Low Gas Permeability Research Articles

Gas transport across the low-permeability containment zone of an underground nuclear explosion

Understanding the nature of gas transport from an underground nuclear explosion (UNE) is required for evaluating the ability to detect and interpret either on-site or atmospheric signatures of noble gas radionuclides resulting from the event. We performed a pressure and chemical tracer monitoring experiment at the site of an underground nuclear test that occurred in a tunnel in Nevada to evaluate the possible modes of gas transport to the surface. The site represents a very well-contained, low gas-permeability end member for past UNEs at the Nevada National Security Site. However, there is very strong evidence that gases detected at the surface during a period of low atmospheric pressure resulted from fractures of extremely small aperture that are essentially invisible. Our analyses also suggest that gases would have easily migrated to the top of the high-permeability collapse zone following the detonation minimizing the final distance required for migration along these narrow fractures to the surface. This indicates that on-site detection of gases emanating from such low-permeability sites is feasible while standoff detection of atmospheric plumes may also be possible at local distances for sufficiently high fracture densities. Finally, our results show that gas leakage into the atmosphere also occurred directly from the tunnel portal and should be monitored in future tunnel gas sampling experiments for the purpose of better understanding relative contributions to detection of radioxenon releases via both fracture network and tunnel transport.

Highly Permeable Perfluorinated Sulfonic Acid Ionomers for Improved Electrochemical Devices: Insights into Structure-Property Relationships.

Rapid improvements in polymer-electrolyte fuel-cell (PEFC) performance have been driven by the development of commercially available ion-conducting polymers (ionomers) that are employed as membranes and catalyst binders in membrane-electrode assemblies. Commercially available ionomers are based on a perfluorinated chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low gas permeability and high mechanical strength but introduces significant mass-transport losses in the electrodes. These transport losses currently limit PEFC performance, especially for low Pt loadings. In this study, we present a novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel backbone chemistry induces structural changes in the ionomer, restricting ionomer domain swelling under hydration while disrupting matrix crystallinity. These structural changes slightly reduce proton conductivity while significantly improving gas permeability. The performance implications of this trade-off are assessed, which reveal the potential for substantial performance improvement by incorporation of highly permeable ionomers as the functional catalyst binder. These results underscore the significance of tailoring material chemistry to specific device requirements, where ionomer chemistry should be rationally designed to match the local transport requirements of the device architecture.

Enhanced CO2 permeability of thermal crosslinking membrane via sulfonation/desulfonation of phenolphthalein-based cardo poly(arylene ether ketone)

Thermal crosslinking membranes for gas separation have excellent plasticization resistance compared to polymeric membranes. Their low gas permeability, however, is not high enough for industrial application at low cost. In this study, a method, called the sulfonation/desulfonation of the polymeric precursor, was proposed to enhance the CO2 permeability of thermal crosslinking membranes without significantly sacrificing the CO2/CH4 selectivity. The effects of the degree of sulfonation (DS) on the polymeric chain rigidity, interchain distance, and gas separation performance of thermal crosslinking membranes were investigated using dynamic mechanical thermal analysis, a thermal gravimetric analyser coupled with a mass spectrometer, wide-angle X-ray diffraction, and gas permeation tests. Results indicated that the sulfonation/desulfonation of the polymeric precursor significantly influenced the microstructure and gas separation performance of the derived thermal crosslinking membranes. The interchain distance and microvoids of the thermal crosslinking membranes were greatly enlarged by the sulfonation and desulfonation reaction. The rigidity of the polymeric chain was improved by the formation of interchain hydrogen bonding induced by –SO3H groups, which prevent the melting of the polymeric membrane during heat treatment. The gas permeability of the thermal crosslinking membrane was markedly enhanced while the CO2/CH4 selectivity decreased as the DS increased. The CO2 permeability was up to 2.3 times higher than that of the non-sulfonated thermal crosslinking membrane. The separation performance of the derived crosslinking membranes for CO2/CH4 was positioned near or above the 2008 Robeson upper bound.

Microfluidic system for Caenorhabditis elegans culture and oxygen consumption rate measurements.

