Papers by Violeta Barranco
Journal of The Electrochemical Society
Biocarbon monoliths were obtained from Eucalyptus grandis and the influence of wood anisotropy on... more Biocarbon monoliths were obtained from Eucalyptus grandis and the influence of wood anisotropy on the electrical and electrochemical performance as supercapacitor electrodes was studied. They were produced from wood pieces cut along the transversal and longitudinal direction of the tree trunk, followed by pyrolysis and, for some of them, also by activation with CO2. Monoliths with drilled channels were also obtained. All the monoliths were characterized by SEM, nitrogen adsorption/desorption isotherms, electrical conductivity measurements and electrochemical measurements, the latter in 2M aqueous H2SO4 electrolyte. Electrical conductivity and specific capacitance are higher for the transversal carbon monoliths than for the longitudinal ones. The electrical conductivity reaches values up to 27 S cm−1 for the transversal monolith. The specific capacitance reaches values up to 260 F g−1 for the transversal monolith that was activated and drilled. However, the highest volumetric capacit...
Revista de Metalurgia, 1998
Electrochimica Acta, 2014
ABSTRACT A graphite oxide, obtained on a large scale at low cost as an intermediate in the graphe... more ABSTRACT A graphite oxide, obtained on a large scale at low cost as an intermediate in the graphene production, achieves specific capacitances (159 Fg−1 in H2SO4 and 82 Fg−1 in (C2H5)4NBF4 in acetonitrile) that compete with those of activated carbons and largely surpass the values obtained with graphene nanoplatelets. More promising, the high electrode density leads to volumetric capacitances of 177 and 59 F cm−3 in the aqueous and the organic electrolytes, respectively, which are above most data reported for carbons. In the aqueous electrolyte, the graphite oxide stands out on energy density when compared to graphene nanoplatelets and on power capability if compared to an activated carbon commercialized for supercapacitors, whereas in the organic electrolyte, the limited interlayer spacing restricts the mobility of the larger ions into the expanded graphitic structure. This study also illustrates that the specific surface of carbons measured by standard gas adsorption may not be a relevant parameter as it does not always match the electrochemically active area involved in the energy storage.
Waste and Biomass Valorization, 2014
Wood residues are ordinary wastes in the forestry industry and their valorization is an important... more Wood residues are ordinary wastes in the forestry industry and their valorization is an important issue. Eucalyptus grandis wood dust was chosen as a model wood residue and biocarbons (BCs) and activated BCs were prepared from it and studied as active materials for supercapacitor electrodes. Several ordinary activation methods were used and microporous activated BCs with specific surface areas up to 900 m 2 g -1 , and different content of oxygenated surface groups were obtained. The preparation or activation temperature is the parameter that mainly affects the electrical conductivity. For temperatures above 700°C, the samples reach an electrical conductivity as high as 1 S cm -1 . The specific capacitance of the activated BCs reaches values up to 203 F g -1 in acidic electrolyte. The highest specific capacitance is obtained when chemical activation with ZnCl 2 at 900°C followed by chemical oxidation with nitric acid is used. BCs activated with ZnCl 2 at 900°C and CO 2 at 800°C displayed good rate capability and the maximum power density. Activation with ZnCl 2 at 900°C also leads to BCs with the maximum energy density. These results show that E. grandis wood dust is a promising low cost and environmental friendly precursor for biocarbon electrodes.
The Journal of Physical Chemistry C, 2014
ABSTRACT Specific capacitance of carbons in aqueous KOH electrolyte seems to have two contributio... more ABSTRACT Specific capacitance of carbons in aqueous KOH electrolyte seems to have two contributions, a double-layer capacitance and a pseudocapacitance. Moreover, the specific capacitance increases as the specific surface area does. Here, we report that the pseudocapacitance is associated with the K+ ion and the double-layer capacitance with both K+ and OH– ions. The former ion dominates the capacitance of a real two-electrode supercapacitor. Two microporous carbon monoliths with surface areas similar for micropores below 0.63 nm but different for larger micropores are chosen. There is a correlation between the double-layer capacitance due to those ions and the surface areas due to micropores with sizes above a certain value. It provides information on the size of those ions as they are electroadsorbed at the double layer. The dielectric permittivity associated with the K+ and OH– ion is discussed in relation to the confinement of these electroadsorbed ions in the micropores.
