Aqueous NaBH4 Research Articles

Co–SiO 2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Cobalt clusters–silica nanospheres (15–30 nm) were synthesized using a Co(NH 3) 6Cl 3 template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH 4/NH 3BH 3 solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt–silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.

Catalytic properties of Co/activated carbon catalyst prepared from wheat stalk

For hydrogen generation from an aqueous alkaline NaBH4 solution, a novel biomass precursor for the production of Co/activated carbon (Co/AC)) catalyst was studied in this investigation. To design a hydrogen generator, the hydrogen generation rate was measured using the Co/AC catalyst as a function of calcination time, calcination temperature and impregnation mass ratio of CoCl2/AC. SEM and XRD analysis revealed that the prepared catalyst consisted of a crystalline form of Co3O4 and had a good dispersion and coating properties. It was observed that increasing the solution temperature causes more hydrogen generation. The activation energy for the NaBH4 hydrolysis reaction was calculated to be 37.4 kJ mol−1.

New catalytic route: Hydrogels as templates and reactors for in situ Ni nanoparticle synthesis and usage in the reduction of 2- and 4-nitrophenols

Nickel nanoparticles inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) hydrogel were prepared by reduction of Ni(II) ions absorbed within hydrogel network. TEM images confirmed that in situ formed nickel particle in p(AMPS) hydrogel networks are about 100 nm. These nickel metal nanoparticles containing hydrogel-composites were utilized as catalysts and reaction media for the reduction reactions of aromatic nitro compounds, 2- and 4-nitrophenols with aqueous NaBH 4. The reduction rate constants at four different temperatures (30, 40, 50 and 60 °C) and activation parameters were calculated. The activation energies ( E a) for 4- and 2-nitrophenols are 25.70 and 38.69 kJ mol −1, respectively. It was found that these types of hydrogel-composite catalyst systems can be used repetitively up to five times with 100% conversion and only with 25% reduction in the initial reduction rate.

Fabrication of Copper Damascene Patterns on Polyimide Using Direct Metallization on Trench Templates Generated by Imprint Lithography

Facile imprint and wet chemical processes were used to fabricate copper damascene patterns on polyimide substrate. Poly(amic acid) substrate with trench structures as template has been successfully prepared by imprint lithography using a poly(dimethylsiloxane) mold. The doped Ni(2+) ions into a template through ion-exchange reaction were reduced by an aqueous NaBH(4) solution, resulting in the formation of a nickel thin layer along the surface structure of the template. The resulting nickel films can act as catalyst for subsequent electrodeposition of copper. After electrodeposition, a polishing process was carried out for removing excess deposited copper films, followed by imidization of the substrate. The resulting damascene structured copper films exhibited fine and good adhesion with the polyimide substrate, and they could be utilized for good application in the fields of minute copper circuit patterns on insulating substrates.

Методика расчета плотности, вязкости и электропроводности растворов Na(K)BH4 – Na(K)BO2 – – Na(K)OH – H2O, используемых в водородной энергетике

Concentrated water-alkaline mixtures of sodium and potassium borohydrides and borates are used as fuel and a hydrogen source in hydrogen power engineering, including low-temperature fuel cells. The performance of such mixtures is determined by their physicochemical properties. An algorithm to calculate the density, viscosity, and specific electric conductivity of mixed solutions of the five-component water + salt system (Na,K)BH4 + (Na,K)BO2 + (Na,K)OH + H2O based on the quasiadditivity of these properties is proposed. The concentration-temperature dependences of the density, viscosity, and specific conductivity of aqueous KOH, NaOH, KBO2, NaBO2, NaBH4, and KBH4 solutions of any composition in a temperature range of (0 to 60)°C and the whole concentration range are described mathematically. The technique and algorithm of calculation have been verified by comparison with measured properties.

Cellulose/Gold Nanocrystal Hybrids via an Ionic Liquid/Aqueous Precipitation Route

Injection of a mixture of HAuCl4 and cellulose dissolved in the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride [Bmim]Cl into aqueous NaBH4 leads to colloidal gold nanoparticle/cellulose hybrid precipitates. This process is a model example for a very simple and generic approach towards (noble) metal/cellulose hybrids, which could find applications in sensing, sterile filtration, or as biomaterials.

Hollow Ni–SiO 2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Nickel clusters contained within silica nanospheres (20–30 nm) were synthesized by using a Ni(NH 3) 6Cl 2 crystal template method in a polyoxyethylene–nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH 4/NH 3BH 3 solutions. Metallic nickel clusters exist inside the SiO 2 nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.

