H2 Permeance Research Articles

Enhancement of H2 Separation Performance in Ring-Opened Tröger’s Base Incorporating Modified MOFs

Energy-efficient hydrogen (H2) recovery technology is of great significance to developing H2-based economy and accomplishing global carbon-neutrality with minimized worldwide energy consumption. A ring-opened Tröger’s base (TBOR) polymer membrane as a highly H2-selective membrane holds great promise for recovering H2 while partial microporosity loss induced by ring opening reaction deteriorates the H2 permeability across the pure membrane. Herein we introduce polydopamine-modified ZIF-8 (PDA-ZIF-8) nanoparticles into TBOR to develop a permeable membrane for selective H2 separation. The resultant mixed matrix membranes demonstrate the significantly improved H2 permeability, owing to the porous structure of ZIF-8, and efficiently exclude large molecules of CH4 and N2, giving rise to promising H2/CH4 and H2/N2 ideal selectivities. The PDA-ZIF-8 interacts with the secondary amines of TBOR via hydrogen bonds, creating good interfacial adhesion, thus preventing a sharp selectivity loss that occurred in most mixed matrix membranes upon increasing filler loadings. At a maximum ZIF-8 loading of 50 wt %, the pure H2 permeability is 457 Barrer, increasing to 4.2 times as compared with the undoped membrane, and the ideal H2/CH4 selectivity of 57 and ideal H2/N2 selectivity of 59 are achieved. The H2/CH4 separation properties remain unchanged upon increasing feed pressures, indicating the membrane’s good stability when operated at realistic high pressures. The ring-opening functionalization of Tröger’s base has proven to be very useful for fabricating selective mixed matrix membranes and can be extended for designing H2-selective hybrid membranes with other porous fillers.

In-situ interfacial crosslinking of NH2-MIL-53 and polyimide in MOF-incorporated mixed matrix membranes for efficient H2 purification

The key issue to avoiding the degradation of gas separation performance due to the formation of non-selective defects in mixed matrix membranes (MMMs) is to promote the interfacial compatibility of fillers with the continuous polymer matrix. In this work, we report an efficient and simple method to prepare MMMs by crosslinking metal organic frameworks (MOF) and polyamic acid (PAA) (the precursor of polyimide), in which NH2-MIL-53 particles are thermally crosslinked with the PAA during the imidization reaction, forming hydrogen bonds and amide bonds at the interface. The resulting enhanced interfacial force greatly improves the interfacial compatibility of the membrane, which is also more conducive to the separation of H2/CO2. Among the as-prepared samples, PI-NH2-MIL-53 MMMs loaded with 30 wt% MOF exhibit excellent H2 permeability (384.1 Barrer) and H2/CO2 permeation selectivity (16.7), which are significantly higher than the 2008 Robeson upper bound. The membranes also display enhanced mechanical characteristics and long-term stability. Here, building strong interactions on MOF/polymer MMMs using an in-situ cross-linking strategy to enhance membrane performance provides a new opportunity to develop advanced membranes for industrial gas separation applications.

Hydrogen gas permeation in peroxide‐crosslinked ethylene propylene diene monomer polymer composites with carbon black and silica fillers

AbstractThis study investigated the effect of two types of fillers, carbon black (CB) and silica, on the H2 permeation of peroxide‐crosslinked ethylene propylene diene monomer (EPDM) polymers at different pressures (1.2–9.0 MPa). The H2 uptake was linearly correlated with the exposure pressure in all specimens. The H2 solubility in the filled EPDM composites also increased linearly with an increase in the filler content. The H2 solubility was determined by the absorption of polymer networks and adsorption at the filler surface in the CB‐filled EPDM. Meanwhile, the H2 solubility in neat and silica‐filled EPDM was dominated by the polymer network absorption. In the filled EPDM, H2 diffusivity decreased because the filler increased the tortuosity of the polymer. The effects of filler on H2 permeation were largest in the high‐abrasion and semi‐reinforcing furnaces, while the effects were lowest in the silica filler. This trend was associated with the surface area and interface of the fillers. The correlations of the average diffusivity (or permeability) with the filler content and crosslink density of the composites were observed and discussed. From the resulting relationships, we can predict the H2 permeation properties of the compounded EPDM candidates, when used as seal materials, under high‐pressure environment in H2‐refueling stations.

