Gas Transport Pathways Research Articles

Two-Dimensional COF-Three-Dimensional MOF Dual-Layer Membranes with Unprecedentedly High H2/CO2 Selectivity and Ultrahigh Gas Permeabilities.

Composite membranes embodying multilayered architecture have been on an uptrend to tap the synergy between different materials to attain new heights in gas separation performance. In the light of sustainable materials research, covalent organic frameworks (COFs) and metal-organic frameworks (MOFs) have emerged as cutting-edge platforms for molecular-sieving membranes owing to their phenomenal surface areas, ultrahigh porosities, and precise control over chemical functionalities. In this study, we report for the first time a three-dimensional (3D) MOF-mediated strategy where a specially designed MOF film provides the binding sites along the vertical direction to anchor the two-dimensional (2D) COF structural building units. The strong chemical bonding between the 3D MOF and 2D COF provides a new outlook to fabricate 2D COF-based composite membranes. The π-stacked columns of 2D H2P-DHPh COF that can contribute to direct pathways for gas transport render the resulting membrane incredibly promising for high-flux gas separation. Besides, the chemical synergy between the MOF and COF endows the thus-developed H2P-DHPh COF-UiO-66 composite membrane with unprecedented H2/CO2 gas mixture selectivity (32.9) as well as ultrahigh H2 (108 341.3 Barrer) and CO2 permeabilities, which significantly outperform the present Robeson upper bound and polymer membranes hitherto reported.

Efficient CO2 Separation of Multi-Permselective Mixed Matrix Membranes with a Unique Interfacial Structure Regulated by Mesoporous Nanosheets.

A facile strategy to elevate gas separation performances of polymers is to introduce a versatile particle. In this study, the novel F-Ce nanosheets are synthesized, and then F-Ce is functionalized with 1-ethyl-3-methylimidazole thiocyanate (ionic liquids, ILs), obtaining multifunctional f-F-Ce nanosheets by the facile and environment-friendly methods. The multifunctional f-F-Ce nanosheets are incorporated into the Pebax (Pebax 1657) matrix to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The f-F-Ce nanosheets play versatile parts in elevating membrane gas separation performance. On the one hand, f-F-Ce tends to arrange horizontally and constructs a unique interfacial structure for cross-layer CO2 transport in MMMs. On the other hand, the abundant mesopores from f-F-Ce construct high-speed CO2 transport channels in MMMs and notably elevate the gas permeability. Moreover, the as-prepared MMMs separate CO2 efficiently due to the comprehensive improvements of diffusivity selectivity, solubility selectivity, and reactivity selectivity. First, the high aspect ratio of f-F-Ce provides the tortuous pathways for gas transport and generates the rigid interface between the Pebax matrix and f-F-Ce nanosheets, increasing the diffusivity selectivity. Second, SCN- groups from ILs show excellent affinity to CO2, enhancing the solubility selectivity. Third, amine groups from ILs with abundant methylimidazole generate reversible reaction with CO2 to elevate reactivity selectivity. Consequently, the f-F-Ce-doped MMMs display excellent CO2 permeability and CO2/CH4 selectivity. In particular, the MMM incorporated with 8 wt % f-F-Ce displays a CO2 permeability of 1823 Barrer and a CO2/CH4 selectivity of 35, overcoming the Robeson upper bound line (2008).

