Ni–Fe–B catalysts for NaBH4 hydrolysis

A series of Ni–Fe–B catalysts with different Fe/(Fe + Ni) molar ratios, used for the hydrolysis of NaBH₄, were prepared by chemical reduction of NiCl₂ and FeCl₃ mixed solution with NaBH₄. The measurements revealed that the catalysts with the molar ratio of Fe/(Fe + Ni) (30%) exhibited the highest catalytic activity, and the optimal reduction temperature is 348 K. In addition, the effects of the concentration of NaBH₄, NaOH and the hydrolytic temperature of NaBH₄ were discussed in detail. The results show that the reaction rate of hydrolysis first rises up and then goes down subsequently with the increase of NaBH₄ concentration, as well as the concentration of NaOH. The activation energy of the hydrolysis for Ni–Fe–B catalysts is fitted to 57 kJ/mol. The maximum value of hydrogen generation is 2910 ml/(min g) at 298 K.     

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.     

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.     

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.     

Efficient catalytic properties of Co–Ni–P–B catalyst powders for hydrogen generation by hydrolysis of alkaline solution of NaBH4

The aim of the present work is to study the catalytic efficiency of amorphous Co–Ni–P–B catalyst powders in hydrogen generation by hydrolysis of alkaline sodium borohydride (NaBH₄). These catalyst powders have been synthesized by chemical reduction of cobalt and nickel salt at room temperature. The Co–Ni–P–B amorphous powder showed the highest hydrogen generation rate as compared to Co–B, Co–Ni–B, and Co–P–B catalyst powders. To understand the enhanced efficiency, the role of each chemical element in Co–Ni–P–B catalyst has been investigated by varying the B/P and Co/Ni molar ratio in the analyzed powders. The highest activity of the Co–Ni–P–B powder catalyst is mostly attributed to synergic effects caused by each chemical element in the catalyst when mixed in well defined proportion (molar ratio of B/P = 2.5 and of Co/(Co + Ni) = 0.85). Heat-treatment at 573 K in Ar atmosphere causes a decrease in hydrogen generation rate that we attributed to partial Co crystallization in the Co–Ni–P–B powder. The synergic effects previously observed with Co–Ni–B and Co–P–B, now act in a combined form in Co–Ni–P–B catalyst powder to lower the activation energy (29 kJ mol⁻¹) for hydrolysis of NaBH₄.     

The effects of plasma treatment on electrochemical activity of Co–W–B catalyst for hydrogen production by hydrolysis of NaBH4

A plasma treatment of Co–W–B catalyst increases the rate of hydrogen generation from the hydrolysis of NaBH₄. The catalytic properties of Co–W–B prepared in the presence of plasma have been investigated as a function of NaBH₄ concentration, NaOH concentration, temperature, plasma applying time, catalyst amount and plasma gases. The Co–W–B catalyst prepared with cold plasma effect hydrolysis in only 12 min, where as the Co–W–B catalyst prepared in known method with no plasma treatment in 23 min. The activation energy for first-order reaction is found to be 29.12 kJ mol⁻¹.     

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 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.     

Performance evaluation of hydrogen generation system with electroless-deposited Co–P/Ni foam catalyst for NaBH4 hydrolysis

In this work, the performance of a hydrogen generation system with an electroless-deposited Co–P/Ni foam catalyst for NaBH₄ hydrolysis was evaluated. The performance of a hydrogen generator using a combination of Co/γ-Al₂O₃ and Co–P/Ni foam catalysts was also evaluated in order to address the shortcomings with the individual catalysts. The generator had high conversion efficiency, fast response characteristics, and strong catalyst durability. Hydrogen generation tests were performed to investigate the effect of the composition of the NaBH₄ solution on the hydrogen generation properties. The generator's conversion efficiency decreased with an increase in the amount of solute dissolved in NaBH₄ solution because of the accumulation of precipitates on the catalyst, and NaOH concentration had a greater effect on the hydrogen generation properties than did NaBH₄ concentration. According to these results, the hydrogen generation system with the Co–P/Ni foam catalyst is suitable as a hydrogen supplier for proton exchange membrane fuel cells owing to the strong durability and inexpensive cost of the catalyst.     

