960 research outputs found
D.H. Lawrence, La Volpe, traduzione e cura di Stefania Michelucci, edizione bilingue
No full textIt is the bilingual and critical edition of D.H. Lawrence's The Fox in the series, Elsinore, Collana di Classici Inglesi, edited and translated by Stefania Michelucci
The volume consists of a long introduction to the text, pp 11-37, of a biographical article on the author and his work (l'autore e l'opera), pp. 39-45), of a note to the text (pp. 47-48) (English and Italian, page to page, pp. 49-227) of explicatory notes (pp. 229-243) and of a biographical section (pp. 245-252)
Optimization of a Fe-N-C electrocatalyst supported on mesoporous carbon functionalized with polypyrrole for oxygen reduction reaction under both alkaline and acidic conditions
No full textA series of FeeNeC non-noble metal electrocatalysts for oxygen reduction reaction (ORR) are synthesized using mesoporous carbon (MPC) as C source, polypyrrole (PPY) as N source and Fe(II) acetate as Fe source. In the first part, the effects of the addition of polyvinylpyrrolidone (PVP) and performing a heat treatment on the MPC-PPY support before the impregnation with Fe2þ ions are investigated. In the second part, the best catalyst obtained in the first part is used as a support, and the influence of a second pyrolysis treatment performed with or without further impregnation with Fe2þ is investigated. The materials are characterized by FESEM, TEM, EDX, BET-porosimetry, XPS, and FTIR. The electroactivity towards ORR is assessed with a rotating disk electrode (RDE) apparatus in both acidic and alkaline conditions. The different synthesis pathways examined have a direct influence on the ORR activity. The electroactivity and micropores content increases after the second heat treatment
Activity of Co-N multi walled carbon nanotubes electrocatalysts for oxygen reduction reaction in acid conditions
No full textTwo catalysts are synthesized by wet impregnation of multi walled carbon nanotubes (MWCNT) with a complex formed between Co(II) ions and the nitrogen-containing molecule 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ), followed by one or two identical heat treatments in N2 atmosphere at 800 °C for 3 hours. Catalysts are fully characterized by FESEM, EDX, BET, XRD, FTIR, TGA, XPS analyses, and electrochemical techniques. The electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalysts in acid conditions is assessed by means of a rotating disk electrode (RDE) apparatus and a specific type of cell equipped with a gas diffusion working electrode (GDE). In both testing approaches, the catalyst heat-treated twice (Co-N/MWCNT-2) exhibits higher electroactivity than the catalyst heat-treated once (Co-N/MWCNT-1). Chronoamperometries both in RDE and GDE cell are also performed, showing less electroactivity decay and better current performance for the catalyst heat-treated twic
Surface chemistry and reactivity of Pd/BaCeO3∙2ZrO2 catalyst upon sulphur hydrothermal treatment for the total oxidation of methane
No full textStarting from metal nitrates and glycine, 2% Pd/BaCeO3∙2ZrO2 catalyst was prepared by solution combustion synthesis and tested towards the total oxidation of methane. The catalyst underwent heavy sulphur-hydrothermal treatment at 800 °C up to 450 h. The catalyst was fully characterized (XRD, BET, SEM, O2-TPD, FTIR analysis and catalytic activity via CH4-TPC) every 150 h. With ageing, catalytic activity tests demonstrated that the catalyst was heavily poisoned after 150 h; then it recovered the catalytic activity after 300 h, with a resulting performance better than the one reached in the fresh status. At the end of the sulphur-hydrothermal treatment, after 450 h, the catalyst resulted heavily poisoned again. On the fresh catalyst surface, IR analysis of CO adsorption evidenced the formation of highly dispersed Pd metal clusters and Pd ions. After 300 h of sulphur hydrothermal ageing, the increased catalytic activity towards methane combustion was probably supported by the segregation of ZrO2 and CeO2. Moreover, subsurface and bulk sulphate formation was detected with ageing and Pd metal species were not anymore available for CO coordination, probably because hindered by sulphate deposits. Prevailing ageing mechanisms resulted in the oxidation of the surface Pd metal particles and surface-bulk sulphates formation, the latter destroying the starting crystallographic structure, leading thus to the final catalytic activity deca
