Preparation of a Mg-Based alloy with a high hydrogen-storage capacity by adding a polymer CMC via milling in a hydrogen atmosphere

Samples with compositions of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt) (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (named Mg-10CMC) were prepared through milling in a hydrogen atmosphere (transformation-involving milling). After activation, Mg-5CMC had a larger amount of hydrogen absorbed in 60 min, U (60 min), than Mg-10CMC and milled Mg at 593 K. At the cycle number (CN) of four, Mg-5CMC had a very high beginning hydrogen uptake rate (1.45 wt% H/min) and a very large effective hydrogen-storage capacity of about 7.4 wt%. Mg-5CMC released 4.76 wt% H in 60 min at 648 K in hydrogen of 1.0 bar. It is believed that CMC melted during milling, and that since CMC has high viscosity, sliding between Mg particles and hardened steel balls was prevented, leading to effective milling (generation of defects and cracks and reduction of particle size). As far as we know, this study is the first in which a polymer CMC was added to Mg to improve the hydrogen uptake and release properties of Mg.     

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.     

Hydrolysis of AlLi/NaBH4 system promoted by Co powder with different particle size and amount as synergistic hydrogen generation for portable fuel cell

Hydrogen generation from the hydrolysis of aluminum lithium/sodium borohydride (referred to as AlLi/NaBH₄) system activated by Co powder with different particle size and amount was evaluated in this paper. The designed aluminum–lithium–cobalt (referred to as Al–Li–Co/NaBH₄) systems including Al-5 wt% Li-50 wt% nano Co, Al-7.5 wt% Li-25 wt% nano Co, Al-5 wt% Li-50 wt% micro Co, and Al-7.5 wt% Li-25 wt% micro Co had 100% hydrogen yield at 323 K. The hydrogen generation rates of these systems were regulated by Co species, Co amount, as well as consecutive runs of NaBH₄ hydrolysis. The underlying activation mechanism, including the formation of Al_0.94Co_1.06 alloy and highly active and stable Co-based catalyst has been elaborated in this study. Experimental data present an inexpensive and highly efficient hydrogen source for portable fuel cell.     

Hydrogen generation from catalytic hydrolysis of sodium borohydride solution using Cobalt–Copper–Boride (Co–Cu–B) catalysts

Co–Cu–B, as a catalyst toward hydrolysis of sodium borohydride solution, has been prepared through chemical reduction of metal salts, CoCl₂·6H₂O and CuCl₂, by an alkaline solution composed of 7.5wt% NaBH₄ and 7.5wt% NaOH. The effects of Co/Cu molar ratio, calcination temperature, NaOH and NaBH₄ concentration and reaction temperature on catalytic activity of Co–Cu–B for hydrogen generation from alkaline NaBH₄ solution have been studied. X-ray diffraction (XRD), scanning electron microscope (SEM) and Nitrogen adsorption–desorption isotherm have been employed to understand the results. The Co–Cu–B catalyst with a Co/Cu molar ratio of 3:1 and calcinated at 400 °C showed the best catalytic activity at ambient temperature. The activation energy of this catalytic reaction is calculated to be 49.6 kJ mol⁻¹.     

Experimental study of hydrogen production process with aluminum and water

This study reported a novel hydrogen production experimental set up, which utilizes the chemical reaction between aluminum and water to produce hydrogen. The developed experimental setup had an aluminum powder spraying subsystem integrated within the overall setup. The effectiveness of this hydrogen production experimental set up was improved using 149-μm aluminum powder, and nitrogen gas as the medium to facilitate the spraying of the aluminum powder. Furthermore, the study utilized sodium hydroxide as the reaction promoter. The various experimental conditions implemented during the testing process included changes in the water temperature and system inputs. The criteria used to evaluate the system performance were the hydrogen yield and hydrogen production rate. The tap water was able to achieve a full hydrogen yield due to its composition, however, the 50% increase in NaOH mass trial was able to achieve a higher yield of 97.15% and 95.44% for the 3g and 6g aluminum sample test respectively. Furthermore, seawater was found to achieve a yield of 58.8%, which can be considered a viable option for future testing. Furthermore, seawater's abundance also adds to its viability for future testing. Also, the study results showed that an increase in reaction temperature best facilitates a chemical reaction taking place. This was evident during the staring temperature of the water test for the 6g aluminum samples. For instance, the maximum hydrogen production rate for the 70 °C was 35.04 mL/s, while the smallest peak for hydrogen production rate was observed using the 40 °C as the starting temperature. The 40 °C test produced a maximum hydrogen production rate value of 27.99 mL/s.     

