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Aryl‐ether‐free anion‐exchange ionomers (AEIs) and membranes (AEMs) have become an important benchmark to address the insufficient durability and power‐density issues associated with AEM fuel cells (AEMFCs). Here, we present aliphatic chain‐containing poly(diphenyl‐terphenyl piperidinium) (PDTP) copolymers to reduce the phenyl content and adsorption of AEIs and to increase the mechanical properties of AEMs. Specifically, PDTP AEMs possess excellent mechanical properties (storage modulus>1800 MPa, tensile strength>70 MPa), H2 fuel‐barrier properties (7.6 A cm−2 current density) and 1.38 W cm−2 at 80 °C in H2/O2 and H2/air, respectively, along with a specific power (PPD/catalyst loading) over 8 W mg−1, which is the highest record for Pt‐based AEMFCs so far., Poly(alkyl‐terphenyl piperidinium) membranes and ionomers display outstanding hydrogen‐barrier properties and mechanical properties as well as excellent hydroxide‐ion conductivity that results in an excellent power density of 2.58 W cm−2 and 1.38 W cm−2 at 80 °C in H2/O2 and H2/air, respectively, along with a new, outstanding specific power in alkaline‐exchange‐membrane fuel cells.

Improving the chemical resistance of membranes without sacrificing their molecular sieving performance is highly challenging. Herein, a novel scalable methodology was developed for fabricating solvent-resistant nanofiltration membranes based on metal–polymer coordination (MPC) through a facile yet highly effective method. The controlled deposition of copper(I) iodide enabled the fine-tuning of the molecular sieving performance of MPC membranes by altering both their chemistry and morphology. Spectroscopic and morphological analyses were conducted to elucidate the microscopic and macroscopic properties of the membranes. The formation of coordination bonds between the metal and polybenzimidazole chains protected the membranes from dissolving in harsh organic solvents. Additionally, computational modeling was performed to reveal the stabilization energy and fractional free volume (FFV). Our work opens more sustainable avenues for robust membrane fabrication without conventional crosslinking, which requires reactive chemicals.

Polymer membranes have attracted interest in many areas, such as desalination, water treatment, gas separation, and energy storage and generation. Membrane fabrication requires large amounts of solvents for polymer dissolution. These solvents often show toxicity and need to be replaced by greener solvents to avoid adverse effects on human health and increase sustainability of the production processes. The need to use non-toxic compounds is increasing with the strong growth of the global membrane market. This review focuses on green solvents and green materials to prepare polymer-based membranes for the steadily increasing range of applications. Membrane fabrication techniques, choice of emerging green solvents, economic evaluation, and application areas will be comprehensively and critically reviewed. This review provides important selection guidelines for greener solvents for chemists, chemical engineers, and material scientists, focusing on organic chemicals and polymer processing. Furthermore, a simple cost analysis for a typical green solvent is provided, and its impact on the membrane fabrication cost is discussed. This journal is

Low-cost anion exchange membrane (AEM) water electrolyzers (AEMWEs) are a new technology for the production of high-purity hydrogen; however, their current density and durability are far lower than those of proton exchange membrane water electrolyzers (PEMWEs). Here, we report poly(fluorenyl-co-aryl piperidinium) (PFAP)-based anhydrous cathode AEMWEs that exceed the state-of-the-art PEMWEs with respect to current density. In addition to a rational electrode design, PFAP-based AEMs with a high water diffusivity and ion conductivity are crucial for high-performance AEMWEs. Using platinum-group-metal (PGM) catalysts, the present AEMWEs achieved a new record current density of 7.68 A cm−2 at 2.0 V with a 1 M KOH anode, which surpasses that of state-of-the-art PEMWEs (6 A cm−2 at 2.0 V). PGM-free AEMWEs displayed an excellent current density of 1.62 A cm−2 at 2.0 V. Importantly, PGM and PGM-free AEMWEs operated stably under a 0.5 A cm−2 current density at 60 °C for more than 1000 h. This work sheds light on current high-performance AEMWEs.

Though membrane separation has been an efficient and energy-saving technique for dealing with wasted mixed chemical matter, the concomitant environmental pollution has become a big issue in the dev...

Two‐dimensional nanosheets have shown great potential for separation applications because of their exceptional molecular transport properties. Nanosheet materials such as graphene oxides, metal–organic frameworks, and covalent organic frameworks display unique, precise, and fast molecular transport through nanopores and/or nanochannels. However, the dimensional instability of nanosheets in harsh environments diminishes the membrane performance and hinders their long‐term operation in various applications such as gas separation, water desalination, and ion separation. Recent progress in nanosheet membranes has included modification by crosslinking and functionalization that has improved the stability of the membranes, their separation functionality, and the scalability of membrane formation while the membranes’ excellent molecular transport properties are retained. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes., Modification of nanosheet membranes by crosslinking and functionalization has improved their stability, their separation functionality, and the scalability of membrane production while retaining the membranes’ excellent molecular transport properties. These improvements have enhanced the potential of nanosheet membranes in practical applications such as separation processes.

Thermally Rearranged (TR) polymers and Mixed Matrix Membranes (MMMs) are two effective approaches used to advance the performance of gas separation membranes. Conversion of thermally activated groups in TR membranes result in hourglass-shaped cavities and unusually high permselectivity, whereas the inclusion of nanoparticles with engineered pore volume, window size and/or surface chemistry in MMMs can add fast and selective pathways for gas transport. In this study, we explored the effects of combining these two approaches by adding ultra-porous and highly thermostable PAF-1 nanoparticles into the TR-able polymer, 6FDA-HAB5DAM5 (DAM). Gas separation performances of TR-MMMs were evaluated by comparison with the pure polymer and another TR-MMM bearing an already thermally-treated PAF-1 additive (cPAF). While both additives enhanced gas transport, only PAF-1 stabilized the TR conversion reaction and improved the TR-MMM's material properties. Minor variations in cPAF surface changed the TR-MMM interfacial interactions as well as other properties crucial to the application of advanced membrane materials, namely aging, plasticization, and mechanical stability. By combining thermal rearrangement process with PAF-1, TR-MMM demonstrated a 55-fold increase in CO2 gas permeability (37-fold for H2) at similar gas selectivities, but without the handling issues observed for the pure TR polymer membrane.

To develop new cost-effective and high performance ion exchange membranes (IEMs) for redox flow battery applications, poly(arylene ether sulfone) random copolymer membranes (BPSHs) with surface nano-crack coatings (P-BPSH) were prepared using a hydrophobic atmospheric plasma treatment. The effect of the nano-cracks on the membranes' ion transport properties and the performance of the vanadium redox flow batteries (VRFBs) were evaluated to better understand the feasibility of using this technique in membrane ionic selectivity. The ion-selective nano-crack surface significantly improved the proton selectivity, from 32.95 to 74.20, over vanadium (VO2+) ions. Consequently, the VRFB cell assembled using a P-BPSH-60 membrane showed higher coulombic and energy efficiencies compared to a VRFB with a pristine BPSH-60 membrane. The energy efficiency of the P-BPSH-60 membrane (85.37%) is comparable to that of a Nafion® 117 membrane (85.11%). The improved battery performance demonstrated that the surface nano-crack coating layer effectively blocked the transport of vanadium ions through the IEM without distinct reduction of the proton conductivity. The results suggest a promising strategy to enhance membrane proton selectivity over vanadium ions.

