Highly efficient acid-treated cobalt catalyst for hydrogen generation from NaBH4 hydrolysis

The effect of cobalt-based catalysts, i.e. CoCl₂(20 wt% Co)/Al₂O₃ treated by different acids, on NaBH₄ hydrolysis was investigated. Five acids were used: oxalic acid, citric acid, acetic acid, sulfuric acid and hydrochloric acid. Two ways of acid treatment were considered: (i) ex-situ addition of acid to CoCl₂(20 wt% Co)/Al₂O₃ at room temperature and (ii) in-situ addition by mixing CoCl₂, Al₂O₃ and acid (one-step process). Both ways showed that adding an acid to the catalyst contributed to an important increase of the catalytic activity towards the NaBH₄ hydrolysis. The best performances were obtained with the catalysts treated with either HCl or CH₃COOH as the global activity of CoCl₂(20 wt% Co)/Al₂O₃ was increased up to 50%.     

Improved hydrogen generation from alkaline NaBH4 solution using cobalt catalysts supported on modified activated carbon

Hydrogen production from alkaline sodium borohydride (NaBH₄) solution via hydrolysis process over activated carbon supported cobalt catalysts is studied. Activated carbons are used in their original form and after liquid phase oxidation with HNO₃. The changes in surface functional groups of the activated carbon are detected by FTIR spectroscopy. The effects of HNO₃ oxidation on the properties of the activated carbon and the resulting catalyst performance are investigated. FTIR analysis reveals that the oxidative treatment leads to the formation of various functional groups on the surface of the activated carbon. Cobalt catalysts supported on the modified activated carbon are found to exhibit higher activity and stability.     

Microstructural control of catalyst-loaded PVDF microcapsule membrane for hydrogen generation by NaBH4 hydrolysis

Polymer microcapsules were prepared and used as catalyst support for hydrogen generation from sodium borohydride. Polyvinylidene fluoride (PVDF) porous microcapsule membranes immobilized with metal salt (cobalt (II) chloride hexahydrate) catalyst and cobalt–boron catalyst were prepared, denoting them as MS and MP method respectively. Non-solvent coagulation bath consisting of a mixture of water and isopropanol (IPA) were used to prepare the microcapsules. The compositions of the non-solvents were changed with a ratio of 10:90 (v/v%)–50:50 (v/v%) with 1 wt% NaOH and 0.5 wt% NaBH₄. The effects of a number of parameters such as the kinds of additives, the size and morphology of the resulting microcapsules were studied on hydrogen generation. The structures and physical–chemical properties of the metal catalyst-loaded microcapsule membranes were characterized using SEM and EDX. The MS method used in preparing the microcapsule showed good performance in hydrogen generation from sodium borohydride. There was also improved performance in hydrogen generation with increasing IPA composition used in the metal salts loaded microcapsule preparation. The control of three regions inside the microcapsules (hollow region, crust region and skin layer) as well as the specific loading of metal catalysts gave a good hydrogen generation performance. The catalyst-loaded microcapsule also maintained an appreciable performance and stability after many runs of hydrolysis reaction for the hydrogen generation.     

Highly active heteropolyanions supported Co catalysts for fast hydrogen generation in NaBH4 hydrolysis

This paper reports on the use of Co supported catalyst for the hydrolysis of NaBH₄. Various materials with different acid/base surface properties have been chosen as supports (hydrotalcites, KF/Al₂O₃, heteropolyanions). The supports and the Co-containing catalysts were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma, nitrogen adsorption. The NaBH₄ hydrolysis reaction was studied in a liquid phase calorimeter coupled with a gas counter in order to follow at the same time the kinetics and the heat of reaction. Co supported on heteropolyanions showed great results in terms of reaction rate. Cobalt dispersed on heteropolyanions is a real promising catalytic system for the development of hydrogen generation in PEM fuel cells for portable devices.     

A durable ruthenium catalyst for the NaBH4 hydrolysis

Ru-active carbon (Ru/C) catalysts are prepared by impregnation reduction method for hydrogen generation via hydrolysis of alkaline sodium borohydride (NaBH₄) solution. The corresponding activity and durability of the prepared catalysts are tested in an immobile bed reactor. The variation of hydrogen generation rate with the increasing of flux and concentration of NaBH₄ solution is measured. The durability of the catalysts prepared under various reductive pH values and reductants is tested by using different concentrations of NaBH₄ solution (10 & 15 wt%). It is found that the durability of catalyst in 15 wt% NaBH₄ solution is longer than that in 10 wt% NaBH₄ solution. The deactivation of Ru/C catalysts is considered as the comprehensive effect of three factors: the loss of Ru, the deposition of byproducts on the catalyst surface and the aggregation of Ru particles.     

