Alumina nanofiber-stabilized ruthenium nanoparticles: Highly efficient catalytic materials for hydrogen evolution from ammonia borane hydrolysis

Effective catalysts for hydrogen generation from ammonia borane (AB) hydrolysis should be developed for the versatile applications of hydrogen. In this study, ruthenium nanoparticles (NPs) supported on alumina nanofibers (Ru/Al₂O₃-NFs) were synthesized by reducing the Ru(Ш) ions impregnated on Al₂O₃-NFs during AB hydrolysis. Results showed that the Ru NPs with an average size of 2.9 nm were uniformly dispersed on the Al₂O₃-NFs support. The as-synthesized Ru/Al₂O₃-NFs exhibited a high turnover frequency of 327 mol H₂ (mol Ru min)^?1 and an activation energy of 36.1 kJ mol^?1 for AB hydrolysis at 25 °C. Kinetic studies showed that the AB hydrolysis catalyzed by Ru/Al₂O₃-NFs was a first-order reaction with regard to the Ru concentration and a zero-order reaction with respect to the AB concentration. The present work reveals that Ru/Al₂O₃-NFs show promise as a catalyst in developing a highly efficient hydrogen storage system for fuel cell applications.     

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.     

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.     

Visible-light-enhanced catalytic hydrolysis of ammonia borane using RuP2 quantum dots supported by graphitic carbon nitride

Hydrolytic dehydrogenation of ammonia borane (AB) driven by efficient catalysts has attracted considerable attention and is regarded as a promising strategy for hydrogen generation. Herein, RuP₂ quantum dots supported on graphitic carbon nitride (g-C₃N₄) were successfully prepared by in-situ phosphorization, yielding a highly efficient photocatalyst toward AB hydrolysis. The catalysts were characterized by field-emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron microscopy, inductively coupled plasma atomic emission spectroscopy, UV–visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. A conventional water-displacement method was employed to record the hydrogen volume as a function of reaction time. Owing to visible-light irradiation, the initial turnover frequency of the AB hydrolysis was significantly enhanced by 110% (i.e., 134 min^?1) at room temperature. Furthermore, the apparent activation energy decreased from 67.7 ± 0.9 to 47.6 ± 1.0 kJ mol^?1. The photocatalytic hydrolysis mechanism and catalyst reusability were also investigated.     

Ruthenium(0) nanoparticles supported on silica coated Fe3O4 as magnetically separable catalysts for hydrolytic dehydrogenation of ammonia borane

Ruthenium(0) nanoparticles supported on bare or silica-coated magnetite are prepared by impregnation of ruthenium(III) ions followed by their reduction with aqueous solution of sodium borohydride on the surface of support. These magnetically isolable catalysts are used in hydrogen generation from the hydrolysis of ammonia borane at room temperature. They conserve their initial catalytic activity even after the fifth reuse in the hydrolysis reaction. Ruthenium(0) nanoparticles supported on bare magnetite and silica-coated magnetite provide turnover frequency values of 29 min^?1 and 127 min^?1 and in hydrolytic dehydrogenation of ammonia borane at 25.0 ± 0.1 °C. Thus, coating of the surface of magnetite with silica results in a significant enhancement in catalytic activity of ruthenium(0) nanoparticles in hydrogen generation from the hydrolysis of ammonia borane.     

Hexagonal boron nitride supported ruthenium nanoparticles as highly active catalysts for ammonia borane hydrolysis

Ammonia borane (AB) hydrolysis is a comparative strategy for developing the sustainable hydrogen economy. Considering the hydrolysis cannot occur kinetically at low temperature, a suitable catalyst is indispensable. In this work, the dispersed ruthenium nanoparticles are stabilized on hexagonal boron nitride (h-BN) via an adsorption-in situ reduction procedure. Various characterization techniques are adopted for elucidating the structure-performance relationship of the obtained catalysts for the hydrolytic dehydrogenation of AB. In the presence of the resultant Ru/h-BN catalysts, the corresponding turnover frequency (1177.5 min^?1) in alkaline solution at 303 K and the apparent activation energy (24.1 kJ mol^?1) are superior to most literature previously reported. Our work provides a facile fabrication method for metal-based catalysts, which are highly promising in chemical storage material hydrolysis.     

