Hydrogen production by aluminum corrosion in hydrochloric acid and using inhibitors to control hydrogen evolution

This study reports on the systematic assessment of hydrogen (H₂) production by corrosion of aluminum alloy (AA) in hydrochloric acid (HCl) at different temperature. Rare earth inhibitors, lanthanum (La) and cerium (Ce) have been applied to control the H₂ production process. The production process is based on electrochemical reaction of aluminum (anodic reaction) in the HCl solution, which has a high concentration of hydrogen ions (H⁺), the H⁺ ions are reduced and H₂ is evolved. Preliminary results showed that an increase in temperature of working solution produced an increase of the H₂ production rate. The H₂ production rate increases because acid can prevent aluminum passivation during H₂ evolution. The rare earth inhibitors La and Ce control the H₂ evolution, especially, when using mixture of both inhibitors. This result demonstrates a synergistic effect between the La and the Ce inhibitors. X-ray diffraction studies were performed on the surface structure before and after immersion, and a scanning electron microscope (SEM) was used to study the morphology of the AA.     

A novel method for generating hydrogen by hydrolysis of highly activated aluminum nanoparticles in pure water

A simple method with 100% efficiency for generating pure hydrogen in large scale by hydrolysis of highly activated aluminum in water was established. In this activation method, Aluminum is milled using salt particles (as nano-miller) with different salt to aluminum mole ratios. Due to their brittle nature, salt particles are fractured during milling and their sharp edges chop aluminum particles into pieces. This leads to an increment in hydrolysis kinetics. Meantime, salt particles are driven into newly created surfaces of aluminum particles, producing salt gates that will be removed in water environment, causing hydrogen generation reaction to proceed. The other product of reaction is aluminum oxide hydroxide (AlOOH) which is nature-friendly and can be easily separated from water. The highest average rate of hydrogen generation was 75 ml/min per 1 g of aluminum.     

Room-temperature hydrogen release from activated carbon-confined ammonia borane

In chemical hydrogen storage, nanoconfinement (or nanoscaffolding) is an efficient approach to reduce the size of the particles of boron hydrides such as ammonia borane (AB, NH₃BH₃) at nanoscale while destabilizing its molecular network. It involves the dehydrogenation of AB at temperatures lower than 100 °C and hinders the formation of undesired gaseous by-products such as borazine. Herein, commercial activated carbon (AC) with a specific surface area of 716 m² g⁻¹ and a porous volume of 0.36 cm³ g⁻¹ was used as host material for AB nanoconfinement. A composite activated carbon-ammonia borane (AC@AB) was successfully prepared by infiltration in cold conditions (0 °C). Its dehydrogenation was followed by volumetric method, FTIR, XRD, TGA, DSC, GC–MS and ¹¹B MAS NMR. The most striking result is that the nanoconfined AB, being highly destabilized, dehydrogenates in ambient conditions, even at 3–4 °C. It is demonstrated that dihydrogen is formed according to two pathways that simultaneously take place. The first one is the dehydrogenation through inter- and/or intra-molecular reactions between protonic H and hydridic H of AB, and the second one is the acid-base reaction between protonic H of COO−H groups present on the AC surface and hydridic H of AB.     

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.     

On-demand hydrogen generation by the hydrolysis of ball-milled aluminum composites: A process overview

The hydrolysis of aluminum (Al) is a relatively simple method for on-demand hydrogen generation for niche (low-power, <1 kW) proton exchange membrane fuel cell applications. The hydrolysis of Al in neutral pH water and under standard ambient conditions is prevented by the presence of a thin surficial oxide layer. A promising method to enable Al's spontaneous hydrolysis is by its mechanochemical activation (ball milling) with certain metals (e.g., Bi, Sn, In, Ga). This overview presents several aspects relating to the changes occurring in Al particles during ball milling, e.g., the structural and morphological behavior of Al during ball milling procedures (with and without the presence of activation metals), and the distribution and homogenization of Al and various activation metals. The formation of galvanic cells between anodic Al and cathodic activation metals (relative to Al) is discussed. A summary of the existing Al composites for on-demand hydrogen generation is presented. The paper concludes with a discussion of activation metal recovery, and the effects thereof on the economic feasibility of Al composites for hydrogen generation.     

