H2 Permeance Research Articles

Boosting the H2/CO2 and H2/N2 selectivities of a graphene oxide membrane by shrinking the membrane interlayer spacing via thermal treatment

Graphene oxide (GO) membranes have been widely studied and used for gas separation processes, but some structural changes are necessary to guarantee high membrane selectivities. The thermal reduction process stands out for reducing the interlayer channel size of the GO nanosheets to improve the molecular sieving mechanism. Herein, thermally annealed GO layers were deposited on the outer surface of porous alumina hollow fiber substrates and the produced composite membranes were tested for selective hydrogen (H2) separations. The influence of the thermal annealing process at different mild temperatures (80 and 160 °C) on the characteristics of the GO structure was investigated towards the improvement of the membrane efficiency for H2 separation. ATR-FTIR results confirmed the elimination of oxygenated groups, and XRD analyses showed the GO interlayer space decreased from 8.71 to 7.38 Å after the thermal annealing process at 160 °C. The GO thermally annealed membrane presented an H2 permeance of 2032.47 ± 101.69 GPU and an H2/N2 selectivity of 12.16 ± 0.30, which is 315% greater than the selectivity of the pristine GO membrane. Hence, the application of the thermal reduction method to produce GO membranes with greater selectivities is a viable alternative to deal with gas separation processes.

Hierarchical and defect-free metal-organic framework membranes deep-rooted within flexible nanofiber substrate

Defect-free MOFs membrane on flexible substrate is challenging and promising for industrial applications. In this work, electrospun nanofiber substrates were employed to construct deep-rooted and defect-free ZIF-8 membranes by a symbiotic layer composed of interpenetrated nanofibers and ZIF-8. Nanofibers provide sufficient nucleation sites to construct an interpenetrated “symbiotic layer”, which further supports ZIF-8 growing to be defect-free. Importantly, benefiting from this symbiotic layer, the rigidity difference between substrate and ZIF-8 is well balanced, resulting in ZIF-8 membrane deep-rooted within the support. Furthermore, tannic acid (TA), was combined to modulate the surface chemistry and inter-crystalline defects of ZIF-8 membranes. Finally, a hierarchical ZIF-8 membrane with nanofibers as flexible substrates were obtained. The prepared PAN/TA2-NZIF-80.25 membrane exhibits H2 permeance of 2408 GPU and H2/CO2 selectivity of 21.80. Specifically, compared with the reported MOFs membrane for H2 separation, the H2 permeance of this work locates in a very high region, while proper H2/CO2 separation factor is still remained, exceeding the 2008 upper bound of H2/CO2 separation. Importantly, this membrane presents stable microstructures and separation performance after twisting. The proposed deep-rooted and defect-free ZIF-8 membrane on flexible substrate is competitive to achieve industrial application.

Study on gas permeability and selectivity in metal oxide-doped g-C3N4/PC membranes with metal-doped fillers

This investigation explores the permeation characteristics of hydrogen (H2), carbon dioxide (CO2), and oxygen (O2) using metal oxide@g-C3N4/polycarbonate (M@CN/PC) membranes. This study involves the testing of various metals, namely lithium (Li), magnesium (Mg), and silicon (Si), with different filler percentages of M@g-C3N4 (3% and 10%). The permeability assessments were carried out at room temperature under a 40 psi pressure. The characterization of fillers and membranes was conducted using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Furthermore, we have also measured the permeability of H2, CO2, and O2, and evaluated the selectivity ratios of H2/CO2, H2/O2, and CO2/O2. Both permeability and selectivity were found to increase with M@CN content.

Molecular-scale hybrid membranes containing benzimidazole linkages on large-area α-alumina tubes for H2 purification

H2/CO2 separation is important in industry. Polymer, inorganic and hybrid membranes have been reported, however, high performance membranes with good scalability and large area are still lacked. Here, we fabricated a series of molecular-scale hybrid membranes (MHMs) containing benzimidazole linkages on rough α-alumina tubes. The membranes, with an area of 37.7 cm2 for each, exhibited a H2/CO2 selectivity of 14.2 (with a corresponding H2 permeance of 29.5 GPU) at 423 K and high H2 permeance of 310 GPU (with a corresponding H2/CO2 selectivity of 9.37) at 523 K. The membranes had good pressure and temperature tolerance. Besides, a two-stage membrane system was designed to study the effect of pressure and membrane area on hydrogen production.

