1,721,202 research outputs found
Templating induced behavior of platinum-free carbons for oxygen reduction reaction
No full textThe aim of this work is to investigate the effect that pore shape and morphology may introduce in the behavior of some platinum free catalysts for the oxygen reduction reaction (ORR). Samples of the catalyst are obtained heat-treating a reactant mixture with constant composition and using a variety of templating procedures, i.e. shape-imprinting materials (like high surface area silica and Black Pearls 2000), and some self-templating processes (freeze-drying and in-situ generation of gas bubbles). Reaction products are characterized by XPS, BET and electrochemical methods. Analysis of results shows that the ORR catalyst activity depends in a complex manner on structural and morphological features, being not only affected, as expected, by surface area and pore width, but also by the pore shape. In a detailed examination a relation in fact emerges between ORR activity and relative abundance of micro- and mesopores of different size and pore shape
Water-dependent structural and chemical relaxation of bulk Co3O4 from cobalt nitrate decomposition
No full textThe cell size of Co3O4 powders from exhaustively long cobalt nitrate decompn. (T = 260-850 °C) is shown to depend on heating temp. and to expand upon prolonged room temp. aging (1 yr). By means of TGA and gas mass analyses, water from the starting salt is bound to the product oxide to various extents and is spontaneously released over time. Excess non-stoichiometric oxygen is left unaffected. A relation is obsd. between expanding cell size and decreasing bound water, suggesting that water is dissociatively accommodated in the lattice. The result is not within current defectivity models for Co3O
Oxide electrodes. A new technique to bind oxide powders onto Au substrates
No full textA technique is described to obtain supported oxide powder electrodes. Preformed powders are first embedded into a gold substrate, as reported by Totir et al. and then made to adhere in place by heating at T .apprx. 260-300°C in flowing oxygen. This latter step is of the greatest importance to obtain reliable electrodes for use in aq. electrolytes. Electrode stability and reproducibility are examd. on voltammetric and O2 evolution results using Co3O4 as a sensitive test oxide material. Many independent Au-Co3O4 electrodes compare favorably with one another and with graphite-supported electrodes from an unrelated, room temp. binding technique. Substrate and oxide-substrate junction effects are minimized
Influence of alkali metal cations on the rate of oxygen evolution from a mixed Mg-LiCoO2 oxide
No full textO2 evolution from a mixed Mg-LiCoO2 oxide is investigated in base solns. of alkali metal cations (0.1-2 M LiOH, KOH, or CsOH) without added supporting electrolytes. Tafel slopes range 30-50 mV/decade, scarcely related to the used alkali. However, Tafel lines are displaced to more pos. potentials in passing from CsOH to KOH and LiOH at the same concn., and moreover, reaction orders with respect to OH- decrease from .apprx.3 to .apprx.1 along the same alkali sequence with fractional rather than integer values. The reaction mechanism is examd. on the assumption that Temkin-type adsorption conditions apply to the many reacting intermediates possibly involved. Anal. equations representing Tafel slope and reaction order in Temkin conditions are derived and reported for many frequently adopted O2 evolution pathways, most of them for the first time. From these equations, the exptl. behavior is reconciled with a const. mechanism (Kobussen's path) in which the rate-detg. step varies depending on the alkali cation, shifting forward in the sequence of elementary steps from early positions in CsOH and KOH to the last one in which mol. O2 is released in LiOH. Cation interactions with reacting surface sites apparently intervene to modify the reaction activation free energy profile, stronger for Li+ than K+ and Cs+. Structural relations with Li+ (and Mg2+) sites in the oxide lattice may be involved. However, the interaction sequence, Li+ > K+ > Cs+, is similar to that obsd. at the interface of many structurally and chem. unrelated oxides suspended in water and is attributed to entropic contributions from interactions of water mols. bonded in the hydration ion cosphere and at the oxide-soln. interface
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
Methanol-Tolerant Pt-Free Materials for ORR in DMFC
No full textIn September 2015 193 Member Countries of the United Nations signed the 2030 Agenda. In this historical document, approved by UN General Assembly, 17 Sustainable Development Goals to be achieved by 2030 were set. The seventh goal is “Affordable and Clean Energy”, i.e. guaranteeing everyone access to an economical, reliable, sustainable and modern energy system.
Electrochemical systems represent good candidates to reach this goal, both as energy storage systems, e.g. fuel cells and zinc-air batteries, and conversion systems, e.g. supercapacitors. In the former, the reduction reaction represents the most challenging aspect since the oxygen reduction reaction (ORR) is characterized by a sluggish kinetic, which limits the energy-conversion efficiency [5-6] and needs an efficient catalyst. Platinum is the most used material, but it is characterized by high costs, limited availability, and technological limitations, as Ostwald ripening and coalescence. The worldwide research to replace Pt with a Platinum Group Metals free material with relatively similar efficiency, higher stability but lower costs started in the sixties with the seminal work of Jasinsky on metal phthalocyanines. Since then, many articles about metal-doped nitrogen- modified carbon-based materials with very astonishing results have been published.
The use of these materials in direct methanol fuel cells (DMFCs) has been explored and studied in the last few years. These power supply systems are very promising since they are characterized by a good efficiency and a high fuel energy density (6.1 Wh g−1). However, an important aspect that must be considered in the development of this system is the tolerance to methanol of the cathode material since methanol crossover through the membrane from anode to cathode causes a reduction of cell voltage of about 0.1-0.2 V (with Pt-based cathode).
In this presentation some data about methanol-tolerance of Pt-free carbon-based materials, prepared by using an easy synthetic method, will be presented. Results are interesting and promising, since the good performance of these materials is maintained up to a MeOH concentration of about 5M.
These instructions are an example of what a properly prepared meeting abstract should look like. Proper column and margin measurements are indicated
Metodi elettroanalitici per lo studio e la determinazione di acidi nucleici : KEYNOTE Lecture
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe 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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