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.     

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.     

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.     

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.     

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.     

Co,Ni-based nanoparticles supported on graphitic carbon nitride nanosheets as catalysts for hydrogen generation from the hydrolysis of ammonia borane under broad-spectrum light irradiation

From the viewpoint of tailoring the atomic and nanoscale structures of semiconductors to enhance the solar-to-hydrogen energy conversion, we employed an in-situ gas template-assisted co-polymerization route, where melamine and 2,4,6-triaminopyrimidine were co-monomers and NH₄Cl was the in-situ gas template, to synthesize porous broad-spectrum light-responsive carbon nitride nanosheet (termed as CNN) species with increased π-electron availability. Then we developed CNN-supported Co and Ni nanoparticles (NPs) for catalytic hydrogen generation from aqueous ammonia borane (NH₃BH₃) under light irradiation (λ ≥ 420 nm) at room temperature. Though all the Co-based catalysts had the similar activities with total turnover frequency (TOF) values of 37.5–44.1 min⁻¹ in the dark, they exhibited significantly different and enhanced photocatalytic activities. Remarkably, the optimized catalyst had a total TOF value of 123.2 min⁻¹, exceeding the values of reported non-noble metal catalysts. Moreover, the porous CNN species possessed the C-substitution for N, tunable narrow bandgaps of 0.71–2.34 eV and efficient separation of photogenerated charge carriers. This resulted in the enriched electron density of metal NPs and the apparent quantum yield of 66.9% at 420 nm.     

Catalytically active rhodium nanoparticles stabilized by nitrogen doped carbon for the hydrolysis of ammonia borane

We report the preparation of an ammonia borane hydrolysis catalyst for use in hydrogen production by dispersing Rh nanoparticles on a nitrogen-doped carbon (NPC) support. The resulting Rh/NPC catalyst had a measured turnover frequency of 473.5 min^?1, higher than that of many previously reported Rh-based catalysts. This catalyst could also be reused eight times. The large surface area and abundant nitrogen-functional species of NPCs facilitate dispersion of Rh nanoparticles on their surface, providing numerous catalytically active sites for ammonia borane hydrolysis, thereby leading to high catalytic activity. This study demonstrates that NPC support can be used to prepare highly active catalysts.     

Boron nitride supported NiCoP nanoparticles as noble metal-free catalyst for highly efficient hydrogen generation from ammonia borane

Herein, ternary metal phosphides NiCoP nanoparticles supported on porous hexagonal boron nitride (h-BN) was fabricated via hydrothermal-phosphorization strategy. The as-prepared Ni_0.8Co_1.2P@h-BN exhibited excellent catalytic performance for the hydrogen generation from ammonia borane (AB) hydrolysis, with an initial turnover frequency of 86.5 mol(H₂) mol(Ni_0.8Co_1.2P) ⁻¹ min⁻¹ at 298 K. The experimental outcome can be attributed to the synergistic effect between Ni, Co and P, as well as the strong metal-support interaction between NiCoP and h-BN. This study presents a new paradigm for supporting transition metal phosphides, and provides a new avenue to develop high performance and low cost non noble metal catalysts for hydrolysis of AB.     

Room temperature hydrolytic dehydrogenation of ammonia borane catalyzed by Co nanoparticles

Amorphous and well dispersed Co nanoparticles (less than 10 nm) have been in situ synthesized in aqueous solution at room temperature. The as-synthesized Co nanoparticles possess high catalytic activity (1116 L mol⁻¹ min⁻¹) and excellent recycling property for the hydrogen generation from aqueous solution of ammonia borane under ambient atmosphere at room temperature. The present low-cost catalyst, high hydrogen generation rate and mild reaction conditions (at room temperature in aqueous solution) represent a promising step toward the development of ammonia borane as a viable on-board hydrogen-storage and supply material.     

Pd nanoparticles anchoring to core-shell Fe3O4@SiO2-porous carbon catalysts for ammonia borane hydrolysis

A modified Stöber method is applied to synthesize the magnetic core-shell Fe₃O₄@SiO₂ particles, followed by compositing a series of porous glucose-derived carbon with ZnCl₂ as etchant. Then, ultrafine Pd nanoparticles (NPs) are successfully anchored to the resulting Fe₃O₄@SiO₂-PC composites with an in-situ reduction strategy. The particle sizes of Pd NPs are mainly centered in the range of 2.3–4.3 nm in the as-prepared Pd/Fe₃O₄@SiO₂-PC catalysts, owning a hierarchical porous structure with high specific surface area (S_BET = 626.0 m² g⁻¹) and large pore volume (V_p = 0.61 cm³ g⁻¹). Their catalytic behavior for the hydrogen generation from ammonia borane (AB) hydrolysis is investigated in details. The corresponding apparent activation energy is as low as 28.4 kJ mol⁻¹ and the reaction orders with AB and Pd concentrations are near zero and 1.10 under the present conditions, respectively. In addition, the magnetic catalysts, which could be easily separated out by a magnet, are still highly active even after nine runs, revealing their excellent reusability.     