The catalyst-free hydrolysis behaviors of NaBH4–NH3BH3 composites

NaBH₄–NH₃BH₃ composites were prepared by high-energy ball-milling processes for hydrogen generation through hydrolysis. After ball milling, there were no new phases found in the XRD patterns of NaBH₄–NH₃BH₃ composites. The experimental results demonstrate that when the molar ratios of NaBH₄–NH₃BH₃ composites range from 1:4 to 2:1, these composites can release above 90% hydrogen in 30 min at 70 °C. Comparing with neat NaBH₄ or NH₃BH₃, the hydrolysis properties of these composites are greatly enhanced. And the hydrolysis reaction mechanism is turned out to be more explicit as Na₂B₄O₅(OH)₄·8H₂O appears in the hydrolysis products. Since the preparation processes of these composites are simple and cost-effective and the hydrolysis of these composites achieves efficient hydrogen release, it is promising that this kind of composites can be applied in hydrogen generation.     

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.     

Effect of various Co–B catalyst synthesis conditions on catalyst surface morphology and NaBH4 hydrolysis reaction kinetic parameters

The objective of this work is to study the effect of various Co–B catalyst synthesis conditions on the catalyst surface morphology and kinetic parameters. The Co–B catalyst was synthesized on IR-120/TP-207 resin surface by using ion exchange and chemical reduction method using NaBH₄ as a reduction agent. The reduction conditions which were investigated here were: reduction temperature, NaBH₄ concentration, pH value, NaBH₄ adding flowrate and different types of resins. The result shows reduction temperature gives the most dramatic effect on surface morphology which is caused by competing reactions of reduction and hydrolysis. Low reduction temperature resulted in a slower Co–B reduction rate and made the catalyst surface denser with a branched structure. This created more surface area than higher reduction temperatures. Low reduction temperature catalyst had the better performance on NaBH₄ hydrolysis reaction for hydrogen generation rate. The optimal reduction temperature of the Co–B/IR-120 is 25 °C. The L-H model was used to regress kinetic parameters from the experiment data. The frequency factor, activation energy and adsorption constant are 1.17 × 10⁹ mol gcat⁻¹ min⁻¹, 70.65 kJ mol⁻¹, and 6.8 L mol⁻¹ at 40 °C, respectively. Finally, the TP-207 resin was used instead of IR-120. After scanning for all catalyst synthesis conditions, the Co–B/TP-207 had the higher catalyst loading, faster hydrogen generation rate and more stable than Co–B/IR-120.     

CuO–NiO/Co3O4 hybrid nanoplates as highly active catalyst for ammonia borane hydrolysis

Dehydrogenation of hydrogen-rich chemicals, such as ammonia borane (AB), is a promising way to produce hydrogen for mobile fuel cell power systems. However, the practical application has been impeded due to the high cost and scarcity of the catalysts. Herein, a low-cost and high-performing core-shell structured CuO–NiO/Co₃O₄ hybrid nanoplate catalytic material has been developed for the hydrolysis of AB. The obtained hybrid catalyst exhibits a high catalytic activity towards the hydrolysis of AB with a turnover frequency (TOF) of 79.1 mol_H2 mol cat⁻¹ min⁻¹. The apparent activation energy of AB hydrolysis on CuO–NiO/Co₃O₄ is calculated to be 23.7 kJ.mol⁻¹. The synergistic effect between CuO–NiO and Co₃O₄ plays an important role in the improvement of the catalytic performance. The development of this high-performing and low-cost CuO–NiO/Co₃O₄ hybrid catalytic material can make practical applications of AB hydrolysis at large-scale possible.     

Graphene modified Co–B catalysts for rapid hydrogen production from NaBH4 hydrolysis

Graphene oxide (GO) modified Co–B catalysts for NaBH₄ hydrolysis have been synthesized by the chemical reduction in this work. The structural features and catalytic performance of as-prepared samples have been investigated and discussed as a function of amounts of GO. According to structure characterization, the catalysts still retain the amorphous structure of Co–B alloy with the addition of GO, while GO exists as reduced GO (r-GO). The textural analysis and morphology observation indicate that the appropriate amount of GO in Co–B catalyst results in the obvious increase of specific surface area and uniform clustered morphology, which contributes to improve active surface area for catalytic reactions. The results of surface species characterization show that the electron density at active Co sites increases due to an electron transfer from B to Co facilitated by r-GO. It has been found that 50 mg GO modified Co–B catalyst exhibits especially high activity with a hydrogen generation rate of 14.34 L min⁻¹·g_catalyst⁻¹ and much lower activation energy of 26.2 kJ mol⁻¹ for hydrolysis reaction of NaBH₄. Meanwhile, the reusability evaluations show that the catalyst preserves high stability which can still maintain 81.5% of its initial activity after 5 catalytic cycles.     