Encapsulation of a Single Metal Nanoparticle with Tunable Size in a Monodisperse Polymer Microcapsule

A versatile approach to fabricate monodisperse poly[styrene-co-(divinyl benzene)] (PS-co-DVB) microcapsules that contain a single gold nanoparticle (AuNP) has been demonstrated. Using the PS-co-DVB microcapsule as a microreactor, aqueous HAuCl(4) and NaBH(4) solutions are subsequently infiltrated. The size of the resulting AuNP inside of the PS-co-DVB microcapsules is easily tunable by controlling the repeated infiltration cycles of aqueous HAuCl(4) and NaBH(4) . PS-co-DVB microcapsules that contain a single silver and palladium nanoparticle are also obtained by following a similar protocol.

Effect of the preparation conditions of carbon-supported Pt catalyst on PEMFC performance

Carbon-supported Pt catalysts were prepared using NaBH4 as a reducing agent in either ethylene glycol or water for use as a cathode catalyst in PEMFCs (polymer electrolyte membrane fuel cells). Aqueous NaBH4 solution was used to reduce Pt precursor and to produce the Pt-W catalyst, while Pt-E and Pt-E-base catalysts were synthesized using NaBH4 in ethylene glycol for the reduction of Pt. Compared to Pt-W catalyst, Pt-E and Pt-E-base catalysts have higher Pt dispersion and larger EAS (electrochemically active surface area) due to the stabilizing effect of ethylene glycolic NaBH4 solution on Pt particles. In addition, increasing pH of the preparation solution improved the Pt dispersion (Pt-E-base). In unit cell tests the performance of Pt catalysts decreased in the following order: Pt-E-base > Pt-E > Pt-commercial > Pt-W. Higher metal dispersion and larger EAS are believed to be responsible for the superior performance of Pt-E catalysts, particularly Pt-E-base, compared to other catalysts.

Sequential Electrochemical Oxidation and Site-Selective Growth of Nanoparticles onto AFM Probes

In this work, we reported an approach for the site-selective growth of nanoparticle onto the tip apex of an atomic force microscopy (AFM) probe. The silicon AFM probe was first coated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) through a chemical vapor deposition (CVD) method. Subsequently, COOH groups were selectively generated at the tip apex of silicon AFM probes by applying an appropriate bias voltage between the tip and a flat gold electrode. The transformation of methyl to carboxylic groups at the tip apex of the AFM probe was investigated through measuring the capillary force before and after electrochemical oxidation. To prepare the nanoparticle terminated AFM probe, the oxidized AFM probe was then immersed in an aqueous solution containing positive metal ions, for example, Ag+, to bind positive metal ions to the oxidized area (COOH terminated area), followed by chemical reduction with aqueous NaBH 4 and further development (if desired) to give a metal nanoparticle-modified AFM probe. The formation of a metal nanoparticle at the tip apex of the AFM probe was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA).

Ionic Liquids of Bis(alkylethylenediamine)silver(I) Salts and the Formation of Silver(0) Nanoparticles from the Ionic Liquid System

We have prepared novel ionic liquids of bis(N-2-ethylhexylethylenediamine)silver(I) nitrate ([Ag(eth-hex-en)(2)]NO(3) and bis(N-hexylethylenediamine)silver(I) hexafluorophosphate ([Ag(hex-en)(2)]PF(6)), which have transition points at -54 and -6 degrees C, respectively. Below these transition temperatures, both the silver complexes assume amorphous states, in which the extent of the vitrification is larger for the eth-hex-en complex than for the hex-en complex. The diffusion coefficients of both the complex cations, measured between 30 (or 35) and 70 degrees C, are largely dependent on temperature; the dependence is particularly large in the case of the eth-hex-en complex cation below 40 degrees C. Small-angle X-ray scattering studies showed that the bilayer structure of the metal complex is formed in the liquid state for both the silver complexes. A direct observation of the yellowish [Ag(eth-hex-en)(2)]NO(3) liquid by transmission electron microscopy (TEM) indicates the presence of nanostructures, as a microemulsion, of less than 5 nm. Such structures were not clearly observed in the [Ag(hex-en)(2)]PF(6) liquid. Although the [Ag(eth-hex-en)(2)]NO(3) liquid is sparingly soluble in bulk water, it readily incorporates a small amount of water up to [water]/[metal complex] = 7:1. Homogeneous and uniformly sized silver(0) nanoparticles in water were created by the reduction of the [Ag(eth-hex-en)(2)]NO(3) liquid with aqueous NaBH(4), whereas silver(0) nanoparticles were not formed from the [Ag(hex-en)(2)]PF(6) liquid in the same way.