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.     

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.     

Ru nanoparticles loaded on tannin immobilized collagen fibers for catalytic hydrolysis of ammonia borane

A kind of Ru-based catalyst was prepared by using a natural polyphenolic polymer (bayberry tannin, BT) immobilized on collagen fiber (CF) as the stabilizer and carrier of Ru nanoparticles (NPs) and characterized to detect its main physicochemical properties. The CF-BT-Ru catalyst was found to be in an orderly fiber morphology with Ru NPs with about diameter of 2.6 nm highly distributed on the surface. The research on catalytic activity of CF-BT-Ru focused on the hydrolysis of ammonia borane (AB) to produce hydrogen. The influences of Ru loading, Ru dosage, AB concentration and temperature on the catalytic AB hydrolysis were investigated in detail, and the related thermodynamic parameters (activation energy (E_a), activation entropy (△S), activation enthalpy (△H) and Gibbs free energy (△G)) were calculated. The experimental results indicated that CF-BT-Ru exhibited high catalytic activity. Its turnover frequency (TOF) was as high as 322 ${\text{mol}}_{{\text{H}}_2}?{\text{mol}}_{\text{Ru}}^{?1}?{\text{min}}^{?1}$ and E_a was as low as 32.41 kJ mol^?1 for AB hydrolysis. Moreover, CF-BT-Ru exhibited satisfied reusability and stability. Its activity lost only one-fifth and no obvious agglomeration and leakage of Ru NPs were found after repeated use for 5 times.     

Coupling ultralow-content ruthenium with nickel hydroxide via corrosion engineering for highly efficient hydrogen generation from ammonia borane

Efficient and controllable release of hydrogen from solid hydrogen storage materials is a promising way to produce hydrogen safely and on-demand. The development of economical, highly active, easily recyclable catalysts is critical for practical applications, which remains a great challenging. Herein, the easily controllable and cost-effective corrosion strategy is ingeniously developed to simply prepare ultralow-content ruthenium coupled with nickel hydroxide on nickel foam (Ru–Ni–NF). After experiencing the spontaneous oxidation-reduction reactions between the reactive NF and Ru³⁺, ultrafine Ru nanoparticles decorated nickel hydroxide nanosheets are in situ intimately grown on porous NF networks. The optimal Ru–Ni–NF catalyst exhibits the excellent performance for catalytic hydrolysis of ammonia borane with a high turnover frequency (TOF) of 539.6 mol_H2 mol_Ru^?1 min^?1 at 298 K and a low apparent activation energy of 36.4 kJ mol^?1, due to the synergistic effect between Ru nanoparticles and nickel hydroxide nanosheets. Furthermore, the Ru–Ni–NF catalyst possesses easy separation and outstanding durability, which is superior to powdered catalysts. This study provides a facile and economical strategy for the preparation of ultralow-content noble metal supported metal foam-type catalysts for dehydrogenation of ammonia borane.     

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.     

Enhanced catalytic performance of CuNi bimetallic nanoparticles for hydrogen evolution from ammonia borane hydrolysis

Ammonia borane (AB, NH₃BH₃) hydrolysis is an effective way to safely generate hydrogen. However, a suitable catalyst is indispensable because the hydrolytic reaction cannot take place kinetically at room temperature. In this work, CuNi alloy nanoparticles are immobilized on porous graphitic carbon nitride (g-C₃N₄) with a facile adsorption-chemical reduction method. Benefiting from the hierarchical porous structure of the support, the interesting alloy effect of Cu and Ni, as well as the synergistic effect between g-C₃N₄ and the CuNi alloys, the optimal Cu_0·7Ni_0.3/g-C₃N₄ catalyst displays excellent catalytic performance in AB hydrolysis, such as high turnover frequency (2.08 min⁻¹, at 303 K), low apparent activation energy (23.58 kJ mol⁻¹), and satisfactory durability. The results verify that the optimal catalyst has particular potential in hydrogen energy utilization due to the advantages such as the facile preparation procedure, low cost and excellent catalytic behavior.     

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.     

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.     

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).     

Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.