Fabrication of hollow silica–alumina composite spheres and their activity for hydrolytic dehydrogenation of ammonia borane

In this study, we investigated the influence of the preparation conditions of hollow silica–alumina composite spheres on their activity for the hydrolytic dehydrogenation of ammonia borane. Hollow silica–alumina composite spheres were prepared by polystyrene template method, and the polystyrene template particles were removed by calcination. The as-prepared hollow spheres were calcined at 523–873 K for 3 h. From the results of elemental analysis, polystyrene templates were completely removed by calcination at 873 K. small particles around the hollow spheres were observed from the images of transmission electron microscopy. To obtain homogeneous hollow spheres, the as-prepared hollow spheres were calcined at 873 K for 0–12 h. From the results of transmission electron microscopy, homogeneous hollow spheres were obtained by calcination for 0 h. The activity of the hollow spheres was the 2.6 times higher that of the hollow spheres calcined for 3 h. From the results of activity tests and ammonia temperature-programming desorption, the activity of the hollow spheres depends on amount of acid sites.     

Fabrication of hollow metal oxide–nickel composite spheres and their catalytic activity for hydrolytic dehydrogenation of ammonia borane

In this paper, we report an effective approach to the fabrication of hollow titania–nickel composite spheres, hollow zirconia–nickel composite spheres, and hollow silica–nickel composite spheres. In this approach, metal oxide–nickel composite shells were coated on polystyrene particles by the sol–gel method and the polystyrene templates were dissolved subsequently, or even synchronously, in the same medium to form hollow spheres. Neither additional dissolution nor a calcination process was needed to remove the polystyrene templates. The as-prepared hollow metal oxide–nickel composite spheres were characterized by transmission electron microscopy. The catalytic activities of hollow titania–nickel composite spheres, hollow zirconia–nickel composite spheres, and hollow silica–nickel composite spheres for hydrolytic dehydrogenation of aqueous NaBH₄/NH₃BH₃ solution were compared. The evolutions of 64, 58, and 18 mL hydrogen were finished in about 49, 69, and 162 min in the presence of the hollow titania–nickel composite spheres, hollow zirconia–nickel composite spheres, and hollow silica–nickel composite spheres from aqueous NaBH₄/NH₃BH₃ solution, respectively. The molar ratios of the hydrolytically generated hydrogen to the initial NH₃BH₃ both in the presence of hollow titania–nickel composite spheres, hollow zirconia–nickel composite spheres, and hollow silica–nickel composite spheres are 2.8, 2.4, and 0.1 (the theoretical value of 3.0), respectively, indicating that the hollow titania–nickel composite spheres and hollow zirconia–nickel composite spheres show much higher hydrogen evolution rates and the amount of hydrogen evolution via hydrolytic dehydrogenation of ammonia borane than the hollow silica–nickel composite spheres. From the results of ATR-IR spectra, a certain amount of residual PS templates exists in hollow silica–nickel composite spheres, and the amount of the residual PS templates were able to be reduced by increasing the amount of aqueous ammonia solution used for the preparation. The catalytic activity of hollow silica–nickel composite spheres increases when the amount of residual PS templates decreases.     

One-step synthesis of Cu@FeNi core–shell nanoparticles: Highly active catalyst for hydrolytic dehydrogenation of ammonia borane

This paper investigates a facile and one-step synthesis of trimetallic magnetic Cu@FeNi core–shell nanoparticles, which are composed of crystalline Cu cores and amorphous FeNi shells, at room temperature under ambient atmosphere within 2 min. It is found that among the Cu@FeNi system, Cu_0.4@Fe_0.1Ni_0.5 shows the best synergistic performance for catalyzing the hydrolytic dehydrogenation of ammonia borane with the activation energy of 32.9 kJ/mol, being lower than most of the reported data, and the catalytic activity of Cu_0.4@Fe_0.1Ni_0.5 is much better than its monometallic, bimetallic and trimetallic counterparts whether in states of pure metals, alloys or physical mixtures. Further, the present catalyst has a good recycle stability with an easy magnetic separation method.     