Mitochondrial respiration is a key signature for the assessment of mitochondrial functioning and mitochondrial dysfunction is related to many diseases including metabolic syndrome and aging-associated conditions. Here, we present a microfluidic Caenorhabditis elegans culture system with integrated luminescence-based oxygen sensing. The material used for the fabrication of the microfluidic chip is off-stoichiometry dual-cure thiol-ene-epoxy (OSTE+), which is well-suited for reliably recording on-chip oxygen consumption rates (OCR) due to its low gas permeability. With our microfluidic approach, it was possible to confine a single nematode in a culture chamber, starting from the L4 stage and studying it over a time span of up to 6 days. An automated protocol for successive worm feeding and OCR measurements during worm development was applied. We found an increase of OCR values from the L4 larval stage to adulthood, and a continuous decrease as the worm further ages. In addition, we performed a C. elegans metabolic assay in which exposure to the mitochondrial uncoupling agent FCCP increased the OCR by a factor of about two compared to basal respiration rates. Subsequent treatment with sodium azide inhibited completely mitochondrial respiration.

Towards Relative Permeability Measurements in Tight Gas Formations

Relative permeability is a concept used to convey the reduction in flow capability due to the presence of multiple fluids. Relative permeability governs the multiphase flow, therefore it has a significant importance in understanding the reservoir behavior. These parameters are routinely measured on conventional rocks, however their measurement becomes quite challenging for low permeability rocks such as tight gas formations. This study demonstrates a methodology for relative permeability measurements on tight gas samples. The gas permeability has been measured by the Step Decay method and two different techniques have been used to vary the saturations: steady state flooding and vapor desorption. Series of steady-state gas/water simultaneous injection have been performed on a tight gas sample. After stabilization at each injection ratio, NMR T2, NMR Saturation profile and low pressure Step Decay gas permeability have been measured. In parallel, progressive desaturation by vapor desorption technique has been performed on twin plugs. After stabilization at each relative humidity level the NMR T2 and Step Decay gas permeability have been measured in order to compare and validate the two approaches. The techniques were used to gain insight into the tight gas two phase relative permeability of extremely low petrophysical properties (K<100 nD, phi < 5 pu) of tight gas samples of Pyrophyllite outcrop. The two methods show quite good agreement. Both methods demonstrate significant permeability degradation at water saturation higher than irreducible. NMR T2 measurements for both methods indicates bimodal T2-distributions, and desaturation first occurs on low T2 signal (small pores). Comparison of humidity drying and steady-state desaturation technique has shown a 12-18 su difference between critical water saturation (Swc) measured in gas/water steady-state injection and irreducible saturation (Swirr) measured by vapor desorption.

Impact of dry density, saturation, and confinement on gas permeability of clay-barrier materials

The safe isolation of high-level radioactive waste from the human environment is a key requisite in the nuclear fuel cycle. Deep geological repositories (i.e. >500m) in a suitable rock mass, involving both engineered and natural barriers is currently the most favoured option for the disposal of high-level nuclear waste. Complex Thermal-Hydro-Mechanical and Chemical (THMC) phenomena are anticipated during the repository lifetime. The formation of gasses (e.g., as a result of oxidation processes) and their possible migration through the engineered barrier system (EBS) could jeopardise the main barrier functions. This paper focuses on the experimental study of the gas flow process through clay-barrier materials, particularly on the effect of degree of saturation, clay initial dry density, and confinement stress on gas permeability. It is shown that the initial dry density of the clay has a significant impact on gas flow, especially at low saturations. As expected, lower gas permeability values were obtained near saturation. Confinement has a minor impact on gas flow, at least for the range of stresses investigated in this paper.

Unveiling the role of gas permeability in air cathodes and performance enhancement by waterproof membrane fabricating method

Air cathode is the most popular oxygen reduction reaction (ORR) cathode with various applications in energy conversion and environmental purification. Understanding the role of gas permeability in air cathodes is crucial for its fabrication and operation optimizations. Herein, the correlations between gas permeability and performance are investigated by two experimental setups. One measures the gas permeability and the other evaluates the pressure-dependent performance. The results show two distinct ORR performances with respect to the gas permeability. The performance in low gas permeability is shown to depend on the gas permeability, oxygen partial pressure and solution convection, with obvious limiting current observed. Once the gas permeability surpasses a threshold value, suggested as 2 × 10−12 m, the performance becomes less dependent on those factors, without limiting current observed. These observations are further mathematically demonstrated by the rate limiting process based on an oxygen transport model of air cathodes. An appropriately high gas permeability can eliminate the oxygen gas transport limitation and is vital for the performance enhancement. Following this principle, a novel waterproof membrane-based air cathode with high gas permeability is proposed, enabling cost savings in operation and production, and thus has great potential in practice.

