Active Area Research Articles

Concentric circular flow field to improve mass transport in large-scale proton exchange membrane water electrolysis cells

Uniform reactant supply is challenging for high-performance proton exchange membrane water electrolysis (PEMWE) in renewable energy storage. The anode flow-field pattern, anode flow-field orientation, and stoichiometric ratio influence mass transport. In this study, the performances of two flow-field patterns were compared for a single PEMWE cell with an active area of 100 cm2. Straight serpentine was used as the reference model and a concentric circle with an arc shape was designed. In addition, the optimal anode flow field orientation and stoichiometric ratio were determined. The results indicate that the optimal anode flow-field pattern differs depending on the stoichiometric ratio. At low flow rates, mass transfer via diffusion was dominant; therefore, a straight serpentine flow was preferred. In contrast, a concentric circle, which induces a significant differential pressure between adjacent channels, is preferable at a high flow rate. This is because convection is dominant in mass transfer. Maintaining a stoichiometric ratio of 10 or more is recommended during the operation. At a ratio of less than 10, the reactant was depleted at a high current density, and the mass transfer resistance increased. In addition, water is better distributed by gravity and buoyancy when the electrolyte membrane is parallel to the ground, and the anode flow path is above the porous medium. This leads to high PEMWE cell performance.

From Catalyst Ink to PEM Fuel Cell Stack: First Full-Size Screen Printed Catalyst Layers Tested within a Generic Stack

This study presents a comprehensive investigation and research platform to introduce a production process chain from catalyst ink to a generic stack level. Screen printed catalyst layers are upscaled to meet industrial active areas of 283 cm² and decal transferred onto the polymer electrolyte membrane with a roll calender, which process parameters were optimized. Afterwards, the subgaskets and gas diffusion layers were applied, and a short stack has been assembled. For the first time, screen printed catalyst layers have been tested within a short stack of automotive size, showing the same performance as its commercial references. This sets the starting point for a successful manufacturing process and stack testing platform, which is valuable especially for CCM material and component manufacturers as well as the research community.

Performance Characteristics of a Free-Breathing Polymer Electrolyte Fuel Cell with Various Channel Shapes

This study utilized a small free-breathing fuel cell, with an active area of 4 cm2 (2 cm x 2cm), and channel cathodes with various channel shapes, to experimentally investigate the effect of channel structure on cell performance, to numerically analyze the natural convection air flow in channels, and to compare with the results of performance characterisitics. The results indicated that, compared with a conventional cathode separator with four straight channels (with a width of 3 mm, a depth of 3 mm, and a rib width of 2 mm), cell performance was improved by eliminating some of the channel ribs and increasing the opening ratio, up to a point. A separator with 2 mm square ribs rotated by 45° further improved cell performance. However, when the opening ratio exceeded 72% with a straight center rib of 2 mm width, cell performance leveled off. The analysis results revealed that separators with modified channels promoted natural convection.

Spatially Resolved Analysis of the Influence of Three-Dimensional Flow Field Structures on Loss Processes in PEMFCs

This study introduces a novel measurement device and technique to spatially resolve the influence of 3D flow field structures consisting of extended metal meshes on the performance distribution in PEMFCs. The newly designed segmented cell enables not only the measurement of the current distribution but also local electrochemical impedance spectra, subsequently analyzed by the distribution of relaxation times. The 3D flow field structures provide, despite of an increased HFR, an advantage at high current densities. The spatially resolved DRT analysis enabled the identification of polarization processes revealing that the gas diffusion process is greatly reduced compared to a conventional channel-rib design. In particular, the 3D coarse mesh shows promising advantages for application under high current densities. The findings from this study provide valuable insights into the local power and resistance distribution, enabling optimization of the flow field design and improvement of the performance of fuel cells with large active areas.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.

From Catalyst Ink to PEM Fuel Cell Stack: First Full-Size Screen Printed Catalyst Layers Tested within a Generic Stack

This study presents a comprehensive investigation and research platform to introduce a production process chain from catalyst ink to a generic stack level. Screen printed catalyst layers are upscaled to meet industrial active areas of 283 cm² and decal transferred onto the polymer electrolyte membrane with a roll calender, which process parameters were optimized. Afterwards, the subgaskets and gas diffusion layers were applied, and a short stack has been assembled. For the first time, screen printed catalyst layers have been tested within a short stack of automotive size, showing the same performance as its commercial references. This sets the starting point for a successful manufacturing process and stack testing platform, which is valuable especially for CCM material and component manufacturers as well as the research community.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.