Polycrystalline zeolitic imidazolate framework ZIF-8 membranes have shown great potential for energy-efficient propylene/propane separation. Their large-scale applications are, however, hampered by...

Mixed matrix membranes (MMMs) with a thermally rearranged (TR) polymer and zeolitic imidazolate framework-8 (ZIF-8) were prepared in this study. ZIF-8 contributed to not only enhancing gas permeability, but also promoting thermal conversion of TR polymer membranes. As a result, TR ZIF-8 MMMs can be prepared at lower temperatures compared to the original TR polymers. The thermal rearrangement process also increased gas separation properties as it contributes to a tunable cavity size and hour-glass shape cavity distributions. Moreover, interfacial voids between the polymer phase and ZIF crystals which usually occur in most MMMs disappeared during thermal rearrangement of the TR polymer. As a result, the TR ZIF-8 MMMs showed excellent hydrogen separation properties with a H2 permeability of 1,206 Barrer, H2/N2 selectivity of 22.3, and H2/CH4 selectivity of 25.7.

Each component of a gas mixture affects the permeation of the other gases. This mutual influence was systematically investigated for binary gas mixtures that included CO2, N-2, CH4, H-2, and CO permeating through thermally rearranged poly(benzoxazole-co-imide) (TR-PBOI) membranes. The mixed gas permeation was measured at 35 degrees C at up to 5 bar of feed pressure. Sorption isotherms of binary mixtures were calculated using the Grand Canonical Monte Carlo approach for quantifying the sorption contribution to the permeation. The diffusivity contribution was estimated by using the permeability value. How and how much CO2 (the most soluble gas) and H-2 (the fastest diffusing gas among the gas species tested) affect each other's permeation as well as the permeation of the other gases were specifically addressed, including a discussion based on sorption and diffusion contributions. The permeance of CO2 and H-2 remained unchanged, whereas the permeance of the other gases was reduced by the presence of CO2 or increased by the presence of H-2.

Aliphatic/alicyclic (Al)-containing polyimides (PIs), including fully-Al-PIs and partially-Al-PIs, are widely employed in electric, electronics, optical materials, and other advanced material fields. Examples include high speed multiplayer printed wiring boards, alignment films for liquid-crystal displays, fuel cells, batteries, gas separation membranes, pervaporation membranes, biomedical applications, and composites/hybrid materials. In the past decades, research has focused on the synthesis and molecular design of fully-Al-PIs and partially-Al-PIs. However, the effects of aliphatic/alicyclic segments on the performance of fully-Al-PIs and partially-Al-PIs and their potential applications are not clear. Therefore, an overall clarification of aliphatic/alicyclic-containing monomers, the effects of aliphatic/alicyclic segments on PI performance, as well as recent applications for advanced technology are important topics for further study. This review systematically summarizes the available aliphatic/alicyclic monomers and clarifies the influence of aliphatic/alicyclic-containing segments in chain backbones on the morphology and properties of the resulting PIs. Further, the use of PIs in applications for advanced materials is discussed, along with the outlook for the future of aliphatic/alicyclic-containing polyimides and their advanced applications.

Description, Cascaded microporosity localized on membrane surfaces markedly improved selective transport of small molecules., In membrane-based separation, molecular size differences relative to membrane pore sizes govern mass flux and separation efficiency. In applications requiring complex molecular differentiation, such as in natural gas processing, cascaded pore size distributions in membranes allow different permeate molecules to be separated without a reduction in throughput. Here, we report the decoration of microporous polymer membrane surfaces with molecular fluorine. Molecular fluorine penetrates through the microporous interface and reacts with rigid polymeric backbones, resulting in membrane micropores with multimodal pore size distributions. The fluorine acts as angstrom-scale apertures that can be controlled for molecular transport. We achieved a highly effective gas separation performance in several industrially relevant hollow-fibrous modular platform with stable responses over 1 year.

Artificial lung (AL) membranes are used for blood oxygenation for patients undergoing open-heart surgery or acute lung failures. Current AL technology employs polypropylene and polymethylpentene membranes. Although effective, these membranes suffer from low biocompatibility, leading to undesired blood coagulation and hemolysis over a long term. In this work, we propose a new generation of AL membranes based on amphiphobic fluoropolymers. We employed poly(vinylidene-co-hexafluoropropylene), or PVDF-co-HFP, to fabricate macrovoid-free membranes with an optimal pore size range of 30-50 nm. The phase inversion behavior of PVDF-co-HFP was investigated in detail for structural optimization. To improve the wetting stability of the membranes, the fabricated membranes were coated using Hyflon AD60X, a type of fluoropolymer with an extremely low surface energy. Hyflon-coated materials displayed very low protein adsorption and a high contact angle for both water and blood. In the hydrophobic spectrum, the data showed an inverse relationship between the surface free energy and protein adsorption, suggesting an appropriate direction with respect to biocompatibility for AL research. The blood oxygenation performance was assessed using animal sheep blood, and the fabricated fluoropolymer membranes showed competitive performance to that of commercial polyolefin membranes without any detectable hemolysis. The data also confirmed that the bottleneck in the blood oxygenation performance was not the membrane permeance but rather the rate of mass transfer in the blood phase, highlighting the importance of efficient module design.

Producción Científica, Mixed matrix membranes (MMMs) have been obtained by blending an aromatic ortho-hydroxypolyimide (PIOH) or an ortho-acetylpolyimide (PIOAc) with different loading amounts (15 and 30 wt %) of a microporous polymer network (PPN), which was obtained from the reaction of triptycene and isatin. The excellent thermal resistance of the PPN (above 500 °C) allowed it to be used as a filler to successfully prepare thermally rearranged polybenzoxazole (TR-PBO)-MMMs obtained from the thermal treatment of the above MMMs. Moreover, PPN showed relatively good compatibility with the polyimide matrix, which improved the TR-PBO formation. The gas separation performances of these MMMs before and after the thermal process were studied for five representative gases (He, O2, N2, CO2, and CH4). For the MMMs derived from ortho-functional polyimides, the gas permeability considerably increased for all of the gases, whereas the selectivity for gas pairs, such as CO2/N2 and CO2/CH4, remained similar. Thus, the selectivity-permeability performance of PIOH- and PIOAc-MMMs containing 30 wt % of PPN (PIOH30 and PIOAc30) surpassed the 1991 Robeson limit for the CO2/CH4 gas pair. In the case of TR-PBO-MMMs (TROH and TROAc-MMMs), the thermal rearrangement process led to an increase in the gas permeability, showing values much better than those observed for the TR-PBO material employed as a MMM matrix. The selectivity values were a little bit lower than the pristine TR-PBO membranes. The CO2 permeability of TROAc30 was 1036 barrer with a CO2/CH4 selectivity of 28, surpassing the 2008 Robeson limit., Agencia Estatal de Investigación - Fondo Europeo de Desarrollo Regional - Unión Europea (projects PID2019-109403RB-C22, CTQ2017-89217-P and PID2019-109403RB-C21), Junta de Castilla y León (project VA224P20), Ministerio de Ciencia, Innovación y Universidades - ICT (project RTI2018-096652-B-I00), Ministry of Trade, Industry & Energy of South Korea.(project 20202020800330)

