Chitosan-mediated Co–Ce–B nanoparticles for catalyzing the hydrolysis of sodium borohydride

Highly dispersed Co–Ce–B nanoparticles supported on chitosan-derived carbon (Co–Ce–B/Chi–C) were synthesized through chemical reduction and carbonization. The morphology and microstructure of the Co–Ce–B/Chi–C nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller adsorption analysis. This nanocomposite had uniform morphology and large surface area, and it showed high catalytic activity for NaBH₄ hydrolysis and good cycle stability. Compared with unsupported Co–Ce–B particles, this nanocomposite showed greatly increased catalytic activity for NaBH₄ hydrolysis. A remarkably high hydrogen generation rate of 4760 mL^?1 min^?1 g^?1 at 30 °C was achieved with low activation energy of 33.1 kJ mol^?1. These results indicate that the Co–Ce–B/Chi–C nanocomposite is a promising catalyst for on-demand hydrogen generation via NaBH₄ hydrolysis.     

Bacterial cellulose derived carbon as a support for catalytically active Co–B alloy for hydrolysis of sodium borohydride

The fast release of hydrogen from borohydride is highly desired for a fuel cell system. However, the generation of hydrogen from borohydride is limited by the low activity and low stability of the catalyst. Herein, a highly active catalyst is synthesized through a simple one-step chemical reduction using bacterial cellulose (BC) derived carbon as a support for the active Co–B alloy. The morphology and microstructure of the BC/Co–B nanocomposite are characterized by SEM, TEM, XRD, and BET adsorption analysis. The BC/Co–B possesses high surface area (125.31 m² g^?1) high stability and excellent catalytic activity for the hydrolysis of NaBH₄. Compared with unsupported Co–B nanocomposite or commercial carbon supported Co–B, the BC/Co–B nanocomposite shows greatly improved catalytic activity for the hydrolysis of NaBH₄ with a high hydrogen generation rate of 3887.1 mL min^?1 g^?1 at 30 °C. An activation energy of 56.37 kJ mol^?1 was achieved for the hydrolysis reaction. Furthermore, the BC/Co–B demonstrated excellent stability. These results indicate that the BC/Co–B nanocomposite is a promising candidate for the hydrolysis of borohydrides.     

Mesoporous Co–B nanocatalyst for efficient hydrogen production by hydrolysis of sodium borohydride

Two types of mesoporous Co–B nanocatalysts were prepared by the reduction of cobalt chloride with Sodium Borohydride (SBH) in the presence of cationic and non-ionic surfactant templates, namely n-cetyl-trimethyl-ammonium bromide (CTAB) and Pluronic (P123) respectively. Nitrogen adsorption–desorption isotherms revealed the presence of slit-like pores on the catalyst surface which provide high effective surface area. These surface enhanced catalysts were tested for hydrogen production by hydrolysis of sodium borohydride. The mesoporous Co–B catalysts showed much higher activity (4 times) in comparison to the non-porous Co–B, which can be attributed to the higher surface area of the mesoporous structures. Co–B/P123 catalyst showed the highest hydrogen generation rate owing to the presence of wide uniform pores which facilitated easier interaction of the reactants to release hydrogen. The lack of stability in the pore structure is observed at elevated temperatures for both the mesoporous Co–B catalyst.     

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.     

Novel Ni–Co–B hollow nanospheres promote hydrogen generation from the hydrolysis of sodium borohydride

Ni–Co–B hollow nanospheres were synthesized by the galvanic replacement reaction using a Co–B amorphous alloy and a NiCl₂ solution as the template and additional reagent, respectively. The Ni–Co–B hollow nanospheres that were synthesized in 60 min (Ni–Co–B-60) showed the best catalytic activity at 303 K, with a hydrogen production rate of 6400 mL_hydrogenmin^?1g_catalyst^?1 and activation energy of 33.1 kJ/mol for the NaBH₄ hydrolysis reaction. The high catalytic activity was attributed to the high surface area of the hollow structure and the electronic effect. The transfer of an electron from B to Co resulted in higher electron density at Co sites. It was also found that Ni was dispersed on the Co–B alloy surface as result of the galvanic replacement reaction. This, in turn, facilitated an efficient hydrolysis reaction to enhance the hydrogen production rate. The parameters that influenced the hydrolysis of NaBH₄ over Ni–Co–B hollow nanospheres (e.g., NaOH concentration, reaction temperature, and catalyst loading) were investigated. The reusability test results show that the catalyst is active, even after the fifth run. Thus, the Ni–Co–B hollow nanospheres are a practical material for the generation of hydrogen from chemical hydrides.     