Durability of Newly Developed Polyphenylene-Based Ionomer Membranes in Polymer Electrolyte Fuel Cells: Accelerated Stress Evaluation

Perfluorosulfonic acid (PFSA) membranes such as Nafion® have been widely used as the electrolyte for polymer electrolyte fuel cells (PEFCs) due to their high proton conductivity and chemical stability. However, their fully fluorinated chemical structure leads to high production cost, low glass transition temperature and high gas permeability, which tend to impede the widespread application of PEFCs. To address these problems, sulfonated hydrocarbon (HC) membranes have been researched over the past decade. In our previous study,1 we investigated a sulfonated benzophenone poly(arylene ether ketone) semiblock copolymer (SPK-bl-1, SPK, Figure 1a)2 and a phenylene poly(arylene ether ketone) semiblock copolymer (SPP-bl-1, SPP, Figure 1b)3 membrane under accelerated open circuit-voltage (OCV) conditions appropriate for FCVs. The results indicate that a simple hydrophilic structure that does not include ketone groups leads to increased chemical stability versus radical attack decomposition.On the other hand, an SPP membrane quickly decomposed when subjected to a Fenton’s reagent test, which may be attributed to the presence of heteroatoms in the hydrophobic structure. Based on these results, we developed a new hydrocarbon membrane that consists solely of phenylene groups, which is designated a sulfonated poly(phenylene) quinquephenylene (SPP-QP, Figure 1c).4 In the present research, we focus on the durability of the SPP-QP membrane, in comparison with previous results for HC membranes (SPP and SPK) under identical accelerated OCV conditions.1 The properties of the membranes are listed in Table 1. We have designated these combinations of MEA components as cell types 1, 2 and 3 cells, as listed in Table 2. The membrane designations, e.g., “SPP-QP type #” (Figure 2), simply refer to the same membrane tested in different cell configurations. During the durability evaluations, the exhaust water from both sides of the cells was collected and then analyzed by ion chromatography (IC). After the durability evaluations, the post-test membrane electrode assemblies (MEAs) were analyzed with nuclear magnetic resonance (NMR) spectroscopy. The cell voltages were continuously measured during the accelerated OCV stress evaluation, and the hydrogen leak current density and the composition of the water that was drained from each cell were measured every 200 h by use of LSV and IC, respectively, as shown in Figures 2a–2c. The cell voltage for the SPP-QP type 1 cell decreased significantly after 700 h. In the case of SPP-QP type 2 and type 3 cells, the cell voltages maintained high values for over 1000 h, as well as those for the SPP cell and SPK cell (Figure 2a). The hydrogen leak current density also behaved nearly the same for each of the cells, except for the SPP-QP type 1 cell, which reached ca. 100 times higher H2 leakage at 800 h than those of the others (Figure 2b). The emitted concentration values of sulfate decreased in the order SPK » SPP > SPP-QP type 1 > SPP-QP type 2 ≈ SPP-QP type 3(Figure 2c). The intrinsic chemical stabilities of the SPP-QP, SPP and SPK membranes were evaluated with Fenton’s reagent. These results indicated that the SPP-QP membranes had much higher intrinsic chemical stability compared to those of SPP and SPK membranes, which was reflected in the results of the accelerated OCV stress evaluation. We also studied approaches to mitigate the mechanical stress by use of GDLs5 and gaskets in order to evaluate the chemical stability of the membranes under accelerated conditions in MEAs.6 Acknowledgement This work was partially supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell (SPer-FC)” Project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The authors are grateful to Panasonic Corporation for kindly providing the experimental GDL as soft GDL. Also, the authors are grateful to Honda R&D Co., Ltd. for kindly providing the accelerated OCV stress-evaluation protocol. References1) R. Shimizu, J. Tsuji, N. Sato, J. Takano, S. Itami, M. Kusakabe, K. Miyatake, A. Iiyama, and M. Uchida, J. Power Sources, 367, 63 (2017).2) T. Miyahara, T. Hayano, S. Matsuno, M. Watanabe, and K. Miyatake, ACS applied materials & interfaces, 4, 2881 (2012).3) J. Miyake, T. Mochizuki, and K. Miyatake, ACS Macro Letters, 4, 750 (2015).4) J. Miyake, R. Taki, T. Mochizuki, R. Shimizu, R. Akiyama, M. Uchida, and K. Miyatake, Science Advances, 3, eaao0476 (2017).5) H. Ishikawa, T. Teramoto, Y. Ueyama, Y. Sugawara, Y. Sakiyama, M. Kusakabe, K. Miyatake, and M. Uchida, J. Power Sources, 325, 35 (2016).6) R. Shimizu, K. Otsuji, A. Masuda, N. Sato, M. Kusakabe, A, Iiyama, K. Miyatake, and Makoto Uchida, J. Electrochem. Soc, 166 (7) F3105-F3110 (2019) Figure 1

