1,721,203 research outputs found
ELECTRON MICROSCOPY AND SMALL-ANGLE X-RAY SCATTERING ANALYSIS OF THE CATALYST LAYER DEGRA
No full textThe catalyst layer is one of the most critical components of a PEM fuel cell. The catalyst, in the form of platinum nanoparticles, tends to aggregate and sinter during operation, with the consequence to reduce its active area thus the efficiency of the entire fuel cell. This paper aims to highlight the efficiency of scanning electron microscopy (SEM) and synchrotron small-angle X-ray scattering (SAXS) to characterize the catalyst layer degradation of a commercial MEA for high temperature PEM fuel cells. SEM is an effective tool for the surface analysis of the samples, since it is able to obtain a magnification from 10x up to 105x. SAXS is a suitable technique to investigate the structural features of colloidal scale (between 10 and 103 Å). The paper presents in detail the analysis of three MEAs: one is a virgin sample, one was operated discontinuously in a single fuel cell, one operated in a 25 cells stack. The experiments show the degradation of the catalyst layer after operation. In particular, the agglomeration of the Pt particles leads to a growth in size from 5 nm up to 8 nm
Phase diagram of 3beta-(N-(N,N-dimethylaminoethane)-carbamoyl)-cholesterol-dioleoylphosphatidylethanolamine/DNA complexes suggests strategies for efficient lipoplex transfection
Full text linkLipid mixing upon deoxyribonucleic acid-induced liposomes fusion investigated by synchrotron small-angle x-ray scattering
No full textMultipart cationic lipid/deoxyribonucleic acid DNA complexes lipoplexes were prepared, for the first time, by adding linear fragments of DNA to mixed lipid dispersions containing two distinct populations of cationic liposomes exhibiting different lipid headgroups and a number of systematic variations in relevant physical-chemical parameters. Upon DNA-induced fusion of liposomes, large lipid mixing at the molecular level occurs. As a result, highly organized mixed lipoplexes form spontaneously. By varying the composition of lipid dispersion, the physical properties of the emerging lipid carrier, i.e., the surface charge density and membrane thickness, can be modulated and distinct DNA packing densities can also be achieved
Simultaneous in situ and Time-Resolved Study of Hierarchical Porous Films Templated by Salt Nanocrystals and Self-Assembled Micelles
No full textTime-resolved simultaneous experiments using synchrotron radiation have been realized to study in situ the concurrent formation of different templates in hierarchical porous thin films. Silica hybrid organic-inorganic films have been dip-coated and processed to obtain two porous nanostructures: spherical ordered mesopores templated by surfactant micelle, and cubic pores formed by crystallization of sodium chloride salts. The experimental setup has allowed following in real time the chemical-physical processes behind the formation of the two different templating agents. During deposition, the self-assembly and organization of the micelles have been studied by grazing incidence small-angle X-ray scattering while the crystallization of the salt template has been monitored by wide-angle X-ray scattering. After processing, the films have been further characterized by transmission electron microscopy, two-dimensional grazing incidence small-angle X-ray scattering and X-ray diffraction. The in situ analysis has revealed a short time delay between micelles and salt crystals formation; the micelles self-assemble and organize at the end of the first evaporation stage, when ethanol evaporates, while salt starts nucleating and growth only during the second stage, when water evaporation begins
Universality of DNA Adsorption Behavior on the Cationic Membranes of Nanolipoplexes.
Full text linkNanolipoplexes have emerged worldwide as the most pRev.alent synthetic gene delivery system. Nowadays, it is accepted that complete DNA protection and a precise control of the physical attributes of emerging complexes are major steps toward rational design of efficient nanocarriers. Here we Rev.ise the mechanism of DNA adsorption to the cationic membranes of lipid nanovectors. Here we show that both the DNA-binding ability of cationic membranes and the one-dimensional DNA packing density inside the complex depen on the cationic lipid/anionic DNA charge ratio. Remarkably, both these distributions are rescaled on universal curves when plotted against γ, a dimensionless quantity expressing the ratio between the area of cationic membranes and that occupied by DNA molecules. As a result, the DNA condensation on the surface of lipid nanocarriers can be regarded as a two-step process. Our findings indicate a successful way to the rational design of next-generation drug delivery nanocarriers
Experimental analysis on the influence of operating profiles on high temperature polymer electrolyte membrane fuel cells
Full text linkThe Energy System lab at the University of Trieste has carried out a study to investigate the reduction in performance of high temperature polymer electrolyte membrane (HTPEM) fuel cell membrane electrode assemblies (MEAs) when subjected to different ageing tests. In this study, start and stop cycles, load cycles, open circuit voltage (OCV) permanence and constant load profile were considered. Polarization curves (PC) together with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data were recorded during the ageing tests to assess the fuel cell per-formance. In this paper, experimental data are presented to confirm the test methodology previ-ously proposed by the authors and to quantitatively correlate the performance degradation to the operational profiles. It was demonstrated that OCV condition, start and stop and load cycling in-crease degradation of the MEAs with respect to constant load operation. As expected, the OCV is the operational condition that influences performance degradation the most. Finally, the MEAs were analyzed with synchrotron small angle X-ray scattering (SAXS) technique at the Austrian SAXS beamline at Elettra-Sincrotrone Trieste to analyze the nano-morphological catalyst evolution. As for the catalyst morphology evolution, the ex situ SAXS methodology proposed by the authors is confirmed in its ability to assess the catalyst nanoparticles aggregation
Simultaneous in situ and Time-Resolved Study of Hierarchical Porous Films Templated by Salt Nanocrystals and Self-Assembled Micelles
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