Salicylaldimine-Ni complex supported on Al2O3: Highly efficient catalyst for hydrogen production from hydrolysis of sodium borohydride

In this study, the Ni-based complex catalyst containing nickel of 1% supported on Al₂O₃ is used as for the hydrogen production from NaBH₄ hydrolysis. The maximum hydrogen production rate from hydrolysis of NaBH₄ with Ni-based complex catalyst supported on Al₂O₃ containing nickel of 1% is 62535 ml min^?1 g^?1 (complex catalyst containing 1 wt% Ni). The resulting complex catalyst is characterised by XRD, XPS, SEM, FT-IR, UV, and BET surface area analyses. The Arrhenius activation energy is found to be 27.29 kJ mol^?1 for the nickel-based complex catalyst supported on Al₂O₃. The reusability of the catalyst used in this study has also been investigated. The Ni-based complex catalyst supported on Al₂O₃ containing nickel of 1% is maintained the activity of 100% after the fifth use, compared to the first catalytic use. The n value for the reaction rate order of NaBH₄ is found to be about 0.33.     

New reactor design for catalytic sodium borohydride hydrolysis

Hydrogen supply to a fuel cell for portable consumer products requires a simple and safe technology for its storage and on-demand production. Hydrogen production by hydrolysis of sodium borohydride solution in the presence of metal catalyst could be a promising and feasible method.     

Kinetics of Ru-catalyzed sodium borohydride hydrolysis

Chemical hydrides have been identified as a potential medium for on-board hydrogen storage, one of the most challenging technical barriers to the prospective transition from gasoline to hydrogen-powered vehicles. Systematic study of the feasibility of the sodium borohydride systems, and chemical-hydride systems more generally, requires detailed kinetic studies of the reaction for use in reactor modeling and system-level experiments. This work reports an experimental study of the kinetics of sodium borohydride hydrolysis with a Ru-on-carbon catalyst and a Langmuir-Hinshelwood kinetic model developed based on experimental data. The model assumes that the reaction consists of two important steps: the equilibrated adsorption of sodium borohydride on the surface of the catalyst and the reaction of the adsorbed species. The model successfully captures both the reaction's zero-order behavior at low temperatures and the first-order behavior at higher temperatures. Reaction rate constants at different temperatures are determined from the experimental data, and the activation energy is found to be 66.9 kJ mol⁻¹ from an Arrhenius plot.     

New insights on the mechanism of vapour phase hydrolysis of sodium borohydride in a fed-batch reactor

This study aims to produce H₂ from sodium borohydride (NaBH₄) and to initiate its hydrolysis at elevated temperature in the absence of a catalyst. Experimental results indicated that the hydrogen generation yield increased up to %99 at 150 °C in the NaBH₄ concentration of %5 wt in the acidic medium. It can be concluded that experimental characterization of the by-products is quite important since they affected the reaction mechanism or pathway. When the experiments are carried out under aqueous condition, the primary by- product is sodium metaborate while it is boric acid under acidic condition. It is postulated that by-product boric acid decreased the mass transfer limitation due to its higher solubility that prevents the formation of shell and thus increases the contact area between NaBH₄ and vapor. A series of fed-batch reactions were performed to confirm the hypothesis, and the conversions of NaBH₄ reached 99% under the acidic condition.     

Preparation of pompon-like Co-B nanoalloy by a room-temperature solid-state-reaction as a catalyst for hydrolysis of borohydride solution

Pompon-like Co-B alloy composed of nanosheets with a large specific surface area of 202.4 m² g^?1 was synthesized via a facile room-temperature solid-state-reaction. By changing the mass ratios of CoCl₂·6H₂O to CO(NH₂)₂ in the synthesis, the morphology of the Co-B alloy can be controlled. Correspondingly, the specific surface area can increase from ca. 43.4–202.4 m² g^?1. When the pompon-like Co-B severs as a catalyst for the hydrolysis of NaBH₄, the hydrogen generation rate can be up to $8\text{.}26{\text{L}}_{\text{hydrogen}}{\text{min}}^{\mathrm{?}1}{{\text{g}}_{\text{catalyst}}}^{\mathrm{?}1}$. This value is larger compared with those of many other Co-B nanoalloys in previous reports. Additionally, the corresponding activated energy for the hydrolytic reaction is as low as 25 kJ mol^?1, hinting that the pompon-like Co-B catalyst possesses superior catalytic performance. The pompon-like Co-B alloy has the advantages of low cost, good recoverability, as well as high activity, which may find practical application in NaBH₄ hydrolysis for hydrogen production.     

