1,721,197 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
Study of photoelectrochemical behavior of copper oxides based materials using X-ray absorption spectroscopy
No full textThe use of sunlight to convert water into fuel is very attractive and ambitious since H2 is considered to be the energy carrier of the future thanks to its high mass energy density and its environmental friendliness [1,2]. Copper oxides-based photocathodes are attractive for their absorption in the visible range, low cost, high abundance and easy synthetic protocols as well as high photoactivity [3,4].
Two p-type semiconducting copper based materials has been prepared, characterized and tested as a photocathode for H2 production: CuO and Cu2O. The first one is prepared by thermal treatment of nanocrystalline CuI, which shows high efficiency in light conversion and interesting self-protection properties [5].
Cu2O instead was prepared by electrochemical deposition from a lactate-stabilized Cu++ bath [3]. Viceversa the main drawback of Cu(I) oxide is its lack of stability during photoelectrochemical conditions. For this material the influence of a metallic underlayer (Au, Cu) between the semiconductor itself and the FTO support was studied, together with the presence of a small load of Pt catalyst.
In-situ and in-operando techniques like X-ray absorption near edge structure (XANES), Extended X-Ray Absorption Fine Structure (EXAFS) and Fixed Energy X-ray Absorption Voltammetry (FEXRAV) [6] allow us to better understanding materials behavior. We observe changes in copper oxidation states upon light and/ or applied potential. Moreover, the role of methanol as hole-scavenger during photoelectrochemical experiment has been studied. FEXRAV measurements allow following the material degradation processes and defining the stability windows. With differential light and dark XANES spectra, we investigated the local changes in electronic structure upon spectroelectrochemical conditions. These results will allow us obtaining more stable system for photoelectrochemical hydrogen production.
References
[1] G. Centi, S. Perathoner, ChemSusChem. 3 (2010) 195–208.
[2] F. Malara, A. Minguzzi, M. Marelli, S. Morandi, R. Psaro, V. Dal Santo, A. Naldoni, ACS Catal. 5 (2015) 5292–5300.
[3] A. Paracchino, V. Laporte, K. Sivula, M. Grätzel, E. Thimsen, Nat. Mater. 10 (2011) 456–461.
[4] C. Li, T. Hisatomi, O. Watanabe, M. Nakabayashi, N. Shibata, K. Domen, J.-J. Delaunay, Energy Environ. Sci. 8 (2015) 1493–1500.
[5] T. Baran, S. Wojtyła, C. Lenardi, P. Ghigna, E. Achilli, S. Rondinini, A. Minguzzi, ACS Appl. Mater. Interfaces. (submitted).
[6] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. D’Acapito, E. Achilli. P. Ghigna. Anal. Chem. (2013), 85, 7009-7013
CavityMicroTips (CM_T) for the investigation of photocathode materials
No full textThe H2 production by photoelectrochemical water splitting is one the main goals in solar energy conversion studies. While the photoelectrocatalytic system for the oxygen evolution reaction (OER) requires the combined contribution of photoconverter and OER-electrocatalysts, the hydrogen evolution reaction (HER) could in principle be achieved using the p-type Cu2O photocatalyst alone, as discussed in [1] in terms of performances of electrodeposited thin p-Cu2O layers.
In the present communication we report preparation and characterisation of different photoelectrocatalyst as disperse phase materials, with the aim of overcoming the intrinsic instability of Cu2O photoconverter and to increase the rate of hydrogen production. The test are performed by conventional voltamperometric techniques and by SECM in the tip generation/substrate collection mode,. Here a cavity micro-electrode is used as tip (CM_T) [2], in lieu of the usual disk, as support for the nanoparticles.
As pointed out in previous works [2,3,4], cavity micro-electrodes present several advantages, and in particular the unique feature of eliminating the use of any gluing agent or additive to avoid any loss of material as in conventional electrode supports. In addition they can be easily emptied and refilled with new samples for screening between different materials and for reproducibility tests.
[1] A. Paracchino, J. C. Brauer, J.-E. Moser, E. Thimsen, M. Graetzel, J Phys Chem C, 116 (2012) 7341-7350
[2] S. Morandi, A. Minguzzi, submitted
[3] C. Locatelli, A. Miguzzi, A. Vertova, P. Cava, S. Rondinini, Anal. Chem. 83 (2011) 2819-2823
[4] A. Minguzzi, C. Locatelli, O. Lugaresi, A. Vertova, S. Rondinini, Electrochim. Acta 114 (2013) 637-642
A. K. Satpati, A. J. Bard, Anal. Chem. 84 (2012) 9498−950
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
SECM for the study and the screening of photoelectrode architectures
No full textPhotoelectrochemical water splitting represents an ideal system for the storage of sunlight energy through the production of H2. While many researchers find and design new promising semiconductors, an important effort is dedicated to the research of materials to be deposited on top of the semiconductors (overlayers) to improve the performance of the resulting photoelectrode architecture. The role of overlayers was initially addressed to their ability of improving interfacial reactions or quenching surface traps[1] . However, further study highlighted their more is likely related to an induced modification of the semiconductor electron density[2] or the ability of storing the photogenerated holes thus decreasing the probability of charge recombination [3,4]. This greatly extends the possible candidates for overlayers and requires new efficient screening methods.
