Experimental investigation of solar assisted hydrogen production from water and aluminum

Sustainable production of hydrogen at high capacities and low costs is one the main challenges of hydrogen as a future alternative fuel. In this paper, a new hydrogen production system is designed and fabricated to investigate hydrogen production using aluminum and solar energy. Numerous experiments are performed to evaluate the hydrogen production rate, quantitatively and qualitatively. Moreover, correlations between the total hydrogen production volume over time and other parameters are developed and the energy efficiency and conversion ratio of the system are determined. Also, a method is developed to obtain an optimal and stable hydrogen production rate based on system scale and consumed materials. It is observed that at low temperatures, the hydrogen production volume, efficiency and COP of the system increase at a higher sodium hydroxide molarity. In contrast, at high temperatures the results are vice versa. The maximum hydrogen production volume, hydrogen production rate, reactor COP and system efficiency using 0.5 M NaOH solution containing 3.33 g lit^?1 aluminum at 30 °C are 6119 mL, 420 mL min^?1, 1261 mL H₂ per 1 g of Al, and 16%, respectively.     

Enhanced rate of hydrogen production by corrosion of commercial aluminum

Hydrogen has been produced by corrosion of technical grade aluminum Al-6061. Al-6061 is an alloy containing a small percentage of several elements, mainly Mg and Si. It has been verified that this alloy is corroded faster and produces more hydrogen per unit of time than pure aluminum. This result is due to facilitation of corrosion at grain boundaries in aluminum alloys. Hydrogen production rates have been dramatically accelerated by decreasing the size of aluminum particles. Thus Al-6061 turnings have been produced with a lathe and then they were compressed to create porous pellets with a density of 72% compared to solid pure aluminum. These pellets can produce hydrogen in concentrated KOH solutions at very high rates reaching 66.7 ml min⁻¹. This method is safe and reproducible and it may find important application as a means to “store” hydrogen in the form of porous Al-6061 pellets.     

Electrochemical hydrogen and electricity production by using anodes made of commercial aluminum

Two commercial aluminum alloys have been studied as anodes for simultaneous electrochemical hydrogen and electricity production, as compared with pure aluminum. Both are very active in corrosive hydrogen production and functional as anodes in aluminum-air batteries. Both produced approximately 3 times more hydrogen than pure aluminum while their electrochemical characteristics were substantially preserved with only small modifications with respect to pure aluminum. Devices employing commercial aluminum anodes can be constructed and may be used for producing both hydrogen and electricity at the expense of aluminum.     

Synergistic hydrogen generation from aluminum, aluminum alloys and sodium borohydride in aqueous solutions

A new method to produce high purity hydrogen using reactions of aluminum and sodium borohydride with aqueous alkaline solutions is described. This process mainly consumes water and aluminum (or its alloys) which are cheaper raw materials than the borohydride. As a consequence, this process could be competitive for in situ production of hydrogen. Moreover, a synergistic effect has been observed in hydrogen production rates and yields combining aluminum or aluminum alloys with sodium borohydride in aqueous solutions. Good results have been obtained for powders of Al, Al/Si and Al/Co alloys. The development of this idea could improve yields and reduce costs in power units based on fuel cells which use borohydride as raw material for hydrogen production.     

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.     

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.     

Combined hydrogen production and power generation from aluminum combustion with water: Analysis of the concept

In this paper the combined production of hydrogen and power based on the aluminum combustion with water is investigated. Furthermore, a concept system is proposed that is potentially able to provide pressurized hydrogen and high temperature steam along with heat and work at the crankshaft. The system demonstrates high energy conversion efficiency, and it fully complies with environment sustainability requirements.     

Molten salt-enhanced production of hydrogen by using skimmed hot dross from aluminum remelting at high temperature

The skimmed hot dross generated in secondary production of aluminum contains high amount of metallic aluminum and also the potential heat. An innovative process for hydrogen generation using skimmed hot dross from aluminum remelting industry is proposed in this work. The reaction behavior between skimmed dross and water steam in terms of hydrogen evolution variation at high temperature is studied. The results show that the inherent salts in the dross could accelerate the hydrogen generation at temperature region of 600–850 °C by dissolving the amorphous and γ-Al₂O₃ product layer in water steam atmosphere. The maximum aluminum conversion degree was found to be more than 60%, and the hydrogen evolution rate was over 60 cm³ g^?1 min^?1 when skimmed dross with 30 wt% Al was used in non-isothermal test. The mechanism related to the texture responding of alumina layer with different amount of salts additives and temperatures is discussed.     