Effects of salinity on growth, hematological parameters, gill microstructure and transcriptome of fat greenling Hexagrammos otakii

The fat greenling, Hexagrammos otakii, is an emerging aquaculture species and is being evaluated for production in recirculating aquaculture systems (RAS). To better understand the tolerance of H. otakii to varying environmental salinity in actual aquaculture operations, the effects of salinity on survival, growth, hematological parameters, gill microstructure and gill transcriptome were investigated. Juvenile H. otakii (22.0± 1.8 g; 11.2 ± 0.7 cm) were reared at different salinities, 6.7 ± 0.1 PSU (7 PSU), 12.3 ± 0.1 PSU (12 PSU), 18.2 ± 0.1 PSU (18 PSU), 23.9 ± 0.6 PSU (24 PSU), and 28.9 ± 0.8 PSU (29 PSU) in triplicated RASs for five weeks, and the impacts of salinity on these endpoints were evaluated. Fish in the 7 PSU group exhibited significantly lower survival, final weight, feed conversion ratio, and specific growth rate than fish in other treatments. While no statistically significant differences were found among mean white blood cell counts, red blood cell counts and hemoglobin concentrations, mean corpuscular volume was significantly lower in the 7 PSU group than in other groups. At the histological level, there were smaller numbers and smaller volume of mitochondria-rich cells in the 7 PSU group, and the numbers of pavement cells and mucous cells were significantly higher than in other groups. Transcriptome sequencing for a sample of individuals from the 7 PSU, 18 PSU and 29 PSU groups indicated that gene expression in the gills of H. otakii differed significantly among groups. Gene ontology (GO) enrichment showed differential expression between the 7 PSU and 29 PSU groups for seven genes with activities as neurotransmitter transmembrane transporters and neurotransmitter: sodium symporters. Comparing to the 18 PSU group, 16 genes with activities in gas or oxygen transport were down-regulated in the 7 PSU group. No such differences in expression of gas transport genes was found between the 18 PSU and 29 PSU groups. Overall, our exploratory transcriptome analysis suggested that fish in the low-salinity 7 PSU group exhibited high gene expression in the osmoregulation and gas transport pathways. Our results at the histological and gene expression levels suggest why rearing juvenile H. otakii in salinities of 12–29 PSU is optimal for commercial aquaculture production.

Contribution of plant-induced pressurized flow to CH4 emission from a Phragmites fen

The widespread wetland species Phragmites australis (Cav.) Trin. ex Steud. has the ability to transport gases through its stems via a pressurized flow. This results in a high oxygen (O2) transport to the rhizosphere, suppressing methane (CH4) production and stimulating CH4 oxidation. Simultaneously CH4 is transported in the opposite direction to the atmosphere, bypassing the oxic surface layer. This raises the question how this plant-mediated gas transport in Phragmites affects the net CH4 emission. A field experiment was set-up in a Phragmites-dominated fen in Germany, to determine the contribution of all three gas transport pathways (plant-mediated, diffusive and ebullition) during the growth stage of Phragmites from intact vegetation (control), from clipped stems (CR) to exclude the pressurized flow, and from clipped and sealed stems (CSR) to exclude any plant-transport. Clipping resulted in a 60% reduced diffusive + plant-mediated flux (control: 517, CR: 217, CSR: 279 mg CH4 m−2 day−1). Simultaneously, ebullition strongly increased by a factor of 7–13 (control: 10, CR: 71, CSR: 126 mg CH4 m−2 day−1). This increase of ebullition did, however, not compensate for the exclusion of pressurized flow. Total CH4 emission from the control was 2.3 and 1.3 times higher than from CR and CSR respectively, demonstrating the significant role of pressurized gas transport in Phragmites-stands.

The Role of Microfabric and Laminae on Pore Structure and Gas Transport Pathways of Marine Shales from Sichuan Basin, China

