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.     

Room temperature hydrogen generation from aqueous ammonia-borane using noble metal nano-clusters as highly active catalysts

Nano-clusters of noble metals Ru, Rh, Pd, Pt and Au have been supported on γ-Al₂O₃, C and SiO₂, of which the catalytic activities have been investigated for hydrolysis of NH₃BH₃. Among these catalysts, the Ru, Rh and Pt catalysts exhibit high activities to generate stoichiometric amount of hydrogen with fast kinetics, whereas the Pd and Au catalysts are less active. Support effect has been studied by testing the hydrogen generation reaction in the presence of Pt supported on γ-Al₂O₃, VULCAN^® carbon and SiO₂, and it is found that Pt on γ-Al₂O₃, which has the smallest particle size, is the most active. Concentration dependence of the hydrogen generation from aqueous NH₃BH₃ solutions has been investigated in the presence of Pt/γ-Al₂O₃ by keeping the amount of Pt/γ-Al₂O₃ catalyst unchanged, which exhibits that the hydrogen release versus time (ml H₂ min⁻¹) does not significantly change with increasing the NH₃BH₃ concentration, indicating that the hydrogen release rate is not dependent on the NH₃BH₃ concentration and the high activity of the Pt catalyst can be kept at high NH₃BH₃ concentrations. Activation energies have been measured to be 23, 21 and 21 kJ mol⁻¹ for Ru/γ-Al₂O₃, Rh/γ-Al₂O₃ and Pt/γ-Al₂O₃ catalysts, respectively, which may correspond to the step of B–N bond breaking on the metal surfaces. The particle sizes, surface morphology and surface areas of the catalysts have been obtained by TEM and BET experiments.     

Characterization of hydrogen generation for fuel cells via borane hydrolysis using an electroless-deposited Co-P/Ni foam catalyst

The effect of an electroless-deposited Co-P/Ni foam catalyst on H₂ generation kinetics in ammonia borane (NH₃BH₃) solution and the cyclic behaviour (durability) of the catalyst are investigated. The electroless-deposited Co-P is composed of an inner flat layer and outer layer that consists of an aggregate of spherical particles. The H₂ generation rate/projected area of the Co-P/Ni foam catalyst is much higher than that of a Co-P/Cu sheet catalyst. The activation energy (E_a) for the hydrolysis of NH₃BH₃ using the Co-P/Ni foam catalyst is calculated to be 48 kJ mol⁻¹. After the first cycle, the H₂ generation rate decreases dramatically, i.e., by 16%, due to a decrease in surface area caused by the partial separation of spherical Co-P particles. Between the first and sixth cycles, the H₂ generation rate decreases gradually (by 14%) on account of a decrease in the number of P atoms that create active metallic Co sites on catalytic surface. After six cycles, about 70% of the initial H₂ generation rate remains constant. The study reveals a promising means of hydrogen generation for polymer electrolyte membrane fuel cells.     

Hydrogen generation from hydrolysis of NH3BH3 by an electroplated Co–P catalyst

This paper investigates the effect of an electroplated Co–P catalyst on hydrogen generation kinetics from hydrolysis of NH₃BH₃. The Co–P catalyst is composed of an amorphous Co–P phase and Co nanoparticles. An increase in NH₃BH₃ concentration caused the hydrogen generation rate to increase dramatically. The Co–P catalyst shows a large hydrogen generation rate for 2 wt% NH₃BH₃ solution at 30 °C. This is 1.8 times higher than that of the Pt/C catalysts and 6 times higher than that of Ru catalysts. The activation energy for hydrolysis of NH₃BH₃ by the Co–P catalyst is calculated to be 22 kJ/mol, which is close to that of noble metal-based catalysts.     

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.     

Simple synthesis of Cu2O–CoO nanoplates with enhanced catalytic activity for hydrogen production from ammonia borane hydrolysis

The development of inexpensive and high performing catalysts for ammonia borane (NH₃BH₃) hydrolysis is crucial for hydrogen production. In our research, a high-performance plate-like Cu₂O–CoO nanocomposite catalyst for NH₃BH₃ hydrolysis has been developed for the first time. In the hydrolytic reaction, both Cu₂O and CoO are separately inactive, while Cu₂O–CoO nanoplates show a high turnover frequency of 34.1 mol_hydrogen min⁻¹ mol_cat⁻¹, which is attributed to the synergistic effect between Cu₂O and CoO. It is interesting to discover that the induction time for the hydrolytic reaction is reduced to null when a small amount of Cu₂O is introduced into CoO. The reaction kinetics of NH₃BH₃ hydrolysis catalyzed by Cu₂O–CoO is also investigated. This work may provide other researchers some valuable insights into designing inexpensive and synergistic catalysts with enhanced catalytic activity for NH₃BH₃ hydrolysis for hydrogen production.     

