Membrane Lifetime Research Articles

Assessing the degradation pattern and mechanism of membranes in polymer electrolyte membrane fuel cells using open-circuit voltage hold and humidity cycle test protocols

As the degradation of polymer electrolyte membranes (PEMs) shows catastrophic failures with pinholes and cracks, studies on PEM degradation are essential to improve the reliability and lifetime of polymer electrolyte membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs). However, the investigation of the degradation patterns and understanding of the degradation mechanisms of PEMs are still very limited at the PEMFC MEA level. Herein, open-circuit voltage (OCV) hold (chemical degradation) and humidity cycle test (mechanical degradation) protocols are applied to assess the durability of membrane components of PEMFC MEAs. OCV hold test is conducted at low relative humidity (30%) and OCV condition for 540 h. Humidity cycle test (5000 cycles) is carried out under repeating low (0%) and high (150%) relative humidities. We investigate degradation patterns and mechanisms of PEMs for MEAs after OCV hold and humidity cycle tests using various electrochemical and physicochemical analyses tools. The present study, by providing fundamental understanding of major degradation mechanisms, generates scientific information regarding design tools for the fabrication of highly durable PEMs. Additionally, this study, through accelerated degradation tests, can provide baseline information regarding the durability and lifetime of PEMs by statistically analyzing the deterioration pattern of MEAs.

Improvement of Performance and Lifetime of Polybenzimidazole Membranes in High Temperature Fuel Cells by Incorporation of Muscovite

Polybenzimidazole (PBI) is a basic aromatic heterocyclic polymer with excellent thermal and chemical stability. The phosphoric acid (PA) doped PBI and its derivative membranes have high proton conductivity, low gas permeability, good fuel impurity tolerance, and excellent oxidative and thermal stability at temperatures up to 200 °C [1], hence, PA doped PBI is a promising candidate for high-temperature proton exchange membrane fuel cells. However, PA doped PBI membranes also has some limitations, including the dehydration of phosphoric acid above 140 °C, PA leaching out of the membranes, and deterioration of membrane mechanical strength especially at high acid doping level.The incorporation of clay minerals into membranes attract a great interest due to their hygroscopicity, high surface area and cheap cost [2]. The hygroscopic properties of clay minerals can increase the humidity inside the membranes, interact with PA molecules and maintain a strong proton conductivity. Here we present work on the incorporation of a cheap muscovite into the PBI membrane. As the muscovite is highly hygroscopic and has hydroxyl groups on the surface, an optimal cell performance was observed when the loading of muscovite is 1 wt.%. The PBI membrane with 1 wt.% muscovite showed the membrane resistance of 189 mohm cm2 and peak power density of 612 mW cm-2 at 150 °C, 26% higher than the pure PBI membrane with the membrane resistance of 235 mohm cm2 and the power density of 485 mW cm-2. Furthermore, the durability of inorganic-organic composite membranes was tested by an accelerated stress test (AST) operating the membrane electrode assembly between 0.6 A cm−2 and 1.0 A cm−2 [3]. After running around 50 h AST, the composite PBI membrane with 1 wt.% muscovite showed much lower degradation (9.3% at 0.6 A cm−2 and 12.8% at 1.0 A cm−2) than the pure PBI membrane (11.2% at 0.6 A cm−2 and 22.6% at 1.0 A cm−2). The improved durability of the composite membranes might be explained by the muscovite forming hydrogen bonding with PA molecules and polymer chains, which alleviates the degradation of polymer chains and PA leaching out of the membranes. The PA distribution and retention properties of the composite membranes were also characterized by energy dispersive X-ray spectroscopy and electron probe micro-analysis.

