Simple and fast fabrication of polymer template-Ru composite as a catalyst for hydrogen generation from alkaline NaBH4 solution

Polymer template-Ru composite (Ru/IR-120) catalyst was prepared using a simple and fast method for generating hydrogen from an aqueous alkaline NaBH₄ solution. The hydrogen generation rate was determined as a function of solution temperature, NaBH₄ concentration, and NaOH (a base-stabilizer) concentration. The maximum hydrogen generation rate reached 132 ml min⁻¹ g⁻¹ catalyst at 298 K, using a Ru/IR-120 catalyst that contained only 1 wt.% Ru. The catalyst exhibits a quick response and good durability during the hydrolysis of alkaline NaBH₄ solution. The activation energy for the hydrogen generation reaction was determined to be 49.72 kJ mol⁻¹.     

Catalytic hydrolysis of sodium borohydride by a novel nickel–cobalt–boride catalyst

With the aim of designing an efficient hydrogen generator for portable fuel cell applications nickel–cobalt–boride (Ni–Co–B) catalysts were prepared by a chemical reduction method and their catalytic hydrolysis reaction with alkaline NaBH₄ solution was studied. The performance of the catalysts prepared from NaBH₄ solution with NaOH, and without NaOH show different hydrogen generation kinetics. The rate of hydrogen generation was measured using Ni–Co–B catalyst as a function of the concentrations of NaOH and NaBH₄, as well as the reaction temperature, in the hydrolysis of alkaline NaBH₄ solution. The hydrogen generation rate increases for lower NaOH concentrations in the alkaline NaBH₄ solution and decreases after reaching a maximum at 15 wt.% of NaOH. The hydrogen generation rate is found to be constant with respect to the concentration of NaBH₄ in the alkaline NaBH₄ solution. The activation energy for hydrogen generation is found to be 62 kJ mol⁻¹, which is comparable with that of hydrogen generation by a ruthenium catalyst.     

Controllable hydrogen generation by use smart hydrogel reactor containing Ru nano catalyst and magnetic iron nanoparticles

In this study, p(AMPS) hydrogels are synthesized from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) via a photo polymerization technique. The hydrogels are used as template for metal nanoparticles and magnetic ferrite nanoparticles, and also as a catalysis vessel in the generation of hydrogen from the hydrolysis of NaBH₄. Approximately 5 nm Ru (0) and 20-30 nm magnetic ferrite particles are generated in situ inside this p(AMPS) hydrogel network and then used as a catalysis medium in hydrogen production by hydrolysis of sodium boron hydride in a basic medium. With an applied external magnetic field, the hydrogel reactor, containing Ru and ferrite magnetic particles, can be removed from the catalysis medium; providing on-demand generation of hydrogen. The effect of various parameters such as the initial concentration of NaBH₄, the amount of catalyst and temperature on the hydrolysis reaction is evaluated. The activation energy for hydrogen production by Ru (0) nanoparticles is found to be 27.5 kJ mol⁻¹; while the activation enthalpy is 30.4 kJ mol⁻¹. The hydrogen generation rate in presence of 5 wt% NaOH and 50 mg p(AMPS)-Ru catalyst is 8.2 L H₂ min⁻¹ g Ru.     

Method of preparing Ru-immobilized polymer-supported catalyst for hydrogen generation from NaBH4 solution

A method of preparing a polymer-supported catalyst for hydrogen generation is introduced in this article. This polymer-supported catalyst is the structure of ruthenium (Ru) nanoparticle immobilized on a monodisperse polystyrene (PSt) microsphere. The diameter of the Ru nanoparticle is around 16 nm, and the diameter of the PSt microsphere is 2.65 um. This preparation method is accomplished by two unique techniques: one is sodium lauryl sulfate/sodium formaldehyde sulfoxylate (SLS/SFS) interface-initiated system, the other is 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester (GMA-IDA) chelating monomer. By taking advantage of these two techniques, Ru³⁺ ion will be chelated and then reduced to Ru⁽⁰⁾ nanoparticle over PSt surface predominantly. The hydrolysis of alkaline sodium borohydride (NaBH₄) solution catalyzed by this Ru-immobilized polymer-supported catalyst is also examined in this article. It reveals that the hydrogen generation rate is 215.9 ml/min g-cat. in a diluted solution containing 1 wt.% NaBH₄ and 1 wt.% NaOH, and this Ru-immobilized polymer-supported catalyst could be recycled during the reaction.     