Nanosizing ammonia borane with nickel – An all-solid and all-in-one approach for H2 generation by hydrolysis

Ammonia borane NH₃BH₃ (AB) and nickel (Ni) have been considered together as an all-solid and all-in-one material for H₂ generation by hydrolysis at 20–50 °C. Our novel approach, denoted Ni/AB, consists of AB nanoparticles within a Ni matrix. Upon contact with water, Ni/AB readily hydrolyzes and liberates H₂ with a turnover frequency of 13.8 mol(H₂) mol_Ni^?1 min^?1 at 43.3 °C. The apparent activation energy, determined over the temperature range 23.5–50.4 °C, is low, with 19.5 ± 4.1 kJ mol^?1. These results imply that such a Ni matrix embedding AB acts as an effective catalyst. Beyond the catalytic performance, this is the first report of the successful utilization of an all-solid and all-in-one approach for the hydrolysis of AB, and the work brings unique perspectives for one-shot catalytic systems.     

Borohydride in ionic liquids for tailored hydrogen release

H₂ as an environmentally benign energy carrier could answer the world's continuously increasing demand for sustainable energy sources, especially in portable fuel cell applications. Thereby, H₂ storage is the key issue. In the present work, we developed a liquid H₂ storage material based on BH₄^? and ionic liquids for tailored H₂ release under ambient conditions using various catalysts as releasing agents. Thereto, we synthesized four BH₄^? ionic liquids via ionic exchange. The most promising BH₄^? based ionic liquids are 1-Ethyl-3-methylimidazolium BH₄^? and 1-Propyl-3-methylimidazolium BH₄^?, containing up to 3 wt% releasable hydrogen and the latter being liquid at standard temperature. The hydrolysis of 1-Ethyl-3-methylimidazolium BH₄^? with various supported metal catalysts (Pt/C, Pt/CNT, Ru/CNT, Pd/CNT, 5 wt% metal) and H₂O (8, 16, 24 eq.) was assayed. The highest yield was obtained with 24 eq. H₂O and Pt/CNT. The catalysts were characterized via X-ray photoelectron spectroscopy and transmission electron microscopy/energy-dispersive X-ray spectroscopy. To calculate the catalyst activities, the dispersion and size distribution of the metal particles were determined. Recycling of Pt/CNT showed a reasonable stability of the catalyst activity over four recycling runs. In order to avoid spontaneous crystallization of 1-Ethyl-3-methylimidazolium BH₄^? as a storage material, 1-Propyl-3-methylimidazolium BH₄^? was introduced. The hydrolysis yield was significantly increased by the use of acidic catalysts, such as HCl and Amberlyst 36. Further enhancement of the H₂ yield was achieved by adopting a semi batch process, continuously adding 1 M HCl to 1-Propyl-3-methylimidazolium BH₄^?. The H₂ release correlated approximately linearly with the acid addition rate, excluding liquid-liquid mass transfer limitations during the hydrolysis. Based on ¹¹B NMR analysis, a reaction mechanism of the hydrolysis of BH₄^? ionic liquid with HCl as catalyst is proposed.     

Epoxy-activated acrylic particulate polymer-supported Co–Fe–Ru–B catalyst to produce H2 from hydrolysis of NH3BH3

Epoxy-activated acrylic particulate polymer, namely Eupergit CM, supported Co–Fe–Ru–B catalyst (EP/Co–Fe–Ru–B) for the first time was used to produce H₂ from hydrolysis of NH₃BH₃. The EP/Co–Fe–Ru–B showed very effective performance in the production of H₂ from the hydrolysis of NH₃BH₃. Various techniques such as XRD, SEM-EDS, ICP-OES, and TEM have been used to characterize these catalysts. The parameters on the hydrolysis reaction of NH₃BH₃ such as the effect of metal amount, the effect of Ru percentage, the effect of NH₃BH₃ concentration, the effect of NaOH concentration, the amount of catalyst, temperature, and catalyst durability were investigated in detail. Eupergit CM based polymer support and Ru particles have been found to be highly effective in H₂ production reactions. The hydrogen production rate (HGR) of the EP/Co–Fe–Ru–B catalyst was found to be 36,978 mL/min/g_cat, which was quite good compared to the values reported in the literature. In addition, the activation energy (Ea) of the polymer-supported Co–Fe–Ru–B catalyst was determined as 24.91 kJ/mol.     

