Co-SiO2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Cobalt clusters-silica nanospheres (15-30 nm) were synthesized using a Co(NH₃)₆Cl₃ template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH₄/NH₃BH₃ solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt-silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.     

Hydrolytic dehydrogenation of ammonia borane catalyzed by carbon supported Co core-Pt shell nanoparticles

Co core-Pt shell nanoparticles (denoted as Co_1−x@Pt_x where x = 0.33, 0.43, 0.60, 0.68, 0.82) and carbon supported Co core-Pt shell nanoparticles (denoted as Co_1−x@Pt_x/C where x = 0.60, 0.68, 0.82) (Co_1−x@Pt_x/C = 43%), which are synthesized through a polyol reduction process with oleic acid as a surfactant, have been investigated as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃) at 25 ± 0.5 °C. The as-prepared Co core-Pt shell nanoparticles are uniformly dispersed on carbon surface with diameters of about 3 nm. It is found that the catalysts show favorable performance toward the hydrolysis of NH₃BH₃ and the catalytic activity is associated with the ratio of Pt to Co. Among the catalysts studied, Co_0.32@Pt_0.68/C (Co_0.32@Pt_0.68/C = 43%) displays the highest catalytic performance, delivering a high hydrogen-release rate of 4874 mL min⁻¹ g⁻¹ (per catalyst).     

One-step synthesis of graphene supported Ru nanoparticles as efficient catalysts for hydrolytic dehydrogenation of ammonia borane

Ru nanoparticles supported on graphene have been synthesized via a one-step procedure using methylamine borane as reducing agent. Compared with NaBH₄ and ammonia borane, the as-prepared Ru/graphene NPs reduced by methylamine borane exhibit superior catalytic activity towards the hydrolytic dehydrogenation of ammonia borane. Additionally, the Ru/graphene NPs exhibit higher catalytic activity than its graphene free counterparts, and retain 72% of their initial catalytic activity after 4 reaction cycles. A kinetic study shows that the catalytic hydrolysis of ammonia borane is first order with respect to Ru concentration, the turnover frequency is 100 mol H₂ min⁻¹ (mol Ru)⁻¹. The activation energy for the hydrolysis of ammonia borane in the presence of Ru/graphene NPs has been measured to be 11.7 kJ/mol, which is the lowest value ever reported for the catalytic hydrolytic dehydrogenation of ammonia borane.     

Mo remarkably enhances catalytic activity of Cu@MoCo core-shell nanoparticles for hydrolytic dehydrogenation of ammonia borane

Ammonia borane (AB) has been identified as one of the most promising candidates for chemical hydrogen storage. However, the practical application of AB for hydrogen production is hindered by the need of efficient and inexpensive catalysts. For the first time, we report that the incorporation of Mo into Cu@Co core-shell structure can significantly improve the catalytic efficiency of hydrogen generation from the hydrolysis of AB. The Cu_0.81@Mo_0.09Co_0.10 core-shell catalyst displays high catalytic activity towards the hydrolysis dehydrogenation of AB with a turnover frequency (TOF) value of 49.6 molH₂ mol_cat^?1 min^?1, which is higher than most of Cu-based catalysts ever reported, and even comparable to those of noble-metal based catalysts. The excellent catalytic performance is attributed to the multi-elements co-deposition effect and electrons transfer effect of Cu, Mo and Co in the tri-metallic core-shell NPs.     

Hollow Ni-SiO2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Nickel clusters contained within silica nanospheres (20-30 nm) were synthesized by using a Ni(NH₃)₆Cl₂ crystal template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH₄/NH₃BH₃ solutions. Metallic nickel clusters exist inside the SiO₂ nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.     