Promoting effect of W doped in electrodeposited Co–P catalysts for hydrogen generation from alkaline NaBH4 solution

Amorphous Co–W–P catalysts were prepared on Cu substrates by electrodeposition, which have been investigated as the catalyst for hydrogen generation from alkaline NaBH₄ solution. The surface morphology and chemical composition of the as-prepared Co–W–P catalysts were analyzed in relation to the cathodic current density and the electrodeposition time. The hydrogen generation rate for the optimized Co–W–P catalyst is measured to be 5000 mL (min g-catalyst)⁻¹ at 30 °C. From hydrogen generation tests in solutions with the various concentrations of NaBH₄ and NaOH, there were optimum concentrations for both NaBH₄ and NaOH, above or below which the hydrogen generation rate decreased. Furthermore, the as-prepared catalyst also showed good cycling capability and the activation energy for hydrolysis of NaBH₄ by the Co–W–P catalyst was calculated to be 22.8 kJ/mol, which was lower than other reported Co-based catalysts.     

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.     

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.     

An effective synthesis route for improving the catalytic activity of carbon-supported Co–B catalyst for hydrogen generation through hydrolysis of NaBH4

A novel method for synthesis of carbon-supported cobalt boride catalyst was developed for hydrogen generation from catalytic hydrolysis of NaBH₄ solution. The activated carbon and carbon black supported catalysts prepared by “reduction–precipitation” method were found to be much more active than those prepared by conventional “impregnation–reduction” method inspite of the same Co content. A maximum hydrogen generation was achieved using carbon black supported Co–B, which lowers the activation energy to 56.7 kJ mol⁻¹. The effects of NaOH concentration (1–15 wt.%), NaBH₄ concentration (5–20 wt.%) and reaction temperature (25–40 °C) on the performance of the most active catalyst (Co–B/C_B) were investigated in detail. The results indicated that this catalyst can be used in a hydrogen generator for mobile applications such as PEMFC systems due to its high catalytic activity and simple preparation method.     

Hydrogen generation from hydrolysis of sodium borohydride using Ni–Ru nanocomposite as catalysts

Magnetic nickel–ruthenium based catalysts on resin beads for hydrogen generation from alkaline NaBH₄ solutions were synthesized with combined methods of chemical reduction and electroless deposition. Factors, such as solution temperature, NaBH₄ loadings, and NaOH concentration, on performance of these catalysts on hydrogen production from alkaline NaBH₄ solutions were investigated. Furthermore, characteristics of these nickel–ruthenium based catalysts were carried out by using various instruments, such as SEM/EDS, XPS, SQUID VSM and BET. These catalysts can be easily recycled from spent NaBH₄ solution with permanent magnets owing to their intrinsic soft ferromagnetism and, therefore, reducing the operation cost of the hydrogen generation process. A rate of hydrogen evolution as high as ca. 400 mL min⁻¹ g⁻¹ could be reached at 35 °C in 10 wt% NaBH₄ solution containing 5 wt% NaOH using Ni–Ru/50WX8 catalysts. Activation energy of hydrogen generation using such catalysts is estimated at 52.73 kJ mol⁻¹.     

