Gas Diffusion Pathways Research Articles

Constructing high-performance micro fuel electrodes for reversible proton ceramic electrochemical cells

Reversible proton ceramic electrochemical cells (R-PCECs) are of great interest as efficient energy conversion device. Optimization of structural design can enhance the mechanical properties and gas transport of the cells, resulting in improved electrochemical performance. In this study, we developed a 7-channel micro-monolithic R-PCEC for the first time, with uniform channel distribution and smaller gas diffusion pathway length using phase inversion/extrusion technique. The assembled cell with Ni-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (Ni-BZCYYb, fuel electrode support) | BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb, electrolyte) | PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF, air electrode) structure showed a peak power density of 0.94 W cm−2 at 700 °C in fuel cell mode and electrolysis current density of 2.17 A cm−2 at 700 °C with an operating voltage of 1.3 V. Additionally, electrochemical impedance spectroscopy (EIS) further indicated that the diffusive polarization of the structured cell was effectively reduced compared to single-channel counterpart.

In Situ Fabrication of SnO2 Nanowalls for Robust Acetylene Sensing at Low Temperature.

Acetylene (C2 H2 ) monitoring in real time and online is essential for erasing transformer risks and guaranteeing normal equipment operation and operator safety. This study examines the direct fabrication of ultrathin SnO2 nanowalls on Ag-Pd substrates using a simple solvothermal method that doesn't demand the use of any additional motivators or templates. The thickness and shape of the nanowalls can be controlled by varying the cetyl trimethyl ammonium bromide (CTAB) concentration in the solvent. As observed, the gas sensor (SnO2 -3) fabricated by 2.4 g CTAB exhibits superior gas-sensing features. This is primarily due to the hollow structure constructed by the arrangement of nanowalls, which delivers not only enough gas diffusion pathways but also enough reaction sites during the gas sensing processes. The findings suggest that low-cost SnO2 nanowalls created using a straightforward procedure could be taken into consideration as prospective candidates for use in industrial C2 H2 sensing applications.

Control of gas selectivity and permeability through COF-GO composite membranes for sustainable decarbonization and hydrogen production

A promising way to address modern environmental and energy supply challenges is via rapid implementation of decarbonization and hydrogen production technologies. Development of gas separation membranes with high selectivity and permeability is essential for these processes but is still a bottleneck. Our research focuses on achieving precise control of gas diffusion pathways through on-demand regulation of material interactions in thin composite membranes. We combine 2D covalent organic frameworks (COFs) and graphene oxide (GO) to create COF-GO composite membranes with desirable nanosheet stacking, controllable thicknesses and pathways for gases. By pH-assisted self-assembly, we fine-tune material interactions and achieve simultaneous enhancement of permeability and selectivity by increasing membrane thickness and regulating the interactions between COF and GO nanosheets by pH. At a thickness of 1.3 μm, the COF-GO membrane, assembled under pH 4, demonstrates good working characteristics for H2/CO2 equimolar mixture (at room temperature and 1 bar), with a H2 permeability of 366 Barrer, selectivity of 15.6, and long-term stability exceeding 200 h. This work paves the way for tailored, performing gas separation with long-term stability. It guides the unique 2D transport mechanism to be utilized under practical conditions. Our research offers a novel strategy for the design of composite membranes from two-dimensional (2D) materials for gas separation technologies. It contributes to sustainable decarbonization and hydrogen production solutions, bringing us closer to a greener, more environmentally friendly future.