Beyond Nafion: Structure-Property Relationships in Novel Perfluorinated Ionomers with Tunable Transport Properties

Rapid improvements in fuel cell performance have been driven by the development of commercially available ionomers used as membranes and catalyst binders in membrane electrode assemblies (MEAs). Commercially available ionomers share a semi-crystalline polytetrafluoroethylene (PTFE) matrix, which imparts low gas permeability and high mechanical and makes them attractive membrane materials. At the same time, the slow permeation of gases (i.e., oxygen and hydrogen) through the ionomers introduces significant mass-transport losses in the catalyst layers, ultimately limiting fuel cell performance. In this study, we present a new family of perfluorinated ionomers that incorporate an amorphous matrix based on a perfluoro(2-methylene 4-methyl-1,3-dioxolane) (PFMMD) backbone. The introduction of a PFMMD backbone disrupts the crystallinity of the matrix, increases the ionomers’ free volume, and significantly improves their gas permeability (permeability >3x that of Nafion). On the other hand, the dioxolane backbone increases the glass transition temperature of the matrix, restricting its mobility, which in turn limits the ionomer domain swelling and reduces its proton conductivity. In this presentation, I will present a facile and flexible synthesis method for PFMMD-based ionomers with tunable sulfonic acid content. Furthermore, I will describe structure-property relationships in these materials derived from a combination of transport measurements (i.e., water uptake, proton conductivity, and permeability) and morphological characterization through Small- and Wide-angle X-ray scattering. Lastly, I will discuss the implication and potential utilization of these new materials for improved fuel cell performance. The results presented here underscore the significance of tailoring materials chemistry to specific requirements of fuel cell or electrolysis MEAs.

Compressive strength and hygric properties of concretes incorporating microencapsulated phase change material

This study evaluated the compressive strength and hygric properties of concrete incorporating 0%, 3%, and 5% microencapsulated phase change material (PCM). Results show that compressive strength decreases with microencapsulated PCM addition, but remains satisfactory for usage as structural concrete. Porosity increases with microencapsulated PCM addition but remains in the range of that of ordinary concrete. For all tested concretes (control mix, mixes with damaged and undamaged microcapsules PCMs), very low gas-permeability was found; while sorption/desorption isotherms resulted in low moisture contents at the highest humidity level and the data followed a hysteresis loop indicating pore blocking mechanism.

Cast extrusion of low gas permeability bioplastic sheets in PLA/PBS and PLA/PHB binary blends

ABSTRACTBinary blends based on polylactic acid (PLA) and other biodegradable polyesters from renewable sources (namely, polybutylene succinate (PBS) and poly-3-hydroxybutyrate (PHB)) were prepared by reactive compounding extrusion. The achieved polymeric compounds were reprocessed by cast extrusion to manufacture the corresponding bioplastic sheets. Three different binary blends, one of which also including tocopherol, an oxygen scavenger, were investigated to ensure high-barrier of the bioplastic sheets to oxygen permeation. Physical, mechanical and chemical properties of the bioplastic sheets were, therefore, comparatively evaluated by differential scanning calorimetry, infrared spectroscopy, tensile tests and gas permeability. The experimental results showed a remarkable improvement in the oxygen barrier properties, especially on sheets manufactured in the PLA/PHB binary blend, without negatively affecting their thermo-mechanical response. Based on experimental evidences, the PLA/PHB binary blend is found to be extremely promising for the development of bio-based and biodegradable polymeric materials with low oxygen permeation, that is, for the development of suitable alternatives to conventional and highly pollutant oil-based plastics.

