Superefficient thin film multilayer catalyst for generating hydrogen from sodium borohydride

A multilayer catalyst consisting of a electrophoretically deposited thin film of carbon nanotubes (CNTs) on a substrate of carbon fibers, followed by a coating of polymer-derived silicon carbonitride (SiCN), which is then decorated with a monolayer of transition metals is shown to perform at the upperbound of the phenomemological prediction from an earlier work [1]. A figure-of-merit for first order kinetics is equal to 4600 L min⁻¹ [NaBH₄]⁻¹ g_met⁻¹, which is nearly 30 times the value reported in literature, is achieved. This high FOM is attributed to the CNT-thin film, as opposed to the thick CNT-paper used in previous work, thus needing merely 0.15 wt% quantities of precious metals for effective catalysis. This new architecture corroborates the concepts that: (i) the catalytic activity derives mainly from the surface of the CNT substrate, and (ii) the silicon carbonitride interlayer is instrumental in dispersing the transition metals into a monolayer. The hydrogen generation rate (HGR) for zero order kinetics, which is obtained when [NaBH₄] > 0.03 M, is measured to be 75 L min⁻¹ g_met⁻¹, which is among the higher values reported in the literature. The present multilayer catalysts are able to perform without fading for many cycles, presumably because the bondings in the substrate are predominantly covalent. This feature adds further uniqueness to this multilayer catalyst.     

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.     

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.     

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.     

Fabrication and characterization of poly(tannic acid) coated magnetic clay decorated with cobalt nanoparticles for NaBH4 hydrolysis: RSM-CCD based modeling and optimization

Hydrogen generation from sodium borohydride (NaBH₄) hydrolysis in the presence of metal catalysts is a frequently used and encouraging method for hydrogen storage. Metal nanoparticle-supported catalysts are better recyclability and dispersion than unsupported metal catalysts. In this study, the synthesis and characterization of a polymer-supported catalyst for hydrogen generation using NaBH₄ have been investigated. For the synthesis of polymeric material, first of all, kaolin (KLN) clay has been magnetically rendered by using the co-precipitation method (Fe₃O₄@KLN) and then coated with poly tannic acid (PTA@Fe₃O₄@KLN). Then, the catalyst loaded with cobalt (Co) nanoparticles have been obtained with the NaBH₄ reduction method (Co@PTA@Fe₃O₄@KLN). The surface morphology and structural properties of the prepared catalysts have been determined using methods such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS) and vibrating sample magnetometer (VSM). The optimization of the most important variables (NaBH₄ amount, NaOH amount, catalyst amount, and metal loading rate) affecting the hydrolysis of NaBH₄ using the synthesized polymeric catalysts was carried out using response surface methodology (RSM). Depending on the evaluated parameters, the desired response was determined to be hydrogen production rate (HGR, mL/g min). HGR was 1540.4 mL/g_cat. min. in the presence of the Co@PTA@Fe₃O₄@KLN at optimum points obtained via RSM (NaBH₄ amount 0.34 M, NaOH amount 7.9 wt%, catalyst amount 3.84 mg/mL, and Co loading rate 6.1%). The reusability performance of the catalyst used in hydrolysis of NaBH₄ was investigated under optimum conditions. It was concluded that the catalyst is quite stable.     

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.     

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

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

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.     

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.     

Highly stable and controllable CoB/Ni-foam catalysts for hydrogen generation from alkaline NaBH4 solution

In this work, a series of shaped CoB/Ni-foam catalysts were directly synthesized by using a convenient and simple electroless plating method. Despite the low loading amount of CoB, the catalysts showed high catalytic performance in the hydrolysis of NaBH₄ solution, and the maximum hydrogen generation rate reached 1930 mL min^?1 (g CoB)^?1 in 1 wt % NaBH₄ + 5 wt % NaOH solution at 293 K. The catalysts demonstrated distinct stability, and the hydrogen generation rate was almost unchanged after 6 cycles. Furthermore, the catalysts could be easily recovered from the reaction system by a magnet. These characteristics make CoB/Ni-foam a high performance and cost effective catalyst for practical applications of hydrogen generation.     

