Reduction Of Membrane Thickness Research Articles

Fabrication of Coffee‐ring Nanostructured Membranes for Organic Solvent Nanofiltration

Organic solvent nanofiltration (OSN) plays important roles in pharmaceutical ingredients purification and solvent recovery. However, the low organic solvent permeance under cross‐flow operation of OSN membrane hampers their industrial applications. Herein, we report the construction of coffee‐ring structured membrane featuring high OSN permeance. A water‐insoluble crystal monomer that dissolved in EtOH/H2O mixed solvent was designed to react with trimesoyl chloride via interfacial polymerization. Owing to the diffusion of EtOH to n‐hexane, coffee‐ring nanostructure on the support membrane appeared, which served as the template for construction of coffee‐ring structured membrane. The optimal nanostructured membrane demonstrated 2.6‐fold enhancement in the effective surface area with reduced membrane thickness. Resultantly, the membrane afforded a 2.7‐fold enhancement in organic solvent permeance, e.g., ~ 13 LMH/bar for MeOH, without sacrificing the rejection ability. Moreover, due to the rigid monomer structure, the fabricated membrane shows distinctive running stability in active pharmaceutical ingredients purification and the ability for concentration of medicines.

Fabrication of Coffee-Ring Nanostructured Membranes for Organic Solvent Nanofiltration.

Organic solvent nanofiltration (OSN) plays important roles in pharmaceutical ingredients purification and solvent recovery. However, the low organic solvent permeance under cross-flow operation of OSN membrane hampers their industrial applications. Herein, we report the construction of coffee-ring structured membrane featuring high OSN permeance. A water-insoluble crystal monomer that dissolved in EtOH/H2O mixed solvent was designed to react with trimesoyl chloride via interfacial polymerization. Owing to the diffusion of EtOH to n-hexane, coffee-ring nanostructure on the support membrane appeared, which served as the template for construction of coffee-ring structured membrane. The optimal nanostructured membrane demonstrated 2.6-fold enhancement in the effective surface area with reduced membrane thickness. Resultantly, the membrane afforded a 2.7-fold enhancement in organic solvent permeance, e.g., ~13 LMH/bar for MeOH, without sacrificing the rejection ability. Moreover, due to the rigid monomer structure, the fabricated membrane shows distinctive running stability in active pharmaceutical ingredients purification and the ability for concentration of medicines.

Effect of air-loading on the performance limits of graphene microphones

As a consequence of their high strength, small thickness, and high flexibility, ultrathin graphene membranes show great potential for pressure and sound sensing applications. This study investigates the performance of multi-layer graphene membranes for microphone applications in the presence of air-loading. Since microphones need a flatband response over the full audible bandwidth, they require a sufficiently high mechanical resonance frequency. Reducing membrane thickness facilitates meeting this bandwidth requirement, and therefore, also allows increasing compliance and sensitivity of the membranes. However, at atmospheric pressure, air-loading effects can increase the effective mass, and thus, reduce the bandwidth of graphene and other 2D material-based microphones. To assess the severity of this performance-limiting effect, we characterize the acoustic response of multi-layer graphene membranes with a thickness of 8 nm in the pressure range from 30 to 1000 mbar, in air and helium environments. A bandwidth reduction by a factor ∼2.8× for membranes with a diameter of 500 μm is observed. These measurements show that air-loading effects, which are usually negligible in conventional microphones, can lead to a substantial bandwidth reduction in ultrathin graphene microphones. With analytical and finite element models, we further analyze the performance limits of graphene microphones in the presence of air-loading effects.

Tailoring fully crosslinked polyamide layers on optimized polyacrylonitrile supports via coactive delayed phase inversion and alkaline hydrolysis for brine treatment through pervaporation

