Author(s): I. Visoly-Fisher, A. Mescheloff, M. Gabay, C. Bounioux, L. Zeiri, M.Sansotera, A.E. Goryachev, A. Braun, Y. Galagan, E.A. Katz
Source: Solar Energy Materials & Solar Cells
Volume: 134 Pages: 99-107
Published: Mar (2015)
We have demonstrated accelerated degradation studies of organic photovoltaic materials using concentrated sunlight, where the atmosphere, temperature and illumination intensity were independently controlled. Testing various schemes for controlling the sample temperature under concentrated sunlight showed that heating of P3HT:PCBM was caused by photons at the absorbed wavelength range and dissipation of excess photon energy, and not necessarily by IR photon absorption. Sunlight chopping was found to be an effective method for independent temperature control under illumination by concentrated sunlight.
The first accelerated degradation tests using sunlight concentration applied to P3HT:PCBM blends were reported. P3HT:PCBM blends exposed to concentrated sunlight in the presence of traces of oxygen/ humidity showed degradation induced by photo-oxidation of the P3HT backbone within the P3HT:PCBM blend, which is significantly thermally accelerated, in agreement with previous observations. However, this could be demonstrated in a time scale of minutes and hours, that is, significantly accelerated. Exposure of well encapsulated P3HT:PCBM films to concentrated sunlight demonstrated stability up to 3,600 sun?hours, corresponding to about 1.6 years of operating time. This result was obtained at 300 suns exposure after merely 12 h, demonstrating the advantage of using concentrated sunlight for accelerated stability tests. These tests can therefore combine extremely high acceleration factors with profound understanding of the effect of various, independently controlled factors on the degradation mechanisms.
Author(s): Sara Gatto, Maurizio Sansotera, Federico Persico, Massimo Gola, Carlo Pirola, Walter Panzeri, Walter Navarrini, Claudia L. Bianchi
Source: Catalysis Today
Volume: 241 Pages: 8-14
Published: Mar (2015)
The photoabatement of perfluorooctanoic acid in aqueous solution has been performed with a commercial nano-sized TiO2-based photocatalyst content of 0.66 g/L under an UV irradiation of 95 W/m2. PFOA degradation intermediates were investigated by HPLC-MS and 19F-NMR analysis. Evidences of adegradation mechanism based on two competitive pathways are discussed: photo-redox and beta-scission pathways. Shorter perfluorinated carboxylic acids, CnF2n+1COOH (n = 1-6), as expected degradation intermediates, were identified and their concentration trends over time were determined. The apparent pseudo-first order kinetic constant expressed as rate of PFOA disappearance was also measured: kapp 0.1296 h-1. The influence of fluoride ions on TiO2 surface was analyzed by XPS technique, revealing asurface modification that affects the performances of the catalyst.
Author(s): Federico Persico, Maurizio Sansotera, Claudia L. Bianchi, Carlo Cavallotti, Walter Navarrini
Source: Applied Catalysis B: Environmental
Volume: 170 Pages: 83-89
Published: Jan (2015)
The photodegradative activity of titanium dioxide immobilized into a multilayered transparent fluoropolymeric matrix was studied. The photoactive coating was developed by applying a TiO2-containing fluorinated ionomeric dispersion and a perfluorinated amorphous polymer in an appropriate sequence directly on the UV source. The multilayered coating photocatalytic activity toward hydrosoluble organic pollutants was evaluated in clear as well as in highly turbid conditions obtained by dispersing barium sulfate microparticles in the polluted solution. Rhodamine B-base was chosen as reference organic pollutant. The photoabatement rates with TiO2-embedded fluorinated coating in clear solution and turbid conditions were 0.0923 min-1 and 0.0546 min-1, respectively. In both clear and turbid conditions, TiO2-embedded transparent coating revealed higher photocatalytic activity than merely dispersed TiO2. This behavior was particularly evident at low pollutant concentrations. In addition, catalyst immobilization prevented TiO2 separation and catalyst losses, allowing the development of a simple and efficientcontinuous apparatus.