Poly(N-vinyl-2-pyrrolidone)-stabilized ruthenium supported on bamboo leaf-derived porous carbon for NH3BH3 hydrolysis

In this work, poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium nanoparticles (NPs) supported on bamboo leaf-derived porous carbon (Ru/BC) has been synthesized via a one-step procedure. The structure and morphology of the as-synthesized samples were characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM). As a catalyst for hydrogen generation from the hydrolysis of ammonia-borane (AB, NH₃BH₃) at room temperature, Ru/BC stabilized with 1 mg of PVP exhibited high activity (TOF = 718 mol_H2·mol_Ru⁻¹·min⁻¹) and low activation energy (E_a = 22.8 kJ mol⁻¹). In addition, the catalyst could be easily recovered and showed fairly good recyclability with 55.6% of the initial catalytic activity retained after ten experimental cycles, which confirmed that PVP could stabilize the Ru NPs and prevent their agglomeration on BC surface. Our results suggest that PVP-stabilized Ru/BC is a highly efficient catalyst for the hydrolysis of AB.     

Preparation and catalytic activity of thin-film cobalt–tungsten–boron for the hydrolysis of ammonia borane

In this work, cobalt–tungsten–boron nanoparticles (Co–W–B) have been successfully deposited on foam Ni to manufacture thin-film catalysts by electroless plating technique and applied in hydrogen generation from ammonia borane (NH₃BH₃) hydrolysis. Physicochemical properties of Co–W–B nanoparticles are characterized by XRD (Powder X–ray diffraction), SEM (Scanning electron microscopy), and EDS (Energy dispersive X–ray spectroscopy). It is observed that Co–W–B showed irregular spherical structure on the surface of foam Ni substrate. An increase of depositional pH value in the preparation process leads to the change of particle size. When the pH value is equal to 11.5, as-synthesized Co–W–B exhibits the smaller particle size, which suggests that depositional pH value has directly impacted the nucleation and growth of catalysis particles. The optimized Co–W–B catalyst displays higher catalytic activity toward NH₃BH₃ hydrolysis with a specific rate of hydrogen generation of 12933.3 mL min^?1·g^?1 at room temperature. Moreover, the lower apparent activation energy of 47.3 kJ mol^?1 is achieved. Compared with previously reported catalysts, the as-obtained catalytic performance is situated at the better rank. Moreover, the reusability has been investigated under the mild NH₃BH₃ hydrolysis conditions. It reveals that as-fabricated thin-film Co–W–B maintains excellent durability after five cycles. A possible mechanism for the released hydrogen from NH₃BH₃ hydrolysis using Co–W–B catalyst has been proposed.     

Improved catalytic performance of metal oxide catalysts fabricated with electrospinning in ammonia borane methanolysis for hydrogen production

Electrospun Ni and Cu metal oxide catalysts are successfully synthesized through electrospinning and conventional sol-gel methods to show advantages of electrospinning on catalytic performance in ammonia borane (NH₃BH₃) methanolysis for hydrogen production. An experimental assessment is presented by the characterization of interior and exterior properties of all catalysts and their catalytic activity towards NH₃BH₃ methanolysis. The systematic studies are performed in order to figure out of kinetic interpretation. Catalytic NH₃BH₃ methanolysis reactions are carried out at different catalyst amounts (5–15 mg), initial NH₃BH₃ concentrations (0.36–6.0 M) and temperatures (20–50 °C). Thanks to the higher pore volume/S_BET ratio, fiber type nanostructured Cu oxide catalyst exhibits the highest catalytic activity compared with sol-gel prepared ones. The results of kinetic studies show that the fiber type Cu oxide catalyst catalyzed methanolysis of NH₃BH₃ and follows the first order reaction kinetic model with 35 kJ mol⁻¹ activation energy value.     