The Journal of Physical Chemistry C, 2010
Carbon nanofibers (CNFs) show a high electrical conductivity but a reduced specific surface area ... more Carbon nanofibers (CNFs) show a high electrical conductivity but a reduced specific surface area that limits their use as electrode materials for supercapacitors. In this work, amorphous CNFs, with a relatively high electrical conductivity are easily activated in KOH, using certain KOH/CNF weight ratios. Activation does not produce any important change in the shape, surface roughness, diameter, graphene sheet size, and electrical conductivity of starting nanofibers. However, activation leads to new micropores and larger surface areas as well as a higher content of basic oxygen groups. They clearly enhanced the specific capacitance, attaining values higher than those reported for other activated CNFs. In this study, the effects of micropore size and oxygen content on the specific capacitance are discussed for three electrolytes: H 2 SO 4 , KOH, and (CH 3 CH 2 ) 4 NBF 4 . Moreover, a good cycle life is found for the most activated CNFs.
Surface and Coatings Technology, 2010
... Avda. Gregorio del Amo 8, 28040, Madrid, Spain. b, Instituto de Ciencias de Materiales de Mad... more ... Avda. Gregorio del Amo 8, 28040, Madrid, Spain. b, Instituto de Ciencias de Materiales de Madrid, ICMM, Consejo Superior de Investigaciones Científicas, CSIC, Sor Juana Inés de la Cruz, 3, Cantoblanco, 28049, Madrid, Spain. c, ...
Journal of Power Sources, 2014
ABSTRACT The monoliths studied in this work show large specific surface areas (up to 1600 m2 g−1)... more ABSTRACT The monoliths studied in this work show large specific surface areas (up to 1600 m2 g−1), high densities (up to 1.17 g cm−3) and high electrical conductivities (up to 9.5 S cm−1). They are microporous carbons with pore sizes up to 1.3 nm but most of them below 0.75 nm. They also show oxygen functionalities. The electrochemical behavior of the monoliths is studied in three-electrode cells with aqueous H2SO4 solution as electrolyte. This work deals with the contribution of the sulfate ions and protons to the specific capacitance of carbon monoliths having different surface areas and different contents of oxygen groups. Protons contribute with a pseudocapacitance (up to 152 F g−1) in addition to the double layer capacitance. Sulfate ions contribute with a double layer capacitance only. At the double layer, the capacitance of the sulfate ions (up to 291 F g−1) is slightly higher than that of protons (up to 251 F g−1); both capacitances increase as the surface area increases. The preference of protons to be electroadsorbed at the double layer and the broader voltage window of these ions account for their higher contribution (70%) to the double layer capacitance.
Journal of The Electrochemical Society, 2012
Carbon nanocoils (CNCs) are coiled carbon nanofibers of ca. 10 nm in fiber diameter, and 10-20 nm... more Carbon nanocoils (CNCs) are coiled carbon nanofibers of ca. 10 nm in fiber diameter, and 10-20 nm in internal coil diameter. They are prepared through several oxidation treatments, which lead to a graduate content in surface oxygen groups evolving as either CO or CO 2 in temperature-programmed desorption. The CNCs show a moderate surface area (40-240 m 2 g −1 ) and a relatively high electrical conductivity (0.1-0.2 S cm −1 ). Some CNCs are activated to develop surface area. The electrochemical behaviour of CNCs as supercapacitor electrode is studied in the electrolytes H 2 SO 4 and Et 4 NBF 4 . From the parameters C 1 (overall specific capacitance measured at 1 mA cm −2 ), S BET (BET specific surface area), and CO and CO 2 content, the plots of C 1 /S BET vs. CO/S BET and vs. CO 2 /S BET are analyzed. In the acidic electrolyte, the oxygen groups evolving as CO 2 contribute significantly to enhance C 1 in addition to the groups evolving as CO. C 1 /S BET shows a linear dependence, with high slope, on CO 2 /S BET , and an exponential dependence on CO/S BET . In the organic electrolyte, the two kinds of oxygen groups contribute less to C 1 . The specific pseudocapacitance and double layer capacitance are determined and discussed in relation to the CO and CO 2 content and the S BET value.