Monodisperse nickel–palladium alloy nanoparticles supported on reduced graphene oxide as highly efficient catalysts for the hydrolytic dehydrogenation of ammonia borane

Addressed herein is the catalysis of reduced graphene oxide-supported monodisperse NiPd alloy nanoparticles (NPs) (rGO-NiPd) in the hydrolytic dehydrogenation of ammonia borane (AB). This is the first example of the use of NiPd alloy NPs as catalyst in the hydrolytic dehydrogenation of AB. Monodisperse NiPd alloy NPs (3.5 nm) were synthesized by co-reduction of nickel(II) acetate and palladium(II) acetylacetonate in oleylamine (OAm) and borane-tert-butylamine complex (BTB) at 100 °C. The current recipe allowed to control the composition of NiPd alloy NPs and to study the composition-controlled catalysis of rGO-NiPd in the hydrolytic dehydrogenation of AB. Among the all compositions tested, the Ni₃₀Pd₇₀ was the most active one with the turnover frequency of 28.7 min⁻¹. The rGO-Ni₃₀Pd₇₀ were also durable catalysts in the hydrolytic dehydrogenation of AB providing 3650 total turnovers in 35 h and reused at six times without deactivation. The detailed reaction kinetics of hydrolytic dehydrogenation of AB revealed that the reaction proceeds first order with respect to the NiPd concentration and zeroth order with respect to the AB concentration. The apparent activation energy of the catalytic dehydrogenation of AB was also calculated to be E_a^app = 45 ± 2 kJ*mol⁻¹.     

Copper–iron mixed oxide catalyst precursors prepared by glycine-nitrate combustion method for ammonia borane dehydrogenation processes

The influence of the properties of copper ferrite, prepared by the combustion method from glycine-nitrate precursor, on the kinetics of NH₃BH₃ hydrolysis, thermolysis and hydrothermolysis are presented. As-prepared and annealed samples were studied by X-ray diffraction, scanning electron microscopy, differential dissolution, and attenuated total reflection infrared spectroscopy. It has been shown that in the hydrolysis and hydrothermolysis of NH₃BH₃, the as-prepared combustion product, which mainly consisted of a cubic spinel Cu_0.67Fe_2.33O₄ with Fe²⁺ higher content, had the highest activity, as compared with oxides of copper and iron and the annealed samples. According to transmission electron microscopy and X-ray diffraction, in the reaction medium copper ferrite is reduced to nanosized Cu⁰ and Fe⁰. This allowed the average rate of H₂ evolution per 1 g of the composition to be increased from 30 to 76 ml⋅min⁻¹, as compared with non-catalytic process. The high gravimetric hydrogen capacity (7.3 wt%) was observed at 90 °C.     

Hydrolytic dehydrogenation of ammonia borane and methylamine borane catalyzed by graphene supported Ru@Ni core–shell nanoparticles

Ru@Ni core–shell nanoparticles (NPs) supported on graphene have been synthesized by one-step in situ co-reduction of aqueous solution of ruthenium (III) chloride, nickel (II) chloride, and graphene oxide (GO) with ammonia borane (AB) as the reducing agent under ambient condition. The as-synthesized NPs exhibit much higher catalytic activity for hydrolytic dehydrogenation of AB than the monometallic, bimetallic alloy (RuNi/graphene), and graphene-free core–shell (Ru@Ni) counterparts. Additionally, the Ru@Ni/graphene NPs facilitate the hydrolysis of AB, with the turnover frequency (TOF) value of 340 mol H₂ min⁻¹ (mol Ru)⁻¹, which is among the highest value reported on Ru-based NPs so far, and even higher than the reversed Ni@Ru NPs. Furthermore, the as-prepared NPs exert satisfied durable stability and magnetically recyclability for the hydrolytic dehydrogenation of AB and methylamine borane (MeAB). Moreover, this simple synthetic method can be extended to other Ru-based bimetallic core–shell systems for more applications.     

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.     

Highly efficient catalytic dehydrogenation of dimethyl ammonia borane via monodisperse palladium–nickel alloy nanoparticles assembled on PEDOT

Addressed herein, the synthesis of the monodisperse poly(3,4-ethylenedioxythiophene)(PEDOT) supported palladium–nickel nanomaterials (3.32 ± 0.36 nm) and their applications as a catalyst in dimethylamine-borane (DMAB) dehydrogenation is outlined. Microwave assistance procedure was used in preparation of nanomaterials where palladium and cobalt cations were reduced in PEDOT solution (Pd–Ni@PEDOT) in microwave conditions. The characterization of the nanocatalyst was performed by using UV-VIS, XRD, XPS, TEM and HR-TEM-EELS analyses. The Pd–Ni@PEDOT NPs were found to be highly effective and stable for the dehydrogenation of DMAB. The catalytic activity of Pd–Ni@PEDOT was one of the highest one among the all prepared catalysts in literature even at lower temperatures and concentrations, yielding to give high turnover frequency (451.2 h^?1) and low E_a (50.78 ± 2 kJ/mol) for dehydrocoupling of DMAB.     

