Examinando por Autor "Plaza, Jorge"

Mostrando 1 - 9 de 9

Composite Titanium Silicon Carbide as a Promising Catalyst Support for High-Temperature Proton-Exchange Membrane Fuel Cell Electrodes
(Wiley, 2016-01-20) Lobato, Justo; Zamora, Hector; Plaza, Jorge; Rodrigo, Manuel Andrés
This manuscript focuses on the assessment of a composite titanium silicon carbide (SiCTiC) as a catalyst support for high-temperature proton-exchange membrane fuel cells (HT-PEMFCs). The support showed very high thermal and electrochemical resistances under harsh conditions (phosphoric acid). Pt nanoparticles were successfully deposited on the new SiCTiC support and it demonstrated a higher stability (lower agglomeration of the nanoparticles) than the more conventional Vulcan carbon-based catalyst, both in a commercial formulation and as prepared in the lab, with the same procedure as that used for the novel carbide material under very harsh conditions.
Enhancement of high temperature PEMFC stability using catalysts based on Pt supported on SiC based materials
(Elsevier, 2016-12-05) Zamora, Hector; Plaza, Jorge; Cañizares, Pablo; Lobato, Justo; Rodrigo, Manuel Andrés
With the aim of overcome the carbon supports of high temperature Proton Exchange Membrane Fuel cells (HT-PEMFC) electrodes, two novel non-carbonaceous support based on SiC have been assessed, SiC and SiCTiC. 40% wt. Pt was successfully deposited on them and they were physicochemical and electrochemically characterized. Both catalysts on SiC based materials showed a very high electrochemical stability in the half cell experiments in comparison with Pt on carbon support, showing a lower degradation rate of the electrochemical surface area (ECSA). Membrane Electrode Assemblies (MEAs) were prepared with the different catalysts and tested in a single cell (25 cm2) operated at 160 °C. The Pt/SiCTiC showed a good performance and the highest stability in the fuel cell tests carried under the same operation conditions. © 2016 Elsevier B.V.
Evaluation of nZVI for the degradation of atrazine in heterogeneous Fenton-like systems at circumneutral pH
(Elsevier, 2021) Plaza, Jorge; Arencibia, Amaya; López-Muñoz, María José
The requirement of acidification for the successful of the Fenton processes in water treatment has promoted the search for new strategies to work at pH close to neutrality. With this objective, in this work the use of nZVI has been evaluated for the oxidative elimination of 10 mg L−1 of atrazine at circumneutral pH with nZVI/UVA, nZVI/H2O2, and nZVI/H2O2/UVA systems. While UVA irradiation of sole nZVI was ineffective for degrading the herbicide, the addition of H2O2 boosted up the reaction, with the nZVI/H2O2/UVA system attaining the highest degradation rate. The inhibition of the reaction upon addition of tert-butanol as scavenger pointed out the significant role of hydroxyl radicals in the atrazine oxidation. The characterization of fresh and spent samples, carried out by XRD, SEM, TEM, and nitrogen adsorption-desorption experiments, confirmed the presence of ferric oxidized compounds responsible of the heterogeneous photo-Fenton-like reactions. On the basis of the degradation products determined by high performance liquid chromatography (HPLC), a scheme of atrazine degradation pathways in the ZVI/H2O2/UVA system was proposed in which the reaction is mainly initiated by alkylic oxidation rather than dechlorination. Finally, the effect on the atrazine oxidation rate of the water constituent species was analyzed in different water matrices (pure, supply, simulated and secondary effluent real water). Considered individually, Cl−, SO42−, HCO3−, and DOC, showed a moderate inhibitory effect on atrazine degradation kinetics, but their combination could explain the significant decrease of efficiency detected in the real secondary effluent water compared to less complex matrices.
High Stability Electrodes for High Temperature Proton Exchange Membrane Fuel Cell by Using Advanced Nanocarbonaceous Materials
(Wiley, 2017-09-18) Zamora, Hector; Plaza, Jorge; Cañizares, Pablo; Rodrigo, Manuel Andrés; Lobato, Justo
This work studies the stability and performance of a cathodic electrode for high-temperature proton exchange membrane (HT-PEMFC) systems prepared with a carbon nanosphere (CNS) based microporous layer and carbon nanofibers (CNFp) used as a catalyst support. The obtained results are compared with a standard Vulcan carbon XC72 based electrode. With this purpose, two membrane−electrode assemblies (MEAs) were prepared using the cathodic electrodes and tested in a 25 cm2 HT-PEMFC system. Preliminary short-life tests around 330 h were carried out with both MEAs. During the tests, different characterization procedures, consisting of polarization curves, spectroscopy impedance analysis, cyclic voltammetry and linear sweep voltammetry were performed in order to evaluate the evolution of the main stability and performance parameters of the MEAs. Results showed that the application of these new materials increases positively the stability of the MEA in comparison with the standard Vulcan carbon XC72 material, with a negligible decrease in the performance of the advanced MEA during all tests, making these results very promising to overcome the service lifetime limitations of these systems.
Improved Electrodes for High Temperature Proton Exchange Membrane Fuel Cells using Carbon Nanospheres
(Wiley, 2016-04-14) Zamora, Hector; Plaza, Jorge; Cañizares, Pablo; Lobato, Justo; Rodrigo, Manuel Andrés
This work evaluates the use of carbon nanospheres (CNS) in microporous layers (MPL) of high temperature proton exchange membrane fuel cell (HT-PEMFC) electrodes and compares the characteristics and performance with those obtained using conventional MPL based on carbon black. XRD, hydrophobicity, Brunauer–Emmett–Teller theory, and gas permeability of MPL prepared with CNS were the parameters evaluated. In addition, a short life test in a fuel cell was carried out to evaluate performance under accelerated stress conditions. The results demonstrate that CNS is a promising alternative to traditional carbonaceous materials because of its high electrochemical stability and good electrical conductivity, suitable to be used in this technology.
