUR (2009 – 2010) and PRIN 2008 - 2008N7CYL5_004 funds are gratefully acknowledged. C. L. wish to thank the Oronzio and Niccolò De Nora Foundation for her Research Fellowships
1. Yu-Hung Shing, Guggilla Vidya Sagar, Shawn D. Lin, J. Phys Chem. C. 2008, 112 (1) 123-130, DOI:10.1021/jp071807h
2. S. Ardizzone, C. Bianchi, L. Borgese, G. Cappelletti, C. Locatelli, A. Minguzzi, S. Rondinini, A.Vertova, P. Ricci, C. Cannas, A. Musinu, J. Appl. Electrochem. 2009, 39: 2093-2105 DOI: 10.1007/s10800-009-9895-
Electroreduction of benzyl chloride on silver-based electrode materials in acetonitrile media: the role of water and of Ag surface
No full textElectroreduction of benzyl chloride on silver-based electrode materials in acetonitrile media: the role of water and of Ag surface
O. Lugaresi, A. Minguzzi, C. Locatelli, S. Rondinini, A. Vertova
Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano, via Golgi, 19 20133 Milano - Italy, tel. +39-02-50314216, fax+39-02-503 14203, [email protected]
The remarkable electrocatalytic activity of silver is well documented in the literature [1] and recently, the combination of electrochemical, spectroscopic and theoretical studies [2], using benzyl chloride (BzCl) as model organic compound, has demonstrated that the reduction pathway implies the formation sequence of silver-substrate/product adducts, starting from a weakly adsorbed benzyl chloride-Ag specie, followed by the strongly adsorbed benzyl radical-Ag and benzyl anion-Ag species. The last ultimately desorbing to give the final reaction products.
In this context the present contribution discusses the effect on the voltammetric signal of the presence of small amounts of water in the acetonitrile used as solvent. The source of proton from water may affect the normal reaction pathway and change the electrode activity. This provokes significant variations in electrode currents and potentials even at very low water content, thus providing an internal diagnostic signal for the quality of the solvent. This has immediate application to the comparison between electrode materials (e.g., massive silver, silver nanocubes and Ag-nanocubes supported on carbon) prepared by different procedures, and allows to evidence the effects of the morphology and size of silver particles on their electroactivity.
[1] S. Rondinini, A. Vertova, "Electroreduction of Halogenated Organic Compounds", in Electrochemistry for the Environment, Ch. Comninellis, and G. Chen, (Eds.), Springer, 2010, DOI 10.1007/978-0-387-68318-8
[2] Yi-Fan Huang, De-Yin Wu, An Wang, Bin Ren, Sandra Rondinini, Zhong-Qun Tian, and Christian Amatore "Bridging the Gap between Electrochemical and Organometallic Activation: Benzyl Chloride Reduction at Silver Cathodes", J. Amer. Chem. Soc. 2010, 132, 17199-17210; DOI: 10.1021/ja106049
Electro- and photo-electrochemical water splitting as studied by In-Operando X-Rays Absorption Spectroscopy
No full textIn this work we show our most recent results obtained by in-operando X-Ray absorption spectroscopy on hydrous/amorphous [1] and on crystalline/dry [2] iridium oxide electrodes as electrocatalysts for the oxygen evolution reaction (OER). In all cases, XAS evidenced the role of Ir active sites, and the relevant oxidation states assumed during the catalytic cycle. Moreover, the local structure is not significantly influenced by the applied potential, thus suggesting a negligible reorganization energy of the catalyst.On the bases of these results, we were able to directly observe, by means of spectro-photoelectrochemical experiments, the charge transfer between a semiconductor (α-Fe2O3) and hydrous IrOx, the latter used as overlayer for generating a high performance photoanode architecture in photoelectrochemical water splitting[3]. The aim is to clarify the ambiguous role of oxygen evolving catalysts used as overlayers on top of photoanodes in photoelectrochemical water splitting cells. Previous literature suggested that the real benefit of covering hematite with overlayers like iridium or cobalt oxides is not due to an increase of the reaction rate but to a decrease of the electron density in the hematite[4] or to the storage of photogenerates holes[5]. These effects are likely more important when hydrous overlayer, that can act as adapting catalysts[6], are considered. All these hypotheses can explain the observed improved hole lifetime and reduce recombination with electrons. The experimental approach is similar to the one adopted to study Ir oxide particles electrocatalysts[1,2]. In the present case, FEXRAV [7] and XANES have been used to probe changes in the charge state of Ir while the hematite was illuminated with a 410nm diode. Thanks to this setup, we were able to observe an increase of the density of empty Ir 5d states during hematite illumination and in correspondence of water spitting in the photoelectrochemical cell. The main conclusion is that a charge (hole) transfer between hematite and iridium occurs only when the hematite is illuminated. Hydrous iridium oxide is therefore capable of withdrawing holes from the semiconductor thus increasing the probability of interface reaction rather than charge recombination.
