Preparation, testing and modelling of a hydrogen selective Pd/YSZ/SS composite membrane

A palladium selective tubular membrane has been prepared to separate and purify hydrogen. The membrane consists of a composite material, formed by different layers: a stainless steel support (thickness of 1.9 mm), an yttria-stabilized zirconia interphase (thickness of 50 μm) prepared by Atmospheric Plasma Spraying and a palladium layer (thickness of 27.7 μm) prepared by Electroless Plating. The permeation properties of the membrane have been tested at different operating conditions: retentate pressure (1-5 bar), temperature (350-450 °C) and hydrogen molar fraction of feed gas (0.7-1). At 400 °C, a permeability of 1.1 × 10⁻⁸ mol/(s m Pa^0.5) and a complete selectivity to hydrogen were obtained. The complete retention of nitrogen was maintained for all tested experiment conditions, with both single and mixtures of gases, ensuring 100% purity in the hydrogen permeate flux.A rigorous model considering all the resistances involved in the hydrogen transport has been applied for evaluating the relative importance of the different resistances, concluding that the transport through the palladium layer is the controlling one. In the same way, a model considering the axial variations of hydrogen concentration because of the cylindrical geometry of the experimental device has been applied to the fitting of the experimental data. The best fitting results have been obtained considering Sieverts’-law dependences of the permeation on the hydrogen partial pressure.     

Assessing the reactivity of TiCl3 and TiF3 with hydrogen

TiCl₃ and TiF₃ additives are known to facilitate hydrogenation and dehydrogenation in a variety of hydrogen storage materials, yet the associated mechanism remains under debate. Here, experimental and computational studies are reported for the reactivity with hydrogen gas of bulk and ball-milled TiCl₃ and TiF₃ at the temperatures and pressures for which these additives are observed to accelerate reactions when added to hydrogen storage materials. TiCl₃, in either the α or δ polymorphic forms and of varying crystallite size ranging from ～5 to 95 nm, shows no detectable reaction with prolonged exposure to hydrogen gas at elevated pressures (～120 bar) and temperatures (up to 200 °C). Similarly, TiF₃ with varying crystallite size from ～4 to 25 nm exhibits no detectable reaction with hydrogen gas. Post-exposure vibrational and electronic structure investigations using Fourier transform infrared spectroscopy and x-ray absorption spectroscopy confirm this analysis. Moreover, there is no significant promotion of H₂ dissociation at either interior or exterior surfaces, as demonstrated by H₂/D₂ exchange studies on pure TiF₃. The computed energy landscape confirms that dissociative adsorption of H₂ on TiF₃ surfaces is thermodynamically inhibited. However, Ti-based additives could potentially promote H₂ dissociation at interfaces where structural and compositional varieties are expected, or else by way of subsequent chemical transformations. At interfaces, metallic states could be formed intrinsically or extrinsically, possibly enabling hydrogen-coupled electronic transfer by donating electrons.     

Ultra-pure hydrogen production via ammonia decomposition in a catalytic membrane reactor

In this work two alternatives are presented for increasing the purity of hydrogen produced in a membrane reactor for ammonia decomposition. It is experimentally demonstrated that either increasing the thickness of the membrane selective layer or using a small purification unit in the permeate of the membranes, ultra-pure hydrogen can be produced. Specifically, the results show that increasing the membrane thickness above 6 μm ultra-pure hydrogen can be obtained at pressures below 5 bar. A cheaper solution, however, consists in the use of an adsorption bed downstream the membrane reactor. In this way, ultra-pure hydrogen can be achieved with higher reactor pressures, lower temperatures and thinner membranes, which result in lower reactor costs. A possible process diagram is also reported showing that the regeneration of the adsorption bed can be done by exploiting the heat available in the system and thus introducing no additional heat sources.     