Ruthenium(0) nanoparticles supported on nanotitania as highly active and reusable catalyst in hydrogen generation from the hydrolysis of ammonia borane

Ruthenium(0) nanoparticles supported on the surface of titania nanospheres (Ru(0)/TiO₂) were in situ generated from the reduction of ruthenium(III) ions impregnated on nanotitania during the hydrolysis of ammonia borane. They were isolated from the reaction solution by centrifugation and characterized by a combination of advanced analytical techniques. The results reveal that highly dispersed ruthenium(0) nanoparticles of size in the range 1.5–3.3 nm were formed on the surface of titania nanospheres. Ru(0)/TiO₂ show high catalytic activity in hydrogen generation from the hydrolysis of ammonia borane with a turnover frequency value up to 241 min⁻¹ at 25.0 ± 0.1 °C. They provide unprecedented catalytic lifetime measured by total turnover number (TTO = 71,500) in hydrogen generation from the hydrolysis of ammonia borane at 25.0 ± 0.1 °C. The report also includes the results of kinetic study on the catalytic hydrolysis of ammonia borane depending on the temperature to determine the activation energy of the reaction (E_a = 70 ± 2 kJ/mol) and the catalyst concentration to establish the rate law of the reaction.     

A physico-chemical study of an NH3BH3-based reactive composition for hydrogen generation

In order to reduce the use of fossil energies, the development of new technologies, such as those concerning fuel cells, is required. However, fuel cells currently involve issues of storing and generating hydrogen. Borohydride materials, like ammonia borane (NH₃BH₃), seem to present an interesting solution to these problems. In fact, NH₃BH₃ contains 19.6 wt.% of hydrogen, of which a high percentage can easily be released by moderate heating. Understanding and controlling the behaviour of ammonia borane would allow the development of a safe, lightweight and compact hydrogen storage system. The final purpose would consist in having a device that is able to be integrated in nomad applications such as GSM, PDA; or in thermal accumulators. The present study reports on thermal decompositions of ammonia borane doped with various percentages of NH₄NO₃. Differential scanning calorimetry (DSC) permitted an understanding of the thermal behaviour of the material, and the detection of released hydrogen was examined by evolved gas analysis on a thermo-gravimetric analyser (TGA) coupled to a mass spectrometer (MS). Finally, in order to avoid fuel cell malfunctioning due to pollutant gases, an identification of the decomposition products was carried out.     

Ultrafine cobalt–molybdenum–boron nanocatalyst for enhanced hydrogen generation property from the hydrolysis of ammonia borane

The hydrolysis of ammonia borane (NH₃BH₃) is recognized as an efficient way of hydrogen generation if it can be effectively catalyzed. In this work, a series of cobalt–molybdenum–boron (Co–Mo–B) nanoparticles (NPs) on copper (Cu) foil are introduced as catalysts for NH₃BH₃ hydrolysis by electroless deposition method. The influence of the depositing pH value on the catalytic property is investigated by adjusting the pH value ranged from 10.5 to 12.0. By optimizing the value to 11, the ultrafine Co–Mo–B NPs with the grain size around 4.3 nm show the best catalytic property for NH₃BH₃ hydrolysis. The hydrogen generation rate reaches 5818.0 mL·min⁻¹·g⁻¹ when the hydrolysis temperature is 298 K. The thermodynamic tests show that the lower activation energy (E_a) is estimated to be 59.3 kJ·mol⁻¹. It can be found that the catalytic property in this work overtakes that of partial non-precious metal NPs, and is even better than some precious metal NPs previously reported. The hydrolysis reaction of NH₃BH₃ catalyzed by ultrafine Co–Mo–B NPs is a non-spontaneous process. In addition, the cycling ability of the ultrafine Co–Mo–B NPs is also studied and the results demonstrate that the catalyst is a recyclable one toward the hydrolysis of NH₃BH₃ under mild reaction conditions.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.     

Magnetically recyclable Ni@h-BN composites for efficient hydrolysis of ammonia borane

The magnetic Ni@h-BN composites containing the uniform Ni nanoparticles supported on h-BN nanosheets have been prepared via a facile solvothermal method. The as-prepared samples show high catalytic performance for H₂ generation from the ammonia borane aqueous solution, especially for the Ni@h-BN with 25.0 wt% Ni content. Moreover, the Ni@h-BN composites possess a good ferromagnetic property at room temperature, endowing them with rapid magnetic separation to recycle. The kinetics of the hydrolysis of ammonia borane over the Ni@h-BN composites were further investigated in detail. It is found that the hydrogen generation was highly dependent on the catalyst amount and the reaction temperature. The activation energy of the hydrolysis reaction of ammonia borane is found to be 47.3 kJ mol^?1 over the Ni@h-BN with 25.0 wt% Ni content. Considering the good catalytic activities for H₂ release, the Ni@h-BN composites are expected to find important application in fuel cells and the related fields.     

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.     

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.