Effect of Co/BH4 ratio in the synthesis of Co–B catalysts on sodium borohydride hydrolysis

Cobalt boride is known to act as a catalyst to facilitate the hydrolysis reaction of sodium borohydride. The catalytic nature of cobalt boride is immensely dependent upon the synthesis procedure and reaction conditions used, especially on the relative amount of Co(II) and borohydride used for catalyst preparation. In the current work a set of catalysts were prepared by varying the cobalt(II) and borohydride ratio in the reactant solution. The prepared catalysts were well characterized using different characterizing tools like XRD, FTIR, FEG-SEM, FEG-TEM, ICP-AES and XPS. The effect of the catalyst on the hydrolysis of sodium borohydride was thoroughly studied and reported in the current work. The catalytic activity of the catalyst was observed to be highly dependent on the reduced cobalt content. It was observed that the excess amount of borohydride used to synthesize the catalyst, was not increasing the catalytic activity after the complete reduction of cobalt.     

Deactivation,reactivation and memory effect on Co–B catalyst for sodium borohydride hydrolysis operating in high conversion conditions

A system with a continuous reactor to produce hydrogen by sodium borohydride hydrolysis was designed and built. The purpose was to test a supported Co–B catalyst durability upon cycling and long life experiments in high conversion conditions. A Stainless Steel monolith was built and calcined to improve adherence. For comparison a Ru–B catalyst was tested upon cycling. Both Co–B and Ru–B catalysts are durable during 6 cycles and then deactivate. A known reactivation procedure has proven to be more effective for the Co–B than for the Ru–B catalyst. This is related to stronger adsorption of B–O based compounds on the Co–B catalyst which is reversible upon acid washing. For the Ru–B catalyst deactivation may be more related to particle agglomeration than to the adsorption of B–O based species. The continuous system enlarges the catalysts durability because of the continuous borate elimination at elevated temperatures.     

Sodium borohydride hydrolysis on highly efficient Co–B/Pd catalysts

Cobalt–Boron (Co–B) catalysts are prepared on the nickel foam substrate (NiFS) by in situ reduction of Co²⁺ ions in sodium borohydride (NaBH₄) solution for the catalytic generation of hydrogen from NaBH₄. The formation of Co–B catalysts on the substrate is much faster by using a dip-coating and extended drying (“dry-dip-coating method”) followed by chemical reduction as compared to that prepared by a conventional dip-coating method followed by chemical reduction. The dry treatment results in a significant reduction in the re-dissolution of the dip-coated Co–B catalysts during the following dipping processes. Co–B catalysts on Pd modified NiFS have also been prepared using dry-dip-coating method. The factors affecting the performance of the catalysts such as dipping time, calcination temperature, Co–B loadings, Pd formation time and operating temperature, are studied. The best catalytic activity and stability is obtained on Co–B on Pd modified NiFS.     

Polypyrrole supported Co–W–B nanoparticles as an efficient catalyst for improved hydrogen generation from hydrolysis of sodium borohydride

Effective and reusable catalysts with high performance are essentially necessary for NaBH₄ based on-demand hydrogen generators to the widespread use for energy conversion in fuel cell power systems. Herein, we report a facile synthesis of surfactant-directed polypyrrole-supported Co–W–B nanoparticles as a robust catalyst for efficient hydrolysis of NaBH₄ reaction. This non-noble metal catalyst provides much higher catalytic activity than a conventional cobalt boride catalyst. By incorporating tungsten to catalyst composition and tuning molar ratio of W/(Co + W), about a four-fold higher hydrogen generation rate was attained compared to bare Co–B. Among the all catalysts tested, Co–W–B/PPy with 7.5% W possessed the remarkable catalytic performance of 9.92 L min^?1 g^?1 and high stability over five cycles with the apparent activation energy of 49.18 kJ mol^?1.     