Effects of various factors on the hydrogen isotope separation efficiency of a novel hydrophobic platinum-polytetrafluoroethylene catalyst

The application of platinum supported on polytetrafluoroethylene (Pt/PTFE) as a composite catalyst for the separation of hydrogen isotopes holds much promise but warrants further refinement for improved performance. The objective of the present study was to examine the performance of a new hydrophobic Pt/PTFE catalyst during hydrogen-water exchange-based deuterium separation. The influence of diverse factors such as flow rate, column height, temperature, the volume ratio of filler to catalyst, and flow mode (co-current or counter-current), and so on, on catalytic performance was investigated. The deuterium conversion rate from co-current exchange was superior to that from counter-current exchange. Decreasing the hydrogen flow rate, increasing the feed water flow rate, and decreasing the molar flow ratio of hydrogen to water improved the deuterium conversion rate. In terms of layered filling of the catalyst column, adding more hydrophilic fillers improved the deuterium conversion rate. The characterization results highlight the high catalytic activity of the Pt/PTFE catalyst for hydrogen-water exchange, as well as its high stability in water.     

Enhanced hydrogen purification by graphene - Poly(Dimethyl siloxane) membrane

In this study, a nanocomposite graphene oxide (GO) incorporated poly (dimethyl siloxane) (PDMS) membrane was produced and used for the purification of hydrogen (H₂₎ by separating the (CO₂). The produced membrane was characterized and the single-gas permeability test was performed. Effects of GO addition, trans-membrane pressure and membrane thickness on the gas separation performance of membrane were evaluated as a function of permeability and CO₂/H₂ selectivity. GO addition increased the CO₂/H₂ selectivity and H₂ purification performance. The highest CO2 permeability of 3670 Barrer and CO₂/H₂ selectivity of 11.7 were obtained when the GO loading was 0.5 wt% when the trans-membrane pressure was 0.2 Mpa.     

Bi-functional hydrogen membrane for simultaneous chemical reaction and hydrogen separation

As a novel approach to simultaneous water–gas shift (WGS) reaction and separation for the production of hydrogen, a bi-functional membrane was successfully prepared using a simple coating method. The catalyst materials, Pt and CeO₂, were directly coated over the surface of a Pd–Au dense membrane for excluding slow hydrogen diffusion through the conventional catalyst bed. The coated catalyst layer did not significantly affect the hydrogen permeance of the bare membrane, due to the presence of metal within the catalyst compositions which acted as a bridge for the surface diffusion of hydrogen atoms. As a result of WGS reaction within the novel membrane reactor at 380 °C, the CO conversion was 2 times higher than that of no hydrogen separation. The catalyst-deposited membrane can make the “simultaneous chemical reaction and separation” more feasible and relatively simple, if the more robust catalysts can be loaded with the increased active surface area and the multi-membrane module reactor adopted the coin-shape bi-functional membranes can be designed to completely treat the CO and separate hydrogen from the CO mixture.     

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.     

Dehydrogenation properties of doped LiAlH4 compacts for hydrogen generator applications

Lithium aluminum hydride (LiAlH₄) is an attractive hydrogen source for fuel cell systems due to its high hydrogen storage capacity and the moderate dehydrogenation conditions. In this contribution, TiCl₃- and ZrCl₄-doped LiAlH₄ powders are prepared and pelletized under different compaction pressures in a uniaxial press. At constant 80 °C and a hydrogen partial pressure of 0.1 MPa, the maximal hydrogen release of suchlike LiAlH₄ compacts amounts to 6.64 wt.%-H₂ (gravimetric capacity) and 53.88 g-H₂ l⁻¹ (volumetric capacity). The hydrogen release properties of the doped LiAlH₄ compacts are studied systematically under variation of the compaction pressure, temperature and hydrogen partial pressure. Furthermore, the volume change of doped LiAlH₄ compacts during dehydrogenation as well as their short-term storability are investigated (shelf life).     

