Membranes For H2 Separation Research Articles

Exploring the environmental performance of electroless plated palladium alloy membranes for H2 separation: A cradle-to-gate life cycle study

Metal-based membranes have emerged as a promising solution, providing selective permeability and impressive durability. However, a comprehensive understanding of their environmental performance across their entire life cycle remains elusive. This research offers a comprehensive life cycle assessment (LCA) of electroless plated palladium alloy-based membranes for hydrogen separation. It evaluates the environmental impacts across various stages, from the synthesis of supports to the application of intermediate and selective layers. Key findings include the identification of alumina supports and graphite intermediate layers as having minimal environmental impacts, and the Pd–Cu membrane as the most sustainable choice among palladium alloy membranes. This research advances our understanding of the eco-friendly performance of palladium based H2 separation membranes, guiding the development of more sustainable hydrogen separation technologies.

A high selective and permeable C7N6 monolayer membrane for H2 purification: First-principles and molecular dynamics simulations

Designing efficient membranes for hydrogen purification and separation is highly desired because of the development of the hydrogen economy. Using the combination methods of density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we theoretically investigated the performance of the C7N6 monolayer for H2 purification and separation. Our DFT calculations indicate that H2 molecules would permeate through the C7N6 monolayer with a relatively low energy barrier (0.689 eV), and the C7N6 monolayer has an ultra-high selectivity of 7.47 × 106, 5.71 × 109, 1.19 × 1011, and 1.08 × 1012 for H2/O2, H2/CO2, H2/CO, and H2/N2 at even high temperature of 500 K, respectively. The MD simulations confirmed that the high selectivity and permeability of the H2 gas above 500 K. Even at higher temperatures of 800 to 1000 K, almost all of H2 gas can be separated by the C7N6 membrane without any other foreign gases passing through the membrane, indicating that the C7N6 monolayer can be used as an ultra-high performance H2 purification and separation membrane on the practical conditions as the C7N6 monolayers are dynamically, thermodynamically, and mechanically stable.

Ultrasound assistance in the sensitization and activation of porous Al2O3 supports for improving the hydrogen separation of Pd/Al2O3 composite membranes

Pd membrane on porous Al2O3, an important composite membrane for H2 separation, is typically fabricated by electroless plating, and thus the quality of the Pd membrane is critically dependent on the seeding process. Here, a facile ultrasonication-assisted sensitization-activation process is used to load catalytic particles on porous Al2O3, subsequently followed by electroless plating of 5-μm-thick Pd membranes for H2 separation. Uniformly distributed catalytic particles with even sizes are loaded onto Al2O3 only under an optimal power of the ultrasonic agitation, then catalyzing electroless Pd membranes with a better surface topography and less defective microstructure. The optimal Pd membrane achieves a sound hydrogen flux of 0.157 mol m−2 s−1 and high H2/N2 selectivity of 1835 under 723 K and 105 kPa pressure difference. Moreover, this particular Pd/Al2O3 exhibits high stability in (a) Pd membrane microstructures and (b) H2/N2 permeating fluxes without elemental interfacial diffusion even under long-term (156 h) at a high temperature (723 K).

Dimethoxydimethylsilane-derived silica membranes prepared by chemical vapor deposition at 973 K exhibiting improved thermal/hydrothermal stability

With the aim of developing thermally/hydrothermally stable silica membranes for H2 separation, dimethoxydimethylsilane-derived silica membranes were prepared via chemical vapor deposition (CVD) at various temperatures. This process employed a substrate having an intermediate layer with a gallium-loaded γ-alumina coating that had been calcined at 1073 K. The data demonstrate that this intermediate layer was itself thermally stable at 1073 K and hydrothermally stable at 973 K. A systematic evaluation of membrane performances under thermal/hydrothermal conditions confirmed that membranes prepared at 973 K were more stable than those fabricated at 873 K under dry conditions. In addition, the loss in H2 permeance under hydrothermal conditions was lower in the case that the CVD temperature was 973 K. Hence, to ensure stability, the temperature at which such membranes are employed should be lower than the CVD processing temperature.

Recent Advancements in Metal-Organic Framework-Based Membranes for Hydrogen Separation: A Review.