Author(s): Maurizio Sansotera, Cristian Gambarotti, Antonino Famulari, Alberto Baggioli, Raffaella Soave, Francesco Venturini, Stefano V. Meille, Ivan Wlassics, Walter Navarrini
Volume: 70 Pages: 5298-5309
Published: Aug (2014)
Perfluoroalkyl radicals, generated by thermal decomposition of perfluorodiacyl peroxides, react selectively with quinone rings of 1,4-naphthoquinones. In the presence of a non-conjugated alkene such as 1-hexene, perfluoroalkyl radicals add to the double bonds of the olefin forming a radical adduct, which selectively adds to the naphthoquinone ring. Several perfluorodiacyl peroxides have been synthesized and used for the direct and alkene-mediated functionalization of naphthoquinones. Geometrical parameters and electron density topology of all perfluorodiacyl peroxides have been calculated by the density functional formalism and quantum theory of atoms in molecules to attempt a rationalization of the experimental reactivity.
Source: Journal of Power Sources
Volume: 258 Pages: 351-355
Published: Jul (2014)
Linear perfluoropolyether (PFPE) peroxide was used to confer superhydrophobic surface properties to gas diffusion layer (GDL) by means of direct functionalization of a GDL based on carbon cloth (CC) material. The thermal decomposition of a linear PFPE peroxide produces linear PFPE radicals that covalently bond the unsaturated moieties on the surface. Perfluorinated radicals are directly and covalently bound to the carbonaceous structure of the CC without any spacer that could decrease both thermal and chemical stability of the GDL. The obtained CC hydrophobicity exceeded the superhydrophobicity threshold and was enduringly stable. The relationship between the linkage of fluorinated chains and the variations of surface chemical?physical properties were studied combining X-ray photoelectron spectroscopy (XPS), resistivity measurements, scanning electron microscopy (SEM) and contact angle measurements. Despite the excellent insulating properties of the PFPE polymer, the functionalized carbonaceous materials substantially retained their conductive properties. The PFPE-modified GDLs were tested in a single fuel cell at the lab scale. The cell tests were run at two temperatures (60C and 80C) with a relative humidity (RH) of hydrogen and air feeding gases equal to 80/100% and 60/100%, respectively.
Author(s): Maurizio Sansotera, Federico Persico, Carlo Pirola, Walter Navarrini, Alessandro Di Michele, Claudia L. Bianchi
Source: Applied Catalysis B: Environmental
Volume: 148-149 Pages: 29-35
Published: Apr (2014)
The degradation of perfluorooctanoic acid (PFOA) in water was investigated both as photolysis and photocatalysis by slurry titanium dioxide. Different surfactant concentrations, the catalyst nature and concentration as well as the irradiation power of the UV lamp were evaluated. The reactions were conducted using merely the natural dissolved oxygen (DO), in order to simulate conditions of non-enriched water, as industrially feasible. The photomineralization of PFOA was monitored by total organic carbon (TOC) analysis and ionic chromatography (IC). Finally, the photocatalytic powder was analyzed at different reaction times by X-ray photoelectron spectroscopy (XPS) and by X-ray powder diffraction (XRD) technique in order to study and interpret the catalyst deactivation phenomena occurred during the treatment.
Daan Heskes1, Valentina Rizzi2, Matteo Chiesa1, Walter Navarrini2, Maria Vittoria Diamanti2, Marco Stefancich1
1 Laboratory for Energy and NanoScience (LENS), Institute for Future Energy Systems (iFES), Masdar Institute of Science and Technology, P.O.Box 54224, Abu Dhabi, UAE
2Dipartimento di Chimica, Materiali ed Ingegneria Chimica ”G. Natta”, Politecnico di Milano, via L. Mancinelli, 7, 20131 Milano, Italy
In this work the (anti-)icing properties of anodized aluminium with different surface chemistries are investigated. In order to obtain anti icing coatings use is made of the surface chemistry as well as the structure of the surface, which are often also related to the hydrophobicity of surface . Recently it was shown that anodized alumina surface, which have a honeycomb like surface structure, can exhibit superhydrophobic properties . In addition to the structural part of the coating also different surfaces chemistries are investigated; bare alumina, silanized and perfluorinated anodized alumina surfaces as well as liquid impregnated surfaces. Characterization is done macroscopically as well as microscopically. Macroscopically the ice adhesive energy, the contact angle and contact angle hysteresis is experimentally measured. The ice adhesive energy is obtained by subjecting the iced samples to a guided impact test. On the Microscopic scale the properties of the surface are investigated using different methods of Atomic Force Microscopy. In order make fully use of the Atomic Force Microscopy imaging also the different surface chemistries on flat samples are examined. First the surface topography of the sample probed to obtain the surface roughness. Using Scanning Kelvin Probe Microscopy the surface potential of the different samples are mapped . Combining these scales of measurement can enhance the understanding of these kinds of surfaces.