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.     

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.     

Synthesis and characterization of GO-PpPDA/Ni–Mn nanocomposite as a novel catalyst for methanol electrooxidation

The graphene oxide-poly (p-phenylene diamine) (GP) composite is synthesized through in-situ polymerization of p-phenylene diamine on GO sheets and used as an efficient support material for electrodeposition of Ni and Mn. The resulting GP/Ni–Mn catalyst shows high catalytic activity, stability and durability for methanol electrooxidation. The surface area of GP composite is calculated to be about 28% and 36% higher than GO and PpPDA, respectively. In addition, combining Ni and Mn demonstrated some synergetic effect for methanol electrooxidation. The electrochemical active surface area of GP/Ni–Mn is about 1.625 cm², which is much higher than GP/Ni and GP/Mn. GP/Ni–Mn nanocomposite presented 87.3% of the peak current after 5 h and almost 83.16% of the maximum current for 500 cycles. The excellent characteristics of this composite are attributed to high surface area, high electrochemical active surface area and fine distribution of metallic particles on the support material.     

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.     

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.     

Co/CuO–NiO–Al2O3 catalyst for hydrogen generation from hydrolysis of NaBH4

This paper presents hydrogen generation measurements from the hydrolysis of NaBH₄ aqueous solutions catalyzed by Co doping on single, bimetallic and trimetallic oxide supports (Co/CuO, Co/NiO, Co/Al₂O₃, Co/NiO–Al₂O₃, Co/CuO–Al₂O_3, and Co/CuO–NiO–Al₂O₃). Support materials are synthesized by the co-precipitation method. Then, Co is doped into support materials by the impregnation method. It is found that Co/CuO–NiO–Al₂O₃ catalyst exhibited high reaction activity with a maximum hydrogen generation rate (HGR) of 2067.2 ml min^?1 g_cat^?1 at 25 °C. The effect of temperature of the solution, Co amount, and recyclability of the catalyst on hydrogen generation with Co/CuO–NiO–Al₂O₃ catalyst is investigated in detail. In addition, the highest HGR for Co/CuO–NiO–Al₂O₃ catalyst is obtained at 55 °C as 6460.0 ml min^?1 g_cat^?1. The activation energy is calculated to be 31.59 kJ mol^?1 using Co/CuO–NiO–Al₂O₃ catalyst. Co/CuO–NiO–Al₂O₃ catalyst exhibits zero-order reaction kinetics concerning NaBH₄ concentration. In addition, the Co/CuO–NiO–Al₂O₃ catalyst provided high reusability after 5 cycles.     

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.     

Development of a planar μDMFC operating at room temperature

A co-planar micro Direct Methanol Fuel Cell (μDMFC) configuration was designed, developed and tested. The system geometry consisted of anodic and cathodic micro-channels arranged in the same plane. Firstly, micro-channels for a uniform distribution of oxygen and methanol were designed and realized on a polymeric substrate of polycarbonate. Then, the deposition of the catalytic elements inside the micro-channels by a spray-coating technique was carried out. Micro-channels were then covered by a catalyzed membrane containing separate anode and cathode layers. Different cell configurations were built, tested and evaluated. It was observed that the open circuit voltage varied significantly as a function of the membrane humidification degree and distance between anode and cathode channels in this planar design. In the presence of a large distance between the anode and cathode channel, the OCV reached 0.97 V. This high OCV reflected the absence of methanol cross-over due to the specific planar configuration. Regrettably, the overall cell impedance (ohmic and polarization resistance) limited the performance. A maximum power density of 1.3 mW cm⁻² (active area) was achieved at room temperature with the smallest distance between anode and cathode (0.25 mm).     

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.     

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.     

Synthesis,characterization and performance of a novel Ni–Co/GO-TiO2 for electrooxidation of methanol and ethanol

In order to find out electrocatalysts based on non-precious metals, Ni–Co/GO-TiO₂ composite with different amounts of nickel and cobalt is prepared and the impacts of TiO₂ nanoparticles on GO support are highlighted. Composition, morphology and textural features of the synthesized materials are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, N₂ adsorption-desorption isotherms and field emission scanning electron microscopy equipped with energy-dispersive X-ray analysis. The electrochemical activity of the prepared catalysts toward methanol and ethanol electrooxidation in alkaline media is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. Results confirmed that adding TiO₂ nanoparticles to graphene oxide can increase the surface area, porosity and electrochemically active surface area of the support material. The composition with the equal amount of nickel and cobalt precursors exhibited the highest current density for methanol and ethanol electrooxiation equal to 121.07 and 145.28 mA/cm², respectively. Stability test results demonstrated that this sample maintains 94.1% and 87.5% of initial current density after 7200 s for the electrooxidation of ethanol and methanol in 1.0 M KOH, respectively. All results confirm the synergic effect of Ni and Co for the alcohols oxidation in alkaline media and equal amount of Ni and Co leads to the best catalytic performance with the highest current density, lowest impedance and maximum stability.     

