High-performance cobalt–tungsten–boron catalyst supported on Ni foam for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are highly wanted in developing on-demand hydrogen generation system for practical onboard application. By using a modified electroless plating method, we have prepared a robust Co–W–B amorphous catalyst supported on Ni foam (Co–W–B/Ni foam catalyst) that is highly effective for catalyzing hydrogen generation from alkaline NaBH₄ solution. It was found that the plating times, calcination temperature, NaBH₄ and NaOH concentrations all exert considerable influence on the catalytic effectiveness of Co–W–B/Ni foam catalyst towards the hydrolysis reaction of NaBH₄. Via optimizing these preparation and reaction conditions, a hydrogen generation rate of 15 L/min g (Co–W–B) has been achieved, which is comparable to the highest level of noble metal catalyst. In consistent with the observed pronounced catalytic activity, the activation energy of the hydrolysis reaction using Co–W–B/Ni foam catalyst was determined to be only 29 kJ/mol. Based on the phase analysis and structural characterization results, the mechanism underlying the observed dependence of catalytic effectiveness on the calcination temperature was discussed.     

Dehydrogenation of Ammonia Borane with transition metal-doped Co–B alloy catalysts

The catalytic performance of transition metal-doped Co–B ternary alloys were tested for H₂ generation by hydrolysis of Ammonia Borane (AB). Chemical reduction method was used to dope Co–B catalyst with various transition metals, namely Cu, Cr, Mo, and W, using their corresponding metal salts. All transition metals induce significant promoting effects on the Co–B catalyst by increasing the H₂ generation rate by about 3–6 times as compared to the undoped catalyst. The effect of metal dopant concentration on overall catalyst structure, surface morphology, and catalytic efficiency were examined by varying the metal/(Co + metal) molar ratio. Characterizations such as XPS, XRD, SEM, BET surface area measurement, and particle size analysis were carried out to understand the promoting role of each dopant metal during AB hydrolysis. Dopant transition-metals, in either oxidized or/and metallic state, act as an atomic barrier to avoid Co–B particle agglomeration thus preserving the effective surface area. In addition, the oxidized species such as Cr³⁺, Mo⁴⁺, and W⁴⁺, act as Lewis acid sites to enhance the absorption of OH⁻ group to further assist the hydrolysis reaction over alloy catalysts. The promoting nature of transition metal dopants in Co–B alloy powders is demonstrated by the evaluated low activation energy of the rate limiting step and high H₂ generation rate (2460 ml H₂ min⁻¹ (g of catalyst)⁻¹ for Co–Mo–B) in the hydrolysis of AB.     

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.     

Amorphous cobalt–boron/nickel foam as an effective catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are of interest for the development of on-board hydrogen generation systems for fuel-cell vehicles. In the present study a modified electroless plating method was developed for the preparation of amorphous Co–B catalyst supported on Ni foam. Compared to the conventional electroless plating method, the newly developed method is more effective and produces Co–B catalyst with much higher catalytic activity. The catalytic activity of the supported Co–B catalyst was found to be highly dependent on the plating times and calcination conditions. Through optimization of these preparation conditions we were able to prepare a catalyst capable of a hydrogen generation rate of 11 l (min g)⁻¹ (catalyst) in a 20 wt.% NaBH₄ + 10 wt.% NaOH solution. Preliminary phase analyses and microstructure characterization were performed to understand the effects of preparation conditions on the catalytic activity of the Co–B catalyst.     

Hydrogen generation from hydrolysis of solid sodium borohydride promoted by a cobalt–molybdenum–boron catalyst and aluminum powder

Direct use of solid sodium borohydride (NaBH₄) to react with minimized amount of water provides a straightforward means for increasing the hydrogen density of the system. But meanwhile, the resulting solid–liquid reaction system always suffers from serious kinetic problem. Our study found that the cobalt–molybdenum–boron (Co–Mo–B) catalyst prepared using an ethylene glycol solution of cobalt chloride is highly effective for promoting the hydrolysis reaction of solid NaBH₄. Particularly, a combined usage of small amounts of Co–Mo–B catalyst, aluminum powder and sodium hydroxide enables a rapid and high-yield hydrogen generation from the hydrolysis reaction of solid NaBH₄. A systematic study has been conducted to investigate the property dependence of the system on the components. In addition, the by-products of reaction were analyzed using powder X-ray diffraction and thermogravimetry/differential scanning calorimetry/mass spectroscopy techniques. Our study demonstrates that the multi-component system with an optimized composition can fulfill over 95% fuel conversion, yielding 6.43 wt% hydrogen within 3 min. The favorable combination of high hydrogen density, fast hydrogen generation kinetics and high fuel conversion makes the newly developed solid NaBH₄-based system promising for portable hydrogen source applications.     