Mechanochemical activation of aluminum with gallams for hydrogen evolution from water

A new method has been developed for mechanochemical activation of aluminum: the metal is treated with a gallam, and the “alloy” is processed in a high-energy ball mill. Kinetic parameters of the reaction between activated aluminum and water (hydrogen evolution rate and yield) under standard conditions are presented. The dependences of the hydrogen evolution rate on the composition and amount of the gallam and on the reaction temperature are reported. The storage behavior of activated aluminum has been investigated.     

Electrochemically engineering defect-rich nickel-iron layered double hydroxides as a whole water splitting electrocatalyst

It is well proved that fabricating more defects on basal plane of layered double hydroxides (LDHs) is one of effective ways to boost the electrocatalytic performance for oxygen evolution reaction (OER). For the first time, the nickel iron LDHs (NiFe LDHs) with hierarchical morphology and abundant defects are simultaneously constructed by one-step electrodeposition (ED) strategy with easy operation, time-saving and green chemistry. Remarkably, the morphology is elaborately tailored by changing the species of doped anions which is unique. Also, the X-ray photoelectron spectroscopy (XPS) results elucidate that the Fe sites are in electron-rich state in LDHs which is revealed to enhance the catalytic activity strongly arising from the generation of oxygen vacancy. To deliver the current density of 10 mA cm⁻², the optimal NiFe LDHs require the overpotential of 128, 106 mV for OER and hydrogen evolution reaction (HER), and achieve 100 mA cm⁻² at the overpotential of 237, 242 mV, respectively. As a bifunctional electrocatalyst, the NiFe LDHs exhibit the current density of 10 mA cm⁻² at a cell voltage of 1.55 V and 100 mA cm⁻² at 1.76 V, which are lower than that of most of benchmarking materials reported previously.     

Apparent kinetics of hydrogen production with water-slurried aluminum delivery in aqueous sodium hydroxide solutions

Kinetic models were fit to experimental hydrogen production data from a stirred microspherical aluminum corrosion reactor, one model for each of two Al initial conditions prior to immersion in aqueous sodium hydroxide at pH 13.17–13.48: (i) air-dry, and (ii) water-suspended for 0.5–2 h, of which the latter has not been studied. Data fitting was fairly precise $\left(R^2\mathrm{>}0.97\right)$, and results were confirmed by comparison to shrinking core models of the reaction time. Key findings were a low reaction order in hydroxide (0.46 for slurry and 0.55 for dry based reactions), along with relatively lower apparent activation energy and frequency factor for the slurry reactions (60.15, versus 64.75 kJ/mol for initially dry Al, with $\text{SE}\approx 2.5\text{kJ}/\text{mol}$), and just a slight effect of Al delivery mode on overall rates. Explanatory rate-limiting mechanisms were hypothesized following a model of a dissolving film over the corroding Al with analysis of diffuse electric double layer charging and transport resistance effects.     

A mini-type hydrogen generator from aluminum for proton exchange membrane fuel cells

A safe and simple hydrogen generator, which produced hydrogen by chemical reaction of aluminum and sodium hydroxide solution, was proposed for proton exchange membrane fuel cells. The effects of concentration, dropping rate and initial temperature of sodium hydroxide solution on hydrogen generation rate were investigated. The results showed that about 38 ml min⁻¹ of hydrogen generation rate was obtained with 25 wt.% concentration and 0.01 ml s⁻¹ dropping rate of sodium hydroxide solution. The cell fueled by hydrogen from the generator exhibited performance improvement at low current densities, which was mainly due to the humidified hydrogen reduced the protonic resistivity of the proton exchange membrane. The hydrogen generator could stably operate a single cell under 500 mA for nearly 5 h with about 77% hydrogen utilization ratio.     

Aluminum and aluminum alloys as sources of hydrogen for fuel cell applications

Production of hydrogen using aluminum and aluminum alloys with aqueous alkaline solutions is studied. This process is based on aluminum corrosion, consuming only water and aluminum which are cheaper raw materials than other compounds used for in situ hydrogen generation, such as chemical hydrides. In principle, this method does not consume alkali because the aluminate salts produced in the hydrogen generation undergo a decomposition reaction that regenerates the alkali. As a consequence, this process could be a feasible alternative for hydrogen production to supply fuel cells. Preliminary results showed that an increase of base concentration and working solution temperature produced an increase of hydrogen production rate using pure aluminum. Furthermore, an improvement of hydrogen production rates and yields was observed varying aluminum alloys composition and increasing their reactive surface, with interesting results for Al/Si and Al/Co alloys. The development of this idea could improve yields and reduce costs in power units based on fuel cells which use hydrides as raw material for hydrogen production.     

