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.     

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.     

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.     

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.     

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.     

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.     

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.     

CoMoB nanoparticles supported on foam Ni as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane solution

We report on CoMoB nanoparticles supported on foam Ni as catalysts for hydrogen generation from hydrolysis of ammonia borane (NH₃BH₃) solution. The CoMoB/foam Ni catalysts with different molar ratios of Co²⁺and MoO₄²⁻ were synthesized via the electroless-deposition technique at ambient temperature. In order to analyze the phase composition, chemical composition, microstructure, and electron bonding structure of the as-prepared samples, powder X–ray diffraction (XRD), inductively coupled plasma-mass spectroscopy (ICP-MS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used. The results showed that CoMoB nanoparticles were variously dispersed on the surface of the foam Ni and the catalytic activity correlated with the molar ratio of Co²⁺ and MoO₄²⁻. The highest hydrogen generation rate was 5331.0 mL min⁻¹ g_cat⁻¹ at 298 K, and the activation energy was calculated to be 45.5 kJ mol⁻¹ toward the hydrolysis of NH₃BH₃ solution. The better catalytic activity was largely attributed to the smaller particle size, higher surface roughness and the novel three-dimensional cone-like architectures of the obtained samples. The kinetic results show that the hydrolysis of NH₃BH₃ is a first-order reaction in catalyst concentration. In addition, the reusability experiment exhibited that the catalytic activity was reduced after 5 cycles and the reason of the decay was also investigated.     

PVP-stabilized platinum nanoparticles supported on modified silica spheres as efficient catalysts for hydrogen generation from hydrolysis of ammonia borane

Ammonia borane (AB) is considered to be a promising solid hydrogen carrier. In this work, poly(N-vinyl-2-pyrrolidone) (PVP)-protected platinum nanoparticles are supported on γ-methacryloxypropyltrimethoxysilane (γ-MPS) modified silica spheres (Pt-PVP/SiO₂(M)), which are firstly used as highly efficient catalysts for hydrolysis of AB. Platinum nanoparticles possess a tiny size of 2–3 nm and are uniformly dispersed over modified silica spheres. Pt-PVP/SiO₂(M) catalysts with a Pt loading amount of 1.30 wt% show the highest catalytic activity with a turnover frequency (TOF) value of 371 mol_H2 mol_Pt^?1 min^?1 (866 mol_H2 mol_Pt^?1 min^?1 corrected for the surface atoms) at 25 °C. The activation energy is calculated to be 46.2 kJ/mol. Furthermore, owing to the synergistic effect between the modifier of silica spheres and the capping agent of metal nanoparticles, Pt-PVP/SiO₂(M) catalysts have a higher loading amount (8.7 and 6.5 times) and TOF value (4.8 and 5.5 times) than the counterparts prepared without γ-MPS and PVP, respectively.     

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.     

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.     

Magnetically separable transition metal nanoparticles as catalysts in hydrogen generation from the hydrolysis of ammonia borane

It reviews the available reports on the preparation and use of magnetically separable transition metal nanoparticles (TMNs) as reusable catalysts for the hydrolytic dehydrogenation of ammonia borane (AB). After a short introduction, the review starts with the papers on the employment of intrinsically magnetic TMNs as catalysts for releasing H₂ gas from AB, which includes colloidal nanoparticles of intrinsically magnetic metals, TMNs in combination with materials having large surface area, and multimetallic composites containing at least one intrinsically magnetic metal together with an additional component usually acting as support or stabilizer. This is followed by a section reviewing the papers on core-shell multimetallic nanoparticles with one intrinsically magnetic metal in either core or shell used for catalyzing the hydrolysis of AB. It follows the review of papers on TMNs supported on Fe₃O₄, CoFe₂O₄, or Co₃O₄ forming magnetically separable catalysts for the same reaction. Then, a short section reviews the available reports on metal nanoparticles supported on carbon-coated iron. The last section gives a summary list of conclusions.     

Carbon-supported small Rh nanoparticles prepared with sodium citrate: Toward high catalytic activity for hydrogen evolution from ammonia borane hydrolysis

Hydrogen generation from the hydrolysis of ammonia borane (AB) over heterogeneous catalysts is essential for practical applications. Herein, efficient hydrogen evolution from AB hydrolysis over the carbon-supported Rh nanoparticles synthesized with sodium citrate (Rh/C-SC) was achieved at 25 °C. The turnover frequency value of Rh/C-SC was 336 mol H₂ (mol_Rh min)^?1, whereas that of Rh/C catalyst only yielded a value of 134 mol H₂ (mol_Rh min)^?1. The improvement of the catalytic performance of Rh/C-SC catalyst could be attributed to the small Rh particles with highly active surface areas, which were prepared by using sodium citrate as the stabilizing agent. This result indicates that sodium citrate can be applied as a useful stabilizing agent for synthesizing active metal nanoparticles, thus highly promoting the practical application of AB system for fuel cells.     

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.     