A novel method of co-hydrolysis of polyacrylonitrile (PAN) support to host polyamide (PA) formation using coactive delayed phase inversion is presented to synthesize high-performance pervaporation membranes. Pure water in the coagulation bath was replaced with a 1.0 M sodium hydroxide solution maintained at 50 °C, allowing concurrent hydrolysis and delayed phase inversion. The characterization results revealed a smoother surface morphology, a higher carboxylic group content, improved hydrophilicity, and an ideal O/N ratio (∼1) of the PA layer on the co-hydrolyzed PAN (HPAN-Co) support compared with the PA layer on the post-hydrolyzed PAN (HPAN-Post) support. Furthermore, the typical pattern observed in PA-HPAN-Post, with a plethora of finger-like pores followed by macrovoids, completely disappeared and was replaced by a uniform and fine microvoid structure in PA-HPAN-Co, with an approximately 50 % reduction in membrane thickness. This led to a reduction in membrane swelling and salt transport without compromising the permeation flux. The pervaporation tests with a 10 wt% NaCl feed at 70 °C using PA-HPAN-Co showed a 99.97 % salt rejection ability and a 74.2 kg m−2h−1 flux, which is 33 % higher than the permeate flux of PA-HPAN-Post. Thus, the PA-HPAN-Co membrane is highly recommended for pervaporative desalination, considering the enhanced performance and scalability of the synthesis technique.

An efficient composite membrane to improve the performance of PEM reversible fuel cells

In this study innovative composite Nafion/GO membranes are tested at different GO loading (0.5% wt., 1% wt. and 1.5% wt.) in electrolyser and fuel cell mode (Unitized reversible fuel cell). Baseline Nafion membranes were used for comparison.Water uptake (WU), ion exchange capacity (IEC), tensile strength, TGA (thermogravimetric analysis) and SEM (scanning electron microscope) analysis are discussed. The SEM revealed the inclusion of GO into the Nafion matrix while the TGA showed an increased thermal stability of the membrane attributed to the inclusion of the carbon material. Moreover, the addition of GO improves the membrane tensile strength, obtaining a maximum enhancement of nearly 90%, while reducing the elongation ratio (80% for the Nafion and 45% for the 1.5% wt. GO membrane). Water uptake increased when increasing the content of GO due to its hydrophilic nature recording the highest values for the membrane with 1.5%wt. of GO (23% against 10% for the Nafion). An increase of IEC (almost 14%) is noticed when GO content is increased. The beneficial effect of GO on the IEC can be attributed to a non-uniform distribution of GO into the Nafion matrix but needs further investigation.Both fuel cell and electrolyser polarization curves were carried out using MEAs with an active area of 9 cm2 and a thickness of 50 μm. The temperature and the pressure were set to 20 °C and 1 atm respectively. Regarding fuel cell mode, the optimum loading of GO has been found to be 0.5%, registering the highest performance, 13% higher than Nafion. Regarding the electrolyser mode, the GO 0.5% wt. membrane, showed performance comparable to the Nafion. A comparison between Nafion based membranes at higher thicknesses showed that, adopting GO, it is possible to obtained similar performance with a reduced membrane thickness, keeping almost equal the performance and the average round trip efficiency (26.1% for the GO and 26.6% for the Nafion). In commercial applications such characteristics allows to strongly reduce the cost of materials.Durability and stability of the GO/Nafion membrane should be properly investigated in successive studies as such membranes are subjected to a rapid deterioration of their performance.