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.     

Polymer-graphene hybride decorated Pt nanoparticles as highly efficient and reusable catalyst for the dehydrogenation of dimethylamine–borane at room temperature

Addressed herein, we report a reduced graphene oxide (rGO) nanosheet coupled with polyaniline (PANI) for platinum (Pt) nanoparticles as supporting materials. The PANI-coupled rGO (PANI@rGO) nanosheet is prepared by a simple one-step chemical assembly strategy, and Pt nanoparticles are anchored on the support of PANI@rGO through the reaction of PANI with a platinum salt. The designed PANI efficiently exposes the surface of rGO sheets and stabilizes metal nanoparticles. Consequently, the Pt@PANI-rGO catalyst exhibits good reusability, durability and high catalytic performance for dimethylamine–borane dehydrogenation reaction. The structure morphology and properties of Pt@PANI-rGO NPs were characterized by using several different techniques such as UV–Vis, XPS, TEM, XRD and HR-TEM-EDX analyses. This newly prepared catalyst can be reused again at low concentrations and temperature. They showed a high turnover frequency (42.94 h^?1) and low E_a value of 15.1 ± 2 kJ/mol for DMAB dehydrocoupling in the ambient conditions. The proposed nano architecture offers a new pathway to promote the performances of rGO in various applications; moreover, this work provides a powerful and universal synthetic strategy for such an architecture.     

Study on the role of Pt and Pd in Pt–Pd/TiO2 bimetallic catalyst for H2 oxidation at room temperature

The hydrogen safety issue is spotlighted as the hydrogen process is extended. For this reason, we studied catalysts for H₂ oxidation at room temperature to ensure hydrogen safety. Catalysts were prepared by different preparation methods and compared to evaluate the role of Pt and Pd in Pt–Pd/TiO₂ catalysts. The catalytic activity was significantly enhanced when activity metal size was small and it was exposed to catalyst surface to a high Pd ratio. For the 0.1%Pt-0.9%Pd/TiO₂ catalyst, high hydrogen conversion of 90% was obtained under the condition of 0.5% hydrogen injection. To understand the correlation between activity and characteristics of catalyst, the physicochemical characteristics of the various catalysts were investigated by X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation and reduction (TPOR) and Field Emission-Transmission Electron Microscope (FE-TEM) analysis. From these analysis, it was found that Pt served the role of highly dispersion of active metal (Pt–Pd) and as with increasing Pd ratio of active metal, hydrogen activity was increased, which indicates that hydrogen oxidation had proceeded on the Pd site. Finally, the valence state of the Pd influenced hydrogen oxidation activity of Pt–Pd/TiO₂, which increased with increasing ratio of Pd⁰/Pd_Total.     

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.     

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.     

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.     

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.     

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.     

Room temperature hydrogen generation from hydrolysis of ammonia–borane over an efficient NiAgPd/C catalyst

NiAgPd nanoparticles are successfully synthesized by in-situ reduction of Ni, Ag and Pd salts on the surface of carbon. Their catalytic activity was examined in ammonia borane (NH₃BH₃) hydrolysis to generate hydrogen gas. This nanomaterial exhibits a higher catalytic activity than those of monometallic and bimetallic counterparts and a stoichiometric amount of hydrogen was produced at a high generation rate. Hydrogen production rates were investigated in different concentrations of NH₃BH₃ solutions, including in the borates saturated solution, showing little influence of the concentrations on the reaction rates. The hydrogen production rate can reach 3.6–3.8 mol H₂ mol_cat⁻¹ min⁻¹ at room temperature (21 °C). The activation energy and TOF value are 38.36 kJ/mol and 93.8 mol H₂ mol_cat⁻¹ min⁻¹, respectively, comparable to those of Pt based catalysts. This nanomaterial catalyst also exhibits excellent chemical stability, and no significant morphology change was observed from TEM after the reaction. Using this catalyst for continuously hydrogen generation, the hydrogen production rate can be kept after generating 6.2 L hydrogen with over 10,000 turnovers and a TOF value of 90.3 mol H₂ mol_cat⁻¹ min⁻¹.