Hydrogen generation from the hydrolysis of aluminum promoted by Ni–Li–B catalyst

In this study, the high activity Ni–Li–B catalysts were fabricated through wet chemical reduction method. Their morphological structures, crystallinity, surface area and composition were examined by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) method and energy-dispersive X-ray spectroscopy (EDS). The aluminum-water reaction tests were explored in the range of temperatures from 35–75 °C. It was found that water could react with aluminum to generate hydrogen gas. The yield and hydrogen generation rate were significantly increased when all prepared catalysts were added into the reaction. The Ni–Li–B (X_LiCl = 0.1 g) catalyst exhibited the highest cumulative hydrogen volume of 201.3 ml with an average hydrogen production rate of 0.50 ml min⁻¹ at 55 °C. This phenomenon could be pointed to the emergence of the micro galvanic cell formed by the Ni–Li–B, Li/Ni–Li–B, Li and Al, which accelerated aluminum to rapidly react with water.     

Hydrogen generation via the reaction of an activated aluminum slurry with water

Presented here is the formulation and characterization of a stable aluminum slurry fuel that reacts readily and exothermically with liquid water to produce hydrogen gas and AlOOH (boehmite). Bulk pure aluminum is first surface-treated with a gallium-indium eutectic, then ground into a powder and suspended in mineral oil containing 4–8 wt% fumed silica as a shear-thinning agent. Aluminum mass fractions of up to 65 wt% are shown here. This formulation results in a slurry fuel that can be pumped continuously at low power while remaining in suspension for over 2 months. The fuel is also shown here to exhibit a high degree of reaction completion (93.4%) with a total measured energy density of 28.7 MJ/L and specific energy of 17.5 MJ/kg. Finally, to show the feasibility of using this fuel for on-demand hydrogen production in a representative power system, a prototype continuous-flow reactor was developed, and validation experiments were performed, the results of which are presented here.     

Hydrogen generation by aluminum‐water reaction in acidic and alkaline media and its reaction dynamics

The additives AlCl₃, CoCl₂, Al(OH)₃, Ca(OH)₂, and NaAlO₂ are added to water to regulate its pH value (pH = 2‐13) in this study. The effects of media on the aluminum‐water reaction are investigated. Up to an increase in temperature, the hydrogen generation rate in different media increases. H⁺, OH^?, Cl^?, or Co produced from the additive favors the initial removal of the oxide film and aluminum corrosion. Therefore, the initial hydrogen generation rate increases in acidic and alkaline media. The synergistic effect of the formed fresh Co and Cl^? catalyzes aluminum‐water reactions. However, the amount of hydrogen decreases with increasing mass of CoCl₂ because of agglomeration of the catalyst Co. The higher concentration of OH^? ions aids hydrogen generation. However, the reaction rate became slow after the rapid consumption of OH^?, when the concentration of OH^? was relatively small. Hydrogen is quickly generated and Al is completely reacted upon following additions of Al due to the cooperation between H⁺, Cl^?, OH^? ions, and the formed Al(OH)₃.     

Hydrogen generation utilizing alkaline sodium borohydride solution and supported cobalt catalyst

Supported Co catalysts with different supports were prepared for hydrogen generation (HG) from catalytic hydrolysis of alkaline sodium borohydride solution. As a result, we found that a γ-Al₂O₃ supported Co catalyst was very effective because of its special structure. A maximum HG rate of 220 mL min⁻¹ g⁻¹ catalyst and approximately 100% efficiency at 303 K were achieved using a Co/γ-Al₂O₃ catalyst containing 9 wt.% Co. The catalyst has quick response and good durability to the hydrolysis of alkaline NaBH₄ solution. It is feasible to use this catalyst in hydrogen generators with stabilized NaBH₄ solutions to provide on-site hydrogen with desired rate for mobile applications, such as proton exchange membrane fuel cell (PEMFC) systems.     