Solder paste is the main interconnect material to use between FBGA type packages and main boards. It is consisted of different types of solder powers (in case of type 3 size is 25∼45um) and flux. Many paste parameters, such as paste composition, printing stencil aperture and reflowing profile, influence the printing performance and the reflow process of solder pastes. Flux in solder paste is classified into mainly water-soluable and no-clean flux depending on the applications. No-clean flux contained solder paste has been used in most of applications such as module, SSD etc. But, water-soluable flux contained solder paste is required in SiP module applications to prevent any possible corrosion failure due to flux residue in underfilled module. However, water-soluable flux is very sensitive by humidity in storage condition. Activation and viscosity of flux can be degraded by uncontrolled environment and caused unexpected rotation to resulted in poor solder joint self align. In general, the rheology of solder paste is complicated and affect the shape of solder joint depending on ratio of moisture absoption. If the mixture of solder paste absorb the moisture, the solder paste could be easily slumped and package component is slipped or rotated during the reflow process, result in poor solder joint quality such as non-wet. There are several methods to detect the poor solder joint quality after SMT, such as X-ray and Optical Inspection. The benefits of X-ray inspection are broad in scope due to the ability of X-rays to see through packages including. But X-ray method is restricted to used in massive production due to its poor detection resolution and low efficiency of analytical time. Especially, the poor self-align quality like non-wet joint could not be easily detected by X-ray only after SMT, so the failure samples could be outflow to customers. The main purpose of this study was to investigate effective monitoring methods for replacing sampling X-ray measurement. The existing automatic optical inspection (AOI) equipment can be used to check out the defect of the electronic products, such as solder bridging, non-wet and so on. In this paper, the solder joint self-align trend (amount of rotation) was calculated by M-AOI (Mounting-AOI of package before reflow) and S-AOI (Solidifying-AOI after reflow) data. The trends of M-AOI and S-AOI was compared with non-wet failure rate at final test and X-ray inspection result for relevant properties of solder paste such as viscosity, thixotropy, acidity and so on. AOI data shows well-matched trend with amount of rotation of package and non-wet failure rate of solder joints with regard to floor time of solder paste. As a result, new monitoring method using AOI is proposed and confirm usefulness to replace the sampling X-ray measurement as massively useful tool to check the joint quality after reflow process, and also will be used to control the moisture level of solder paste to ensure the proper rheology for SMT assembly.

The membrane market has grown rapidly over the past several decades, supported by continuous improvements in membrane performance, module and process design, and fouling control. However, such growth will be unsustainable with current membrane fabrication methods that employ significant amounts of toxic solvents (e.g., N-methylpyrrolidone, dimethylacetamide, and dimethylformamide), thereby producing billions of liters of contaminated wastewater each year. A possible solution is to identify greener alternatives with appropriate properties that are compatible with conventional polymers. In this work, we employed a novel green solvent, Rhodiasolv PolarClean®, that is less toxic than current solvents and eco-friendly, while exhibiting the necessary properties to be employed as a solvent for membrane preparation via the nonsolvent-induced phase separation (NIPS) method. Rhodiasolv PolarClean® has been successfully applied to membrane preparation for water desalination and reclamation by ultrafiltration (UF) and nanofiltration (NF) with conventional polymers, including polysulfone (PSF), polyethersulfone (PES), and cellulose acetate (CA). The UF membranes prepared from PES/Pluronic F127 and PSF/polyvinylpyrrolidone exhibited pure water permeabilities greater than 314.5 ± 57.8 L m−2 h−1 bar−1 and tensile strength 3.78 ± 0.12 MPa with BSA rejection of 98.1 ± 0.4%. Cellulose acetate membrane used for NF applications demonstrated pure water permeability of 1.5 ± 0.25 L m−2 h−1 bar−1 with NaCl and MgCl2 rejection of 85.1 ± 5.7% and 93.2 ± 4.7%, respectively. The performance of the prepared membranes was competitive with current state-of-the-art membranes across all applications, indicating immediate applicability to improving the sustainability of membrane fabrication processes.

Since thermally rearranged (TR) polymers were known as high gas permeable and processable materials, fabricating high performance hollow fiber (HF) membranes have been tried using them. However, an unexpected drawback emerged which is the gas productivity loss by thermal densification of skin layers during thermal treatment above their glass transition temperature (Tg). In this work, we used a recently reported crosslinked-TR (XTR) polybenzoxazole to develop a new class of high-flux TR hollow fibers by directly exploiting the thermal densification phenomenon. The TR temperature range (320–460 °C) and Tg (394 °C) were determined by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The chain rigidity of the XTR polymer increased during an isotherm treatment at its Tg, suggesting a restricted densification. Surprisingly, the undesired pinhole-defects (pore diameter 400 °C), forming an ultrathin defect-free skin layer on thermally-densified XTR hollow fiber membranes. The pore-healed XTR hollow fibers exhibited an outstanding CO2 permeance of ~2300 GPU and a CO2/N2 selectivity of 17.4 with a skin thickness of 103 nm.

It is of great interest to form polycrystalline metal–organic framework (MOF) thin films on polymer substrates or MOF/polymer composites for their practical applications in sensing and separation. It is, however, quite challenging to fabricate high-quality MOF thin films on polymer substrates or MOF/polymer composites in a facile manner. Herein, we report a simple in situ method to fabricate high-quality zeolitic-imidazolate framework ZIF-8 thin films supported on polymers as well as ZIF-8/polymer composites by doping polymers with zinc ions followed by solvothermal treatment in a linker solution. The effects of key synthesis parameters on the microstructures of ZIF-8 thin films and composites were systematically studied. Formation of ZIF-8 crystals was confirmed using ATR-FTIR, EDX, XRD, SEM, and TEM. While continuous ZIF-8 films were observed on the substrate surfaces, it was revealed that ZIF-8 particles formed inside the substrates as well (i.e., ZIF-8/polymer mixed-matrix layers). The thicknesses of the mixed-matrix layers were demonstrated to be controllable by varying the kinetics of alkali hydrolysis. The method was applied to a family of ZIFs (i.e., ZIF-8 and ZIF-67) and mixed-metal ZIF-8 analogues, proving its versatility. Finally ultra-thin well-intergrown ZIF-8 membranes were prepared by secondarily growing ZIF-8 films on Matrimid® hollow fibers, showing promising propylene/propane separation performances.