Effect of synthesis conditions on performance of a hydrogen selective nano-composite ceramic membrane

A hydrogen-selective nano-composite ceramic membrane was prepared by depositing a dense layer composed of SiO₂ and Al₂O₃ on top of a graded multilayer substrate using co-current chemical vapor deposition (CVD) method. The multilayer substrate was made by dip-coating a macroporous α-alumina tubular support by a series of boehmite solutions to get a graded structure. Using DLS analysis, it was concluded that decreasing hydrolysis time and increasing acid concentration lead to smaller particle size of boehmite sols. XRD analysis was carried out to investigate the structure of intermediate layer and an optimized calcination temperature of 973 K was obtained. SEM images indicated the formation of a graded membrane with a porous intermediate layer having a thickness of about 2 μm and a dense top selective layer with a thickness of 80–100 nm. Permeation tests showed that H₂ permeance flux decreased from 5 × 10⁻⁵ mol m⁻² s⁻¹ Pa⁻¹ for a fresh substrate to 6.30 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ after 6 h of deposition, but H₂ selectivity over N₂ increased considerably from 5.6 to 203.     

Modeling of transient hydrogen permeation process across a palladium membrane

Transient mass transfer processes of hydrogen permeating through a Pd membrane are modeled to aid in predicting the hydrogen transport behavior. The model is established in terms of the quasi-steady time and the steady permeation rate. Meanwhile, four important parameters are considered; they are the permeation lag time, the initial permeation rate, the concave up period and the concave down period. A unit step function is embedded in the model to account for the effect of the hydrogen permeation lag at a lower pressure difference. Corresponding to the lower, the moderate and the higher pressure differences (i.e. 3, 5 and 8 atm), though the hydrogen permeation undergoes a three-stage, a two-stage and a one-stage processes, respectively, these processes can be predicted well by an arc tangential function. By introducing an adjusting parameter in the arc tangential function, there exists an optimal value of the adjusting parameter when the pressure difference is lower. In regard to the moderate and higher pressure differences, the predictions agree with experiments well if the adjusting parameter is sufficiently large. Physically, the unit step function is used to account for the controlling mechanisms of hydrogen diffusion toward the membrane and the spillover of the hydrogen across the membrane. The initial jump parameter represents the rapid response of the initial hydrogen permeation. The adjusting parameter can be used to describe the relative importance of the concave up and the concave down periods.     

Characteristics of a multi-pass membrane reactor to improve hydrogen recovery

Membrane reactors are a potential tool to produce high purity hydrogen on-site but sufferfrom immense losses in hydrogen recovery under reaction conditions. For high-temperature operations, these losses mostly occur due to the presence of lesser permeable gases in the reformate that develop into a concentration polarization barrier around the membrane. Based on our previous findings, a multi-pass design was manifested to alleviate hydrogen losses through the membrane tested with synthetic gas mixtures. The same design is currently employed to establish improvement in hydrogen recovery under reaction conditions. Having a catalyst and membrane integrated into a single unit termed as a membrane reactor, its performance is optimized with varying membrane assembly and catalyst bed configurations. This study shows that a packed bed multi-pass membrane reactor is an optimal design to target high hydrogen recovery. Further, multi-pass membrane reactor design also improves the hydrogen recovery in fluidized bed operations which opens immense scope for future studies.     

Synthesis of thin amine-functionalized MIL-53 membrane with high hydrogen permeability

A thin amine-functionalized MIL-53 membrane with high permeability of hydrogen was successfully prepared on a porous α-Al₂O₃ support by using the secondary growth method. Seeded α-Al₂O₃ supports were prepared by a dip-coating technique. In contrast, a discontinuous membrane was obtained by using unseeded support under the same synthesis conditions, implying that the seeds play the key role in the formation of compact membranes. The resulting compact membranes were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation testing. Results showed that the thickness of the as-prepared membrane was around 2 ∼ 4 μm. Hydrogen permeance of the as-prepared membrane reached a remarkable value of 1.5 × 10⁻⁵ mol m⁻² s⁻¹·Pa⁻¹ at room temperature under a 0.1 MPa pressure drop. The ideal H₂/CO₂ selectivity was found to be 4.4. In addition, the influence of seeding solution on the membrane performance was investigated. We found that the membrane permeance decreased and the ideal selectivity increased when the seeding solution content was increased.     