Asymptomatic Carotid Artery Stenosis, Cognitive Function, and the Impact of Carotid Revascularization: A Narrative Review

ObjectivesThe association between asymptomatic carotid artery stenosis and impaired cognition, and the cognitive changes after revascularization remain active areas of interest in the field of carotid disease. This narrative review focuses on the association between carotid artery atherosclerosis and impaired cognitive function, proposed mechanisms, and the effects of carotid revascularization on cognition. MethodsA critical review of the literature to identify studies evaluating carotid artery stenosis, cognition, and carotid revascularization was performed using PubMed to query the MEDLINE database through March 2023. ResultsMany studies demonstrate a link between carotid disease and cognitive impairment but direct evidence is lacking. Revascularization may offer cognitive benefits but the effect is likely subtle and affected by the choice of revascularization procedure. ConclusionsIntegrating cognitive outcomes into ongoing randomized controlled trials such as the nested CREST-H arm of the CREST-2 trial hold promise for offering new insight into the role of carotid artery stenosis and carotid revascularization on cognition.

Spatially Resolved Analysis of the Influence of Three-Dimensional Flow Field Structures on Loss Processes in PEMFCs

This study introduces a novel measurement device and technique to spatially resolve the influence of 3D flow field structures consisting of extended metal meshes on the performance distribution in PEMFCs. The newly designed segmented cell enables not only the measurement of the current distribution but also local electrochemical impedance spectra, subsequently analyzed by the distribution of relaxation times. The 3D flow field structures provide, despite of an increased HFR, an advantage at high current densities. The spatially resolved DRT analysis enabled the identification of polarization processes revealing that the gas diffusion process is greatly reduced compared to a conventional channel-rib design. In particular, the 3D coarse mesh shows promising advantages for application under high current densities. The findings from this study provide valuable insights into the local power and resistance distribution, enabling optimization of the flow field design and improvement of the performance of fuel cells with large active areas.

Fabrication of a graphene@Ni foam-supported silver nanoplates-PANI 3D architecture electrode for enzyme-free glucose sensing.

Reliable and cost-effective glucose sensors are in rising demand among diabetes patients. The combination of metals and conducting polymers creates a robust electrocatalyst for glucose oxidation, offering enzyme-free, high stability, and sensitivity with outstanding electrochemical results. Herein, graphene is grown on nickel foam by chemical vapor deposition to make a graphene@nickel foam scaffold (G@NF), on which silver nanoplates-polyaniline (Ag-PANI) 3D architecture is developed by sonication-assisted co-electrodeposition. The resulting binder-free 3D Ag-PANI/G@NF electrode was highly porous, as characterized by x-ray photoelectron spectroscopy, Field emission scanning electron microscope, x-ray diffractometer, FTIR, and Raman spectroscopy. The binder-free 3D Ag-PANI/G@NF electrode exhibits remarkable electrochemical efficiency with a superior electrochemical active surface area. The amperometric analysis provides excellent anti-interference performance, a low limit of deduction (0.1 nM), robust sensitivity (1.7 × 1013µA mM-1cm-2), and a good response time. Moreover, the Ag-PANI/G@NF enzyme-free sensor is utilized to observe glucose levels in human blood serums and exhibits excellent potential to become a reliable clinical glucose sensor.

Achieving high capacity by controlling the size of Fe/Co-N-C(t) in the cathode of lithium-oxygen batteries

Two samples are synthesized in a bimetallic system of iron and cobalt using a Metal-Organic Framework (MOF). The duration of precursor addition to the reaction vessel is controlled to synthesize Fe/Co-N-C(10 h) and Fe/Co-N-C(At once). The structural properties of the samples are analyzed using XRD, Raman, FT-IR, SEM, TEM, BET, TGA and ICP. Electrochemical tests are performed to evaluate the activity of the prepared catalysts as lithium-oxygen battery cathode materials. The Fe/Co-N-C(At once) sample, with its larger surface area, shows a greater discharge capacity of 8670 mAhg-1 compared to the Fe/Co-N-C(10 h) sample, which has a discharge capacity of 8339 mAhg-1. However, the Fe/Co-N-C(10 h) sample has a larger electrochemical active surface area due to the presence of more metals in the MOF shell. This results in higher ORR/OER activity in an alkaline environment and greater stability (180 h) as a lithium-oxygen battery cathode compared to the Fe/Co-N-C(At once) sample, which exhibits stability for 90 h.