Facile infiltration of polyethyleneimine as a strong CO2 retardant in scalable dual-polymer membranes for H2/CO2 separation

Successful pre-combustion CO2 capture from synthetic gas for H2 production requires effective membrane separation technology. While polymer-based membrane materials offer promising industrial scalability, they generally lack a sufficiently high H2/CO2 selectivity to make this process energy-efficient. In this work, we have designed a scalable dual-polymer blend membrane consisting of sulfonated polyphenylsulfone (sPPSU) and polybenzimidazole (PBI), and then being infiltrated with amine-rich poly(ethyleneimine) (PEI) molecules as effective CO2 retardants to substantially elevate the H2/CO2 selectivity. PEI molecules were infiltrated into the dual-polymer matrix via solution-treatment to crosslink the polymer network and retard CO2 transport using its amine-rich nature. The PEI infiltration dramatically increased the H2/CO2 selectivity of the dual-polymer matrix from 4.6 to up to 59.3 while maintaining a minimum H2 permeability of 2.49 Barrer at a low temperature of 35 °C, which not only surpasses the Robeson upper bound but also places the newly developed membrane among the best-performing polymer-based membranes. More importantly, the solution infiltration of PEI incurs no phase segregation, maintaining the polymer mechanical robustness, which is crucial for industrial scaling. This study offers promising opportunities to develop three-polymer membrane systems for H2/CO2 separation using synergistic polymer blends and CO2-retarding molecules.

Theoretical investigation of supramolecular organic framework membranes for hydrogen purification

Given that SOF materials have both inorganic and organic properties and are easy to prepare and structurally designable, this paper carries out the microbehavioral analysis and membrane design of SOF-8, SOF-9, and SOF-10 membranes for the hydrogen purification process of RMFCs. Since three materials have complementary performance characteristics for hydrogen purification, this paper focuses on the gas separation behavior of these three composite membranes using molecular dynamics simulations. Results showed that the SOF-9a+10a composite membranes could 100% block CO2 and CO, and displayed an excellent H2 permeability of 6.118 × 105 GPU during H2/CO2 separation, which exceeded the industry standard by nearly 105 times. Additionally, the SOF-9a+8 and SOF-10a+8 composite membranes improved gas selectivity and maintained high H2 permeability. Moreover, microdiffusion analyses revealed that the small pore sizes and irregular-shaped pore channels effectively hindered CO2 and CO transport. Microscopic analysis shows the potential of SOF composite membranes for gas separation.

Wrinkled metal-organic framework thin films with tunable Turing patterns for pliable integration.

Flexible integration spurs diverse applications in metal-organic frameworks (MOFs). However, current configurations suffer from the trade-off between MOF loadings and mechanical compliance. We report a wrinkled configuration of MOF thin films. We established an interfacial synthesis confined and controlled by a polymer topcoat and achieved multiple Turing motifs in the wrinkled thin films. These films have complete MOF surface coverage and exhibit strain tolerance up to 53.2%. The enhanced mechanical properties allow film transfer onto various substrates. We obtained membranes with large H2/CO2 selectivity (41.2) and high H2 permeance (8.46 × 103 gas permeation units), showcasing negligible defects after transfer. We also achieved soft humidity sensors on delicate electrodes by avoiding exposure to harsh MOF synthesis conditions. These results highlight the potential of wrinkled MOF thin films for plug-and-play integration.

Molecular Density Fluctuations Control Solubility and Diffusion for Confined Aqueous Hydrogen.