Cobalt–iron–boron catalyst-induced aluminum–water reaction

Hydrogen generation based on the corrosion of aluminum has been evaluated with regard to its possible application in on-board mobile and portable power sources. In this study, the aluminum–water reaction induced by Co–Fe–B has been examined. SEM results have shown that the chain-like Co–Fe–B catalyst forms a network structure under the influence of an external magnetic field. Co–Fe–B is actually a mixture of cubic Fe and amorphous Co–Fe–B. The Fe content in Co–Fe–B increases with increasing mass of FeCl₃ used in its synthesis. An increase in the Fe content in Co–Fe–B shortens the induction time and improves the amount of hydrogen generated owing to the formation of Fe/Al, Co–Fe–B/Al, and Co–Fe–B/Fe micro galvanic cells. However, an increase in the Co–Fe–B content slightly decreases the amount of hydrogen generated owing to its agglomeration and oxidation. With increasing temperature, both the reaction rate and the amount of hydrogen generated are improved. The activation energy of this reaction, calculated from the maximum reaction rates at different temperatures, is 40 kJ mol⁻¹. Hydrogen is rapidly generated, without an induction time, upon the addition of consecutive batches of Al, because the occurrence of the high concentration of OH⁻ ions effectively accelerates the corrosion of Al.     

Hydrogen generation by the reaction of Al with water promoted by an ultrasonically prepared Al(OH)3 suspension

A high-activity Al(OH)₃ suspension is prepared by the reaction of Al with water using an ultrasonic procedure. The above Al(OH)₃ suspension could considerably promote the Al-water reaction and hydrogen-generation under ambient condition. This Al(OH)₃ suspension has a good stability in air and its activity increases with decreasing the particle sizes of Al powder to prepare it. The mechanism analyses reveal that the Al(OH)₃ particles in ultrasonically prepared Al(OH)₃ suspensions are very fine, which could effectively dissociate water molecules and promote the hydration of the passive oxide film on Al particle surfaces, speeding up the Al-water reaction. As the present Al(OH)₃ suspension is chemically neutral and there is no special treatment for Al powder, the present method provides a viable way to generate hydrogen for portable application.     

Hydrogen generation using activated aluminum/water reaction

The effective parameters for the Al-water reaction are studied. Salts such as sodium chloride (NaCl), potassium chloride (KCl) and barium chloride (BaCl₂) were added to Al particles and the mixture were alloyed via high-energy ball milling. It was observed that the reaction of Al/water is evolved and the reaction induction time declined significantly by the application of BaCl₂ as new modifier in comparison with NaCl and KCl. The X-ray diffraction patterns revealed that the other valuable reaction byproduct is AlOOH, which can be calcinated to gamma or alpha alumina. Microstructure of alloys were studied via FESEM and it was observed that as the time of ball milling increased the size of particles decreased. Increasing of the salt to Al powder ratio lead to increasing of hydrogen yield as well as hydrogen production rate. Effect of NaOH alkaline solution was also investigated and according to the results, solutions with higher concentration of NaOH generate higher amount of hydrogen.     

Enhanced hydrogen generation from graphite-mixed aluminum hydroxides catalyzed Al/water reaction

The high catalytic effect of a graphite-mixed Al(OH)₃ nanoparticles (NPs) for the hydrogen generation from the reaction of Al and water is reported. These graphite-mixed Al(OH)₃ NPs were synthesized through a simple solvothermal procedure. Characterization using powder X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) were carried out. The results show that small amounts of graphite added into Al(OH)₃ NPs could significantly enhance the hydrolysis reaction of Al and H₂O reaction, releasing 1360 mL g^-1 hydrogen in 20 min at room temperature. This reaction accomplishes 100% yield of hydrogen using 1 g modified Al(OH)₃ in 1 g Al and 200 g water. The synthesized graphite-mixed Al(OH)₃ exhibits good activity-stability, which can be used for multiple Al/water reactions. This work demonstrates a novel and possible way to generate hydrogen for portable devices.     