In this report, we introduced spirobiindane group to poly(arylene ether sulfone) (PES) to build the structure of polymers with intrinsic microporosity (PIMs). A novel PESs (QOH-SBIs), which have spirobiindane and tetra(quaternary ammonium) hydroxide pendant moieties, were synthesized for anion-conducting binder material in membrane electrode assembly (MEA) of solid alkaline exchange membrane fuel cell (SAEMFC). The time-lag method was used to check the high gas permeability of the polymers. The high permeability is due to the micro-pores at the molecular level that is formed by the difference in chain thicknesses between two alternating units, thick spirobiindane group and thin arylene ether sulfone group. QOH-SBIs shows a semi-rigid chain conformation in a solution. The inter-chain spacing and chain conformation were measured with wide angle X-ray diffraction (WAXD) and small angle neutron scattering (SANS), respectively. High gas permeability directly affected the performance of SAEMFC. The MEA with spirobiindane-modified PES shows much higher maximum power density than that of spirobiindane-free PESs.

Amino functionalized boron nitride nanosheets (FBN) were incorporated into a crosslinked, thermally rearranged polyimide (XTR) to fabricate FBN-XTR nanocomposite membrane. The FBN-XTR membrane exhibited a small decrease in H2 permeability but demonstrated a remarkably increased H2 gas selectivity over other gases, compared with XTR. The XTR membrane heat-treated at 425 °C had a H2 permeability of 210 Barrers and a H2 /CH4 separation factor of 24.1, whereas the nanocomposite membrane with 1 wt % FBN exhibited a H2 permeability of 110 Barrers and H2 /CH4 separation factor of 275, an order of magnitude greater. At 1 wt % FBN loading, the FBN-XTR membrane showed three times higher tensile strength and 60 % higher elongation than pristine XTR membrane. In addition, FBN-XTR was found to be able to be readily processed into thin-film membranes for practical H2 separation applications.

In the field of membrane technology, the combined nonsolvent-thermally induced phase separation (N-TIPS) method is a versatile technique to prepare macroporous membranes with narrow pore size distribution. However, its full potential in hollow fiber preparation has been hindered due to the formation of a dense skin layer via rapid mass exchange at the solvent-nonsolvent interface. In this study, a simple and effective solution is proposed to eliminate the dense skin layer and prepare a highly porous, macroporous membrane. We employed a triple spinneret to apply a transient coating layer to prevent the polymer dope solution from directly contacting the nonsolvent, which is regarded as the main cause of dense skin layer formation. Interestingly, depending on the choice of transient coating fluid, the fluid acts as a selective layer to facilitate unidirectional diffusion of the solvent into the nonsolvent while blocking the nonsolvent inflow. By controlling the solvent-nonsolvent exchange and thermal gradient in tandem, we show that a convenient control over NIPS and TIPS kinetics can be achieved. Several solvents, ranging from conventional solvents such as dibutyl phthalate (DBP) and N-methyl-2-pyrrolidone (NMP) to environmentally-friendly solvents such as acetyl tributyl citrate (ATBC) and methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (PolarClean®), were employed as the transient coating layer to investigate the effects of different solvents on the formation of macroporous hollow fiber membranes. It was observed that as the hydrophobicity of the coating layer increased, the prepared membrane exhibited a more porous morphology with a larger pore size. Moreover, the tensile strength of the prepared fibers improved from 3.4 ± 0.1 MPa to 7.7 ± 0.3 MPa, the pure water permeability increased from 1 to 988 L m−2 h−1 bar−1, and the membrane exhibited a narrow pore size distribution.

Polymer hollow fibers have great potential as cost-effective scalable substrates for the practical applications of highly propylene-selective ZIF-8 membranes. We report ultrathin ZIF-8 membranes supported on porous Matrimid® polymer hollow fibers via microwave-assisted seeding and microfluidic secondary growth. Densely-packed ZIF-8 seed layers were rapidly prepared on polymeric hollow fibers under microwave heating. The seed layers were then secondarily grown into well-intergrown ZIF-8 membranes under the continuous flow of the growth solution. The effects of synthesis parameters on the microstructures of ZIF-8 seed crystals were systematically studied. The resulting ZIF-8 membranes were characterized with XRD and SEM, showing well-intergrown ZIF-8 films formed on the bore of hollow fibers. The unique nature of the current technique enables facile formation of ultrathin ZIF-8 membranes on either the bore or shell side of hollow fibers with a thickness of ~ 800 nm. Propylene/propane binary gas permeation measurements showed an average separation factor of ~ 46 and propylene permeance of ~ 55 GPU.

To develop membrane materials for gas separation, a series of semi-alicyclic polyimides was synthesized using one-step thermal solution imidization from an alicyclic dianhydride with non-planar twisted structure, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA). All synthesized polyimides exhibited amorphous structures and superior thermal stability, with high glass transition temperatures (242–288 °C) withstanding high operation temperature and pressure. They also showed excellent solubility in many polar organic solvents commonly used in the fabrication of gas separation membranes. The gas permeation properties of the polyimide membranes were measured for six representative gases (H2, CO2, O2, CO, N2, and CH4). The gas permeabilities and selectivities of polyimide membranes were significantly influenced by the chemical structure of the diamines, which could be explained reasonably by the kinetic diameter of gases, the fractional free volumes, and d-spacing values of the polyimides. Two DOCDA-based polyimides showed very high selectivities for H2/CH4 and CO2/CH4 and slightly low permeabilities for H2 and CO2, which performances were comparable to the commercial polyimide materials such as P84® and Matrimid® used in gas separation field.

Poly(vinylidene fluoride) (PVDF)/polysulfone (PSF) hollow-fiber (HF) membranes with high mechanical strength and satisfactory water permeance using a green fabrication technique were investigated by varying the compositions of coating fluid and bore fluid during membrane spinning using a triple spinneret. The results demonstrated that the HF membranes using hydrophobic coating fluid provided a skinless structure with higher water permeance than those produced from a hydrophilic coating fluid or polymer solution. These skinless PVDF/PSF membranes showed 99.96% rejection of a ginseng extract solution with different concentrations via direct contact membrane distillation (DCMD) but relatively poor stability and rejection behavior for saline water due to the poor hydrophobicity of the membrane. To improve the hydrophobic properties of PVDF/PSF membranes for saline water, two hydrophobic modification methods (i.e., chemical modification and physical modification) were employed and compared. Modified membranes showed enhanced hydrophobic properties as characterized by XPS, FTIR analysis, and stability tests. In the separation of saline water (35 g/L salts and 0.1 mM sodium dodecyl sulfate), modified membranes showed higher water flux and rejection than pristine membrane. The modified membrane showed greater than 99.99% rejection and outstanding stability even after operation for 120 h. This work provides skinless fiber-aligned PVDF/PSF hollow-fiber membranes with different surface properties for diverse systems via DCMD, such as concentration of food extract or separation of saline water.

