1,354,114 research outputs found
Titania-Based Freestanding Electronically Conductive Electrospun Anodes with Enhanced Performance for Li-Ion Batteries
No full textA conductive composite binder made of poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and polyethylene oxide is utilized in a freestanding electrospun anode, loaded with high amounts of TiO2 for Li-ion batteries (LIBs). This kind of conductive binder polymer which enhances the performance of the cell is used for the first time. To prove the superior characteristics of these PEDOT:PSS binder-based electrodes, the polyvinylidene fluoride-based fibrous anode was also prepared by electrospinning. The electrospinning condition was thoroughly investigated and optimized to reach a robust fully covered fibrous network. The performed electrochemical characterizations show that PEDOT:PSS is electrochemically active and leads to an increased gravimetric capacity up to about 302 mA h/g at 0.2 C. After 100 cycles, PEDOT:PSS-based anodes showed a stable cycling performance which is comparable with commercial titanate-based electrodes. The outstanding performance of the electrodes is attributed to the improved titania loading and the electronically conductive highly porous network which contributed to charge-transfer kinetics. This study shows the potential of PEDOT:PSS as a conductive binder for other active materials in LIBs and self-standing electrodes for lower resistance and higher specific capacity
Electrospun Nanotubular Titania and Polymeric Interfaces for High Energy Density Li-Ion Electrodes
No full textIn the current study, for the first time, electrospinning of nanotubular structures was developed for Li-ion battery high energy density applications. For this purpose, titania-based nanotubular materials were synthesized and characterized. Before electrospinning with PVDF to obtain a self-standing electrode, the nanotubes were modified to obtain the best charge-transferring structure. In the current study, for the first time, the effects of various thermal treatment temperatures and durations under an Ar-controlled atmosphere were investigated for Li+ diffusion. Electrochemical impedance spectroscopy, cyclic voltammograms, and galvanostatic intermittent titration technique showed that the fastest charge transfer kinetics belongs to the sample treated for 10 h. After optimization of electrospinning parameters, a fully nanotube-embedded fibrous structure was achieved and confirmed by scanning electron microscopy and transmission electron microscopy. The obtained flexible electrode was pressed at ambient and 80 °C to improve the fiber volume fraction. Finally, the galvanostatic charge/discharge tests for the electrospun electrode after 100 cycles illustrated that the hot-pressed sample showed the highest capacity. The polymeric network enabled the omission of metallic current collectors, thus increasing the energy density by 14%. The results of electrospun electrodes offer a promising structure for future high-energy applications
CeO2 nanorod decorated NrGO additives for boosting PEMFC performance
No full textThis study presents a novel and highly efficient CeO2-based type of additives to improve the performance of PEM fuel cells. Cerium(IV) oxide (CeO2) nanorods and CeO2 nanorod decorated nitrogen-doped reduced graphene oxide (NrGO) (CeO2/NrGO) were synthesized and utilized to enhance the ORR performance of PEMFCs. With a low energy transition between Ce+3 to Ce+4 and its high catalytic activity, CeO2 could promote O2 reduction. The structural properties of CeO2 nanorods and the CeO2/NrGO composite were investigated using XRD, RAMAN, SEM, TEM, TGA, BET, and XPS. The synthesized CeO2 nanorods and CeO2/NrGO composite were mixed with a low platinum loading (0.09 mgPt.cm−1), and ex-situ electrochemical characterizations were performed (CV and LSV) to evaluate their catalytic activities. Fuel cell performance tests and in-situ impedance analyses were also conducted to confirm the electrochemical results. Compared to commercial Pt/C-based MEA (269 mW.cm−2), the addition of both CeO2 nanorods (382 mW.cm−2) and CeO2/NrGO (389 mW.cm−2) to the catalyst layer showed a significant enhancement in fuel cell performance, due to the unique oxygen buffer ability of the synthesized additives
Nanofiber based hybrid sulfonated silica/P(VDF-TrFE) membranes for PEM fuel cells
No full textIn this study, novel nanofiber based-hybrid proton conducting membranes for polymer electrolyte membrane (PEM) fuel cells were fabricated via electrospinning method using sulfonated silica particles (S–SiO2) as a functional additive. Here, poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) was used as the carrier polymer during electrospinning step for the fabrication of PEM fuel cell membrane structure for the first time in literature. The effect of electrospinning conditions, i.e. namely, solvent, carrier polymer, electrospinning voltage, relative humidity, and flow rate on the uniformity of the resultant electrospun mats, and the average fiber diameter, respectively, were investigated in detail. Furthermore, electrospinning was conducted with poly(vinylidene fluoride) (PVDF) as the carrier polymer to compare with (P(VDF-TrFE)) as well. S–SiO2 particles were homogeneously distributed along the carrier polymer without any noticeable bead formation. After electrospinning, fiber mats were transformed into dense membranes via hot-pressing and subsequent Nafion® impregnation. After obtaining the densified membrane, proton conductivity, water uptake and mechanical strength of the hybrid membranes were examined and reported as well. Consequently, hybrid membrane with P(VDF-TrFE) carrier exhibited a superior proton conductivity (102 mS/cm) benchmarked with PVDF carrier polymer containing membrane (43 mS/cm) and solution casted Nafion® membrane (95 mS/cm) at the same conditions
