Asymmetric Porous Membranes Research Articles

High-Performance Asymmetric Porous Anion Exchange Membrane with Controllable Morphology via Solvent Evaporation and Water Etching

High-Performance Asymmetric Porous Anion Exchange Membrane with Controllable Morphology via Solvent Evaporation and Water Etching

Effect of annealing on the morphology and properties of poly(lactic acid)/polyhedral oligomeric silsesquioxane asymmetric porous membranes prepared through non‐solvent induced phase separation and its application

AbstractNon‐solvent induced phase separation (NIPS) method was employed to fabricate biodegradable poly(lactic acid) (PLA) nanocomposite membranes. Morphological studies using scanning electron microscopy revealed that all the membranes prepared display asymmetric structures comprising finger‐like macropores. The incorporation of modified polyhedral oligomeric silsesquioxane (POSS) particles into the PLA matrix resulted in enhanced crystallinity, mechanical, and thermal properties. Annealing of the membranes was performed to explore the influence of temperature on the morphology and properties. After annealing, membranes become more thin and compact, and drastic enhancement in crystallinity is also observed. Consequently, Young's modulus experiences a significant improvement. The reduction in oil absorption capacity after annealing can be attributed to the higher level of crystallinity, reduced porosity, and smaller pore diameter observed in the annealed membranes. Additionally, the unannealed PLA nanocomposite membranes demonstrated exceptional oil absorption capacity, reaching approximately 88%. It is foreseeable that these PLA/POSS nanocomposite membranes possess the potential to be utilized as effective tools for oil–water separation, offering the advantage of mitigating secondary pollution.

Mechanical enhancement and high linearity health monitoring of composite materials based on CNTs/PSF/PI film sensor with ultra-low SWCNTs doping content.

A new type of embedded composite material health monitoring nano-sensor is designed to ensure that the unique material advantages of nanofillers can be maximized. The carbon nanotubes (CNTs)/polysulfone (PSF)/polyimide (PI) thin film sensor in this paper is obtained by the self-assembly of a PSF/PI asymmetric porous membrane which is prepared by a phase inversion method through vacuum filtration of SWCNTs. It is a new structure for a practical CNT sensor that can take into account both 'composite health monitoring and damage warning' and 'composite mechanical enhancement'. The new structure of the CNTs/PSF/PI film sensor is divided into two parts. The upper part consists of small-aperture finger-like holes filled with SWCNTs (the SWCNT content is 0.0127 mg cm-2). The lower part consists of large-aperture cavities conducive to resin infiltration, which enhance the interface bonding force between the sensor and the composite material. This unique structure allows the CNTs/PSF/PI film sensor to change the influence of the embedded sensor from 'introducing defects' to 'local enhancement', and the mechanical strength of the enhanced specimen can reach up to 1.68 times that of the original specimen, and the service interval can reach 2.01 times that of the original specimen. In addition, the CNTs/PSF/PI film sensor also has good sensitivity (GF = 2.54) and extremely high linearity (R2 = 0.9995), and has excellent follow-up and interface bonding ability. It can also maintain excellent fatigue resistance and stability over 46 500 vibration cycles, which provides new research ideas and research methods for the field of composite-life monitoring sensors.

Glycerol-tailored asymmetric polyethersulfone membranes with uniform ion transport for stable lithium metal batteries

Advancing the performance and stability of lithium metal batteries is crucial for future energy storage devices. One of the major challenges for practical applications of Li metal batteries is to mitigate the formation of Li dendrites during cycling. In this work, we prepared a series of asymmetrically structured polyethersulfone (PES) membranes, consisting of a nanoporous skin layer and a bulk with macrovoids, by incorporating different amounts of glycerol during membrane preparation. Under optimal conditions, the asymmetric PES membrane made with 1.2 wt% of glycerol (PES-G1.2) possesses a thin skin layer with a uniform nanopore distribution, which is ideal for regulating the ion flux near the Li anode surface, thus suppressing Li dendrite formation. Our results demonstrate that the PES-G1.2 possesses exceptional ionic conductivity of 1.76 mS cm−1, Li+ transference number of 0.52, and high compatibility with Li electrode. Additionally, the Li/PES-G1.2/LiFePO4 cells also present a remarkable rate capability with specific capacity of 150 mAh g−1 at 0.2 C and 81 mAh g−1 at 10 C, respectively, and 90 % of capacity can be retained after 100 charge-discharge cycles under 0.2 C. These findings shed light on the unique properties of asymmetric porous membrane as well as its promising potential for applications in lithium metal batteries.