Hydrogen generation from NaBH4 hydrolysis catalyzed by cobalt (0)-Deposited cross-linked polymer brushes: Optimization with an experimental design approach

Proposing a novel catalyst that achieves catalytic hydrolysis of metal hydrides is an important stage in developing a hydrogen storage system. In this study, a cross-linked gel brush-cobalt (0) composite (Co@P4VP_GB@PMC) has been synthesized to obtain hydrogen from NaBH₄ solution. The morphology, structure, and composition of the obtained catalyst have been characterized by, FTIR, SEM, EDX, BET, XRD, ICP-MS and XPS. The parameters that significantly affect the hydrolysis of NaBH₄ (such as NaBH₄ concentration, NaOH amount, catalyst amount, and temperature) have been investigated using response surface methodology (RSM), an optimization method that has gained increasing importance in recent years. The hydrogen generation rate (HGR) was 4499 mL/min g_cat for Co@P4VP_GB@PMC when the NaBH₄ amount was 241.52 mM, NaOH amount 5 wt%, catalyst amount 10.55 mg and temperature 58.9 °C. Moreover, the apparent activation energy (E_a) for the catalytic hydrolysis reaction has been 41.27 kJmol^-1 obtained under optimum conditions. Additionally, the Co@P4VP_GB@PMC catalyst displayed significant reusability performance for up to five cycles without major loss of its activity. Compared with metal catalysts, this new cross-linked polymer gel brush-cobalt catalyst has excellent potential applications for hydrogen production by hydrolysis of metal hydrides due to its simple synthesis, low cost, and the easy availability of raw materials.     

Carbon spheres from lactose as green catalyst for fast hydrogen production via methanolysis

Micrometer sized carbon spheres (CSs) are prepared in a single step using lactose precursor via hydrothermal method. These CSs are chemically modified with 3-chloro-2-hydroxypropyl ammonium chloride (CHPACl) and triethylenetetramine (TETA) to generate amine groups on the particle surface. Modified CSs with TETA was protonated with HCl as CSs-TETA-HCl that the zeta potential is increased to +40.3 ± 0.70 from ?51.4 ± 4.66 mV. The catalytic performance of CSs are tested as catalysts in the methanolysis of NaBH₄, and the best catalytic performance as 2586 mL min^?1 g^?1 hydrogen generation rate (HGR) was obtained by CSs-TETA-HCl catalyst at 298 K as metal free catalyst. Furthermore, various parameters such as the amount of NaBH₄, the reaction temperature, and the reusability of CSs-TETA-HCl particles are investigated. More importantly, relatively low activation energy, 23.82 kJ mol^?1 for CSs-TETA-HCl catalyzed NaBH₄ methanolysis reaction is obtained in comparison to metal nanoparticle and metal free catalysts reported for the same purpose in the literature.     

Effect of phosphoric acid addition on the hydrogen production from hydrolysis of NaBH4 with Cu based catalyst

Cu based catalysts were synthesized in water and methanol solvents by chemical reduction with sodium borohydride (NaBH₄). The obtained catalyst was used to catalyze the NaBH₄ hydrolysis reaction with phosphoric acid (H₃PO₄) including different concentrations. Surface morphology and structural properties of the Cu based catalysts prepared in water and methanol solvents were studied using by X-ray diffraction (XRD), scanning electron microscopy (SEM), surface area measurements and Fourier-transform infrared spectroscopy (FTIR) analyses, respectively. The catalytic activity of the catalysts has been tested by measuring the hydrogen production rate by the acidified hydrolysis of NaBH₄. The maximum hydrogen production rates in the hydrolysis reaction including 0.25 M H₃PO₄ using the Cu based catalyst prepared in water and methanol solvents were 825 and 660 ml g^?1min^?1, respectively. At the same time, the hydrogen production experiments were carried out from this hydrolysis reaction with only H₃PO₄ and NaBH₄ interactions without using Cu metal catalyst. The activation energy obtained based on the nth order reaction model was found to be 61.16 kJ mol^?1.     