Process parametric testing and simulation of carbon membranes for H2 recovery from natural gas pipeline networks

The construction of H2 infrastructure is crucial for accomplishing an H2 economy in the future, however, the current cost of H2 transportation is relatively expensive due to the lack of infrastructure. One of the alternatives is to inject H2 into the existing natural gas pipeline networks, which is subsequently recovered by membrane technology for end-users. In this work, the high-performance cellulose-derived asymmetric carbon hollow fiber membrane developed in previous work was tested for H2/CH4 separation. The experimental results demonstrated the outstanding separation performance and good stability of the developed carbon membrane with H2 permeance of up to 21.3 GPU and H2/CH4 separation factor of up to 96 at 50 ℃ under different feed pressures of 5–40 bar and H2 concentrations of 5–25 vol%. The techno-economic feasibility analysis for H2 recovery from the natural gas pipeline networks was conducted. A two-stage carbon membrane system was designed to produce high-purity H2 (>99.7 vol%) by UniSim simulation. Notably, the higher 1st-stage feed pressure (8–40 bar) and the higher feed H2 content (5–25 vol%) significantly lessened the required membrane areas, contributing to reducing the major expense on H2 recovery cost. Moreover, the influences of the process operating factors (e.g., feed H2 content, feed pressure, etc.) on H2 recovery cost were systematically explored, and the results indicated the considerable impact of process design on H2 recovery cost.

Hetero-Polycrystalline Membranes with Narrow and Rigid Pores for Molecular Sieving.

Molecular sieving membranes have great potential for energy-saving separations, but they suffer from permeability-selectivity trade-off limitation. In this report, simultaneous hetero-crystallization and hetero-linker coordination of metal-organic framework (MOF) hollow fiber membranes through one-pot synthesis for precise gas separation is reported. It is found that the hetero-polycrystalline membranes consist of 2D and 3D MOF phases and are defect-free and roughly orientated, hetero-linker exchange of 3D phase by larger geometric ones can narrow transport pathway, and framework rigidification occurs and thus fixes MOF channels. The prepared membranes are robust and reproducible, and exhibit substantially improved performance, with H2 /CO2 , H2 /N2 , and H2 /CH4 selectivities up to 361, 482, and 541, respectively, accompanied by high H2 permeance over 1100gas permeation units, which can easily outclass trade-off upper bounds of state-of-the-art membranes.

Simultaneously enhanced gas permeability, selectivity and aging stability of carbon molecular sieve membranes by the molecule doping of silicon

Simultaneously enhancing the gas permeability, selectivity and aging stability of carbon molecular sieve membrane (CMSM) is extremely difficult. Facing such poser, a novel silicon doped CMSM at molecular level was prepared by copolymerizing siloxane with single Si–O–Si unit into the backbone of polyimide (PI). This can effectively avoid prior separated structure or multiple Si–O–Si structures and strongly alter the chains packing and thermostability of PI, finally determine the pore structure and thermodynamic behavior. The simple design adjustment simultaneously exhibits the triple enhanced effects on the gas permeability, selectivity and aging stability. The best molecule doped CMSM exhibits the ultra-high H2 permeability (12482 Barrer, 87% higher), 26% higher H2/CH4 selectivity, and 32% higher H2/N2 selectivity than pure PI based CMSM. Additionally, such CMSM also has a much better aging stability than pure CMSM and most reported CMSMs. After stabilization, it still maintains a high H2 permeability (8000 Barrer). And the hyper-aging CMSM also exhibits a good aging resistance showing a H2 permeability of 5300 Barrer, as well as high selectivity of H2/CH4 (125) and H2/N2 (106) after 35 days. This work opens a new way on designing CMSM with excellent performance through heteroatom doping to need future application.