Highly Durable and Active Electrocatalysts Using Pt Nanorod Catalysts Supported on Nb Doped SnO2 for Polymer Electrolyte Fuel Cells Operating at Wide Temperature Range

The improvement of the durability and activity in cathode catalyst is required toward the wide spread use of polymer electrolyte fuel cells. One of the interesting catalysts is the Pt catalysts supported on SnO2 (Pt/M-SnO2, M = Nb, Ta) without carbon additives [1,2]. The durability (startup/shutdown, load cycling) and oxygen reduction reaction (ORR) activity of the Pt/M-SnO2 is superior to those of commercial Pt catalysts supported on carbon black (Pt/CB) etc. [3-8]. The non-carbon support of M-SnO2 nanoparticles has a unique carbon-like microstructure of a fused-aggregate network structure, which supply the essential function of the electronically constructing pathways via necking of each support particles and the gas diffusion pathways via the open pores surrounded by particles. The Pt nanorod catalyst on M-SnO2 also improves the ORR activity as shown in the catalyst design concept (Fig. 1)[9]. The IV performance of the single cell using the Pt nanorod/Nb-SnO2 cathode catalyst layers at operating temperatures from 80oC to 120oC is quite high to approach the NEDO target performance (Fig. 2) with keeping high durability. The catalyst is considered to have possibilities for application of the heavy-duty vehicles operating at wide-temperature range (< 120oC)[10]. Acknowledgments This work was partially supported by funds for the project “Electrolytes, Catalysts and Catalyst layers with Extraordinary Efficiency, power and Durability for PEFCs-2030 (ECCEED’30) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, and JSPS KAKENHI Grant Number (23H02059) from the Ministry of Education, Culture, Sports, Science and Technology. References A. Masao, S. Noda, F. Takasaki, K. Ito, K. Sasaki, Electrochem. Solid-State Lett.,12, B119 (2009).E. Fabbri, A. Rabis, R. Kötz, T.J. Schmidt, Phys. Chem. Chem. Phys., 16, 13672 (2014).K. Kakinuma, M. Uchida, T. Kamino, H. Uchida, M. Watanabe, Electrochim. Acta, 56, 2881 (2011).Y. Senoo, K. Kakinuma, M. Uchida, H. Uchida, S. Deki, M. Watanabe, RSC Adv., 6, 321800 (2014).Y. Chino, K. Taniguchi, Y. Senoo, K. Kakinuma, M. Watanabe, M. Uchida, J. Electrochem. Soc., 162, F736 (2015).K. Kakinuma, R. Kobayashi, A. Iiyama, M. Uchida, J. Electrochem. Soc., 165, J3083 (2018).K. Kakinuma, K. Suda, R. Kobayashi, T. Tano, C. Arata, I. Amemiya, S. Watanabe, M. Matsumoto, H. Imai, A. Iiyama, M. Uchida, ACS Appl. Mater. Interfaces 11, 34957 (2019).K. Kakinuma, M. Hayashi, T. Hashimoto, A. Iiyama, M. Uchida, ACS Appl. Energy Mater., 3, 6922 (2020).G. Shi, T. Tano, D.A. Tryk, A. Iiyama, M. Uchida, K.Kakinuma, ACS Catal., 11, 5222 (2021).K. Kakinuma, H. Taniguchi, T. Asakawa, T. Miyao, M. Uchida, Y. Aoki, T. Akiyama, A. Masuda, N. Sato, A. Iiyama J. Electrochem. Soc. 169 (2022) 044522. Figure 1

Spatial O2 Profile in Coix lacryma-jobi and Sorghum bicolor along the Gas Diffusion Pathway under Waterlogging Conditions.

While internal aeration in plants is critical for adaptation to waterlogging, there is a gap in understanding the differences in oxygen diffusion gradients from shoots to roots between hypoxia-tolerant and -sensitive species. This study aims to elucidate the differences in tissue oxygen concentration at various locations on the shoot and root between a hypoxia-tolerant species and a -sensitive species using a microneedle sensor that allows for spatial oxygen profiling. Job's tears, a hypoxia-tolerant species, and sorghum, a hypoxia-susceptible species, were tested. Plants aged 10 days were acclimated to a hypoxic agar solution for 12 days. Oxygen was profiled near the root tip, root base, root shoot junction, stem, and leaf. An anatomical analysis was also performed on the roots used for the O2 profile. The oxygen partial pressure (pO2) values at the root base and tip of sorghum were significantly lower than that of the root of Job's tears. At the base of the root of Job's tears, pO2 rapidly decreased from the root cortex to the surface, indicating a function to inhibit oxygen leakage. No significant differences in pO2 between the species were identified in the shoot part. The root cortex to stele ratio was significantly higher from the root tip to the base in Job's tears compared to sorghum. The pO2 gradient began to differ greatly at the root shoot junction and root base longitudinally, and between the cortex and stele radially, between Job's tears and sorghum. Differences in the root oxygen retention capacity and the cortex to stele ratio are considered to be related to differences in pO2.