Visualization Guided Mitigation of Mechanical Membrane Degradation in Fuel Cells

Dynamic operational power demands from a fuel cell, especially in transportation applications, are known to causefluctuations in its relative humidity (RH) and temperature [1]. This leads to repetitive in-plane compressive and tensile stress build-up in the confined perfluorosulfonic acid (PFSA) ionomer membranes due to constraining of their cyclic swelling and shrinkage under hydrated and dehydrated states, respectively. The ionomer’s dynamic water sorption characteristics during these hygrothermal variations lead to catalyst coated membrane (CCM) deformation and cyclic mechanical stresses resulting in structural fatigue and micro-crack development at high stress accumulation sites [2]. Lately, laboratory-based X-ray computed tomography (XCT) was used for non-destructive four-dimensional (4D) visualization and microstructural analysis of fuel cell parts showing novel insights on their failure processes [3,4]. The objective of the present work is to leverage 4D XCT visualization to design and demonstrate novel mitigation strategies for mechanical membrane degradation in fuel cells. A custom designed X-ray transparent fixture housing a small-scale single cell fuel cell was subjected to 2 min. each of wet and dry cycles with N2 gas at anode and cathode compartments, thereby causing fatigue-based membrane damage [5]. 3D tomographic data sets of same membrane electrode assembly (MEA) locations were acquired as a function of degradation time, which facilitated to study the damage development and growth. As a baseline for this work, a non-bonded MEA with high surface roughness gas diffusion layers (GDLs) demonstrated that the primary membrane failure mode was CCM buckling into GDL voids/pores [6]. To overcome this failure mode, two separate mitigation approaches are explored in the present work: (i) a commercial GDL with low surface roughness; and (ii) bonding of MEA to arrest buckling. Furthermore, a multi-physics finite element method (FEM) model is developed to simulate the contact interaction at the catalyst layer | GDL interface and non-uniformity in the GDL microstructure. The XCT findings are correlated with the numerical model to perceive the specific impact of GDL surface features on the development and distribution of membrane failures.Similar to the baseline MEA, membrane crack development was observed to be the key failure mode for both mitigation approaches. When the two mitigation designs are compared at similar cycling stages with the baseline (Fig. 1), however, the size and density of membrane cracks is drastically reduced. Since both mitigation strategies are tested using the same accelerated stress test protocol as the baseline, it is hereby established that each approach provides substantial mitigation against fatigue driven mechanical membrane degradation, predominantly due to reduced severity of CCM buckling deformation, resulting in a doubling of the membrane lifetime in each case. Complementary finite element simulations corroborate the experimental findings and further estimate the critical GDL void sizes to prevent CCM buckling and the required interfacial MEA adhesion quality to stabilize the MEA for overall membrane durability. Acknowledgements Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, and Ballard Power Systems through an Automotive Partnership Canada grant. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program.

Compressive Creep of Perfluorosulfonic Acid Membranes in Controlled Environments

For proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs) to be commercially viable, PEMs must perform over long operational times in liquid environments under compression and therefore must exhibit good mechanical stability when hydrated [1], [2]. While a hydrated environment is an intrinsic result of the operation and membrane’s conductive function, it undermines PEM stability [3]. They are under unique mechanical stresses due to differential pressure affecting the active area, and high sealing pressures to prevent off-board leaks, thus, high differential pressure in PEMWEs makes compressive creep a great concern [4]. However, mechanical stability of PEMs is commonly characterized by tensile testing [5], the applicability of which to electrolyzers or technologies with similar cell designs is unclear. In this study, a compression setup was developed to monitor creep response of hydrated PEMs in situ and in controlled temperature.Water-splitting electrolyzers are a key technology for enabling the hydrogen economy and reshaping the renewable energy landscape. Among the most viable candidates for the low-temperature electrolyzers is the proton-exchange membrane (PEM) water-splitting electrolyzers (PEMWEs), which uses an ion-conductive polymer solid-electrolyte. Stability, in liquid environments at temperatures ranging from 50 to 80 °C, is an important aspect of PEM design considerations. While hydration, pressure, and temperature are used as design parameters for optimizing electrolyzer performance, their role in durability is not established [5]. This creates a gap between performance and lifetime assessment of membranes for electrolyzers. Thus, there is need for a metric that could capture membrane durability by accounting for performance operators. This study identifies compression creep as a potential material stability metric that can account for the operation-dependent variables, such as pressure, dehydration, and temperature, and provides guidance for better assessment of membrane lifetime in electrolyzers and similar electrochemical devices.Our results show compressive response of perfluorosulfonic acid (PFSA) membranes is significantly different than tensile behavior in both dry and hydrated states [6]. Moreover, PEMs exhibit creep response under compression with continuous decrease in its thickness over 24 hours, with a dependence on the applied pressure and temperature [6]. This work demonstrates the importance of studying the mechanical properties of PEMs under compression, which is more relevant to the stress-states the membrane undergoes during operation in an electrolyzer and similar electrochemical devices.