Stability, durability, and reusability studies on transition metal-doped Co–B alloy catalysts for hydrogen production

In addition to high catalytic efficiency the catalyst must also comprise important features like high stability in severe conditions, ability to be recycled several times and should have high tolerance against deactivation. This work is oriented specifically to study these properties of already developed efficient transition-metal doped Co–B alloy catalyst. Various transition metals, namely Ni, Fe, Cu, Cr, Mo, and W, were singly added as dopants in Co–B catalyst by chemical reduction of the corresponding metal salts. These alloy catalysts were calcinated, in Ar atmosphere, at 673, 773, and 873 K in order to investigate the stability of the powders at elevated temperatures. The catalytic performances of these treated catalyst powders were tested for H₂ generation by catalytic hydrolysis of sodium borohydride (NaBH₄). The alloy powders were exposed to ambient condition for several days to test their tolerance against deactivation and self life. After separation from the reaction course and after rinsing, the catalyst powders were tested for several cycles to evaluate the reusability property. The observed changes in the catalytic activity were discussed on the basis of structural and morphological variations. The Co–B catalyst, when doped with Ni, Mo, and W metals showed high stability and resistance against deterioration, as function of both time and use, as compared to Cr- and Fe-doped alloy powders. A much lower performance with respect to calcination temperature, holding time, and number of cycles was established for Cu doped Co–B catalyst powder.     

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.     

Improved H2 production rate by hydrolysis of Ammonia Borane using quaternary alloy catalysts

Co–M–B–P quaternary alloy catalyst powders (where M = Cr, Mo, W, and Cu) were synthesized by chemical reduction method to improve the catalytic performance of Co–B catalyst for hydrogen production by hydrolysis of Ammonia Borane (AB). The catalytic activity increases significantly due to the combined promoting effects induced by M and P in quaternary alloy as compared to binary Co–B catalyst. The promoting roles of each doping element in Co–B catalyst during AB hydrolysis were studied using XPS, XRD, SEM, and BET surface area analyses. Each transition element, present in the form of either oxides or metal, acts as an atomic barrier to prevent Co–B particle agglomeration to increase the effective surface area. At the same time these species also act as Lewis acid sites to improve the absorption of the reactants on to the surface. Inclusion of phosphorous, in addition, is able to create higher number of Co-active sites on the surface, which was inferred from XPS analysis. Among all the alloy catalysts, Co–Cr–B–P showed the highest H₂ generation rate, which was mainly attributed to the collective effects of Cr and P in forming the catalyst surface having higher surface area and more Co-active sites. On the contrary, in the case of Cu doped Co–B catalyst, the inclusion of P considerably lowers the surface area, which decreases the catalytic activity.     

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.     

Electrochemical oxidation behavior of Mg–Li–Al–Ce–Zn and Mg–Li–Al–Ce–Zn–Mn in sodium chloride solution

Mg–Li–Al–Ce–Zn and Mg–Li–Al–Ce–Zn–Mn alloys were prepared using a vacuum induction melting method. Their electrochemical oxidation behavior in 0.7 M NaCl solution was investigated by means of potentiodynamic polarization, potentiostatic oxidation, electrochemical impedance technique and scanning electron microscopy examination. Their utilization efficiencies and performances as anode of metal–hydrogen peroxide semi-fuel cell were determined. The Mg–Li–Al–Ce–Zn–Mn exhibited higher discharge activity and utilization efficiency than Mg–Li–Al–Ce–Zn, and gave improved fuel cell performance. The utilization efficiency of Mg–Li–Al–Ce–Zn–Mn is comparable with that of the state-of-the-art magnesium alloy anode AP65. The magnesium–hydrogen peroxide semi-fuel cell with Mg–Li–Al–Ce–Zn–Mn anode presented a maximum power density of 91 mW cm⁻² at room temperature. Scanning electron microscopy and electrochemical impedance studies indicated that the alloying element Mn prevented the formation of dense oxide film on the alloy surface and facilitated peeling off of the oxidation products.     

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.     

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.     

Hydrolysis of sodium borohydride solutions both in the presence of Ni–B catalyst and in the case of microwave application

In this study, the nickel boron (Ni–B) catalyst was studied in the microwave environment for hydrogen production from the hydrolysis of a sodium borohydride solution to release H₂. The catalytic activity of the Ni–B catalyst was measured by hydrogen production from the hydrolysis of sodium borohydride. The catalytic properties of the Ni–B catalyst in the microwave medium were examined by considering parameters such as NaOH concentration, NaBH₄ concentration, catalyst amount, temperature, and microwave power. Thus, the results obtained from the experiments carried out with Ni–B catalyst both in non-microwave and microwave media were compared. In the experiments, under microwave irradiation, the best result was the release of hydrogen gas from the Ni–B catalyst by applying 100 W of microwave energy at 40 °C. Activation energy values were calculated using the reaction rate constants obtained at different temperatures in the nth order kinetic model and the Langmuir - Hinshelwood model.     