Hydrogen generation by hydrolysis of NaBH4 with efficient Co–P–B catalyst: A kinetic study

Amorphous catalyst alloy powders in form of Co–P, Co–B, and Co–P–B have been synthesized by chemical reduction of cobalt salt at room temperature for catalytic hydrolysis of NaBH₄. Co–P–B amorphous powder showed higher efficiency as a catalyst for hydrogen production as compared to Co–B and Co–P. The enhanced activity obtained with Co–P–B (B/P molar ratio = 2.5) powder catalyst can be attributed to: large active surface area, amorphous short range structure, and synergic effects caused by B and P atoms in the catalyst. The roles of metalloids (B and P) in Co–P–B catalyst have been investigated by regulating the B/P molar ratio in the starting material. Heat-treatment at 773 K in Ar atmosphere causes the decrease in hydrogen generation rate due to partial Co crystallization in Co–P–B powder. Kinetic studies on the hydrolysis reaction of NaBH₄ with Co–P–B catalyst reveal that the concentrations of both NaOH and catalyst have positive effects on hydrogen generation rate. Zero order reaction kinetics is observed with respect to NaBH₄ concentration with high hydride/catalyst molar ratio while first order reaction kinetics is observed at low hydride/catalyst molar ratio. Synergetic effects of B and P atoms in Co–P–B catalyst lowers the activation energy (32 kJ mol⁻¹) for hydrolysis of NaBH₄. The stability, reusability, and durability of Co–P–B catalyst have also been investigated and reported in this work. It has been found that by using B/P molar ratio of 2.5 in Co–P–B catalyst, highest H₂ generation rate of about ∼4000 ml min⁻¹ g⁻¹ can be achieved. This can generate 720 W for Proton Exchange Membrane Fuel Cells (0.7 V): which is necessary for portable devices.     

Effects of electroless deposition conditions on microstructures of cobalt–phosphorous catalysts and their hydrogen generation properties in alkaline sodium borohydride solution

Cobalt–phosphorous (Co–P) catalysts with a high hydrogen generation rate in alkaline sodium borohydride (NaBH₄) solution are developed by electroless deposition. The microstructures of the Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed as a function of the electroless deposition conditions such as the pH and temperature of the Co–P bath. The electroless-deposited Co–P catalysts are composed of nano-crystalline Co and amorphous Co–P. The size of the nano-crystalline Co particles dispersed in amorphous Co–P matrix depends largely on the electroless deposition conditions. Moreover, Co–P catalysts with finer crystalline Co exhibit a higher hydrogen generation rate. In particular, the Co–P catalysts formed in a pH 12.5 bath at 60–70 °C exhibit the best hydrogen generation rate of 3300 ml min⁻¹ g⁻¹-catalyst in 1 wt.% NaOH + 10 wt.% NaBH₄ solution at 30 °C, which is 60 times faster than that obtained with a Co catalyst.     

Fabrication of porous Co–Ni–P catalysts by electrodeposition and their catalytic characteristics for the generation of hydrogen from an alkaline NaBH4 solution

Porous Co–Ni–P catalysts were made on Cu substrates by electrodeposition in order to generate hydrogen from an alkaline sodium borohydride (NaBH₄) solution. We investigated the effects of the cathodic current density and the electrodeposition time on the surface morphology and chemical composition of the Co–Ni–P catalysts. The hydrogen generation characteristics from an alkaline NaBH₄ solution using these catalysts in an alkaline NaBH₄ solution were then investigated. The cathodic current density significantly affected the growth behavior and catalytic properties of the Co–Ni–P electrodeposits. Co–Ni–P catalysts grew two-dimensionally at a low cathodic current density of 0.01 A cm⁻². By contrast, at a cathodic current density of more than 0.05 A cm⁻², three-dimensional growth of the catalysts occurred due to the large cathodic overpotential. In addition, the rates of hydrogen generation were found to be higher for the three-dimensional catalysts than the two-dimensional catalysts. Three-dimensional growth of the Co–Ni–P catalysts continued as the electrodeposition time increased from 1 to 10 min at a cathodic current density of 0.1 A cm⁻². The surface areas of the three-dimensional Co–Ni–P catalysts increased gradually with electrodeposition time, resulting in their catalytic efficiency for the hydrolysis of NaBH₄ being improved. The hydrogen generation rate was also influenced by the concentrations of the NaOH and NaBH₄ in the alkaline NaBH₄ solution. The hydrogen generation rate increased gradually with increasing NaOH concentration. By contrast, there was an optimum concentration of NaBH₄, above which the hydrogen generation rate decreased. Finally, the hydrogen generation rate from Co–Ni–P catalysts was found to decrease due to the precipitation of by-products.     

