1,720,973 research outputs found
Performance evaluation of poly(vinylidene fluoride)- vinyl benzyl trimethyl ammonium chloride copolymer as anion exchange membranes for fuel cell applications
No full text7 figures, 1 table.In recent years, poly(vinylidene fluoride) (PVDF) and its family of copolymers have started to gain increasing attention as potential systems to produce chemically and mechanically stable anion exchange membranes (AEMs). Here, a novel anion exchange membrane has been synthesized by chemical grafting of a vinyl benzyl trimethylammonium chloride monomer to the PVDF backbone. The resulting PVDF-VB copolymer was investigated under three ionic forms, i.e., Cl–, HCO3–, and OH–, comparing the swelling capability, mechanical robustness, transport properties, and ionic conductivity. In its hydroxylated form, the PVDF-VB membrane exhibited efficient OH– transport under both long and short ranges and achieved a conductivity value of 20 mS/cm at 80 °C and 90% RH. For the first time, the single H2–O2 fuel cell performance of PVDF-VB was investigated, resulting in a beginning-of-life OCV of 1.04 with a peak power density of 118 mW cm–2 at 70M.H.R., I.N., and C.S. acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 1409 published on September 14, 2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU – Project Title UNIRE – CUP H53D23007910001, Grant Assignment Decree No. 1409 adopted on September 14, 2022 by the Italian Ministry of Ministry of University and Research (MUR). The ICB-CSIC authors (D.S. and P.F.N.) acknowledge Grant PID2020-115848RB-C21 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe
Advanced processing and characterization of Nafion electrolyte films for solid-state electrochromic devices fabricated at room temperature on single substrate
No full textThe design and development of effective solid-state electrolytes represent an emerging challenge towards the fabrication of electrochromic (EC) and multifunctional devices, such as photoelectrochromics, with benefits in terms of reduced cost, environmental impact as well as safety. Here, we present the processing and the characterization of a suitable Nafion film with the certain thickness of 8 μm used as electrolyte layer in a novel solid-state EC device fabricated at room temperature (RT) on a single substrate (both glass and plastics) with an architecture based on a substrate/ITO/WO3/Nafion-film/ITO configuration. In particular, we focused on the morphological characteristics, proton conductivity and water molecular dynamics of Nafion film in order to provide insight into the EC behavior of these novel devices. EIS analysis performed over a wide range of RH and temperature, showed good proton conductivity values (e.g. 4.42 × 10− 3 S cm− 1 at 30 °C and 50% RH), suitable for practical EC operation. At the same time, high values of water self-diffusion coefficients (D) and the spin-lattice relaxation times (T1) were measured by NMR spectroscopy, proving a similar behavior as well as the same proton conduction mechanism with that observed for thicker Nafion membrane (50 μm thick) prepared by solution casting. These findings were confirmed by the water uptake measurements since both the film and the membrane showed a water uptake value of about 24 wt%. Furthermore, a homogenous, uniform and very smooth surface (Ra of 0.94 nm) with small grain size (ca. 50 nm) was observed by SEM and AFM analysis. Noteworthy, the Nafion film ensured high optical properties, interfacial robustness and electrochemical stability to EC device: cyclability (300 CV cycles), long-term durability of at least 1000 chronoamperometric cycles
Modelling Lithium‐ion Transport Properties in Sulfoxides and Sulfones with Polarizable Molecular Dynamics and NMR Spectroscopy
Full text linkWe present a computational study of the structure and of the transport properties of electrolytes based on Li[(CF3SO2)2N] solutions in mixtures of sulfoxides and sulfones solvents. The simulations of the liquid phases have been carried out using molecular dynamics with a suitably parametrized model of the intermolecular potential based on a polarizable expression of the electrostatic interactions. Pulse field gradient NMR measurements have been used to validate and support the computational findings. Our study show that the electrolytes are characterized by extensive aggregation phenomena of the support salt that, in turn, determine their performance as conductive mediums
An NMR study on the molecular dynamic and exchange effects in composite nafion/sulfated titania membranes for PEMFCs
No full textSulfated titania nanoparticles were evaluated as inorganic additives in composite Nafion based membranes, to be considered as advanced electrolyte in proton exchange membrane (PEM) fuel cells (FCs). Three different filler loadings respect to the polymer were comparatively investigated to elucidate the effect of the inorganic particles on membrane peculiar properties and finally establish the most effective electrolyte composition. Water dynamics
were investigated by NMR spectroscopy, including pulsed-field-gradient diffusion and 1H spectral analyses conducted as a function of temperature (20-130 °C), and by water content measurements, providing a general description of the water management inside the systems and of the effects of the fillers.
Due to its strong acidity and hydrophilicity, sulfated titania was found to improve both the water retention and diffusion in the composite membranes in respect to plain recast Nafion, in the whole range of investigated temperatures, with a significant impact in the region of high temperatures and very low water content.
In this work, self-diffusion coefficients data were interpreted in terms of a simple “two sites” model involving exchange between relatively bound and mobile water sites to discuss the nature of water dynamics and the state(s) of the water (bound and free states) both inside composite and filler-free membranes, as well as its interaction with the hydrophilic polymer sites and particles surface. A quantitative analysis was elaborated to estimate the number of water molecules involved in the hydration shell of the hydrophilic groups of both polymer and filler, as function of the membrane water content. Despite the
simplicity of this “bound/free water exchange” model, we obtain consistent values corresponding to about thirteen water molecules per sulfonic group
Lithium‐Ion Transport Properties in DMSO and TEGDME: Exploring the Influence of Solvation through Molecular Dynamics and Experiments
No full textThis study explores the properties of aprotic electrolytes via the application of experimental methods, including nuclear magnetic resonance spectroscopy and electrochemical techniques, along with molecular dynamic modeling. The aim is to provide a quantitative description of the physico-chemical properties of two well-established electrolytes (case studies), each exhibiting significantly distinct dielectric properties: a LiTFSI (Lithium bis(trifluoromethanesulfonyl)imide) solution in dimethyl sulfoxide (DMSO, dielectric constant & varepsilon; =46.68) and a LiTFSI solution in tetraethylene glycol dimethyl ether (TEGDME, & varepsilon; =7.71). We obtained a comprehensive insight into the properties of the electrolytes at both the macroscopic-collective and molecular levels with particular emphasis on the interactions between the Li ions and solvent molecules. We discovered remarkable disparities in the structural arrangements, solvation behaviors, and bulk-related properties of these electrolyte systems, particularly in response to temperature changes.A new set of experimental observables along with molecular dynamics has been used to characterize the conductive, electrochemical and structural properties of aprotic electrolytes based on LiTFSI in DMSO and TEGDME. The remarkable difference in their behavior, especially in response to temperature changes, was mapped onto their structural and solvation features. imag
Aprotic electrolytes beyond organic carbonates: transport properties of LiTFSI solutions in sulphur based solvents
No full textThis work illustrates a physico-chemical study of the structural, dynamic, and transport properties of electrolytes made of LiTFSI solutions in sulphoxide and sulphone solvent mixtures. Experimental measurements, by Raman and NMR spectroscopies, as well as electrochemical impedance spectroscopy, reveal the formation of a variety of ionic aggregates depending on the solvent composition that significantly affect the ion mobility and conductivity of the electrolyte. Mixtures containing tetrahydrothiophene-1-oxide exhibit a larger ion mobility due to a rapid exchange mechanism between solvent molecules, whereas the use of tetramethylene sulphone favors the formation of ionic aggregates due to the strong dipolar interactions between solvent molecules
(Invited) Development of Cost-Effective Anion Exchange Membranes for Water Electrolyzers
No full text
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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