Hydrogen desorption behavior of vanadium borohydride synthesized by modified mechano-chemical process

The vanadium borohydride was synthesized by a mechano-chemical milling method and its hydrogen desorption performance was evaluated. The effect of cooling during milling process on the hydrogen desorption behavior was also investigated. Nearly pure hydrogen was detected using a mass spectrometer coupled with a simultaneous thermal analyzer. Thermogravimetric method was conducted to determine the initial desorption temperature and the amount of hydrogen released from the hydride. The initial desorption temperature of vanadium borohydride was found below 100 °C, with an enthalpy change of 25.4 kJ/mol V(BH₄)₃. The amount of hydrogen released from the hydride prepared by milling but without cooling was 0.25 wt%, while that prepared with controlled cooling at 20 °C was 1 wt%. A beneficial effect of enhanced hydrogen release to 2.2 wt% from borohydride was found if multi-walled carbon nanotubes (MWCNTs) were added as an additive.     

Carbon-supported Pd catalysts: Influences of nanostructure on their catalytic performances for borohydride electrochemical oxidation

In the present work, a Pd catalyst supported on multiwalled carbon nanotubes (MWCNTs) is successfully synthesized and its property as the anode material for borohydride oxidation is investigated. Compared with other carbon-supported Pd catalysts, the Pd/MWCNT catalyst exhibits improved polarization properties due to its smaller Pd particles dispersing homogeneously on carbon nanotubes. The hydrogen evolution behavior on the Pd/activated carbon sample is found to be very sensitive to the concentrations of NaOH and NaBH₄ in the solution. On the other hand, borohydride oxidation on Pd/carbon black and Pd/MWCNT displays reaction mechanisms near the 4e stoichiometry. It is thus supposed that the primary direct borohydride oxidation on Pd may be a 4e reaction. The simultaneous electro-oxidation of adsorbed hydrogen occurs conditionally, depending on its relative activity with the direct oxidation of BH₄⁻.     

Catalytic hydrolysis of sodium borohydride solution for hydrogen production using thermal plasma synthesized nickel nanoparticles

In the present study nickel nanoparticles were synthesized by thermal plasma route. In this method we obtained highly crystalline almost spherical nanoparticles with maximum number of particles having size around 30–50 nm. These nanoparticles were thoroughly characterized and employed as a catalyst for hydrogen production using hydrolysis of sodium borohydride (NaBH₄). The effect of initial concentration of NaBH₄, pH and temperature of solution on the rate of hydrogen production was investigated. Nickel nanoparticles exhibits first order reaction with respect to NaBH₄ concentration at elevated temperatures. After hydrolysis, the nickel nanoparticles showed presences of B–O and B–OH species on the nickel surface. The catalyst was found to be stable during 5 sequential cycles of test.     

Hydrogen from sodium borohydride and fossil source: An energetic and economical comparison

In this paper, sodium borohydride (NaBH₄) is examined as a method of hydrogen storage and transport, and compared with hydrogen obtained from fossil sources. This chemical hydride has a very high storage density capability due to its large hydrogen content. Hydrogen is released as the main product of the reaction of NaBH₄ with water, with sodium metaborate (NaBO₂) as a by-product. The main disadvantage of the process is the production cost of the borohydride.     

Controlling the growth of NaBH4 nanoparticles for hydrogen storage

Sodium borohydride (NaBH₄) is a promising hydrogen storage material due to its potential for reversible hydrogen storage with high hydrogen capacity (10.8 mass%). However, the temperature at which hydrogen can be released from NaBH₄ is too high (> 500 °C) for practical use and the reversible release of hydrogen is only feasible under severe conditions of temperature and pressure. Nanosizing is an effective strategy to improve the hydrogen properties of NaBH₄. In this context, control over the particle size of NaBH₄ has become important. Herein, we report on a solvent evaporation method for the synthesis of isolated NaBH₄ nanoparticles with varying mean particle sizes and morphologies. In particular, the effects of surfactants’ carbon chain lengths, their steric hindrance and functional groups in facilitating the stabilisation of NaBH₄ nanoparticles of various sizes and shapes were investigated. Longer linear carbon chains bearing hard type functional groups were found to favour the growth of smaller NaBH₄ nanoparticles.     

Magnesium borohydride as a hydrogen storage material: Synthesis of unsolvated Mg(BH4)2

Different methods for preparation of unsolvated magnesium borohydride, a promising material for hydrogen storage, based on exchange reaction of MgCl₂ with lithium and sodium borohydride in different solvents have been evaluated. A convenient scalable method for synthesis of pure Mg(BH₄)₂ by ball milling a mixture of MgCl₂ and NaBH₄ in diethyl ether has been developed. Crystalline stable low and high temperature phases, as well as a new metastable phase of unsolvated magnesium borohydride have been prepared.     

