1,721,174 research outputs found
New hybrid inorganic-organic proton conducting membranes for PEMFC: synthesis, properties and conduction mechanisms
Full text linkElectrochemical devices for the conversion of chemical energy into electrical power, such as proton exchange membrane fuel cells (PEMFCs), are of intense interest to industry and the scientific community because of their high energy conversion efficiency, low environmental impact, and the possibility for use in a wide variety of applications from portable electronic devices to light-duty electric vehicles. At the core of the fuel cell is a PEM that allows the transport of hydrogen ions, evolved at the anode, to the cathode where oxygen is reduced to water. Todays prevalent PEMs feature perfluorinated main chains functionalized with perfluoroether side chains terminated with acidic -SO3H groups. These materials (DupontTM Nafion®, Asashi Aciplex®, Dow®, and Flemion®) generally are characterized by a high chemical, thermal and mechanical stability; they also exhibit good proton conductivity at high levels of hydration. The hydration requirements limit the widespread commercial use of conventional PEMs, which have inadequate proton conductivity at temperatures above 90C and at low values of relative humidity. Fuel cells capable of operating above 120C at low levels of hydration would: obviate the need of bulky and expensive water management modules, simplify thermal management; and reduce the impact of catalyst poisons such as carbon monoxide. In an effort to overcome the limitations of conventional PEMs, this work reports the synthesis and characterization of new proton conducting membrane alternatives to classic fluorinated polymers for application in PEMFCs. The materials were synthesized according to two distinct strategies: 1) dope a Nafion membrane in order to improve its thermo-mechanical properties and proton conductivity or extend its operating conditions to temperatures above 100°C and an anhydrous environment; 2) synthesize and characterize proton exchange membranes based on polybenzimidazole and polysulfone as an alternative to perfluorinated polymers.
The first point regarded the study of two different systems obtained by doping a Nafion membrane with the [(ZrO2)(Ta2O5)0.119] inorganic “core-shell” nanofiller or with two different proton conducting ionic liquids, triethylammonium methanesulfonate and triethylammonium perfluorobutanesulfonate. The study of new PEMs alternative to fluorinated polymers has been developed considering polybenzimidazole and sulfonated poly(p-phenylenesulfone) membranes whose properties have been modulated by the addition of phosphoric acid and an hybrid filler or poly(1-oxotrimethylene) and silica, respectively. All the proposed materials were extensively characterized in terms of their thermal, mechanical, structural and electrical properties in order to highlight the interactions between the different components present within the membranes. These interactions govern the membranes macroscopic properties that need to be improved in order to optimize and predict the behavior of these materials under operating conditions in fuel cells.Celle a combustibile basate su membrane a scambio protonico (PEMFCs) sono dispositivi elettrochimici per la conversione di energia chimica in energia elettrica. Le PEMFCs suscitano notevole interesse sia nel mondo industriale che accademico a causa della loro elevata efficienza di conversione, basso impatto ambientale e vasta gamma di utilizzo che spazia dall’elettronica portatile fino all’autotrazione.
All’interno della cella a combustibile si trova la membrana a scambio protonico (PEM), che consente il trasferimento di protoni dall’anodo al catodo.
Attualmente le membrane polimeriche a scambio protonico maggiormente utilizzate sono costituite da polimeri fluorurati funzionalizzati con gruppi polieterei terminanti con gruppi acidi (tipicamente -SO3H). Questi materiali (DupontTM Nafion®, Asashi Aciplex®, Dow®, and Flemion®) generalmente presentano elevata stabilità chimica, termica e meccanica ma tuttavia mostrano valori di conducibilità sufficienti per il loro impiego in cella a combustibile solo per elevati livelli di idratazione. La scarsa conducibilità protonica dei polimeri perfluorurati per temperature maggiori di 90°C e bassi livelli di idratazione limita fortemente il loro utilizzo su larga scala.
Celle a combustibile che operano a temperature superiori a 120°C e bassi livelli di idratazione non necessitano dell’introduzione di sistemi di umidificazione e raffreddamento, riducendo il costo e semplificando la realizzazione ed ingegnerizzazione del dispositivo finale. Inoltre, l’aumento di temperatura riduce l’avvelenamento del catalizzatore da contaminanti esterni come ad esempio il monossido di carbonio.
Al fine di superare le limitazioni delle PEMs convenzionali, questo lavoro di tesi riporta la sintesi e la caratterizzazione di nuove membrane polimeriche a conducibilità protonica alternative ai classici polimeri fluorurati per applicazioni in celle a combustibile.
I materiali sono stati sintetizzati seguendo due diverse strategie: 1) drogare una membrane di Nafion al fine di aumentare il suo intervallo di stabilità termico e meccanico e la sua conducibilità protonica così da estenderne le condizioni operative di utilizzo a temperature maggiori di 90°C e per bassi o nulli livelli di idratazione; 2) sintetizzare e caratterizzare PEMs basate su polibenzimidazolo e polisulfone come materiali alternativi ai classici polimeri fluorurati.