This study investigated the effects of microfabric and laminae on the pore structure and gas transport pathways of the Silurian Longmaxi shales from Sichuan Basin. 23 shale samples with varied lithofacies were comprehensively investigated by mineralogy, organic geochemistry, pycnometry, and low-pressure nitrogen adsorption analysis. The fabric and laminae of these samples were identified using petrographic microscope and scanning electron microscopy. Permeabilities were measured using the nonsteady-state method on both perpendicular and parallel to bedding shales. The effective pore diameter controlling gas transport was estimated from gas slippage factors obtained in permeability measurements. These values were also compared to those calculated using the Winland equation. Siliceous shales studied are faintly laminated to nonlaminated and have larger porosity and specific surface area. Argillaceous/siliceous mixed shales are well laminated, whereas argillaceous shales contain many oriented clay flakes along the lamination. Both porosity and surface area are positively correlated with TOC content. Unlike most conventional reservoirs, there is a negative correlation between porosity and permeability values of the samples studied. Permeabilities parallel to bedding, ranging from 0.4 to 76.6 μD, are in control of the oriented clay flakes and silty microlaminae. Permeability anisotropy values of the shales vary between 1.3 and 49.8. Samples rich in oriented clay flakes and microlaminated fabric have relatively larger permeability and permeability anisotropy values. The effective transport pore diameters derived from gas slippage measurements are slightly lower than those calculated from the Winland equation. However, both methods have shown that the effective transport pore diameters of argillaceous shales (averaging 552 nm) are significantly higher than siliceous shales (averaging 198 nm), which underlines the control of microfabric, rather than porosity, on gas transport pathways of the shales studied.

Coal breakage using abrasive liquid nitrogen jet and its implications for coalbed methane recovery

Coalbed methane (CBM) is an important global energy resource. However, reservoir damage and wellbore collapse caused by water and chemical additives invasion are major obstacles that restrict the economic exploitation of CBM. Abrasive liquid nitrogen (LN2) jet assisted-drilling, a non-aqueous technique, is expected to improve drilling efficiency and simultaneously protect formations. To determine its feasibility and the effects of critical parameters, a series of laboratory experiments considering various jetting schemes were conducted. The coal-breakage mechanism was highlighted based on macro and micro analysis. Subsequently, we proposed an innovative CBM stimulation approach referred to as Radial Abrasive LN2 Jet drilling (ALN-RJD) that uses abrasive LN2 jet to drill multiple laterals radiating out from a main borehole. Then, the potential application of this method for CBM recovery enhancement in an economic feasible way was discussed using the numerical simulation and Net Present Value (NPV) method. The results show that the abrasive LN2 jet has superior coal-breakage performance attributed to four coupled effects: high-velocity jet impact, thermal shock, abrasive erosion, and gasification cracking. Moreover, the ALN-RJD can significantly increases the gas production by creating conductive pathways for gas transport in complex lateral-fracture networks. Besides, the economic analysis indicated that ALN-RJD can achieve higher NPV than those of conventional CBM development methods. The key findings of this study are expected to provide a viable alternative for the sustainable development of CBM resources in a profitable and environmentally acceptable manner.

Highly permeable Thermally Rearranged Mixed Matrix Membranes (TR-MMM)

Thermally Rearranged (TR) polymers and Mixed Matrix Membranes (MMMs) are two effective approaches used to advance the performance of gas separation membranes. Conversion of thermally activated groups in TR membranes result in hourglass-shaped cavities and unusually high permselectivity, whereas the inclusion of nanoparticles with engineered pore volume, window size and/or surface chemistry in MMMs can add fast and selective pathways for gas transport. In this study, we explored the effects of combining these two approaches by adding ultra-porous and highly thermostable PAF-1 nanoparticles into the TR-able polymer, 6FDA-HAB5DAM5 (DAM). Gas separation performances of TR-MMMs were evaluated by comparison with the pure polymer and another TR-MMM bearing an already thermally-treated PAF-1 additive (cPAF). While both additives enhanced gas transport, only PAF-1 stabilized the TR conversion reaction and improved the TR-MMM's material properties. Minor variations in cPAF surface changed the TR-MMM interfacial interactions as well as other properties crucial to the application of advanced membrane materials, namely aging, plasticization, and mechanical stability. By combining thermal rearrangement process with PAF-1, TR-MMM demonstrated a 55-fold increase in CO2 gas permeability (37-fold for H2) at similar gas selectivities, but without the handling issues observed for the pure TR polymer membrane.