Metal-organic frameworks (MOFs) are promising porous materials that have huge potential for gas separation when put in the membrane configuration. MOFs have huge potential due to certain salient features of the MOFs such as excellent pore size, ease of tuning the pore chemistry, higher surface area, and chemical and thermal stabilities. MOFs have been explored for various gas separation and storage applications. This review discusses various approaches for fabricating MOFs-based membranes for the separation of H2 gas from a variety of feeds having various gases CO2, CO, N2, and CH4 as impurities. The emphasis has been put on three types of membranes for H2 separation which include MOFs-based hollow fibrous/tubular/disk membranes, MOFs-based mixed matrix membranes (MMMs), and MOFs-based stand-alone membranes. In addition, various challenges such as reducing inhomogeneity between MOFs and polymeric matrices have also been discussed. Similarly, the approaches to successfully decorating MOFs on different supports in different configurations have been explained. The possible ways of improving the MOFs-based membranes for H2 have also been discussed.

Rapid synthesis of ultra-microporous metal-organic framework tubular Ni-LAP membranes for H2 separation by linker salt method

Recently, the development of pillar-layered metal-organic frameworks (MOFs) is receiving more and more attention because of their pore surface chemistry tunability and designability. In this work, we firstly synthesized various sizes of high-quality Ni-LAP [Ni2(L-asp)2(pz)] (L-asp = l-aspartic acid, pz = pyrazine) crystals key for secondary growth by manipulating the crystal thermal dynamics and kinetics of Ni-LAP synthesis solution simply through choosing the Ni(OAc)2 as metal source and pretreatment at 40 °C, followed by the fabrication of defect-free Ni-LAP membranes as a model in a short time of 4 h using the linker salt method. It is found the pretreatment of Ni(OAc)2 precursor solution at 40 °C with continuous stirring for 6 h can effectively promote deprotonation to form 250 nm crystals. The linker salt method enables a greener and more rapid synthesis of Ni-LAP membranes, with continuous and compact Ni-LAP membranes, where soluble metal precursors and organic linking salts provide the synthesis solution a higher degree of supersaturation, both of which play an important role in the rapid preparation of Ni-LAP membranes. The preparation parameters of the Ni-LAP membranes were investigated in detail, and the results from the Ni-LAP membrane gas separation performance showed that the preferential (111) orientation membrane (M9) exhibited the best H2/CO2 separation performance with separation factor of 23.8 and H2 permeance of 2.11 × 10−7 mol m−2 s−1 Pa−1 compared to the preferential (002) orientations (M3), which may attributed to the preferential (111) orientation being at an angle to the optimal a-axis aperture perpendicular to the support thereby reducing the mass transfer resistance. Furthermore, the generation of corrosive nitric acid during the preparation process can be greatly reduced and replaced by eco-friendly potassium nitrate. The superiority of the pore structure and the remarkable stability of these MOF membranes show the potential for H2 purification. Moreover, our preparation route demonstrates the universality of preparing other isomorphs, such as Ni-LAB and Co-LAP membranes.

Selectivity enhancement by the presence of HOF + CNT composite membranes investigated by non-equilibrium molecular dynamics

Hydrogen purification through membrane separation offers convenience and suitability for on-site operation, especially in automotive fuel cells that utilize reformed methanol as a hydrogen source. In this study, the molecular dynamics simulation method was employed to investigate the micro-separation mechanism of hydrogen purification using multi-walled carbon nanotubes (MWNTs) and hydrogen-bonded organic frameworks (HOFs) as membrane materials. Novel composite membranes combining different HOF and MWNT materials were designed to enhance the interaction energy with CO2. The results demonstrated that these composite membranes exhibited higher selectivity in the separation of H2/CO2 gas mixtures, achieving higher hydrogen permeability compared with individual HOF and MWNT membranes. Notably, the PhTCz1 + CNT, UPC-H4a + CNT, and TCPP-1,3-DPP + CNT-3 composite membranes demonstrated 100 % CO2 retention and reached a maximum flux hydrogen of 4.782 × 105 GPU, which was higher than traditional membranes by 6 orders of magnitude. Furthermore, the PhTCz1 + CNT-3 composite membrane had a significant ability to simultaneously intercept CO2 and CO. The MD calculation results show that this newly synthesized HOF + CNT composite membrane material can provide high permeability as well as ultrahigh selectivity simultaneously, making it a prospective H2 separation membrane with superior performance.