This paper reports the preparation of mixed matrix membranes (MMMs) by incorporating a two-dimensional zeolitic imidazolate framework-L (ZIF-L) into a highly gas permeable hydroxyl group-containing polyimide (PI) for hydrogen separation. ZIF-L has a leaf-shaped morphology with excellent CO2 adsorption properties due to strong interaction between ZIF-L and CO2 molecules. The dispersion of ZIF-L crystals in the polymer phase increased CO2 adsorption and restricted CO2 transport through MMMs, resulting in a significant increase of H2 selectivity over CO2. The gas transport properties of MMMs with a ZIF-L loading up to 20 wt% were investigated, and the results showed such MMMs had a H2 permeability of 260 Barrers and ideal H2/CO2 selectivity of 13.4 at room temperature. The membranes presented here have the potential for large-scale fabrication for hydrogen separation applications.

Though membrane distillation (MD) has been considered as a promising desalination process, it is still required to develop a desirable membrane which has high water flux and long-term stability for practical use in the MD process. In our previous work, thermally rearranged nanofiber membranes (TR-NFMs), which exhibited high water flux (80 kg m−2 h−1) and salt rejection (> 99.99%) as well as outstanding long-term stability (more than 180 h), were first introduced as a promising candidate for MD applications. However, nascent TR-NFM is susceptible to fluctuations in operating conditions due to insufficient liquid entry pressure with water (LEPw). In continuation of our enhanced hydrophobic TR-NFM study, we develop fluorine-containing thermally-rearranged nanofiber membranes (F-TR-NFMs) for MD applications for the first time. F-TR-NFMs showed enhanced hydrophobic properties such as high water contact angle (143°), high LEPw (1.3 bar), and high effective evaporation area (EEA) due to the introduction of fluorine atoms in the backbone of the TR membrane. As the result, the developed F-TR-NFMs exhibited outstanding MD performance (114.8 kg m−2 h−1 of water flux and > 99.99% of salt rejection at feed and permeate temperatures of 80 °C and 20 °C, respectively) and excellent energy efficiency (52.1% at feed and permeate temperatures of 50 °C and 20 °C, respectively). The long-term stability of F-TR-NFM is also investigated over more than 250 h of operation time.

Thin film composite (TFC) polymer membranes are ubiquitous in membrane-based liquid separation processes, especially in reverse osmosis (RO). While the ultrathin polyamide separating layer employed in TFC membranes has exhibited excellent performance in many liquid separation processes, the polymer support has been identified as a bottleneck to practical applications. In this work, we report a highly porous, thermally and chemically robust support comprising a thermally rearranged polymer which is combined with a polyamide active layer to form a thermally rearranged, thin film composite (TR-TFC) polymer membrane for general use in liquid separation, and for environmentally-friendly power generation. The precursor polymer has good processability for scale-up of synthesis and membrane fabrication. After thermal rearrangement, the developed TR-TFC membranes containing polybenzoxazole-co-imide can be utilized in separations in any organic liquids, including under harsh environments such as dimethyl formamide even at elevated temperatures, with a remarkable performance. Moreover, the membrane achieves 40 W m−2 of power density through pressure retarded osmosis using a concentrated brine, similar to those obtained from RO plants. These results points to the possibilities for next-generation TFC polymer membranes for general use in liquid separation and power generation.

Membrane-based liquid filtration systems have been highlighted as a key green process engineering platform for process intensification. While these systems have been successfully commercialized in desalination and micro/ultra/nanofiltration, it is yet challenging to expand the limited operating conditions (ambient temperature in an aqueous environment) of the currently available membranes, and to solve the exacerbating environmental burden during the fabrication of polymeric membranes. Herein, a new green and compact fabrication method is proposed for both (i) fabricating a robust membrane that can function beyond the typical operating conditions of conventional membranes and (ii) minimizing waste creation and production time. In this work, contrary to the conventional phase inversion method, a spray-coating technique was employed to fabricate a thin composite membrane with high temperature stability and fast solvent permeability. The proposed compact fabrication method can reduce the carbon footprint and the usage of polymers and solvents more than twofold, and eliminate the time-consuming coagulation and washing steps, both of which generate an enormous amount of solvent-contaminated wastewater (up to 50 billion liters per year). Furthermore, the process used dimethyl sulfoxide to bypass conventional N,N-dimethylformamide and N-methyl-2-pyrrolidone as a green solvent, and can simultaneously fabricate a membrane ready to use within a half-day. The resulting membrane exhibited remarkable stability and performance for the separation of solutes in N,N-dimethylformamide, even at elevated temperatures not feasible with conventional polymeric membranes, and so it is a candidate for potential use in the pharmaceutical and fine chemical industries.

Thermally rearranged (TR) polymers are an important class of microporous polymers with remarkable gas transport performance, particularly suitable for CO2 permeation and separation over large gas molecules. The fabrication of TR polymers into ultrathin membranes is highly desirable for practical application, but it is very challenging. In this work, a 2D scaffold of graphene oxide (GO) nanosheets was formed inside a TR polymer to assist the fabrication of a defect-free and ultrathin (less than 40 nm) selective layer of thermally rearranged polybenzoxazole-co-imide (TR-PBOI) membranes for energy-efficient CO2 separation. The GO scaffold inside the polymer phase not only enabled the formation of the ultrathin selective layer of TR-PBOI, but also provided mechanical robustness. The resulting membrane showed remarkable gas permeance, while maintaining the gas selectivity of the pristine polymer. In particular, it had a CO2 permeance of 1784 GPU and a CO2/CH4 selectivity of 32, whereas the freestanding TR-PBOI membrane only exhibited a CO2 permeance of 3.7 GPU with a CO2/CH4 selectivity of 35. In other words, the rGO–PBOI (TR-PBOI with reduced GO) membrane has 482 times higher CO2 permeance than the TR-PBOI freestanding membrane at a similar CO2/CH4 selectivity.

