Browsing by Author "Ortiz, Inmaculada"
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- Challenges arising from the use of TiO2/rGO/Pt photocatalysts to produce hydrogen from crude glycerol compared to synthetic glycerolPublication . Ribao, Paula; Esteves, M. Alexandra; Fernandes, Vitor; Rivero, María J.; Rangel, C. M.; Ortiz, InmaculadaABSTRACT: Photoreforming has emerged as a novel technology expected to obtain chemical energy through solar energy transformation. In this way, sustainable valorization of glycerol, a biodiesel by-product, to clean fuels is a promising alternative to help meet the world's growing energy demand. In this work, TiO2/rGO(x)/Pt(y) photocatalysts have been developed for hydrogen production from synthetic and crude glycerol solutions. The effect of several key operating parameters (including vol% of glycerol, pH, catalyst loading, wt% of GO, wt% of Pt, temperature, and light source) on hydrogen production rate has been studied. The results indicated different optimal operating parameters depending on glycerol origin, achieving up to 70.8 and 12.7 mmol h(-1) g(-1) of hydrogen using synthetic glycerol and crude glycerol, respectively. Additionally, GO nanosheets and Pt nanoparticles strongly influenced the hydrogen production rate but not the overall reaction mechanism. Impurities contented in crude glycerol are key factors in developing realistic hydrogen production processes.
- Comprehensive review and future perspectives on the photocatalytic hydrogen productionPublication . Corredor, Juan; Rivero, María J.; Rangel, C. M.; Gloaguen, Frederic; Ortiz, InmaculadaABSTRACT: Hydrogen represents a renewable energy alternative that may positively contribute to get over the global energy crisis while at the same time reducing its environmental burden. Overcoming the challenge of reaching this potential could be helped by careful choice of hydrogen (H-2) sources. Photocatalytic generation of H-2, although a minor alternative, appears to be a very good option at the time that liquid wastes are being degraded; therefore, this approach has given rise to an increasing number of interesting studies.Here, we aim to provide an integrated overview of the different photocatalytic, heterogeneous, homogeneous and hybrid systems. First, we categorize the units and mechanisms that take part in the photocatalytic process, and secondly we analyze their role and draw comparative conclusions. Thus, we analyze the role of (i) the electron source to carry out proton reduction, (ii) the proton source, which can be free protons in the medium or a proton donor compound, (iii) the catalyst nature and concentration, and (iv) the photosensitizer nature and concentration. We also provide an analysis of the influence of the solvent, especially in homogenous systems as well as the influence of pH. We provide a comparison of the photocatalytic performance, highlighting the advantages and disadvantages, of different systems. Thus, this review is, on the one hand, an update on the state of the art of photocatalytic generation of H-2 from a full perspective that integrates homogeneous, heterogeneous and hybrid systems, and, on the other, a source of useful information for future research.
- New modified Nafion-biphosphonic acid composite membranes for enhanced proton conductivity and PEMFC performance [Resumo]Publication . Teixeira, Fatima; Sá, A.I. De; Teixeira, António P. S.; Ortiz-Martínez, V. M.; Ortiz, A.; Ortiz, Inmaculada; Rangel, C. M.ABSTRACT: The performance of PEM fuel cells critically depends on their proton exchange membrane structural and chemical stabilities as well as on their proton conductivity. Limitations of commercially available Nafion membranes to operating at temperatures above 80 ºC have fostered the interest in research and development of new membranes [1,2]. The aim of this work is the preparation of new modified Nafion composite membranes, with a bisphosphonic acid moiety, a promising proton carrier exhibiting good proton donating/accepting properties and thermal stability. Synthesis and characterization were undertaken of a series of bisphosphonic acid derivatives and their incorporation into a Nafion matrix, by casting. The new membranes were characterized by ATR-FTIR and SEM along with their ion exchange capacity and water-uptake. The evaluation of their proton conductivity was carried out by electrochemical impedance spectroscopy, at various temperature and relative humidity (RH) conditions. The incorporation of BPs dopants enhances the proton conductivity, with all membranes exhibiting higher values than Nafion N-115, tested in the same experimental conditions. Selected membranes were integrated into a fuel cell MEA, using a single cell assembly, with an active area of 2.5x2.5 cm2 and a catalyst loading of 0.5 mgPtcm-2. Performance was evaluated, using an air fed cathode, at temperatures from 30 ºC to 80 ºC. Membrane doped with BP2 showed the best performance, with higher power density outputs than Nafion N-115 shown at all temperatures.