Nanoarchitecturing hydrogen electrode with intimately coupled ion-conducting and catalytic phases for enhanced intermediate-temperature steam electrolysis

Intermediate-temperature solid oxide electrolysis cells (IT-SOECs) have recently attracted great interest in steam electrolysis. However, the performance of IT-SOECs is substantially influenced by the polarization loss encountered at the traditional hydrogen electrode interface. Herein, we reported an innovative approach to address this challenge by modifying the interface of hydrogen electrode and electrolyte. NiO-BaZr0.1Ce0.7Y0.2O3-δ (NiO-BZCY) nanocomposite with an even distribution of NiO and BZCY was synthesized by a one-step combustion method and utilized to fabricate a hydrogen electrode functional layer (HFL). In comparison with the conventional hydrogen electrode fabricated by the ball-milling method, the developed double-layer hydrogen electrode structure exhibits a gradient porosity with macropores at the electrode substrate and micropores at HFL. The optimized electrode microstructure provides both adequate gas diffusion pathway and enlarged three-phase-boundary for effective electrochemical reaction. Consequently, the polarization loss is significantly reduced, leading to a discernible enhancement in the electrolysis performance of the IT-SOECs.

Effects of plastic contamination on carbon fluxes in a subtropical coastal wetland of East China

Coastal wetlands are recognized as carbon sinks that play an important role in mitigating global climate change because of the strong carbon uptake by vegetation and high carbon sequestration in the soil. Over the last few decades, plastic waste pollution in coastal zones has become increasingly serious owing to high-intensity anthropogenic activities. However, the influence of plastic waste (including foam waste) accumulation in coastal wetlands on carbon flux remains unclear. In the Yangtze Estuary, we investigated the variabilities of vegetation growth, carbon dioxide (CO2) and methane (CH4) fluxes, and soil properties in a clean Phragmites australis marsh and mudflat and a plastic-polluted marsh during summer and autumn. The clean marsh showed a strong CO2 uptake capacity (a carbon sink), and the clean mudflat showed a weak CO2 sink during the measurement period. However, polluted marshes are a significant source of CO2 emissions. Regardless of the season, the gross primary production and vegetation biomass of the polluted marshes were on average 9.5 and 1.1 times lower than those in the clean marshes, respectively. Ecosystem respiration and CH4 emissions in polluted marshes were significantly higher than those in clean marshes and mudflats. Generally, the soil bulk density and salinity in polluted marshes were lower, whereas the median particle size was higher at the polluted sites than at the clean sites. Increased soil porosity and decreased salinity may favor CO2 and CH4 emissions through gas diffusion pathways and microbiological behavior. Moreover, the concentrations of heavy metals in the soil of plastic-polluted marshes were 1.24–1.49 times higher than those in the clean marshes, which probably limited vegetation growth and CO2 uptake. Our study highlights the adverse effects of plastic pollution on the carbon sink functions of coastal ecosystems, which should receive global attention in coastal environmental management.