Comparative study of moisture transfer of polyethersulfone-based membranes and kraft paper

The efficiency of membrane-based enthalpy exchangers primarily depends on the moisture permeability of the membranes used. While traditional kraft paper membranes exhibit favorable moisture adsorption properties, they lack durability and are prone to bacterial growth. To overcome these limitations, alternative membrane materials, including polyethersulfone (PES) film, asymmetric porous PES membrane (P-MEM), and composite membrane (C-MEM) comprising PES and polyether block amide (PEBAX), have been investigated. These membranes' physical properties and water adsorption affinity were compared with that of conventional kraft paper. Experimental measurements of moisture permeation and adsorption equilibrium were conducted to evaluate the moisture transfer properties of the membranes under different operating conditions. The experimental and modeling results showed that the moisture transfer resistance of the membranes varied depending on the material and temperature, with a lower degree of dependence on the surrounding fluid humidity. C-MEM exhibited the highest moisture resistance, followed by kraft paper, while P-MEM and PES had the lowest resistance. Additionally, the moisture diffusivity and activation energies for moisture transport were determined for each membrane.

Capillary infiltration kinetics in highly asymmetric porous membranes and the resulting debonding behaviors

Reliable bonding of high-performance membranes onto polymeric supporting structures is critical for capitalizing their potentials within practical filtration applications. The successful bonding typically requires infiltration of the membrane pores by a thermoplastic polymer, driven by capillary pressure and/or external pressure. In this work, we systematically examine the capillary infiltration of a polypropylene (PP) within polyethersulfone (PES) membranes with a highly asymmetric pore structure, a nominal pore size of 20 nm, and varying degrees of hydrophilicity. Most significantly, the infiltration kinetics was strongly influenced by the asymmetric pore structure in two aspects: (1) the time to achieve full infiltration from the large-pore side was approximately 4 times shorter than that from the tight-pore side; (2) When bonding from the tight-pore side, the infiltration depth, L(t) showed L (t) ∼ t1.6, instead of characteristic L (t) ∼ t0.5. The accelerated infiltration rate over time was successfully modelled with the Cai model using depth-dependent pore size that captures the asymmetric pore structure. Furthermore, chemical modification reduced the initial infiltration rate only, which is attributed to the reduction in surface porosity. No significant difference in infiltration kinetics at the later stage was observed. Mechanical integrity tests of the bonded samples display complex debonding behaviors including complete peeling, incomplete peeling, and complete membrane failure. The peel force corresponding to membrane failure appeared larger than the other two debonding modes, all of which showed insignificant dependence on the membrane chemistry or infiltration depth. Post-mortem analysis of the completely peeled sample showed PP nanofibers were pulled out of the PES membranes during debonding, emphasizing relatively weak mechanical interlocking due to the low surface porosity.

Air-to-Air Heat and Moisture Recovery in a Plate-Frame Exchanger Using Composite and Asymmetric Membranes.

The present work studied an air-to-air exchanger comprising a flat plate module with a diagonal channel and a counterflow configuration for the air streams. The objective of this study was to remove moisture and sensible heat from an exhaust air stream by indirect contact with another air stream. The temperature and flow rate of the exhaust air was in the range of 40–80 °C and 1–5 L·min−1, respectively, and the fresh ambient air to exhaust air flow ratio was 1–5. An asymmetric porous membrane (P-MEM), a thin film composite membrane (C-MEM), and a kraft paper were used as the core for the heat exchange module. The most influential parameter was the humid air temperature, with a direct positive effect (50–60%) due to the increase in the kinetic energy of the water molecules. The other effective parameter was the flow rate of the humid gas with a reverse effect on the enthalpy exchanger performance (25–37%). The ratio of “fresh” air to “exhaust” air had the lowest positive effect (8–10%) on the total effectiveness. The sensible effectiveness of different membranes under the studied conditions was relatively the same, showing their similar heat conductivity. However, the kraft paper showed the best performance compared to the synthetic membranes due to having a porous/hydrophile texture. P-MEM with an asymmetric porous texture showed the closest performance to kraft paper. Furthermore, it was found that under limited conditions, such as higher temperatures (70 and 80 °C) and flow rates (5 L·min−1) for the humid air, the performance of P-MEM was a little better than the kraft paper. However, C-MEM with the lowest total effectiveness and overall heat transfer coefficient (150–210 W·m−2·K−1) showed that the hydrophile PEBAX layer could not contribute to moisture recovery due to its high thickness.