The chain interactions of hydroxyl polyimide (HPI) precursors, such as chain packing and π-π stacking interactions, significantly affect the microstructures and gas separation performance of the resulting thermally rearranged polybenzoxazoles (TR-PBOs). In this study, HPIs with various 2,2′-substituents in their anhydrides (BPDA-AP, PBPDA-AP, and 12FPBPDA-AP) were prepared through polycondensation of three dianhydrides (4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (PBPDA), and 2,2′-bis(3″,5″-ditrifluoromethylphenyl)-4,4′,5,5′-biphenyltetracarboxylic dianhydride (12FPBPDA)) with 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AP). The dihedral angles and rotational barriers for PBPDA and 12FPBPDA were considerably larger than those for BPDA. Thus, the inter- and intra-molecular chain interactions were more pronounced for BPDA-AP than for PBPDA-AP and 12FPBPDA-AP. Consequently, the glass transition and TR temperatures of the HPIs were in the order of BPDA-AP > PBPDA-AP > 12FPBPDA-AP, whereas fractional free volume (FFV) and interchain distances followed the opposite trend. After TR, the FFV and interchain distances of the TR-PBO from BPDA-AP increased more than those from PBPDA-AP and 12FPBPDA-AP, whereas the π-π stacking interactions in BPDA-AP were well maintained. Consequently, BPDA-AP-450 exhibited the highest increase in gas permeability relative to its HPI precursor but the poorest plasticization resistance among fully converted TR-PBOs. This work demonstrated that chain packing played a crucial role in the TR behavior, microstructures, and gas transport properties of TR-PBOs.

Anion exchange membrane fuel cells (AEMFCs) have advanced rapidly in the past four years, while the majority of the state-of-the-art AEMFCs relies on unrealistic and uneconomical operating conditions, particularly a high hydrogen flow rate (>1000 mL min−1). Here, we report a poly(fluorenyl aryl piperidinium) (PFAP) ionomer that enables high power of AEMFC with low hydrogen flow rate (≤100 mL min−1 for 5 cm2 cell). The high water permeability of the ionomer is beneficial to prevent anode flooding under moderate relative humidity. The relationship between hydrogen flow rate and limiting current density is revealed based on PFAP copolymers. Specifically, the peak power density of AEMFC is 1.77 W cm−2 with a H2 flow rate of 75 mL min−1, retaining >70% power density from the H2 flow rate of 1000 mL min−1 (2.42 W cm−2). Importantly, the present AEMFCs display much higher hydrogen utilization efficiency above 90% and hydrogen fuel power (∼30 W cm−2 L−1) than previously reported AEMFCs ( 110 h.

To increase the efficiency of a closed-loop hybrid system consisting of membrane distillation (MD) and pressure retarded osmosis (PRO) processes, thermally rearranged nanofibrous membranes (TR-NFMs) via electrospinning were proposed in this study. Two fluorine-based modifications were performed on TR-NFMs to optimize their affinity with water. Hydrophobicity of TR-NFM was enhanced by atmospheric plasma coating (TR-NFM-Rx) to increase liquid entry pressure of water (LEPw) for MD applications. On the other hand, for PRO applications, gas-phase direct fluorination was applied on TR-NFM (TR-NFM-Fx) to improve its hydrophilicity by replacing the C–H bond of a TR polymer with a C–F bond. Before measuring the performance of the hybrid system, the MD performance was calculated from the mass transfer model based on the temperature and concentration of the solution to confirm the operating conditions of the MD-PRO hybrid system. The resulting TR-NFM-R40 showed an excellent water flux of 51.5 L/m2 hr at 70 °C despite a 3 M NaClaq operating solution that is unfavorable for MD performance. In the PRO process, thin film composite membrane (TR-TFC-F5) also exhibited outstanding power density of 120 W/m2 at 27 bar using 3 M NaClaq and D.I. water as operating and feed solutions, respectively. During 180 h continuous operation of MD-PRO hybrid system, the resulting average power density was about 90 W/m2 and average MD water flux was about 45–50 L/m2 hr at 70 °C using 3 M NaClaq operating solution. In conclusion, the developed TR membranes for MD-PRO hybrid system provides an insight into the future of energy harvesting technology.

Poly(aryl-co-aryl piperidinium) (c-PAP) copolymers have recently demonstrated great successes in anion exchange membranes (AEMs) and ionomers for AEM fuel cells (AEMFCs). Here, we present a series of in-situ styrene-crosslinked c-PAP (x-PAP-PS) membranes to further enhance the mechanical strength, dimensional stability, and water retention capacity of c-PAP AEMs. Specifically, x-PAP-PS AEMs simultaneously possess high ion conductivity (>150 mS cm−1), tensile strength (>80 MPa), and chemical and mechanical durability (~90 % ion conductivity and mechanical strength maintaining in 1 M NaOH at 80 °C for 2160 h). Additionally, x-PAP-PS-based AEMFCs reached peak power densities (PPDs) of 2.23 W cm−2 in H2–O2 and 1.32 W cm−2 in H2-air at 80 °C. Importantly, compared to pristine c-PAP AEMs, x-PAP-PS AEMs display higher water retention capacity at low relative humidity (RH), and the corresponding AEMFCs reach PPDs >1 W cm−2 with Pt/C at 30 %/30 % RH at 90 °C. Moreover, the x-PAP-PS-based AEMFCs can be operated stably under a 0.4 A cm−2 current density at 60 °C for ~120 h.

Poly(vinylidene fluoride) (PVDF) membranes are widely employed for water treatment but mainly limited by their hydrophobic properties that increase the separation resistance. To make hydrophilic PVDF membranes, inorganic layer coated PVDF blend hollow fiber membranes are reported here. PVDF/polysulfone (PSF) blend hollow fiber membranes with pore size of ~110 nm were fabricated using PolarClean as a green solvent. Then, a facile and green method was employed to in-situ grow an inorganic layer (including TiO2 and Al2O3 layers) on these high strength membranes. Pluronic L61 was used as a dispersing agent to distribute the precursors in isopropanol, and enhanced adhesive strength between the polymer membrane and inorganic particles as characterized by XPS. The inorganic layers on the PVDF/PSF membrane surface both improved the mechanical strength from 7.7 MPa to 9.2 MPa and decreased the membrane roughness from ~50 nm to ~10 nm. The water permeance of the composite membranes can be finely tuned from 50 to 500 Lm−2h−1bar−1. In addition, the resulting membranes simultaneously enhanced the separation performance and anti-fouling performance characterized by bovine serum albumin (BSA) rejection behavior and flux recovery rate (FRR), respectively. The best BSA rejection and FRR of the PVDF/PSF-inorganic composite membranes reach 95% and 72.2%, respectively. The anti-fouling performance of composite membranes is mainly attributed to the decreased membrane roughness and enhanced hydrophilic properties compared with pristine PVDF/PSF membranes. Furthermore, the in-situ grown inorganic layers on the PVDF/PSF membrane surface effectively prevent foulants from blocking the pore channels as they are easily washed by the hydraulic washing method.