(Invited) MEA Technologies for PEM Electrolyzers: Overview and Perspectives

Hydrogen has gained increasing attention recently as an alternative energy carrier leading towards a sustainable hydrogen economy [1]. Green hydrogen has less pollution (water as the only byproduct) and higher energy density than its counterpart fossil fuels. Additionally, it has much higher refueling speed than lithium-ion batteries, which makes it’s more suitable for mobility applications.Proton exchange membrane (PEM) water electrolysis is one of the most popular approaches for green hydrogen generation due to its high efficiency and high differential pressure operation capability [2]. The membrane electrode assembly (MEA) is the core of a PEM electrolyzer in which water molecules are spilt into hydrogen and oxygen molecules. In this overview, the challenges and paths regarding the MEA materials, operation/diagnosis/maintenance, and final recycling will be discussed.An electrolyzer MEA contains an anode and cathode made of platinum group metal (PGM) catalysts, a perfluorosulfonic acid (PFSA) membrane, and other gasketing materials. PGM catalysts are a major source of the cost of the PEM electrolyzer stack. Ir black based catalysts have been used for decades in the PEM electrolyzer industry. Due to the high cost and scarcity of Ir, efforts have been dedicated to reducing the catalyst loading and developing highly active catalysts [3]. The membrane is another major component of a PEM electrolyzer. 5 mil and 7 mil thick membranes have been used in electrolyzer industries. However, the ionic resistive losses of these relatively thick PEMs significantly reduce the efficiency of the MEA. Hence, reducing membrane thickness has been a central topic for PEM electrolyzer membrane development. With the progressive thinning of the PEM, the hydrogen gas crossover will become significant, which will compromise the safe operation of a PEM electrolyzer system. An effective gas recombination layer in the PEM is therefore urgently needed to mitigate the resulting higher hydrogen crossover. Additionally, the mechanical stresses imposed due to operation at high differential pressure operation (up to 40 bar) increases the attractiveness of a reinforcement layer.The unique properties of the membrane and catalysts in an MEA also require ultra-pure feed water. However, this cannot always be guaranteed. Metal ions will leach out from system plumbing and the DI system can’t always effectively remove all ions from tap water. The contamination will also poison the catalysts in an MEA. It is therefore critical to establish a universal method to efficiently identify the issue and recover the MEA performance.It is expected that the MEA can last 60k to 90k hours [4]. Though functionality may be compromised at the this point, the value in the PGM catalysts, and to a lesser extent membrane, and other carbon-based materials [5] remains. MEA recycling thus needs to be considered at the very early stage of the large-scale PEM electrolyzer application. Tradition calcination approaches for catalyst refinery is not optimized for PEM MEAs due to the presence of the PFSA membrane. The burning of MEAs will not only waste costly PFSA material but also poses a threat to the environment due to carbon and fluoride emissions. Current research efforts have focused on catalyst recycling and reuse/repurpose of PFSA based materials.[1] Oliveira, A. M., Beswick, R. R. & Yan, Y. A green hydrogen economy for a renewable energy society. Current Opinion in Chemical Engineering 33, 100701 (2021).[2] Ayers, K. et al. Perspectives on low-temperature electrolysis and potential for renewable hydrogen at scale. Annual review of chemical and biomolecular engineering 10 (2019).[3] Mittelsteadt, C. (Invited) Ir Strangelove: Or How I Learned to Stop Worrying and Embrace the PEM. ECS Meeting s MA2022-01, 1335-1335 (2022).[4] Schmidt, O., Future cost and performance of water electrolysis: an expert elicitation study. International journal of hydrogen energy 42 (2017), 30470-30492.[5] Sverdrup, H. U. & Ragnarsdottir, K. V. A system dynamics model for platinum group metal supply, market price, depletion of extractable amounts, ore grade, recycling and stocks-in-use. Resources, Conservation and Recycling 114, 130-152 (2016)

Effects of graphene oxide membrane thickness reduction on microstructure and crossflow separation performance in kraft black liquor dewatering

Reduced graphene oxide (rGO) membranes are emerging as viable candidates for energy-efficient fractionation of multicomponent biomass streams, such as kraft black liquor (BL). Increased fluxes in rGO membranes under crossflow conditions – while maintaining high solute rejections – are highly desirable for improving the economics of such processes. We have conducted a detailed experimental study of a series of rGO membranes with progressively lower thicknesses (from 130 nm to 40 nm). The influence of the membrane thickness and the membrane microstructure is analyzed in terms of its effects on water permeation flux, divalent salt rejection, and molecular weight cutoff (MWCO) measurements using dye molecules. A selected rGO membrane (70 nm) showing both high fluxes and rejections was scaled up to a 650 cm2 sheet and used for extended crossflow operation under real BL streams for more than 22 days. Techno-economic calculations reveal significant positive effects of membrane thickness reduction on the economics of BL dewatering.

Nanofiltration through cylindrical nanopores end-grafted with polyelectrolytes

Taking account of the effects of polyelectrolytes friction, osmotic pressure, and dielectric saturation, a continuum model is adopted to investigate the rejection and permeability of cylindrical nanopores end-grafted with pH-regulated polyelectrolytes (PEs). In addition to a detailed simulation for the behavior of the system considered under various conditions, the intriguing phenomena and underlying mechanisms are also discussed. The results gathered suggest that end-grafted nanopores show a better rejection than the corresponding bare nanopores, and the real rejection is dictated by the mean volumetric flux. Complete coverage of PEs over the cross section of a nanopore will not improve its rejection due to the hindrance in flow rate. However, both partial grafting of nanopore feed side and reducing membrane thickness can promote permeability and maintain the level of rejection. The rejection for the case where the subunits of a PE layer are localized near the outer ring of a nanopore cross section is better than that for the case where they are localized near its inner ring. The former also shows a higher permeability than the latter. By end-grafting a nanopore with 8-nm radius, its rejection for 100 mM KCl is comparable to that for a bare nanopore with 2-nm radius, although the flow rate in the former is one-order-of-magnitude larger than in the latter. This reveals that end-grafting has the potential for enlarging nanopore, thereby opening a new avenue of raising permeability while maintaining rejection simultaneously.