Interfacial co-weaving of AO-PIM-1 and ZIF-8 in composite membranes for enhanced H2 purification

Porous asymmetric composite membranes (ACMs) have attracted intensive attentions in energy-efficient gas separations. However, fabricating ACMs with defect-free interface and enhanced selectivity without sacrificing permeability remains great challenge. Herein, a major step towards this goal is proposed by employing an efficient co-weaving strategy to regulate interfacial microstructure of ACMs with bilayer geometry on porous substrates. The double layers are constructed by in-situ growing zeolitic imidazolate frameworks-8 (ZIF-8) on the surface of amidoxime-functionalized polymer of intrinsic microporosity-1 (AO-PIM-1) layer (denoted as AO-PIM-1@ZIF-8). The pre -designed amidoxime groups on the AO-PIM-1 backbone provide abundant coordinate sites for Zn (ΙΙ) ions, offering advantages for building a continuous membrane. Consequently, the obtained AO-PIM-1@ZIF-8 membrane demonstrates remarkable performance in H 2 /CO 2 separations, with the H 2 /CO 2 selectivity of 11.97 and the H 2 permeability of up to 5688 Barrer at 298 K and 1 bar. Both the H 2 permeability and H 2 /CO 2 selectivity exceed most of reported ACMs, and far surpassed Robeson’s 2008 upper bound by taking advantage of the molecular sieving effect of interfacial layer formed by co-weaving of AO-PIM-1 chains with ZIF-8. This is contributed either by position-space renormalisation for AO-PIM-1 chains or pore space partition in ZIF-8 at the interface. The study reports herein offer an alternative route to develop high-performance composite membranes for improved gas separations. • Two continuous composite membranes were prepared using a simple fabrication method. • Co-weaving strategy was used to eliminate the interfacial defects. • H 2 /CO 2 separations of the as-made membrane far exceeded Robeson’s 2008 upper bound. • This performance was from the molecular sieving effect of the interfacial layer.

Cover Image, Volume 139, Issue 10

The cover image by Sujith Athiyanathil and Smitha Manholi shows FE SEM images of surface and crosssectional morphologies of Poly (ε-caprolactone) (PCL) porous asymmetric membranes fabricated in six different solvents using the NIPS method and using water as a non-solvent. This study presents the fabrication of poly (ε-caprolactone) phase inversion membrane, which is a biodegradable polymer in six different casting solvents: N, N-Dimethyl formamide (DMF), N-methyl-2-pyrrolidone (NMP), Tetra Hydro Furan (THF), Tri ethyl phosphate (TEP), 1,4-Dioxane, and Acetone. The project aims to study the effects of casting solvents on the precipitation kinetics, membrane morphology, and permeation performance for water filtration applications. DOI: 10.1002/app.51720

Salt storage and induced crystallisation in porous asymmetric inorganic membranes

Processing brines to recover strategic mineral salts using evaporation ponds requires large surface areas and are slow, even in arid climates. Here we show a novel membrane macropore storage mechanism that induces fast salt crystallisation in mesoporous top-layers in inorganic asymmetric membranes, stemming from 789 million nucleation points per metre square of surface area. During membrane pervaporation, dissolved salts are retained mainly in the macropores of the substrate which subsequently provide ideal conditions for crystal nucleation and growth on the membrane surface upon drying. This novel pore storage mechanism is attained owing to the solution flow modulation of the mesoporous titania and gamma-alumina layers that is counterbalanced by the flow of water during pervaporation. Therefore, pore size control is imperative to avoid flooding in the macroporous substrate. This work further shows the fundamental properties of the salt storage mechanism described by a single salt production coefficient, and a global salt production coefficient for metal chloride salts. This technology could potentially be considered for unlocking and process strategic global minerals from brines.

Phase transited asymmetric membrane floating nanoparticles: a means for better management of poorly water-soluble drugs.