Indirect hydrolysis of sodium borohydride: Isolation and crystallographic characterization of methanolysis and hydrolysis by-products

The use of sodium borohydride as a means for hydrogen generation has focused on the base-stabilized hydrolysis reaction, while literature for the methanolysis of sodium borohydride remains scarce. Sodium borohydride methanolysis is an alternative for hydrogen production from sodium borohydride and has a number of advantages over hydrolysis reactions in terms of by-product handling. Previous studies have shown that the presence of water in methanol significantly retards the rate of hydrogen evolution from NaBH₄. This article reports the production of hydrogen from NaBH₄ using rigorously dried methanol. In addition, the solid-state structure of the methanolysis by-product is reported, which lends pertinent information for its hydrolysis for methanol recovery. Also reported is the solid-state structure of the hydrolysis by-product.     

Hydrogen generation from sodium borohydride with Ni and Co based catalysts supported on Co3O4

Hydrogen is an alternative and clean energy carrier, but there are still some production related problems. In this aspect, it is crucial to efficiently generate hydrogen from hydrogen rich materials such as sodium borohydride. In this study, Co₃O₄ supported Ni and Co catalysts are synthesized via microwave irradiation technique for hydrogen generation from sodium borohydride. In this context, firstly, Co₃O₄ support material is synthesized by chemical method. Then, Ni and Co catalysts are decorated onto Co₃O₄ support material by microwave irradiation-polyol method. Prepared catalysts and support material are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-mass spectrometer (ICP/MS). A new system is designed by our group in order to determine the activity of the prepared catalysts for hydrogen generation. The effects of different initial NaOH concentrations on hydrogen generation rate are investigated. It is observed that the rate of hydrogen generation increased with an increase in initial NaOH concentration. Co-Co₃O₄ catalyst at 10% NaOH initial concentration shows the highest hydrogen generation rate as 2823 ml/g_cat.min. In summary, Co-based catalysts are exhibited more activity than Ni-based catalysts in terms of hydrogen generation.     

A composite of borohydride and super absorbent polymer for hydrogen generation

To develop a hydrogen source for underwater applications, a composite of sodium borohydride and super absorbent polymer (SAP) is prepared by ball milling sodium borohydride powder with SAP powder, and by dehydrating an alkaline borohydride gel. When sodium polyacrylate (NaPAA) is used as the SAP, the resulting composite exhibits a high rate of borohydride hydrolysis for hydrogen generation. A mechanism of hydrogen evolution from the NaBH₄-NaPAA composite is suggested based on structure analysis by X-ray diffraction and scanning electron microscopy. The effects of water and NiCl₂ content in the precursor solution on the hydrogen evolution behavior are investigated and discussed.     

Development of highly efficient and reusable Ruthenium complex catalyst for hydrogen evolution

Herein, we report an efficient, environmentally friendly and stable catalyst development to hydrogen evolution from sodium borohydride hydrolysis. For this purpose, Ruthenium complex catalyst successfully fabricated via 5-Amino-2,4-dichlorophenol-3,5-ditertbutylsalisylaldimine ligand and RuCl₃·H₂O salt. Ru complex catalyst was identified with X-Ray Diffraction Analysis, Infrared Spectroscopy, Elemental Analysis, Transmission electron microscopy, Scanning Electron Microscope and Brunauer-Emmett-Teller Surface Area Analysis. According to the analysis results, it was confirmed that Ru complex catalyst was successfully synthesized. Ru complex was used as a catalyst in NaBH₄ hydrolysis. The kinetic performance of Ru complex catalyst was evaluated at various reaction temperatures, various sodium borohydride concentration, catalyst concentration and sodium hydroxide concentration in hydrogen evolution. The apparent activation energy for the hydrolysis of sodium borohydride was determined as 25.8 kJ mol^?1. With fully conversion, the promised well durability of Ru complex was achieved by the five consecutive cycles for hydrogen evolution in sodium borohydride hydrolysis The hydrogen evolution rates were 299,220 and 160,832 mL H₂ g_cat^?1 min^?1 in order of at 50 °C and 30 °C. Furthermore, the proposed mechanism of Ru complex catalyzed sodium borohydride hydrolysis was defined step by step. This study provides different insight into the rational design and utilization and catalytic effects of ruthenium complex in hydrogen evolution performance.     