Hydrogen generation utilizing alkaline sodium borohydride solution and supported cobalt catalyst

Supported Co catalysts with different supports were prepared for hydrogen generation (HG) from catalytic hydrolysis of alkaline sodium borohydride solution. As a result, we found that a γ-Al₂O₃ supported Co catalyst was very effective because of its special structure. A maximum HG rate of 220 mL min⁻¹ g⁻¹ catalyst and approximately 100% efficiency at 303 K were achieved using a Co/γ-Al₂O₃ catalyst containing 9 wt.% Co. The catalyst has quick response and good durability to the hydrolysis of alkaline NaBH₄ solution. It is feasible to use this catalyst in hydrogen generators with stabilized NaBH₄ solutions to provide on-site hydrogen with desired rate for mobile applications, such as proton exchange membrane fuel cell (PEMFC) systems.     

A highly active Co-B catalyst for hydrogen generation from sodium borohydride hydrolysis

Co-B catalysts were prepared by the chemical reduction of CoCl₂ with NaBH₄ for hydrogen generation from borohydride hydrolysis. The catalytic properties of the Co-B catalysts were found to be sensitive to the preparation conditions including pH of the NaBH₄ solution and mixing manner of the precursors. A Co-B catalyst with a very high catalytic activity was obtained through the formation of a colloidal Co(OH)₂ intermediate. The ultra-fine particle size of 10 nm accounted for its super activity for hydrogen generation with a maximum rate of 26 L min⁻¹ g⁻¹ at 30 °C. The catalyst also changed the hydrolysis kinetics from zero-order to first-order.     

Co3O4 hollow fiber: An efficient catalyst precursor for hydrolysis of sodium borohydride to generate hydrogen

Sodium borohydride (NaBH₄) is one of promising hydrogen storage materials for practical application, and the development of high-efficient catalysts for NaBH₄ hydrolysis to generate hydrogen is of critical importance. In this communication, Co₃O₄ hollow fiber composed of nanoparticles array was served as catalyst precursor and facilely prepared by combustion method with template of the absorbent cotton. For characterization, FE-SEM, HRTEM, EDS, XRD, FTIR and ICP were applied, respectively, and typical water-displacement method was performed to evaluate the catalytic activity. Using a solution composed of 10 wt% NaBH₄ and 2 wt% NaOH, hydrogen generation rate was up to 11.12 L min^?1 g^?1 (25 °C), which is much higher than that of the commercial cobalt oxides and similar catalyst precursors reported in literature.     

Catalytic hydrolysis of sodium borohydride in an integrated reactor for hydrogen generation

Chemical hydrides, such as sodium borohydride (NaBH₄), offer promising gravimetric and volumetric hydrogen storage densities. The overall system energy density depends on the reactor performance. In this study, a novel intergrated reactor design in which catalyst bed is integrated with a heat exchanger for autothermal operation showed significant improvements in reactor performance. Over 200% enhancement in reactor throughput was achieved with the integrated reactor at 99% fuel conversion with constant reaction temperature profiles over a wide range of fuel flow rates. Impacts of improved performance on system operation and overall energy density of chemical hydride based hydrogen storage system were also discussed.     

Hydrogen generation from sodium borohydride solution using a ruthenium supported on graphite catalyst

The catalyst with high activity and durability plays a crucial role in the hydrogen generation systems for the portable fuel cell generators. In the present study, a ruthenium supported on graphite catalyst (Ru/G) for hydrogen generation from sodium borohydride (NaBH₄) solution is prepared by a modified impregnation method. This is done by surface pretreatment with NH₂ functionalization via silanization, followed by adsorption of Ru (III) ion onto the surface, and then reduced by a reducing agent. The obtained catalyst is characterized by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Very uniform Ru nanoparticles with sizes of about 10 nm are chemically bonded on the graphite surface. The hydrolysis kinetics measurements show that the concentrations of NaBH₄ and NaOH all exert considerable influence on the catalytic activity of Ru/G catalyst towards the hydrolysis reaction of NaBH₄. A hydrogen generation rate of 32.3 L min⁻¹ g⁻¹ (Ru) in a 10 wt.% NaBH₄ + 5 wt.% NaOH solution has been achieved, which is comparable to other noble catalysts that have been reported.     