Factors Affecting Hydroxide Ion Concentrations in Bipolar Membranes

The useful lifetime of bipolar ion exchange membranes is often limited by nucleophilic attack by hydroxide ions on the ionic groups and polymer backbone in the anion exchange layers (AELs). This is especially problematic in water treatment applications for making acid and base from salt solutions. This research investigated the effect of bulk electrolyte composition, current density, membrane thickness, ion exchange capacity, and bulk solution pH value on hydroxide ion concentrations inside the AELs of a bipolar membrane. Onedimensional Nernst-Plank equations were solved for the species Na+, Cl-, OH- and H+ within 20-100 μm thick anion and cation exchange layers with fixed charged densities ranging from 0.5-2.0 eq/L. In 1 M NaCl solutions at neutral pH values, hydroxide concentrations in the AEL reached as high as 2.2 M at a current density of 100 mA/cm2. In 1 M NaOH solutions, hydroxide ion concentrations reached as high as 3.77 M. Hydroxide concentrations in the AEL were significantly affected by the ratio of Cl- to hydroxide ions in the bulk electrolyte. Where hydroxide concentrations in the bulk electrolyte were an order of magnitude lower than chloride concentrations, membrane hydroxide concentrations were nearly proportional to the current density. Increases in ion exchange capacity and AEL thickness resulted in increased membrane hydroxide ion concentrations. Membrane concentrations of hydroxide ions can be minimized by operation at low current densities, with high background electrolyte concentrations using thin membranes with low ion exchange capacities and producing base concentrations less than 0.1 M.

Water distribution and performance variation in a transparent PEMFC with large active area

Water management is a key factor affecting the performance and lifetime of proton exchange membrane fuel cells. A transparent single fuel cell with an active area of 100 cm2 was designed in this paper to characterize the water distribution. High-strength transparent borosilicate glass was used as the end plate to ensure uniform clamping forces, and a water-cooling chamber was adopted for the uniform temperature distribution. The effects of temperature, humidity, flow rate and pressure on the cell performance were investigated. It was found that in a certain range, a large cathode flow resulted in a relatively stable power output and a low level of water distribution. However, a better cell performance and higher level of water distribution can be observed with lower temperature, higher operation pressure and higher humidity. The actual voltage was determined by a compensatory calculation through the voltage changes caused by all of the influencing factors, and the compensatory voltages were quite close to each other. The results showed that under 40 °C and 60 °C, 0 Bar and 1.5 Bar, and 50 RH% and 100 RH%, the compensated voltages were 0.873 V and 0.864 V, 0.869 V and 0.855 V, and 0.843 V and 0.844 V, respectively.

Fouling of microfiltration membranes by bidisperse particle solutions

Fouling of filtration membranes is a key process that degrades performance and reduces membrane lifetime. Nevertheless, obtaining direct information about fouling mechanisms is still a significant challenge, especially fouling that occurs within the internal pore spaces. Here, we combined highly multiplexed single-particle tracking methods with alternating laser excitation, which allowed the direct visualization of the transport of nanoparticles within microfiltration membranes, where the advective motion and retention of 200 nm and 40 nm diameter particles was simultaneously imaged within filtration membranes with 650 nm nominal pore size, as membranes became increasingly fouled as a function of total particle throughput. We found that internal membrane fouling consisted of three stages, fouling site formation, fouling site growth, and fouling site coalescence. Larger particles had a greater chance to be retained initially, nucleating the fouling sites. These sites tended to capture other particles passing through the membrane, causing the fouling sites to grow in size. Eventually, isolated fouling sites grew large enough to coalescence with neighboring sites, blocking a large region of membrane pores, leading to significant fouling. Importantly, the presence of small numbers of large particles significantly increased the retention of small particles and also accelerated the rate of particle retention. This mechanistic information about internal membrane fouling will assist in the design and optimization of filtration processes to reduce membrane fouling and expand the fundamental understanding of complex mass transport of polydisperse particle distributions.