Sustainable H2 production/separation by integration of solid oxide electrolyzer, biomass gasifier and H2 separation membrane: A techno-economic/environmental evaluation and multi-objective optimization

Hydrogen as a clean fuel can simultaneously respond to the challenges of energy shortage and environmental issues, provided that it is produced in a clean and cheap way. In this research, a hydrogen production system based on the combination of a solid oxide electrolyzer with a gasifier and a hydrogen separation membrane has been studied from a techno-economic outlook. In order to achieve a proper approximation of the levelized cost of hydrogen (LCOH), an elaborated economic analysis has been performed considering all aspects, where the life of the hydrogen separation membrane (HSM) and the solid oxide electrolyzer (SOE) has been taken into account. Finally, the minimization of the levelized cost of hydrogen and the levelized carbon dioxide emission (LCE) was carried out through multi-objective optimization. The cost of selling hydrogen was determined according to the various payback times. According to the conducted optimization, it is possible to obtain the minimum levelized cost of hydrogen of 3.63 $/kg. This condition leads to the levelized emission of 10.17 kg CO2/kg H2. Also, the system has the ability to bear levelized CO2 emissions up to 2.92 kg CO2/kg H2, so that the levelized cost of H2 production is 6.45 $/kg. In the four optimal conditions obtained from the optimization, considering the payback time of 5 years, the cost of selling the produced H2 can be 3.64 $/kg, 6.45 $/kg, 5.98 $/kg, and 5.29 $/kg.

Development and hydrogen permeation of freeze-cast ceramic membrane

BaCe0.65Zr0.20Y0.15O3-δ - Gd0.2Ce0.8O2-δ (BCZY-GDC) is currently one of the most investigated composites as ceramic membranes for H2 separation and membrane reactors. In this context, we will present for the first time the possibility to exploit the ice-templating method coupled with screen printing to obtain hierarchically-structured proton-conducting ceramic membranes. All the processing steps to obtain a defect free dense/porous structure were considered and analysed. In particular, the formulation of screen printing ink was optimized in terms of nature/amount of deflocculant and type of starting BCZY powder. An innovative membrane constituted by a 50 %-porous support with well-organized and aligned porosity and a 13 ± 3 μm thick dense layer on the top, was produced. The compressive strength (20.6 ± 5.6 MPa), were considered acceptable for practical applications. Promising H2 fluxes of 0.36 and 0.42 mL min-1 cm−2 at 750 °C, using a feed stream with 50 and 80% H2 in He (H2 %vol.) respectively, were obtained.

Metallic Supported Pd-Ag Membranes for Simultaneous Ammonia Decomposition and H2 Separation in a Membrane Reactor: Experimental Proof of Concept

The use of ammonia as a hydrogen carrier requires efficient cracking technology. A promising solution is the use of a membrane reactor (MR), which enables both ammonia decomposition and hydrogen separation to take place within the same device, providing advantages in terms of efficiency and compactness compared to conventional systems. The literature reports that ceramic-supported double-skinned Pd-Ag membranes show outstanding performance for hydrogen separation as well as good stability of the separation layer during ammonia decomposition. However, their sealing in the reactor may result in leakage increase, while their mechanical stability remains an unresolved issue. To circumvent these limitations, the use of metallic supported Pd-based membranes is recommended, due to their higher mechanical stability and ease of sealing and integration in the reactor. In this work, we propose the development of robust metallic supported hydrogen-selective membranes for integration in membrane reactors for ammonia cracking. A conventional Pd-Ag membrane was prepared on a low-cost porous Hastelloy X tubular filter, modified with α-Al2O3/γ-Al2O3 to reach the desired surface quality. The membrane was then tested for ammonia decomposition in a MR configuration, showing the ability to reach >99% NH3 conversion above 475 °C with H2 feed recovery >60%. The results achieved pave the way towards a possible substitute for the ceramic-supported alternatives.