The effect of various factors on the hydrogen generation by hydrolysis reaction of potassium borohydride

Potassium borohydride (KBH₄) reacted very slowly with water to liberate 4 mol of hydrogen/mol of compound at room temperature. The hydrolysis and stability conditions of KBH₄ investigated depend on KBH₄ concentrations, concentration of alkaline solutions, temperatures and electrical field intensity. Yield of produced hydrogen by self-hydrolysis of KBH₄ increases as the temperature increased and it produced 53.9% yield at the end of 300 min at 60 °C. The reaction rate order of hydrolysis of KBH₄ in aqueous solution is found at about 0.7–0.8 and the activation energy for hydrolysis is calculated as 14,700 kJ/mol. Potassium borohydride is stable both in room temperature and in aqueous alkaline solution. In this study, the electrical field that is not needed for catalytic activity was used for the hydrolysis of KBH₄ aqueous solution. It was found that 6 mol of hydrogen/mol of potassium borohydride was liberated in the presence of electrical field, whereas 4 mol of hydrogen was produced in the absence of electrical field per mol of potassium borohydride.     

A durable ruthenium catalyst for the NaBH4 hydrolysis

Ru-active carbon (Ru/C) catalysts are prepared by impregnation reduction method for hydrogen generation via hydrolysis of alkaline sodium borohydride (NaBH₄) solution. The corresponding activity and durability of the prepared catalysts are tested in an immobile bed reactor. The variation of hydrogen generation rate with the increasing of flux and concentration of NaBH₄ solution is measured. The durability of the catalysts prepared under various reductive pH values and reductants is tested by using different concentrations of NaBH₄ solution (10 & 15 wt%). It is found that the durability of catalyst in 15 wt% NaBH₄ solution is longer than that in 10 wt% NaBH₄ solution. The deactivation of Ru/C catalysts is considered as the comprehensive effect of three factors: the loss of Ru, the deposition of byproducts on the catalyst surface and the aggregation of Ru particles.     

Hydrogen generation from hydrolysis of sodium borohydride by cubic Co–La–Zr–B nano particles as novel catalyst

Cubic Co–La–Zr–B nano particles were prepared in situ for the first time from the reduction of Co(II), La(III) and Zr(IV) chloride by sodium borohydride in methanol under reflux condition. Poly N-vinyl-2-pyrrolidone (PVP) as stabilizing agent was used for preparation of Co–La–Zr–B nano particles. Obtained powders were characterized by XRD, BET, ICP, SEM, TEM and UV–vis techniques. XRD patterns declare that under argon atmosphere only metalboride phase has been crystallized and it was not seen any oxide phase of metals. TEM image depicts that PVP stabilized nano particles are square shaped particles that containing many nanoclusters. Cubic Co–La–Zr–B nano particles were also confirmed by SEM image. Co–La–Zr–B is highly active catalysts for hydrogen generation from the hydrolysis of sodium borohydride. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 53 kJ mol⁻¹) and effects of the catalyst dosage, amount of NaBH₄, and temperature on the rate of the catalytic hydrolysis of sodium borohydride. Catalytic hydrolysis of NaBH₄ is first order with respect to the catalyst concentration and also first order to the NaBH₄ concentration in the case of cubic Co–La–Zr–B nano particles.     

Highly efficient and reactivated electrocatalyst of ruthenium electrodeposited on nickel foam for hydrogen evolution from NaBH4 alkaline solution

Cyclic life of catalyst for hydrolysis of sodium borohydride is one of the key issues, which hinder commercialization of hydrogen generation from sodium borohydride (NaBH₄) solution. This paper is aimed at promoting the cyclic life of Ru/Ni foam catalysts by employing an electro-deposition method. The effect of hydrolysis parameters on hydrolysis of sodium borohydride was studied for improving the catalytic performance. It is found that the hydrogen generation rate (HGR) of the hydrolysis reaction catalyzed by Ru/Ni foam catalyst can reach as high as 23.03 L min^?1 g^?1 (Ru). The Ru/Ni foam catalyst shows good catalytic activity after a cycleability test of 100 cycles by rinsing with HCl, which is considered as more effective method than rinsing with water for recovering the performance of Ru/Ni foam catalyst.     

Hydrogen adsorption simulations in isomorphous borohydride and imidazolate frameworks: Evaluations using interpolation

We simulate hydrogen adsorption on two topologically identical crystalline solids using the grand canonical Monte Carlo (GCMC) method. One solid is the γ - magnesium borohydride, γ-Mg(BH₄)₂, the first borohydride crystal with a permanent porosity. The other solid is ZIF-72, Zn(dcIm)₂, a zinc imidazolate framework synthesized with dichloroimidazole (dcIm) ligands. Both solids maintain narrow sized pore networks, capable of storing molecular hydrogen. We introduce an interpolation scheme for the temperature dependence of adsorption isotherms. The interpolation employs a special control function based on the adsorption enthalpy. We compare the hydrogen capacities of the two samples at variable temperatures and pressures and attribute the discrepancies to the implicit surface texture and size of the confinements. Notably, the porous Mg(BH₄)₂ can physically adsorb 3.44 wt% H₂ at cryogenic temperatures that is cumulative to the already high content of 14.9 wt% of atomic hydrogen bound on the boron atoms. This content makes the γ-Mg(BH₄)₂ one of the most hydrogen rich solids reported to date.     