Journal of Biomedical Materials Research Part A, 2007
Oxidation of Ti6Al4V at 5008C for 1 h in air results in the formation of an outer ceramic layer t... more Oxidation of Ti6Al4V at 5008C for 1 h in air results in the formation of an outer ceramic layer that improves osteoblast behavior and decreases Ti and Al ion release. In this work, alumina blasted Ti6Al4V alloy has been thermally treated and its in vitro biocompatibility has been assessed. Roughness of the blasted alloy was not found significantly altered after heat treatment while chemical surface analysis indicated an increase in stable TiO 2 and Al 2 O 3 oxides. Cell attachment, spreading, cytoskeleton organization as well as cell proliferation, viability, and procollagen I peptide secretion of human primary osteoblasts, impaired on alumina blasted Ti6Al4V, were found to be greatly enhanced on the thermally oxidized blasted alloy. Other informative markers of the osteoblastic phenotype such as alkaline phosphatase, osteocalcin, osteoprotegerin, and mineralized nodule formation were evaluated and indicated that osteoblasts responded at the same extent on untreated and thermally treated blasted alloys. Taken together, our in vitro results indicate that thermal oxidation of alumina blasted Ti6Al4V may favor successful osseointegration by promoting early interactions of osteoblastic cells and the modified surface alloy.
Journal of Biomedical Materials Research Part A, 2006
Thermal oxidation treatments of Ti6Al4V, at 500 and 700°C, for 1 h result in the formation of an ... more Thermal oxidation treatments of Ti6Al4V, at 500 and 700°C, for 1 h result in the formation of an outer "ceramic" layer of rutile, which enhances osteoblast response. In the present study, we have measured in vitro Ti and Al ion release from Ti64 alloy in the as-received state and after thermal oxidation treatments at 500 or 700°C, to culture medium under standard cell-culture conditions. Concentrations of both Ti and Al released from both thermal oxidation treatments were lower than from polished alloy. Al was released from the treated or untreated surfaces in substantially lower extent than Ti. Titanium and aluminium ions affected primary human osteoblast proliferation, metabolic activity, and differentiation in a dose-dependent manner. Treatments with individual Ti or Al metal ions in similar concentration ranges than released from the surfaces did not alter osteoblast response, which also remained unaffected after treatments with combinations of Ti plus Al applied in the proportional relations than detected in ion-release experiments. We then selected higher concentrations of Ti that impaired osteoblast proliferation and differentiation, while the proportional lower concentrations of Al did not alter osteoblast behavior. In spite of its inert character, it was found that Al significantly enhanced the deleterious effect of Ti on osteoblast differentiation. Therefore, thermal oxidation treatments of Ti6Al4V alloy may improve the biocompatibility of the alloy by reducing both Ti and Al release, and thus attenuating ion-mediated interference with osteoblast differentiation.
Electrochimica Acta, 2007
... a Centro Nacional de Investigaciones Metalúrgicas, CENIM, Consejo Superior de Investigaciones... more ... a Centro Nacional de Investigaciones Metalúrgicas, CENIM, Consejo Superior de Investigaciones Científicas, CSIC, Avda. Gregorio del Amo 8, 28040 Madrid, Spain. Received 24 July 2006; revised 12 December 2006; accepted 15 December 2006. ...
Colloid and Polymer Science, 2010
Abstract Silver ions being less toxic than silver nano-particles, a more safe material can be obt... more Abstract Silver ions being less toxic than silver nano-particles, a more safe material can be obtained to be used as antimicrobial coating. This can be achieved by using thiol chemistry and covalently attach the silver nanoparticles in the coating. Our aim is to produce a coating having ...
