Papers by Diego Germán Lamas
Acta Crystallographica Section A Foundations and Advances, 2021
Journal of Alloys and Compounds, 2020
Single-phased La 0.6 Sr 0.4 Co 1-y Fe y O 3-d (y = 0.2, 0.5, 0.8) nanorods exhibiting the rhomboh... more Single-phased La 0.6 Sr 0.4 Co 1-y Fe y O 3-d (y = 0.2, 0.5, 0.8) nanorods exhibiting the rhombohedral perovskite-type phase were synthesized by a pore-wetting technique. We studied their chemical composition, crystal and electronic structures, morphology and hyperfine properties as a function of the Co/Fe content of the samples. Our results demonstrate that Co cations exhibit a slightly lower oxidation state than Fe ones, resulting in a higher oxygen non-stoichiometry d for Co-rich samples. In addition, the values of d determined in this work for nanostructured samples are much higher than those reported in the literature for bulk materials. This can be attributed to the high degree of defects in nanomaterials and is probably one important factor in the high electrochemical performance for the oxygen reduction reaction of nanostructured La 0.6 Sr 0.4 Co 1-y Fe y O 3-d IT-SOFC cathodes, which have been reported in a previous work.
Materials Sciences and Applications, 2019
In this work, we study the influence of the average crystallite size and dopant oxide on the redu... more In this work, we study the influence of the average crystallite size and dopant oxide on the reducibility of CeO2-based nanomaterials. Samples were prepared from commercial Gd2O3-, Sm2O3-and Y2O3-doped CeO2 powders by calcination at different temperatures ranging between 400 and 900ºC and characterized by X-ray powder diffraction, transmission electron microscopy and BET specific surface area. The reducibility of the samples was analyzed by temperatureprogrammed reduction and in situ dispersive X-ray absorption spectroscopy techniques. Our results clearly demonstrate that samples treated at lower temperatures, of smallest average crystallite size and highest specific surface areas, exhibit the best performance, while Gd2O3doped ceria materials display higher reducibility than Sm2O3-and Y2O3-doped CeO2.
Acta Crystallographica Section A Foundations of Crystallography, 2008
Lanthanum strontium cobaltites, La0.4Ba0.6CoO3-x, which have a perovskite-type structure, are pro... more Lanthanum strontium cobaltites, La0.4Ba0.6CoO3-x, which have a perovskite-type structure, are promising electrode materials for solid oxide fuel cells (SOFCs). The purpose of the present study is to investigate the crystal structure of the cubic Pm-3m perovskitetype La0.4Ba0.6CoO3-x at room temperature and at high temperature by neutron diffractometry. Neutron diffraction data were collected in air by a diffractometer HERMES with a 150 multi-detector system. A furnace with MoSi2 heaters was placed on the sample table, and used for neutron diffraction measurements at high temperatures (J. Am. Ceram. Soc. 85 (2002) 2925). The experimental data were analyzed assuming the cubic perovskite-type structure by Rietveld method. La and Ba atoms were placed at the special position 1b 1/2, 1/2, 1/2 of the Pm-3m symmetry. Co and O atoms were put at the 1a 0, 0, 0 and 3d 1/2, 0, 0 sites, respectively. The calculated profile agreed well with the observed one taken at room temperature (Figure). The refined crystal s t r u c t u r e o f La0.4Ba0.6CoO3-x is similar with t h a t o f c u b i c La0.6Sr0.4CoO3-x at 1531K reported in our previous work [J. Appl. Crystallogr., 40 (2007) 1166].
Acta Crystallographica Section A Foundations of Crystallography, 2011
We have determined the phase diagram of nanopowdered ZrO 2 containing 10 to 14 mol% Sc 2 O 3 with... more We have determined the phase diagram of nanopowdered ZrO 2 containing 10 to 14 mol% Sc 2 O 3 with average crystallite sizes ranging from 30 nm up to 100 nm by X-ray powder diffraction, using the D10B-XPD synchrotron beam line of LNLS (Campinas, Brazil). Our study shows that the boundaries of c or t", β and γ phases strongly depend on both, Sc 2 O 3 content and crystallite size. The transition temperatures related to cooling and heating processes decrease for decreasing crystallite sizes. In addition, the experimental results corresponding to a whole heating/cooling cycle indicate the presence of a clear hysteresis effect. This work was supported by FAPESP (Brazil), LNLS (Brazil), CNPq (Brazil, PROSUL Program); ANPCyT (Argentina) and Latin-American Centre for Physics (CLAF).
The Journal of Physical Chemistry C, 2017
In this work we outline the mechanisms contributing to the oxygen reduction reaction in nanostruc... more In this work we outline the mechanisms contributing to the oxygen reduction reaction in nanostructured cathodes of La 0.8 Sr 0.2 MnO 3 (LSM) for Solid Oxide Fuel Cells (SOFC). These cathodes, developed from LSM nanostructured tubes, can be used at lower temperatures compared to microstructured ones, and this is a crucial fact to avoid the degradation of the fuel cell components. This reduction of the operating temperatures stems mainly from two factors: (i) the appearance of significant oxide ion diffusion through the cathode material in which the nanostructure plays a key role and (ii) an optimized gas phase diffusion of oxygen through the porous structure of the cathode, which becomes negligible. A detailed analysis of our Electrochemical Impedance Spectroscopy supported by first-principles calculations point toward an improved overall cathodic performance driven by a fast transport of oxide ions through the cathode surface.