The effects of operating conditions on hydrogen production from sodium borohydride using Box-Wilson optimization technique

Sodium borohydride is the most investigated boron compound among hydrogen-carrier materials by researchers because of its stable structure, relatively high hydrogen storage capacity (NaBH₄, 10.8% hydrogen by weighing), comparatively cost-efficiency, and non-flammability. This study aims to produce hydrogen from sodium borohydride solution whose hydrolysis was carried out both in the absence of any catalysts at above 100 °C. In order to increase the rate of hydrogen production using NaBH₄ solution, the initial concentration of HCl and temperature were optimized using the Box- Wilson method. The field of the highest dehydrogenation yield was shown by drawing contour plot for the second order model. As a result of the experiments, the highest dehydrogenation yield (100%) of this solution was achieved in 3.76 M HCl concentration and at 157 °C; besides, the reaction time was the least under these conditions.     

Highly active porous Co–B nanoalloy synthesized on liquid-gas interface for hydrolysis of sodium borohydride

Porous Co–B nanoalloy is a low-cost and highly active catalyst towards the hydrolysis of sodium borohydride (NaBH₄). In this study, a facile and room-temperature hydrogen bubble-assisted method was developed to prepare porous Co–B nanoalloy (Co-B_bubble) materials exhibiting high catalytic activity. The obtained materials are characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometer, transmission electron microscopy and surface area experiments. It is found that the hydrogen bubbles generated in-situ in the reaction system can act as template, which played an important role in determining the porous architecture of the final Co–B product. In the hydrolysis of sodium borohydride for hydrogen generation, the porous Co-B_bubble nanoalloy materials exhibit high catalytic activity with mass normalized rate constant of 5.31 L_hydrogen min^?1 g_catalyst^?1; a value which is much higher than those obtained for many other Co–B catalysts recently reported in the literature. The apparent activation energy (Ea) of the catalytic process is found to be ca. 30 kJ mol^?1. It is proposed that the high catalytic performance and low cost of Co-B_bubble nanoalloy catalyst can be a promising material candidate in the hydrolysis of sodium borohydride for hydrogen production for commercial applications.     

Exergy and energy analysis of hydrogen production by the degradation of sodium borohydride in the presence of novel Ru based catalyst

Chemically possible hydrogen storage material of the most important and widely used metal hydride compound is sodium borohydride. A current research issue is the development of systems that allow regulated hydrogen generation employing appropriate catalysts for the creation of hydrogen gas from the hydrolysis of sodium borohydride (NaBH₄). In this study, controlled hydrogen production from alkali solution of NaBH₄ was aimed. On hydrogen generation rate (HGR), the effects of NaBH₄ and alkaline solution concentrations, catalyst quantity, and temperature were examined. Considering the energy and exergy analysis, which have gained importance in the international arena in recent years, in this study, the exergy energy analysis of the environment in which the sodium borohydride solution is located was performed. The best one of the Ru-based catalysts synthesized in different atomic ratios was determined as 90:10 RuCr. The surface characterization of the obtained catalyst was carried out using scanning electron microscope (SEM-EDX) and X-ray diffractometer (XRD). In the kinetic calculations, the activation energy was calculated as 35,024 kj/mol and the reaction ordered n was found to be 0,65. By applying exergy and energy analysis to the hydrogen production step, the energy and exergy efficiency of the system were found to be 24% and 7%, respectively.     

Effect of magnesium on sodium borohydride synthesis from anhydrous borax

This paper describes the effect of magnesium (Mg) addition on sodium borohydride (NaBH₄) synthesis from anhydrous borax (Na₂B₄O₇) in the presence of the hydrogen atmosphere. NaBH₄ synthesis has been investigated at a temperature of 550 °C and 25 bar hydrogen pressure experimentally. The reactions were carried out in a stainless steel batch reactor placed in a vertical furnace. The extent of reaction was monitored by observing pressure decrease in the system. Aqueous ammonia was used to extract NaBH₄ from the reaction mixture. Highly pure sodium borohydride was obtained after evaporation of the solvent. Characterization of the product was made by the X-ray powder pattern studies. It was found that the amount of Mg plays an important role in NaBH₄ formation. Increasing the amount of Mg resulted in appreciable increase in NaBH₄ formation. The NaBH₄ yield reached in the experiments was found to be 93% in a single batch process.