Progress in sodium borohydride as a hydrogen storage material: Development of hydrolysis catalysts and reaction systems

Over the past decade, sodium borohydride (NaBH₄) has been extensively investigated as a potential hydrogen storage material. The development of catalyst materials for on demand NaBH₄ hydrolysis, and the design of practical reaction systems for hydrogen storage based on NaBH₄ are key research areas. Progress in the former area has been promising, with many non-noble catalysts being reported with activities comparable to those of higher-cost noble metal catalysts. However, the design of practical hydrogen storage systems remains a critical issue, as identified by the U.S. Department of Energy (DOE) in their “No-Go” recommendation in 2007. The problems of by-product precipitation and catalyst blockage at high NaBH₄ concentrations must be addressed in order to produce a hydrogen storage system capable of meeting the DOE target of 5.5 wt% H₂ (2015). It is likely that a new, novel reaction system design will be required to achieve these targets, given the limitations identified in conventional systems. Moreover, a new process for regenerating spent NaBH₄ will need to be developed, in order to lower its cost to a viable level for use as a transportation fuel.     

Synthesis of bifunctional non-noble monolithic catalyst Co-W-P/carbon cloth for sodium borohydride hydrolysis and reduction of 4-nitrophenol

Amorphous Co-W-P catalysts, which were prepared on carbon cloth (CC) by electrodeposition, have been investigated as bifunctional non-noble catalysts for the hydrogen generation from alkaline NaBH₄ solution and the reduction of 4-nitrophenol by NaBH₄. Scanning electron microscopes (SEM), energy dispersive X-ray spectrometer (EDX), and X-ray diffraction (XRD) were used to characterize the Co-W-P/CC catalysts. The hydrogen generated catalytic properties of as-prepared catalysts with different content of P and the stability were investigated in the alkaline NaBH₄ solution of 5 wt% NaBH₄ and 2 wt% NaOH. The activation energy for hydrolysis of NaBH₄ by the Co-W-P catalyst was also probed at different temperature, and the results show that the obtained Co-W-P/CC catalysts exhibit very low apparent active energy (Ea = 27.18 kJ mol^?1). Finally, we detect the catalytic activity of Co-W-P/CC in the reduction of 4-nitrophenol for the first time, and it also presents outstanding catalytic capability with the apparent rate constant (k_app) of 11.91 × 10^?3 s^?1. These characteristics indicate that the Co-W-P/CC catalysts possess a potential application on both the sodium borohydride hydrolysis and reduction of 4-nitrophenol.     

Anchored cobalt film as stable supported catalyst for hydrolysis of sodium borohydride for chemical hydrogen storage

Electrodeposition was used to deposit cobalt over polycarbonate membrane (PCM), which was used as stable supported catalyst in hydrolysis of sodium borohydride NaBH₄. We selected PCM as support owing to its lightness, easy handling, stability, and porous structure with nanosized channels. Our primary objective was to obtain a catalytic film resistant to both physical degradation and delamination while H₂ bubbled on its surface. A thin film consisting of mushroom-like cobalt nanoarchitectures were prepared. By SEM, we observed that it is strongly embedded into the PCM thickness, with the anchoring occurring through the channels. This shaped catalyst was mechanically stable and did not show degradation during the reaction. The main results are reported and discussed in details herein.     

Synthesis of ruthenium nanoparticles deposited on graphene-like transition metal carbide as an effective catalyst for the hydrolysis of sodium borohydride

The graphene-like transition metal carbide (Ti₃C₂X₂(X = OH, F)) which was synthesized from etching the layered Ti₃AlC₂ material was applied as a carrier for depositing Ru nanoparticles (Ru/Ti₃C₂X₂). The as-prepared nanocomposites were characterized by SEM, TEM, XRD, XPS and FTIR. During the hydrolysis process, Ru nanoparticles were uniformly generated on the surface of the carrier and acted as catalysts for the hydrogen generation from hydrolysis of NaBH₄ at room temperature. It was found that the catalyst Ru/Ti₃C₂X₂ exhibited excellent catalytic activity toward the hydrolysis of sodium borohydride with a hydrogen generation rate of 59.04 L H₂/g_Ru•min and an activation energy of 22.1 kJ/mol.     