Numerical Simulation of Two-Phase System of “Combustible Liquid – Solid Fuel” Combustion in a Fixed Bed

Investigation of combustion of complex heterogeneous systems and particularly of twophase “combustible liquid – solid fuel” systems is topical because of the need to improve combustion of multicomponent and non-standard fuels as well as for resolution of specific ecological problems. The qualitative and quantitative peculiarities of combustion of two model combustible systems, notionally corresponding to the “sawdust – oil” and “wood chips – oil” mixtures are investigated numerically. The main peculiarity of the systems is volatility of the fluid component, being gaseous-flow driven inside porous media. A one-dimensional plain problem of combustion of compact layer with the ignition from the bottom and from the upper side is considered. It is demonstrated that due to low gas permeability of the fine-dispersed solid matrix (sawdust), air flow velocity is relatively low which results in slow formation of the combustion front (the characteristic time is tens of minutes). In case of coarse solid phase (wood chips), airflow rate is higher and corresponding time of temperature fronts formation is smaller (a few minutes). Both for the cases of fine-dispersed and coarse particles solid matrix phase, when set on fire from below, the fluid component is evacuated from the hot zone before the combustion front is formed. Since that, the main characteristics of the temperature front dynamics correspond to “dry” fuel system. In case of upper side ignition the combustion wave is formed at the time of the order of 100 s (when the used magnitudes of parameters are being used again), then it spreads downstream of the layer, accompanied by incomplete oxidation of solid fuel and complete combustion of oxygen. The effect of incomplete solid fuel combustion was noted earlier in the investigations of combustion of lean coal layer and some other systems. The velocity of the combustion wave propagation does not differ much for the cases of upper side and bottom side ignition. But the time of establishing the quasi-stationary velocity of the front to the steady-state value at the initial stage is much less in case of bottom side ignition. The results obtained by the authors can be utilized for optimization of multi-phase fuels combustion in compact layer, the regime parameters of in-situ combustion method of oil recovery increase as well as for improvement of some specific chemical processes.

Effects of bentonite on physical, mechanical and barrier properties of cellulose nanofibril hybrid films for packaging applications

There is an increasing attention to cellulose nanofibrils (CNFs) for food packaging applications due to their abundance, biodegradability, and low gas permeability. In this work, oxygen and water barrier performance is studied for bio-nanocomposite films formed by incorporation of two types of bentonite (PGN and PGV) at different loads (15, 30 and 45 wt%) into continuous CNF matrix. The resulting hybrid films were analyzed for their morphology, surface energy, mechanical strengths as well as water/oxygen barrier qualities. Both types of bentonite lowered the CNF degradation temperature and strength to some degree for reasons not so clear but perhaps due to partial disruption of the CNF H-bond network. It was revealed from microscopic study that clay particles form a layer within cellulose chains, resulting in alteration of composite structure. The contact angle analysis by polar and nonpolar liquids, suggested the PGN-containing samples were more hydrophilic; clay induced polar functionalities to the composite. While 15% PGN load reduced the water vapor transmission rate from 425 to 375 g/m2 day, higher proportions of bentonite negatively affected this trend. Also, analysis of oxygen transmission rate showed the PGN effectively restricted the oxygen passage in dry state and to a lower extent at higher relative humidity. In WVTR analysis, PGN showed a superior performance over PGV attributable to its crystalline structure as evident in XRD patterns. The proposed hybrid CNF-BNT films in this study can present an eco-friendly alternative in packaging materials, especially where penetration of water vapor and oxygen is to be avoided.

Block Copolyesters Containing 2,5-Furan and trans-1,4-Cyclohexane Subunits with Outstanding Gas Barrier Properties.

