A hydrogen purification and storage system using metal hydride

This work is to develop a new hydrogen purification and storage system for daily start and stop (DSS) operations. The new system enables us to minimize emissions of carbon dioxide by using compact and highly efficient fuel cells. The new system first removes carbon monoxide, which is poisonous to metal hydride, from reformed gas by using a special carbon monoxide adsorbent. After removing carbon monoxide, the reformed gas is introduced to a metal hydride bed to purify and store hydrogen. Some 100 NL/h Laboratory scale apparatus was operated in daily start and stop operations for 100 cycles for a total of 150 h with quite good efficiency. The new process has achieved an 83% hydrogen recovery ratio in one-month DSS operations.     

Two-step water splitting thermochemical cycle based on iron oxide redox pair for solar hydrogen production

This study deals with solar hydrogen production from the two-step iron oxide thermochemical cycle (Fe₃O₄/FeO). This cycle involves the endothermic solar-driven reduction of the metal oxide (magnetite) at high temperature followed by the exothermic steam hydrolysis of the reduced metal oxide (wustite) for hydrogen generation. Thermodynamic and experimental investigations have been performed to quantify the performances of this cycle for hydrogen production. High-temperature decomposition reaction (metal oxide reduction) was performed in a solar reactor set at the focus of a laboratory-scale solar furnace. The operating conditions for obtaining the complete reduction of magnetite into wustite were defined. An inert atmosphere is required to prevent re-oxidation of Fe(II) oxide during quenching. The water-splitting reaction with iron(II) oxide producing hydrogen was studied to determine the chemical kinetics, and the influence of temperature and particles size on the chemical conversion. A conversion of 83% was obtained for the hydrolysis reaction of non-stoichiometric solar wustite Fe_(1−y)O at 575 °C.     

Modeling hydrogen production for injection into the natural gas grid: Balance between production,demand and storage

For hydrogen injection into the natural gas grid a model has been developed to obtain a balance between production, demand and storage. Due to the relation between atmospheric temperature and natural gas demand, the variation in the gas demand is very large. Consequently, in case of a more or less constant mole fraction of hydrogen in natural gas the demand for hydrogen will also vary considerably. Injection of ten percent hydrogen into the natural gas (in The Netherlands) requires already the production of about two billion cubic meters of hydrogen per year. Considering the variation in demand, most probably large-scale storage of hydrogen is needed because the flexibility in production is limited for economic and technical reasons. On the other hand, storage of hydrogen will also increase the costs. In this paper, we report on the balance between hydrogen production, demand and storage. A number of variables for controlling the production will be taken into consideration. Also the possibility of production without a buffer will be discussed.     

Perovskite oxides successfully catalyze the electrolytic hydrogen production from oilfield wastewater

Although Pt/C has long been regarded as the most effective HER catalyst, the use of complicated water systems is challenged by high costs and contaminant interference. Therefore, it was shown in this paper that a low-cost perovskite oxide, SrCo_0.7Fe_0.3O_3-δ(SCF-X, where X denotes annealing temperature), could be used in oil-field wastewater to promote electrochemical reactions for hydrogen production and that its catalytic activity can be impacted by calcination temperature. And, the outstanding catalytic activity of SCF-800 and 850 is primarily caused by crystal structure distortions and the presence of Co³⁺/Co⁴⁺ coupling pairs as a result of electron transfer between Co and Fe, which increases the concentration of reactive oxygen species. Furthermore, there is now more interest in SCF-850 due to its exceptional stability. In complicated systems, the current work provides a feasible route for perovskite catalysts to produce hydrogen.     