Shaking table simulation of soft sediment deformation structures in lacustrine sediments

Soft sediment deformation structures (SSDSs) in lacustrine sediments could record paleoearthquakes in tectonically active areas. However, their interpretations of deformation and triggering mechanisms still exist disagreement due to the lack of understanding of natural formation processes of SSDSs. In this study, two large shaking table experiments of saturated lacustrine sedimentary sequences, including Model 1 (simple stratigraphic system of thick silty-clay and sand layer) and Model 2 (stratigraphic systems of thin silty-clay and sand alternating layers) were carried out at the different peak ground accelerations (PGA) in order to simulate the earthquake-triggered SSDSs on the basis of field investigation in Tashkorgan of western China. The results showed that there were no SSDSs formed at the PGA 0.125g, and the excess pore-water pressure ratio (γμ) measured in the sand layer was lower than 0.1; sand volcanos, pipes and sand veins were formed at the PGA 0.25g, and the γμ value of the sand layer reached about 0.2 with the maximum liquefied depths of nearly 30 cm, indicating that weak liquefaction occurred in the sand layer; sand volcanos, pipes, sand veins, diapirs, load and flame structures, ball-and-pillow structures, silty-clay deformation structures were formed at the PGA 0.5g and 0.8g, and the γμ value of sand layer reached about 0.91 and 0.94 with the maximum liquefied depths of nearly 60 cm and 100 cm, respectively. The γμ value of silty-clay layers measured in all the tests was lower than 0.1, indicating that little liquefaction but thixotropy happened in the silty-clay layers. The tests showed that liquefied SSDSs could form at the PGA 0.25g, while thixotropic and gravity-driven SSDSs could form until the PGA reached 0.5g. This study also provided insights for a single or closely spaced shaking events being responsible of superposed deformed beds. The simulated SSDSs have striking resemblance to that of ones identified in the field, supporting the earthquake triggering of SSDSs in the Tashkorgan area.

Terahertz conductivity mapping of thin films on smart textiles

Smart textiles that promise to become sensors and actuators for multiple applications are an active area of research. Conductive textiles formed by coating a fabric with a conductive film will play a key role in such applications. Here we present contactless mapping of the terahertz (THz) conductivity of thin conductive films deposited on textiles. These conductivity maps enable non-destructive assessment of the conductivity of such layers and therefore the identification and localization of non-uniformities in local conductivity. The THz measurements are quantitatively consistent with four-point probe measurements of the same areas.

Structure and properties of the cellulose fibres spun from imidazolium-based carboxylate functionalized zwitterionic liquid

Dissolution of cellulose without further derivatization has been an active area of research in recent years. There are still challenges in developing a commercially viable solvent system for the dissolution and regeneration of cellulose as films and fibres. We report here a process for making cellulose fibres through the dry-jet wet spinning method by utilizing aqueous zwitterionic liquid (ZIL), viz., (6-(1-(2-methoxyethyl) imidazol-3-io)-hexanoate), in which oxyethylene substituted imidazolium-based cation and a carboxylate anion is covalently tethered. Our results suggest that 11 % ZIL dope could be successfully prepared and spun under industrially viable process conditions. The resultant fibres have properties comparable to that of commercial-grade Lyocell fibres. Particularly, the cellulose fibres spun from a cellulose ZIL solution exhibited a denier of 1.2–1.6, a tenacity of 3.5–4.0 g per denier (gpd), and an elongation at break of 8–10 %, which is comparable to cellulose fibres produced using ionic liquid and N-methyl-morpholine-N-oxide (NMMO) solvent. Cellulose fibres obtained from zwitterionic liquid have a crystallinity of 60 %, which is comparable to Lyocell fibres. To the best of our knowledge, this is the first report to demonstrate the successful spinning of regenerated cellulose fibres using zwitterionic liquids with mechanical properties comparable to commercial Lyocell fibres.

Renewable Diesel Production over Mo-Ni Catalysts Supported on Silica

Nickel catalysts promoted with Mo and supported on silica were studied for renewable diesel production from triglyceride biomass, through the selective deoxygenation process. The catalysts were prepared by wet co-impregnation of the SiO2 with different Ni/(Ni + Mo) atomic ratios (0/0.84/0.91/0.95/0.98/1) and a total metal content equal to 50%. They were characterized by XRD, XPS, N2 physisorption, H2-TPR, and NH3-TPD. Evaluation of the catalysts for the transformation of sunflower oil to renewable (green) diesel took place in a high-pressure semi-batch reactor, under solvent-free conditions. A very small addition of Mo, namely the synergistic Ni/(Ni + Mo) atomic ratio equal to 0.95, proved to be the optimum one for a significant enhancement of the catalytic performance of the metallic Ni/SiO2 catalyst, achieving 98 wt.% renewable diesel production. This promoting action of Mo has been attributed to the significant increase of the metallic Ni active phase surface area, the suitable regulation of surface acidity, the acceleration of the hydro-deoxygenation pathway (HDO), the creation of surface oxygen vacancies, and the diminution of coke formation provoked by Mo addition.

Stretchable Sweat Lactate Sensor with Dual-Signal Read-Outs.