Hydrogen generation from aqueous acid-catalyzed hydrolysis of sodium borohydride

In this study, the hydrogen feed from both Ru-catalyzed and organic acid-catalyzed hydrolysis of NaBH₄ was studied in terms of hydrogen generation rate and integrated PEMFC performance. Hydrogen feed generated from the conventional Ru-catalyzed hydrolysis of NaBH₄ caused a drastic loss of PEMFC performance. It was found that the presence of sodium ion in hydrogen feed was a main factor that increased the interfacial resistance of fuel cell and, consequently, reduced the performance. Acid-catalyzed hydrolysis with powder form of NaBH₄ was adopted in order to minimize the detrimental effect of sodium ion. The hydrogen feed from acid-catalyzed hydrolysis was quite dry so that even water vapor, the carrier of sodium ion, was not detected after condensation of hydrogen feed. It was confirmed by the several experiments that the hydrogen release rate can be controlled by varying the injection rate and concentration of aqueous acid. Various organic acids were employed in the production of hydrogen and found that acidity, acid type and chemical structure are also important factors on hydrolysis of NaBH₄. The performance from the integrated acid-catalyzed hydrogen generation system with PEMFC was quite stable and no significant loss was observed contrary to that from the integrated Ru-catalyzed hydrogen generation system–PEMFC test. This result also clarified that the detrimental effect of sodium ion could be removed by minimizing the water vapor in this manner. Based on the experiment of acid-catalyzed hydrolysis, a small-scale hydrogen-generating device was designed and fabricated, from which hydrogen release was controlled by the acid concentration and injection rate of aqueous acid solution.     

A novel and active ruthenium based supported multiwalled carbon nanotube tungsten nanoalloy catalyst for sodium borohydride hydrolysis

At present, a novel and active catalyst, RuW/MWCNT catalyst, was successfully synthesized to complete the hydrolysis reaction of sodium borohydride (NaBH₄). The activity of Ru catalyst was increased by adding tungsten (W) to ruthenium (Ru) on multi-walled carbon nanotube (MWCNT) support. Surface characterization of the catalyst was performed with scanning electron microscope (SEM-EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmissing electron microscope (TEM) analysis methods. SEM-EDX revealed that RuW (95:5) catalyst metal ratio was obtained at desired nominal ratio. XRD characterization revealed that W addittion to the Ru structure increased its activity by forming an alloy. W addition Ru altered the electronic structure of the Ru. Parameters affecting the hydrolysis performance of RuW/MWCNT catalyst such as temperature, amount of catalyst, NaBH₄ concentration and sodium hydroxide (NaOH) concentration were investigated. Adding NaOH to the reaction vessel reduced the activity of the RuW/MWCNT catalyst. From the hydrolysis measurements, the activation energy of RuW(95–5)/MWCNT catalyst was found to be 16.327 kjmol^?1, the reaction order as 0.61 and the initial rate as 95,841,4 mL H₂g_catmin^?1. The stability of the RuW/MWCNT catalyst was tested using 5 times and it was observed that this novel RuW/MWCNT catalyst could complete the hydrolysis reaction despite repeated use.     

Water consumption during solid state sodium borohydride hydrolysis

In this paper nickel acetate catalyzed sodium borohydride cartridges have been prepared and hydrolyzed with water for hydrogen production. Two technological solutions have been tested to increase the overall hydrogen yield, namely a porous water diffuser and a hydrophobic membrane. The first was used to improve water diffusion inside the hydride while the second to confine water inside the cartridge. The generated hydrogen flow showed a very reproducible behavior. Hydrogen promptly evolved just after water was pumped into the cartridge. After some initial peaks, a constant hydrogen flow has been recorded for the whole reaction time. The constant flow was related to the presence of the porous diffuser. The use of a hydrophobic membrane to confine the water inside the cartridge allowed to increase the overall hydrogen yield: about 6 water molecules per mol of hydride were required to complete the reaction. The reaction product was identified by XRD as Na₂B₂O₄*8H₂O. The cartridge hydrogen gravimetric content, based on water and sodium borohydride weight, was as high as 4.64%.