Hydrogen production by catalytic hydrolysis of sodium borohydride in batch reactors: new challenges

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 generation and storage system using sodium borohydride at high pressures for operation of a 100 W-scale PMF stack

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

Batch solid sodium borohydride hydrolysis for hydrogen generation : the role of reactor bottom shape

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

Impact of the reactor bottom shape on the solid sodium borohydride hydrolysis for hydrogen generation

Sodium borohydride (NaBH4) is a chemical hydride that produces hydrogen (H2) ‘on-demand’ through the reaction with water, and exhibits high gravimetric hydrogen storage capacity (10.8 wt.%). NaBH4 has been appointed as an efficient energy/hydrogen carrier for use with fuel cells [1-6]. Unfortunately, problems also exist with NaBH4 hydrolysis: H2 production rates are not sufficiently fast, reaction completion is not always reachable and effective gravimetric (and volumetric) H2 storage capacity is far from the theoretical value. 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, 3 and 4 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), reveal - 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

Development of rice lines with gene introgression from the wild Oryza glumaepatula by the AB-QTL methodology.

Wild rice of the species Oryza glumaepatula is found Brazil and has been used to broaden the genetic basis of irrigated rice populations in Embrapa breeding programmes. The objective of this study was to demonstrate and discuss approaches used in the development of Oryza sativa lines containing genes transferred from Oryza glumaepatula, resulting in introgression lines with a broader genetic basis and high yield. First of all, genes were transferred from the wild species to cultivated rice by the AB-QTL methodology. Eighteen families were selected using QTL analysis and agronomical performance data. After the heterosis test, the families CNAi 9020 and CNAi 9024 were selected and submitted to microsatellite marker-assisted selection. Thirty-five lines were then selected with high plant vigour, high tiller and panicle number per plant, high grain yield of the main crop, and a strong regrowth capacity which makes the use of ratoons a feasible alternative

Water management in direct methanol fuel cells

Direct methanol fuel cell (DMFC) are a promising power source for micro and portable applications due to their high energy density and inherent simplicity of operation with methanol as the liquid fuel. Present state-of-the-art optimised operating conditions are elevated cell temperatures to improve the anode reaction, high air stoichiometries to prevent cathode flooding and dilute methanol solutions to mitigate methanol crossover. These very dilute fuel solutions require the presence of a high amount of water leading to a reduction of the energy density of the system. More concentrated methanol solutions would be preferable in order to achieve energy densities needed for portable power applications. However, the possibility of using highly concentrated methanol solutions at the anode is limited by the significant water loss from the anode to cathode occurring in the DMFC due to electro-osmotic drag and molecular diffusion through the membrane. So, low crossover of both methanol and water through a polymer membrane in a DMFC is essential for using high concentration methanol in portable power applications. In this work, the results of a simulation study using a previous developed model for DMFCś are presented. Particular attention is paid to the water distribution across the cell. The influence of different parameters (such as methanol concentration, membrane thickness and gas diffusion media) over the water transport and on the cell performance is studied. The model used to predict the water transport was validated with recent published data