Ga-Doped ZnO Microbelts Based Resistive-type Sensor for Detection of Acetylene Gas

Structural materials with shorter gas diffusion pathways, lower electrical resistance, and crystal size play a vital role in resistive-type gas sensors. In the present work, ZnO was doped with Ga to lower its electrical resistance and inhibit crystal growth for acetylene sensing. Ga-doped ZnO microbelts were synthesized by electrospinning a solution containing metal precursors and quillaja saponin as a template for the evolution of the belt structure, followed by calcination to achieve microbelts with a BET surface area of 68.5 m2 g–1, an average pore size of 4.6 nm, and ZnO crystals as small as 16.5 nm. The Ga-doped ZnO microbelts exhibited a response (Ra/Rg) of up to 21.0, and a fast response (7.6 s) to 20 ppm acetylene at 400 °C in dry conditions. The materials also showed outstanding repeatability of response of 10.04 ± 0.04 against 10 cycles of 5-ppm acetylene, a response of 2.0 to acetylene as low as 0.2 ppm, and excellent selectivity against 5 ppm of hydrogen, pentane, toluene, carbon monoxide, and methane. The results suggested that Ga doping could effectively improve the electrical conductivity and acetylene sensing performance of ZnO-based sensors.

Engineering three-dimensionally ordered mesoporous structure of TiO2 for the fast responsive NH3 gas sensor at ambient conditions

Engineering TiO2 nanostructures with a unique fast responsive property for NH3 detection under ambient conditions remains a great challenge in the sensor industry as TiO2 is active at an elevated temperature of more than 200 °C. Despite this obstacle, in this work, the hierarchical three-dimensional ordered mesostructured (3DOM) of TiO2 with designed morphology and pore orientation was developed for the NH3 gas sensor at room temperature. The hybrid TiO2 templates, polymethyl methacrylate (PMMA) and pluronic 123 (P123), were employed during an evaporation-induced self-assembly synthesis. The 3DOM TiO2 was identified to be in a pure anatase phase and showed a honeycomb-like morphology with the walls made of well-connected fine TiO2 particles. The micelle formation time of P123 and the size of PMMA affected the thickness of well-connected nanoparticles of 3DOM TiO2. The optimized micelle formation time for producing the highest sensitivity to the NH3 gas of the P123 and the PMMA size was 15 h and 250 nm, respectively. The NH3 gas sensors were further engineered by laminating the suspended 3DOM TiO2 on a Cu screen printing chip. Interestingly, the low detection limit of 0.1 ppm of NH3 gas sensing was obtained at ambient conditions. Moreover, the systematic gas diffusion pathway with fast response and the grain-controlled transducer process were enhanced when using the 3DOM TiO2 compared to the pristine TiO2 nanoparticles. This work clearly demonstrates that the engineering-designed hierarchical 3DOM structure could provide a fast responsive and low detection limits NH3 sensors at ambient conditions.

The leaf anatomical trade-offs associated with plant ecological strategy variation

Plant functioning depends on variation in resource economics traits (acquisition vs. conservation) and the size of plants and their parts (the ‘global spectrum of plant form and function’). The anatomical basis of single traits (e.g., leaf mass per area; LMA) is generally understood, but little is known regarding the relationship between anatomical trade-offs and ecological strategies (representing integrated suites of traits). We hypothesised correlations between the relative extent of leaf tissue types and Grime’s Competitor Stress-tolerator Ruderal (CSR) strategies, principally a trade-off between structural (mechanical/fibro-vascular) vs. photosynthetic (chlorenchyma and intercellular airspace; ICAS) tissues, for ecologically contrasting herbaceous angiosperms in northern Italy. Specifically, that in the lamina portion, the trade-off represents the economics spectrum (S-R selection), but in the midvein portion, it reflects the mechanical constraints inherent to supporting large leaves (i.e., varies with C-selection). We used microscopy and image analysis to determine the relative cross-sectional area of tissues from transverse leaf sections (lamina and midvein portions) of angiosperms of contrasting CSR strategies. Principal components analysis (PCA) determined that the main trade-off (PCA1) was between mechanical/fibro-vascular tissues vs. ICAS/epidermis/chlorenchyma, but that this was associated with the economics spectrum (R- to S-selection) in the lamina, and with size (C-selection) for the midvein. A secondary trade-off in both lamina and midvein portions involved ICAS (i.e., the internal gas diffusion pathway) vs. chlorenchyma/epidermis (light capture), associated with S- to R-selection, respectively. Our results confirm the expectation that ecological strategy variation has a basis in underlying trade-offs between tissues with contrasting metabolic/architectural (i.e., economics/size-related) roles.