CuO–Ru0.3@Co3O4 nanocomposites act as a tandem catalyst for dehydrogenation of ammonia borane and hydrogenation of nitrobenezene

The development of catalysts with high activity for tandem reaction are all the ways pursued by chemists. Herein, CuO–Ru_0.3@Co₃O₄ has been synthesized and used as efficient tandem catalyst to promote the release of hydrogen from hydrolytic dehydrogenation of ammonia borane (AB) to catalyze the hydrogenation of nitrobenezenes (NBs). The catalyst exhibits the TOF of 29.87 min^?1 and provides the apparent activation energy of 45.2 kJ mol^?1 for the hydrolytic dehydrogenation of AB. Additionally, benefited from the magnetic separation capability, up to 99% of its initial catalytic activity is retained after four catalytic cycles.     

Enhanced catalytic activity of NiM (M = Cr,Mo, W) nanoparticles for hydrogen evolution from ammonia borane and hydrazine borane

In this work, a series of Ni_1-xM_x (M = Cr, Mo, W) nanoparticles (NPs) have been successfully synthesized via a simple surfactant-aided co-reduction method and employed as highly efficient and cost effective catalysts for hydrogen generation from aqueous solution of ammonia borane (NH₃BH₃, AB) at room temperature. It is found that the as-synthesized NiM NPs (M = Cr, Mo, W) exhibit much higher catalytic performance for the hydrolysis of AB as compared to that of pure Ni NPs. In addition, among all the Ni_1-xM_x (M = Cr, Mo, W) NPs, the Ni_0.9Cr_0.1, Ni_0.9Mo_0.1, and Ni_0.8W_0.2 NPs show the highest catalytic activities with the turnover frequency (TOF) values of 10.7, 27.3 and 25.0 mol H₂ (mol metal min)^?1, respectively. Remarkably, these optimized NiM catalysts can also perform efficiently in the hydrolysis of hydrazine borane (N₂H₄BH₃, HB). The present low-cost and high-performance of the NiM catalysts system may encourage the practical application of AB and HB as the promising chemical hydrogen storage materials.     

Ni–B and Zr–Ni–B in-situ catalytic performance for hydrogen generation from sodium borohydride,ammonia borane and their mixtures

In this study, the parameters on the catalytic hydrolysis of the sodium borohydride (NaBH4, SBH) and ammonia boranes (NH3BH3, AB) mixtures were investigated such as the effect of Zr additive in the catalyst, using in-situ or powder catalysts, the molar ratio of the SBH/AB mixture (2, 4, 8, neat SBH, neat AB) and temperature. As the catalyst, in-situ synthesized Ni–B and Zr–Ni–B for the first time were used to produce H₂ from hydrolysis of the SBH and AB mixtures. The SBH and AB mixtures were used to determine provided or not an effect on reaction. Catalyst preparation and hydrolysis reactions took place in the same reactor spontaneously for in-situ works. The Zr–Ni–B catalyst gives better results than Ni–B and increases efficiency at 25 °C and 35 °C temperature. When Zr–Ni–B catalyst compared experimentally among themselves, the best yield result at 45 °C temperature, for neat SBH, mole ratio in 4 and mole ratio in 8, as 87%, 86% and 83% respectively. For hydrolysis reactions with Zr–Ni–B catalyst, activation energies of SBH and AB were calculated as 45.23 kJ/mol and 79.76 kJ/mol, respectively. SEM, BET, XPS analyzes have been used to characterize these catalysts. The addition of Zr provided increase effect on the surface area. The surface area increases from 44.33 m²/g to 175.50 m²/g.     