Molten salt electrochemical production and in situ utilization of hydrogen for iron production

The low voltage electrochemical extraction of iron from iron oxide powder is reported. Hydrogen gas can be generated in molten LiCl at 660 °C by the electrochemical decomposition of steam at a voltage as low as only 0.97 V. Interestingly, individual submicrometer-sized iron oxide particles simply immersed in the melt can directly be reduced to semi-spherical metallic iron particles with a particle size of about 5 μm under the influence of hydrogen gas generated in-situ in the molten salt. The direct reduction of Fe₂O₃ powder, instead of sintered Fe₂O₃ pellets, which are commonly used as the cathode in the conventional molten salt electro-deoxidation processes, enhances the simplicity, energy consumption and the reaction kinetics of the molten salt hydrogen reduction process. In this method, the bottom surface of the graphite crucible acts as the cathode, resulting in a high rate of hydrogen cations discharge, hence a high current. The high temperature and low voltage characteristics of this method offer a scalable strategy for direct reduction of metal oxide particles in a green and low-cost way, where there is no requirement for the compaction of metal oxide powders into pellets. The mechanism involved in this hydrogen production and utilization methodology is discussed.     

Self-oriented iron oxide nanorod array thin film for photoelectrochemical hydrogen production

In this work, iron films were deposited on fluorine-tin-oxide coated glass substrate using radio frequency sputtering. Self-oriented iron oxide nanorod array thin films were obtained by anodizing the sputtered films. Anodization was carried out in an ethylene glycol solution containing 0.1 M NH₄F and various content of water. We studied the mechanism of anodization of iron thin films, and investigated the effects of some parameters on the properties of the iron oxide thin films.     

Catalytic hydrogen storage in cerium nickel and zirconium (or aluminium) mixed oxides

Interaction of hydrogen with a series of cerium nickel and zirconium (or aluminium) mixed oxides _CeM0.5NixOy${\mathrm{CeM}}_{0.5}{\mathrm{Ni}}_x{\mathrm{O}}_y$ (M=Zr$\mathrm{M}=\mathrm{Zr}$ or Al, 0?x?3$0?x?3$) has been studied in the 50–800 °C temperature range. Hydrogenation of 2-methyl-1,3-diene (isoprene) under helium flow in the absence of gaseous hydrogen is used to reveal and titrate reactive hydrogen species present in the solid previously treated under _H2${\mathrm{H}}_2$ at various temperatures. The _CeM0.5NixOy${\mathrm{CeM}}_{0.5}{\mathrm{Ni}}_x{\mathrm{O}}_y$ mixed oxides are large catalytic hydrogen reservoirs and among the solids studied, the highest amount of hydrogen (about 10 wt%, 540 g/L) is stored in _CeZr0.5Ni1Oy${\mathrm{CeZr}}_{0.5}{\mathrm{Ni}}_1{\mathrm{O}}_y$ pretreated in _H2${\mathrm{H}}_2$ at about 200 °C. Compared to the binary mixed oxides _CeNixOy${\mathrm{CeNi}}_x{\mathrm{O}}_y$, the presence of M allows to increase the hydrogen storage and give a better stability to the system, in particular, with temperature. Different physico-chemical techniques (TPR, TGA …) have been used to characterize the solids studied.     

Simplified, plate-type Pd membrane module for hydrogen purification

A simplified, plate-type membrane module for hydrogen separation has been designed. It can be constructed without the need for a complicated bonding apparatus and tested without any module chamber. A double o-ring sealing mechanism was applied for easier assembly and ensured module-sealing. The assembled membrane module has good performance in a high-pressure test. The module is suitable for application as a compact hydrogen purification system due to its simple assembly.     

Developing a mathematical tool for hydrogen production,compression and storage

Among the few lessons learned presented in the literature, authors put in evidence the on-going need to investigate on station components and their integration. The specific power consumption of station units with on-site hydrogen generation is often subject to uncertainty, and it would have been desirable to find more details about the energy contribution of each component. To address this gap, this paper focuses on the development of a mathematical modeling as a dynamic and multi-physical design tool to predict the energy performance of hydrogen production systems. Particularly, the model aims to describe and analyze the energy performance of two different electrolyzer technologies (PEM and Alkaline), integrated with a compressor system and gaseous buffer storage. Multiple tank options and a switching strategy are investigated, as well as a control system to simulate a real infrastructure operation. Auxiliaries and components related to the thermal management system have been also included. A carbon-footprint analysis follows the energy one, focusing on the CO₂ emission reduction. Comparisons between literature data and model show that the hydrogen system proposed model is suitable to evaluate systems with respect to energy efficiency and system performance. The model could be a powerful tool for exploring control strategies and understanding the contributions to the overall energy consumption from the various internal components as a guide to researchers aiming for improved performance.     