Innovations in wearable sweat sensors hold great promise to provide deeper insights into molecular level health information non-invasively. Lactate, a key metabolite present in sweat, holds immense significance in assessing physiological conditions and performance in sports physiology and health sensing. This paper presents the development and characterization of stretchable electrodes with ultrahigh active surface area of 648 % for lactate sensing. The as-printed stretchable electrodes were functionalized with an electron transfer layer comprising Toluidine Blue O and multi-walled carbon nanotubes (MWCNTs), and an enzymatic layer consisting of lactate dehydrogenase with β-Nicotinamide adenine dinucleotide as the cofactor for lactate selectivity. This sensor achieves a dual-signal read-out in which both electrochemical and fluorescence signals were obtained during lactate detection, demonstrating promising sensor performance in terms of sensitivity and reliability. We demonstrate the robustness of the dual-signal sensor under simulated conditions of physical deformation and shifted excitation. Under these compromised conditions, the performance of the stretchable electrodes remained largely unaffected, showcasing their potential for robust and adaptable sensing platforms in wearable health monitoring applications.

Multi‐Scale Simulation of Reverse‐Bias Breakdown in All‐Perovskite Tandem Photovoltaic Modules under Partial Shading Conditions

Herein, a multi‐scale simulation approach to quantify the impact of nonuniformities in cell‐level performance on the photovoltaic characteristics of monolithically interconnected large‐area all‐perovskite tandem modules under partial shading conditions is presented, addressing a crucial aspect of the up‐scaling challenge for this promising photovoltaic technology. To this end, current–voltage characteristics of small‐area all‐perovskite tandem solar cells are obtained for dark and illuminated cases from a calibrated optoelectronic device model using drift–diffusion simulation coupled to a quantum transport formalism for the band‐to‐band tunneling underlying the Zener breakdown. These current–voltage curves are computed for varying density of mobile ions and subsequently used as local 1D coupling laws connecting the 2D electrodes in a quasi‐3D large‐area finite‐element simulation approach that then provides the module characteristics under consideration of spatial variation in active area quality related to mobile ion density. The simulation reveals the appearance of localized current hot spots for the case where the shaded cell is strongly reverse biased.

Building a General Algorithm for Seismic Hazard Analysis in the Sunda Arc through Geodynamic Simulations

Abstract Because of its well-documented subduction zone and outer island arc, Sumatra provides a unique setting for studying and forecasting earthquakes within the seismically active Sunda Arc. This study builds on previous research that utilized Global Positioning System data and the Akaike information criterion to analyze probabilistic seismic hazard functions. However, this study replaces surface displacement rate data with a forward model derived from previous fault modeling results to create a more broadly applicable earthquake forecasting algorithm. Although the best-fit model patterns generated by this new algorithm are consistent with past studies, the forward model demonstrates a lower degree of fit compared to models utilizing natural surface displacement data. This discrepancy highlights the need to refine the fault parameter models to estimate surface displacement rates. Despite this limitation, the study makes a valuable contribution by developing a general algorithm applicable to other subduction zones within the Sunda Arc region. With further refinement and incorporation of more accurate fault modeling and data, this algorithm has the potential to formulate the best-fit earthquake spatial forecast models. This approach could be applied to other seismically active areas, particularly those near subduction zones.

Lifetime evaluation and material failure analysis of a PEMFC prepared using commercial materials

ABSTRACT Hydrogen fuel cells are vital for green energy to replace traditional energy. However, their lifetime is an important factor limiting their development. In this study, commercial materials were used to prepare proton exchange membrane fuel cells (PEMFCs), and pure oxygen was used as the cathode gas to accelerate their lifetime evaluation. The components of the membrane electrode assembly were characterized, and significant thinning was observed in the local proton exchange membrane (PEM). Therefore, the uniformity of the internal conditions of the fuel cell is the key to ensure a long lifetime. The hydrophilicity of the gas diffusion layers increased as the carbon disorder increased via the adsorption of hydrophilic chain segments produced by PEM degradation. The growth of platinum particles in the catalyst layer reduced the electrochemical active area of the catalyst, but the reduction rate slowed and then stabilized. This study of the lifetime of PEMFCs and changing properties of commercial materials clarifies the existing problems of fuel cells and contributes to the development of long-life fuel cells.

Computational Analysis of a Novel Iterative Scheme with an Application

The computational study of fixed-point problems in distance spaces is an active and important research area. The purpose of this paper is to construct a new iterative scheme in the setting of Banach space for approximating solutions of fixed-point problems. We first prove the strong convergence of the scheme for a general class of contractions under some appropriate assumptions on the domain and a parameter involved in our scheme. We then study the qualitative aspects of our scheme, such as the stability and order of convergence for the scheme. Some nonlinear problems are then considered and solved numerically by our new iterative scheme. The numerical simulations and graphical visualizations prove the high accuracy and stability of the new fixed-point scheme. Eventually, we solve a 2D nonlinear Volterra Integral Equation (VIE) via the application of our main outcome. Our results improve many related results in fixed-point iteration theory.