Size-Induced Ferroelectricity in Antiferroelectric Oxide Membranes.

Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve in antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing antiferroelectrics for high-energy-density storage applications, understanding their size effects will provide key information for optimizing device performances at small scales. Here, the fundamental intrinsic size dependence of antiferroelectricity in lead-free NaNbO3 membranes is investigated. Via a wide range of experimental and theoretical approaches, an intriguing antiferroelectric-to-ferroelectric transition upon reducing membrane thickness is probed. This size effect leads to a ferroelectric single-phase below 40nm, as well as a mixed-phase state with ferroelectric and antiferroelectric orders coexisting above this critical thickness. Furthermore, it is shown that the antiferroelectric and ferroelectric orders are electrically switchable. First-principle calculations further reveal that the observed transition is driven by the structural distortion arising from the membrane surface. This work provides direct experimental evidence for intrinsic size-driven scaling in antiferroelectrics and demonstrates enormous potential of utilizing size effects to drive emergent properties in environmentally benign lead-free oxides with the membrane platform.

Microstructure and hydrogen transport properties of (V90Cr5Al5)90Cu10 alloy membranes

Our newly developed V90Cr5Al5 hydrogen permeable alloy has been extended to enhance malleability by Cu alloying. The resulting (V90Cr5Al5)90Cu10 consists of bcc-(V) and fcc-(Cu) phases and can be cold rolled into a thin membrane with a thickness of 0.1 mm due to the introduction of the ductile copper phase. After rolling and annealing, (V90Cr5Al5)90Cu10 contains finer grains and a higher percentage of special grain boundaries compared to the as-cast case. The rolled/annealed (V90Cr5Al5)90Cu10 exhibits a lower hydrogen diffusivity than the as-cast one, but a significantly improved hydrogen permeation flux due to the reduced membrane thickness and the inverse relationship of flux and thickness. Typically, a pronounced high hydrogen flux of ∼72 cc H2 cm−2min−1 was achieved at a hydrogen pressure difference of 0.6 MPa at 673 K. In comparison with V90Cr5Al5, Cu alloyed membranes exhibit enhanced resistance against hydrogen embrittlement and enhanced long-term hydrogen permeation stability at 673 K.

Phosphoric acid pre-treatment to tailor polybenzimidazole membranes for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) use ion-selective membranes for transporting ionic species while separating the positive and negative electrolytes. In this paper, we report phosphoric acid doped polybenzimidazole (PBI) membranes that yield high ionic selectivity and conductivity in VRFBs. The phosphoric acid pre-treatment swells the PBI matrix irreversibly and increases its sulfuric acid doping in VRFB electrolytes. The pre-treated membranes show comparable area resistance with Nafion-212 with better selectivity towards vanadium ions. A low resistance was obtained with a reduced membrane thickness, which can reduce the overall cost of materials. The VRFB using an optimized phosphoric acid pre-treated PBI membrane demonstrates coulombic, voltage, and energy efficiencies of 99.7, 90.3, and 90.0%, respectively, at 40 mA cm−2 while achieving ∼40% higher discharge capacity compared to Nafion-212. Furthermore, the VRFB cell shows excellent cycling stability, i.e., only 6.8% or 0.068% per cycle capacity decay for 100 cycles while maintaining coulombic efficiency at >99.9% (98.5% coulombic efficiency for Nafion-212 with a capacity decay of 0.42% per cycle) proving the effectiveness of pre-treatment of phosphoric acid on PBI membranes.