Applied Surface Science, 2014
This paper studies the changes in chemical composition of the thin oxide surface films induced by... more This paper studies the changes in chemical composition of the thin oxide surface films induced by heating in air at 200ºC for time intervals from 5 minutes up to 60 minutes on the freshly polished commercial AZ31 and AZ61 alloys with a view to better understanding their protective properties. This thermal treatment resulted in the formation of layers enriched in metallic aluminium at the interface between the outer MgO surface films and the bulk material. A strong link was found between the degree of metallic Al enrichment in the subsurface layer (from 10 to 15 at %) observed by XPS (X-ray photoelectron spectroscopy) in the AZ61 treated samples and the increase in protective properties observed by EIS (Electrochemical Impedance
Acta Biomaterialia, 2011
The long-term interfacial bond between an implant and bone may be improved by creating a rough su... more The long-term interfacial bond between an implant and bone may be improved by creating a rough surface on the implant in order to increase the surface area available for bone/implant apposition. A natural consequence of surface roughening is an increase in metal ion release, which is itself a surface dominated process. Based on this fact, the aim of this work is to study the influence of the microstructure and topography on the barrier properties of oxide scales thermally generated at 700 °C for 1h on Ti6Al4V surfaces after blasting with Al(2)O(3) particles (coarse) or SiO(2) and ZrO(2) particles (fine). The microstructural and topographical characterization of the thermally treated blasted surfaces has been studied by means of scanning electron microscopy coupled with energy dispersive X-ray analysis, contact profilometry and X-ray diffraction. The barrier properties and corrosion behaviour of the oxide layers have been studied by means of electrochemical impedance spectroscopy (EIS) in Hank's solution. Thermal treatment at 700 °C for 1h promotes the formation of oxide scales with different morphologies and crystalline structures depending on the degree of deformation of the blasted surface. The oxide scale grown on the finely blasted sample has a pine needle-like morphology which is mainly formed of anatase TiO(2). In contrast, the oxide scale grown on the coarsely blasted sample has a globular morphology formed mainly of rutile TiO(2). The differences in morphology, i.e. fine or coarse, of the oxide scales influence the corrosion response of the blasted thermally treated samples in Hank's solution. The EIS results permit evaluation of the different oxide scales from the capacitance and resistance values obtained in the high-frequency region and show a good correlation between the morphology and barrier properties. Oxidation treatment at 700 °C for 1h of Ti6Al4V samples coarsely blasted with Al(2)O(3) improves the corrosion behaviour due to an increase in the thickness of a compact, ordered and more structurally stable oxide scale. This is due to the globular morphology of the rutile (TiO(2)) structure maintaining an average surface roughness suitable for optimal osseo-integration with long-term interfacial bonding between the implant and bone.
Acta Biomaterialia, 2009
In this work, the in situ interaction between Ti-6Al-4V alloy and osteoblastic cells has been stu... more In this work, the in situ interaction between Ti-6Al-4V alloy and osteoblastic cells has been studied by electrochemical techniques as a function of time. The interaction has been monitored for cell adhesion and growth of human osteoblastic Saos-2 cells on Ti-6Al-4V samples. The study has been carried out by electrochemical techniques, e.g., studying the evolution of corrosion potential with exposure time and by electrochemical impedance spectroscopy. The impedance results have been analyzed by using different equivalent circuit models that simulate the interface state at each testing time. The adhesion of the osteoblastic cells on the Ti-6Al-4V alloy leads to surface areas with different cell coverage rates, thus showing the different responses in the impedance diagrams with time. The effect of the cells on the electrochemical response of Ti-6Al-4V alloy is clearly seen after 4 days of testing, in which two isolated and well-differentiated time constants are clearly observed. One of these is associated with the presence of the cells and the other with a passive film on the Ti-6Al-4V alloy. After 7 days of culture, the system is governed by a resistive component over a wide frequency range which is associated with an increase in the cell coverage rate on the surface due to the extracellular matrix.
A commercially available dense carbon monolith (CM) and four carbon monoliths obtained from it ha... more A commercially available dense carbon monolith (CM) and four carbon monoliths obtained from it have been studied as electrochemical capacitor electrodes in a two-electrode cell.
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Papers by Violeta Barranco