Highly Durable and Active Electrocatalysts Using Pt Nanorod Catalysts Supported on Nb Doped SnO2 for Polymer Electrolyte Fuel Cells

In proton exchange membrane fuel cells (PEMFCs) operating with the use of Pt/carbon (Pt/C) cathode catalysts, severe corrosion of the carbon support has been recognized at high potentials. The improvement of the catalyst durability with high activity is required for heavy use applications. Alternative candidate catalysts with high durability and high activity are Pt catalysts supported on non-carbon ceramic supports [1,2]. Our group confirmed that Pt catalysts supported on SnO2 (Pt/M-SnO2, M = Nb, Ta) without carbon additive were superior in durability (startup/shutdown, load cycling) and oxygen reduction reaction (ORR) activity to those of commercial Pt catalysts, e.g., supported on either graphitized carbon black (Pt/GCB, TEC10EA30E, TKK) or carbon black (Pt/CB, TEC10E50E, TKK), by evaluation of membrane-electrode assemblies (MEA) [3-9]. The non-carbon support of SnO2 nanoparticles has a unique carbon-like microstructure consisting of a fused-aggregate network structure, which enhances the electronically conducting pathways via the aggregated microstructure and gas diffusion pathways via the open pores in the microstructure. We have also proposed ways to design the Pt nanorod supported on the Nb-SnO2 based on the catalyst design concept (Fig. 1)[10]. The cell performance using the Pt/SnO2 cathode catalyst layers at operating temperatures from 80oC to 120oC is quite promising for the development of high-power density (Fig. 2) with simultaneous high durability. Acknowledgments This work was partially supported by funds for the project “Electrolytes, Catalysts and Catalyst layers with Extraordinary Efficiency, power and Durability for PEFCs-2030 (ECCEED’30) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, and JSPS KAKENHI Grant Number (20H02839) from the Ministry of Education, Culture, Sports, Science and Technology. References A. Masao, S. Noda, F. Takasaki, K. Ito, K. Sasaki, Electrochem. Solid-State Lett., 12, B119 (2009).E. Fabbri, A. Rabis, R. Kötz, T.J. Schmidt, Phys. Chem. Chem. Phys., 16, 13672 (2014).K. Kakinuma, M. Uchida, T. Kamino, H. Uchida, M. Watanabe, Electrochim. Acta, 56, 2881 (2011).Y. Senoo, K. Kakinuma, M. Uchida, H. Uchida, S. Deki, M. Watanabe, RSC Adv., 6, 321800 (2014).Y. Chino, K. Taniguchi, Y. Senoo, K. Kakinuma, M. Watanabe, M. Uchida, J. Electrochem. Soc., 162, F736 (2015).K. Kakinuma, R. Kobayashi, A. Iiyama, M. Uchida, J. Electrochem. Soc., 165, J3083 (2018).K. Kakinuma, K. Suda, R. Kobayashi, T. Tano, C. Arata, I. Amemiya, S. Watanabe, M. Matsumoto, H. Imai,Iiyama, M. Uchida, ACS Appl. Mater. Interfaces 11, 34957 (2019).K. Kakinuma, M. Hayashi, T. Hashimoto, A. Iiyama, M. Uchida, ACS Appl. Energy Mater., 3, 6922 (2020).G. Shi, T. Tano, D.A. Tryk, A. Iiyama, M. Uchida, K.Kakinuma, ACS Catal., 11, 5222 (2021). Figure 1