Elucidating the process of hydrogen generation from the reaction of sodium hydroxide solution and ferrosilicon

For the first time, the process of hydrogen evolution from ferrosilicon 75 using sodium hydroxide solution has been investigated as a function of temperature using a combination of X‐ray photoelectron spectroscopy, X‐ray diffraction and physical measurements. Ferrosilicon 75, a mixture of silicon (~50 wt.%) and iron disilicide (~50 wt.%), has been shown to produce hydrogen by the action of sodium hydroxide solution on the silicon only, with the iron disilicide acting in the role of spectator/protector species for the silicon. Neither iron disilicide alone nor ferrosilicon 45, which does not contain a pure metallic silicon phase, was found to generate hydrogen under similar reaction conditions, further indicating that the presence of a pure metallic silicon phase is essential for hydrogen generation. As the iron disilicide acts as a diluent for the active silicon, it is hypothesized that this would result in a slower release of hydrogen than that which would be obtained from the reaction of silicon alone, which may be useful for applications which require a long‐term, sustained release of hydrogen. A hydrogen yield of 462.5 mL/g and a maximum hydrogen generation rate of 83 mL/min g were obtained within 10 min of reaction with 40 wt.% NaOH at 348 K. © 2017 The Authors. International Journal of Energy Research Published by John Wiley & Sons Ltd.     

Improving hydrogen production from the hydrolysis of ammonia borane by using multifunctional catalysts

A novel multifunctional catalytic system has been developed for efficient hydrogen generation through the hydrolysis of ammonia borane. This system combines Pd NPs with acid sites and amines, which are both task-specific functionalities able to destabilize the N → B dative bond. The acidity of the support (zeolites of different structure and SiO₂/Al₂O₃ ratio) used to disperse the Pd NPs causes an increase in the hydrogen production rate. However, the positive effect of incorporating p-phenylenediamine in the catalyst is much more pronounced, causing a two-fold increase in the activity of the catalyst. The combined effect of the different functionalities yields excellent performance in the hydrolysis of ammonia borane, greatly enhancing the activity of the metal-based catalyst and reducing the activation energy of the catalyzed reaction.     

Preparation and characterization of activated aluminum powder by magnetic grinding method for hydrogen generation

In this paper, activated aluminum powder was prepared by magnetic grinding with a homemade equipment and hydrolyzed in alkaline solution to produce hydrogen. The results showed that the prepared aluminum powder could improve hydrolysis reactivity effectively and have high hydrogen yield in alkaline solution (up to 1340 mL/g). It was found that grinding time, reaction temperature and grinding media could significantly affect the hydrolysis reaction while alloy components had little effect. Aluminum powder ground for 40 min can produce hydrogen 1340 mL/g within 6 min under optimal reaction temperature of 323 K. Copyright © 2013 John Wiley & Sons, Ltd.     

An assessment of the viability of hydrogen generation from the reaction of silicon powder and sodium hydroxide solution for portable applications

The gravimetric hydrogen storage efficiency of silicon has been widely reported as 14 wt.%, suggesting that this material should be an excellent hydrogen generation source for portable applications. However, in the case of the reaction of silicon powder with 20 wt.% sodium hydroxide solution at 50 °C, the observed production of hydrogen fails to realize these high expectations unless a large excess of basic solution is used during the reaction, rendering the use of silicon in such systems uncompetitive compared with chemical hydride based technologies. By investigating the molar ratio of water:silicon from a large excess of water towards the stoichiometric 2:1 ratio dictated by the reaction equation, this study shows that for the reaction of silicon in 20 wt.% sodium hydroxide solution, the quantity of hydrogen produced decreases as the 2:1 ratio expected from the equation for the reaction is approached. Furthermore, in order to reach 80% of the theoretical efficacy, a molar ratio of 20:1, or 12 mL of 20 wt.% sodium hydroxide solution per gram of silicon, would be required. These results suggest that the actual gravimetric hydrogen storage capacity is less than 1%, casting doubts as to whether the use of silicon for hydrogen generation in real systems would be possible. © 2016 The Authors. International Journal of Energy Research published by John Wiley & Sons Ltd.     

Application of activated aluminum powder for generation of hydrogen from water

This work presents a parametric investigation of aluminum–water reaction to generate hydrogen, using a novel activated aluminum powder. An original thermo-chemical process involving a small fraction of a lithium-based activator enables a spontaneous reaction of the activated aluminum particles with water, which otherwise would not react due to the existence of an oxide or hydroxide surface layer. Experiments have shown that a fast, self sustained reaction of activated aluminum with water takes place even at room temperature and, for appropriate operating conditions, results in a practically 100% yield of hydrogen generation. The reaction rate may be controlled by the aluminum particle size, water temperature, metal activation conditions and metal/water mass ratio. The method demonstrates safe and compact hydrogen storage (11 wt% compared to the aluminum). Among its potential applications may be fuel cells, as well as automotive and marine propulsion.     