Hydrogen-Peroxide-Based Fuel Cells for Space Power Systems

A fuel cell using nontraditional fuel and oxidizer is investigated in this research. H 2 O 2 is used in this unique fuel cell directly at the cathode. Two types of reactant, namely, a gas-phase hydrogen and an aqueous NaBH 4 solution, were used as fuel at the anode. The direct utilization of H 2 O 2 and NaBH 4 at the electrodes, as seen in experiments, results in >30% higher voltage output compared to the ordinary H 2 /O 2 fuel cell. Further, the unique combination of NaBH 4 and H 2 O 2 , both of which are in an aqueous form, has numerous advantages from an operational point of view. This design is inherently compact compared to other cells that use gas-phase reactants. Consequently, the peroxide-based fuel cell is well suited for space power applications where air is not available and a high-energy density fuel is essential.

Direct metallization of nickel on polymeric template patterns for fabrication of copper circuits on glass substrates

We demonstrate a chemical route to depositing nickel granular layer patterns using ion-doped precursor templates, which can be used as adhesive interlayers for fabrication of copper circuit patterns on glass substrates. The poly(amic acid) templates were first dispensed from solution onto the glass surface using a fine-precision dispenser, followed by Ni2+ ion doping through selective ion exchange reaction. The reduction treatment using aqueous NaBH4 solution allowed the formation of a nickel granular layer on the poly(amic acid) surface, which could catalyze subsequent electrodeposition of copper. The resulting copper/nickel/polyimide-layered structure showed good adhesion with the glass substrate. This work can benefit the understanding of the growth process of metallic thin films via the direct metallization process and provide important experimental data for developing novel fabrication processes for copper circuit patterns on glass substrates.

Simple and fast fabrication of polymer template-Ru composite as a catalyst for hydrogen generation from alkaline NaBH 4 solution

Polymer template-Ru composite (Ru/IR-120) catalyst was prepared using a simple and fast method for generating hydrogen from an aqueous alkaline NaBH 4 solution. The hydrogen generation rate was determined as a function of solution temperature, NaBH 4 concentration, and NaOH (a base-stabilizer) concentration. The maximum hydrogen generation rate reached 132 ml min −1 g −1 catalyst at 298 K, using a Ru/IR-120 catalyst that contained only 1 wt.% Ru. The catalyst exhibits a quick response and good durability during the hydrolysis of alkaline NaBH 4 solution. The activation energy for the hydrogen generation reaction was determined to be 49.72 kJ mol −1.

Pulsed-laser deposition of nanostructured Pd/C thin films: A new entry into metal-supported catalysts for hydrogen producing reactions

Carbon-supported palladium thin films were synthesized at room temperature by KrF excimer pulsed laser deposition by using oriented pyrolytic graphite and Pd target. By changing the experimental conditions, a range of structures, from smooth to porous cluster-assembled carbon films were obtained prior to deposition of the Pd films. High amount of sp 2 coordinated graphitic carbon embedded with large degree of disorder is observed in these carbon films. Surface morphology was studied by using scanning electron microscopy, while compositional analysis was performed by using energy dispersive spectroscopy. Structural analysis was performed using Raman spectroscopy and Fourier transform infrared spectroscopy. The importance of morphology and chemical structure of carbon films on their catalytic activity was investigated by using the hydrolysis of aqueous NaBH 4 as a reference process. Pd/C film produced by pulsed laser deposition are here demonstrated to be a better catalyst than Pd/C powder because of the high content of sp 2 bonding carbon atoms arranged into the porous and irregular surface of the carbon film.

High-active nickel catalyst of NiB/SiO2 for citral hydrogenation at low temperature

Abstract A high-active supported nickel catalyst of NiB/SiO2 was obtained by impregnation-chemical reduction for liquid-phase hydrogenation. The precursor salt of nickel was mounted on SiO2 by impregnating, drying and calcination at an appropriate temperature without being decomposed, and then reduced with aqueous NaBH4 solution. The factors that governed the preparation of NiB/SiO2 catalysts were examined by the hydrogenation of butyraldehyde. The NiB/SiO2 catalysts were characterized as an ultrafine and amorphous structure, which were much more active than NiB and Ni/SiO2, a conventional supported nickel catalyst reduced by H2. The optimal catalyst of 5% NiB/SiO2 was used to hydrogenate citral to citronellal and citronellol, which was about 14 times as active as NiB, but less selective than NiB. Nevertheless, the reaction could be performed at room temperature to promote the selectivity. A high yield of citronellal/citronellol of about 98% and a yield of citronellal of about 84% over 5% NiB/SiO2 were obtained at a low temperature of 30 °C.