Monodisperse palladium–nickel alloy nanoparticles assembled on graphene oxide with the high catalytic activity and reusability in the dehydrogenation of dimethylamine–borane

Herein, a highly efficient and stable palladium nickel nanoparticles (PdNi NPs) supported on graphene oxide (GO) was synthesized, characterized and applied for the dehydrogenation of dimethyl ammonia borane (DMAB). The monodisperse PdNi NPs has been synthesized via the ultrasonic double solvent reduction method in the presence of oleylamine and GO as support matrices. The structure morphology and properties of PdNi@GO NPs were characterized by using different techniques such as UV–VIS, XPS, TEM, HRTEM and XRD methods. The PdNi@GO NPs was found to be highly effective and stable in the dehydrogenation of DMAB. This catalyst with the turnover frequency of 271.9 h^?1 shows one of the best results among the all prepared catalysts in literature for the dehydrogenation of DMAB. The apparent activation parameters of the catalytic dehydrogenation reaction were also calculated; apparent activation energy (E_a,app) = 38 ± 2 kJ mol^?1, activation enthalpy (ΔH^#_,app) = 35 ± 1 kJ mol^?1 and activation entropy (ΔS^#_,app) = ?102 ± 1 J K^?1 mol^?1.     

Co–B nanoparticles supported on carbon film synthesized by pulsed laser deposition for hydrolysis of ammonia borane

Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of Ammonia Borane (AB) to produce molecular hydrogen. Amorphous Co–B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) were used during deposition of carbon films to obtain extremely irregular and porous carbon support with high surface area prior to Co–B film deposition. Surface morphology of the catalyst films was studied using Scanning Electron Microscopy, while structural characterization was carried out using X-Ray diffraction. The hydrogen generation rate attained by carbon-supported Co–B catalyst film is significantly higher as compared to unsupported Co–B film and conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co–B nanoparticles with better dispersion and tolerance against aggregation. The efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)⁻¹) and exceptionally high H₂ generation rate (13.5 L H₂ min⁻¹ (g of Co)⁻¹) by the hydrolysis of AB.     

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.     

Hierarchically alloyed Pd–Cu microarchitecture with tunable shapes: Morphological engineering,and catalysis for hydrogen evolution reaction of ammonia borane

Some uniquely microstructured bi/poly-metal alloys containing lesser or no noble metal have been testified to be cost-effective catalysts suitable for solvolytic dehydrogenation of ammonia borane, which expects the intensive study on their morphological engineering and synergistic mechanism. To this, we here introduce a facile and flexible fabricating protocol, i.e. stepwise wet-chemical reduction route, to purposefully modulate the orientated growth of Pd–Cu alloyed crystals via joint operation of adding suitable additives and adjusting temperature. The characterization of phase composition and evaluation of catalytic ability regarding as-fabricated Pd–Cu nanocrystals with diverse morphological features (e.g. concave tetrahedron, cube, polyhedron, nanosphere, nanowire, worm-like, seaurchin-like, flower-like, etc.) demonstrates that the nanocrystals have homogeneous alloyed phase, holding significantly enhanced catalytic activity and durability. The formation of synergistic effect due to charge transfer from Cu to Pd gives rise to electron enrichment around Pd atomic nucleus, facilitating the adsorption of H to form metal-H species, thus promoting the dehydrogenation of ammonia borane. The difference of catalytic activity of the Pd–Cu nanocrystals with different shapes reveals their morphologic dependent nature, endowing the uniquely shaped bimetal nanocrystals with exceptional catalytic performance. The concave tetrahedron shaped Pd–Cu alloyed nanocrystals hold the excellent catalytic activity almost equivalent to that of noble metal Pd, catalyzing hydrolytic reaction of ammonia borane at 298 K with the apparent activation energy of 31.18 kJ/mol, and maintaining 89% of the incipient catalytic ability after 5 recycling runs. Theoretically, the suggested morphologic tuning strategy can be also applied in fabricating other bi/poly metal alloy catalysts, with great practical potential and development prospects.     

Investigation on microstructures of NiO–YSZ composite and Ni–YSZ cermet for SOFCs

NiO–YSZ composites and Ni–YSZ cermets were successfully performed for solid oxide fuel cell applications. These composites must have enough porosity and appropriate microstructure for transferring the fuel gases. In this study, ball-milling was used as a simple, cost-effective method for the purpose of mixing the raw materials. The homogeneity of NiO–YSZ composites was examined by Map mode of SEM. NiO–YSZ composites were reduced at the high temperature under the controlled atmosphere to fabricate Ni–YSZ cermet. Variations in the anode phases were investigated by XRD and microstructure and porosity of composites were observed by SEM. Effective parameters like temperatures and the amount of pore former were investigated on open porosity, bulk density, electrical conductivity as well as electrochemical impedance of NiO–YSZ composites and Ni–YSZ cermet. A thin layer of YSZ was deposited by EPD as an electrolyte on NiO–YSZ composites which had various amount of open porosity, to study its effect on the performance of semi-cells by electrochemical impedance.     