Computational Investigation of Dual Filler-Incorporated Polymer Membranes for Efficient CO2 and H2 Separation: MOF/COF/Polymer Mixed Matrix Membranes.

Mixed matrix membranes (MMMs) composed of two different fillers such as metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) embedded into polymers provide enhanced gas separation performance. Since it is not possible to experimentally consider all possible combinations of MOFs, COFs, and polymers, developing computational methods is urgent to identify the best performing MOF-COF pairs to be used as dual fillers in polymer membranes for target gas separations. With this motivation, we combined molecular simulations of gas adsorption and diffusion in MOFs and COFs with theoretical permeation models to calculate H2, N2, CH4, and CO2 permeabilities of almost a million types of MOF/COF/polymer MMMs. We focused on COF/polymer MMMs located below the upper bound due to their low gas selectivity for five industrially important gas separations, CO2/N2, CO2/CH4, H2/N2, H2/CH4, and H2/CO2. We further investigated whether these MMMs could exceed the upper bound when a second type of filler, a MOF, was introduced into the polymer. Many MOF/COF/polymer MMMs were found to exceed the upper bounds showing the promise of using two different fillers in polymers. Results showed that for polymers having a relatively high gas permeability (≥104 barrer) but low selectivity (≤2.5) such as PTMSP, addition of the MOF as the second filler can have a dramatic effect on the final gas permeability and selectivity of the MMM. Property-performance relations were analyzed to understand how the structural and chemical properties of the fillers affect the permeability of the resulting MMMs, and MOFs having Zn, Cu, and Cd metals were found to lead to the highest increase in gas permeability of MMMs. This work highlights the significant potential of using COF and MOF fillers in MMMs to achieve better gas separation performances than MMMs with one type of filler, especially for H2 purification and CO2 capture applications.

Hydrothermal Stability of Hydrogen-Selective Carbon-Ceramic Membranes Derived from Polybenzoxazine-Modified Silica-Zirconia.

This work investigated the long-term hydrothermal performance of composite carbon-SiO2-ZrO2 membranes. A carbon-SiO2-ZrO2 composite was formed from the inert pyrolysis of SiO2-ZrO2-polybenzoxazine resin. The carbon-SiO2-ZrO2 composites prepared at 550 and 750 °C had different surface and microstructural properties. A carbon-SiO2-ZrO2 membrane fabricated at 750 °C exhibited H2 selectivity over CO2, N2, and CH4 of 27, 139, and 1026, respectively, that were higher than those of a membrane fabricated at 550 °C (5, 12, and 11, respectively). In addition to maintaining high H2 permeance and selectivity, the carbon-SiO2-ZrO2 membrane fabricated at 750 °C also showed better stability under hydrothermal conditions at steam partial pressures of 90 (30 mol%) and 150 kPa (50 mol%) compared with the membrane fabricated at 500 °C. This was attributed to the complete pyrolytic and ceramic transformation of the microstructure after pyrolysis at 750 °C. This work thus demonstrates the promise of carbon-SiO2-ZrO2 membranes for H2 separation under severe hydrothermal conditions.

Poly(vinyl alcohol) mediated bifunctional ZIF-BN nanocomposite for the high-selectivity H2 separation membrane

We combined the advantages of the 2-methylimidazole zinc salt (ZIF-8) and hydroxylated boron nitride (OH-BN) materials to prepare a new bifunctional separation material, namely ZIF-BN. In this, spherical ZIF-8 materials fill the macroporous structure of OH-BN sheets by coordination bonds due to the edge effect. Furthermore, a series of ZIF-BN/PVA membranes were prepared using the vacuum-assisted filtration of the layer-by-layer for the gas separation study. The trace amounts of PVA connect adjacent ZIF-BN sheets through hydrogen bonds, without covering the pore structures of ZIF-8 materials. Based on this exclusive strategy for preparing membranes, the obtained membranes exhibit superior H2 separation performances. Compared with the pure PVA membrane, the H2 permeability, H2/CO2 selectivity, and H2/N2 selectivity of the ZIF-BN/PVA-8 membrane have increased (54, 13, & 12)-fold, to (600 Barrer, 97.2, & 173.6), respectively. This strategy provides a facile way to design new bifunctional membranes for gas separation applications.