Three-dimensional CFD analysis of PEMFC with different membrane thicknesses

PEM fuel cell (PEMFC) is a potential candidate for future source of power used in different applications such as transportations, stationary and portable power. PEMFC consists of different parts including membrane, bipolar plate, flow channel, gas diffusion and catalyst layers. Membrane is one of the most important components of a PEMFC and its physical and geometrical features significantly affect PEMFC efficiency. In this paper, a three-dimensional, single-phase computational model has been improved to scrutinize membrane thickness effect on the PEM fuel cell performance using the ANSYS PEM Fuel Cell Module. Membrane thicknesses are in the range of a range of 0.0127 to 0.189 mm. The results reveal that a decrease in membrane thickness augments the current density at 0.4 and 0.6 V. The peak current density of 3.12 A/cm 2 is achieved with 0.027 mm membrane thickness compared the model current density of 1.26 A/cm 2 obtained by the model with 0.128 mm membrane thickness at 0.4 V. Oxygen consumption and water production also enhance with reducing membrane thickness at 0.4 and 0.6 V. However change thickness of the membrane has a negligible impact on impact pressure drop in the flow channel. It is found that optimization of membrane thickness are necessary for attaining high efficiency.

Asymmetric Ba0.5Sr0.5Co0.8Fe0.2O3-Δ Membrane for Oxygen Permeation: Synergetic Fabrication By Magnetron Sputtering Deposition and Selective Laser Annealing

The Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) mixed ionic electronic conductor (MIEC) is considered to be one of the most promising perovskite-based materials for oxygen transport exhibiting high oxygen permeability. Such oxygen-permeable perovskite membrane maybe applied to increase efficiency of combustion or reforming processes of new fuels such as green ammonia. An approach to elevate the oxygen permeability of BSCF membranes is reduction of membrane thickness, as the permeation process is mostly controlled by bulk diffusion. Since self-standing thin membranes are not sufficiently mechanically stable, asymmetric membranes consisting of a thin layer membrane deposited onto a porous bulk support are usually employed. . In this work, planar BSCF thin film membranes of 1 to 2 and 15 to 20 µm thickness were successfully synthesized by a combination of magnetron sputtering (MS) and thermal annealing (TA) and/or selective laser annealing (SLA) processes. Thin films appeared to be pinhole-free with a high crystallinity of a single perovskite phase and a microstructure that showed suitability for oxygen permeation applications. Correlations between thin film properties and MS process parameters (e.g. power, Ar/O2 ratio, pressure, etc.) and TA&/SLA parameters were established and optimised as key factors for producing thin film membrane exhibiting high oxygen flux and good stability. A variation of the oxygen flux through the BSCF asymmetric membrane as well as the porous substrate is presented as a function of temperature and also oxygen partial pressures applied to both sides of the membrane allowing for calculation of permeability of the deposited thin film. Figure 1

Minimising non-selective defects in ultrathin reduced graphene oxide membranes with graphene quantum dots for enhanced water and NaCl separation

• Ultrathin GQDs/rGO membranes are prepared through a two-step assembly method. • The strong π–π interaction between GQDs and rGO enables the coverage of defects. • GQDs/rGO membranes achieve both high water permeance and high NaCl rejection. Reduced graphene oxide (rGO) membranes have been intensively evaluated for desalination and ionic sieving applications, benefiting from their stable and well-confined interlayer channels. However, rGO membranes generally suffer from low permeability due to the high transport resistance resulting from the narrowed two-dimensional (2D) channels. Although high permeability can be realized by reducing membrane thickness, membrane selectivity normally declines because of the formation of non-selective defects, in particular pinholes. In this study, we demonstrate that the non-selective defects in ultrathin rGO membranes can be effectively minimised by a facile posttreatment via surface-deposition of graphene quantum dots (GQDs). The resultant GQDs/rGO membranes obtained a good trade-off between water permeance (14 L⋅m −2 ⋅h −1 ⋅MPa −1 ) and NaCl rejection (91%). This work provides new insights into the design of high quality ultrathin 2D laminar membranes for desalination, molecular/ionic sieving and other separation applications.