Numerous membrane models have been developed and tested for the simulation of membrane processes. However, these models are often either simplified or only validated with a narrow range of experimental data. For the model-based process design of membrane systems it is necessary to have a validated and accurate model which is accurate for the range of possible operating conditions under consideration. Hence, in this study a modeling framework is developed for hollow fiber membranes which can be adjusted systematically to accurately predict the performance of a given membrane. Mixed-gas (CO2/O2/N2 and CO2/N2) separation experiments are carried out over a range of different feed conditions to evaluate membrane performance and to provide reliable measurements of gas permeance. In particular the feed pressure (1–4 bar), permeate pressure (0.1–0.5 bar) and feed flow rates (0.096–0.4 N m3/h) are varied in these experiments (the ranges specified in brackets). Interpolation of these measured permeance allows for the accurate prediction of membrane performance at any conditions inside the measured range. A tanks-in-series modeling approach is employed here where the number of tanks (used to represent the membrane behavior in a numerical formulation) can be adjusted to calibrate and fit the membrane model to experimental results. For the membranes tested in this study it is found that using a relatively small number of tanks both minimizes the difference between model and experimental results and reduces the numerical complexity in the membrane model.

Recently developed crosslinked-thermally rearranged (XTR) polymeric membranes, which show enhanced gas separation, are applicable for CO2 separation from post-combustion gases. Moreover, the resulting thermally rearranged polybenzoxazole (TR-PBO) structure that is thermally induced from hydroxyl-polyimides (HPI) provides high thermal and chemical resistance, which is favorable for gas separation applications containing condensable gases such as water vapor. Herein, the influence of water vapor on the CO2 capture efficiency was evaluated using XTR poly(benzoxazole-co-imide) (XTR-PBOI) hollow fiber membrane modules which were compared with crosslinked HPI (XHPI) in mixture gas and single gases for CO2 and N2. The results revealed that the permeate CO2 flow rate in the hydrophobic XTR-PBOI module showed enhanced separation performance, whereas the flow rate severely decreased in the relatively hydrophilic XHPI module, reflecting more significant capillary condensation effect in the XHPI membranes. Both membrane modules showed excellent plasticization resistance, and the XTR-PBOI hollow fiber membrane module presented reasonable long-term stability over 240 h.

In this work, the aging behavior of a thermally rearranged polybenzoxazole-co-imide (TR-PBOI) mixed matrix membrane loaded with 0.5 wt.% of oxidized multi-wall carbon nanotubes (MWCNT) was evaluated and then compared to a pure TR polymeric membrane prepared from the same precursor. To the best of authors knowledge, this is the first report of a mixed matrix membrane being prepared through the dispersion of MWCNTs within a thermally rearranged polymer matrix for CO2 separation. Microporous structures were created in both membranes when thermally rearranged at 375 °C, facilitating fast mass transfer ideal for membrane gas separation. The TR mixed matrix membrane with oxidized CNTs demonstrated improved separation properties with regard to both permeability and selectivity compared to the pure TR polymeric membrane due to a greater degree of thermal rearrangement (11.3%) than what was exhibited by the TR membrane (6.7%). Moreover, the high CO2 solubility typical of TR polymers coupled with diffusivity enhancements improved the CO2/N2 selectivity. The addition of oxidized CNTs to the TR-PBOI polymer did not significantly influence the aging behavior of the mixed matrix membrane. Both pure TR-PBOI and mixed matrix membranes exhibited an increase in CO2 selectivity due to physical aging. The improved separation properties in conjunction with an unchanged membrane stability over time suggested that the addition of CNTs to pure TR membranes could be an excellent approach toward improving the performance of thermally rearranged membranes applied toward gas separation.

Herein, we introduce a novel membrane-based process for lithium recovery and compare it to the conventional solar evaporation followed by chemical precipitation process. Conventional technologies have limitations to meet the recent demand for massive lithium production due to several drawbacks of solar evaporation. Recently, in order to reduce the dependency of solar evaporation, several technologies have been proposed such as precipitation, ion-exchange, liquid-liquid extraction, adsorption, and electrodialysis. We suggest a novel membrane-based lithium recovery process by combining membrane distillation (MD) and nanofiltration (NF) to concentrate a brine solution containing lithium and to remove divalent ions. The proposed membrane-based process was demonstrated to concentrate 100 ppm lithium solution in artificial brine to 1200 ppm lithium solution within several days and exhibited up to 60 times higher water flux (22.5 L m−2 h−1) than that of solar evaporation (0.37 L m−2 h−1 at 30 °C and 0.56 L m−2 h−1 at 50 °C). Moreover, the NF process can suppress crystal formation to prevent process failure while alleviating the massive chemical usage of the conventional process. As a result, the proposed membrane-based process showed a possibility to utilize the low concentration of lithium brine with one-tenth of capital cost, process time, and foot-print of the conventional process, and represented a competitive operating cost with the conventional process which can be reduced further by harnessing the waste heat from the industrial plants and solar energy.

Membrane-integrated gas separation is of great interest due to its energy-saving and economic merits. Although easy-to-process polymer membranes have shown potential, insufficient gas permeation and low stability in harsh environments limit their use in practical applications. Here, we demonstrate nanoporous and rigid semi-interpenetrating polymer networks (SIPNs) by incorporating crosslinked network into polymer matrices, accompanying interpenetration and thermal rearrangement (TR) to construct an optimized microporous structure where nanometric and sub-nanometric pores coexist parallel to the gas transport direction. The resulting TR-SIPN improves gas transport without sacrificing separation efficiency since the nanometric and sub-nanometric pores serve as molecular highways and selective bottlenecks, respectively. Furthermore, the plasticization resistance against condensable gases was enhanced due to improved polymer rigidity of the TR-SIPNs. Our study suggests wide applicability of polymer membranes for aggressive gas separations such as natural gas sweetening and olefin/paraffin separation.

Here, we demonstrate the improved electrochemical performance and stability of end-group cross-linked anion exchange membranes (AEM) for the first time via the introduction of imidazolium groups in poly(arylene ether sulfone) (Imd-PAES). A novel feature of the cross-linking reaction is that basic additives are not required to prevent gelation with the cationic functional groups. In this work, the sodium salt of 3-hydroxyphenylacetylene acted directly as the end-group cross-linker, and it was cross-linked by thermal treatment at 180 °C. The gel fraction and hydroxide conductivity of the cross-linked membranes (XE-Imds) depended on the cross-linking temperature and time. The prepared XE-Imd70 (70 refers to the degree of functionalization) membranes with an ion exchange capacity (IEC) of 2.2 meq g−1 achieved a high hydroxide conductivity (107 mS cm−1). This material also showed good single cell performance (XE-Imd70: 202 mA cm−2 at 0.6 V and a maximum power density of 196.1 mW cm−2) at 80 °C, 100% relative humidity (RH), and improved durability and alkaline stability. The excellent hydroxide conductivity and electrochemical performance of XE-Imd70 was due to the fact that the ion cluster size of XE-Imd membranes was larger (12.1–14 nm) than that of E-Imd (5.5–8.14 nm), indicating that XE-Imd membranes have a closely associated ion-clustered morphology, which was confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) measurements.