Influence of some metal ions on the structure and properties of doped β-PbO2

The lead dioxide active mass of positive lead-acid battery plates is a gel-crystal system with proton and electron conductivity of the hydrated gel zones. This paper discusses the influence of Sn²⁺, Sb³⁺, Co²⁺, Mg²⁺ and Al³⁺ ions, added to the formation electrolyte, upon the stoichiometry, structure and phase composition of the PbO₂ positive active material (PAM) of lead-acid batteries. PAM samples doped with the above metal ions are characterized by: X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and chemical analysis. The obtained results show that different metal ions are incorporated in different quantities in the PbO₂ particles. Under the influence of dopants, the stoichiometric coefficient of lead dioxide decreases, i.e. dopants increase the non-stoichiometry of PbO₂. The foreign ions in the formation electrolyte exert strong influence on the microstructure of PAM and change the proportion between crystal and hydrated gel zones in the particles.     

Polymer-graphene hybride decorated Pt nanoparticles as highly efficient and reusable catalyst for the dehydrogenation of dimethylamine–borane at room temperature

Addressed herein, we report a reduced graphene oxide (rGO) nanosheet coupled with polyaniline (PANI) for platinum (Pt) nanoparticles as supporting materials. The PANI-coupled rGO (PANI@rGO) nanosheet is prepared by a simple one-step chemical assembly strategy, and Pt nanoparticles are anchored on the support of PANI@rGO through the reaction of PANI with a platinum salt. The designed PANI efficiently exposes the surface of rGO sheets and stabilizes metal nanoparticles. Consequently, the Pt@PANI-rGO catalyst exhibits good reusability, durability and high catalytic performance for dimethylamine–borane dehydrogenation reaction. The structure morphology and properties of Pt@PANI-rGO NPs were characterized by using several different techniques such as UV–Vis, XPS, TEM, XRD and HR-TEM-EDX analyses. This newly prepared catalyst can be reused again at low concentrations and temperature. They showed a high turnover frequency (42.94 h^?1) and low E_a value of 15.1 ± 2 kJ/mol for DMAB dehydrocoupling in the ambient conditions. The proposed nano architecture offers a new pathway to promote the performances of rGO in various applications; moreover, this work provides a powerful and universal synthetic strategy for such an architecture.     

Tuning morphology and structure of Fe–N–C catalyst for ultra-high oxygen reduction reaction activity

Exploring efficient and durable non-precious metal catalysts for oxygen reduction reaction (ORR) has long been pursued in the field of metal-air batteries, fuel cells, and solar cells. Rational design and controllable synthesis of desirable catalysts are still a great challenge. In this work, a novel approach is developed to tune the morphologies and structures of Fe–N–C catalysts in combination with the dual nitrogen-containing carbon precursors and the gas-foaming agent. The tailored Fe–N₁/N₂–C-A catalyst presents gauze-like porous nanosheets with uniformly dispersed tiny nanoparticles. Such architectures exhibit abundant Fe-N_x active sites and high-exposure surfaces. The Fe–N₁/N₂–C-A catalyst shows extremely high half-wave potential (E_1/2, 0.916 V vs. RHE) and large limiting current density (6.3 mA cm⁻²), far beyond 20 wt% Pt/C catalyst for ORR. This work provides a facile morphological and structural regulation to increase the number and exposure of Fe-N_x active sites.     

Influence of coexisting Al2O3 on the activity of copper catalyst for water–gas-shift reaction

Influence of coexisting Al₂O₃ on the catalytic activity for low-temperature water–gas-shift (LT-WGS) reaction over Cu catalyst was investigated. The catalytic activity of Cu/Al₂O₃ catalyst increased with decreasing mesopore size when S/C ratio was 2.2, whereas the catalytic activity with S/C ratio = 4.6 increased with increasing mesopore size. IR measurement combined with kinetic study suggested that the low catalytic activity of Cu/CeO₂ catalyst comes from the restriction of CO adsorption on Cu⁰ by bidentate-type carbonate formed on the strong basic site of CeO₂ support. On the other hand, it was found that bidentate-type carbonate was not formed on Cu/Al₂O₃ showing high catalytic activity for LT-WGS reaction.