Stability and kinetic studies of MOF‐derived carbon‐confined ultrafine Co catalyst for sodium borohydride hydrolysis

A mesoporous carbon‐confined cobalt (Co@C) catalyst was fabricated by pyrolysis of macroscale Co‐metal–organic framework (MOF) crystals and used to catalyze NaBH₄ hydrolysis for hydrogen production. To reveal the structural changes of cobalt nanoparticles, we characterized the fresh and used Co@C catalysts using X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and N₂ adsorption. This MOF‐derived Co@C exhibits high and stable activity toward NaBH₄ hydrolysis. No obvious agglomeration of Co nanoparticles occurred after five consecutive runs, implying good resistance of Co@C composite to metal aggregation. The kinetics of NaBH₄ hydrolysis was experimentally studied by changing initial NaBH₄ concentration, NaOH concentration, and catalyst dosage, respectively. It was found that the hydrogen generation rate follows a power law: r = A exp (?45.0/RT)[NaBH₄]^0.985[cat]^1.169[NaOH]^?0.451 .     

Poly (acrylic acid)/polysaccharides IPN derived metal free catalyst for rapid hydrogen generation via NaBH4 methanolysis

Polymeric catalysts have displayed great performance for catalytic hydrogen generation. However, the reported metal free polymeric catalysts for NaBH₄ methanolysis are mainly limited to coating strategy where the catalytic activity fade after few cycles. Herein, we report an interpenetrating polymer network (IPN) strategy for rapid and highly recyclable NaBH₄ catalytic methanolysis to produce hydrogen (H₂) gas. In this study, we prepared poly(acrylic acid)/polysaccharide IPN via Pickering tempted polymerization. The hydrogen generation performance was studied employing different parameters where maximum HGR of 8182 mL H₂ min^?1 g^?1 of CAP. The activation energy Ea, enthalpy and entropy were calculated to be 62.99 kJ mol^?1, 32.25 kJ mol and ?130.92 J mol K^?1, respectively. Above all, CAP kept cyclic performance to 100% even at the 7th cycle. We confirmed the reproducibility of approach with other natural polysaccharides. This was due to strong chain entanglement of IPN synthesis which forces the active sites to stay in place during cyclic catalysis reaction. Thus, the IPN strategy ensures longer catalyst life for catalytic methanolysis of NaBH₄ for H₂ generation.     

A study on hydrogen generation from NaBH4 solution using Co-loaded resin catalysts

Hydrogen production via chemical processes has gained great attention in recent years. In this study, Co-based complex catalyst obtained by adsorption of Co metal to Amberlite IRC-748 resin and Diaion CR11 were tested for hydrogen production from alkaline NaBH₄ via hydrolysis process. Their catalytic activity and microstructure were investigated. Process parameters affecting the catalytic activity, such as NaOH concentration, Co percentage and catalyst amount, as well as NaBH₄ concentration and temperature were investigated. Furthermore, characteristics of these catalysts were carried out via SEM, XRD and FT-IR analysis. Hydrogen production rates equal to 211 and 221 ml min⁻¹ g_cat⁻¹ could be obtained with Amberlite IRC-748 resin and Diaion CR11 Co based complex catalysts, respectively. The activation energies of the catalytic hydrolysis reaction of NaBH₄ were calculated as 46.9 and 59.42 kJ mol⁻¹ for Amberlite IRC-748 resin and Diaion CR11 based catalysts respectively kJ mol⁻¹ from the system consisting of 3% Co, 10 wt% NaBH₄ and 7 wt% NaOH as well as 50 mg catalyst dosage. It can be concluded that Co-based resins as catalysts for hydrogen production is an effective alternative to other catalysts having higher rate.     

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.     

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.     

Synthesis,characterization and 1-propanol electrooxidation application of carbon nanotube supported bimetallic catalysts

In this study, 1-propanol electrooxidation activities of Pt and Bi catalysts synthesized by NaBH₄ co-reduction and sequential reduction methods are compared. The characterization of the catalysts supported carbon nanotube (CNT) is determined by XRD, SEM-EDX, TEM, and ICP-MS analyzes. In the TEM results, it is seen that Pt and Bi metal nanoparticles are dispersed into carbon nanotubes. Electrochemical measurements of CV, CA, and EIS are applied to investigate the catalytic activities of catalysts for 1-propanol electrooxidation. Bi@Pt/CNT catalyst exhibits the highest catalytic activity (24.212 mA/cm² and 1950.06 mA/mg Pt), long-term stability and lowest resistance. As a result, it was concluded that the catalyst activity increased with the sequential reduction method and the Bi@Pt/CNT catalyst was promising with its high activity value for direct alcohol fuel cells.     

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.