An alkaline direct NaBH4–H2O2 fuel cell with high power density

A high performance alkaline direct borohydride–hydrogen peroxide fuel cell with Pt–Ru catalyzed nickel foam as anode and Pd–Ir catalyzed nickel foam as cathode is reported. The electrodes were prepared by electrodeposition of the catalyst components on nickel foam. Their morphology and composition were analyzed by SEM–EDX. The effects of concentrations of NaBH₄ and H₂O₂ as well as operation temperature on the cell performance were investigated. The cell exhibited an open circuit voltage of about 1.0 V and a peak power density of 198 mW cm⁻² at a current density of 397 mA cm⁻² and a cell voltage of 0.5 V using 0.2 mol dm⁻³ NaBH₄ as fuel and 0.4 mol dm⁻³ H₂O₂ as oxidant operating at room temperature. Electrooxidation of NaBH₄ on Pt–Ru nanoparticles was studied using a rotating disk electrode and complete 8e⁻ oxidation was observed in 2 mol dm⁻³ NaOH solution containing 0.01 mol dm⁻³ NaBH₄.     

Hydrogen generation by hydrolysis of ammonia borane with a nanoporous cobalt-tungsten-boron-phosphorus catalyst supported on Ni foam

In this study, quaternary cobalt-tungsten-boron-phosphorus porous particles supported on Ni foam (Co-W-B-P/Ni), which are prepared through ultrasonification-assisted electroless deposition route, have been investigated as the catalyst for hydrogen generation (HG) from hydrolysis of ammonia borane (NH₃BH₃, AB). Compared with Ni-supported binary Co-B and ternary Co-W-B catalysts, the as-synthesized Co-W-B-P/Ni shows a higher HG rate. To optimize the preparation parameters, the molar ratio of NaBH₄/NaH₂PO₂·H₂O (B/P) and the concentration of Na₂WO₄·2H₂O (W) have been investigated and the catalyst prepared with B/P value of 1.5 and W concentration of 5 g L⁻¹ shows the highest activity. The results of kinetic studies show that the catalytic hydrolysis of AB is first order with respect to the catalyst and AB concentrations. By using the quaternary catalyst with a concentration of 0.5 wt % AB, a HG rate of 4.0 L min⁻¹ g⁻¹ is achieved at 30 °C. Moreover, the apparent activation energy for the quaternary catalyst is determined to be 29.0 kJ mol⁻¹, which is comparable to that of noble metal-based catalysts. These results indicate that the Co-W-B-P/Ni is a promising low-cost catalyst for on-board hydrogen generation from hydrolysis of borohydride.     

Ni–B and Zr–Ni–B in-situ catalytic performance for hydrogen generation from sodium borohydride,ammonia borane and their mixtures

In this study, the parameters on the catalytic hydrolysis of the sodium borohydride (NaBH4, SBH) and ammonia boranes (NH3BH3, AB) mixtures were investigated such as the effect of Zr additive in the catalyst, using in-situ or powder catalysts, the molar ratio of the SBH/AB mixture (2, 4, 8, neat SBH, neat AB) and temperature. As the catalyst, in-situ synthesized Ni–B and Zr–Ni–B for the first time were used to produce H₂ from hydrolysis of the SBH and AB mixtures. The SBH and AB mixtures were used to determine provided or not an effect on reaction. Catalyst preparation and hydrolysis reactions took place in the same reactor spontaneously for in-situ works. The Zr–Ni–B catalyst gives better results than Ni–B and increases efficiency at 25 °C and 35 °C temperature. When Zr–Ni–B catalyst compared experimentally among themselves, the best yield result at 45 °C temperature, for neat SBH, mole ratio in 4 and mole ratio in 8, as 87%, 86% and 83% respectively. For hydrolysis reactions with Zr–Ni–B catalyst, activation energies of SBH and AB were calculated as 45.23 kJ/mol and 79.76 kJ/mol, respectively. SEM, BET, XPS analyzes have been used to characterize these catalysts. The addition of Zr provided increase effect on the surface area. The surface area increases from 44.33 m²/g to 175.50 m²/g.     

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.     

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.     

Improved hydrogen generation from alkaline solution using carbon-supported as catalysts

Carbon-supported Co–B catalysts with various loading contents were prepared by impregnation–chemical reduction method. The XRD, ICP, SEM and TEM analyses revealed that the as-prepared Co–B catalysts were in amorphous form with the composition of Co_2.0–3.3B and the carbon-supported Co–B catalysts had a good dispersion and coating condition. The hydrogen generation measurement showed that the average hydrogen generation rate at was for unsupported Co–B catalyst, while it was 1268.1, 1482.1 and for the carbon-supported catalysts with the Co–B loading of 30.0, 15.6 and 7.44 wt%, respectively. The activation energy of the 30.0 wt% Co–B loading catalyst for the hydrogen generation reaction was measured to be . Compared with the unsupported Co–B catalyst, the as-prepared carbon-supported catalysts presented higher activity for hydrolysis of NaBH₄ aqueous solution, indicating their potential application in mobile hydrogen production for fuel cells.