Numerical prediction of gas migration properties in Callovo‐Oxfordian (COx) argillite using morpho‐mathematical operations

SummaryThe feasibility study of long‐term radioactive waste storage in low‐permeable rocks has been performed by considering various damage and failure scenarios. This study aims at the numerical investigation of gas (mainly produced by corrosion of metallic parts) migration properties through the low‐permeable formation of Callovo‐Oxfordian argillite. Traditional methods, based on macroscopic approaches or homogeneous transport properties, are inappropriate to analyze this issue at the mesoscopic/microscopic scale. In this study, realistic porous space morphologies are constructed through union of excursions of random fields considering different experimental pore size distributions. Afterwards, purely geometric analysis of pore space is conducted by morpho‐mathematical operations for the purpose of the extraction of preferential gas transport pathways and the prediction of the gas entry pressure, the gas breakthrough pressure, and the following imbibition process.

X-ray Computed Tomography Visualization of the Woody Char Intraparticle Pore Structure and Its Role on Anisotropic Evolution during Char Gasification

X-ray computed tomography (CT) was used to visualize the intraparticle structure of woody biomass and its chars. Additionally, the impact of the intraparticle structure on gasification characteristics was investigated. The chars derived from ramin (hardwood) and Japanese cypress (softwood) were gasified under an O2/Ar atmosphere. X-ray CT was used to observe the intraparticle structure. As a result, X-ray CT performed well in visualizing relatively large pores of over 5 μm. The ramin chars had larger pores aligned along the transverse direction in comparison to Japanese cypress chars. The pores aligned along the grain direction were dominant in both chars. Although the gasification rate of both chars was similar, the impact of the anisotropic intraparticle structure originating from the nature of wood manifested in the evolution of the particle shape during gasification controlled by internal diffusion. This was due to large pores acting as gas transport pathways inside the chars. The gasification advanced along the transverse direction in the ramin chars and resulted in the formation of an ellipse shape, although the initial shape was a cylinder. On the contrary, in the Japanese cypress chars, the gasification progressed only along the grain direction and the cylindrical shape was maintained.

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

The Lower Cambrian Niutitang and Lower Silurian Longmaxi shales in the Middle‐Upper Yangtze area are considered the primary shale gas units targeted for development in China. To shed some light on the difference in nanopore structures between Niutitang and Longmaxi shales, systematic comparative investigations were conducted using various techniques, including geochemical analyses, field emission scanning electron microscopy (FE‐SEM), high‐pressure mercury intrusion porosimetry (MIP), and low‐pressure N2/CO2 adsorption techniques. The results show that both Niutitang and Longmaxi shales have high total organic carbon (TOC) content and complex mineral compositions. The porosity of Longmaxi shales is higher than that of Niutitang shales, with an average value of 3.26% and 2.04%, respectively. Interestingly, for both shale formations, the mesopores (2–50 nm) are the major contributors to pore volumes, whereas the specific surface area is dominated by micropores (<2 nm). For the mesopore size distributions (PSDs) calculated from the N2 adsorption, the Longmaxi shales have a dominant pore size ranging from 10 to 60 nm. In contrast, there are more fine mesopores (2–8 nm) in the Niutitang shales. Furthermore, we found that numerous nanoscale pores are well‐developed within graptolite‐derived organic matter (OM) in the Longmaxi shales. These interconnected graptolite periderm pore systems may not only provide a storage space for both adsorbed and free gas but also serve as pathways for gas transport. The Niutitang shales developed relatively fewer OM pores with smaller diameters, lower OM surface porosity, and lower connectivity compared to the Longmaxi shales. The differences in OM pore structure partly explain why there is a large production difference between these two formations.