Graphene supported Pt–Ni bimetallic nanoparticles for efficient hydrogen generation from KBH4/NH3BH3 hydrolysis

Developing highly efficient and stable supported bimetallic nanoparticles catalysts via a facile strategy is one of the most admirable methods for sustainable hydrogen production from borohydride hydrolysis. Herein, we developed a facile technology for rapidly and straightforwardly manufacturing Pt–Ni bimetallic nanoparticles (BNPs) supported by partially reduced graphene oxide (prGO) with excellent catalytic activity and outstanding durability for hydrogen production from KBH₄ and NH₃BH₃ alkaline solution. The uniformly dispersed Pt₄₀–Ni₆₀ BNPs with a statistical size of around 2.6 nm exhibited a surprising catalytic activity of 23,460 mol-H₂·h^?1·mol-Pt^?1 at 308 K, moreover, whose activity was high up to 80% of the first time even after 30 runs, demonstrating an outstanding stability. The apparent activation energy for dehydrogenation of KBH₄ and NH₃BH₃ were respectively about 27.8 and 33.6 kJ/mol for the prepared Pt₄₀–Ni₆₀/prGO catalyst. The extraordinary catalytic activity of the Pt₄₀–Ni₆₀/prGO catalyst owing to the strong charge transfer effect between Pt–Ni BNPs and graphene.     

Catalytic activities of non-noble metals for hydrogen generation from aqueous ammonia–borane at room temperature

We have studied catalytic performance of supported non-noble metals for hydrogen generation from aqueous NH₃BH₃ at room temperature. Among the tested non-noble metals, supported Co, Ni and Cu are the most catalytically active, with which hydrogen is released with an almost stoichiometric amount from aqueous NH₃BH₃, whereas supported Fe is catalytically inactive for this reaction. Support effects on the catalytic activity have been investigated by testing the hydrogen generation reaction in the presence of Co supported on γ-Al₂O₃, SiO₂ and C and it is found that the Co/C catalyst has higher activity. Activation energy for hydrogen generation from aqueous NH₃BH₃ in the presence of Co/γ-Al₂O₃ was measured to be 62 kJ mol⁻¹; this may correspond to the step of BN bond breaking. Particle size, surface morphology and surface area of the supported metal catalysts were examined by X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) and BET experiments. It is found that with decreasing the particle size the activity of the supported catalyst is increased. The low-cost and high-performance supported non-noble metal catalysts may have high potential to find its application to the hydrogen generation for portable fuel cells.     

Metal ion-imprinted hydrogel with magnetic properties and enhanced catalytic performances in hydrolysis of NaBH4 and NH3BH3

Metal ion-imprinted (IIH) poly(2-acrylamido-2-methyl-1-propansulfonic acid) p(AMPS) hydrogels were prepared by using a free-radical polymerization technique in the presence of metal ions (M = Co (II) or Ni (II)). Using metal ion-imprinted hydrogels (IIHs), and non-metal ion-imprinted (NIH) hydrogels as template for the preparation of Co and Ni catalyst systems, the hydrolysis kinetics of NaBH₄ and NH₃BH₃ were investigated. The catalytic performances of IIHs and NIHs were compared in terms of effect on hydrolysis kinetics of NaBH₄ and NH₃BH_3. To increase the amounts of Co nanoparticles within p(AMPS) hydrogel for better catalytic activity, several reloading and reduction cycles of Co (II) ions were carried out, and the prepared p(AMPS)-Co composite catalyst systems were tested for hydrogen generation from the hydrolysis of NaBH₄. As the number of Co (II) loading and reduction cycles increased, the amount of metal catalysts and the catalytic performance of composites increased. Kinetics studies were carried out on three times Co (II) ion loaded and reduced p(AMPS)-Co catalyst systems (containing 36.80 mg/g Co). Three time Co (II)-loaded catalyst systems provided very fast hydrolysis kinetics for NaBH₄, and provided magnetic field responsive behavior. The hydrolysis reaction of NaBH₄ was completed within 50 s, under the described conditions at 60 °C. It was demonstrated that the synthesized catalyst systems can be used ten times repetitively without significant loss of catalytic activity (86.5%).     