Hydrogen generation from water and aluminum promoted by sodium stannate

A new process to obtain H₂ from H₂O using Al corrosion in Na₂SnO₃ solutions is described. Results showed an enhancement of H₂ production rates using Na₂SnO₃ instead of NaOH at the same pH. A side reaction of Al in Na₂SnO₃ solutions has been found, which consumes Al to produce metallic Sn. H₂ yield depends chiefly on Al/Na₂SnO₃ molar ratio for experiments with Na₂SnO₃ concentrations above 0.025 M, reaching higher yields with higher Al/Na₂SnO₃ ratios. The maximum H₂ production rates are proportional to the initially added Al mass. Two different shrinking core models for examining the kinetics of H₂ generation are verified and the activation energy (E_a) is 73 ± 6 kJ mol⁻¹, confirming a rate control by a chemical step. A mechanism of Al corrosion in Na₂SnO₃ solutions is proposed and compared with the mechanism in NaOH and NaAlO₂ solutions.     

Hydrogen generation from water by means of activated aluminum

An important part of the hydrogen energy problems is the search of hydrogen sources for feeding hydrogen–air fuel cells. One of the most convenient methods for hydrogen generation is based on oxidation of aluminum by water. In this paper the method of aluminum activation based on the application of gallium alloys (gallams) is suggested.     

A review: Hydrogen generation from borohydride hydrolysis reaction

In this review, a convenient hydrogen generation technology based on sodium borohydride and water as hydrogen carriers has been summarized. The recent progresses in the development of the hydrogen generation from sodium borohydride hydrolysis are reviewed. The NaBH₄ hydrolysis behavior is discussed in detail. From reported results, it is considered that hydrogen generation from sodium borohydride hydrolysis is a feasible technology to supply hydrogen for the PEMFC. It has been found that the reported results are encouraging although there are some engineering problems that lie ahead. The critical issues of this hydrogen generation technology have been highlighted and discussed.     

Carbon-supported cobalt catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost transition metal catalysts with high performance are attractive for the development of on-board hydrogen generation systems by catalytic hydrolysis of sodium borohydride (NaBH₄) in fuel cell fields. In this study, hydrogen production from alkaline NaBH₄ via hydrolysis process over carbon-supported cobalt catalysts was studied. The catalytic activity of the supported cobalt catalyst was found to be highly dependent on the calcination temperatures. The hydrogen generation rate increases with calcination temperatures in the range of 200–400 °C, but a high calcination temperature above 500 °C led to markedly decreased activity. X-ray diffraction patterns reveal that the catalysts experience phase transition from amorphous Co–B to crystalline cobalt hydroxide with increase in calcination temperatures. The reaction performance is also dependent on the concentration of NaBH₄, and the hydrogen generation rate increases for lower NaBH₄ concentrations and decreases after reaching a maximum at 10 wt.% of NaBH₄.     

Effects of amalgam on hydrogen generation by hydrolysis of aluminum with water

Hydrogen generated by hydrolysis of metal aluminum with water exhibits some potential merits such as system simplicity, safety and controllability. However aluminum is prone not to react with water at low temperatures due to the passive oxide film formed on its surface. In the present investigation, mercury or zinc amalgam acting as a catalyst was employed to promote the aluminum hydrolysis reaction and the hydrogen evolution performance of the aluminum surface covered by mercury and zinc amalgam thin film was evaluated. The results showed that in the presence of mercury or zinc amalgam the hydrolysis of aluminum with water to generate hydrogen could occur at room temperature. The hydrogen evolution rate was strongly dependent on reaction temperature and the maximum hydrogen generation rate of 43.5 cm³ h⁻¹ cm⁻² was obtained at 65 °C for the case coated with zinc amalgam. Zinc amalgam showed a more pronounced effect on aluminum activation and hydrogen generation rate than mercury only. The apparent activation energy calculation showed that the aluminum hydrolysis induced by zinc amalgam has a lower value of 43.4 kJ mol⁻¹ than the case coated by mercury (74.8 kJ mol⁻¹). The X-ray diffraction results revealed that the byproduct is bayerite. The hydrolysis mechanism of aluminum in the presence of mercury or zinc amalgam was proposed based on the microscope observation. The aluminum hydrolysis reaction was found to take place at the mercury/water interface and the moving species in mercury or zinc amalgam thin film to sustain the hydrolysis reaction was aluminum particles.     