Construction of Proton Transport Highways Induced by Polarity-Driving in Proton Exchange Membranes to Enhance the Performance of Fuel Cells.

The approach to constructing proton transport channels via direct adjustments, including hydrophilia and analytical acid concentration in hydrophilic domains, has been proved to be circumscribed when encouraging the flatter hydrophilic-hydrophobic microphase separation structures and reducing conductivity activation energy. Here, we propose a constructive solution by regulating the polarity of hydrophobic domains, which indirectly varies the aggregation and connection of hydrophilic ion clusters during membrane formation, enabling orderly self-assembly and homogeneously distributed microphase structures. Accordingly, a series of comb-shaped polymers were synthesized with diversified optimization, and more uniformly distributed ion cluster lattices were subsequently observed using high-resolution transmission electron microscopy. Simultaneously, combining with density functional theory calculations, we analyzed the mechanism of membrane degradations caused by hydroxyl radical attacks. Experimental results demonstrated that, facilitated by proper molecule polarity, beneficial changes of bond dissociation energy could extend the membrane lifetime more than the protection from side chains near ether bonds, which were deemed to reduce the probability of attacks by the steric effect. With the optimal strategy chosen among various trials, the maximum power density of direct methanol fuel cell and H2/air proton exchange membrane fuel cell was enhanced to 95 and 485 mW cm-2, respectively.

Experimental and Numerical Study of Proton Exchange Membrane Fuel Cells with a Novel Compound Flow Field.

Excess water seriously affects the performance and lifetime of proton exchange membrane fuel cells (PEMFCs). This study proposes a novel compound flow field, which is named the active drainage flow field (ADFF). The new design enhances the drainage performance by under-ribs flow, while the output performance is very close to that of the conventional serpentine flow field (CSFF). Additionally, the ADFF bipolar plate has been taken as a cathode while retaining CSFF as an anode; the combination shows a good output performance under high relative humidity. The peak power density has reached to 0.59 W/cm2, which is 13% higher than that of the CSFF.

Microplastics destabilize lipid membranes by mechanical stretching

Estimated millions of tons of plastic are dumped annually into oceans. Plastic has been produced only for 70 y, but the exponential rise of mass production leads to its widespread proliferation in all environments. As a consequence of their large abundance globally, microplastics are also found in many living organisms including humans. While the health impact of digested microplastics on living organisms is debatable, we reveal a physical mechanism of mechanical stretching of model cell lipid membranes induced by adsorbed micrometer-sized microplastic particles most commonly found in oceans. Combining experimental and theoretical approaches, we demonstrate that microplastic particles adsorbed on lipid membranes considerably increase membrane tension even at low particle concentrations. Each particle adsorbed at the membrane consumes surface area that is proportional to the contact area between particle and the membrane. Although lipid membranes are liquid and able to accommodate mechanical stress, the relaxation time is much slower than the rate of adsorption; thus, the cumulative effect from arriving microplastic particles to the membrane leads to the global reduction of the membrane area and increase of membrane tension. This, in turn, leads to a strong reduction of membrane lifetime. The effect of mechanical stretching of microplastics on living cells membranes was demonstrated by using the aspiration micropipette technique on red blood cells. The described mechanical stretching mechanism on lipid bilayers may provide better understanding of the impact of microplastic particles in living systems.

Identifiability Analysis of Degradation Model Parameters from Transient CO2 Release in Low-Temperature PEM Fuel Cell under Various AST Protocols

The detrimental effects of the catalyst degradation on the overall envisaged lifetime of low-temperature proton-exchange membrane fuel cells (LT-PEMFCs) represent a significant challenge towards further lowering platinum loadings and simultaneously achieving a long cycle life. The elaborated physically based modeling of the degradation processes is thus an invaluable step in elucidating causal interaction between fuel cell design, its operating conditions, and degradation phenomena. However, many parameters need to be determined based on experimental data to ensure plausible simulation results of the catalyst degradation models, which proves to be challenging with the in situ measurements. To fill this knowledge gap, this paper demonstrates the application of a mechanistically based PEMFC modeling framework, comprising real-time capable fuel cell performance, and platinum and carbon support degradation models, to model transient CO2 release rates in the LT-PEMFCs with the consistent calibration of reaction rate parameters under multiple different accelerated stress tests at once. The results confirm the credibility of the physical and chemical modeling basis of the proposed modeling framework, as well as its prediction and extrapolation capabilities. This is confirmed by an increase of only 29% of root mean square deviations values when using a model calibrated on all three data sets at once in comparison to a model calibrated on only one data set. Furthermore, the unique identifiability and interconnection of individual model calibration parameters are determined via Fisher information matrix analysis. This analysis enables optimal reduction of the set of calibration parameters, which results in the speed up of both the calibration process and the general simulation time while retaining the full extrapolation capabilities of the framework.