Atomic interface engineering: Strawberry-like RuO2/C hybrids for efficient hydrogen evolution from ammonia borane and water

Efficient hydrogen production plays a key role in establishing hydrogen economy in the current world. In this study, we fabricated ultrafine RuO₂ nanoparticles on carbon black to form a strawberry-like RuO₂/C hybrid, using by a solid-phase grinding and subsequent low-temperature annealing. The synthesized hybrid displays very low reaction activation energy (28.5 KJ mol^?1) for hydrogen evolution from ammonia borane. In case of hydrogen evolution from alkaline water, it also exhibits a remarkably improved electrocatalytic activity than a commercial Pt/C, with an ultra-low overpotential of 8 mV (at 10 mA cm^?2). For the above bifunctional catalyst, the formed C–Ru–C bonds between the ruthenium oxide and carbon result in the ultrahigh activity of the hybrid, as evidenced by DFT results. This work offers a guideline to synthesize efficient metal-based (Ru, Pd, Rh, Ir, Au, etc.) catalysts with smart structures for catalysis.     

Improving hydrogen production from the hydrolysis of ammonia borane by using multifunctional catalysts

A novel multifunctional catalytic system has been developed for efficient hydrogen generation through the hydrolysis of ammonia borane. This system combines Pd NPs with acid sites and amines, which are both task-specific functionalities able to destabilize the N → B dative bond. The acidity of the support (zeolites of different structure and SiO₂/Al₂O₃ ratio) used to disperse the Pd NPs causes an increase in the hydrogen production rate. However, the positive effect of incorporating p-phenylenediamine in the catalyst is much more pronounced, causing a two-fold increase in the activity of the catalyst. The combined effect of the different functionalities yields excellent performance in the hydrolysis of ammonia borane, greatly enhancing the activity of the metal-based catalyst and reducing the activation energy of the catalyzed reaction.     

Ceria supported ruthenium nanoparticles: Remarkable catalyst for H2 evolution from dimethylamine borane

Ceria supported ruthenium nanoparticles (Ru⁰/CeO₂) are synthesized by impregnation of Ru³⁺ ions on CeO₂ powders followed by sodium borohydride reduction of Ru³⁺/CeO₂. Their characterization was achieved using analytical methods including TEM, XRD, BET, SEM, and XPS. All the results reveal the formation of ruthenium(0) nanoparticles in 1.8 ± 0.3 nm size on CeO₂ support. Ru⁰/CeO₂ nanoparticles show high activity in catalyzing the H₂ evolution from dimethylamine borane (DMAB). Ru⁰/CeO₂ nanoparticles with 0.55% wt Ru provide the highest turnover frequency (812 h⁻¹) for releasing H₂ from DMAB at 60 °C and a total of 2500 turnovers before deactivation. High activity of Ru⁰/CeO₂ nanoparticles for catalytic dehydrogenation of DMAB is attributable to the reducible nature of CeO₂ support. Ce³⁺ defects formation in ceria under reducing conditions of dehydrogenation causes accumulation of negative charge on the oxide support, which makes oxide surface attractive for the ruthenium(0) nanoparticles. This, in turn, causes an enhancement in the metal-support interaction and thus in catalytic activity. The XPS analysis of bare ceria and Ru⁰/CeO₂ demonstrates the increase in the concentration of Ce³⁺ defects after catalysis. Ru⁰/CeO₂ nanoparticles are also reusable catalyst for H₂ evolution from DMAB retaining 40% of initial activity after 4th run of reaction. The catalytic activity of Ru⁰/CeO₂ nanoparticles and activation energy of catalytic dehydrogenation are compared with those of the other ruthenium based catalysts known in literature.     

Nanoporous Ni-based catalysts for hydrogen generation from hydrolysis of ammonia borane

We report nanoporous Ni, Ni–Fe, and Ni–Pt as catalysts for hydrogen generation from hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB). The Ni and Ni–Fe nanoparticles with diameters of 20–25 nm were synthesized by a colloidal method in starch-containing aqueous solution. They exhibited considerable in situ catalytic performance but severely lost activity after separating from the reaction solution. Nanoporous Ni_1−xPt_x (x = 0.01, 0.08 and 0.19) with particle size below 5 nm was prepared from the isolated Ni nanoparticles through a replacement reaction. After centrifugation, drying, washing, and annealing, the obtained nanoporous Ni–Pt could attain remarkable activity, high hydrogen generation rate and efficiency, and low activation energy.     

Pd nanoparticles supported on MIL-101 as high-performance catalysts for catalytic hydrolysis of ammonia borane

Well dispersed ultrafine Pd NPs have been immobilized in the framework of MIL-101, and tested for the catalytic hydrolysis of ammonia borane. The powder XRD, N₂ adsorption–desorption, TEM, and ICP-AES were employed to characterize the Pd@MIL-101 catalyst. The as-synthesized Pd@MIL-101 exhibit the highest catalytic activity toward hydrolysis of AB among the Pd-based nano-catalysts ever reported, with the TOF value of 45 mol H₂ min⁻¹ (mol Pd)⁻¹.     

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.