Molybdenum addition to modified iron oxides for improving hydrogen separation in fixed bed by redox processes

A system to produce hydrogen with high purity and without CO₂ emissions briefly consists of two operating units: production and separation. The coupling of the steam-iron process to the cracking of methane can manage that goal. However the steam-iron process needs an active and stable redox solid at moderate temperatures. The most suitable (pure iron oxide) suffers quick and strong deactivation mainly due to the structural changes upon reduction-oxidation cycles. Among those tested in our laboratory, one promising solid was proposed: 98 wt%Fe₂O₃–1.75 wt%Al₂O₃–0.25 wt%CeO₂. In this work, the expensive and rare cerium has been substituted by molybdenum. After optimizing the Mo amount in the solid, the long lasting experiments show that the new triple oxide, 98 wt%Fe₂O₃–1.75 wt%Al₂O₃–0.25 wt%MoO₃, in spite of some initial deactivation, maintains slightly better hydrogen production rates than the cerium sample. At temperature and conditions studied the Mo-solid was able to run, without coke formation, under real exhaust gas from natural gas thermocatalytic decomposition, producing about 8.1 g of high purity (>99.995%) hydrogen h⁻¹ kg of solid⁻¹. This means a natural gas processing of about 68 Nm³ h⁻¹ 1000 kg of solid⁻¹ (at 67% conversion of methane to hydrogen).     

Time and frequency domain analysis of hydrogen permeation across PdCu metallic membranes for hydrogen purification

Hydrogen permeation is a process used in the industry for purification purposes. Palladium alloys (PdAg and PdCu) are commonly used as membrane material. In this communication, we report on the kinetics of hydrogen permeation across Pd_0.47Cu_0.53 metallic membranes which can be used in catalytic crackers of biofuels. The permeation mechanism is a multi-step process including surface chemisorption of molecular hydrogen (upstream side of the membrane), hydrogen diffusion across bulk regions, hydrogen recombination (downstream side of the membrane) and evolution. The role of different operating parameters (temperature, surface state, sample microstructure) is analyzed and discussed using both time and frequency domain experiments. Experimental pneumato-chemical impedance diagrams show that there is no significant rate-limitation at surfaces, except at low temperatures close to room temperature. Diffusion-controlled transport of hydrogen across the membrane is rate-determining. However, the value of the hydrogen diffusion coefficient does not rise exponentially with operating temperature in the 40–400 °C temperature range under investigation, as expected for a thermally activated diffusion process. At temperatures as low as 300 °C, new rate-limitations appear. They can be attributed to recrystallization and/or phase transformation processes induced by temperature and the presence of hydrogen.     

Enhancement of anaerobic hydrogen production by iron and nickel

The effects of iron and nickel on hydrogen (H₂) production were investigated in a glucose-fed anaerobic Continuous Flow Stirred Tank Reactor (ACSTR). Both iron and nickel improved the reactor performance and H₂ production was enhanced by 71% with the sole iron or nickel supplementation. In all cases, H₂ production yield was increased by lowering both ethanol and total metabolites production and increasing butyrate production. Furthermore, iron and nickel slightly increased biomass production while glucose degradation decreased with the supplementation of nickel. Dynamic changes in bacterial composition as analyzed by 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE) revealed that hydrogen was produced mainly by Clostridium butyricum strains and that nickel addition decreased the microbial diversity.     