Effective remedy to gastrointestinal (GI) side effects caused by poorly water-soluble drugs remains a challenge. Researching for novel techniques to reduce these side effects and increase patient adherence to medical treatment is of interest. The current study aims to develop an innovative nano-sized gastro-retentive drug delivery for better management of poorly water-soluble drugs. A non-disintegrating ibuprofen-asymmetric membrane floating nanoparticle (Ibuprofen-AMFNP) was prepared by phase inversion technique to increase the gastric residence of the drug. Powder characterization, solubility, in vitro buoyancy, effect on in vivo inflammatory markers, and polymer diffusibility studies were conducted on the prepared formulation. All UV-spectrophotometric analysis was accomplished through a fiber optic system. The prepared Ibuprofen-AMFNPs were in the nano range of 114.45nm ±1.31nm. The formulation was buoyant for 12h in the dissolution media indicating increased gastric residence, had better solubility and powder characteristics compared to the pure drug. Scanning electron microscopy revealed an outer non-porous and inner porous asymmetric membrane. Ibuprofen-AMFNP followed Higuchi drug release kinetics (p=0.9925) and had a Fickian diffusion release mechanism (n=0.05). Polymer diffusibility study showed that the 24h stored formulation had faster drug release with no lag time (-923.08nm/h) compared to a fresh formulation (2526.32nm/h). The prepared nano-formulation showed a higher percentage of anti-inflammatory (85.144%) effect compared to the pure drug (78.336%). Ibuprofen-AMFNP is envisioned to help reduce drug-related GI side effects, improve drug delivery, and thereby increase patient adherence to medical treatment.

PVDF Composite Membranes with Hydrophobically-Capped CuONPs for Direct-Contact Membrane Distillation.

Water scarcity is an imminent problem that humanity is beginning to attempt to solve. Among the several technologies that have been developed to mitigate water scarcity, membrane distillation is of particular note. In the present work, CuO nanoparticles capped with 1-octanethiol (CuONPs@CH) or 1H,1H,2H,2H-perfluorodecanethiol (CuONPs@CF) are prepared. The nanoparticles are characterized by FT-IR and TGA methods. Two weight losses are observed in both cases, with the decomposition of the organic fragments beginning at 158 °C and 230 °C for CuONPs@CF and CuONPs@CH, respectively. Flat sheet PVDF composite membranes containing nanoparticles are prepared by the casting solution method using nanoparticle concentrations that ranged between 2–20% with a non-woven polyester fabric as support. The obtained membranes showed a thickness of 240 ± 40 μm. According to water contact angle (87° for CuONPs@CH and 95° for CuONPs@CF, both at 10% w.t) and roughness (12 pixel for CuONPs@CH and 14 pixels for CuONPs@CF, both at 10% w.t) determinations, the hydrophobicity of membranes changed due to a decrease in surface energy, while, for naked CuONPs, the roughness factor represents the main role. Membranes prepared with capped nanoparticles showed similar porosity (60–64%). SEM micrographs show asymmetric porous membranes with a 200-nm surface pore diameter. The largest finger-like pores in the membranes prepared with CuONPs, CuONPs@CH and CuONPs@CF had values of 63 ± 10 μm, 32 ± 8 μm, and 45 ± 10 μm, respectively. These membranes were submitted to a direct contact membrane distillation module and flux values of 1.8, 2.7, and 3.9 kg(m2·h)−1 at ΔT = 30 °C were obtained for the CuONPs, CuONPs@CH, and CuONPs@CF, respectively. The membranes showed 100% salt rejection during the testing time (240 min).

ASYMMETRIC CELLULOSE ACETATE MEMBRANES USED IN SEPARATION APPLICATIONS

This work focused on the use of cellulose acetate polymer for the preparation of porous asymmetric membranes using a phase inversion process. These membranes were characterised by scanning electron microscopy, a bubble-point method and sorption measurements. The preparation method used induced membrane anisotropy. The capacity of the membranes in the removal of electrolyte (NaCl) from aqueous solution was investigated. A good retention of 58.6% and a high flux rate of 8.9 × 10–4 m/s using NaCl solution of 200 mg/L concentration were obtained by cellulose acetate membranes prepared with water as non-solvent. The results showed that the membrane performance was affected by the membrane structure, which was determined by the conditions of membrane preparation.

Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review.

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995–2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency.