Fast hydrogen generation from NaBH4 hydrolysis catalyzed by carbon aerogels supported cobalt nanoparticles

Carbon aerogels (CAs) with oxygen-rich functional groups and high surface area are synthesized by hydrothermal treatment of glucose in the presence of boric acid, and are used as the support for loading cobalt catalysts (CAs/Co). Cobalt nanoparticles distribute uniformly on the surface of ACs, creating highly dispersed catalytic active sites for hydrolysis of alkaline sodium borohydride solution. A rapid hydrogen generation rate of 11.22 L min⁻¹ g_(cobalt)⁻¹ is achieved at 25 °C by hydrolysis of 1 wt% NaBH₄ solution containing 10 wt% NaOH and 20 mg the CAs/Co catalyst with a cobalt loading of 18.71 wt%. Furthermore, various influences are systematically investigated to reveal the hydrolysis kinetics characteristics. The activation energy is found to be 38.4 kJ mol⁻¹. Furthermore, the CAs/Co catalyst can be reusable and its activity almost remains unchanged after recycling, indicating its promising applications in fuel cell.     

Synthesis of solid-state NaBH4/Co-based catalyst composite for hydrogen storage through a high-energy ball-milling process

Solid-state composites of NaBH₄ and Co-based catalyst have been fabricated for hydrogen generation via a novel mechanochemical technique, i.e. the high-energy ball milling, in which the gravimetric storage capacity of hydrogen has reached 6.7 wt%, meeting the 2010 target of at least 0.06 kg H₂/kg set by the U.S. Department of Energy (DOE). The active catalysts used in the hydrolysis reaction of sodium borohydride for hydrogen generation are mainly cobalt oxides. Controlled addition of water, namely water used as a limiting agent, to the solid composites of NaBH₄ and Co-based catalyst greatly improves the H₂ storage capacity and resolved the issues of low gravimetric H₂ storage in conventional aqueous system of sodium borohydride. Factors influencing the performance of hydrogen production such as amounts of H₂O added, catalyst loadings and durations of ball-milling processes are investigated. Moreover the hydrolyzed products of NaBH₄ and spent catalysts are analyzed as well.     

Highly efficient and reactivated electrocatalyst of ruthenium electrodeposited on nickel foam for hydrogen evolution from NaBH4 alkaline solution

Cyclic life of catalyst for hydrolysis of sodium borohydride is one of the key issues, which hinder commercialization of hydrogen generation from sodium borohydride (NaBH₄) solution. This paper is aimed at promoting the cyclic life of Ru/Ni foam catalysts by employing an electro-deposition method. The effect of hydrolysis parameters on hydrolysis of sodium borohydride was studied for improving the catalytic performance. It is found that the hydrogen generation rate (HGR) of the hydrolysis reaction catalyzed by Ru/Ni foam catalyst can reach as high as 23.03 L min^?1 g^?1 (Ru). The Ru/Ni foam catalyst shows good catalytic activity after a cycleability test of 100 cycles by rinsing with HCl, which is considered as more effective method than rinsing with water for recovering the performance of Ru/Ni foam catalyst.     

Hydrogen generation from solid NaBH4 with catalytic solution for planar air-breathing proton exchange membrane fuel cells

In the pursuit of the development of alternative mobile power sources with high energy densities, this study elucidated a new hydrogen generation approach from solid NaBH₄ using a new catalyst, sodium hydrogen carbonate (NaHCO₃), which was placed in a small and compact cartridge. A planar air-breathing PEMFC system fitted with the cartridge has been investigated for testing hydrogen generation from NaBH₄ and NaHCO₃. NaHCO₃ allowed the hydrogen cartridge to control hydrogen generation and to improve the power density, fuel efficiency, energy efficiency, and cell response. The cell performance of solid NaBH₄ air-breathing PEMFC system strongly depended on the operating conditions: the feeding rates and concentrations of catalytic solutions for NaBH₄ hydrolysis. In various concentrations (5 - 12 wt %) of NaHCO₃ aqueous solutions, 10 wt % NaHCO₃ aqueous solution exhibited the highest maximum power density of 128 mW cm⁻² at 0.7 V, which was estimated to be a Faradic efficiency of 78.4% and an energy efficiency of 46.3%. The data illustrated that NaHCO₃ was an effective catalyst for hydrogen generation with the solid NaBH₄, which is considered as a hydrogen carrier for air-breathing micro PEMFCs operated without auxiliary hydrogen controller or devices.     