References
[1] A. Minguzzi, O. Lugaresi, E. Achilli, C. Locatelli, A. Vertova, P. Ghigna, Rondinini S., Chem. Sci., 2014, 5, 3591-3597
[2] A. Minguzzi, C. Locatelli, O. Lugaresi, E. Achilli, G. Cappelletti, M. Scavini, M. Coduri, P. Masala, B. Sacchi, A. Vertova, P. Ghigna, S. Rondinini, submitted
[3] A. Minguzzi, O. Lugaresi, E. Achilli, F. D'Acapito, A. Naldoni, F. Malara, C. Locatelli, A. Vertova, S. Rondinini, P. Ghigna, In preparation
[4] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant PNAS, 2012, 109, 15640–15645
[5] L. Badia-Bou, E. Mas-Marza, P. Rodenas, E M. Barea., F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 2013, 117, 3826−3833
[6] F. Lin, S.W. Boettcher Nature Materials, 2014, 13, 81-86
[7] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. d'Acapito, E. Achilli, P. Ghigna, Anal. Chem. 2013, 85, 7009-7013
Bifunctional electrocatalytic IrO2-SnO2 nanopowders : the kinetic of the oxygen Reduction Reaction by Rotating Disk Electrode
No full textProton Exchange Membrane Fuel Cell (PEMFCs) are currently developed as devices for distributed power supply. In these systems the Oxygen Reduction Reaction (ORR) at the cathode causes large overpotentials at the lower operating temperatures. Currently, Pt-based electrocatalysts are the most widely used at low temperature1, then the development of platinum free catalysts able to reduce the significant voltage losses at the cathode is therefore highly demanded.
Among the different materials that can replace platinum in an acidic environment, IrO2-based catalysts are very promising2, particularly in view of the development of bi-functional fuel cell/water electrolysis systems. IrO2, pure and in admixture with other cheaper oxides, is well known for both its stability in acidic media and its electrocatalytic activity for Oxygen Evolution Reaction3 (OER).
On this ground, ORR activity of IrO2-based nanostructured powders with different Ir contents, synthesized by sol-gel technique, was evaluated using Glassy Carbon Rotating-Disk Electrode (GC-RDE) as the support, and a thin Nafion® film as gluing agent. RDE allows one to study the activity of a material under fast and well-defined mass transfer conditions, so charge transfer limitations can be singled out. The catalytic behaviour of the ORR was evaluated both by voltammetric techniques in HClO4 0.1M at 25°C.
The results demonstrate the high activity of these materials, even at low IrO2 contents. Interesting features about the dependence of the ORR kinetics on the IrO2 loading are highlighted
Simultanea determinazione mediante square wave anodic stripping voltammetry di "platinum group metals (PGMs)" e Pb in matrici ambientali
No full textIl presente lavoro, riguarda la determinazione di Pt(II), Pd(II), Rh(III) e Pb(II) mediante voltammetria di ridissoluzione anodica ad onda quadra (SWASV).
La procedura analitica è stata verificata mediante l’analisi di materiali standard di riferimento.
La precisione e l’accuratezza, espresse rispettivamente come deviazione standard relativa ed errore relativo, sono risultate inferiori al 6 % in tutti i casi.
Viene valutata la possibilità di usare l’area di picco come parametro strumentale1. Sono valutate inoltre le possibili interferenze2. Una volta messa a punto su soluzioni acquose di riferimento e verificata su materiali standard di riferimento, la procedura analitica proposta è stata trasferita ed applicata su campioni reali prelevati in ecosistemi diversamente influenzati dal traffico veicolare.
Nel presente lavoro viene anche discusso un confronto critico con misure spettroscopiche effettuate sugli stessi campioni.
1. C. Locatelli, C. Electroanalysis 2003, 15, 1397-1402.
2. C. Locatelli, C.; G. Torsi, G. J. of Electroanal. Chem. 2001, 509, 80-89
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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