The doped Co on Rh/Ni@Ni–N–C that weakened the catalytic performance for ammonia borane hydrolysis

Alloy catalyst has been widely studied and used for hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB) with excellent catalytic performance due to the synergistic effect of bimetal. Herein, a series of Rh_1-xCo_x/Ni@Ni–N–C catalysts were prepared by an impregnation reduction method. The optimized Rh_0.75Co_0.25/Ni@Ni–N–C catalyst exhibited good catalytic performance with turnover frequency of 223.08 mol_H2 mol_cat^?1 min^?1 at 303 K, but decreased the catalytic performance compared with Rh/Ni@Ni–N–C. According to the XPS and Raman analysis, the RhCo alloy nanoparticles could be loaded at the defect position of Ni@Ni–N–C, and the Co nanoparticles occupied the intercalation between Rh and the defective site of the carrier, which could weaken the catalytic activity of AB hydrolysis. Based on the above research, we proposed the catalytic mechanism of the activation of the RhCo–H species. This work provides a new strategy for designing alloy-supported nano-catalysts.     

Enhanced catalytic behavior of h-BN supported CuNi bimetallic catalysts in hydrolytic dehydrogenation of NH3BH3

The hydrolysis of ammonia borane (NH₃BH₃, AB) is an efficient strategy for high-purify hydrogen evolution. However, it is indispensable to develop a suitable catalyst because this reaction is kinetically infeasible at room temperature. In this work, we prepared a series of nano hexagonal boron nitride (h-BN) supported CuNi bimetallic catalysts through a facile adsorption-chemical reduction procedure. The effects of various molar ratios of Cu to Ni and CuNi loadings on AB hydrolysis were investigated in details. Benefitting from the proper porous structure, the interesting alloy effect of Cu and Ni, as well as the synergistic effect between h-BN and CuNi, 20 wt% Cu_0.5Ni_0.5/h-BN displays the highest catalytic activity among the as-prepared catalysts. Apart from satisfactory durability, the corresponding hydrogen generation rate, turnover frequency at 303 K in base solution and apparent activation energy are 2437.0 mL g^?1 min^?1, 6.33 min^?1 and 23.02 kJ mol^?1, respectively, which are very outstanding compared with many previous results. Our work not only provides a proper non-precious metal catalyst for hydrogen generation from the hydrolysis of chemical hydrogen storage materials but also offers a facile strategy for synthesizing metallic functional materials.     

Method to release hydrogen from ammonia borane for portable fuel cell applications

Ammonia borane (AB, NH₃BH₃) is considered to be a promising hydrogen storage material as it contains 19.6 wt% hydrogen. It is difficult, however, to release hydrogen from AB. Thermolysis, catalytic hydrolysis and heat generated by additional reactive mixtures are usually employed, but these methods have disadvantages that limit their use for portable applications. In this paper, we demonstrate a new approach to release hydrogen, which does not require any catalyst and produces relatively high hydrogen yield and environmentally benign byproducts. It involves nano-aluminum (nAl)/water combustion reaction, which provides heat for AB dehydrogenation and releases additional hydrogen from water. To facilitate higher H₂ yield from thermolysis, as compared to hydrolysis, AB is spatially separated from the nAl/water mixture using a concentric cylindrical container. The effect of the container design on hydrogen generation is studied and optimized. This study also includes transient temperature and pressure measurements, and product characterization using mass spectrometer and ¹¹B NMR. This approach provides H₂ yield up to 9.5 wt% on material basis. Our experimental results and analysis show that a proposed power source based on this method is promising for portable electronic devices.     

Carbon supported bimetallic Ru‐Co catalysts for H2 production through NaBH4 and NH3BH3 hydrolysis

This work investigates the effect of the addition of small amounts of Ru (0.5‐1 wt%) to carbon supported Co (10 wt%) catalysts towards both NaBH₄ and NH₃BH₃ hydrolysis for H₂ production. In the sodium borohydride hydrolysis, the activity of Ru‐Co/carbon catalysts was sensibly higher than the sum of the activities of corresponding monometallic samples, whereas for the ammonia borane hydrolysis, the positive effect of Ru‐Co systems with regard to catalytic activity was less evident. The performances of Ru‐Co bimetallic catalysts correlated with the occurrence of an interaction between Ru and Co species resulting in the formation of smaller ruthenium and cobalt oxide particles with a more homogeneous dispersion on the carbon support. It was proposed that Ru^°, formed during the reduction step of the Ru‐Co catalysts, favors the H₂ activation, thus enhancing the reduction degree of the cobalt precursor and the number of Co nucleation centers. A subsequent reduction of cobalt and ruthenium species also occurs in the hydride reaction medium, and therefore the state of the catalyst before the catalytic experiment determines the state of the active phase formed in situ. The different relative reactivity of the Ru and Co active species towards the two investigated reactions accounted for the different behavior towards NaBH₄ and NH₃BH₃ hydrolysis.