Regeneration of spent-NaBH4 back to NaBH4 by using high-energy ball milling

High-energy ball milling was employed to regenerate spent-sodium borohydride, i.e., mainly the sodium metaborate (NaBO₂), back to sodium borohydride (NaBH₄) by a reaction with magnesium hydride (MgH₂). The samples were characterized using scanning electron microscopy (SEM), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy. In general, as the ball-milling duration increases, the yield of NaBH₄ increases accordingly and leads to an extreme value of 76%, when MgH₂ in stoichiometric excess by 40% was initially present in ball mills.     

The effect of the concentration of hydrochloric acid and acetic acid aqueous solution for fast hydrogen production from methanol solution of NaBH4

The semi-methanolysis reactions with hydrochloric acid and acetic acid were used for the hydrogen production from sodium borohydride (NaBH₄). The effects of the NaBH₄ concentration, hydrochloric acid and, acetic acid concentration, and temperature on the reactions were investigated. The maximum hydrogen production rates in the semi-methanolysis with 1 M hydrochloric acid and acetic acid were 4875 and 3960 ml min^?1, respectively. At the same time, the semi-methanolysis reactions with the acids are completed within 4 and 5 s, respectively. The power law kinetic model is performed for kinetic studies. Activation energies for the semi-methanolysis reactions of NaBH₄ in the presence of hydrochloric acid and acetic acid were found as 5.84 and 2.81 kJ mol^?1, respectively.     

Kinetics of NaBH4 hydrolysis on carbon-supported ruthenium catalysts

In this work, different shapes (powder and spherical) of ruthenium-active carbon catalysts (Ru/C) were prepared by impregnation reduction method for hydrogen generation (HG) from the hydrolysis reaction of the alkaline NaBH₄ solution. The effects of temperature, amount of catalysts, and concentration of NaOH and NaBH₄ on the hydrolysis of NaBH₄ solution were investigated with different shapes of Ru/C catalysts. The results show that the HG kinetics of NaBH₄ solution with the powder Ru/C catalysts is completely different from that with the spherical Ru/C catalysts. The main reason is that both mass and heat transfer play important roles during the reaction with Ru/C catalysts. The HG overall kinetic rate equations for NaBH₄ hydrolysis using the powder Ru/C catalysts and the spherical catalysts are described as r = A exp (−50740/RT) [catalyst]^1.05 [NaOH]^−0.13 [NaBH₄]^−0.25 and r = A exp (−52,120/RT) [catalyst]^1.00 [NaOH]^−0.21 [NaBH₄]^0.27 respectively.     

Novel fabrication of solid-state NaBH4/Ru-based catalyst composites for hydrogen evolution using a high-energy ball-milling process

Solid-state NaBH₄/Ru-based catalyst composites have been fabricated for hydrogen generation through a high-energy ball-milling process, providing uniform dispersion of resin-supported Ru³⁺ catalysts among pulverized NaBH₄ (SBH) particles, so as to increase the contacts of SBH with active catalytic sites. Consequently, the gravimetric hydrogen storage capacity as high as 7.3 wt% could be achieved by utilizing water as a limiting reagent to overcome the issue of deactivated catalysts whose active sites are often blocked by precipitates caused by limited NaBO₂ solubility occurring in conventional aqueous SBH systems for hydrogen productions. Products of hydrolyzed SBH that greatly influence the gravimetric H₂ storage capacity are found to be most likely NaBO₂·2H₂O and NaBO₂·4H₂O from SBH/H₂O reacting systems with initial weight ratios, SBH/H₂O = 1/2 and 1/10, respectively, according to the TGA and XRD analyses.     