Improving CO2 separation performance by incorporating MWCNTs@mSiO2 core@shell filler in mixed matrix membranes

To improve CO2 separation performance in mixed matrix membranes (MMMs), a novel mesoporous silica‐coated on the outer surface of multi‐walled carbon nanotube (MWCNTs@mSiO2) core@shell filler was synthesized and dispersed into Pebax MH 1657 (TPE) matrix. The introduced mSiO2 layer on the outer surface of MWCNTs have a favorable effect on the dispersion and compatibility of MWCNTs@mSiO2 core@shell filler in TPE matrix. Most importantly, the pore channels of mesoporous silica and MWCNTs constructed the feasible gas transport pathways for CO2 permeation in MMMs. The MMMs presented the best CO2 separation performance when the content of MWCNTs@mSiO2 in TPE matrix was 10 wt%. The CO2 permeability and CO2/CH4 selectivity of TPE‐MWCNTs@mSiO2‐10 membrane were 379 Barrer and 39 for CO2/CH4 mixed‐gas, respectively. The CO2 permeability and CO2/N2 selectivity of TPE‐MWCNTs@mSiO2‐10 membrane were 364 Barrer and 58 for CO2/N2 mixed‐gas, respectively. POLYM. COMPOS., 39:4486–4495, 2018. © 2017 Society of Plastics Engineers

A simplified parametrised model for lung microstructures capable of mimicking realistic geometrical and mechanical properties

The respiratory zone of mammalian lungs contains several millions of so-called alveoli. The geometrical and mechanical properties of this microstructure are crucial for respiration and influence the macroscopic behaviour of the entire organ in health and disease. Hence, if computational models are sought to gain more insight into lung behaviour, predict lung states in certain scenarios or suggest better treatment options in early stages of respiratory dysfunction, an adequate representation of this microstructure is essential. However, investigating the real alveolar architecture requires complex medical-imaging methods and would be computationally extremely expensive. Even worse, there is currently no way of obtaining the real patient-specific microstructure in vivo. Hence, we present a fast and easy to compute parametrised model of lung microstructures based on tetrakaidecahedra which can represent both geometrical and mechanical properties of the parenchyma. We show that gas transport pathways and stress and strain distributions are comparable to real alveolar microstructures and even capable of capturing variations present in biology. The created parametrised lung microstructure models can be utilized in finite element simulations to study, e.g., alveolar flow phenomena, particle deposition, or alveolar stresses and strains during mechanical ventilation. Due to the simpler geometry of the parametrised microgeometries compared to imaging-based microstructures, remarkable savings in CPU time can be achieved. We show that our model requires a minimum of 10% of the computational time for computing the same strain state in structural mechanics simulations compared to imaging-based alveolar microstructures.

Reversed thermo-switchable molecular sieving membranes composed of two-dimensional metal-organic nanosheets for gas separation

It is highly desirable to reduce the membrane thickness in order to maximize the throughput and break the trade-off limitation for membrane-based gas separation. Two-dimensional membranes composed of atomic-thick graphene or graphene oxide nanosheets have gas transport pathways that are at least three orders of magnitude higher than the membrane thickness, leading to reduced gas permeation flux and impaired separation throughput. Here we present nm-thick molecular sieving membranes composed of porous two-dimensional metal-organic nanosheets. These membranes possess pore openings parallel to gas concentration gradient allowing high gas permeation flux and high selectivity, which are proven by both experiment and molecular dynamics simulation. Furthermore, the gas transport pathways of these membranes exhibit a reversed thermo-switchable feature, which is attributed to the molecular flexibility of the building metal-organic nanosheets.