Simultaneous Dechlorination and Advanced Oxidation Using Electrically Conductive Carbon Nanotube Membranes.

Electrically conductive membranes have shown significant promise in combining conventional separations with in situ contaminant oxidation, but little has been done to consider chlorine removal. This study demonstrates the simultaneous chlorine removal and oxidation of organic compounds during filtration using an electrochemically assisted electrically conductive carbon nanotube (CNT) membrane. As much as 80% of chlorine was removed in the feed by CNT membranes at the initial phase of continuous filtration. The efficacy of these CNT membranes toward chlorine removal was dependent on the mass of CNTs within the membranes and the applied pressure to the membranes, indicating the central role of available CNT active sites and sufficient reaction time. Furthermore, the removal mechanism of chlorine by CNTs was revealed by studying the degradation of benzoic acid and cyclic voltammetry on the membrane surface. Reactive oxidants were generated by the reductive decomposition of chlorine through the catalytic interaction with CNTs. Subsequently, electrical potentials were applied to the CNT membrane surfaces during the filtration of chlorinated feed waters. The simultaneous decomposition of chlorine and oxidation of benzoic acid were significantly enhanced by applying a cathodic current to CNT membranes enabling continuous dechlorination. The cathodic current applied to CNT membranes is believed to regenerate CNT membranes by providing electrons for the reductive decomposition of chlorine. In situ chemical-free dechlorination coupled with membrane filtration offers great opportunity to reducing the environmental impact of desalination, while maximizing the lifetime of reverse osmosis membranes and demonstrating greener approaches available to industrial water treatment.

Mitigation of chemical degradation in perfluorosulfonic acid proton exchange membrane using regenerable hindered amine functionalized carbon quantum dots

The chemical stability of perfluorosulfonic acid (PFSA) has a significant impact on the lifetime of a proton exchange membrane (PEM). Herein, we describe the design and fabrication of a novel PEM containing hindered amine functionalized carbon quantum dots (HA-CQDs) to improve the PEM's chemical stability. The novel CQDs are prepared by a hydrothermal reaction using citric acid as the carbon source, while groups of the free radical scavenger 4-amino-2, 2,6,6-tetramethylpiperidine are used to modify the oxygen-containing groups on the CQDs' surface. Benefiting from the introduction of the radical-scavenging groups, the HA-CQDs effectively eliminate active free radicals, thereby improving the PEM's chemical stability. Mass loss, FTIR, SEM, and SAXS are used to evaluate the PEM's chemical stability, surface morphology, and proton conduction by side-chain functional groups via free radicals. The electrochemical performance of the oxidized PEM is evaluated from proton conductivity and single-cell performance, and the free radical scavenging capability is characterized using the 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) radical method. Our work reveals that introducing hindered amines can eliminate the free radicals generated by electrochemical reactions and effectively mitigate the chemical degradation of a PEM. This paper provides a promising way to improve the chemical stability of PFSA and enhance the lifetime of PEMs.

Anaerobic membrane bioreactor for the production of bioH2: Electron flow, fouling modeling and kinetic study