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.     

Operating maps of a combined hydrogen production and power generation system based on aluminum combustion with water

The performance of a novel hydrogen production and energy conversion system based on the aluminum-water reaction is addressed by means of a lumped and distributed parameter numerical approach. The interest on this type of technology arises because of the possibility of obtaining at the same time different secondary energy sources, such as hydrogen and heat and mechanical work, with very low pollutant and greenhouse gas emissions.In this paper the numerical models of the main components adopted in the system are developed, including the combustion chamber, the steam/hydrogen turbine and the heat exchangers. The behavior of the whole system is investigated for different configurations and energy conversion cycles, i.e. electric energy production only and combined heat and power production, in order to determine the operating maps in terms of efficiency, power output, pressure and temperature in the main sections, mass flow rates and the hydrogen yield. The numerical analysis of the thermo-dynamic behavior of the power unit is aimed at assessing the guidelines that will lead to the construction of a first prototype of this system.Finally, the use of a cogeneration system based on the aluminum combustion with water system for on-site small scale hydrogen production for feeding a hydrogen refueling station is explored. The proposed system is compared with other technologies as well as the case of large scale hydrogen production and delivery.     

Conjugated processes of bulk aluminum and hydrogen combustion in water-oxygen mixtures

The article deals with the investigation of the combustion of aluminum bulk samples in water vapor, an aqueous solution of hydrogen peroxide (33.1 wt%), and water-oxygen mixture at uniform heating of the reactor (1 K/min) up to 773 K. It is revealed that the major portion of hydrogen peroxide is decomposed directly in aqueous solution. The resulting oxygen, as well as oxygen added to the water, provided oxidation of only a part of hydrogen (≈25%) released during the complete oxidation of aluminum by water. The time dependences of the reactants’ temperature and pressure, as well as the temperature corresponding to the onset of the H₂ release were determined. The most intense oxidation of aluminum in water vapor was noted within the temperature range of 593–769 K, as well as in a hydrogen peroxide solution at 548–693 K, and in H₂O/O₂ mixture at 567–742 K. It is revealed that the oxidation of hydrogen with oxygen intensifies water oxidation of aluminum to a greater extent than it follows from the heat effects of H₂ oxidation. As a result of oxidation, a loose powder of aluminum oxide nanoparticles was obtained.     

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.     

Spatially resolved hydrogen desorption from aluminum hydride observed by magnetic resonance imaging

Light metal hydrides represent a promising class of materials for hydrogen storage. However, there are several technical challenges to overcome before their potential can be realized. Key among these is the often adverse absorption and desorption kinetics, which are a function of intrinsic reaction rates and practical operating temperatures. Modifying and controlling these kinetics require a thorough understanding of the hydrogen absorption and desorption processes. In this study, we have investigated the thermal decomposition of aluminum hydride, AlH₃, with Magnetic Resonance Imaging in order to visualize spatially the progress and extent of the reaction.     

In situ generation of hydrogen from water by aluminum corrosion in solutions of sodium aluminate

A new process to obtain hydrogen from water using aluminum in sodium aluminate solutions is described and compared with results obtained in aqueous sodium hydroxide. This process consumes only water and aluminum, which are raw materials much cheaper than other compounds used for in situ hydrogen generation, such as hydrocarbons and chemical hydrides, respectively. As a consequence, our process could be an economically feasible alternative for hydrogen to supply fuel cells. Results showed an improvement of the maximum rates and yields of hydrogen production when NaAlO₂ was used instead of NaOH in aqueous solutions. Yields of 100% have been reached using NaAlO₂ concentrations higher than 0.65 M and first order kinetics at concentrations below 0.75 M has been confirmed. Two different heterogeneous kinetic models are verified for NaAlO₂ aqueous solutions. The activation energy (E_a) of the process with NaAlO₂ is 71 kJ mol⁻¹, confirming a control by a chemical step. A mechanism unifying the behavior of Al corrosion in NaOH and NaAlO₂ solutions is presented. The application of this process could reduce costs in power sources based on fuel cells that nowadays use hydrides as raw material for hydrogen production.