Hydrogen trapped at intermetallic particles in aluminum alloy 6061-T6 exposed to high-pressure hydrogen gas and the reason for high resistance against hydrogen embrittlement

Hydrogen (¹H) trapped at intermetallic particles (IPs) in an aluminum alloy, 6061-T6, was visualized with secondary ion mass spectrometry (SIMS) by precisely excluding the false signal which is caused by background hydrogen (H_BG). The interference of the H_BG was avoided by a unique continuous pre-sputtering (pre-digging) by a primary ion beam of SIMS into a sample in combination with silicon sputtering prior to the SIMS measurement of the sample and we succeeded in visualizing the exact signal of ¹H trapped by IPs at subsurface layer of the sample charged in high-pressure hydrogen gas. The thermal desorption analysis clarified that the desorption energy (E_d) of the IPs was 200 kJ/mol or higher, which was extremely higher than E_d for lattice interstice, dislocations, and vacancies. High density hydrogen was concentratedly trapped at IPs in the subsurface layer in contact with the hydrogen gas. This nature causes an extremely low effective hydrogen diffusivity of 6061-T6 of the order of 10^?14 m²/s even at 200 °C and may eventually give a high HE resistance to 6061-T6.     

Kinetics study on the generation of hydrogen from an aluminum/water system using synthesized aluminum hydroxides

Kinetics study on the generation of hydrogen from an Al/water system is performed. The reaction is affected by three major factors such as the concentration of hydroxyl ions (pH values), catalysts, and temperature. However, these factors are interacted and sometimes difficult to separate. This study demonstrates how these factors affect the generation of hydrogen in an Al/water system. Aluminum hydroxide, Al(OH)₃ (bayerite phase), synthesized using a chemical solution method, is proved to be a very effective catalyst for the reaction of Al and water. Approximately 95% yield (1300 mL) of hydrogen is produced from 1 g Al in 10 mL water using 3 g Al(OH)₃ catalyst at room temperature within 1 minute. The generation rate of hydrogen is accelerated due to the catalyst Al(OH)₃ and the exothermic heat. In this report, a ball‐mixing process, the ratio of Al:Al(OH)₃:H₂O, and the reacting temperatures are investigated to clarify the effect of catalyst Al(OH)₃. The synthesized Al(OH)₃ catalyst is found to reduce the activation energy of Al/water reaction from 158 kJ/mol to 73.3~76.9 kJ/mol. The roles of hydroxyl ions (ie, pH values), temperature, and catalyst on this phenomenal reaction are explained using a kinetics study and the concept of Fick first law. The 3 factors all improve the flux of hydroxyl ions through the passive Al₂O₃ layer; therefore, the generation of hydrogen is enhanced.     

Highly efficient hydrolysis of magnetic milled powder from waste aluminum (Al) cans with low‐concentrated alkaline solution for hydrogen generation

Currently, recycling waste aluminum materials are of significant importance for reducing environmental pollution and improving economic efficiency. In this paper, aluminum (Al) powder prepared from waste Al cans with magnetic grinding method was directly used in hydrolysis for hydrogen generation. The prepared waste Al cans powder was characterized by scanning electron microscope (SEM), X‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), atomic absorption spectrophotometer (AAS), and density analysis. The results showed that grinding time, NaOH concentration, and reaction temperature affected the hydrolysis rate and hydrogen yield markedly; 1 g of Al cans powder with grinding time of 40 minutes could produce 1296‐mL hydrogen within 6 minutes under the optimal reaction conditions. The reaction kinetics study demonstrated that the hydrolysis of Al cans powder is kinetically controlled while hydrolysis of Al cans flakes is diffusively controlled. The hydrolysis mechanism was also predicted based on the experimental results and kinetic study. The generation of hydrogen from hydrolysis of waste Al cans powder with low‐concentrated alkaline solution is a promising way to diminish environmental pollution and instrument corrosion.     

Development and demonstration of a deployable apparatus for generating hydrogen from the hydrolysis of aluminum via sodium hydroxide

Emergency and backup power is often enabled through the use of petrochemical based fuels and combustion-based generator systems, and while reliable, these backup power systems fail when petrochemical supplies are disrupted due to refinery, oil outages, or transportation delays. Fuel cells in some cases can serve as a backup to these traditional generators, but they also are fuel-limited to supplies of available energy sources. Recent work conducted in our laboratories focused on the development of a “backup” emergency hydrogen generation system that could be employed when existing energy stockpiles have failed or depleted. Specifically, aluminum metal can be used to generate hydrogen for fuel cells via hydrolysis with sodium hydroxide. In this paper, we summarize the engineering work to produce a deployable aluminum to hydrogen generator which is capable of producing 3.75 kg of hydrogen per day from scrap aluminum feedstocks. The generator was built upon an aircraft deployable pallet, allowing for hydrogen to be generated remotely in cases of power and fuel outages.     