Material research related to membrane has become a trending topic for gas purification with a strong focus on delivering better separation performance. This review conveys that this criterion alone is inadequate when holistically evaluating new materials for gas separation, so a broader set of criteria is needed. Consideration of additional criteria will focus material research on new formulations with a higher likelihood of commercialization. Through a comprehensive evaluation of most emerging organic materials against those criteria, we demonstrate that, the use of organic microporous materials that mimic the gas sieving functionality of adsorbent materials presents an ultimate solution for membrane gas separation. By plotting gas permeation performances by these emerging polymer materials against their structural properties, we reveal that, polymeric membranes exhibit a strong correlation between gas permeability and BET surface area. This implies a significant role for BET surface area in mass transfer. By identifying the architectural design pathway for these polymer materials to meet proposed criteria, this review provides guidance for polymer research into membrane gas separation technology, as well as other applications such as energy storage and heterogeneous catalysis.

Physical aging in high free-volume polymer membranes is one of the main hurdles limiting their application in gas separation. The recovery of membrane separation properties without the need to disassemble the module, although challenging, would provide significant advantages for applications in various fields. In this work, an in situ restoring procedure for the recovery of mass transport in aged membrane modules made of thermally rearranged polymer membranes was developed in which the modules were exposed to methanol at 80 °C. The thermally rearranged hollow fiber membrane modules were subjected to long-time operation to investigate their aging: the CO 2 and N 2 permeances were monitored at different temperatures, pressures, and feed compositions over a total period of 727 days with two long-time runs of 185 and 263 days, interspersed by a stand-by period of 240 days, and with each run followed by a restoring. In both long-time runs, CO 2 and N 2 permeance dropped as a result of aging, whereas the selectivity remained nearly constant. The permeances were fully recovered after the proposed restoring procedure was applied, demonstrating its efficacy and repeatability for membrane aging recovery, even for an extremely aged membrane exposed to various conditions for nearly two years.

Microporous polyvinylidene difluoride (PVDF) hollow fiber membranes were fabricated via a thermally-induced phase separation (TIPS) method using an environmental-friendly hydrophobic solvent, acetyl tributyl citrate (ATBC, tradename Citroflex ® A4 ). To maximize membrane tensile strength, the TIPS method was fully utilized by spinning fibers with high polymer content. It was observed that the fiber quality was significantly affected by the dope and bore flow rates and compositions, and an appropriate spinning range was established. The prepared membranes were subsequently stretched to tune the porosity, mean pore size, permeability, tensile strength, and fiber strain. A design of experiment (DOE) analysis was conducted using a 3-factor quadratic model to optimize the stretching conditions and to understand the effects of the parameters and interactions thereof. The permeability of the stretched membranes improved by a factor of 35 (15.1–538 L m −2 h −1 bar −1 ), and the tensile strength increased from 7.2 MPa to 8.4 MPa at the expense of the fiber strain. The DOE analysis revealed that the stretching ratio positively affects the permeability and porosity but decreases the fiber strain. On the other hand, it was determined that the stretching temperature positively influences the permeability and fiber strength. The stretched membranes exceeded the PVDF performance upper bound prepared by the TIPS method. The membranes were primarily in the α-phase polymorph, and stretching the fibers up to 40% at 90 °C did not induce any detectable β-phase crystals. The proposed preparation method offers a feasible and sustainable alternative to fabricate hollow fibers membranes with high tensile strength and high permeability.

A comprehensive study evaluated the mixed-gas (CO2/N2/O2) separation performance of thermally rearranged polybenzoxazole-co-imide (TR-PBOI-AD5) hollow fiber membranes fabricated in-house (pure-gas CO2 permeance of 481 GPU and ideal CO2/N2 selectivity of 17.7). The criteria for the determining the two major operating conditions (pressure ratio and feed flow rate) were identified in order to deliver optimal separation performance with low process energy consumption. By varying the feed CO2 concentrations, it was found that a single-stage operation using TR-PBOI-AD5 (produced by bis-APAF and DAM as the TR-able and non-TR-able diamines, respectively, based on 6FDA) hollow fiber membranes was not sufficient to meet the required 90% permeate CO2 purity target, while a two-stage operation using the same membranes led to a permeate CO2 purity (81%) closer to the target value. The comparison study among the TR polymer membranes and three other polymer membranes highlighted the significance of an appropriate choice of a mixed-gas separation operating scheme to fully utilize the exceptional permeation properties of the recently developed high performance membranes such as TR polymeric membranes.

Anion exchange membrane fuel cells (AEMFCs) have attracted great interest as a low-cost fuel cell technology for clean energy conversion and utilization for the future. AEMFCs have been considered the most promising succedaneum to proton exchange membrane fuel cells (PEMFCs) for addressing the cost issues associated with PEMFCs due to utilizing non-platinum group metals as electrocatalysts under alkaline conditions (such as Ag, Ni, and Co). Herein, we focus on a critical topic of AEMFCs—-anion-exchange polyelectrolytes (AEPs)—which are essential materials for low-cost AEMFCs. Specifically, AEPs have been used as anion-exchange membranes (AEMs) and binders (or ionomers) in AEMFCs. Years of study have allowed AEMFCs to recently achieve unprecedented progress, specifically in terms of power density and durability. These properties are comparable to or higher thanPEMFCs due to the recent development of high performance AEPs. Currently, most AEPs focused on the application of AEMs, and the importance of ionomer research has not been widely recognized. Moreover, a comprehensive review involving a systematic performance comparison of the state-of-the-art AEMs and ionomers is still lacking, making future research on AEMFCs unclear. This review systematically and comprehensively summarizes the development of AEPs and highlights the importance of cationic species and polymer backbone structures on durability with an emphasis on the importance of ionomer research. We further describe the differences between AEMs and ionomers by comparing the advantages and disadvantages of the state-of-the-art AEMs and ionomers to accurately guide future research on AEMFCs. We cover synthetic methods, degradation mechanisms, strategies to enhance performance, water transport behaviors, structure design criteria, and new challenges for AEMs and ionomers. This review is expected to expand further understanding of AEMs and ionomers and provide a future direction for designing AEMs and ionomers for future AEMFCs.

In this study, we report for the first time a pioneering method to prepare membranes with a fibrous morphology via phase inversion with extremely high pore connectivity. Microfiber aligned hollow fiber membranes were prepared via a polymer blend solution consisting of poly (vinylidene fluoride) with polysulfone in PolarClean® as a green solvent. The microfiber structure appeared only when controlled phase separation was performed with polymer blends. A systematic analysis has revealed that the shear rate and the reduced capillary number (α) of a blend solution significantly affected the morphology of the final membrane. The fabricated fibrous membranes exhibited six-fold higher water productivity compared to the best electrospun membranes reported in the literature, yet they remain highly scalable.