This study investigated the evaluation of a new operational protocol for increasing the membrane lifetime during bioH2 production by the anaerobic membrane bioreactor-sequencing batch reactor (AnMBR-SBR) along with a kinetic and membrane fouling study. The certified electron (e-) flow model was applied to investigate the structure of microbial community and metabolism pathway. The AnMBR-SBR was operated under varying applied organic loading rates (OLR). At applied OLR of 0.5 g COD/L.d, the bioH2 production was around 0.39 ± 0.21 L/d, and an increase of applied OLR to 8.0 g COD/L.d led to improve bioH2 production to 14.57 ± 9.06 L/d. At the OLR of 0.5 g COD/L.d, the dominant e- sinks were acetate (52.2%) and butyrate (22.5%). While significant augmentation in butyrate production (49.9%) was observed at OLR of 8.0 g COD/L.d, indicating that bioH2 production was followed by acetate/butyrate pathway. According to the e- flow model, NADH2 balance error at OLR of 0.5 and 1.0 g COD/L.d ranged 3–8%, demonstrating the ferredoxin:hydrogenase system as the main route of bioH2 production by the spore-forming H2 producing bacteria viz., Clostridium or Ethanoligenes species. For other OLRs, the error balance of NADH2 ranged from 21 to 24%, indicating the activation of non-spore-forming bacteria, e.g., Enterobacter, Escherichia, or Klebsiella species that coincide with the spore-forming bacteria.

Effects of the carbon nanotube and polymer amounts on ultrafiltration membranes

Composite membranes with nano-sized inorganic materials have high selectivity, high hydrophilicity, and improved fouling resistance. Blending Carbon Nanotubes (CNTs) in the polymer solution improves membrane properties like hydrophilicity, water permeability, selectivity, and fouling resistance. The effect of the polymer amount, together with the CNT amount in the polymer solution on membrane properties, was investigated in this work. There was more than 10% increase in the hydrophilicity of the membranes with 1% CNT addition, but it was not altered with the polymer amount. The porosity was increased almost 30% by 1% CNT addition in membranes prepared by 10% and 12% polymer concentration (P-10:C-0 and P-12:C-0), but only 16% increase in porosity occurred in membrane prepared by 15% polymer concentration (P-15:C-0). The flux of the P-15:C-0 membrane was increased four times by 1% CNT addition. Besides, fouling resistance of the membranes decreased with increasing polymer amount but increased with increasing CNT amount. BSA rejection increased with increasing polymer amount or CNT amount in the polymer solution. Hence membranes prepared with a higher amount of polymer are more prone to membrane property improvements with CNT addition. The increase in flux and selectivity by CNT addition in all membranes prepared with different polymer concentrations will increase the membrane life-time and reduce the treatment cost.

Self-Anchored Platinum-Decorated Antimony-Doped-Tin Oxide as a Durable Oxygen Reduction Electrocatalyst

The lifetime of commercial proton exchange membrane fuel cells (PEMFCs) is circumscribed by the insufficient durability of commercial catalysts. The use of metal oxide supports in place of carbon significantly increases electrocatalyst durability. Herein, following density functional theory predictions of improved platinum (Pt) stability on antimony-doped tin oxide (ATO) supports, we synthesized ATO whose morphology and crystal structure were engineered using a Pt-anchoring technique. X-ray photoelectron spectroscopy indicated that the Pt anchor sites aided in the reduction of Pt precursors to Pt on the ATO surface. X-ray absorption near-edge spectroscopy revealed the existence of strong metal–support interactions (SMSIs) between Pt and ATO. The combination of SMSIs and high control over Pt dispersion enabled the Pt/Pt-aerogel-ATO (Pt supported on aerogel ATO with Pt anchor sites) electrocatalyst to achieve 2 × the area-specific activity of Pt/C in ex situ testing. In a H2/air PEMFC, Pt/Pt-aerogel-ATO cathodes enabled 20% higher peak power density and <1/6 the loss of active surface area as compared to Pt/C. In a PEMFC under rigorous potential cycling, the Pt/Pt-aerogel-ATO retained its initial peak power density as opposed to a 58% loss for Pt/C. Furthermore, cost models indicate that Pt/Pt-aerogel-ATO is 26% less expensive than Pt/C over its useful lifetime.