Hydrogen's contribution to a sustainable energy transformation requires intermittent storage technologies, e.g., underground hydrogen storage (UHS). Toward designing UHS sites, atomistic molecular dynamics (MD) simulations are used here to quantify thermodynamic and transport properties for confined aqueous H2. Slit-shaped pores of width 10 and 20 Å are carved out of kaolinite. Within these pores, water yields pronounced hydration layers. Molecular H2 distributes along these hydration layers, yielding solubilities up to ∼25 times those in the bulk. Hydrogen accumulates near the siloxane surface, where water density fluctuates significantly. On the contrary, a dense hydration layer forms on the gibbsite surface, which is, for the most part, depleted of H2. Although confinement reduces water mobility, the diffusion of aqueous H2 increases as the kaolinite pore width decreases, also a consequence of water density fluctuations. These results relate to H2 permeability in underground hydrogen storage sites.

Oriented growth of large-area metal-organic framework ZIF-8 membrane for hydrogen separation

Optimal orientation is the key factor to optimize the gas separation performance of metal-organic framework (MOF) membranes. However, it is still greatly challenging to prepare large-area oriented MOF membranes for industrial applications. Herein, we prepared compact and (100) oriented zeolitic-imidazolate framework-8 (ZIF-8) membranes with membrane area up to 500 cm2 on the graphite substrate via support-induced strategy within 2 h. With membrane thickness of only 620 nm, the (100) oriented ZIF-8 membranes exhibit high gas separation performances due to the reduction of inter-crystalline defects and permeation resistance. At 100 °C and 1 bar, the separation factors of H2/CO2, H2/CH4 and H2/C3H8 are 18.5, 58.2 and 101.6, respectively, with H2 permeance of about 160 x 10−9 mol m−2 s−1·Pa−1. The different positions of the 500 cm2 ZIF-8 membrane show complete consistency in orientation and separation performance, recommending this membrane suitable for future industrial applications. Further, also oriented ZIF-67 and MOF-303 membranes can be consistently prepared by this strategy, confirming its versatility for the preparation of large-area MOF membranes.

Crystalline Metal-Organic Framework Coatings Engineered via Metal-Phenolic Network Interfaces.

Crystalline metal-organic frameworks (MOFs) have garnered extensive attention owing to their highly ordered porous structure and physicochemical properties. However, their practical application often requires their integration with various substrates, which is challenging because of their weakly adhesive nature and the diversity of substrates that exhibit different properties. Herein, we report the use of amorphous metal-phenolic network coatings to facilitate the growth of crystalline MOF coatings on various particle and planar substrates. Crystalline MOFs with different metal ions and morphologies were successfully deposited on substrates (13 types) of varying sizes, shapes, and surface chemistries. Furthermore, the physicochemical properties of the coated crystalline MOFs (e.g., composition, thickness) could be tuned using different synthesis conditions. The engineered MOF-coated membranes demonstrated excellent liquid and gas separation performance, exhibiting a high H2 permeance of 63200 GPU and a H2/CH4 selectivity of 10.19, likely attributable to the thin nature of the coating (~180 nm). Considering the vast array of MOFs available (>90,000) and the diversity of substrates, this work is expected to pave the way for creating a wide range of MOF composites and coatings with potential applications in diverse fields.

Crystalline Metal–Organic Framework Coatings Engineered via Metal–Phenolic Network Interfaces

AbstractCrystalline metal–organic frameworks (MOFs) have garnered extensive attention owing to their highly ordered porous structure and physicochemical properties. However, their practical application often requires their integration with various substrates, which is challenging because of their weakly adhesive nature and the diversity of substrates that exhibit different properties. Herein, we report the use of amorphous metal–phenolic network coatings to facilitate the growth of crystalline MOF coatings on various particle and planar substrates. Crystalline MOFs with different metal ions and morphologies were successfully deposited on substrates (13 types) of varying sizes, shapes, and surface chemistries. Furthermore, the physicochemical properties of the coated crystalline MOFs (e.g., composition, thickness) could be tuned using different synthesis conditions. The engineered MOF‐coated membranes demonstrated excellent liquid and gas separation performance, exhibiting a high H2 permeance of 63200 GPU and a H2/CH4 selectivity of 10.19, likely attributable to the thin nature of the coating (~180 nm). Considering the vast array of MOFs available (>90,000) and the diversity of substrates, this work is expected to pave the way for creating a wide range of MOF composites and coatings with potential applications in diverse fields.