Influence of different transition metals on the properties of Me-N-C (Me = Fe, Co, Cu, Zn) catalysts synthesized using SBA-15 as tubular nano-silica reactor for oxygen reduction reaction
No full textDifferent MeeNeC catalysts for oxygen reduction reaction (ORR) are synthesized using Me(II)-phthalocyanines (Me ¼ Fe, Co, Cu, Zn) as a unique precursor molecule, and SBA-15 silica as a sacrificial template. The influence of different transition metals on the pyrolysis process and the consequent physicalechemical properties of the final catalysts were investigated using different characterization techniques such as N2 physisorption, FESEM, EDX, XPS, XRD, and thermogravimetric analysis coupled with mass spectrometry (TGAMS). The ORR activity and selectivity toward a complete 4-electrons reaction were assessed by RDE analysis in alkaline conditions. The ORR activity of the different MeeNeC catalysts decreases in the order Fe > Co > Cu > ZnzH. Microporosity, pyridinic nitrogen content and temperature at which H2 starts to be detected during the pyrolysis are directly related to the ORR activity of the different catalysts
Kinetics of Oxygen Electroreduction on Me-N-C (Me = Fe, Co, Cu) Catalysts in Acidic Medium. Insights on the Effect of the Transition Metal
No full textThe influence of three different transition metals (Me = Fe, Co, Cu) on the oxygen reduction reaction (ORR) kinetics in acidic medium of Me-N-C catalysts synthesized using Me(II)-phthalocyanine as precursors is investigated in this work. Through a detailed electrochemical characterization using cyclic voltammetry and rotating ring-disk electrode, several kinetics parameters such as Tafel slope, reaction order for oxygen and proton, apparent activation energy, selectivity towards hydrogen peroxide production, and kinetics of reduction of adsorbed oxygen were determined. The behavior of these three catalysts is analyzed in detail. A comparison between each other of the catalysts, and with a Pt-based catalyst is done. The results obtained provide clear evidence of the important role played by each transition metal in the formation of more or less effective active sites. The ORR kinetics behavior can be well interpreted according to the occurrence of a redox-mediated coverage of the active sites at low overpotentials (close to the ORR onset), which has influence on the Tafel slope, as well as on the oxygen adsorption and activation energy of the process. The results clearly show that, among the other transition metals considered, Fe is the best performing one in carrying out the ORR
Effects of the current density distribution on a single-cell DMFC by tuning the anode catalyst in layers of gradual loadings: modelling and experimental approach
No full textThe performance of a single cell direct methanol fuel cell (DMFC) is optimized by evaluating the effect of the catalyst distribution in the membrane electrode assembly (MEA) via a 3D multi-physics, multicomponent, two-phase, and not-isothermal model. The model is computed with Comsol® Multiphysics v4.4 platform, with a finite element analysis solver and simulation software. It consists of Maxwell-Stefan, Stokes-Brinckman, extended two-phase Darcy Law, modified Butler-Volmer and Tafel equations to simulate the performance of the DMFC, and to evaluate the electrochemical, fluid-dynamics and thermal phenomena. The use of a 3D model considering porous equation such as Stokes-Brinkman is helpful for understanding, describing the motions and hydrodynamic forces of interacting particles in Stokes flow, which is more realistic regarding catalyst description and validation. Moreover, the model can be used for evaluating intrinsic parameters of novel electrocatalysts. The model is validated against a set of experimental data, showing congruent and convergent data for a commercial 25 cm2 MEA consisting of Nafion® 117 and electrodes (Pt/C at the cathode and Pt:Ru at the anode) at different temperatures and inlet methanol concentrations, confirming the accuracy of the model and the equations applied. The model is used to optimize the catalytic layer distribution to obtain a more uniform current density distribution along the anodic catalyst-membrane interface and a better cell performance. The optimized anodic catalytic distribution has been implemented in a 25 cm2 in-house three-layer MEA and experimentally tested, included a short durability of 26 h, showing better stability compared to a MEA with a classic homogenous catalyst loading distribution
3D Direct Methanol Fuel Cell (DMFC) validation model for analysing new materials and components
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