- New modified Nafion-bisphosphonic acid composite membranes for enhanced proton conductivity and PEMFC performancePublication . Teixeira, Fatima; de Sá, A.I.; Teixeira, António P. S.; Ortiz-Martínez, V. M.; Ortiz, A.; Ortiz, Inmaculada; Rangel, C. M.ABSTRACT: Proton exchange membranes remain a crucial material and a key challenge to fuel cell science and technology. In this work, new Nafion membranes are prepared by a casting method using aryl- or azaheteroaromatic bisphosphonate compounds as dopants. The incorporation of the dopant, considered at 1 wt% loading after previous selection, produces enhanced proton conductivity properties in the new membranes, at different temperature and relative humidity conditions, in comparison with values obtained with commercial Nafion. Water uptake and ionic exchange capacity (IEC) are also assessed due to their associated impact on transport properties, resulting in superior values than Nafion when tested in the same experimental conditions. These improvements by doped membranes prompted the evaluation of their potential application in fuel cells, at different temperatures. The new membranes, in membrane-electrode assemblies (MEAs), show an increased fuel cell maximum power output with temperature until 60 degrees C or 70 degrees C, followed by a decrease above these temperatures, a Nafion-like behaviour when measured in the same conditions. The membrane doped with [1,4-phenylenebis(hydroxymethanetriyl)] tetrakis(phosphonic acid) (BP2) presents better results than Nafion N-115 membrane at all studied temperatures, with a maximum power output performance of similar to 383 mW cm(-2) at 70 degrees C. Open circuit potentials of the fuel cell were always higher than values obtained for Nafion MEAs in all studied conditions, indicating the possibility of advantageous restrain to gas crossover in the new doped membranes.
- Sustainable Additives for the Production of Hydrogen via Sodium Borohydride HydrolysisPublication . Gomez-Coma, Lucia; Silva, Diogo; Ortiz, A.; Rangel, C. M.; Ortiz-Martínez, V. M.; Pinto, A. M. F. R.; Ortiz, InmaculadaABSTRACT: Finding stable solutions for hydrogen storage is one of the main challenges to boosting its deployment as an energy vector and contributing to the decarbonization of the energy sector. In this context, sodium borohydride (NaBH4) has been largely studied as a hydrogen storage material due to its significant advantages, such as low pressure, stability, and high hydrogen storage density. The development of catalysts and additive materials for the on-demand hydrolysis of NaBH4 for hydrogen release is a key research area. This work studies the effects of non-toxic and environmentally friendly additives for the hydrolysis process in terms of yield, lag time, hydrogen generation rate, and gravimetric density. Specifically, four additives, including sodium carboxymethylcellulose (CMC), polyacrylamide (PAM), sodium dodecyl sulfate (SDS), and & beta;-cyclodextrin (BCD), were studied for their application in the storage and release of hydrogen. The best results were provided by the use of sodium carboxymethyl cellulose and polyacrylamide. In the first case, a hydrolysis yield of 85%, a lag time of 70 s, a hydrogen production rate of 1374 mL & BULL;min(-1)& BULL;gcat(-1), and a storage capacity of 1.8 wt% were obtained. Using polyacrylamide as additive, a hydrolysis yield of almost 100% was achieved, although it required a significantly higher time period for complete conversion.