Hydrogen permselective membrane prepared by plasma treatment of porous ceramic substrates

Abstract Demand for hydrogen is increasing as we move toward a decarbonized society. Membrane separation methods have attracted attention as a way to reduce the cost of hydrogen production. In this study, we focused on boron nitride (BN) as a chemically stable porous substrate material. CVD treatment at 250°C has been investigated for porous BN, but selectivity did not develop. Therefore, we focused on atmospheric pressure plasma as a treatment method. The objective of this study is to develop a membrane with high hydrogen selective permeance by immersion in silicon alkoxide after plasma treatment. After plasma treatment for 100 s, the H2 permeance was 3.52×10−6 [mol m−2 s−1 Pa−1] and the H2/N2 permeance ratio was 18.25. Since molecular hydrogen can pass between the BN crystal faces, it is considered that silica reacted with the hydroxy groups formed on BN by plasma treatment and blocked the space between crystals. Therefore, it is suggested that the performance of the separation membrane changes depending on the number and distribution of hydroxyl groups by plasma treatment, and further stabilization is needed.

Development of high hydrogen permselective membranes by using a vapor treatment method

Abstract In recent years, the depletion of energy resources and global warming have led to the promotion of new energy resources. Hydrogen is attracting attention as one of the energy sources for the carbon-neutral society by 2050. Membrane separation is a method for separating and purifying hydrogen. In this study, we focused on developing high hydrogen permselectivity of silica membranes. We investigated the conditions necessary for membrane production to obtain a thin, dense separation layer. The results exhibited that the hydrogen permeation selectivity was enhanced in the silica membrane through the utilization of a 2-step deposition technique, which involves the combination of alternative feed and counter-diffusion chemical vapor deposition (CVD). The H2 permeance achieved by the 2-step method is 1.4×10−6 [mol m−2 s−1 Pa−1], representing 1.4 times higher than that of counter-diffusion CVD. In addition, the permeance ratio, which represents hydrogen selectivity, was significantly enhanced with the 2-step method, with H2/C3H8 = 260, twice as high as with CVD. Elemental mapping analysis of the cross-sectional structure revealed a concentration gradient in the deposited silica within the intermediate layer. This indicates that the silica separation layer may become an asymmetric structure. The 2-step method is expected to yield a thinner dense layer, which could contribute to improved permeance of silica separation membranes by reducing permeation resistance.

Development of a hydrogen permselective silica membrane and its application to the thermochemical water splitting method

Abstract The thermochemical water splitting IS process is one of the hydrogen production method to use a heat directly. The temperature of the thermal decomposition of water (4000 K) can be reduced under 700 K by introducing I2 and SO2 as recycling catalysts. One of the problems in the IS process is that the conversion of the HI decomposition reaction is low at about 20%. If a membrane reactor with the H2 permselective membrane is applied to the HI decomposition reaction, the hydrogen can be extracted to improve the HI conversion. We focus on a counter diffusion CVD method for the preparation method of the membranes. Two reactants (e.g. silica precursor and oxidant) are provided at the opposite side of the porous substrates and hybrid silica is deposited inside the pore of the substrate. The pore sizes are controlled by introducing organic functional groups to silica precursor. In this study, the silica hybrid membrane with high H2 permeation performance and high H2/HI selectivity were developed by introducing organic functional groups. Effects of the organic functional groups were summarized by using a pore model. The HI gas and other inorganic gases permeation performance were tested through silica hybrid membranes.