Acta Crystallographica Section A Foundations and Advances, 2014
In the last years, extensive research has been devoted to develop novel materials and structures ... more In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of nanostructured La0.6Sr0.4CoO3(LSCO) and La0.6Sr0.4(Co;Fe)O3(LSCFO) cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 10000C in order to produce materials with the desired perovskite-type crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic...
Procedia Materials Science, 2012
Gel-combustion syntheses (GCPs) employing different fuels are widely recognized in the literature... more Gel-combustion syntheses (GCPs) employing different fuels are widely recognized in the literature because of their versatility, low cost and experimental flexibility. Besides, they allow to obtain a large amount of a pure, homogeneous nanopowder in a single batch process. In a previous work the authors reported new GCPs for zirconia-ceria nanopowders, syntheses based on nitrates-EDTA and nitrates-TRIS and preliminary results of morphology and structures of the different, obtained powders calcined at selected temperatures. In this article, new results about morphological and structural characterization of nanopowders obtained by fuel-rich and stoichiometric, nitrates-EDTA and nitrates-TRIS GCPs, mainly calcined at 600ºC/2 h, are informed. The characterizations were performed by SEM, TEM, DRX and S BET techniques.
The Journal of Physical Chemistry C, 2015
The aim of this work is to take further insight into the structural stability of cerium−zirconium... more The aim of this work is to take further insight into the structural stability of cerium−zirconium catalysts under reducing, oxidizing and reaction conditions. In situ synchrotron based techniques (XANES and XPD) were used in order to determine the stability of crystal structure and the oxidation state of cerium cations in the reaction conditions prevailing in the catalytic studies. In situ XPD studies in 5 mol % H 2 atmosphere revealed that no structural changes occur until 870°C. At this temperature, the sample synthesized with glycine, which presents lower crystallite agglomeration, segregated a small quantity of a reduced phase. On the contrary, the solid synthesized with lysine, with more agglomerated crystallites, does not show structural changes in all the temperature range. Reoxidation treatments in 5 mol % O 2 revealed that at 750°C the segregated phase disappears and that the original cubic structure is restored. In situ XANES studies in the Ce L III absorption edge indicate that under catalytic reaction conditions, the degree of reduction of Ce 4+ is low, allowing the occurrence of methane oxidation. The solid is capable to deliver the oxygen of its structure when no oxygen is fed into the reactor until the 50% of cerium cations become reduced, triggering the deactivation process. Therefore, it is clear for these studies that the Ce 4+ to Ce 3+ ratio in the lattice is governing the catalytic behavior of the solid. The catalytic results collected during in situ XANES experiments are in excellent agreement with our previous catalytic studies performed with a laboratory fixed bed reactor.
Acta Crystallographica Section A Foundations of Crystallography, 2011
to compare these structures with a range of similar structural motifs present in the literature. ... more to compare these structures with a range of similar structural motifs present in the literature. Conformational differences between our investigated dyes and those complexes with a different counter ion were revealed. This analysis motivated a general enquiry into the influence of the position of attached ligands on the pyridine unit within all known Ruthenium or Iron based dyes containing three bipyridyl groups. The extent of delocalisation of electron density in these pyridine groups was calculated via a bond length variation analysis [2]. This revealed that our complexes were much less delocalised (~4%) than N719 (up to 37%). This delocalisation of the pyridine ring is attributed to the superior charge transfer properties of N719 and thus its better performance in DSC operation. This work has contributed to the basic foundation of molecular engineering wherein lies the ultimate goal of being able to tailor dyes to meet a specific component design of a DSC device.
Acta Crystallographica Section A Foundations of Crystallography, 2008
Acta Crystallographica Section A Foundations of Crystallography, 2011
Catalytic reactions in which the elements of carbon monoxide (CO) and water / alcohols are added ... more Catalytic reactions in which the elements of carbon monoxide (CO) and water / alcohols are added to the double bond of alkenes are referred to as hydrocarbonylations / alkoxycarbonylations [1]. Palladium / phosphine systems are generally the preferred catalysts in these reactions since they work under relatively mild conditions [1]. The regioselectivity (linear to branched ratio) of these Pd-catalyzed reactions has been extensively investigated for styrene and related vinylarenes aimed at the synthesis of non-steroidal anti-inflammatory P.MS.31
Journal of Power Sources, 2013
h i g h l i g h t s A New 60%NiO/Ce 0.9 Zr 0.1 O 2 (ZDC6) nanomaterial was proposed as anode of S... more h i g h l i g h t s A New 60%NiO/Ce 0.9 Zr 0.1 O 2 (ZDC6) nanomaterial was proposed as anode of SOFCs. These anodes were successfully fixed onto SDC disks keeping their high porosity. Dual-chamber SOFCs with these anodes were fully characterized in pure H 2. The SOFCs exhibited good power densities of 75 mW cm À2 when operated at 650 C.