Carbon nanotubes-promoted Co–B catalysts for rapid hydrogen generation via NaBH4 hydrolysis

In this work, multiwalled carbon nanotubes (MWCNTs) promoted Co–B catalysts for NaBH₄ hydrolysis have been designed and synthesized. The structural features of as-prepared catalysts have been investigated and discussed as a function of MWCNTs contents by X-ray diffraction, X-ray photoelectron spectra, N₂ adsorption/desorption isotherms, scanning electron microscope. The results show that the catalysts still maintain an amorphous structure with the addition of carbon nanotubes promoter. However, the appropriate amount of MWCNTs promoter in Co–B catalysts leads to large specific surface area, fine dispersion of active components, increased active sites and high electron density at active sites. Moreover, hydrogen spillover on the catalyst is promoted, which contributes to regeneration of active sites and accelerating catalytic cycle. Among all the experimental samples, it is found that the Co–B catalyst promoted by 10 wt% carbon nanotubes exhibits optimal catalytic activity with remarkably high hydrogen generation rate of 12.00 L min⁻¹·g_catalyst⁻¹ and relatively good stability.     

Effects of deposition time on the H2 generation kinetics of electroless-deposited cobalt–phosphorous catalysts from NaBH4 hydrolysis,and its cyclic durability

The effect of electoless-deposition time of a Co–P catalyst on the kinetics of H₂ generation in an alkaline NaBH₄ solution, and its cyclic durability are investigated. The electroless-deposited Co–P catalyst is composed of both outer spherical Co–P particles and an inner flat Co–P layer. As the deposition time of the Co–P catalyst is increased, the outer spherical Co–P particles grow, and their H₂ generation kinetics increase. However, the weight-normalized reaction rates differ as a function of deposition time, although the weight of the deposited material is proportional to the deposition time. Specifically, the Co–P catalyst deposited for 3 min shows the highest weight-normalized H₂ generation rate than those deposited for other lengths of time. The rate of H₂ generation for the Co–P catalyst is decreased dramatically after one cycle (10 h) due to separation of the Co–P particles from the Co–P plate. Up to the sixth cycle (60 h), the rate of H₂ gradually decreases due to a powerful shock on the catalyst support by expansion of H₂ volume. Beyond six cycles, the catalytic performance of the Co–P catalyst was stable enough for repetitive use.     

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.     

Revision of the NaBO2–H2O phase diagram for optimized yield in the H2 generation through NaBH4 hydrolysis

The binary phase diagram NaBO₂–H₂O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH₄ hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO₂·4H₂O (Na[B(OH)₄]·2H₂O), NaBO₂·2H₂O (Na[B(OH)₄]), NaBO₂·2/3H₂O (Na₃[B₃O₄(OH)₄]), NaBO₂·1/3H₂O (Na₃[B₃O₅(OH)₂]) and NaBO₂ (Na₃[B₃O₆]), and their thermal stabilities have been studied. The boundaries of the different Liquid + Solid equilibria for the temperature range from −10 to 80 °C have been determined, confirming literature data at low temperature (20–50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO₂·4H₂O, occurring at −7 °C, has been determined by DSC. The Liquid–Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO₂·2/3H₂O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH₄ hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO₂–H₂O binary phase diagrams and its consequence related to hydrogen storage through NaBH₄ hydrolysis.     

Highly active porous Co–B nanoalloy synthesized on liquid-gas interface for hydrolysis of sodium borohydride

Porous Co–B nanoalloy is a low-cost and highly active catalyst towards the hydrolysis of sodium borohydride (NaBH₄). In this study, a facile and room-temperature hydrogen bubble-assisted method was developed to prepare porous Co–B nanoalloy (Co-B_bubble) materials exhibiting high catalytic activity. The obtained materials are characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometer, transmission electron microscopy and surface area experiments. It is found that the hydrogen bubbles generated in-situ in the reaction system can act as template, which played an important role in determining the porous architecture of the final Co–B product. In the hydrolysis of sodium borohydride for hydrogen generation, the porous Co-B_bubble nanoalloy materials exhibit high catalytic activity with mass normalized rate constant of 5.31 L_hydrogen min^?1 g_catalyst^?1; a value which is much higher than those obtained for many other Co–B catalysts recently reported in the literature. The apparent activation energy (Ea) of the catalytic process is found to be ca. 30 kJ mol^?1. It is proposed that the high catalytic performance and low cost of Co-B_bubble nanoalloy catalyst can be a promising material candidate in the hydrolysis of sodium borohydride for hydrogen production for commercial applications.     

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.