A semi-global reaction rate model based on experimental data for the self-hydrolysis kinetics of aqueous sodium borohydride

This work studied the self-hydrolysis kinetics of aqueous sodium borohydride (NaBH₄) for hydrogen generation and storage purposes. Two semi-global rate expressions of sodium borohydride and hydrogen ion consumption were derived from an extensive series of batch process experiments where the following parameters were systematically varied: solution temperature (298 K–348 K), NaBH₄ concentration (0.5 wt% to 25.0 wt%), and sodium hydroxide (NaOH) concentration (0.0 wt% to 4.0 wt%). Transient hydrogen generation rates and transient solution pH were measured during the hydrolysis experiments. Given initial conditions (temperature, NaBH₄ concentration, and H⁺ concentration), the two coupled semi-global rate equations can be integrated to obtain the transient time history of H₂ generation (or NaBH₄ consumption) and solution pH (or H⁺ concentration). Comparing analytical results of transient hydrogen generation rate and transient solution pH with experimental data, good agreement was reached for many conditions, especially for elevated solution pH values, levels at which NaBH₄ solutions are used practically.     

Investigating the explosion hazard of hydrogen produced by activated aluminum in a modified Hartmann tube

Metallic powders exposed to water are sources of hydrogen gas that may result in an explosion hazard in the process industries. In this paper, hydrogen production and flame propagation in a modified Hartmann tube were investigated using activated aluminum powder as fuel. A self-sustained reaction of activated aluminum with water was observed at cool water and room temperatures for all treatments. One gram of Al mixed with 5 wt% NaOH or CaO resulted in a rapid rate of hydrogen production and an almost 100% yield of hydrogen generation within 30 min. The flame structures and propagation velocity (FPV) of released hydrogen at different ignition delay times were determined using electric spark ignition. Flame structures of hydrogen were mainly dependent on hydrogen concentration and ignition delay time, likely due to different mechanisms of hydrogen generation and flame propagation. As expected, FPVs of hydrogen in the Hartmann tube increased with ignition delay time. However, the FPV of upward flame propagation was much larger than that of downward flame propagation due to the effect of spreading acceleration at the explosion vent. Once ignited, the FPV of upward flame propagation reached 31.3–162.5 m/s, a value far larger than the 7.5–30 m/s for downward flame propagation. Hydrogen explosion caused by the accumulation of wet metal dust can be far more dangerous than an ordinary hydrogen explosion.     

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.     

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 generation from LiBH4 solution catalyzed by multiwalled carbon nanotubes supported Co–B nanocatalysts for a portable micro proton exchange membrane fuel cell application

LiBH₄ has high hydrogen storage capacities, and could potentially serve as a superior hydrogen storage material. In the hydrolytic process, however, incomplete hydrolysis caused by the agglomeration of its hydrolytic product and un-reacted LiBH₄ limits its full utilization. Furthermore, application of hydrogen generated from LiBH₄ aqueous solution for proton exchange membrane fuel cell (PEMFC) has not been reported yet. In this paper, CNTs-supported Co–B nanocatalyst was used for hydrogen generation from LiBH₄ solution. 22 wt% LiBH₄ alkaline solution can fully release its stoichiometric amount of hydrogen and supply a 2.3 W portable PEMFC stack to run stably. The overall power density of the PEMFC/LiBH₄ solution system with Co–B/CNTs addition is 1020 Wh L⁻¹. Due to the high gravimetric and volumetric hydrogen capacities, the LiBH₄ solution could be used as a promising liquid hydrogen storage material for hydrogen fuel cells-based devices.     

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 from hydrolysis of aluminum/graphite composites with a core–shell structure

Hydrogen generated by hydrolysis of metal aluminum with water is promising for portable fuel cell applications. However aluminum would not react with water to yield hydrogen at ordinary conditions due to the passive oxide film formed on its surface. In the present investigation, the aluminum/graphite composite were prepared by a ball milling process in an attempt to improve the reactivity of aluminum, using sphere-shape aluminum particles and laminate graphite as the initial materials and 2 wt% NaCl as the milling-assisted agent. The TEM observation showed that the Al particles are covered by graphite to form a core–shell structure. Such a Al/graphite composite material exhibited a pronounced hydrolysis reactivity with tap water to generate hydrogen while Al alone did not react with water. The presence of graphite could lower the hydrogen generation reaction temperature below 45 °C. Increasing the reaction temperature could obtain an increased hydrogen generation rate and the maximum hydrogen generation rate of 40 cm³ min⁻¹ g⁻¹ Al was obtained when the reaction temperature was increased to 75 °C. Prolonging milling time could also improve the Al hydrolysis reactivity in the composite particularly at a relatively low temperature. The XRD results identified that the hydrolysis byproducts are bayerite (Al(OH)₃) and boehmite (AlOOH). The microstructure-related hydrolysis reaction mechanism was finally proposed.     