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.     

Feasibility of on-board hydrogen production from hydrolysis of Al-Fe alloy for PEMFCs

The feasibility of using the hydrolysis of Al alloys in an on-board hydrogen generation system for PEMFCs is investigated. Hydrogen produced by the hydrolysis of Al-Fe alloys is supplied directly to a PEMFC. The weight-normalized hydrogen generation rate of sheet Al-1Fe is higher than that of cubic Al-1Fe alloy, and its hydrogen generation rate changes little during hydrolysis in alkali water. Furthermore, during the hydrolysis reaction, the water temperature is stable. Hence, Al-1Fe in sheet form is suitable as a source for on-board hydrogen production from hydrolysis in alkali water. At a current of 10 A, the PEMFC presents a voltage of about 0.71 V, which remains stable for 37 min. However, after 37 min, the cell voltage decreases dramatically to 0 V due to a reduction in hydrogen feeding rate by exhaustion of Al-1Fe. It is particularly notable that on-board hydrogen production using the hydrolysis of Al-Fe alloy exhibits self-humidification, supplying humidity automatically without a humidifier.     

Hydrogen generation from photocatalytic hydrolysis of alkali‐metal borohydrides

The controllable photocatalytic hydrolysis of alkali‐metal borohydrides is studied for hydrogen generation in this work. The results indicate that the photocatalysis of P25 TiO₂ controllably promotes the hydrogen generation rates from alkali‐metal borohydride hydrolysis. Its apparent activation energy is calculated to be reduced from 57.20 to 53.86 kJ mol^?1. This is due to the mechanism of photocatalytic hydrolysis: holes (h⁺) react with BH₄‐ and OH^? to form H₂ and B(OH)₄‐, meanwhile electrons (e^?) react with H⁺ to from H₂. In addition, Ti³⁺‐doped TiO₂ with a crystalline‐disordered core‐shell structure can be generated during the photocatalytic hydrolysis process. The consumption of e^? is identified as the rate‐limiting step in photocatalytic hydrolysis process. Copyright © 2017 John Wiley & Sons, Ltd.     

Formation of aluminium hydride (AlH3) via the decomposition of organoaluminium and hydrogen storage properties

Aluminium hydride (AlH₃) is a promising hydrogen storage material due to its competitive hydrogen storage density and moderate decomposition temperature. However, there is no convenient way to prepare/regenerate AlH₃ from (spent) Al by direct hydrogenation. Herein, we report on a novel approach to generate AlH₃ from the decomposition of triethylaluminium (Et₃Al) under mild hydrogen pressures (10 MPa) with the use of surfactants. With tetraoctylammonium bromide (TOAB), the synthesis led to the formation of nanosized AlH₃ with the known α phase, and these nanoparticles released hydrogen from 40 °C instead of the 125 °C observed with bulk α-AlH₃. However, when tetrabutylammonium bromide (TBAB) was used instead of TOAB, larger nanoparticles believed to be related to the formation of β-AlH₃ were obtained, and these decomposed through a single exothermic process. Despite the possibility to form α-AlH₃ under low conditions of temperature (180 °C) and pressure (10 MPa), TOAB stabilised AlH₃ was found to be irreversible when subjected to hydrogen cycling at 150 °C and 7 MPa hydrogen pressure.     

Innovative hydrogen release from sodium borohydride hydrolysis using biocatalyst-like Fe2O3 nanoparticles impregnated on Bacillus simplex bacteria

For the first time in this innovative study, microorganisms such as Bacillus simplex bacteria, mostly used in biological activity studies, are used as a bio-supporter agent of iron to release hydrogen from sodium borohydride hydrolysis at 25.0 ± 0.1 °C. The goal is to investigate thoroughly sodium borohydride hydrolysis catalyzed by Fe₂O₃ nanoparticles impregnated on microorganism such as Bacillus simplex (BS) bacteria (Fe₂O₃@BS NPs) known with strong antibacterial properties, which makes innovative them a candidate for hydrolysis reaction. This study was focused on the preparation, identification, and catalytic use of biocatalyst-like Fe₂O₃@BS NPs for hydrogen release from the sodium borohydride hydrolysis at 25.0 ± 0.1 °C. The characterization results made after and before hydrolysis reaction using by SEM/SEM-EDX, FT-IR, XRD, UV–vis, XPS, DLS, ELS Zeta potential, ESR, and TEM techniques reveal the formation of highly active, stable, durable, and long-lived biocatalysts-like Fe₂O₃@BS NPs.