Electrospun polyimide fiber membranes for separation of oil-in-water emulsions

• Fouling is a persistent problem in microfiltration of oil/water emulsions. • Electrospun P84 polyimide membranes separate oil/water emulsions efficiently. • Resistance to fouling is due to the oleophobic character of P84. • Membrane performance is completely regenerated by thermal treatment. The separation of emulsified oils from water represents a significant challenge for water reclamation and clean-up, because such droplets remain suspended for long periods of time. Membrane technology offers a solution to such separations, but its major drawback is the requirement for frequent cleaning to remove foulants, which reduces membrane lifetime and incurs additional economic and environmental costs. To address this shortcoming, we examine the separation performance of fibrous membranes of P84 polyimide, a copolymer known for its thermal stability and chemical resistance, fabricated by electrospinning technology. The P84 membranes were challenged by surfactant-stabilized emulsions of dodecane or motor oil in a constant pressure dead-end configuration. The P84 membranes exhibited moderate oil rejections between 85 and 90%, while subsequent foulant removal by heat treatment restored permeate fluxes to essentially 100% of their original values. A comparison of P84 membranes to other common membrane polymers with respect to robustness against fouling shows that the P84 membranes have some advantages, which we attribute to the oleophobic nature of the P84 membrane, as well as the ease of membrane regeneration. These results indicate that the electrospun P84 membrane is a promising candidate for microfiltration of water contaminated by emulsified oil.

High-quality graphene as a coating for polycrystalline tungsten in low-energy helium and deuterium plasma exposures

• Graphene acts as a sputter shield against low energy helium and deuterium plasmas. • High ion fluences can limit the functional range for graphene coatings. • Tungsten fuzz growth can be slowed down by coating polished surfaces with graphene. In the presence of irradiation by energetic ions, plasma facing components (PFCs) tend to develop surface morphologies that lead to mass loss of the wall material, potentially diminishing their lifetime and plasma performance. We explore the performance of graphene as a coating for plasma facing components to protect against sputtering due to low-energy ions. We show that graphene can slow changes in surface morphology of tungsten subjected to energetic-helium and deuterium ion bombardment over a wide range of energies, as tested in the PISCES-A facility at UC-San Diego. We exposed tungsten samples half-coated with graphene in the PISCES-A facility, at energies of 40 and 140 eV and fluences ranging from 1 × 10 24 - 3.6 × 10 25 ions/m 2 . We found that tungsten “fuzz” growth at high fluences (10 24 –10 25 He-D/m 2 ) can be reduced by approximately 30%. At the lower fluence and energy, no fuzz formed. Using scanning electron microscopy and focused-ion beam machining, we investigate these changes in surface morphology. Deuterium results do not show the graphene defect production to be as energy or fluence dependent as helium bombardment. We determine damage to and the lifetime of the graphene membrane with Raman spectroscopy for vacuum components subjected to such extreme environmental conditions.

Nanofiltration membrane for bio-separation: Process-oriented materials innovation.

Nanofiltration (NF) with advantages of high efficiency and low‐cost has attracted increasing attentions in bio‐separation. However, the large‐scale application is limited by the inferior molecular selectivity, low chemical stability and serious membrane fouling. Many efforts, thus, have been devoted in NF materials design for specific applications to enhance the separation efficiency of bio‐products and increase membrane life‐time, as well as reduce the operating cost. This review summarized the recent progress of NF applications in bio‐separation, discussed various demands for NF membrane in the bio‐products purification and corresponding material innovations, finally proposed several practical suggestions for future research, which provided directions and guidance toward further product development and process industrialization.

Data-driven parameterization of polymer electrolyte membrane fuel cell models via simultaneous local linear structured state space identification

In order to mitigate the degradation and prolong the lifetime of polymer electrolyte membrane fuel cells, advanced, model-based control strategies are becoming indispensable. Thereby, the availability of accurate yet computationally efficient fuel cell models is of crucial importance. Associated with this is the need to efficiently parameterize a given model to a concise and cost-effective experimental data set. A challenging task due to the large number of unknown parameters and the resulting complex optimization problem. In this work, a parameterization scheme based on the simultaneous estimation of multiple structured state space models, obtained by analytic linearization of a candidate fuel cell stack model, is proposed. These local linear models have the advantage of high computational efficiency, regaining the desired flexibility required for the typically iterative task of model parameterization. Due to the analytic derivation of the local linear models, the relation to the original parameters of the non-linear model is retained. Furthermore, the local linear models enable a straight-forward parameter significance and identifiability analysis with respect to experimental data. The proposed method is demonstrated using experimental data from a 30 kW commercial polymer electrolyte membrane fuel cell stack.