Efficient hydrolytic dehydrogenation of ammonia borane over ultrafine Ru nanoparticles supported on biomass-derived porous carbon

Ammonia borane hydrolysis is a promising strategy for developing sustainable hydrogen energy. However, this reaction is not kinetically feasible at ambient temperature, thus developing a proper catalyst is indispensable. In this work, Porous carbon is facilely prepared from cattail fibers by using K₂CO₃, and then used to stabilize Ru nanoparticles. The effects of different synthesis parameters for the biomass-derived carbon supports (e. g. K₂CO₃ dosage and calcination temperature) and various catalytic reaction conditions (e. g. the amounts of the catalysts, ammonia borane and NaOH, and reaction temperature) on the hydrolysis rate of ammonia borane are investigated. Benefitting from the interconnected hierarchical pores of the optimal porous carbon (p-C), which was prepared with a mass ratio of 6 : 1 for K₂CO₃ to cattail fibers and calcined at 873 K, and the high dispersion of Ru nanoparticles, the optimal Ru/p-C catalysts exhibit excellent catalytic performance. The corresponding apparent activation energy (28.8 kJ mol^?1) and turnover frequency (744.7 min^?1 in alkaline solution) are superior to many catalysts previously reported. This work offers a competitive catalyst for the hydrolytic dehydrogenation of chemical hydrogen storage materials.     

Methanolysis of ammonia borane catalyzed by magnetically isolable RHODIUM(0) nanoparticles

This article reports the preparation and employment of rhodium (0) nanoparticles (Rh⁰NPs) on the surface of magnetite nanospheres, denoted as Rh⁰@Fe₃O₄, as magnetically isolable nanocatalyst in the methanolysis of ammonia borane (MAB). The monodispersed Fe₃O₄ nanospheres are fabricated by a simple technique and used as nanosupport for Rh⁰NPs which are well stabilized and homogeneously distributed on the surface of nanospheres with a mean particle size of 2.8 ± 0.5 nm. The as-synthesized Rh⁰@Fe₃O₄ has a remarkable TOF value of 184 min⁻¹ in the MAB to produce H₂ gas in RT. Most of all, Rh⁰@Fe₃O₄ nanocatalyst can be reused, evolving 3.0 mol of H₂ gas for a mole of AB, keeping 100% of its initial activity even in the fourth reuse of MAB at 25 °C. Recovery of the Rh⁰@Fe₃O₄ nanocatalyst can be accomplished by simply approaching an external magnet, which eliminates many laborious catalyst removal steps in catalytic reactions. Reported are the outcomes of kinetic investigation, done by altering the concentration of substrate and catalyst together with temperature. Kinetic studies reveal that the catalytic MAB shows dependence on the concentration of reactants and temperature.     

Monodisperse PtCu alloy nanoparticles as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Pt-M alloy nanoparticles (NPs) with well-defined size and compositions exhibit dramatically catalytic performance in chemical reactions. In this work, monodisperse PtCu NPs with controlled size and compositions were synthesized by the co-reduction method in the presence of oleylamine. These NPs have excellent catalytic activities in the hydrolytic dehydrogenation of ammonia borane (AB) and their activities were composition dependent. Among the different-composition PtCu NPs, the Cu₅₀Pt₅₀ NPs exhibit the highest catalytic activity with an initial turnover frequency of 102.5 mol_(hydrogen)·mol_(catalyst)^?1·min^?1 and an apparent activation energy of 36 kJ·mol^?1, which demonstrate the validity of partly replacing Pt by a first-row transition metal on constructing high performance heterogeneous nanocatalysts for the hydrolytic dehydrogenation of AB.     

Hydrolysis of solid ammonia borane

Ammonia borane NH₃BH₃ is a promising hydrogen storage material by virtue of a theoretical gravimetric hydrogen storage capacity (GHSC) of 19.5 wt%. However, stored hydrogen has to be effectively released, one way of recovering this hydrogen being the metal-catalyzed hydrolysis. The present study focuses on CoCl₂-catalyzed hydrolysis of NH₃BH₃ with the concern of improving the effective GHSC of the system NH₃BH₃-H₂O. For that, NH₃BH₃ is stored as a solid and H₂O is provided in stoichiometric amount. By this way, an effective GHSC of 7.8 wt% has been reached at 25 °C. To our knowledge, it is the highest value ever reported. Besides, one of the highest hydrogen generation rates (HGRs, 21 ml(H₂) min⁻¹) has been found. In parallel, the increases of the water amount and temperature have been studied and the reaction kinetics has been determined. Finally, it has been observed that some NH₃ release, what is detrimental for a fuel cell. To summarize, high performances in terms of GHSCs and HGRs can be reached with NH₃BH₃ and since research devoted to this boron hydride is at the beginning we may be confident in making it viable in a near future.     