Change in composition and pore structure of Longmaxi black shale during oxidative dissolution

Owing to the presence of chemically unstable compositions (e.g., clay minerals, carbonate, pyrite, and organic matter (OM)) which are closely related to shale structure failures or dissolution pores, the methods to increase gas well long-term productivity from tight shale matrix need to take into account the chemical interaction of shale with injected fluid. In this study, black shale samples obtained from Lower Silurian Longmaxi formation in Sichuan basin, China were treated with 15wt% hydrogen peroxide (H2O2) for the comprehensive understanding of the change in shale composition and the associated dissolution structures. The measurements of mass loss, total organic carbon content, and mineralogical composition showed that carbonate, reductive inorganic minerals containing ferrous iron (e.g., pyrite and chlorite), and OM in samples exhibited strong dissolution; however, the other minerals behaved in a non-reactive manner at the experimental time scale. After the oxidative treatment for 240h, a large amount of oxidation-induced fractures and dissolution pores were observed by field-emission scanning electron microscopy. The fractures mainly oriented parallel to lamination were attributed to the dissolution of OM and structural alteration of clay minerals. All the dissolution pores seemed to be strongly dependent on the loss of dolomite, pyrite, and OM. Results from high-pressure mercury intrusion and low-pressure nitrogen adsorption analysis showed that these dissolution pores ranging from 10 to 500nm in diameter exhibited a significant increase in pore volume due to the removal of interconnected pore-filling OM, while the volume of pores>1μm in size exhibited a minor increase because the micrometer-size dissolved particles appeared to be discrete or unconnected. Thus the oxidative dissolution could lead to the higher porosity and better connectivity of nanometer-size pore networks in shale samples. The induced fractures reduced the size of diffusion dominant zones in shale matrix, and the dissolution pores increased the size of gas transport pathways into fractures. These results indicate that the injection of H2O2 may play an important role in shale matrix stimulation by oxidative dissolution which is likely to improve matrix diffusivity.

Accelerated Degradation of Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

A gas diffusion layer (GDL) was subjected to accelerated degradation (ageing) via complete submersion in hydrogen peroxide. The impacts of ageing were evaluated through deviations in limiting current densities, oxygen mass transport resistances, and liquid water saturation distributions in the aged GDL compared to pristine materials. For dry (volumetric oxygen concentration of 1%) and partially saturated cathode conditions (volumetric oxygen concentrations of 5%, 10%, and 21%), the fuel cell composed of aged GDLs reached limiting current densities up to 10.3% lower and experienced increases in overall oxygen mass transport resistance of up to 11.5% compared to the pristine GDLs. This performance reduction was attributed to a higher liquid water content in the aged GDL under the flow field channel compared to the pristine GDL. The results suggest that the higher saturation in the channel regions of the aged GDL led to increasingly restrictive gas transport due to the higher average water content and reduced pathways for reactant gas transport, therefore contributing to the reductions in the limiting current. In fuel cell builds with aged and pristine GDLs, up to 13.6 times more liquid water was present in the GDL under the rib compared to that under the channel at limiting current operation.

Enhanced CO2/N2 separation by porous reduced graphene oxide/Pebax mixed matrix membranes

Computational simulations have suggested the enormous potential of using porous graphene-based materials for gas separation. However, this has yet to be demonstrated in a continuous and macroscopic membrane due to the difficulty in membrane fabrication. In this work, we reported a facile process to fabricate the partially porous reduced graphene oxide (PRG) nanosheets from graphene oxide (GO) via a wet chemical process. Then the fabricated PRG was blended into Pebax® 1657 polymer to prepare a mixed matrix gas separation membrane. In order to ensure good dispersion of the PRG nanosheets within the polymeric matrix, the reduction degree of GO should be carefully controlled. In addition, the residual functional groups on the partially reduced nanosheets surface facilitated the formation of highly efficient molecular sieving laminate structures within the mixed matrix membrane: the narrow gas flow galleries (average width of 0.34nm) between the neighbouring nanosheets ensured effective molecular sieving of CO2 against other larger gas molecules, while the mesoscopic pores on the laminate provided rapid gas transport pathways. Finally, the mixed matrix gas separation membrane had substantially improved CO2 permeability as well as CO2/N2 selectivity. This work is the first to report the fabrication of the porous GO-based gas separation membrane, and offers many opportunities to exploit the unique properties of porous GO in the fabrication of various molecular sieving membranes.