Effect of bath composition on properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution

The effect of bath composition on the properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution was investigated by varying the bath composition. The NaH₂PO₂/CoCl₂ and NH₂CH₂COOH/CoCl₂ concentration ratio had a strong effect on the catalyst properties. The effect of NH₂CH₂COOH/CoCl₂ was larger than that of NaH₂PO₂/CoCl₂ for the concentration ratio range with practical deposition rates. The optimum concentration ratio of the coating bath was CoCl₂:NH₂CH₂COOH:NaH₂PO₂ = 1:4:10. As the concentration of each component increased at the optimum concentration ratio, the coating bath decomposed on its own. As the amount of solute dissolved in the coating bath increased, the coating bath became unstable. The optimum composition of the stable coating bath to realize Co–P/Ni foam catalyst with good catalytic activity was 0.1 m (molality, mol/kg) CoCl₂, 0.4 m NH₂CH₂COOH, and 1.0 m NaH₂PO₂. The weight percent of the deposited catalyst and hydrogen generation rate per deposited catalyst of 1 g at optimum composition were 8.39 wt% and 0.93 L/min·g (deposited catalyst), respectively. The bath composition was found to have a great effect on the Co–P/Ni foam catalyst properties and coating bath stability.     

Effect of manufacturing conditions on properties of electroless deposited Co–P/Ni foam catalyst for hydrolysis of sodium borohydride solution

The effects of the deposition time and coating bath with various pH and temperatures on the deposition rate, hydrogen generation rate per deposited catalyst of 1 g, surface morphology, catalyst particle distribution, and microstructure of electroless deposited Co–P/Ni foam catalysts were investigated. The degree of the effects of the parameters was in the following order: pH > temperature > deposition time. The effects of heat treatment temperature on the durability and catalytic activity were also investigated. Durability increased slightly in response to heat treatment, but hydrogen generation reduced owing to sodium sintering and oxide film formation. The optimum conditions were 12.0 (pH), 50 °C (temperature), and 30 min (deposition time) without heat treatment. The weight percent of the deposited catalyst and hydrogen generation rate per deposited catalyst of 1 g under the optimum conditions were 4.86 wt% and 1.49 L/min g (deposited catalyst), respectively. The apparent activation energy of the catalyst manufactured under the optimum conditions was 46.8 kJ/mol. The manufacturing conditions considerably affected the catalyst properties.     

Hydrogen generation from hydrolysis of sodium borohydride by cubic Co–La–Zr–B nano particles as novel catalyst

Cubic Co–La–Zr–B nano particles were prepared in situ for the first time from the reduction of Co(II), La(III) and Zr(IV) chloride by sodium borohydride in methanol under reflux condition. Poly N-vinyl-2-pyrrolidone (PVP) as stabilizing agent was used for preparation of Co–La–Zr–B nano particles. Obtained powders were characterized by XRD, BET, ICP, SEM, TEM and UV–vis techniques. XRD patterns declare that under argon atmosphere only metalboride phase has been crystallized and it was not seen any oxide phase of metals. TEM image depicts that PVP stabilized nano particles are square shaped particles that containing many nanoclusters. Cubic Co–La–Zr–B nano particles were also confirmed by SEM image. Co–La–Zr–B is highly active catalysts for hydrogen generation from the hydrolysis of sodium borohydride. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 53 kJ mol⁻¹) and effects of the catalyst dosage, amount of NaBH₄, and temperature on the rate of the catalytic hydrolysis of sodium borohydride. Catalytic hydrolysis of NaBH₄ is first order with respect to the catalyst concentration and also first order to the NaBH₄ concentration in the case of cubic Co–La–Zr–B nano particles.     