International Journal of Hydrogen Energy, 2014
The development of an economically feasible Solid Oxide Fuel Cell technology has driven the resea... more The development of an economically feasible Solid Oxide Fuel Cell technology has driven the research activity in this area toward the reduction of their operating temperature. New anode materials, with high electrocatalytic activity and resistance to coke deposition when hydrocarbons are used as fuel, have to be developed. The aim of this paper is to give a contribution in this area by studying the effect of Ni substitution by Cu in the NiO (60 wt.%)/ Ce 0.9 Zr 0.1 O 2 cermet recently proposed as a possible anode material. It was observed that the partial replacement of Ni by Cu has produced solids with high reducibility, excellent catalytic and electrocatalytic performances and higher resistance to carbon deposition in the operation with CH 4 .
Catalysis Communications, 2011
ABSTRACT This paper analyzes the influence of synthesis conditions on the reducibility and cataly... more ABSTRACT This paper analyzes the influence of synthesis conditions on the reducibility and catalytic behavior of Ce0.9Zr0.1O2 mixed oxide synthesized by α-amino acid/metallic nitrate combustion processes, through stoichiometric and non-stoichiometric routes. We concluded that the α-amino acid selected and the α-amino acid/nitrate molar ratio strongly influence the reducibility and catalytic activity in the total combustion of methane. Thus, the Ce0.9Zr0.1O2 catalyst synthesized by the stoichiometric route with glycine showed the higher catalytic activity, which, in conjunction with the well-known ionic and electronic conductivities of ceria-based oxides under reducing conditions, positions this solid as an appropriate anode material for methane-fuelled solid oxide fuel cells.
Acta Crystallographica Section A Foundations of Crystallography, 2005
With the recent advances in X-ray technology, chromium radiation (2.29 Å) has become viable for i... more With the recent advances in X-ray technology, chromium radiation (2.29 Å) has become viable for in-house data collection and phasing. Chromium radiation appears to be well suited for measuring anomalous signals from weak anomalous scatterers such as sulfur, selenium, and calcium. In particular, the anomalous scattering strengths of sulphur (f =1.14 e) and selenium (f =2.28 e), the most common intrinsic and derivatized anomalous scatterers, are doubled when using Cr K radiation compared to those for Cu K radiation (1.54 Å, S: f =0.56 e, Se: f =1.14 e). Due to the difficulties in utilizing the K absorption edge of sulphur at 5.02 Å, limited access to X-ray beamlines and related transportation issues, it has become evident that Cr K radiation is very good choice for collecting sulphur anomalous data and a may be an alternative to a synchrotron beamline for collecting selenium anomalous data. This report shows examples of S-SAD and Se-SAD phasing from data collected on an in-house Cr source. To break the phase ambiguity inherent with SAD, the directmethods procedure implemented in the program OASIS-2004 was employed. Phase discrimination using the product of the Sim and Cochran distributions leads to better initial phases and, consequently, to better electron-density maps.
Acta Crystallographica Section A Foundations of Crystallography, 2002
Acta Crystallographica Section A Foundations of Crystallography, 2005
consisting of predominantly-Ti (P6 3 /mmc) [1]. The Ti-6Al-4V rod was machined using both convent... more consisting of predominantly-Ti (P6 3 /mmc) [1]. The Ti-6Al-4V rod was machined using both conventional and high-pressure jet-assisted methods. The depth profile of residual stress was measured using xray diffraction. It was found that the compress residual stress is higher and the deeper under which the compress residual stress exists, for sample cut by high-pressure jet-assisted than for sample cut by conventional method [2]. Using transmission electron microscopy the cross-section of the surface layer was found to consist of a thin outer layer with nano-sized crystals (10 nm) and the substrate of large grains with very high density of dislocations. Electron diffraction reveals that the nano-sized outer layer is highly textured. Furthermore, the study shows that the nano-sized layer has twice the thickness for the high-pressure jetassisted cut sample (1,000 nm) than for the conventionally cut sample (500 nm). This shows that high-pressure jet-assisted cutting resulted in a thick and highly modified outer layer and provides an explanation for the large and deep compressed residual stress after high-pressure jet-assisted cutting of Ti-6Al-4V.
Electrochimica Acta, 2002
Cu UPD on Pt(111) has been studied by XANES and EXAFS in the fluorescence mode, under grazing and... more Cu UPD on Pt(111) has been studied by XANES and EXAFS in the fluorescence mode, under grazing and normal X-rays incidence, in two electrolytic mediums (sulfate solution and chlorine one). For a complete deposited Cu monolayer, with SO42− anions, oxygen atoms in atop site with respect to copper atoms are detected clearly. The Cu–Cu interatomic distance deduced from EXAFS calculations
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Papers by Diego Germán Lamas