Hydrogen production from ammonia borane via hydrogel template synthesized Cu, Ni, Co composites

In situ Co, Cu and Ni nanoparticles were synthesized by chemical reduction of the absorbed Co (II), Cu (II) and Ni (II) ions inside hydrogel networks prepared from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) and were used as a catalyst system in the generation of hydrogen in hydrolysis of ammonia borane (AB). Several parameters affecting the hydrolysis reaction such as the type of the metal, the amount of catalyst, the initial concentration of AB, and temperature, were investigated. The activation energy values in the hydrolysis reaction of AB solution in the presence p(AMPS)-Co, p(AMPS)-Cu and p(AMPS)-Ni catalyst systems were calculated as E_a = 47.7 kJ mol⁻¹, 48.8 kJ mol⁻¹ and 52.8 kJ mol⁻¹, respectively. Thus, the catalytic activity of the metal nanoparticles prepared inside the same hydrogel matrix was found to be Ni < Cu < Co.     

Magnetically recyclable Fe-Ni alloy catalyzed dehydrogenation of ammonia borane in aqueous solution under ambient atmosphere

In this work, we report a very simple method to in situ prepare the Fe_1−xNi_x (x = 0, 0.3, 0.4, 0.5, 0.7 and 1) nano-alloys as the catalysts for H₂ generation from the aqueous NH₃BH₃ solution under ambient atmosphere at room temperature. The prepared nano-alloys possess Pt-like high catalytic activity, especially for the specimen of Fe_0.5Ni_0.5, with which the hydrolysis of NH₃BH₃ would totally complete in only 2.2 min. Moreover, these catalysts can be easily magnetically separated for recycle purpose, and can almost keep the same high activity even after 5 times of recycle under ambient atmosphere. Such alloy catalysts are expected to be useful for fuel cells, metal-air batteries and electrochemical sensors. Moreover, the concepts behind these preliminary results present a wide range of possibilities for the further development of synthesis of air and water-stable magnetic nano-alloys.     

Efficient hydrogen production from ammonia borane hydrolysis catalyzed by TiO2-supported RuCo catalysts

Hydrolysis of ammonia borane provides a reliable pathway for hydrogen production, while suitable catalysts are indispensable to make the hydrolysis reaction reach a considerable rate. In the present work, a series of TiO₂-supported RuCo catalysts have been fabricated by coprecipitation and subsequent reduction of Ru³⁺ and Co²⁺ on the surface of TiO₂ nanoparticles. Transmission electron microscopy and elemental mapping have verified the good distribution of metal species in the catalysts. The fabricated catalysts have shown excellent performance for catalyzing ammonia borane hydrolysis, especially in alkaline solutions with 0.5 M NaOH. For Ru₁Co₉/TiO₂ in which Ru/Co molar ratio is 1:9, the active energy of catalyzed ammonia borane hydrolysis is 33.25 kJ/mol, and a turnover frequency based on Ru as high as 1408 mol_H2/(mol_Ru·min) is obtained at 25 °C. Moreover, when different types of TiO₂ substrates are used, anatase TiO₂-supported catalysts show better catalytic activity than their counterparts with rutile TiO₂ as substrate or mixture of anatase and rutile TiO₂ as substrate.     

Effective hydrolysis of ammonia borane catalyzed by ruthenium nanoparticles immobilized on graphic carbon nitride

Graphic carbon nitride prepared by the thermal decomposition of urea was used a catalyst support for the in situ immobilization of Ru nanoparticles (NPs) (Ru/g-C₃N₄). The catalytic property of Ru/g-C₃N₄ was investigated in the hydrolysis of ammonia borane (AB) in an aqueous solution under mild conditions. Results show that the in situ generated Ru NPs are well dispersed on the surface of g-C₃N₄ with a mean particle size of 2.8 nm. The catalytic performance for AB hydrolysis indicates that 3.28 wt% Ru/g-C₃N₄ exhibits excellent catalytic activity with a high turnover frequency number of 313.0 mol H₂ (mol Ru·min)⁻¹ at room temperature. This strategy may provide an eco-friendly catalytic system for developing a sustainable catalytic route to hydrogen production.     