Biopolymers are gaining increasing importance as substitutes for plastics derived from fossil fuels, especially for packaging applications. In particular, furanoate-based polyesters appear as the most credible alternative due to their intriguing physic/mechanical and gas barrier properties. In this study, block copolyesters containing 2,5-furan and trans-1,4-cyclohexane moieties were synthesized by reactive blending, starting from the two parent homopolymers: poly(propylene furanoate) (PPF) and poly(propylene cyclohexanedicarboxylate) (PPCE). The whole range of molecular architectures, from long block to random copolymer with a fixed molar composition (1:1 of the two repeating units) was considered. Molecular, thermal, tensile, and gas barrier properties of the prepared materials were investigated and correlated to the copolymer structure. A strict dependence of the functional properties on the copolymers’ block length was found. In particular, short block copolymers, thanks to the introduction of more flexible cyclohexane-containing co-units, displayed high elongation at break and low elastic modulus, thus overcoming PPF’s intrinsic rigidity. Furthermore, the exceptionally low gas permeabilities of PPF were further improved due to the concomitant action of the two rings, both capable of acting as mesogenic groups in the presence of flexible aliphatic units, and thus responsible for the formation of 1D/2D ordered domains, which in turn impart outstanding barrier properties.

Oxidative crosslinking of copolyimides at sub-Tg temperatures to enhance resistance against CO2-induced plasticization

Polymer crosslinking via thermal oxidation is a well-established technique that enhances the gas selectivity of a polymer membrane, but usually at the expense of lower gas permeability. As thermal oxidation is typically performed at temperatures higher than the glass transition temperature (Tg) of polymers, large energy footprints are incurred while pore structures in asymmetric membranes – the preferred physical configuration of polymer membranes are collapsed. To overcome these drawbacks, here we report a strategy to simultaneously enhance both gas permeability and selectivity via thermal oxidation at sub-Tg temperatures. This was achieved with a copolymer consisting a component that enhanced Tg, and another component with functional groups that decomposed and induced crosslinking at lower temperatures. We used a series of complementary characterization techniques to pinpoint the actual mechanism underpinning our sub-Tg thermal oxidation approach. Crosslinking slightly reduced the d-space between polymer chains but increased polymer fractional free volume and most importantly, inhibited CO2-induced plasticization. The pure CO2 permeability of the crosslinked polymer reached 88.5 Barrer with a CO2/CH4 ideal selectivity of 38.8, while no plasticization behavior was detected at a CO2 pressure up to 30 atm at 35 °C. When separating CO2:CH4 (1:1) mixed gas at total pressures between 10 and 60 atm, the CO2 permeability and CO2/CH4 selectivity of this crosslinked polymer were reduced to 55 Barrer and 29 due to competitive permeation.

Gas separation properties of polybenzimidazole/thermally-rearranged polymer blends

Polybenzimidazole (PBI) is highly selective for H2 removal from mixtures with CO2, but it exhibits low gas permeabilities. Celazole® PBI was blended with more permeable HAB-6FDA-CI, an ortho-functional thermally rearrangeable polyimide, to improve its gas permeabilities while attempting to maintain high selectivity. A compatibilizer, 1-methylimidazole, enhanced phase dispersion when added to the casting solutions. Films containing 20–40 wt% polyimide exhibited a matrix-droplet morphology as observed by scanning and transmission electron microscopy. Heat treatment at 400 °C under inert atmosphere thermally rearranged the polyimide in the blends. After heat treatment, H2/CO2 selectivities at 35 °C doubled for Celazole® and 20–33 wt% polyimide compatibilized blends, exceeding the 2008 upper bound. Simultaneous increases in both H2 permeability and H2/CO2 selectivity were observed after heat treatment for the 33/67 wt% HAB-6FDA-CI/Celazole® compatibilized blend, which exhibited over twice the H2 permeability of Celazole® and similar selectivity. Heat treatment reduced free volume and induced para-crystallinity in the PBI phase of the blends as evidenced by x-ray scattering. Thermally treated blend films were mechanically flexible and exhibited elastic moduli and tensile strengths similar to Celazole®, despite having low elongation at break.

Impermeable gas barrier coating by facilitated diffusion of ethylenediamine through graphene oxide liquid crystals

A highly impermeable gas barrier coating is developed by intercalating ethylenediamine (EDA) into the nanochannels of graphene oxide (GO). The diffusion of EDA is facilitated in aqueous GO liquid crystal (LC) scaffolds, and the intercalation can be achieved spontaneously in a few seconds. The intercalated EDA not only crosslinks GO but also induces chemical reduction of GO to RGO, making the RGO/EDA coating stable in water. Remarkably, the RGO/EDA coating exhibits extremely low gas permeability ranging from 0.006 to 0.02 barrer for He, H2, N2, and CO2, similar to that of a neat GO film and exceeding the barrier performance of conventional polymers or their composite materials with graphene or nanoclay. The excellent barrier properties can be attributed to the high tortuosity caused by the well-aligned structure of high-aspect-ratio graphene sheets. In addition, the viscoelastic rheological properties of the GOLC could be beneficial for coating RGO/EDA on various substrates with different geometries where gas barrier properties are needed.