In-situ synthesis of [Ni(tzba)0.5(F)(bpy)] membrane with high H2 permeability through ultramicropores and selective CO2 adsorption with strong affinity of uncoordinated N-Ni-F− active sites

To simultaneously purify H2 and capture CO2 in the steam methane reforming (SMR) process for H2 production, a bifunctional metal organic framework (MOF) membrane ([Ni(tzba)0.5(F)(bpy)]) was proposed via an in-situ synthesis method to efficiently permeate H2 through ultramicropores and selectively adsorb CO2 with the strong affinity of uncoordinated N-Ni-F− active sites. Ni(tzba)0.5(F)(bpy) exhibited a good CO2 uptake capacity (4.3 mmol/g at 273 K and 110 kPa) because the F− anionic and exposed uncoordinated tetrazolate N atoms in ligands have an excellent affinity to CO2. Dynamic breakthrough experiments suggested that Ni(tzba)0.5(F)(bpy) achieved efficient separation of CO2 from H2, CH4, and N2. Ni(tzba)0.5(F)(bpy) MOF membrane also shows outstanding H2/CO2 separation performance because the high adsorption capacity of CO2 reduced CO2 mobility. The H2 permeability of 1.59 × 105 Barrer and H2/CO2 ideal selectivity of 14.43 greatly exceeded the latest upper bound. Continuous permeability tests of up to 100 h demonstrated the long-term stability of the Ni(tzba)0.5(F)(bpy) MOF membrane for H2 separation applications. Density functional theory (DFT) calculations clarified the adsorption mechanism of Ni(tzba)0.5(F)(bpy) towards gases.

In-situ etching MOF nanoparticles for constructing enhanced interface in hybrid membranes for gas separation

Metal-organic frameworks (MOFs) based hybrid membranes have great potential for energy-efficient gas separation. However, the defective interface structure greatly depresses their separation performance. In this work, a distinctive interfacial design strategy via in-situ etching ZIF-8 nanoparticles is proposed to construct hybrid membranes with nearly defect-free interfaces. The nanoscale etching of ZIF-8 nanoparticles in polymer matrix with acid group (PI-COOHx) is well controlled by the amount of carboxyl group and reaction time. Owing to the strong coordination interaction between Zn2+ ions and –COOH groups, the residual ZIF-8 nanoparticles are tightly wrapped by polymer matrix. Molecular simulation was performed to study the in-situ etching ZIF-8 in PI-COOHx matrix in molecular level. The resulted hybrid membranes (PI-COOHx/E-ZIF-8) exhibit simultaneously enhanced permeability and selectivity with increasing filler loading content. Benefiting from the rational interfacial design, the effective loading content of ZIF-8 nanoparticles is up to 50 wt% for PI-COOH20/E-ZIF-8 membrane. The H2, CO2, and O2 permeability of the membrane are 3058.6, 1429.0, and 459.0 Barrer, increasing by 468.5%, 288.3% and 348.2%, respectively, of pristine PI-COOH20 membrane, and the gas selectivity for H2/N2, H2/CH4, O2/N2, and CO2/CH4 gas pairs are greatly improved from 20.3, 23.4, 3.9 and 16.0 of pristine PI-COOH20 membrane to 30.7, 37.6, 4.6 and 17.6. The comprehensive separation performance for H2/N2, H2/CH4, and O2/N2 gas pairs surpass the 2008 upper bound and approach the 2015 upper bound. Meanwhile, the CO2 plasticization resistance of PI-COOH20/E-ZIF-8 membrane also achieves significant improvement from 6 bar of PI-COOH20 membrane to 27 bar. This work provides an effective and robust strategy to effectively enhance the interfacial compatibility of hybrid membranes.