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.     

A direct measurement of the heat evolved during the sodium and potassium borohydride catalytic hydrolysis

NaBH₄ and KBH₄ hydrolysis reactions (BH₄⁻ + 4H₂O → B(OH)₄⁻ + 4H₂), which can be utilized as a source of high purity hydrogen and be easily controlled catalytically, are exothermic processes. Precise determination of the evolved heat is of outmost importance for the design of the reactor for hydrogen generation. In this work we present an efficient calorimetric method for the direct measurement of the heats evolved during the catalyzed hydrolysis reaction. A modified Setaram Titrys microcalorimeter was used to determine the heat of hydrolysis in a system where water is added to pure solid NaBH₄ or KBH₄ as well as to solid NaBH₄ or KBH₄ mixed with a Co-based solid catalyst. The measured heats of NaBH₄ hydrolysis reaction were: −236 kJ mol⁻¹, −243 kJ mol⁻¹, −235 kJ mol⁻¹, and −236 kJ mol⁻¹, without catalyst and in the presence of Co nanoparticles, CoO and Co₃O₄, respectively. In the case of the KBH₄ hydrolysis reaction, the measured heats were: −220 kJ mol⁻¹, −219 kJ mol⁻¹, −230 kJ mol⁻¹, and −228 kJ mol⁻¹, without catalyst and with Co nanoparticles, CoO and Co₃O₄, respectively. Also, a comparison was made with an aqueous solution of CoCl₂·6H₂O used as catalyst in which case the measured heats were −222 kJ mol⁻¹ and −196 kJ mol⁻¹ for NaBH₄ and KBH₄ hydrolysis, respectively. The influence of solid NaOH or KOH additions on the heat of borohydride hydrolysis has been investigated as well.     

Electroless-deposited Co–P catalysts for hydrogen generation from alkaline NaBH4 solution

Cobalt–phosphorus (Co–P) catalysts, which were electroless deposited on Cu sheet, have been investigated for hydrogen generation from alkaline NaBH₄ solution. The microstructures of the as-prepared Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed in relation to pH value, NaH₂PO₂ concentration, and the deposition time. Experimental results show that the Co–P catalyst formed in the bath solution with pH value of 12.5, NaH₂PO₂ concentration of 0.8 M, and the deposition time no more than 6 min presents the highest hydrogen generation rate of 1846 mL min⁻¹ g⁻¹. Furthermore, the as-prepared catalyst also shows good cycling capability and the corresponding activation energy is calculated to be 48.1 kJ mol⁻¹. The favorable catalytic performance of the electroless-deposited Co–P catalysts indicates their potential application for quick hydrogen generation from hydrolysis of NaBH₄ solution.     

Accurately measuring the hydrogen generation rate for hydrolysis of sodium borohydride on multiwalled carbon nanotubes/Co–B catalysts

Multiwalled carbon nanotubes supported cobalt–boron catalysts (Co–B/MWCNT) were developed via the chemical reduction of aqueous sodium borohydride with cobalt chloride for catalytic hydrolysis of alkaline NaBH₄ solution. The hydrogen generation (HG) rates were measured on an improved high-accuracy, low-cost and automatic HG rate measurement system based on the use of an electronic balance with high accuracy. The HG of Co–B/MWCNT catalyst was investigated as a function of heat treatment, solution temperature, Co–B loading and supporting materials. The catalyst was mesoporous structured and showed lower activation energy of 40.40 kJ mol⁻¹ for the hydrolysis of NaBH₄. The Co–B/MWCNT catalyst was not only highly active to achieve the average HG rate of 5.1 l min⁻¹ g⁻¹ compared to 3.1 l min⁻¹ g⁻¹ on Co–B/C catalyst under the same conditions but also reasonably stable for the continuous hydrolysis of NaBH₄ solution.     