Co–B nanoparticles supported on carbon film synthesized by pulsed laser deposition for hydrolysis of ammonia borane

Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of Ammonia Borane (AB) to produce molecular hydrogen. Amorphous Co–B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) were used during deposition of carbon films to obtain extremely irregular and porous carbon support with high surface area prior to Co–B film deposition. Surface morphology of the catalyst films was studied using Scanning Electron Microscopy, while structural characterization was carried out using X-Ray diffraction. The hydrogen generation rate attained by carbon-supported Co–B catalyst film is significantly higher as compared to unsupported Co–B film and conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co–B nanoparticles with better dispersion and tolerance against aggregation. The efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)⁻¹) and exceptionally high H₂ generation rate (13.5 L H₂ min⁻¹ (g of Co)⁻¹) by the hydrolysis of AB.     

Hydrogen generation from catalytic hydrolysis of sodium borohydride solution using Cobalt–Copper–Boride (Co–Cu–B) catalysts

Co–Cu–B, as a catalyst toward hydrolysis of sodium borohydride solution, has been prepared through chemical reduction of metal salts, CoCl₂·6H₂O and CuCl₂, by an alkaline solution composed of 7.5wt% NaBH₄ and 7.5wt% NaOH. The effects of Co/Cu molar ratio, calcination temperature, NaOH and NaBH₄ concentration and reaction temperature on catalytic activity of Co–Cu–B for hydrogen generation from alkaline NaBH₄ solution have been studied. X-ray diffraction (XRD), scanning electron microscope (SEM) and Nitrogen adsorption–desorption isotherm have been employed to understand the results. The Co–Cu–B catalyst with a Co/Cu molar ratio of 3:1 and calcinated at 400 °C showed the best catalytic activity at ambient temperature. The activation energy of this catalytic reaction is calculated to be 49.6 kJ mol⁻¹.     

Investigation into hydrolysis and alcoholysis of sodium borohydride in ethanol–water solutions in the presence of supported Co–Ce–B catalyst

The efficacies of attapulgite clay (ATC)-, titanium dioxide (TiO₂)- and silica gel (SG)-supported cobalt–cerium–boron (Co–Ce–B) substances as catalysts were investigated for the alcoholysis and hydrolysis of sodium borohydride (NaBH₄) in ethanol–water solutions. Ce served as a helpful co-catalyst among the prepared Co–Ce–B catalysts, and the catalytic activity decreased in the following sequence: TiO₂-supported > ATC-supported > SG-supported > unsupported. The effects of Ce/(Co+Ce) molar ratio, ethanol concentration, reaction temperature, NaBH₄ concentration and NaOH concentration on the hydrogen production rate were investigated. For the ATC-supported catalyst, when the Ce/(Co+Ce) molar ratio was 10%, the catalyst exhibited the best catalytic activity. Optimal NaBH₄ concentration, NaOH concentration and ethanol concentration to promote hydrogen generation rate was around 8 wt.%, 15 wt.% and 30 wt.%, respectively. It can be found that the addition of ATC greatly improved the recycle ability of the catalysts in the multi-cycle tests. The surface morphology of the catalysts before and after the recycle tests was studied from SEM images. The compositions of the catalysts were determined by XRD and EDS analyses. The occurrence of NaB(OH)₄ in the alcoholysis by-product provided pertinent indications of ethanol recovery after the tests. The value of activation energy in the hydrogen generation process in the presence of ATC-supported Co–Ce–B catalyst was calculated to be 29.51 kJ/mol. An overall kinetic equation was also proposed.     

Polymer hydrogel supported Pd–Ni–B nanoclusters as robust catalysts for hydrogen production from hydrolysis of sodium borohydride

Catalyzed sodium borohydride hydrolysis is a highly valuable method to produce clean hydrogen energy for portable applications. This study provides a new and fast route to preparation of reusable hybrid materials composed of nickel-boron based nanoclusters dispersed in nanoporous poly(acrylamide) hydrogels for catalyzed hydrogen production. Palladium was added to the Ni–B catalysts during chemical reduction under the protection of poly(N-vinylpyrrolidone). The resulting nanoclusters immobilized in the hydrogels were essentially alloy particles with uni-modal size distributions and average diameters ranging from ca. 4–8 nm. Pd exerted significant promoting effects on the activities of the Ni–B catalysts. The highest activity was achieved for Pd–Ni–B nanoclusters with a charge ratio of Pd/Ni = 1/20 in moles, which exhibited activity nearly twice that of a Ni–B catalyst and good recyclability for consecutive uses. The hydrogen production rates also increased with the decreasing particle sizes. The activation energy, enthalpy and entropy for the reaction were determined to be 31.10 kJ mol⁻¹, 28.39 kJ mol⁻¹ and -45.22 J mol⁻¹ K⁻¹, respectively. The activation energy is lower than that of previously reported polymer-stabilized Co(0), Fe(0), or Ni(0) nanoparticle catalysts.     