Synergistic interfacial interaction in polyetherimide/ZIF-7 mixed matrix membranes for enhanced H2/CO2 separation

Mixed matrix membranes (MMMs), consisting of a continuous polymer phase and a discontinuous molecular sieve phase, present a promising alternative to polymeric membranes for gas separations due to their advantages of high processability with outstanding separation efficiency. The suppression of sieve-in-a-cage and filler agglomerations, major challenges in existing MMMs, is systematically validated through a combination of polyimide and zeolitic imidazolate framework-7 (ZIF-7) nanofillers to enhance the H2/CO2 separation performance. The polyetherimide (Ultem) exhibits excellent interfacial interaction with ZIF-7 nanofillers within the MMMs, enabling the accommodation of high ZIF-7 concentrations, up to 40 wt%, due to its hydrophobic nature. The Ultem/ZIF-7 (60/40 wt/wt) MMMs represent significant enhancements in both H2 permeability and H2/CO2 selectivity, showing increases of 35 % and 65 %, respectively, compared to the pristine Ultem membrane. Furthermore, the enhancement in the intrinsic H2/CO2 separation performance of ZIF-7, estimated by the Maxwell equation, is likely attributed to the substantial rigidification of polymer chains in the vicinity of ZIF-7. Additionally, the difference in the activation energy of permeation for H2 and CO2 distinctly increases with ZIF-7 contents, highlighting the importance of the interfacial interaction in the separation performance of MMMs.

Thermally Annealed High-Aspect-Ratio ZIF-8 Nanoplates-Incorporated Mixed Matrix Membranes for Improved H2/CO2 Selectivity.

The main challenge in the preparation of MOF-based mixed matrix membranes is to construct a good interface morphology to improve the gas separation performance and stability of the membranes. Herein, high-aspect-ratio ZIF-8 nanoplates for H2/CO2 separation membranes were synthesized by direct template conversion. The ZIF-8 nanoplates were prepared with the commercial Matrimid polymer to form MMMs by the flat scraping method. The homogeneous dispersion of high-aspect-ratio nanoplates in the membrane and the good compatibility between the filler and the matrix caused by the thermal annealing operation improve the gas separation performance and mechanical properties of MMMs. The H2/CO2 selectivity of MMMs loaded with 30 wt % ZIF-8 nanoplates increased to 10.3, and the H2 permeability was 330.1 Barrer. This synthesis method can be extended to prepare various ZIF nanoplates with elevated aspect ratios to obtain excellent performance fillers for gas separation of MMMs. In addition, the thermal annealing operation allows more efficient gas separation in polymer membranes and is a feasible way to design excellent and stable MMMs.

Deep eutectic solvent engineered GO/ZrO2 nanofiller for mixed matrix membranes: An efficient hydrogen gas separation

AbstractThis study explores fabrication and characterization of mixed matrix membranes (MMMs) for gas separation, employing a cost‐effective solution casting method. Polycarbonate (PC) and polystyrene (PS) blends are combined with graphene oxide (GO) and zirconium dioxide (ZrO2) nanofillers, with and without a deep eutectic solvent (DES) obtained through hydrogen bond exchange. Various MMMs compositions (2–20 wt%) are systematically examined using diverse characterization techniques, including differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, porosity determination, and water contact angle analysis. The MMMs exhibit enhanced gas permeability and selectivity, surpassing conventional membrane materials. Notably, H2 gas permeability reaches outstanding levels, with the composition PC/PS‐DES‐GO/ZrO2 at 20 wt% (PBC20‐IV) demonstrating the highest value of 86.32 Barrer. This superior performance is attributed to the unique properties of ZrO2, increased sorption capacity of GO, and enhanced thermal stability due to DES. Permeability data for CO2, N2, O2, and CH4 also show significant values, aligning with the observed trends in H2 permeability. Robeson's plot for the H2/CO2 gas pair surpasses the 2008 upper bound, placing the MMMs in a novel category for gas separation membranes. The incorporation of DES‐modified nanofiller blend composites presents a promising strategy for the potential production of pure hydrogen.

