Browsing by Author "Ferreira, M. J. F."
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- Batch solid sodium borohydride hydrolysis for hydrogen generation : the role of reactor bottom shapePublication . Ferreira, M. J. F.; Rangel, C. M.; Pinto, A. M. F. R.The present study reports original experimental work on generation of hydrogen, by hydrolysis of solid sodium borohydride with stoichiometric amount of distilled water (H2O/NaBH4: 2, 2.84 and 3 mol/mol), in the presence of a powder unsupported Ni-Ru based catalyst, reused about 320 times. The experiments, performed in two batch reactors with equal internal volume but with different bottom shapes (flat and conical), revealed - for the conical bottom shape with any excess of water - 8.1 H2 wt% and 92 kg H2/m3 (materials-only basis), and a H2 rate of 87.4 L(H2) min-1g-1 catalyst. The role of reactor bottom geometry on the solid NaBH4 hydrolysis - with any excess of water - is, as the authors are aware, for the first time here referred.
- Can small additions of an organic polymer or surfactant to sodium borohydride show the way to high hydrogen storage systems for portable applications?Publication . Ferreira, M. J. F.; Gales, L.; Fernandes, Vitor; Rangel, C. M.; Pinto, A. M. F. R.
- Generation of hydrogen from chemical hydrides under pressure up to 70 BarPublication . Fernandes, Vitor; Esteves, M. Alexandra; Ferreira, M. J. F.; Pinto, A. M. F. R.; Rangel, C. M.Hydrogen production by sodium borohydride through hydrolysis in alkaline solutions has been extensively studied as a production/storage option. The potential application of this option is dependent on an easily controllable catalysed hydrolysis reaction at significant rates to comply with fuel cell feeding but also on the increase of the gravimetric density being of paramount importance, the design and implementation of compact and efficient reactors and the reaction characterization under pressure. In this work, hydrogen generation by the catalyzed hydrolysis of sodium borohydride was studied under pressure up to 70 bar with excellent results
- Hydrogen generation and storage system using sodium borohydride at high pressures for operation of a 100 W-scale PMF stackPublication . Ferreira, M. J. F.; Rangel, C. M.; Pinto, A. M. F. R.A study is reported on the generation and storage of hydrogen from sodium borohydride (NaBH4) solutions in batch reactors, under pressures up to 4 MPa, in the presence of an improved and reused non-noble nickel-based powered catalyst. It follows references [1-10]. The first two purposes of the present work were to study the influence of the solution medium in the volume of hydrogen generated by hydrolysis of NaBH4, with a specific interest in: (1) comparing the performance of water and viscous-elastic solutions, particularly with poly-acrilic-acid (PAA) and carboxyl-methyl-cellulose (CMC) in water; (2) analysing both the influence of the hydrogen pressure and of the solution medium on the hydrogen solubility during reaction, leading to its storage in the liquid phase inside the reactor. Experimental tests were performed, with and without stirring, under controlled and uncontrolled reaction temperature. The temperature of the reactor medium and the hydrogen evolution were monitored and recorded simultaneously with a data acquisition system using Labview software. To monitor the rate of hydrogen generation, the gas pressure inside the reactor was followed with an appropriate pressure probe. A third goal of the work was to accurately measure the solubility of molecular hydrogen in the liquid phase inside the reactor, after successive loadings of reactant solution. As it is well known, when the pressure of the gas increases so does the hydrogen dissolution in the liquid phase. The cumulative volume of hydrogen generated fed a polymer electrolyte fuel cell stack used in a 100 W-scale integrated mobile application.