Advantages of integration with industry for electrolytic hydrogen production

This paper evaluates possible synergies with industry, such as heat and oxygen recovery from the hydrogen production. The hydrogen production technology used in this paper is electrolysis and the calculations include the cost and energy savings for integrated hydrogen production. Electrolysis with heat recovery leads to both cost reduction and higher total energy efficiencies of the hydrogen production. Today about 15–30% of the energy supplied for the production is lost and most of it can be recovered as heat. Utilization of the oxygen produced in electrolysis gives further advantages. The integration potential has been evaluated for a pulp and paper industry and the Swedish energy system, focusing on hydrogen for the transportation sector. The calculated example shows that the use of the by-product oxygen and heat greatly affects the possibility to sell hydrogen produced from electrolysis in Sweden. Most of the energy losses are recovered in the example; even gains in energy for not having to produce oxygen with cryogenic air separation are shown. When considering cost, the oxygen income is the most beneficial but when considering energy efficiency, the heat recovery stands for the greater part.     

Catalytic performance of CoAlZn and NiAlZn mixed oxides in hydrogen production by bio-ethanol partial oxidation

CoAlZn and NiAlZn mixed oxides were prepared by sol–gel method and tested in partial oxidation of bio-ethanol (POE). At lower temperatures, CoAlZn showed higher ethanol conversion and higher selectivity to H₂ and CO than NiAlZn. At higher temperatures, ethanol conversion on both catalysts reached 100%, while selectivity (S) to H₂ and CO became higher on NiAlZn. At 750 °C, NiAlZn showed S(H₂) of 95%, S(CO) of 90%, while for CoAlZn these values were 90% and 83% respectively. Both catalysts were resistant to coking, but the amount of carbon deposits was still lower on NiAlZn. During 50 h on-stream, ethanol conversion and selectivity to H₂ and CO on NiAlZn remained unchanged demonstrating stable performance of the catalyst.     

Magnesium and iron loaded hollow glass microspheres (HGMs) for hydrogen storage

The development of a safe and efficient method for hydrogen storage is essential for the use of hydrogen with fuel cells for vehicular applications. Hollow glass microspheres (HGMs) have characteristics suitable for hydrogen storage and are expected to be a potential hydrogen carrier to be used for energy release applications. The HGMs with 10–100 μm diameters, 100–1000 Å pore width and 3–8 μm wall thicknesses are expected to be useful for hydrogen storage. In our research we have prepared HGMs from amber glass powder of particle size 63–75 μm using flame spheroidisation method. The HGMs samples with magnesium and iron loading were also prepared to improve the heat transfer property and thereby increase the hydrogen storage capacity of the product. The feed glass powder was impregnated with calculated amount of magnesium nitrate hexahydrate salt solution to get 0.2–3.0 wt% Mg loading on HGMs. Required amount of ferrous chloride tetrahydrate solution was mixed thoroughly with the glass feed powder to prepare 0.2–2 wt% Fe loaded HGMs. Characterizations of all the HGMs samples were done using FEG-SEM, ESEM and FTIR techniques. Adsorption of hydrogen on all the Fe and Mg loaded HGMs at 10 bar pressure was conducted at room temperature and at 200 °C, for 5 h. The hydrogen adsorption capacity of Fe loaded sample was about 0.56 and 0.21 weight percent for Fe loading 0.5 and 2.0 weight percentage respectively. The magnesium loaded samples showed an increase of hydrogen adsorption from 1.23 to 2.0 weight percentage when the magnesium loading percentage was increased from 0 to 2.0. When the magnesium loading on HGMs was increased beyond 2%, formation of nano-crystals of MgO and Mg was seen on the HGMs leading to pore closure and thereby reduction in hydrogen storage capacity.     

Firmicutes with iron dependent hydrogenase drive hydrogen production in anaerobic bioreactor using distillery wastewater

Distillery wastewater rich in organics is an inexpensive renewable resource for making first generation biofuel. Distillery wastewaters are mostly treated via the biomethanation route; however, in this study the conditions in sequential batch reactor (SBR) are being set to develop and analyze the microbial community that opted for hydrogen production. An optimum performance condition for a bioreactor was achieved after 40 days of operation, which gave substrate degradation rate of 0.72 kg/m³-day with volumetric hydrogen production of 0.32 mol H₂/m³-day. Study proposes that the dominant Delftia sp., a hydrogen oxidizing bacterium has been replaced during hydrogen production mode with dominant Anaerofilum sp., an anaerobic Firmicute and the iron dependent hydrogenases dominated as functional gene for hydrogen production. Future studies are required where process-engineering interventions could be applied to improve the hydrogen driving biochemical process.     