Performance Requirements of Membrane Reactors for the Application in Renewable Methanol Synthesis: A Techno‐Economic Assessment

AbstractRenewable energy carriers are expected to play a key role in the defossilization of the energy and chemical sector. For renewable methanol synthesis, membrane reactors (MR) have been tested on a laboratory‐scale with promising results. However, membrane performance requirements that allow an economic benefit for their large‐scale deployment are missing. Therefore, a 1D Python MR model is coupled with an AspenPlus process simulation to conduct a techno‐economic assessment with focus on membrane performance. Two synthesis loop configurations are investigated: one where feed and sweep recycle are operated at the same pressure and one where the sweep recycle operates at atmospheric pressure. The results show that both configurations can offer technical benefits, if sufficiently high product separation can be achieved, but that for a compressed sweep recycle no economic benefits are possible. As a consequence, membranes used for methanol synthesis must endure operation at high pressure differences. Furthermore, the results highlight the critical role of the H2 permeance, which should remain below 1 × 10−9 mol m−2 s−1 Pa−1. From an economic standpoint high water permeation has a more beneficial effect than high methanol permeation.

Visualization of the gas permeation in core–shell MOF/Polyimide mixed matrix membranes and structural optimization based on finite element equivalent simulation

Core-shell MOFs recently have suggested the greater potential on gas separation of mixed matrix membranes (MMMs) than the single MOFs. In this work, two core–shell MOFs (ZIF-67@ZIF-8 (ZIF-67@8) and ZIF-8@ZIF-67 (ZIF-8@67)) with adverse structure were specially designed to explore what structure is more conducive to gas separation of MMMs. Moreover, a simplified equivalent simulation based on electrical conductivity of Maxwell model was adopted to predict the gas permeability and the internal gas permeation behavior for core–shell MOF based MMMs. The simulation exhibited the better predicted results than the Felske model and revealed the gas transport pathway. As a result, ZIF-67@8 based MMM with the shell-dependent transport and a thin interlayer had the highest H2 permeability of 224 Barrer and H2/CH4 separation factor of 76.7, which are 180% and 24% higher than neat PI, respectively. Finally, core–shell MOFs based MMMs also showed the lower temperature dependence of permeation for N2 and CH4 compared to pure PI. This work provides a unique method to investigate how core–shell structure affects the gas separation performance of MMMs, especially for equivalent simulation, which not only is proved to play as an efficient tool to predict the gas permeability, but also exhibits a great potential on investigation of gas transport pathway for the further structural optimization.

Enhancing the hydrogen permeation of alumina composite porous membranes via graphene oxide addition

Graphene oxide (GO) membranes have attracted considerable interest for hydrogen (H2) purification applications. However, the addition of GO into matrix materials to enhance the efficiency of H2 permeation remains a challenge. In this study, the fabrication of alumina/graphene oxide (AGO) composites containing varying contents of GO (0.5–3.0 wt.%) was investigated. The AGO composites were formed into pellets and sintered for 2 h at 1500 °C. Accordingly, the presence of GO in the membranes following sintering was confirmed by Raman spectroscopy. Additionally, the porosity of the AGO composites increased from 3.7% to 26.9% as the GO concentration increased from 0.5 wt.% to 3.0 wt.%. Furthermore, the average pore diameter of the AGO composites was in the range of 87–228 nm, and the pore size distribution was unimodal. The performance of the AGO membranes was investigated for the permeance of single gases H2 and N2 at 30–500 °C to evaluate their potential for H2 separation applications. The AGO membranes with a GO addition of 2.5 and 3.0 wt.% exhibited a high hydrogen permeance of 232–410 × 10−6 mol m−2 s−1 Pa−1, which was approximately 10 times greater than that of pristine Al2O3 membrane. Additionally, the ideal H2/N2 selectivity values ranged from 4.02 to 4.20. Furthermore, gas permeation through the AGO membrane was observed to follow the Knudsen diffusion mechanism.

Controlled Covalent Functionalization of ZIF-90 for Selective CO2 Capture & Separation.