Simple and efficient method for functionalizing photocatalytic ceramic membranes and assessment of its applicability for wastewater treatment in up-scalable membrane reactors

A photocatalytically active layer composed of TiO2 (Evonik P25) was successfully deposited on the macroporous (3 µm pore size) permeate side of an asymmetric porous alumina membrane with the aid of a smectite (a synthetic hectorite, Sumecton SWF) by dipping the membranes into an aqueous suspension containing P25 and the smectite. After the heat treatment at 400 °C, the coated hybrid was adhered on the macroporous support enough to be applied for the photocatalytic decomposition of organics (methylene blue and phenol as model molecules) in water. The water permeance of the membranes after the coating with the P25-smectite hybrid was reduced by only 24% compared with that of the pristine membrane, showing that the advantages of the present method for the preparation of the photocatalyst layer on the surface of the macroporous alumina without significant infiltration of the suspension into the support pores. The amount of MB and phenol degraded using the P25-SWF hybrid was equal to 0.007 and 0.023 mmol.L−1, respectively, when the reaction was carried out using the four single-channel tubular membrane reactor at transmembrane pressures of 250 mbar. The implemented photocatalytic membrane reactor can easily be up-scaled by increase the size of the membrane module, with more tubes and longer tubes (lengths up to 1 m are commercially available), paving the way to potential technological applications for the continuous treatment of polluted waters.

Study of Prepared α-Chymotrypsin as Enzyme Nanoparticles and of Biocatalytic Membrane Reactor

Biocatalytic kinetic effect of α-chymotrypsin enzyme has been investigated in its free and pretreated forms (it was covered by a very thin, porous polymer layer, called enzyme nanoparticle) as well as its immobilized form into pores of polysulfone/polyamide asymmetric, hydrophilic membrane. Trimethoxysilyl and acrylamide-bisacrylamide polymers have been used for synthesis of enzyme nanoparticles. Applying Michaelis-Menten kinetics, the KM and vmax values of enzyme-polyacrylamide nanoparticles are about the same, as that of free enzyme. On the other hand, enzyme nanoparticles retain their activity 20–80 fold longer time period than that of the free enzyme, but their initial activity values are reduced to 13–55% of those of free enzymes, at 37 °C. Enzyme immobilized into asymmetric porous membrane layer remained active about 2.3-fold longer time period than that of native enzyme (at pH = 7.4 and at 23 °C), while its reaction rate was about 8-fold higher than that of free enzyme, measured in mixed tank reactor. The conversion degree of substrate was gradually decreased in presence of increasing convective flux of the inlet fluid phase. Biocatalytic membrane reactor has transformed 2.5 times more amount of substrate than the same amount of enzyme nanoparticles and 19 times more amount of substrate than free enzyme, measured in mixed tank reactor.

A novel approach to predict the skin layer porosity of porous asymmetric membranes via gas permeation test

A new approach for estimating the structural parameters of asymmetric porous skin layer membranes fabricated by Loeb-Sourirajan method, to overcome the limitation of the models which are in existence is focused. Agreement between the calculated and the experimental data was then examined for all models to show the superiority of the newly proposed model. In particular, the new model could resolve the imperfections of the presently available models possessing the following superiorities: (i) scanning the entire range of permeance versus pressure diagram, (ii) no limit due to the conditions of data collection, and (iii) in contrast to the presently available models, the proposed model is capable to obtain the surface porosity (ε) and the skin thickness (lp) separately. Interestingly, a high correlation was observed between the results of the wet/dry flow test and the proposed approach. The proposed model also makes it possible to correlate the structural parameters of the membrane with the condition of membrane fabrication.

Asymmetric Porous Membranes with Improving Mass Transfer for Proton Exchange Membrane Water Electrolysis (PEMWE)