Constructing Connected Paths between UiO-66 and PIM-1 to Improve Membrane CO2 Separation with Crystal-Like Gas Selectivity.

Most metal-organic-framework- (MOF-) based hybrid membranes face the challenge of low gas permeability in CO2 separation. This study presents a new strategy of interweaving UiO-66 and PIM-1 to build freeways in UiO-66-CN@sPIM-1 membranes for fast CO2 transport. In this strategy, sPIM-1 is rigidified via thermal treatment to make polymer voids permanent, and concurrently polymer chains are mutually linked onto UiO-66-CN crystals to minimize interfacial defects. The pore chemistry of UiO-66-CN is kept intact in hybrid membranes, allowing full utilization of MOF pores and selective adsorption for CO2 . Separation results show that UiO-66-CN@sPIM-1 membranes possess exceptionally high CO2 permeability (15433.4-22665 Barrer), approaching to that of UiO-66-NH2 crystal (65-75% of crystal-derived permeability). Additionally, the CO2 /N2 permeation selectivity for a representative membrane (23.9-28.6) moves toward that of single crystal (24.6-29.6). The unique structure and superior CO2 /N2 separation performance make UiO-66-CN@sPIM-1 membranes promising in practical CO2 separations.

Chemically stabilised extruded and recast short side chain Aquivion® proton exchange membranes for high current density operation in water electrolysis

Membrane-electrode assemblies based on chemically stabilised short-side-chain proton exchange Aquivion® membranes, prepared by extrusion or recast methods, have been investigated for operation at high current density (3–4 A cm−2) in water electrolysis cells. A thickness of 90 μm was selected for these perfluorosulfonic acid membranes in order to provide proper resilience to hydrogen crossover under differential pressure operation while allowing operation at high currents. The membranes showed proper mechanical strength for high-pressure operation and suitable conductivity to reduce ohmic losses at high current densities. Both membranes showed excellent performance in electrolysis cells by achieving a voltage efficiency better than 85% and 80% (1.85 V) at 3 and 4 A cm−2, respectively, in polarisation curves at 90 °C. A smaller surface roughness was observed from atomic force microscopy for the recast membrane compared to the extruded one. This may affect the intimate contact between the ionic clusters of the membrane and the catalyst agglomerate at the interface producing a catalytic enhancement in the activation region of the polarisation curves in the case of the recast membrane. At high cell voltages, the polarisation resistance was instead slightly lower for the cell based on the extruded membrane. Interestingly, the different characteristics of the membrane-electrodes interface produced lower recoverable losses in durability studies for the recast membrane-based electrolyser allowing stable operation at both 3 and 4 A cm−2. Hydrogen crossover analysis at a differential pressure of 20 bar showed low gas permeation through both membranes allowing for a wide load range (15–100%) and high faradaic efficiency >99% at practical current densities (1–4 A cm−2).

The impact of defect density, grain size, and Cu orientation on thermal oxidation of graphene-coated Cu

Graphene has been shown to be a promising barrier for thermal corrosion due to its low gas and liquid permeability; however, there have been contradictory reports in the literature regarding the mechanisms of oxidation of graphene-coated Cu. This work systematically investigates the effect of chemical vapor deposited graphene grain size, point defect density, and underlying Cu orientation on the thermal oxidation of the underlying Cu in air. For graphene with either small grain size (~0.04–0.4 μm2) or large point defect density (~800 μm−2), oxidizers have relatively unhindered access through these defects to corrode the underlying Cu, and the corrosion is relatively independent of Cu orientation. For graphene with low defect density, the rate of Cu oxidation depends on the Cu crystal orientation on which the graphene is synthesized. Graphene-coated Cu (110) is completely corroded in just 2 min of thermal oxidation at 250 °C, while no surface oxidation for graphene-coated Cu (111) is observed for the same conditions. Thus, corrosion of graphene that is synthesized to achieve large grain size (>~170 μm2) is limited by the weakest graphene/Cu orientation interaction, not the size of the graphene grains, as was previously assumed.