Mixed Matrix Membranes (MMM) with enhanced selectivity and permeability are preferred for gas separations. The porous metal-organic frameworks (MOFs) materials incorporated in them play a crucial part in improving the performance of MMM. In this study, Zeolitic imidazolate frameworks (ZIF-90) are selected to fabricate Polyetherimide (PEI) MMMs owing to their lucrative structural and chemical properties. This work reports new controlled post-synthetic modifications of ZIF-90 (50-PSM-ZIF-90) with ethanolamine to control the diffusion and uptake of CO2. Physical and chemical properties of ZIF-90, such as stability and presence of aldehyde functionality in the imidazolate linker, allow for easy modulation of the ZIF-90 pores and window size to tune the gas transport properties across ZIF-90-based membranes. Effects of these materials were investigated on the performance of MMMs and compared with pure PEI membranes. Performance of the MMMs was evaluated in terms of permeability of different gases and selective separation of CO2 and H2 gas. Results presented that the permeability of all membranes was in the following order, i.e., P(H2) > P(CO2) > P(O2) > P(CH4) > P(C2H6) > P(C3H8) > P(N2), demonstrating that kinetic gas diffusion is the predominant gas transport mode in these membranes. Among all the membranes, permeability of pure PEI membrane was highest for all gases due to the uniform porous morphology. The pure PEI membrane showed highest permeability of H2, which is 486.5 Barrer, followed by 49 Barrer for O2, 29 Barrer for N2, 142 Barrer for CO2, 41 Barrer for CH4, 40 Barrer for C2H6 and 39.6 Barrer for C3H8. Results also confirm the superiority of controlled PSM-ZIF-90-PEI membrane over the pure PEI and ZIF-90-PEI membranes in CO2 and H2 separation performance. The 50-PSM-ZIF-90 PEI membrane exhibited a 20% increase in CO2 separation from methane and a 26% increase over nitrogen compared to the ZIF-90-PEI membrane. The 50-PSM-ZIF-90 PEI membrane showed 15% more H2/O2 separation and 9% more H2/CH4 separation than ZIF-90 PEI membrane. Overall, this study represents the role of controlled PSM in enhancing the property of new materials like ZIF and its application in MMMs fabrication to develop a promising approach for the CO2 capture and separation.

Graphene Nanoribbon Hybridization of Zeolitic Imidazolate Framework Membranes for Intrinsic Molecular Separation.

Zeolitic imidazolate frameworks (ZIFs) are promising for gas separation membrane, but their molecular cut-off differs from that expected from its intrinsic aperture structure because of their flexibility. Herein, we introduced graphene nanoribbons (GNRs) to rigidify the ZIF framework. Because the sp2 edge of the GNRs induces strong anchoring effects, the modified layer can be rigidified. Particularly, when the GNRs were embedded and distributed in the ZIF-8 layer, an intrinsic aperture size of 3.4 Å was observed, resulting in high H2 /CO2 separation (H2 permeance: 5.2×10-6 mol/m2 Pa s, ideal selectivity: 142). The performance surpasses the upper bound of polycrystalline MOF membrane performance. In addition, the membrane can be applied to blue H2 production, as demonstrated with a simulated steam reformed gas containing H2 /CO2 /CH4 . The separation performance was retained in the presence of water. The fundamentals of the molecular transport through the rigid ZIF-8 framework were revealed using molecular dynamics simulations.

Graphene Nanoribbon Hybridization of Zeolitic Imidazolate Framework Membranes for Intrinsic Molecular Separation

AbstractZeolitic imidazolate frameworks (ZIFs) are promising for gas separation membrane, but their molecular cut‐off differs from that expected from its intrinsic aperture structure because of their flexibility. Herein, we introduced graphene nanoribbons (GNRs) to rigidify the ZIF framework. Because the sp2 edge of the GNRs induces strong anchoring effects, the modified layer can be rigidified. Particularly, when the GNRs were embedded and distributed in the ZIF‐8 layer, an intrinsic aperture size of 3.4 Å was observed, resulting in high H2/CO2 separation (H2 permeance: 5.2×10−6 mol/m2 Pa s, ideal selectivity: 142). The performance surpasses the upper bound of polycrystalline MOF membrane performance. In addition, the membrane can be applied to blue H2 production, as demonstrated with a simulated steam reformed gas containing H2/CO2/CH4. The separation performance was retained in the presence of water. The fundamentals of the molecular transport through the rigid ZIF‐8 framework were revealed using molecular dynamics simulations.