Hydrogen is a promising and efficient energy source that can replace fossil fuels. Hydrogen can be obtained from various raw materials, including water. Recently, among various hydrogen production methods, high purity of hydrogen gas can be obtained by hydroelectricity. It also focused on water electrolysis, where efficient and continuous production of hydrogen is possible. Moreover, in terms of efficient and continuous production of hydrogen and environmental effects, PEMWE (Proton Exchange Membrane Water Electrolysis) has been evaluated as the most inspiring technology for producing high purity hydrogen of renewable energy and has the strength to discharge only oxygen by-products without hazards. These days, PEMWE research is surging as demand for hydrogen-based energy increases. Therefore, considerable research has recently been completed on membrane development for PEMWE. Currently, the PFSA (Perfluorosulfonic acid) polymer is used in PEMWE systems. A previous study reported that the thinner the PFSA membrane used for PEMWE, the lower the resistance of the MEA (Membrane Electrode Assembly), resulting in improved single-cell performance. Nevertheless, the single cell operates using a thick electrolyte membrane considering the safety aspects of the PEMWE system. Applying thick electrolytic membranes to PEMWE systems improves physical and chemical durability, but increasing the thickness of the MEA increases the resistance and mass transfer resistance, which degrades the performance of PEMWE. To compensate for these limitations, Previous studies have been conducted to reduce the resistance by modifying the catalyst structure constituting the MEA, but any case hasn't been reported to modify the structure of the membrane for PEMWE.Therefore, in this study, an asymmetric membrane was prepared to improve the performance of the PEMWE single cell by applying a porous structure into a thick membrane to ensure high durability. Research on asymmetric membranes has been conducted in energy fields such as vanadium redox flow batteries, fuel cells, and lithium-ion batteries. As a result of applying an asymmetric membrane to each energy research, it has been reported that the doping amount of the electrolyte increases due to the strengthening of the capillary force according to the porous structure, and accordingly, the ionic conductivity increases, thereby improving the performance of the cell. Besides, studies are showing that the diffusion rate of water and ions increases, and the internal resistance decreases due to the structure of the dense layer and the porous layer.In this study, to apply the performance improvement effect of the previous study to the electrolyte membrane for electrolysis, we referred the porous structure to confirm the performance of the PEMWE single cell. The porous layer of the asymmetric membrane was prepared using a solvent/non-solvent evaporation method. The solvent of the Nafion dispersion solution is alcohol, and the non-solvent is ortho-dichlorobenzene (ODB). The porous surface was prepared using the difference in boiling point and density between the solvent/non-solvent. Through the SEM analysis, the porous layer on the surface of the asymmetric membrane and dense layer on the bottom was observed. The Uniform round micropores distributed on the entire surface of the porous layer, which was below 10 μm. A cross-sectional view showed that the thickness of the asymmetric membrane is 175 ~ 180 μm. As a result of an EIS analysis, the asymmetric membrane showed a tendency to have lower ohmic and mass transfer resistance than the Nafion 117 membrane of the same thickness. Through the evaluation of a single cell performed under 80 ℃ temperature conditions, Nafion 117 was 1.5 A/cm2 and the asymmetric membrane was 2.5 A/cm2, about 1.67 times higher than Nafion117. The results of PEMWE single cell measurement confirmed that the porous structure of the asymmetric membrane improved the material transfer efficiency of the membrane, thus lowering the material transfer resistance, thereby improving the PEMWE performance.

Asymmetric polysiloxane-based SiOC membranes produced via phase inversion tape casting process

Asymmetric porous SiOC membranes with different pore characteristic and membrane morphology were produced for the first time by adapting the phase inversion tape casting technique to the polymer-derived ceramic route. Polymethyl siloxane (MK) was used as a ceramic precursor. The produced tapes were pyrolyzed under N2 atmosphere. The structure and surface characteristics were tailored by changing the pyrolysis temperatures (600 and 1000°C), polyvinylpyrrolidone and solid loading. Scanning electron microscopy analysis revealed the asymmetric morphology composed by a thin skin-layer (average pore size <2μm) and a sponge-like support. The differences in membranes porosity (33–47%) and overall pore size distribution (1–10μm) can be controlled by adjusting the slurry composition. The incorporation of particles improved the slurry processability, enhanced the mechanical flexural resistance of the membrane (20–48MPa), and reduced the average pore size. Higher mechanical strengths and enhanced hydrophilic character are associated with higher pyrolysis temperatures (ceramization process). The water permeation of membranes pyrolyzed at 1000°C were assessed in a dead-end configuration device under different pressures (1–3bar). The obtained water permeation fluxes (6–55m3/m2·h, at 3bar) indicates the advantages of the asymmetric structure which minimizes mass transport limitations.

Charged porous asymmetric membrane for enhancing salinity gradient energy conversion

Abstract Salinity gradient energy is an abundant renewable energy source that can help satisfy the growing global demand for energy. Although current approaches based on membrane design for salinity gradient energy conversion have been demonstrated to improve conversion efficiency they suffer from the trade-off between selectivity and intrinsic resistance of the membranes, which impedes the rates of energy conversion. In this study, a charged porous asymmetric membrane was fabricated, consisting of a thin charged nanopore (~1 nm) layer and a charged porous structure (80–100 nm) layer. Its asymmetric electric potential and charged porous structure increase its affinity to uniport of ions and enables high ion conductivity. While maintaining a high degree of selectivity, the membrane exhibited an intrinsic membrane resistance of 0.53 ± 0.12 Ω·cm2, which was lower than that of the commercial and other reported membranes. The maximum power density reached up to 12.5 W/m2 with a 500-fold salinity gradient. This membrane shows great promise in industrialization and provides new insights into high salinity energy conversion.