Hydrogen liberation from the hydrolytic dehydrogenation of hydrazine borane in acidic media

Addressed herein, the hydrolytic dehydrogenation of hydrazine borane (NH₄BH₃, HB) was reported in acidic media using nitric acid (HNO₃) as a catalyst at room conditions. The aqueous hydrazine borane was treated with HNO₃ solution in different concentrations to liberate H₂. Besides, kinetic data were collected to idetificate the activation parameters, the effect of temperature, acid and hydrazine borane concentrations on the hydrogen production for the hydrolytic dehydrogenation of hydrazine borane in acidic media. It can be said that the acid catalyzed hydrazine borane system can be regarded as a simple system for hydrogen production.     

Hydrogen generation through massive corrosion of deformed aluminum in water

Aluminum, one of most reactive metals, rapidly corrodes in strong acidic or alkaline solutions but passivates at pH of about 5–9. We have determined that the passivation of aluminum in this range of pH, and in particular in regular tap water, can be substantially prevented after milling of aluminum with water-soluble inorganic salts (referred to as “WIS”), such as KCl or NaCl. Ensuing corrosion of Al in tap water, with accompanying release of hydrogen and precipitation of aluminum hydroxide, at normal pressure and moderate temperatures (∼55 °C) is rapid and substantial. For example, ∼92% of the Al in the Al–WIS system when milled for 1 h and ∼81% when milled for 15 min, corrodes in 1 h, with the release of 1.5 mol of hydrogen per each mole of Al consumed in the reaction. Besides gaseous hydrogen, only solid aluminum hydroxides were formed as the reaction byproducts, opening up the possibility of straightforward recycling of the system. The effects of WIS concentration, chemistry of other additives, powder particle size, temperature, and milling conditions on the reaction kinetics are reported.     

Hydrogen generation from hydrolysis of activated Al-Bi,Al-Sn powders prepared by gas atomization method

Highly activated Al-based composite powders with compositions of Al-20Bi and Al-20Sn (wt.%) were prepared by gas atomization method for hydrogen generation. The Al-20Bi powders formed incomplete core–shell structure with Bi aggregating on the powder surface, while the Al-20Sn powders presented eutectic structure with Sn distributed homogeneously on the grain boundaries of Al. The hydrolysis characteristics of these powders were investigated in distilled water. The results showed that the Al-20Bi and Al-20Sn powders exhibited high hydrolysis performance and violently reacted with distilled water at 30 °C. Elevated temperature could significantly shorten the incubation time, as well as improve hydrogen generation rate and conversion yield of the powders. The hydrolysis mechanism and oxidation resistance property of the powders were carefully investigated too. The miscibility gap and the large difference of linear thermal expansion coefficient between Al and Bi are responsible for the activation and high oxidation resistance of the Al-20Bi powders.     

Hydrogen production from hydrolysis of ammonia borane with limited water supply

Effect of limited water supply to hydrolysis of ammonia borane for hydrogen evolution is studied over the cases in which the initial molar ratio of water to ammonia borane (H₂O/AB) is set at 1.28, 2.57 and 4.50. The conversion efficiency of ammonia borane to hydrogen is estimated from the accumulated volume of produced hydrogen gas and the quantitative analysis of hydrolysate by solid-state ¹¹B NMR. Characteristics of hydrogen evolution are significantly influenced by both water dosage and injection rate of water. In the case that water is a limiting agent, namely, H₂O/AB = 1.28, less hydrogen is produced than that predicted stoichiometrically. In contrast, conversion efficiency of ammonia borane reaches nearly 100% for the case with H₂O/AB = 4.50. Injection rate of water to ammonia borane also affect profoundly the produced volume and production rate of hydrogen, if water is used as a limiting agent in the hydrolysis of ammonia borane. Nonetheless, boric acid and metaboric acid are found to be the dominant products in the hydrolysate from XRD, FT-IR and solid-state ¹¹B NMR analysis. The hydrogen storage capacity using limited water supply in this work could reach as high as about 5.33 wt%, based on combined mass of reactants and catalyst.     