On the origin of pronounced O3 gradients in the thunderstorm outflow region during DC3

AbstractUnique in situ measurements of CO, O3, SO2, CH4, NO, NOx, NOy, VOC, CN, and rBC were carried out with the German Deutsches Zentrum für Luft‐ und Raumfahrt (DLR)‐Falcon aircraft in the central U.S. thunderstorms during the Deep Convective Clouds and Chemistry experiment in summer 2012. Fresh and aged anvil outflow (9–12 km) from supercells, mesoscale convective systems, mesoscale convective complexes, and squall lines were probed over Oklahoma, Texas, Colorado, and Kansas. For three case studies (30 May and 8 and 12 June) a combination of trace species, radar, lightning, and satellite information, as well as model results, were used to analyze and design schematics of major trace gas transport pathways within and in the vicinity of the probed thunderstorms. The impact of thunderstorms on the O3 composition in the upper troposphere/lower stratosphere (LS) region was analyzed. Overshooting cloud tops injected high amounts of biomass burning and lightning‐produced NOx emissions into the LS, in addition to low O3 mixing ratios from the lower troposphere. As a dynamical response, O3‐rich air from the LS was transported downward into the anvil and also surrounded the outflow. The ΔO3/ΔCO ratio was determined in the anvil outflow region. A pronounced in‐mixing of O3‐rich stratospheric air masses was observed in the outflow indicated by highly positive or even negative ΔO3/ΔCO ratios (+1.4 down to −3.9). Photochemical O3 production (ΔO3/ΔCO = +0.1) was found to be minor in the recently lofted pollution plumes. O3 mixing ratios within the aged anvil outflow were mainly enhanced due to dynamical processes.

A durable, high-performance hollow-nanofiber cathode for intermediate-temperature fuel cells

Hollow nanofibers of PrBa0.5Sr0.5Co2O5+δ (PBSC), created by an electrospinning process, are assembled into a three dimensional (3D) fibrous porous electrode, providing facile pathways for gas transport and excellent electrical conductivity for efficient charge transfer and, thus, greatly enhancing the rate of oxygen reduction reactions (ORR), as confirmed by the small electrode polarization resistance and low activation energy. A simple geometric modeling suggests that an electrode with longer fibers tends to be more efficient in facilitating mass and charge transfer under the conditions studied. A solid oxide fuel cell based on this 3D fibrous cathode demonstrates a peak power density of 1.11Wcm−2 at 550°C when humidified H2 was used as fuel and ambient air as oxidant. The fibrous architecture also shows excellent stability under the operating conditions. Further and in particular, the high-performance hollow-fiber electrodes are also applicable to other energy storage and conversion systems.

Effect of Electrode Configuration on Nitric Oxide Gas Sensor Behavior.

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%–18% O2 at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity.

Performance of practical-sized membrane-electrode assemblies using titanium nitride-supported platinum catalysts mixed with acetylene black as the cathode catalyst layer

The performance of practical-sized membrane-electrode assemblies (MEAs) using titanium nitride-supported platinum (Pt/TiN) as the cathode catalysts was evaluated with the use of a practical single cell designed for microscale combined heat and power (CHP) applications. The performance can be controlled by adding acetylene black (AB), with the behavior being dominated by the percolation law. The electrical resistance of the MEAs drastically decreased for AB contents greater than 37 vol%. The Pt utilization percentage was close to 100% for Pt/TiN with percolated AB networks. It was also found that the percolated AB networks supplied effective gas transport pathways, which were not flooded by generated water, thus enhancing the oxygen mass transport. The practical-sized MEA using Pt/TiN + 47 vol% AB showed 1.5 times greater mass activity and a comparable performance under a practical operating condition for micro-CHP applications, compared with the MEA using a commercial graphitized carbon black-supported platinum catalyst.