Enhanced hydrogen selectivity of allylhydridopolycarbosilane (AHPCS)-derived silicon carbide membranes via air curing

Hydrogen is a critical element in numerous industrial processes and as a clean energy source. This study investigates Allylhydridopolycarbosilane (AHPCS)-derived membranes as a viable alternative to conventional Silica (Si) membranes for hydrogen separation. The AHPCS membranes were fabricated using a three-step process involving pre-firing at 300 °C in N2, air curing, and pyrolysis at 700 °C in N2. By optimizing the air-curing temperatures, the cross-linking of AHPCS-derived membranes was improved, leading to enhanced hydrogen selectivity. The highest H2 permeance of ∼1 × 10−6 mol/(m2 s Pa), accompanied by H2/N2 selectivity of ∼200 and H2/C3H8 selectivity of 3386, achieved through air curing at 600 °C followed by pyrolysis at 700 °C. AHPCS membranes showcased remarkable selectivity for H2/N2 with low H2 activation energy (3−5 kJ/mol), clearly surpassing silica membranes and demonstrating their superior performance. These findings underscore the potential of AHPCS membranes for gas separation and purification applications, marking a significant stride in membrane science.

Effect of cathode ink formulation on the hydrogen crossover and cell performance of proton exchange membrane water electrolyzers

The permeation of H2 through the membranes of proton exchange membrane water electrolyzers (PEMWEs) is a critical safety concern because of the risk of explosion when H2 mixes with O2 at the anode and increases in concentration. In this study, we investigated the modification of the cathode catalyst layer in the membrane electrode assembly as a strategy for achieving the safe operation of PEMWEs. The effects of the polytetrafluoroethylene (PTFE) content and type of ionomer in the cathode catalyst layer on the dissolved H2 concentration, H2 crossover, and electrochemical performance were investigated. The lowest dissolved H2 concentration and H2 permeation rate were achieved when 8 wt% PTFE was used. Consequently, the H2 volume fraction in O2 at the anode was less than 0.88 %. Additionally, using the Nafion ionomer (D520, ion exchange capacity: 1 mmol g−1), H2 volume fractions of 1.27 % and 1.34 % were obtained at 0.08 and 5 A cm−2, respectively. These values are below the lower explosion limit of H2 in O2 (4 %), implying that the PEMWE can be safely operated in the low-to-high current density range under ambient pressure. These results provide key guidelines for the design of high-safety cathode catalyst layers for PEMWEs.

Highly-efficient hydrogen purification with the T-C3N2 membrane via strain and charge engineering as well as their synergistic effect

The efficient separation and purification of high-purity hydrogen is imperative and desirable. We systematically explored the H2 purification performance of the T-C3N2 membrane with and without biaxial compressive (BC) strain and charge engineering by using MD simulations and DFT calculations. We found that the pure T-C3N2 membrane has relatively poor H2 selectivity as CO2 can also permeate through the membrane, and two modulation methods of BC-strain and charge were thus introduced separately to enhance the H2 separation performance for the first time. The T-C3N2 membrane with BC-strains modulation (1 %–3%) has excellent H2 permeance of 1.60 × 107–1.85 × 107 GPU at 300 K with 15.6 % enhancement with respect to the pure T-C3N2 membrane. The selectivity of H2 over gases (CO, N2, CO2, H2O, CH4) was drastically improved, for example, H2/CH4 is enhanced from 5.8 × 1020 to 2.1 × 1036 under 3 % strain engineering. The introduction of charge (1e–3e, 1e−–2e−) also enhances the H2 permeance of 1.47 × 107–1.68 × 107 GPU and the selectivity at 300 K. In particular, the charge (1e) and (1e−) modulations exhibit a desired permeance-selectivity trade-off for H2 purification with the enhancement of 5 % permeability and at least 1.3 times selectivity of H2 to other gases, respectively. Finally, the synergistic effect of BC-strain and charge on the H2 separation was studied, and it is much superior to separated BC-strain and charge engineering for H2 purification, where the H2 permeance enhances up to 1.86 × 107–1.89 × 107 GPU, and the H2 selectivity at 300 K is also enlarged at least ten times compared with that of the most effective modification of the isolated 2 % BC-strain and 1e charge, indicating synergistic effect further enhances the H2 separation performance. Therefore, the excellent modulations of appropriate BC-strain and charge engineering, particularly for their synergistic effect make the T-C3N2 membrane a promising candidate for highly permeant and selective H2 separation and purification that would be easily realized experimentally.