Lithium polymer batteries and proton exchange membrane fuel cells as energy sources in hydrogen electric vehicles

This paper deals with the application of lithium ion polymer batteries as electric energy storage systems for hydrogen fuel cell power trains. The experimental study was firstly effected in steady state conditions, to evidence the basic features of these systems in view of their application in the automotive field, in particular charge-discharge experiments were carried at different rates (varying the current between 8 and 100 A). A comparison with conventional lead acid batteries evidenced the superior features of lithium systems in terms of both higher discharge rate capability and minor resistance in charge mode. Dynamic experiments were carried out on the overall power train equipped with PEM fuel cell stack (2 kW) and lithium batteries (47.5 V, 40 Ah) on the European R47 driving cycle. The usage of lithium ion polymer batteries permitted to follow the high dynamic requirement of this cycle in hard hybrid configuration, with a hydrogen consumption reduction of about 6% with respect to the same power train equipped with lead acid batteries.     

Synthesis and hydrogen storage properties of lithium borohydride amidoborane complex

A series of mixtures of LiAB/LiBH₄ with different molar ratios were prepared and their hydrogen storage properties were investigated in this study. Among them, a new structure was found in the LiAB/LiBH₄ sample with a molar ratio of 1/1. It is of orthorhombic structure and composed of alternative layers of LiAB and LiBH₄. It shows similar hydrogen desorption behaviors of LiAB–LiBH₄ and LiAB–0.5LiBH₄. For use in hydrogen storage, high hydrogen capacity and low operation temperature are demanded, thus, the dehydrogenation properties of LiAB–0.5LiBH₄ were subsequently measured. Three steps of desorption were observed during the heating process, with a total release of 11.5 wt% H₂ at 500 °C. The reaction path was identified using a combined investigation of XRD and ¹¹B solid state NMR. Dehydrogenation kinetic analyses show that the complex has lower activation energy (61 ± 4 kJ mol⁻¹ H₂) than that of LiAB (71 ± 5 kJ mol⁻¹ H₂). It is likely that dehydrogenation process was promoted due to the presence of LiBH₄.     

An analytical and experimental investigation of high-pressure catalytic steam reforming of ethanol in a hydrogen selective membrane reactor

The objective of this work was to explore the benefits of high-pressure steam reforming of ethanol for the production of hydrogen needed to refuel the high-pressure tanks of fuel cell (polymer electrolyte) vehicles. This paper reports on the potential efficiency benefits and challenges of pressurized reforming and options for dealing with the challenges; it reports the results from experiments in a micro-reactor, followed by a modeling study of the reactor to project the dependence of the hydrogen yields on process parameters. The experiments were conducted in the range of approximately 7–70 atm, 600–750 °C, steam-to-carbon molar ratios of 3–12, and gas hourly space velocities of 8500–83,000 per hour. By placing a hydrogen-transporting palladium-alloy membrane within the catalyst zone, this study quantified the beneficial effect of hydrogen extraction from the reforming zone. The model was used to explore the parameter space to define the reactor and conditions that would be needed to approach the efficiency targets for distributed hydrogen production plants. The results indicate that the tested catalyst was sufficiently active, and the hydrogen yield achieved with the experimental membrane reactor was limited by the low hydrogen flux of the tested membrane. The reactor model predicts that a membrane with at least 20 times higher flux than currently evaluated would be sufficient to generate hydrogen yields to match efficiency targets of 72%.     

Preparation of palladium membrane by bio-membrane assisted electroless plating for hydrogen separation

Palladium membrane was prepared on the inner surface of alumina tube by bio-membrane assisted electroless plating combined with osmosis method (BELP). In this preparation technique, an egg-shell film not only served as a semipermeable membrane to form osmotic system for preparing palladium membrane, but also acted as a protection layer to prevent the contamination of the palladium membrane from the osmotic solution. Moreover, the plating solution was circulated through the tube side to promote the mass transfer on the solid–liquid interface between the plating surface and the solution. The detailed depositing process of the palladium membrane was studied by scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDXS). Both long term operation and temperature cycling test carried out for hydrogen and nitrogen permeation confirmed that the palladium membrane was stable.     