Monte Carlo simulations of surface segregation to discover new hydrogen separation membranes

Surface compositions play a predominant role in the efficiency and lifetime of membranes and catalysts. The surface composition can change during operation due to segregation, thus controlling and predicting the surface composition is essential. Computational modelling can aid in predicting alloy stability, along with designing surface alloys and near-surface alloys that can outperform existing materials. In this work, a computational model to predict surface segregation in ternary alloys is developed. The model, based on Miedema's semi-empirical model and Monte Carlo simulations, enables to predict long- and short-range ordering in the surface and subsurface layers. It is used to screen a vast range of alloy compositions to design a novel ternary Pd-based material for H2 separation membranes. The addition of specific amounts of Cu and Zr to Pd is expected to reduce poisoning and enhance the permeability as compared to pure Pd.

Theoretical investigation on two-dimensional conjugated aromatic polymer membranes for high-efficiency hydrogen separation: The effects of pore size and interaction

Based on two-dimensional conjugated aromatic polymer (2D-CAP), CAP-1S/CAP-1P monolayers were designed by substituting N with S/P atoms for H2 purification. By using MD and DFT approaches, the H2 purification performance and separation mechanisms of CAP-1S/CAP-1P membranes were investigated. Results showed that ultrahigh H2 permeances of 3.546 × 10−5 and 2.593 × 10−4 mol m−2 s−1 Pa−1 were obtained in CAP-1S/CAP-1P, which were almost 104–105 times larger than the industrially acceptable standard. The selectivities of H2 over CO2/CO/CH4/N2 ranged from 5.719 × 1018 to 3.683 × 1039 in CAP-1S and 4.554 × 1013 to 2.153 × 1033 in CAP-1P. From a statistic viewpoint, the CAP-1S/CAP-1P membranes exhibited complete selectivities of H2 over CO2/CO/CH4/N2. The cohesive energies confirmed the high stabilities of CAP-1S/CAP-1P membranes. The minimum energy pathways, energy profiles, electron density, and charge density difference were analyzed to illustrate the significant impact of precise pore size on the H2 separation performance. From a statistic mechanics view, the interaction between gases and CAP-1S/CAP-1P membranes indicated that the long-range Coulomb interactions dominated the gas diffusion processes. Results of this work highlighted CAP-1P as a promising H2 separation membrane and elucidated the promotion mechanism by fine-tunning pore size and interaction between gases and membranes to balance the H2 permeance and selectivity jointly.

Enhanced Hydrogen Permeability of Mixed Protonic–Electronic Conducting Membranes through an In‐Situ Exsolution Strategy

AbstractMixed protonic–electronic conducting (MPEC) ceramic membranes with high H2 permeability and stability are significant for practical H2 separation. CO2‐tolerant lanthanum tungstate oxides have received much attention, but their low H2 permeability is their main problem for membrane applications. Herein, an efficient in‐situ exsolution strategy is proposed to enhance the H2 permeability and CO2 stability of lanthanum tungstate‐type membranes. During H2 permeation, the catalytic Pd nanoparticles are in‐situ generated from the bulk oxide lattices and dispersed evenly on the membrane surfaces, which greatly promotes the H2 surface exchange kinetics. Also, the protonic conductivity of the membranes is effectively improved through the introduction of Pd. Consequently, the H2 permeation flux is increased by 3.5 times and a maximum H2 flux of 1.3 mL min−1 cm−2 is achieved at 1000 °C through the La5.5(W0.6Mo0.4)0.95Pd0.05O11.25‐δ (LWMPd) membrane. The LWMPd membrane shows outstanding long‐term chemical stability during 300 h continuous operation in a CO2‐containing atmosphere. Therefore, this in‐situ exsolution formation of Pd nanoparticles provides effective guidance for developing competitive MPEC membranes for H2 separation and purification.