Co−O−P composite nanocatalysts for hydrogen generation from the hydrolysis of alkaline sodium borohydride solution

In recent years, catalytic hydrolysis of sodium borohydride is considered to be a promising approach for hydrogen generation towards fuel cell devices, and highly efficient and noble-metal-free catalysts have attracted increasing attention. In our present work, Co₃O₄ nanocubes are synthesized by solvothermal method, and then vapor-phase phosphorization treatment is carried out for the preparation of novel Co−O−P composite nanocatalysts composed of multiple active centers including Co, CoO, and Co₂P. For catalyst characterization, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectric spectroscopy (XPS) are conducted. Optimal conditions for catalyst preparation and application were investigated in detail. At room temperature (25 °C), maximum hydrogen generation rate (HGR) is measured to be 4.85 L min⁻¹ g⁻¹ using a 4 wt% NaBH₄ − 8 wt% NaOH solution, which is much higher than that of conventional catalysts with single component reported in literature. It is found that HGR remarkably increases with the increasing of reaction temperature, and apparent activation energy for catalytic hydrolysis of NaBH₄ is calculated to be 63 kJ mol⁻¹. After reusing for five times, the Co−O−P composite nanocatalysts still retains 78% of the initial activity.     

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.     

New electroless plating method for preparation of highly active Co–B catalysts for NaBH4 hydrolysis

Supported non-noble transition metal catalysts are ideal for use in NaBH₄-based hydrogen storage systems because of their low cost, robustness, and ease of handling. We have developed a new low-temperature electroless plating method for preparation of Co–B catalysts supported on Ni foam. This method requires only one plating step to achieve the desired catalyst loading, and has higher loading efficiency than conventional multi-step methods. The produced Co–B catalyst shows higher NaBH₄ hydrolysis activity than those prepared by conventional methods due to increased boron content and nanosheet-like morphology. The pH and NH₃ concentration of the precursor solution were found to have considerable influences on both the catalyst loading and activity. Temperature dependence of hydrogen generation suggests that the catalytically active phase is formed in situ above a certain temperature threshold, which is supported by XPS analysis. The maximum specific hydrogen generation rate is in excess of 24,000 mL min⁻¹ g⁻¹, which is among the highest values for catalysts of this type reported in the literature.     

Superior hydrogen generation from sodium borohydride hydrolysis catalyzed by the bimetallic Co–Ru/C nanocomposite

Sodium borohydride has been widely regarded as a promising hydrogen carrier owing to its greatly hydrogen storing capability (10.8 wt%), high weight density and excellent stability in alkaline solutions. Herein, we first design and synthesize a series of bimetallic M-Ru/C nanocomposites (including Fe–Ru/C, Co–Ru/C, Ni–Ru/C and Cu–Ru/C), via simply alloying of commercial Ru/C with nonprecious metal, for superior H₂ evolution from the NaBH₄ hydrolysis. The result exhibits that H₂ generation is synergetically improved by alloying Ru/C with Co or Ni, while it is hindered by alloying Ru/C with Fe or Cu. Indeed, Co–Ru/C presents the highest efficient catalytic activity for H₂ generation, with the TOF of 117.69 mol(H₂)·mol_Ru^?1·min^?1, whereas Ru/C is only 57.08 mol(H₂)·mol_Ru^?1·min^?1. In addition, the TOF of Co–Ru/C reaches to 436.51 mol(H₂)·mol_Ru^?1·min^?1 (96.7 L(H₂)·g_Ru^?1·min^?1) in the presence of NaOH.