Performance of Quaternized Polybenzimidazole-Cross-Linked Poly(vinylbenzyl chloride) Membranes in HT-PEMFCs

High-temperature proton-exchange membrane fuel cells (HT-PEMFCs) are mostly based on acid-doped membranes composed of polybenzimidazole (PBI). A severe drawback of acid-doped membranes is the deterioration of mechanical properties upon increasing acid-doping levels. Cross-linking of different polymers is a way to mitigate stability issues. In this study, a new ion-pair-coordinated membrane (IPM) system with quaternary ammonium groups for the application in HT-PEMFCs is introduced. PBI cross-linked with poly(vinylbenzyl chloride) and quaternized with three amines (DABCO, quinuclidine, and quinuclidinol) are manufactured and compared to the state-of-the-art commercial Dapazol PBI membrane ex situ as well as by evaluating their HT-PEMFC performance. The IPMs show reduced swelling and better mechanical properties upon doping, which enables a reduction in membrane thickness while maintaining a comparably low gas crossover and mechanical stability. The HT-PEMFC based on the best-performing IPM reaches up to 530 mW cm-2 at 180 °C under H2/air conditions at ambient pressure, while Dapazol is limited to less than 430 mW cm-2 at equal parameters. This new IPM system requires less acid doping than conventional PBI membranes while outperforming conventional PBI membranes, which renders these new membranes promising candidates for application in HT-PEMFCs.

Ideal Positioning of a Pt-Interlayer for H2-O2-Recombination in Polymer Electrolyte Membrane Water Electrolysis

Polymer electrolyte membrane water electrolysis (PEMWE) is a promising technology for the production of hydrogen in future energy scenarios.[1] The main electric voltage loss in PEM electrolysers is caused by the ohmic losses of the polymer electrolyte membrane. However, the reduction of the membrane thickness not only reduces the cell voltage, but also leads to lower faradaic efficiencies, which can be accompanied by severe safety issues. The crossover of the produced hydrogen gas through the membrane into the anodic compartment can lead to explosive gas mixtures (lower explosion limit (LEL) of H2 in O2 is ~ 4 % [2]).[3, 4] Typically, PEM electrolysers operate only up to 2 % H2 in O2 (50 % of LEL). An elevation of the hydrogen pressure during electrolysis enhances the crossover of hydrogen even more.[5] For realizing high market penetrations of PEMWE, a safe operation is essential.In order to meet the safety requirements, mitigation strategies for the reduction of the hydrogen in oxygen content are necessary. When increasing the membrane thickness and reducing the operation temperature are not desired, other mitigation strategies need to be evaluated. The integration of a Pt-interlayer in the polymer electrolyte membrane is one possibility.[6] When hydrogen and oxygen permeate through the membrane, they recombine to water at the platinum particles.Klose et al. proposed that the method of incorporating a recombination layer can be optimized further by evaluating its position.[7] The concentration of oxygen at the interlayer must be high enough to let a sufficient amount of hydrogen recombine. However, the oxygen concentration towards the cathode is much lower than a full recombination of hydrogen requires, which is mainly due to the lower oxygen permeation rate (lower diffusivity, lower gradient). Therefore, it is assumed that a Pt-interlayer close to the anode catalyst layer yields higher recombination rates than an interlayer close to the cathode.In this contribution, the influence of the Pt-interlayer position on the H2 in O2 content was investigated. Catalyst coated membranes (CCMs) based on spray-coated Nafion with Pt-interlayers with a loading of 0.01 mg/cm² at three positions (close to anode, centred, close to cathode, see Figure 1a)) and a reference type (without interlayer) were fabricated. The CCMs were examined with regard to their polarisation behaviour and hydrogen crossover characteristics in a 4 cm² cell. The hydrogen crossover was investigated during electrolysis operation at ambient pressure and at elevated cathode pressures (p c = 10 bar).The resulting membrane thicknesses of the CCMs were ~ 100 µm (in dry state). Since commercial Nafion membranes for water electrolysis applications are available in thicknesses between 25 and 183 µm (N211 and N117, respectively), the present membranes correspond to the state of the art. The electrochemical polarisation behaviour of the CCMs shows that the integration of a Pt-interlayer does not lead to additional voltage losses. At current densities as high as 3.5 A/cm², cell voltages below 2 V were achieved.With regards to H2 crossover, each CCM with interlayer reduced the measurable anodic H2 content in comparison to the reference CCM (Figure 1b)). Additionally, the position of the interlayer affected the resulting H2 content. The H2 content decreased with positioning the interlayer closer to the anode. Thus, a higher recombination rate of hydrogen and oxygen is observed when placing the interlayer close to the anode. Since the available oxygen amount in the membrane has obviously to decrease towards the cathode catalyst layer, the experimental findings reflect the aforementioned theoretical situation.In summary, the results of this study confirm that Pt-interlayers are a suitable mitigation strategy to reduce the H2 in O2 content in PEMWE. Further, it was shown that the positioning of the interlayer affects the results. Since the available amounts of hydrogen and oxygen in the membrane depend on the location in the membrane and on the experimental conditions (e. g. operating pressure), the integration of a recombination interlayer at an optimized position within the membrane offers an effective means to safe PEMWE operation with reduced membrane thickness. This improvement will help to consolidate PEMWE as a key technology for hydrogen generation.Literature:[1] K. Ayers, Annu. Rev. Chem. Biomol. Eng., 2019, 10.[2] H. Janssen, Int. J. Hydorgen Energ., 2004, 29.[3] H. Ito, Int. J. Hydorgen Energ., 2016, 41.[4] S.A. Grigoriev, Int. J. Hydorgen Energ., 2009, 34.[5] P. Trinke, Int. J. Hydorgen Energ., 2017, 42.[6] P. Trinke, Int. J. Hydorgen Energ., 2018, 165.[7] C. Klose, J. Elec. Soc., 2018, 165. Figure 1