Ultrasensitive flexible NO2 gas sensors via multilayer porous polymer film

Micro-nano structure engineering of active materials in sensors have attracted broad attention for hazardous component detection, which enables creating electronic noses that could detect gas analytes efficiently without introducing abundant functional groups and defects. However, challenges still remain on realizing flexible gas sensors with both decent sensing performance and good mechanical robustness, which are extremely important for wearable electronics. Here we present a scalable and facile manufacturing method to construct the three-dimensional (3D) multilayer porous organic semiconductors (OSCs) structure for transistor based gas sensor, showing largely enhanced gas sensing properties as well as bendability down to 1 mm radius with stable operation. The multilayer porous film of OSCs is assembled via breath figure method, followed by layer-by-layer transferring process. The formed 3D porous structure provides efficient hazardous gas diffusion pathways, abundant gas molecules adsorption active sites and immunity towards mechanical deformation simultaneously. Consequently, an obvious increase of responsivity (from 122% to 1053% at 30 ppm) was achieved for NO2 detection, along with an ultralow limit of detection (∼2.3 ppb), and good gas selectivity. This work demonstrates a scalable and low-cost fabrication strategy for high-performance flexible sensors, which delivers an alternative way for next-generation wearable electronics.

Enhanced carbonation curing of cement pastes with dolomite additive

AbstractCarbonation curing of cement‐based materials has recently received increasing attention as a CO2 utilization technology. This study aimed at investigating the effects of carbonation curing on the performance of ordinary Portland cement (OPC) pastes with dolomite additive (DPC). The CO2 uptake capacity, after being normalized to carbonation active components, significantly increased with larger dolomite mixing ratios. For DPC‐25% samples under 2.5 MPa curing pressure, the maximum CO2 uptake capacity reached 23.6 wt%, which was 23% higher than that of pure OPC samples under the same condition. Effects of water to solids (w/s) ratio and temperature on carbonation are two‐sided. The optimum w/s ratio for CO2 uptake capacity of DPC‐15% samples was approximately 0.20, while the optimum temperature was equal to 60℃ or higher than 60℃. The CO2 uptake capacity increased with finer particle size and higher CO2 curing pressures. Compared to large particles, smaller particles are more likely to have a better dilution effect, providing more contact surface for carbonated precipitation. From the pore structure changes perspective, carbonation products filled the interface between the dolomite and amorphous particles. DPC‐25% samples with higher dolomite mixing ratios provided more pores and pathways for gas diffusion, and exhibited a more uniform structure, thereby contributing to the highest compressive strength values of DPC‐25% samples (63.8 MPa) among all the DPC samples. These findings imply the possible feasibility of dolomite as an additive in carbonation cured building materials. © 2022 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Dual-function biomimetic carrier based facilitated transport mixed matrix membranes with high stability for efficient CO2/N2 separation

Realizing efficient carbon capture by high-performance CO2 separation membrane is significant to mitigate the increasing emissions of greenhouse gas CO2. Inspired by the extraordinary CO2 hydration ability of carbonic anhydrase (CA), a biomimetic MOF (CFA-1) which can mimic the CO2 hydration sites of CA but possesses better stability and the lower price was incorporated into Pebax to fabricated high-performance facilitated transport mixed matrix membranes. The optimal membrane has a CO2 permeability of 869 Barrer with a CO2/N2 ideal selectivity of 88.6 at 1 bar and 30 °C, which is 9.2 times and 2.8 times than the pristine Pebax membrane. Such superior CO2/N2 separation performance (far surpasses 2008 upper bound) is original from the dual-function of CFA-1: (1) provide extra pathways for gas diffusion and affinity sites for preferential CO2 adsorption; (2) facilitate CO2 transport in the membrane by efficiently catalyze CO2 hydration reaction. Furthermore, the Pebax/CFA-1 membranes fabricated can also exhibit excellent stability after being treated under high temperature and harsh pH, which is not available in the Pebax/CA membranes. Overall, such biomimetic dual-function MOFs may pave a new avenue to advance the high-performance CO2 facilitated transport membranes with excellent stability.