Preparation and gas separation performance of seeding-free aqueous synthesis ZIF-8 membrane by homologous-like ligands method

Due to the poor heterogeneous nucleation properties of MOFs crystal on ceramic substrates resulting from the absence of interaction of MOFs with support substrate surface, it is usually difficult to prepare well-intergrown MOF membranes on substrate by simple in situ growth. In this work, a novel synthesis strategy was used to prepare defect-free ZIF-8 membranes on α-Al2O3 supports by depositing gold particles modified with 2-mercaptoimidazole which creates pseudo-surfaces to bridge the metal centers with support. The end groups of the 2-mercaptoimidazole guides the heterogeneous nuclei to the support surface as homologous-like ligands. Furthermore, investigation of the metal sources revealed that the ZIF-8 membranes prepared with Zn(OAc)2 as the zinc source possessed more continuous and well-intergrown ZIF-8 membranes with a thickness of about 1 μm compared to other zinc sources. The results of gas separation performance show that the optimized ZIF-8 membranes possess high hydrogen permeance and thermal stability. The gas separation selectivity for binary H2/CH4 mixture reached 20.8 at 150 °C and 1 bar, with a high H2 permeance of about 6.15 × 10−7 mol m−2 s−1Pa−1, which is promising for hydrogen separation and purification. Moreover, free-organic solvents and room temperature growth by our strategy dramatically reduces the difficulty of preparation and environmental destruction, thus offering a new avenue to prepare MOFs membrane with good separation performance.

Room-temperature in situ synthesis of MOF@MXene membrane for efficient hydrogen purification

MXene-based membranes with well-defined nanochannels are promising for gas separation. However, manipulating the interlayer structure to obtain high permeance and selectivity remains a great challenge. Herein, we report the construction of MOF@MXene membrane with significantly enhanced gas permeance and selectivity using room-temperature in situ synthesized MOF-801@MXene nanosheets as building blocks. Specifically, negatively charged MXene nanosheets can anchor Zr-metal ions from the surrounding through electrostatic interaction, and then coordinate with ligands at room temperature, yielding MOF-801 crystals with a particle size of approximately 20 nm uniformly grown on the MXene nanosheets. The membranes were then fabricated by vacuum filtration of the as-synthesized MOF-801@MXene nanosheets on the surface of porous organic substrate. The physicochemical properties of the as-synthesized MOF-801@MXene nanosheets and corresponding membranes were observed by XPS, AFM, SEM, IR, XRD, and gas adsorption analysis. Because the MOF-801 crystals can provide more transport channels for H2 molecules and exhibit high adsorption capacity for CO2 molecules to impede its diffusion, the resulting membranes display excellent gas separation performance with a H2 permeance of 2200 GPU and H2/CO2 selectivity of 26.6. Such a facile preparation method for MOF@MXene membranes could provide valuable insights into the development of advanced materials for molecular separation.

Tunable, strain-controlled nanoporous phosphorene membrane for highly efficient and selective H2/CH4 and H2/CO2 sieving: A combined molecular dynamics simulation and density functional theory study

Using a combined approach of molecular dynamics simulation and density functional theory, we develop a phosphorene nanopore to realize the tunable H2 sieving from mixtures with CH4 or CO2 via introducing the in-plane tensile strain. Our results show that 0%–10% strains exerted on the phosphorene membrane ensures a fast permeation of H2 while completely prohibiting the passage of CH4, demonstrating high efficiency and selectivity. Thanks to the outstanding mechanical flexibility of phosphorene, the strain tension can be utilized to easily control the pore size by which the permeance speed of H2 can be controlled in real time. However, all strained pores allow the passage of CO2, indicating a weaker strain regulation for H2/CO2 sieving by the phosphorene pore. Density functional theory calculations further confirm that the transport of H2 is energetically more favorable than CH4 and CO2 to traverse all phosphorene pores. Our findings exploit a flexible phosphorene membrane for real-time tunable H2/CH4 separation by controlling the in-plane strain.