Il primo punto ha riguardato lo studio di due diversi sistemi ottenuti drogando una membrana di Nafion con il filler inorganico [(ZrO2)(Ta2O5)0.119] oppure con due diversi liquidi ionici a conducibilità protonica, il trietilammonio-metansolfonato ed il trietilammonio-perfluorobutansolfonato.
Lo studio di nuove membrane alternative ai polimeri fluorurati è stato sviluppato considerando membrane di polibenzimidazolo (PBI) e polisulfone solfonato (sPSO2) le cui proprietà sono state modulate dall’aggiunta di acido fosforico e di un filler ibrido a base di silice funzionalizzata (nel caso del PBI) o di poliossotrimetilene e silice (per le membrane a base di sPSO2).
Al fine di delucidare le interazioni esistenti tra i diversi componenti presenti all’interno delle membrane, tutti i materiali sono stati ampiamente caratterizzati dal punto di vista delle loro proprietà termiche, meccaniche, strutturali ed elettriche. Queste interazioni governano le proprietà macroscopiche delle membrane che necessitano di essere migliorate al fine di ottimizzare e prevedere il comportamento di questi materiali in condizioni di esercizio in celle a combustibile
The origin of Behçet’s disease geoepidemiology: possible role of a dual microbial - driven genetic selection.
No full textAbstract
It is recognised that the genetic profiles that give rise to chronic inflammatory diseases, under the influence of environmental agents, might have been implicated in the host defence mechanism against lethal infections in the past. Behçet's disease (BD) is an immune-mediated inflammatory disease, expressed as vasculitis, triggered by environmental factors in genetically susceptible individuals. We carried out a review of published data to draw up an evolutionary adaptation model, as Author's perspective, for genetic susceptibility factors and inflammatory immune response involved in BD pathogenesis. Two lethal infectious agents, Plasmodium Falciparum and Yersinia Pestis, are proposed as the putative driving forces that favoured the fixing of the major genetic susceptibility factors to BD, thus determining its geoepidemiology. Further studies are needed to confirm the validity of this evolutionary model which includes and integrates the key insights of previous hypotheses
Genetic susceptibility to Behcet's disease: role of genes belonging to the MHC region
No full textMethod. Systematic review of the English literature between 1 January 1980 and 31 January 2010 using Medline. Case-control, population-based, observational cohort studies investigating the association between BD and HLA-B*51 subtypes, classical and non-classical HLA alleles and other HLA-related genes were selected. The geographical distribution of BD and these susceptibility genes was also taken into consideration. Case and familial case reports were excluded except for case series with more than two patients. Results. Ninety articles plus 17 obtained from other sources were included in the systematic review. We have found high evidence that a core component of genetic susceptibility to BD is within the MHC region being primarily related to an HLA-B*51 subtype: HLA-B*5101/B*510101. Moreover, HLA-A*26, HLA-B*15, HLA-B*5701 and TNF-alpha -1031C were independently associated with BD. Data suggest that other HLA (HLA-C, HLA-DR) and HLA-related [MHC Class I chain-related gene A (MIC-A), TNF-alpha] genes may play a role in BD co-susceptibility or pathogenesis. Finally, the distinctive geographical distribution of BD suggested an evolutionary selection of HLA-B*51 subtypes as the major susceptibility factors for BD. Conclusion. Further studies must be addressed to clarify the functional relevance of the different genes found to be associated with disease susceptibility and the potential interactions between genes located within and outside the MHC region
Managing CNS Involvement in Systemic Lupus Erythematosus
No full textThe occurrence of neuropsychiatric manifestations in systemic lupus erythematosus (NPSLE) represents a diagnostic and therapeutic challenge for patients and clinicians. In this article we briefly discuss new perspectives on the pathogenesis, diagnosis, attribution and outcome of NPSLE. We speculated on the possible role of a rigorous preventive strategy, which takes into account the existence of associated risk factors that are yet to be fully defined, in the management of NPSLE. Finally, we highlight the management options and focus on the established and newly available treatment protocols for the more challenging, in terms of frequency or severity, clinical features of NPSLE
Broadband dielectric spectroscopy: a tool to study the effects of nanofillers in hybrid membranes for application in PEMFCs
No full textCoronary atherosclerosis using computed tomography coronary angiography in patients with systemic sclerosis: comment on the article by Mok et al
No full textMyocardial positron emission tomography/computed tomography scan revealing right coronary artery involvement in large vessel vasculitis
Full text linkDescription of coronary artery involvement in a patient with Takayasu arteritis detected using a PET/CT perfusion scan in a symptomatic patient with normal coronary angiography
Myocardial positron emission tomography/computed tomography scan revealing right coronary artery involvement in large vessel vasculitis
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