Effect of preparation method on Co–B catalytic activity for hydrogen generation from alkali [formula omitted] solution

A Co–B catalyst is used to generate hydrogen from alkaline aqueous NaBH 4 solutions. This study examined the properties of a Co–B catalyst prepared using different precursors ( CoCl 2 and CoSO 4 ) and NaBH 4 / Co 2 + mole ratios (0.67, 1.5, 3) at calcination temperatures of 130, 250 and 450 ∘ C . As the calcination temperature was increased in N 2 atmosphere mixed with 1% air, the typical amorphous structure of Co–B disappeared and the X-ray diffraction peaks corresponding to Co 3 O 4 became sharper. Metallic Co was formed when a NaBH 4 / Co 2 + mole ratio of 3 was used as the reductant with a corresponding reduction in the rate of H 2 generation. The highest level of H 2 generation (2400 ml/min g) was obtained with CoCl 2 as the precursor, a NaBH 4 / CO 2 + mole ratio of 1.5 as the reductant, and a calcination temperature of 250 ∘ C .

Direct NaBH 4/H 2O 2 fuel cells

A fuel cell (FC) using liquid fuel and oxidizer is under investigation. H 2O 2 is used in this FC directly at the cathode. Either of two types of reactant, namely a gas-phase hydrogen or an aqueous NaBH 4 solution, are utilized as fuel at the anode. Experiments demonstrate that the direct utilization of H 2O 2 and NaBH 4 at the electrodes results in >30% higher voltage output compared to the ordinary H 2/O 2 FC. Further, the use of this combination of all liquid fuels, provides numerous advantages (ease of storage, reduced pumping requirements, simplified heat removal, etc.) from an operational point of view. This design is inherently compact compared to other cells that use gas phase reactants. Further, regeneration is possible using an electrical input, e.g. from power lines or a solar panel. While the peroxide-based FC is ideally suited for applications such as space power where air is not available and a high energy density fuel is essential, other distributed and mobile power uses are of interest.

Determination of mercury in gasoline by cold vapor atomic absorption spectrometry with direct reduction in microemulsion media

The determination of Hg in gasoline by cold vapor atomic absorption spectrometry, after direct aqueous NaBH 4 reduction in a three-component (microemulsion) medium, was investigated. Microemulsions were prepared by mixing gasoline with propan-1-ol and 50% v / v HNO 3 at a 20 : 15 : 1 volume ratio. A long-term homogeneous system was immediately formed this way. After reduction, the Hg vapor generated in a reaction flask was transported to an intermediate K 2Cr 2O 7/H 2SO 4 trap solution in order to avoid poisoning of the Au–Pt trap by the gasoline vapors. A second reduction step was then conducted and the generated Hg vapor transported to the Au–Pt trap, followed by thermal release of Hg 0 and atomic absorption measurement. Purified N 2 was used as purge and transport gas. After multivariate optimization by central composite design calibration graphs showed coefficients of correlation of 0.9999 and a characteristic mass of 2 ng was obtained. Typical coefficients of variation of 5% and 6% were found for ten consecutive measurements at concentration levels of 1 and 8 μg L −1 of Hg 2+, respectively. The limit of detection was 0.10 μg L −1 (0.14 μg kg −1) in the original sample. A total measurement cycle took 11 min, permitting duplicate analysis of 3 samples per hour. The results obtained with the proposed procedure in the analysis of commercial gasoline samples were in agreement with those obtained by a comparative procedure. Gasoline samples of the Rio de Janeiro city have shown Hg concentrations below 0.27 μg L −1.

Introduction of Ag and Ag2S Nanoparticles into Nylon 6 Film and Fiber

Nylon 6 doped with Ag nanoparticles (nylon 6/Ag) was prepared by immersion of nylon 6 in aqueous AgNO3 solution followed by reductive treatment by heating under H2 gas or immersing in an aqueous NaBH4 solution. As a result of either reductions, Ag nanoparticles below 10nm in diameter were successfully dispersed within the nylon 6 matrix. The Ag content and the dispersion state of the Ag nanoparticles can be varied by the concentration of the AgNO3 solutions and the reduction methods, respectively. From the results of the absorbed Ag+ content in nylon 6 via immersion in AgNO3 solution, nylon 6 was found to have some affinity for silver ion. Nylon 6 doped with Ag2S nanoparticles (nylon 6/Ag2S) was also prepared by immersion in AgNO3 aqueous solution and the following immersion of Na2S aqueous solution. Ag2S particles having several nanometers in diameter were dispersed in nylon 6. The nylon 6/Ag2S film showed strong photoluminescence in the near infrared region.