Fast hydrogen generation from NaBH4 hydrolysis catalyzed by carbon aerogels supported cobalt nanoparticles

Carbon aerogels (CAs) with oxygen-rich functional groups and high surface area are synthesized by hydrothermal treatment of glucose in the presence of boric acid, and are used as the support for loading cobalt catalysts (CAs/Co). Cobalt nanoparticles distribute uniformly on the surface of ACs, creating highly dispersed catalytic active sites for hydrolysis of alkaline sodium borohydride solution. A rapid hydrogen generation rate of 11.22 L min⁻¹ g_(cobalt)⁻¹ is achieved at 25 °C by hydrolysis of 1 wt% NaBH₄ solution containing 10 wt% NaOH and 20 mg the CAs/Co catalyst with a cobalt loading of 18.71 wt%. Furthermore, various influences are systematically investigated to reveal the hydrolysis kinetics characteristics. The activation energy is found to be 38.4 kJ mol⁻¹. Furthermore, the CAs/Co catalyst can be reusable and its activity almost remains unchanged after recycling, indicating its promising applications in fuel cell.     

A hybrid aluminum/hydrogen/air cell system

A hybrid aluminum/hydrogen/air cell system is developed to solve the parasitic hydrogen-generating problem in an alkaline aluminum/air battery. A H₂/air fuel cell is integrated into an Al/air battery so that the hydrogen generated by the parasitic reaction is utilized rather than wasted. A systematic study is conducted to investigate how the parasitic reaction and the added H₂/air cell affect the performance of the aluminum/air battery. The aluminum/air sub-cell has an open circuit voltage of 1.45 V and the hydrogen/air sub-cell of 1.05 V. The maximum power density of the entire hybrid system increases significantly by ∼20% after incorporating a H₂/air sub-cell. The system maximum power density ranges from 23 to 45 mW cm⁻² in 1–5 M NaOH electrolyte. The hybrid system is adaptable in concentrated alkaline electrolyte with significantly improved power output at no sacrifice of its overall efficiency.     

Influence of NaOH and Ni catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge

Dewatered sewage sludge was treated with NaOH additive and Ni catalyst in supercritical water in a high-pressure autoclave to examine the effects of separate and combined NaOH additive and Ni catalyst on hydrogen generation. The effects of Ni/NaOH ratio on hydrogen production were also investigated to identify possible catalytic mechanism and interactions. NaOH and Ni, separately or in combination, improved the hydrogen production and hydrogen gasification efficiency. The addition of NaOH additive not only promoted the water–gas shift reaction, but also favored H₂ generation of Ni catalyst by capturing CO₂. The hydrogen yield of combined catalysts with different Ni/NaOH ratios was higher than the theoretical sum of hydrogen yield from the mixture by 10–33%. The largest hydrogen yield, of 4.8 mol per kilogram of organic matter, which was almost five times as much as without catalyst, was achieved with the addition of 3.33 wt% Ni and 1.67 wt% NaOH. The combined NaOH additive and Ni catalyst also improved the gasification of several other dewatered sewage sludges, increasing the hydrogen yield by four to twelve times that seen without catalyst. Combined NaOH additive and Ni catalyst are effective in dewatered sewage sludge gasification at low temperature.     

Carbon nanotubes/aluminum composite as a hydrogen source for PEMFC

Al matrix composites reinforced with 0–5 vol. % carbon nanotubes (CNTs) were fabricated by spark plasma sintering (SPS) to examine their hydrogen generation properties from the hydrolysis of Al in 10 wt. % NaOH solution at room temperature. The 5 vol. % CNTs/Al composite exhibits a maximum hydrogen generation rate of 120 ml/min g, which is about 6 times higher than that of Al without CNTs due to the synergetic effects of the porous Al matrix, which has a large reaction area and galvanic corrosion between the Al matrix and the CNTs. The hydrogen gas generated from the hydrolysis of the CNTs/Al composite has high purity without any production of undesirable CO. PEMFC produced electricity at 10 A and 0.73 V for 13 min, with hydrogen generated from the hydrolysis of 3.5 g–5 vol. % CNTs/Al composite. The CNTs/Al composite was effectively used as a hydrogen source for PEMFC.     