- Hydrogen generation by borohydrides: critical issues for portable applicationsPublication . Fernandes, Vitor; Ferreira, M. J. F.; Pinto, A. M. F. R.; Rangel, C. M.High volumetric and gravimetric efficiency are key to potential hydrogen energy carriers. Sodium borohydride emerges as such potentiality and a storage capacity well within DOE targets for 2015. Limitations exist due to the fact that hydrolysis is restricted by available water and due to the lack of low cost re-usable catalysts. An extensive amount of work has been done in our laboratories on Ni and Ru based catalysts, including synthesis and characterization and solutions have been found for durability, stability and reutilization under operating conditions in small volume batch reactors. Results showed that the Langmuir-Hinshelwood model described fairly well the reaction kinetics for all tested temperatures up to 60ºC and up to reactant exhaustion. In this work, issues such as self-hydrolysis, stability of solutions for storage, water management, some aspects of the catalyzed hydrolysis as well as gas conditioning are studied in order to associate a storage solution with sodium borohydride to a low power air breathing cathode PEM fuel cell.
- Hydrogen production by catalytic hydrolysis of sodium borohydride in batch reactors: new challengesPublication . Ferreira, M. J. F.; Rangel, C. M.; Pinto, A. M. F. R.The present manuscript faces the study of H2 generation and storage from catalytic hydrolysis of sodium borohydride (NaBH4) under pressure. We revisit several works on this topic developed (or under development) by our team in the last four years on some of the most critical issues in this research area, namely catalyst durability/reutilization, gravimetric hydrogen storage density and recyclability. New results are also presented. Hydrogen generation rates and yields and hydrogen storage capacities can be augmented to reach 6 wt%, by adding small amounts of an organic polymer (CMC) to the classic NaBH4 hydrolysis, performed with stoichiometric amount of water in a batch reactor with a conical bottom shape and in the presence of Ni-Ru based catalyst, reused from 300 times. Sodium tetrahydroxoborate, NaB(OH)4), was produced in the presence of CMC additive, and did not show crystalline water in its crystal structure. This latter finding has potential to reduce recycling costs of NaBO2 back to NaBH4 and also increase the overall storage density of systems based on NaBH4 as hydrogen carrier.
- Hydrogen production from sodium borohydride on a Ni-Ru catalyst : an electrochemical studyPublication . Rangel, C. M.; Fernandes, Vitor; Ferreira, M. J. F.; Pinto, A. M. F. R.; Hashimoto, T.; Thompson, G. E.Previous work by the authors has demonstrated a high rate and high yield hydrolysis of sodium borohydride, in the presence of a Ni-Ru catalyst synthesized by wet chemistry. The catalyst has been fully characterized and utilized more than 300 times exhibiting high stability and durability. In this work, results of an electrochemical study are reported using the powder catalyst supported on a Ni foam in order to measure the open circuit potential during hydrogen production and to study the reaction using voltammetry and ac impedance. Production rates were as high as 10 Lmin-1gcat -1 at 65ºC. Electrochemical studies indicated that the hydrogen evolution mechanism corresponds to a Volmer- Heyrovsky type, suggested by a Tafel slope of 117 mVdec-1. Tafel region potentials are in agreement with values found for hydrolysis at the open circuit. The Langmuir-Hinshelwood mechanism explains the hydrolysis of sodium borohydride using a Ni-Ru catalyst. The role of Ni and Ru is briefly discussed.
- NaOH free hydrolysis of sodium borohydride for hydrogen productionPublication . Ferreira, M. J. F.; Gales, L.; Rangel, C. M.; Pinto, A. M. F. R.
- On-demand hydrogen generation by hydrolysis of sodium borohydride in batch reactors: effect of the buffer pressurePublication . Ferreira, M. J. F.; Coelho, F.; Fernandes, Vitor; Rangel, C. M.; Pinto, A. M. F. R.A study was undertaken in order to investigate the potential of hydrogen generation by hydrolysis of sodium borohydride in batch reactors, operating at moderate pressures, in the presence of a reused nickel-ruthenium based catalyst, to feed on-demand a proton exchange membrane fuel cell. The effect of the buffer pressure is explored and hydrogen generation rates are evaluated by changing catalyst amount, operating pressure and successive refueling