Gold as an efficient hydrogen isotope separation catalyst in proton exchange membrane water electrolysis

The development of proton exchange membrane water electrolysis (PEMWE) offers an updating potential for electrolytic hydrogen isotope separation. However, it has a significantly lower separation factor than the traditional alkaline water electrolysis. In this study, we propose gold as a promising cathodic catalyst for efficient hydrogen isotope separation in PEMWE. Au/C has a protium-to-deuterium (H/D) separation factor of 7.47 in PEMWE, about twice that of Pt/C. In addition, the full cell's electrochemical performance is comparable to that of its Pt/C counterpart. The separation mechanism in PEMWE is explained by the transitional hydrogen evolution reaction mechanism from Heyrovsky to Tafel for Pt and the unchangeable Volmer mechanism for Au. The high separation factor for Au is also calculated by the H/D zero-point vibrational energy difference between transition state and reaction state through a simple density functional theory calculation. This work offers an effective strategy to improve hydrogen isotope separation efficiency in PEMWE.     

Characterization of mechanical strength and hydrogen permeability of a PdCu alloy film prepared by one-step electroplating for hydrogen separation and membrane reactors

A single phase, dense PdCu alloy film was prepared by one-step electroplating. The electroplated film was easily delaminated from the SUS electrode by cutting around the edge, and the single alloy film was thus collectable. The phase structure, surface morphologies, and alloy compositions were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The plated film before and after hydrogen permeation tests consisted of a single face-centered cubic α phase and an ordered body-centered cubic β phase, respectively. The atomic ratios of Pd and Cu were 49 and 51 at%, respectively; the Pd and Cu contents were slightly higher and lower than Pd₄₇Cu₅₃, which shows the highest hydrogen permeability among Pd-Cu systems. The as-plated film exhibited high mechanical strength, and its load force at break point and displacement were 3 and 1.7 times those of the as-rolled Pd₄₇Cu₅₃ films. The hydrogen permeability of the plated film with the β phase was almost the same as that of the rolled film and the values reported in literature.     

Analytical prediction of heat capacity of molten AgCl and CuCl with application to thermochemical Cu-Cl cycle for hydrogen production

To sustain our power-dependent world, there is a need for technological innovation in all aspects of science and engineering. Many times, thermophysical and material properties are not well defined for the specific application, which leads to implementing assumptions and approximations from the published data. In the thermochemical copper-chlorine (Cu-Cl) cycle for hydrogen (H₂) production, heat is recovered from cuprous chloride (CuCl) molten salt and it is then reacted with hydrochloric acid (HCl) in stoichiometric proportions to produce the anolyte for the H₂ production step of the cycle. However, the lack of precise thermophysical properties on CuCl heavily hinders the detailed investigations of heat recovery from the molten salt as it cools from 450 °C to 90 °C. In this paper a new method is developed to determine the thermophysical property of CuCl and silver chloride (AgCl) as the molten salts are changing phases to solid. This is achieved by correlating electrochemistry data with thermal data. A model that predicts the specific heat capacity during phase change process is developed based on the existing electromotive force (EMF) and thermal data from literature. Developed model shows the EMF derived specific heat capacity values of AgCl and CuCl are similar with a slight offset since they have similar EMF's at higher temperatures.     

Incorporation of thermally labile additives in polyimide carbon membrane for hydrogen separation

In this study, three thermally labile additives microcrystalline cellulose (MCC), nanocrystalline cellulose (NCC), and polyvinylpyrrolidone (PVP) were introduced to the P84-copolyimide (PI) solution. PI-based carbon tubular membranes were fabricated using dip-coating method, followed by sample characterizations in order to determine their structural morphologies, thermal stability and gas permeation performance. NCC was added as the membrane pore former for the hydrogen gas (H₂) separation. While tests involving pure H₂ and N₂ permeation were carried out at room temperature, carbon membranes were carbonized at a final temperature of 800 °C, with the heating rate of 3 °C/min under the Ar flow. Excellent result of H₂/N₂ selectivity was obtained with value of 430.06 ± 4.16. Addition of NCC has significantly increased the number of pore channels in the membrane, hence, contributing to high gas permeance and selectivity. NCC has shown potential as a good additive for an enhanced hydrogen separation performance.