New Insights in Proton Exchange Membrane Fuel Cell Electrode Microstructure Changes from Accelerated Stress Testing By Microscopy Techniques

The microstructure of the cathode catalyst layer in a proton exchange membrane fuel cell (PEMFC) plays a critical role in the performance and durability of this device towards emission-free mobility. Controlling the catalyst layer microstructure at beginning-of-life (BOL) is a viable path for achieving high fuel cell performance, whereas understanding the microstructural changes due to extended hours under fuel cell working conditions often sheds light on the degradation process and mechanism, contributing to increased knowledge of the structure-performance relationships in the fuel cell electrode. Materials characterization, as an essential tool in understanding the structure-properties-performance relationships in materials science, has been widely used to track the microstructural changes of the cathode catalyst layer. The multiple heterogeneous components in the catalyst layer including catalyst, support and ionomer, as well as various morphologies exhibited such as nanoparticles, nanopores, and polymer ionomer film, create an intrinsically complex problem for characterization and necessitate a characterization technique with sufficiently high resolution to capture the multi-scale evolutions of the catalyst layer properties. Among a wide range of characterization methods, high resolution and scanning transmission electron microscopy (HR and (S)TEM), with energy dispersive spectroscopy (EDS), supported by scanning electron microscopy (SEM) and X-ray computed tomography (XCT) have proven to be some of the best techniques for PEMFC materials characterization [1]. Here we present advanced approaches in characterization and quantification of BOL and end of life (EOL) catalyst coated membranes (CCM) that had been subjected to various accelerated stress tests (AST), revealing new insights in degradation mechanism and impact. The primary porosity (within Pt/C agglomerates with d<5 nm [2]) and secondary porosity (between Pt/C agglomerates with d>5 nm [2]), platinum particle size distribution, platinum loading, ionomer distribution, and carbon structure were characterized and quantified for a supplier CCM, and used as the BOL baseline. ASTs were designed and performed to study the effects of parameters related to startup/shutdown (SU/SD) conditions for the PEMFC [3, 4]. The post-mortem samples were analyzed and compared to the BOL sample to understand the microstructural and compositional changes. The results showed a total porosity drop, mainly stemming from a loss of secondary pores. This could be related to carbon corrosion during SU/SD AST which was reflected in the electrode thickness reduction from the scanning electron microscopy (SEM) images. The particle size distribution (PSD) analysis and ionomer imaging were indicative of further changes through platinum degradation and ionomer re-distribution, respectively. HR-TEM imaging of specially (epoxy-free) prepared samples indicated changes in carbon morphology and degree of crystallinity. The characterization approach was also utilized for the failed samples from the open circuit voltage (OCV) AST and the results revealed porosity, Pt, ionomer and carbon morphological and distribution changes. The SEM-based membrane thickness reduction from OCV AST seemed to exhibit a qualitative trend with the amount of released fluoride measured by an ion selective electrode (ISE) instrument. Multiple characterization techniques were utilized to study the relative humidity (RH) cycling effects on the membrane electrode assembly (MEA). The SEM and X-ray computed tomography (XCT) results revealed that the defects in microporous layer (MPL) could be related to the cracks in the CCM. While the STEM-EDS analysis and quantification showed no changes in Pt distribution and particle size, the porosity distribution was changed due to the stresses during the RH cycling [5, 6]. In summary, the characterization techniques discussed herein seem to be providing important information in guiding the fuel cell community towards improving performance and durability through modification of the electrode microstructure during fabrication and developing appropriate strategies to prolong life.Keywords: Failure Analysis, Polymer Exchange Membrane, Catalyst Layer Structure, Fuel Cell Durability