The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes.

A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased.

Understanding Gas Permeation during High Pressure Operation of PEM Water Electrolyzers

Governments and industries across the world have initiated implementation of clean hydrogen (H2) to achieve zero emissions, yet significant challenges remain for large scale adoption. With the decreasing renewable electricity cost PEM water electrolyzers (PEMWEs) show significant potential for at scale deployment due to their high faradaic efficiency and high operating current density. To reduce the per kilogram price of hydrogen and increase the overall energy efficiency, PEMWEs need to be operated at high differential pressures (30 to 50 bar) to eliminate the need for compression during storage and transportation1. To achieve high faradaic efficiency, thinner membranes are required to reduce voltage losses within the cell. However, thinner membranes exhibit a higher gas permeation rate which leads to increased crossover of hydrogen from the cathode through the membrane to the anode. Such increased crossover of H2 not only reduces the efficiency but can also result in flammable gas mixtures (lower flammability limit for H2 in O2 is 4 %) as Iridium/Iridium oxide (anode catalyst) is inefficient in oxidizing H2 1. The addition of a gas recombination catalyst (GRC) to the membrane is an useful strategy to oxidize permeating H2 and minimize the H2:O2 ratio at the anode.In this study, a high pressure (up to 30 bar) electrolyzer setup is coupled with online gas chromatography-mass spectrometry to understand the H2 gas permeation in membranes as a function of H2 partial pressure and operating current density (simulated by varying the flow rates) as shown in Figure 1 . Effect of the GRC, its loading, and its location on the H2 permeation will be elucidated. Differences induced by the addition of anode and cathode catalyst layers on H2 permeation rates will also be presented.Figure 1. Ex-situ H2 permeation rate at different cathode operating pressure at 80 °C. The anode was maintained at 1 bar of O2 partial pressure Acknowledgement This research is supported by the U.S. Department of Energy (DOE) through the Hydrogen and Fuel Cell Technologies Office, program manager Dave Peterson Reference Bernt, M., Schröter, J., Möckl, M. & Gasteiger, H. A. Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 167, 124502 (2020). Figure 1

Structure-Property-Transport Relationships of Miscible Ionomer Blend Systems

Systematically designing the spatial arrangement is a key to understanding the structure and property relationships of proton-exchange membranes (PEM)/ionomers. Miscible polymer blends provide a cost-effective method for developing new materials in polymer science industries instead of synthesizing new polymers. In this study, commercially available Pentablock Copolymer (PBC(1.0)) ionomers were blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) in varying blend ratios. The FTIR studies showed composition-dependent interaction between the methyl group of PPO and phenyl rings of Polystyrene blocks in PBC(1.0). However, the sulfonate peaks at PBC(1.0): PPO (50:50) blend ratios were significantly reduced . The reduction in the peak intensity at this blend ratio may be attributed to specific interactions within this blend composition. The miscibility of the blends was confirmed by the single glass transition temperature from the DSC studies. And the application of the Fox rule to the experimental glass transition confirmed the conformational rearrangements of the blends. At the same time, applying the Kwei equation to the glass transition temperature confirmed the presence of specific interactions in the PBC(1.0): PPO (50:50) blend ratio observed in FTIR studies. The thermal stability studies demonstrated morphology dependence behavior with the rule of mixtures with the highest stability of 454oC at PBC(1.0): PPO (50:50) blend ratio. Higher stability at the PBC(1.0): PPO (50:50) blend ratio may be attributed to the specific interactions within this composition. High water uptake correlated with enhanced conductivity for the blend membranes, which strongly depended upon the PBC composition in the blend. Gas permeation studies exhibited that the blending can significantly reduce the permeability of H2 without altering its selectivity compared to pure membranes and Nafion, indicating the desired low fuel cross-over during the fuel cell operation. In conclusion, the gas transport and physical properties of the miscible blends showed strong dependence on composition. The morphological transitions that occur due to the compositional changes will be investigated in future studies.