Hydrogen generation from hydrolysis of solid sodium borohydride promoted by a cobalt–molybdenum–boron catalyst and aluminum powder

Direct use of solid sodium borohydride (NaBH₄) to react with minimized amount of water provides a straightforward means for increasing the hydrogen density of the system. But meanwhile, the resulting solid–liquid reaction system always suffers from serious kinetic problem. Our study found that the cobalt–molybdenum–boron (Co–Mo–B) catalyst prepared using an ethylene glycol solution of cobalt chloride is highly effective for promoting the hydrolysis reaction of solid NaBH₄. Particularly, a combined usage of small amounts of Co–Mo–B catalyst, aluminum powder and sodium hydroxide enables a rapid and high-yield hydrogen generation from the hydrolysis reaction of solid NaBH₄. A systematic study has been conducted to investigate the property dependence of the system on the components. In addition, the by-products of reaction were analyzed using powder X-ray diffraction and thermogravimetry/differential scanning calorimetry/mass spectroscopy techniques. Our study demonstrates that the multi-component system with an optimized composition can fulfill over 95% fuel conversion, yielding 6.43 wt% hydrogen within 3 min. The favorable combination of high hydrogen density, fast hydrogen generation kinetics and high fuel conversion makes the newly developed solid NaBH₄-based system promising for portable hydrogen source applications.     

Hydrogen generation from splitting water with Al–Bi(OH)3 composite promoted by NaCl

In this paper, a novel Al–Bi(OH)₃ system hydrogen-generating material is investigated. Hydrolysis experiments show that the hydrolysis properties of the Al–10 wt% Bi(OH)₃ composite are significantly improved by doping with sodium chloride, and the Al–10 wt% Bi(OH)₃–5 wt% NaCl composite has a low activation energy (10.4 kJ mol⁻¹). With the further optimization of milling time, the hydrogen yield of Al–10 wt% Bi(OH)₃–5 wt% NaCl composite reaches 1000 mL g⁻¹ in 1 min. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive spectroscopy and thermogravimetric analysis are applied to characterize the composite and explore the hydrolysis mechanism. The characterization results show that the activation of aluminum mainly comes from three factors: (1) The formation of alumina during ball milling plays an important role in preventing the agglomeration between Al–Bi, Al–Al and Bi–Bi; (2) Bismuth generated during ball milling can form micro-galvanic cell with aluminum to promote the corrosion of aluminum; (3) Sodium chloride as a grinding aid contributes to crush aluminum powder, and chloride ions facilitate the corrosion of aluminum in the hydrolysis process. In addition, the drying method and initial water temperature have a great influence on by-products. The composite is expected to be used in mobile emergency fuel cell due to its rapid hydrogen production capacity.     

Hydrolytic reaction of waste aluminum foils for high efficiency of hydrogen generation

Hydrolyzed waste aluminum foil in low alkaline aqueous solution and concomitant additives are evaluated to generate hydrogen gas. The result of hydrogen generation using wasted Al foil is efficient in comparison with traditional Al powder. A polythene film coated on waste Al foil was removed by immersing into nitric acid for 5 h prior to hydrolyzed reaction. Low alkaline solution (0.75 M NaOH) combined with Bi additives at elevating temperature (70 °C) in waste Al foil-water hydrolysis system enable to increase hydrogen generation rate to 30 ml s^?1 g^?1 and total volume 1300 ml g^?1. The optimized result is attributed to the micro-galvanic cell formation between Al/Bi and removing hydroxide on Al foil surface by alkaline solution. In this report we develop low cost and waste recovery by hydrolyzing waste Al foil. High efficiency of hydrogen generation is achieved by low alkaline concentration and reducing activation energy. Al oxidation mechanism is explained by the linear-parabolic growth model and polarization curves indicate that corrosion potential of Al foils did not abruptly degrade and the corrosion capability with reliability were verified.     

Microstructural control of catalyst-loaded PVDF microcapsule membrane for hydrogen generation by NaBH4 hydrolysis

Polymer microcapsules were prepared and used as catalyst support for hydrogen generation from sodium borohydride. Polyvinylidene fluoride (PVDF) porous microcapsule membranes immobilized with metal salt (cobalt (II) chloride hexahydrate) catalyst and cobalt–boron catalyst were prepared, denoting them as MS and MP method respectively. Non-solvent coagulation bath consisting of a mixture of water and isopropanol (IPA) were used to prepare the microcapsules. The compositions of the non-solvents were changed with a ratio of 10:90 (v/v%)–50:50 (v/v%) with 1 wt% NaOH and 0.5 wt% NaBH₄. The effects of a number of parameters such as the kinds of additives, the size and morphology of the resulting microcapsules were studied on hydrogen generation. The structures and physical–chemical properties of the metal catalyst-loaded microcapsule membranes were characterized using SEM and EDX. The MS method used in preparing the microcapsule showed good performance in hydrogen generation from sodium borohydride. There was also improved performance in hydrogen generation with increasing IPA composition used in the metal salts loaded microcapsule preparation. The control of three regions inside the microcapsules (hollow region, crust region and skin layer) as well as the specific loading of metal catalysts gave a good hydrogen generation performance. The catalyst-loaded microcapsule also maintained an appreciable performance and stability after many runs of hydrolysis reaction for the hydrogen generation.