Highly Durable and Active Pt Nanorod Electrocatalysts Using SnO2 Supports for Polymer Electrolyte Fuel Cells

ABSTRACT Toward the widespread use of fuel cell vehicles, highly durable and active catalysts in polymer electrolyte fuel cells (PEFCs) are required. Pt catalysts supported on non-carbon ceramic supports were proposed to be alternative candidate catalysts with high activity and high durability [1,2]. Our group also confirmed that Pt catalysts supported on SnO2 (Pt/M-SnO2, M = Nb, Ta) without carbon additive were superior in oxygen reduction reaction (ORR) activity with durability (startup/shutdown, load cycling) to those of commercial Pt catalysts supported on carbon (e.g., Pt catalysts supported on either graphitized carbon black (Pt/GCB, TEC10EA30E, TKK) or carbon black (Pt/CB, TEC10E30E, TKK), by evaluation of rotation disk electrode and single cell [3-9]. Our non-carbon support of SnO2 nanoparticles has quite high crystallinity with unique carbon-like microstructure consisting of a fused-aggregate network structure, which enhances the electronically conducting pathways via the aggregated microstructure and gas diffusion pathways via the open pores in the microstructure. The Pt nanorods loaded on the supports with controlling the interface between Pt and the support also enhance the ORR activity, and mitigate the resistance of the cathode catalyst layer (CL). The cell performance using the Pt nanorods loaded on the supports cathode CL is quite promising for the development of high power density with simultaneous high durability at operating temperatures from 80oC to 120oC. Acknowledgments This work was partially supported by funds for the partly supported by the New Energy and Industrial Technology Development Organization (NEDO) Japan, and JSPS KAKENHI Grant Number (B24350093) from the Ministry of Education, Culture, Sports, Science and Technology.

Development of an extended model for the permeation of environmentally hazardous CO2 gas across asymmetric hollow fiber composite membranes

This study presents an extended thermodynamic and phenomenological combined model to mitigate the environmental hazardous acid gas over composite membranes. The model has been applied to an acid gas such as carbon dioxide (CO2) for its permeation through polyetherimide incorporated montmorillonite (Mt) nanoparticles hollow fiber asymmetric composite membranes. The well-established non-equilibrium lattice fluid (NELF) model for penetrating low molecular weight penetrant in a glassy polyetherimide (PEI) was extended to incorporate the other important polymer/filler system features such as tortuosity in acid gas diffusion pathways resulted from layered filler aspect ratio and concentration. The model mentioned above predicts the behavior of acid gas in PEI-Mt composite membranes based on thermodynamic characteristics of CO2 and PEI and tortuosity due to Mt. The calculated results are compared to experimentally determined values of CO2 permeability through PEI-Mt composite asymmetric hollow fiber membranes at varying transmembrane pressures and Mt concentrations. A reasonable agreement was found between the model predicted behavior and experimentally determined data in terms of CO2 solubility, Mt concentration and aspect ratio were calculated based on average absolute relative error (%AARE). The proposed modified model efficiently predicts the CO2 permeance across MMMs up to 3 wt% Mt loadings and 6 bar pressure with ± 10%AARE.

Ultrapermeable Composite Membranes Enhanced Via Doping with Amorphous MOF Nanosheets.

Thin-film composite (TFC) polymeric membranes have attracted increasing interest to meet the demands of industrial gas separation. However, the development of high-performance TFC membranes within their current configuration faces two key challenges: (i) the thickness-dependent gas permeability of polymeric materials (mainly poly(dimethylsiloxane) (PDMS)) and (ii) the geometric restriction effect due to the limited pore accessibility of the underlying porous substrate. Here we demonstrate that the incorporation of trace amounts (∼1.8 wt %) of amorphous metal–organic framework (MOF) nanosheets into the gutter layer of TFC assemblies can simultaneously address these two limitations by the creation of rapid, transmembrane gas diffusion pathways. The resultant PDMS&MOF membrane displayed excellent CO2 permeance of 10450 GPU and CO2/N2 selectivity of 9.1. Leveraging this strategy, we successfully fabricate a novel TFC membrane, consisting of a PDMS&MOF gutter and an ultrathin (∼54 nm) poly(ethylene glycol) top selective layer via surface-initiated atom transfer radical polymerization. The complete TFC membrane exhibits excellent processability and remarkable CO2/N2 separation performance (1990 GPU with a CO2/N2 ideal selectivity of 39). This study reveals a strategy for the design and fabrication of a new TFC membrane system with unprecedented gas-separation performance.