In this communication we will show our most recent outcomes obtained using SECM for studying both semiconductors and overlayers. The main part of the work consists in the study and the screening of overlayers deposited onto hematite (α-Fe2O3) photoanodes [5]. This was mainly done in the substrate generation/tip collection mode on arrays of overlayers deposited onto a common semiconductor layer adopting the method recently proposed for screening electrocatalysts for the oxygen evolution [6] that consists in pulsing the substrate potential to achieve a reduced interference between spots while the tip addresses every spot collecting the generated oxygen.
[1] K. Sivula, F. Le Formal, M. Grätzel, ChemSusChem, 4 (2011) 423-449
[2] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant PNAS, 109 (2012) 15640–15645
[3] L. Badia-Bou, E. Mas-Marza, Rodenas P., E. M. Barea, F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 117 (2013) 3826−3833
[4] F. Lin, S.W. Boettcher, Nature Materials, 13 (2014) 81-86
[5] M. Marelli, A. Naldoni, A. Minguzzi, M. Allieta, T. Virgili, G. Scavia, S. Recchia, R. Psaro, V. Dal Santo, ACS Appl. Mater. Interfaces, 6 (2014) 11997-12004.
[6] A. Minguzzi, D. Battistel, J. Rodriguez-Lopez, A. Vertova, S. Rondinini, A.J. Bard, S. Daniele, J. Phys. Chem. C, 119 (2015) 2941–294
The cavity-microelectrode as a tip for scanning electrochemical microscopy
No full textIn this work, we present and discuss the use of cavity-microelectrodes (C-MEs) used as tip for the scanning electrochemical microscopy (SECM). Cavity-microelectrodes can be filled with a desired finely dispersed material thus compensating for the limited commercial availability of microwires. After discussing the possibility of filling and emptying a cavity-microelectrode with a desired tip shape, the consistency of negative and positive feedback approach curves obtained after filling a Au C-ME was verified. In addition, the tip/C-ME was tested under gas (oxygen) evolution condition, in order to demonstrate that the filling is stable in a wide range of gas fluxes thus extending the possible applications to tip generation/substrate collection mode. Finally, we introduce the use of the proposed system to quantify the rates of parallel reactions occurring at the material inserted in the tip under the tip generation/substrate collection mode
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
In-situ X-ray absorption spectroscopy on (photo )electrocatalysts: new methods and innovative techniques towards new insights on reaction mechanisms
No full textElectrochemical in-situ and in-operando X-ray absorption spectroscopy represents one of the most powerful available tools to study the fine structure and the behaviour of electrode materials. This serves to better elucidate important reaction mechanisms and to better define structure/activity relations.
In this context, the Fixed Energy X-Ray Absorption Voltammetry (1) represents a novel technique for fast and easy preliminary characterization of electrodes and photoelectrodes which consists in recording the absorption coefficient at a fixed energy while varying at will the electrode potential. The energy is chosen close to a core level absorption edge, in order to give the maximum contrast between different oxidation states of an element. It follows that any shift from the initial oxidation state determines a variation of the X-ray absorption coefficient. FEXRAV allows to quickly map the variation of the oxidation states of the element under consideration in a desired potential window.
As a result, FEXRAV gives important information by itself but can also serve as a preliminary screening of the potential window or, more generally, for choosing the best experimental conditions for a better targeted XAS analysis.
This led, for example, to a better understanding of the mechanism of iridium oxide as catalyst for water oxidation: for the first time the co-existence of more than one Ir oxidation state at E >1.23V (RHE) was directly observed and this is consistent with the role of Ir as center of a catalytic cycle (2).
More recently, studies by time-resolved energy dispersive XAS have been carried out with the aim of studying the time-dependence of interfacial phenomena.
(1) Minguzzi, A.; Lugaresi, O.; Locatelli, C.; Rondinini S.; d'Acapito, F.; Achilli, E.; Ghigna, P. Anal. Chem. 2013, 85, 7009-7013.
(2) Minguzzi A., Lugaresi O., Achilli E., Locatelli C., Vertova A., Ghigna P., Rondinini S., Chem. Sci. 2014. 5, 3591
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