Effect of temperature and iron concentration on the growth and hydrogen production of mixed bacteria

Anaerobic mixed culture acclimated with sucrose was used as inoculum in batch experiments to investigate the effects of various parameters on biological hydrogen production from sucrose. In particular, the effect of the culture temperature has been investigated in detail. The optimum of the iron concentration in the external environment on hydrogen production was also studied at different temperatures. Experimental results show that the hydrogen production ability of the anaerobic bacteria was deeply affected by both culture temperature and iron concentration. Increasing the culture temperature favored the production of hydrogen when it was in the range of 25–40 °C, and high sucrose conversion efficiencies (ca. 98%) were consistently obtained with the mixed bacteria at the same time. While the temperature went on increasing to 45 °C, the hydrogen production was almost inhibited. The optimum concentrations of iron for hydrogen production decreased obviously along with increasing the reactor's temperature. For 25, 35, and 40 °C, the maximum production yield of hydrogen were 356.0, 371.7, and 351.1 ml obtained at the iron concentration of 800, 200, and 25 mg FeSO₄l^-1${\mathrm{l}}^{-1}$, respectively.     

Influence of hydrothermal treatment on structural property of NiZrAl mixed-metal oxides and on catalytic steam reforming of glycerol for hydrogen production

NiZrAl layered double hydroxides (LDH) precursors were synthesized by co-precipitation and homogeneous precipitation processes. The introduction of hydrothermal treatment into crystallization showed its significant influences on structure of LDH as well as mixed-metal oxides after thermal decomposition. The characterization results showed that the catalysts prepared by hydrothermal synthesis involved bigger pore diameter of ca. 13.5 nm and wider pore size distribution of 2–60 nm, and hydrothermal treatment was helpful to enhance the reduction of NiO species weakly interacted with support and to enhance the interaction among the metal oxides. Although the Ni dispersion, the surface area as well as the ability of anti-sintering were evidently improved, the ability of coke resistance decreased by 2 times for samples prepared by co-precipitation and by nearly 10 times for the ones prepared by homogeneous precipitation due to the enlarged pores. The maximum value of conversion to gaseous products (96.5%) and minimum deposited coke (36 m_gc/g_cat.) were achieved on NiZrAl-u sample.     

Kinetic investigations of the hydrogen production step of a thermochemical cycle using mixed iron oxides coated on ceramic substrates

A two‐step thermochemical cycle for solar hydrogen production using mixed iron oxides as the metal oxide redox system has been investigated. The ferrite is coated on a honeycomb structure, which serves as the absorber for solar irradiation and provides the surface for the chemical reaction. Coated honeycomb structures have already been tested in a solar receiver reactor in the solar furnace of DLR in Cologne with respect to their water splitting capability and their long‐term stability. The concept of this new reactor design has proven feasible and constant hydrogen production during repeated cycles has been shown. For a further optimization of the process and in order to gain reliable performance predictions more information about the process especially concerning the kinetics of the oxidation and the reduction step are essential. To examine the hydrogen production during the water splitting step a test rig has been built up on a laboratory scale. In this test rig small coated honeycombs are heated by an electric furnace. The honeycomb is placed inside a tube reactor and can be flushed with water vapour or with an inert gas. A homogeneous temperature within the sample is reached and testing conditions are reproducible. Through analysis of the product gas the hydrogen production is monitored and a reaction rate describing the hydrogen production rate per gram ferrite can be formulated. Using this test set‐up, SiC honeycombs coated with zinc ferrite have been tested. The influences of the temperature and the water concentration on the hydrogen production during the water splitting step have been investigated. An analysis of the ferrite conversion was performed using the Shrinking Core Model. A mathematical approach for the peak reaction rate at the beginning of the water splitting step was formulated and the activation energy was calculated from the experimental data. An activation energy of 110 kJ mol⁻¹ was found. Copyright © 2009 John Wiley & Sons, Ltd.