Facet-Dependent Interfacial and Photoelectrochemical Properties of TiO2 Nanoparticles
No full textThe photoelectrochemical properties of titanium dioxide (TiO2) nanoparticles are directly related to the presence of certain facets. The synthesis of such particles is challenged using volatile and sensitive precursors utilizing shape capping agents. In this study, an easier two-step synthesis technique for the preparation of well-specified morphology TiO2 nanocrystals from TiO2 powder is demonstrated. The facet-dependent Fermi level and flat band potential of the prepared particles are calculated and their photoelectrochemical properties are investigated by Cu2+ and Pb2+ photo/electrodeposition. From Cu2+ electrodeposition, it is shown that the presence of {100} and {001} facets in cubic morphology facilitates the electrodeposition with progressive nucleation mechanisms, while the presence of {101} facet in octahedral geometry follows instantaneous nucleation mechanisms. The activity of electroreduction is also related to the flat-band potential which shows the highest activity in Pb2+ electrodeposition for octahedron nanostructure due to the alignment of the reduction potential to the edge of the flat band. Photodeposition of Cu2+ and Pb2+ ions shows identical trends to electrodeposition indicating the facets influence in ion adsorption and structure of the bandgap of morphological TiO2. The findings emphasize the importance of facet-dependent surface adsorption and bandgap structure designing faceted TiO2 nanoparticles for tailored applications
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Electrospun Nanofiber Electrodes for Boosted Performance and Durability at Lower Humidity Operation of PEM Fuel Cells
No full textThe need for the development of new materials and strategies to enhance the performance of the PEM fuel cell at low humidity and platinum (Pt) loadings is becoming increasingly crucial. Due to this fact, the current study presents the fabrication of electrospun sulfonated silica (S-SiO2) as a poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE))-based, flexible, freestanding, and highly porous novel cathode structure for PEM fuel cells. The developed fiber-based P(VDF-TrFE)/Pt/C/S-SiO2cathodes are compared with electrospun PVDF/Pt/C/S-SiO2, PVDF/Pt/C/Nafion, and conventionally sprayed electrodes to evaluate the utility of a new (carrier) P(VDF-TrFE) polymer in electrode structure. Morphological analyses revealed that S-SiO2and Pt/C particles were homogeneously distributed along the fibers without any significant agglomerations. The MEAs prepared by fiber-based P(VDF-TrFE)-Pt/C/S-SiO2cathodes with low Pt loadings (0.1-0.15 mg cmPt-2) demonstrated promising fuel cell performance recording up to 417.7 mW cm-2. It also exhibited a remarkable power output retention (98.2%) under partially humidified conditions. In situ electrochemical measurements reveal that enhanced particle distribution and Pt/S-SiO2surface contact results in the cathode performance surpassing that of conventional sprayed and fiber-based PVDF/Pt/C/Nafion cathodes. The fiber-based P(VDF-TrFE)/Pt/C/S-SiO2cathodes exhibited a promising durability record retaining up to 86.5% of their maximum power output after 30 000 cycles of a Pt-dissolution accelerated stress test (AST). Furthermore, P(VDF-TrFE)-Pt/C/S-SiO2cathodes with high S-SiO2loadings exhibited a 2.7% gain in maximum power density after 1000 cycles of a carbon corrosion durability test
Variations on the Author
No full text“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
All-carbon hybrids for high performance supercapacitors
No full textA hybrid nanostructure with partially reduced graphene oxide (rGO) and carbon nanofibers (CNFs) was fabricated and used as supercapacitor electrodes. A straightforward, environmentally friendly, and low-cost microwave-assisted reduction process was developed for the synthesis of rGO/CNF hybrid structures. The fabricated supercapacitor devices showed a specific capacitance of 95.3 F g−1 and a superior long-term cycling stability. A capacitance retention of more than 97% after 11 000 galvanostatic charge discharge cycles was obtained. These and other results reported in this paper indicate that high-rate, all-carbon, rGO/CNF hybrid nanostructures are highly promising supercapacitor electrode materials
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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