Microporous layer based on SiC for high temperature proton exchange membrane fuel cells
(Elsevier, 2015-08-15) Lobato, Justo; Zamora, Hector; Cañizares, Pablo; Plaza, Jorge; Rodrigo, Manuel Andrés
This work reports the evaluation of Silicon Carbide (SiC) for its application in microporous layers (MPL) of HT-PEMFC electrodes and compares results with those obtained using conventional MPL based on Vulcan XC72. Influence of the support load on the MPL prepared with SiC was evaluated, and the MPL were characterized by XRD, Hg porosimetry and cyclic voltammetries. In addition, a short lifetest was carried out to evaluate performance in accelerated stress conditions. Results demonstrate that SiC is a promising alternative to carbonaceous materials because of its higher electrochemical and thermal stability and the positive effect on mass transfer associated to its different pore size distribution. Ohmic resistance is the most significant challenge to be overcome in further studies. © 2015 Elsevier B.V.
Optimization of thermal exfoliation of graphitic carbon nitride for methylparaben photocatalytic degradation under simulated solar radiation
(The Royal Society of Chemistry, 2023-04) Plaza, Jorge; Arencibia, Amaya; López-Muñoz, María José
Previous studies have shown that the exfoliation of graphitic carbon nitride (g‐C3N4) is essential to obtain materials with good photocatalytic properties. However, in most works the influence of the exfoliation variables were investigated in an unsystematic way by changing the levels of one factor at a time. In this work, a full factorial design 32 was employed to evaluate the influence of temperature and time used in the thermal exfoliation of bulk g‐C3N4 obtained from urea (bulk‐U) on the photocatalytic performance for 5 mg L−1 methylparaben degradation under simulated solar radiation. Based on the thermal stability of the starting bulk‐U the levels of the design were set in the range 400 to 450 oC for temperature and 2 to 6 h for time. The results showed an enhancement of the photocatalytic activity with the increase of both factors, obtaining the maximum response at T = 450 °C and t = 6 h. An economic evaluation at laboratory scale including the main costs derived from the synthesis stage and the photocatalytic degradation procedure was also performed comparing all the exfoliated materials. The total expenses could be minimized without compromising a good photocatalytic activity with the material obtained by exfoliation of bulk‐U at 450 oC for 2 h. A detailed characterization of the materials was carried out by XRD, FTIR, adsorption‐desorption of N2, UV‐Vis DR, and PL spectroscopy. It was inferred that the enhancement of the photocatalytic performance induced by the thermal exfoliation was mainly related to the consequent increase in the surface area and the improvement in the separation of photogenerated charge pairs derived from the unpacking of the stacked layers.
SiCTiC as catalyst support for HT-PEMFCs. Influence of Ti content
(Elsevier, 2017-06-15) Zamora, Hector; Plaza, Jorge; Velhac, P.; Cañizares, Pablo; Rodrigo, Manuel Andrés
This manuscript studies the influence of the titanium content on the main physicochemical properties of a binary silicon carbide- titanium carbide raw material (SiCTiC), to be used as catalyst support in High Temperature PEM fuel cells (HT-PEMFCs). Three SiCTiC samples with 10, 20 and 30% TiC molar content were studied, analysing the most relevant parameters to be used as catalyst support. First, BET surface area, electrical conductivity, thermal resistance in hot acidic media, and electrochemical resistance were the parameters studied. Results achieved show a decreasing of the BET surface area with the increasing of TiC content, but also an enhancement of the electrical conductivity. All materials studied demonstrated high thermal and electrochemical resistance. After the preliminary physicochemical characterization, Pt-based catalysts with a 40% wt. metal content were synthesized using different carbides studied. Platinum particle and crystallite size, real platinum content and distribution, and electrochemical surface area (ECSA) were the parameters studied. SiCTiC with 30% Pt content exhibited a poor Pt dispersion and ECSA value, achieving better results with catalysts prepared using SiCTiC supports with lower Ti content, resulting on good candidates to be used in this kind of technology.
Use of graphitic carbon nitrides as solar-light-driven photocatalysts for the reduction of p-nitrobenzoic acid
(Elsevier, 2024) López-Timoner, Rubén; Arques, Antonio; Amat, Ana María; Plaza, Jorge; Arencibia, Amaya; López-Muñoz, María-José
he use of graphitic carbon nitrides (g-C3N4) as photocatalysts for the reduction of p-nitrobenzoic acid (PNBA) under simulated sunlight has been investigated. The photocatalysts were synthesized through the thermal polymerization of melamine and urea. The effects of the g-C3N4 precursor employed in the synthesis, the thermal exfoliation treatment, the addition of sacriﬁcial agents, and the pH conditions were evaluated. It was found that the presence of carboxylic acids as sacriﬁcial electron donors was required to attain the photocatalytic reduction of PNBA, while amines or alcohols did not lead to any activity for this purpose. Furthermore, it was observed that the precursor used in the synthesis of graphitic carbon nitride had a slight inﬂuence on the photocatalytic ac-tivity, whereas the thermal treatment of the bulk g-C3N4 materials exhibited a favourable effect. The best results were obtained upon addition of oxalic acid at pH = 3 using the carbon nitride exfoliated materials, achieving in these conditions the complete removal of PNBA after ca. 60 min of irradiation. Time resolved proﬁles of p- aminobenzoic acid (PABA) agree with an initial reduction of PNBA to form this compound, followed by oxidation of PABA by reactive oxygen species formed in the reaction medium.