Catalytic dehydrogenation of ammonia borane in non-aqueous medium

Dehydrogenation of Ammonia Borane (NH₃BH₃, AB) catalyzed by transition metal heterogeneous catalysts was carried out in non-aqueous solution at temperatures below the standard polymer electrolyte membrane (PEM) fuel cell operating conditions. The introduction of a catalytic amount (∼2 mol%) of platinum to a solution of AB in 2-methoxyethyl ether (0.02–0.33 M) resulted in a rapid evolution of H₂ gas at room temperature. At 70 °C, the rate of platinum catalyzed hydrogen release from AB was the dehydrogenation rate which was 0.04 g s⁻¹ H₂ kW⁻¹.     

Hydrogen liberation from the hydrolytic dehydrogenation of hydrazine borane in acidic media

Addressed herein, the hydrolytic dehydrogenation of hydrazine borane (NH₄BH₃, HB) was reported in acidic media using nitric acid (HNO₃) as a catalyst at room conditions. The aqueous hydrazine borane was treated with HNO₃ solution in different concentrations to liberate H₂. Besides, kinetic data were collected to idetificate the activation parameters, the effect of temperature, acid and hydrazine borane concentrations on the hydrogen production for the hydrolytic dehydrogenation of hydrazine borane in acidic media. It can be said that the acid catalyzed hydrazine borane system can be regarded as a simple system for hydrogen production.     

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.     

Ruthenium supported on MIL-96: An efficient catalyst for hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

For the first time, ultrafine Ru nanoparticles with mean diameter of 2 nm are successfully deposited on MIL-96 by using a simple liquid impregnation strategy, and tested for catalytic hydrolysis of ammonia borane. The powder X-ray diffraction, N₂ physical adsorption, transmission electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma-atomic emission spectroscopy measurements are employed to characterized the Ru/MIL-96 catalysts. Thanks to the unique 3D structure of MIL-96, Ru NPs supported on MIL-96 exhibit much enhanced catalytic activity compared with other commercial supported materials and graphene, with the TOF value of 231 mol H₂ min⁻¹ (mol Ru)⁻¹, which is among the highest value ever reported. Moreover, this simple method can be extended to facile synthesis of other MOFs supported monometallic and polymetallic NPs for more application.     

Oxygen vacancies and morphology engineered Co3O4 anchored Ru nanoparticles as efficient catalysts for ammonia borane hydrolysis

Developing efficient but facile strategies to modulate the catalytic activity of Ru deposited on metal oxides is of broad interest but remains challenging. Herein, we report the oxygen vacancies and morphological modulation of vacancy-rich Co₃O₄ stabilized Ru nanoparticles (NPs) (Ru/V_O-Co₃O₄) to boost the catalytic activity and durability for hydrogen production from the hydrolysis of ammonia borane (AB). The well-defined and small-sized Ru NPs and V_O-Co₃O₄ induced morphology transformation via in situ driving V_O-Co₃O₄ to 2D nanosheets with abundant oxygen vacancies or Co²⁺ species considerably promote the catalytic activity and durability toward hydrogen evolution from AB hydrolysis. Specifically, the Ru/V_O-Co₃O₄ pre-catalyst exhibits an excellent catalytic activity with a high turnover frequency of 2114 min^?1 at 298 K. Meanwhile, the catalyst also shows a high durability toward AB hydrolysis with six successive cycles. This work establishes a facile but efficient strategy to construct high-performance catalysts for AB hydrolysis.     

Ruthenium nanoparticles immobilized in montmorillonite used as catalyst for methanolysis of ammonia borane

Ammonia borane (AB) is an intriguing molecular crystal material with extremely high hydrogen density. In the present study, we prepared ruthenium (Ru) nanoparticles immobilized in montmorillonite (MMT) and examine its catalytic effect on the methanolysis reaction of AB. The Ru/MMT catalyst was prepared by cation-exchange method followed by hydrogen reduction at elevated temperatures. Property examinations found that the Ru/MMT catalyst was highly effective and robust for promoting the methanolysis reaction of AB. For example, the methanolysis system employing Ru/MMT catalyst exhibited an average hydrogen generation rate of 29 L min⁻¹ g⁻¹ (Ru). The catalyst at its twentieth usage retained 95% of its initial activity and ensured 100% conversion of AB. Kinetics studies found that the methanolysis reaction of AB employing Ru/MMT catalyst follows first-order kinetics with respect to AB concentration and catalyst amount, respectively.