Pilot scale fabrication of lanthanum tungstate supports for H2 separation membranes

This paper reports the fabrication of asymmetric tubular geometry lanthanum tungstate-based membranes for high temperature H2 separation applications. As starting materials, powders with the compositions La28-yW4+yO54+δ (y = 0.848), La28-yW4+yO54+δ (y = 1) and La28-y(W1-xMox)4+yO54+δ (x = 0.3, y = 1) were synthesized by solid state reaction method. Porous, thick-wall tubes made of lanthanum tungstate-based powders with high gas permeability (7–8 x10-15 m2 at 2 bar overpressure) and homogeneous porous microstructure were made by combining a cost-effective solid-state synthesis and thermoplastic extrusion method. Deposition of lanthanum tungstate-based dense thin film (∼20 μm) was achieved on top of porous supports through dip coating technique. The influence of conformation routes, thermal debindering and sintering processes were investigated in detail to achieve defect free H2 transport membranes. Asymmetric geometry membranes with ∼20 μm dense layer thickness supported on porous tubular (∼ 7.5 mm diameter and ∼0.8 mm thick) supports.As a result, a procedure for proton conducting ceramics manufacture was established which can be deployed to fabricate high temperature catalytic membrane reactors for synthetic fuel from gas-to-liquid (GTL) processes.

Mixed Protonic-Electronic Conductivity of SrCe1−xPrxO3−δ

Protonic conductors are gaining use in solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs) as well as for H2 separation membranes. However, for SOFC/SOEC electrode and membrane applications their performance is limited by low electronic conductivity. One of the most promising classes of ceramic proton conductors, perovskites, have highly-tunable compositions allowing for the optimization of both ionic and electronic conductivity. In this work Pr-doped SrCeO3 was studied over a wide range of oxygen partial pressures (pO2’s) and temperatures to determine its defect properties and conductivity. Under reducing conditions Pr-doped SrCeO3 was found to be chemically and structurally stable, with an optimal Pr doping level of 10%. This composition shows greater conductivity compared to previously reported Eu-doped SrCeO3. Under low pO2 Pr-doped SrCeO3 exhibited n-type behavior as conductivity increased with decreasing pO2, suggesting that the electronic conductivity of SrCeO3 is significantly enhanced by Pr doping. Under high pO2 conditions, Pr-doped SrCeO3 exhibited p-type conductivity with higher conductivity in the presence of water affirming its protonic conductivity. This work validates the use of Pr as a means of enhancing electronic conductivity in proton conducting perovskites.

Comparison of ceramic α-alumina and modified γ-alumina membranes for H2 separation

This article provides details of a study that investigates hydrogen (H2) separation, purification and transport behaviour of a ceramic α-alumina membrane and compares it with that of a γ-alumina membrane modified with Boehmite sol.

Influence of rare-earth doping on the phase composition, sinterability, chemical stability and conductivity of BaHf0.8Ln0.2O3-δ (Ln = Yb, Y, Dy, Gd) proton conductors

BaHf0.8Ln0.2O3-δ doped with rare earth elements with different ionic radii (Ln = Yb, Y, Dy and Gd) as candidate materials for solid oxide fuel cells and H2 separation membrane have been prepared. Their phase composition, sinterability, chemical stability and conductivity were studied systematically. The rare earth elements are successfully incorporated into the main phase crystal lattice of barium hafnate to generate a single perovskite phase. The relative density of all samples sintered at 1600 °C reaches above 90%, and Y-doped BaHfO3 has the highest relative density (94.7%) and the biggest grain size (about 1 μm) among all samples. The conductivities of the samples firstly increase and then decrease with the increase of the doped ion radius. Among all samples the conductivity of BaHf0.8Y0.2O3-δ is the highest and reaches 6.02 × 10−3 S cm−1 in wet air at 700 °C, which is attributed to the good sinterability and suitable crystal structure (tolerance factor and free volume). All samples also show excellent chemical stability in the test atmospheres, including saturated H2O steam, pure H2 and CO2, 200 ppm H2S/Ar and boiling water. The Pt/BaHf0.8Y0.2O3-δ electrolyte/Pt single cell was fabricated with a 530 μm-thick disk and its electrochemical properties were tested. The peak power density reaches 10.21 mW cm−2 at 700 °C, which is comparable to similar fuel cells reported. These results suggest that BaHf0.8Y0.2O3-δ is a promising electrolyte candidate for proton-conducting fuel cells.