Hydrogen generation through water splitting reaction using waste aluminum in presence of gallium

The in-situ hydrogen generation through water splitting reaction using waste aluminum wires has been studied in presence of room temperature liquid metal gallium and alkaline activator potassium hydroxide. Various proportions of gallium i.e. 50%, 75%, 90% and 95% (weight by weight of the total metal in reaction) were used in order to study the effect of gallium addition on the water splitting reaction. The effect of addition of gallium on the water splitting reaction was also studied and co-related with various concentrations of activator (0.5 N and 1.0 N aqueous KOH) and reaction temperature (50, 60 and 70 °C). The effect of gallium was found to be more prominent at 0.5 N and 50 °C as compare to the 1.0 N and higher temperatures of 50 and 60 °C. The 12 fold increase in hydrogen generation rate was observed for 0.5 N aqueous KOH at 90% gallium addition and 1.0 N aqueous KOH at 75% gallium addition. The added gallium was completely recovered from the reaction. The Shrinking Core Model has been applied to the experimental data for predicting the rate controlling mechanism. The diffusion was predicted as the rate controlling step for maximum cases.     

Enhancement of hydrogen generation rate in reaction of aluminum with water

The aim of this investigation is to enhance hydrogen generation rate in aluminum–water reaction by improving the activity of aluminum particles and using the heat released during the reaction. This was accomplished by developing fresh surfaces by milling aluminum particles together with salt. Salt particles not only serve as nano-millers, but also surround activated particles and prevent re-oxidation of bare surfaces in the air. Therefore, the activated powder can be easily stored for a long time. Immersing the powder in warm water, the salt covers are washed away and hydrogen begins to release at a high rate until efficiency of 100% is achieved. The rate of reaction depends crucially on initial temperature of water. Hence, the mass of water was reduced to employ released energy to increase water temperature and, consequently, to increase hydrogen production rate. The optimum value of salt-to-aluminum mole ratio for achieving high activation, air-storage capability and 100% efficiency was obtained to be 2. When immersed in water, at initial temperatures of 55 and 70 °C, the powder lead to average hydrogen generation rate of ∼101 and ∼210 ml/min per 1 g of Al, respectively. To increase the rate of corrosion, three different alloys/composites of aluminum were prepared by mechanical alloying and activated with optimum salt-to-aluminum mole ratio. The alloys/composites formed galvanic cells after being immersed in water. In the case of aluminum–bismuth alloy, the average hydrogen generation rate increased to ∼287 and ∼713 ml/min per 1 g of Al, respectively.     

Hydrogen generation by hydrolysis reaction using magnesium alloys with long period stacking ordered structure

In the present work are reported the hydrogen generation performances of Long Period Stacking Ordered (LPSO) compounds with 18R, 14H and 10H-type structures by hydrolysis reaction in simulated seawater solution (35 g/L NaCl). LPSO compounds and LPSO + Mg alloys synthesized by induction melting are described in the light of their microstructural and electrochemical properties. Except for 10H type, all LPSO present improved H₂ generation features compared to pure Mg. Indeed, 80% of the reaction is achieved in less than 40 minutes. The highest generation yield of 90% is obtained for single phase LPSO Mg_87.6Ni_5.5Y_6.9. Alloys containing both Mg and LPSO beneficiate from galvanic coupling between the two phases leading to higher reactivity. The activation energies of 27.3 and 85.4 kJ/mol determined for Mg₉₁Ni₄Y₅ (14H + Mg) and Mg_83.3Cu_7.2Y_9.5 (18R) respectively clearly highlight this benefit from galvanic coupling.