An ab-initio study of hydrogen trapping energetics at BCC tungsten metal-noble gas interfaces

Density functional theory (DFT) calculations have been performed to assess the trapping and segregation strength of hydrogen (H) to noble gas interfaces in tungsten (W). These calculations consist of a supercell containing a slab of BCC W and an initial lattice of FCC noble gas atoms. The interfaces included noble gases of helium, neon, and argon, with densities in the range of 1-4 atoms-per-vacancy (V), and W surface orientations of (100), (110), and (111). We report on the binding energy of H to these interfaces as well as the modification to the migration barriers in the W slab, which together provide information on the segregation strength and de-trapping energy for H at noble gas bubbles. These calculations indicate that the binding energy of H to W-noble gas interfaces varies with surface orientation and decreases with increasing gas density; whereas the H migration energy is sensitive to the noble gas density, surface orientation, and diffusion pathway, and typically increases with gas density. Together, the de-trapping energy of H to these interfaces is shown to depend less significantly on noble gas density. These DFT calculations provide valuable first-principles energetics necessary for mesoscale models, and provide insight into the temperatures required to de-trap tritium from He bubbles in fusion plasma facing components.

Temperature dependent water transport mechanism in gas diffusion layers revealed by subsecond operando X-ray tomographic microscopy

The product water of polymer electrolyte fuel cells (PEFCs) has to pervade the gas diffusion layer (GDL) and can lead to shortages of educt gas diffusion pathways to the catalyst layer hence to significant performance losses. Here we report on efforts made to enable subsecond and submicron operando X-ray tomographic microscopy (XTM) over a wide range of cell operating temperatures. The short XTM scan times allow to quantify the contributions of capillary-fingering and phase-change-induced flow on the overall water transport inside the cathode GDL at two different cell operating temperatures of 40 °C and 80 °C during a current ramp-up process. The results suggest that phase-change-induced water transport dominates the initial increase of saturation levels at typical automotive PEFC operating temperatures of about 80 °C, whereas capillary-fingering driven transport dominates the development of saturation from the beginning to stagnating stage at 40 °C.

Mild temperature-gas separation performance of graphene oxide membranes for extended period: micropore to meso- and macropore readjustments and the fate of membranes under the influence of dynamic graphene oxide changes

Graphene oxide (GO) constitutes an ideal precursor for the creation of ultra-thin films of highly adaptable pore structure that could serve as microporous and mesoporous membranes in gas separation applications. The GO platform furnishes abundant opportunities for adjusting the gas diffusion pathways of membranes, either through the interlayer galleries and the defects of the basal plane or through the non-interlocked edges of GO stacks. Along with the pore structural adaptability of membranes, primary requirement for a sustainable gas separation process is their stable performance. However, the fate of GO membranes when integrated in a gas separation process at mild temperatures (<140 °C) and for extended periods of several months, was never studied up to date. Hence, the shortage of reports on the output of prolonged experimental campaigns raises significant doubts regarding the applicability of GO membranes. This work focused on this part of missing information, revealing that structural readjustments, which are mostly related with the loss of oxygenated functional groups during prolonged exposure at low to moderate temperatures, have a tremendous impact on the permeability properties. Before water removal all the membranes behaved as impermeable barriers but after their conditioning in high vacuum, they were transformed to effective molecular sieves, exhibiting high separation factors for small gas molecules. Structural changes started at 60 °C and escalated at 90 °C. These are reflected by a 2–3 orders of magnitude enhancement of the permeability factors and a change of the gas diffusion mechanism from microporous to Knudsen and eventually to viscous flow.