Hydrogen generation from catalytic hydrolysis of alkaline sodium borohydride solution using attapulgite clay-supported Co-B catalyst

An attapulgite clay-supported cobalt-boride (Co-B) catalyst used in portable fuel cell fields is prepared in this paper by impregnation-chemical reduction method. The cost of attapulgite clay is much lower compared with some other inert carriers, such as activated carbon and carbon nanotube. Its microstructure and catalytic activity are analyzed in this paper. The effects of NaOH concentration, NaBH₄ concentration, reacting temperature, catalyst loadings and recycle times on the performance of the catalysts in hydrogen production from alkaline NaBH₄ solutions are investigated. Furthermore, characteristics of these catalysts are carried out in SEM, XRD and TEM analysis. The high catalytic activity of the catalyst indicates that it is a promising and practical catalyst. Activation energy of hydrogen generation using such catalysts is estimated to be 56.32 kJ mol⁻¹. In the cycle test, from the 1st cycle to the 9th cycle, the average hydrogen generation rate decreases gradually from 1.27 l min⁻¹ g⁻¹ Co-B to 0.87 l min⁻¹ g⁻¹ Co-B.     

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.     

Ru–RuO2/C as an efficient catalyst for the sodium borohydride hydrolysis to hydrogen

How to efficiently hydrolyze NaBH₄ to H₂ has been greatly concerned due to its theoretically high hydrogen storage capacity (10.8 wt. %). In this work, Ru–RuO₂/C catalyst is prepared by the galvanic replacement reaction of Ni based material. By evaluating the hydrolysis activity, analyzing the structure and component of the catalysts and exploring the possible reaction channels, we find that Ru–RuO₂/C has the excellent hydrolysis activity of 16.8 L H₂ min⁻¹ g_cat.⁻¹ in 5 wt. % NaBH₄ and 1 wt. % NaOH solution at 323 K, which is higher than most data in open literature. The more reducible RuO₂ (110) crystal at about 423 K plays an important role in the high hydrolysis activity of Ru–RuO₂/C. The ruthenium oxide facilitates the dissociation of water, a rate-determining step of NaBH₄ hydrolysis to H₂, while Ru acts as an active phase for NaBH₄ dissociation. A synergetic effect of RuO₂ and Ru on Ru–RuO₂/C is crucial to the high hydrolysis activity of sodium borohydride and it can also be kept in repeated experiments.     

Aluminum chloride for accelerating hydrogen generation from sodium borohydride

The present research paper reports preliminary results about the utilization of anhydrous aluminum chloride (AlCl₃) for accelerating hydrogen generation through hydrolysis of aqueous solution of sodium borohydride (NaBH₄) at 80 °C. To the best of our knowledge, AlCl₃ has never been considered for that reaction although many transition metal salts had already been assessed. AlCl₃ reactivity was compared to those of AlCl₃·6H₂O, AlF₃, CoCl₂, RuCl₃ and NiCl₂. With AlCl₃ and a NaBH₄ solution having a gravimetric hydrogen storage capacity (GHSC) of 2.9 wt.%, almost 100% hydrogen was generated in few seconds, i.e., with a hydrogen generation rate (HGR) of 354 L min⁻¹ g⁻¹(Al). This HGR is one of the highest rates ever reported. Higher HGRs were obtained by mixing AlCl₃ with CoCl2, RuCl₃ or NiCl₂. For example, the system RuCl₃:AlCl₃ (50:50 mass proportion) showed a HGR > 1000 L min⁻¹ g⁻¹(Ru:Al). The hydrolysis by-products (once dried) were identified (by XRD, IR and elemental analysis) as being Al(OH)₃, NaCl and Na₂B(OH)₄Cl and it was observed that even in situ formed Al(OH)₃ has catalytic abilities with HGRs of 5 L min⁻¹ g⁻¹(Al). All of these preliminary results are discussed, which concludes that AlCl₃ has a potential as accelerator for single-use NaBH₄-based storage system.