Insights into Interfacial and Bulk Transport Phenomena Affecting Proton Exchange Membrane Water Electrolyzer Performance at Ultra-Low Iridium Loadings.

Interfacial and bulk properties between the catalyst layer and the porous transport layer (PTL) restrict the iridium loading reduction for proton exchange membrane water electrolyzers (PEMWEs), by limiting their mass and charge transport. Using titanium fiber PTLs of varying thickness and porosity, the bulk and interface transport properties are investigated, correlating them to PEMWEs cell performance at ultra‐low Ir loadings of ≈0.05 mgIr cm−2. Electrochemical experiments, tomography, and modeling are combined to study the bulk and interfacial impacts of PTLs on PEMWE performance. It is found that the PEMWE performance is largely dependent on the PTL properties at ultra‐low Ir loadings; bulk structural properties are critical to determine the mass transport and Ohmic resistance of PEMWEs while the surface properties of PTLs are critical to govern the catalyst layer utilization and electrode kinetics. The PTL‐induced variation in kinetic and mass transport overpotential are on the order of ≈40 and 60 mV (at 80 A mgIr −1), respectively, while a nonnegligible 35 mV (at 3 A cm−2) difference in Ohmic overpotential. Thus at least 150 mV improvement in PEMWE performance can be achieved through PTL structural optimization without membrane thickness reduction or advent of new electrocatalysts.

The selective sieving role of nanosheets in the development of advanced membranes for water treatment: Comparison and performance enhancement of different nanosheets

Nanosheets have elicited great enthusiasm in the development of advanced membrane with advantages in the balance of permeability and selectivity, reduction of membrane thickness, enhancement of stabilities and improvement of fouling resistance. Although various nanosheets, such as graphene oxide (GO), MXene, MoS2, 2D metal organic frameworks (MOFs) and 2D covalent organic frameworks (COFs), have been explored as membrane materials for water treatment, their superiorities and deficiencies are different in lamellar membranes in terms of pore size, surface charge, hydrophilicity, stability, toxicity, compatibility with substrates and complexities of preparation, exfoliation and modification. All these properties could influence the application of nanosheets in membrane filtration. The selective sieving mechanisms of nanosheets and their impact on membrane performance were summarized. The common challenges of nanosheets as water treatment membranes and various improving strategies along with the future prospect were discussed.

Thin SAPO-34 zeolite membranes prepared by ball-milled seeds

• Small seeds led to thinner SAPO-34 membranes due to enhanced secondary nucleation. • Ball-milling generated nano seed particles easily. • Ultrafine seed particles produced by ball-milling resulted into thinner membrane. • Outstanding CO 2 -CH 4 separation performance realized on 1.6 μm thick SAPO-34 membrane. Zeolite membranes demonstrated great separation performance for many important separation processes, however, high membrane cost is a major obstacle for its commercial application. Reducing membrane thickness is an effective way of lowering its unit cost, which requires a delicate control of nucleation and crystallization processes. Herein, the effect of seed size on the separation performance of SAPO-34 membranes was studied. Smaller seeds facilitated secondary nucleation which led to thinner membrane with higher CO 2 permeance. Ball-milling of regular SAPO-34 crystals can generate ultra-small seed particles easily, which is even better than tailor-made nano SAPO-34 seeds on reducing membrane thickness. Thin SAPO-34 membrane with thickness ~1.4 μm can be prepared with high reproducibility and high CO 2 permeance ~10.2 × 10 −7 mol·m −2 ·s −1 ·Pa −1 and CO 2 -CH 4 selectivity of 59 were obtained for the separation of equalmolar CO 2 -CH 4 mixture at 4.0 MPa and room temperature.