Highly active cobalt-based catalysts in situ prepared from CoX2 (X = Cl,NO3) and used for promoting hydrogen generation from NaBH4 solution

Two kinds of CoX₂ (X = Cl⁻, NO₃⁻) are adopted as the accelerators for the hydrolysis reaction of NaBH₄, which is a promising H₂-supply method for proton exchange membrane fuel cell (PEMFC). In the reactor, the initial H₂ generation is caused by the reaction between pre-infused CoX₂ solution and subsequently imported NaBH₄ solution, and some precipitates are in situ formed on the catalyst bed by this way; and the following H₂ generation is promoted by these precipitates. It is found that there are competitive reactions during H₂ generation from an NaBH₄ to NaOH solution, the anions of CoX₂ are crucial to the reaction pathways, which led to the formation of highly active Co–B or inactive Co(OH)₂. The effects of the CoX₂ concentration, the NaOH concentration, the NaBH₄ feeding rate and the NaBH₄ concentration on H₂ generation performances are discussed and compared.     

Kinetic models of concentrated NaBH4 hydrolysis

The hydrolysis of NaBH₄ in liquid solution has been extensively studied in the past few years; however, data on the kinetics of self-hydrolysis in concentrated solution are few. This work reports the kinetic modeling of self-hydrolysis of 10–20 wt.% NaBH₄ at 25–80 °C. Also, pH data were obtained independently of the reaction kinetics data. The data obtained from Boron-11 NMR measurements and pH are used to determine kinetic parameters. An empirical power law model is evaluated over a wide pH range. The effects of temperature, pH and initial sodium borohyride concentration are reported. The power law model reproduced the trends of the kinetics of the hydrolysis reaction. In addition, a pseudo first order model derived from a proposed reaction mechanism is evaluated. The behavior of the pseudo first order rate constant k is interpreted in terms of the effect of pH.     

Fully-integrated micro PEM fuel cell system with NaBH4 hydrogen generator

A fully-integrated micro PEM fuel cell system with a NaBH₄ hydrogen generator was developed. The micro fuel cell system contained a micro PEM fuel cell and a NaBH₄ hydrogen generator. The hydrogen generator comprised a NaBH₄ reacting chamber and a hydrogen separating chamber. Photosensitive glass wafers were used to fabricate a lightweight and corrosion-resistant micro fuel cell and hydrogen generator. All of the BOP such as a NaBH₄ cartridge, a micropump, and an auxiliary battery were fully integrated. In order to generate stable power output, a hybrid power management operating with a micro fuel cell and battery was designed. The integrated performance of the micro PEM fuel cell with NaBH₄ hydrogen generator was evaluated under various operating conditions. The hybrid power output was stably provided by the micro PEM fuel cell and auxiliary battery. The maximum power output and specific energy density of the micro PEM fuel cell system were 250 mW and 111.2 W h/kg, respectively.     

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.     

The oxidation of NaBH4 on electrochemicaly treated silver electrodes

This study is related to the development of suitable anode material for the direct borohyride fuel cells (DBFCs). The effect of electroactive Ag oxides upon the oxidation of NaBH₄ was investigated. The treatment of Ag surface with H₂O₂ gave a granulated compact layer which was observed to give a very high current density and good reversibility at lower concentration compared with the electrode treated with NaOH which resulted a fibrous layer with a lower electrocatalytic effect. The mode of surface oxidation was found to have a profound effect upon the behavior of the electrode. It was also observed that there is an optimum NaBH₄ concentration to obtain the maximum current density.     

Carbon-supported cobalt catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost transition metal catalysts with high performance are attractive for the development of on-board hydrogen generation systems by catalytic hydrolysis of sodium borohydride (NaBH₄) in fuel cell fields. In this study, hydrogen production from alkaline NaBH₄ via hydrolysis process over carbon-supported cobalt catalysts was studied. The catalytic activity of the supported cobalt catalyst was found to be highly dependent on the calcination temperatures. The hydrogen generation rate increases with calcination temperatures in the range of 200–400 °C, but a high calcination temperature above 500 °C led to markedly decreased activity. X-ray diffraction patterns reveal that the catalysts experience phase transition from amorphous Co–B to crystalline cobalt hydroxide with increase in calcination temperatures. The reaction performance is also dependent on the concentration of NaBH₄, and the hydrogen generation rate increases for lower NaBH₄ concentrations and decreases after reaching a maximum at 10 wt.% of NaBH₄.