Oxygen Transport Research Articles

Morphological and cytochemical characterization of the peripheral blood cells in Paralichthys olivaceus

The flounder (Paralichthys olivaceus) is a highly nutritious, cultured bony fish with a high economic value. The health of the fish is closely related to its blood cells, which are critical for oxygen transport, natural defense, and immunity. The microstructures, classification, counting and size of peripheral blood cells in P. olivaceus were observed and measured by Wright-Giemsa staining, and the cytochemical characteristics of peripheral blood cells were investigated by different cytochemical staining methods including periodic acid-Schiff (PAS), Sudan black B (SBB), acid phosphatase (ACP), alkaline phosphatase (ALP), peroxidase (POX), and α-naphthol acetate esterase (NAE). Besides, the ultrastructures of different cells were detected by the transmission electron microscope. The results showed that erythrocytes, thrombocytes, lymphocytes, monocytes, and neutrophils constituted the peripheral blood cells in P. olivaceus. More heterochromatins were found in erythrocytes, thrombocytes and neutrophils; however, more organelles with fewer heterochromatins were found in monocytes. Endoplasmic reticulums and phagocytic vesicles were abundant in neutrophils. Lymphocytes were the most abundant in leukocytes, followed by monocytes and neutrophils. The cytochemical staining results showed that all leukocytes were positive for SBB. Most of the lymphocytes were positive for PAS, and monocytes were positive for PAS, ACP, and POX. As for neutrophils, ACP and POX were positive. Both monocytes and neutrophils showed positive for SBB, ACP and POX, indicating that the two kinds of cells play a vital role in phagocytosis and bactericidal action. Only lymphocytes were positive for ALP, indicating that they were important in inflammation and immune response. Some characteristics similarities in peripheral blood cells were showed in P. olivaceus just as the other fishes.

The molecular mechanism under the behavioral and physiological changes of large yellow croaker (Larimichthys crocea) in response to hypoxia

The large yellow croaker (Larimichthys crocea) displays pronounced behavioral changes in response to low oxygen environments, including restlessness, constant floating, and increases in respiratory rate and tail beat frequency. However, the underlying molecular mechanisms governing these behavioral and physiological alterations remain unclear. To address this knowledge gap, the present study employed transcriptome analysis to investigate the molecular responses in the large yellow croaker muscle tissue after the fish were exposed to hypoxic treatment. A total of 4553, 1797, 3222, 3148, and 4815 differentially expressed genes (DEGs) were identified at 1 h, 6 h, 9 h, 24 h, and 72 h after hypoxia treatment, respectively. Subsequent analysis utilizing Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichments unveiled a notable up-regulation of genes related to muscular movement-related pathways, specifically the calcium pathway. This up-regulation coincided with an observed increase in the intracellular Ca2+ concentration and Ca2+ transport enzyme activity, suggesting that hypoxia-induced muscle contraction and relaxation occurred by elevating the intracellular Ca2+ concentration within the muscle tissue. Key DEGs associated with the glycolysis and the TCA cycle pathways were also found to be significantly increased in expression, indicating an activation of energy generation pathways in the muscle of hypoxic large yellow croakers. Conversely, genes related to protein synthesis and cell growth were significantly down-regulated, suggesting an inhibition of energy-consuming processes. Additionally, hypoxia was observed to impact various physiological processes such as oxygen transport, vascular control, and apoptosis. These processes may have been mediated by the up-regulation of HIF-1α and its target genes. Consequently, these results offer novel insights into comprehending the molecular basis of the changes in behavior and physiology of large yellow croaker in response to the stress induced by low oxygen levels.

Cerebral microvascular changes in healthy carriers of the APOE-ɛ4 Alzheimer's disease risk gene.

APOE-ɛ4 is a genetic risk factor for Alzheimer's disease (AD). AD is associated with reduced cerebral blood flow (CBF) and with microvascular changes that limit the transport of oxygen from blood into brain tissue: reduced microvascular cerebral blood volume and high relative transit time heterogeneity (RTH). Healthy APOE-ɛ4 carriers reveal brain regions with elevated CBF compared with carriers of the common ɛ3 allele. Such asymptomatic hyperemia may reflect microvascular dysfunction: a vascular disease entity characterized by suboptimal tissue oxygen uptake, rather than limited blood flow per se. Here, we used perfusion MRI to show that elevated regional CBF is accompanied by reduced capillary blood volume in healthy APOE-ɛ4 carriers (carriers) aged 30-70 years compared with similarly aged APOE-ɛ3 carriers (noncarriers). Younger carriers have elevated hippocampal RTH and more extreme RTH values throughout both white matter (WM) and cortical gray matter (GM) compared with noncarriers. Older carriers have reduced WM CBF and more extreme GM RTH values than noncarriers. Across all groups, lower WM and hippocampal RTH correlate with higher educational attainment, which is associated with lower AD risk. Three days of dietary nitrate supplementation increased carriers' WM CBF but caused older carriers to score worse on two of six aggregate neuropsychological scores. The intervention improved late recall in younger carriers and in noncarriers. The APOE-ɛ4 gene is associated with microvascular changes that may impair tissue oxygen extraction. We speculate that vascular risk factor control is particularly important for APOE-ɛ4 carriers' healthy aging.

Modeling oxygen transport in Cr doped UO2 fuel with the TAF-ID during power transients

This paper proposes an efficient coupling between an oxygen redistribution model and the Thermodynamics for Advanced Fuels-International Database (TAF-ID) to describe the behavior of fission products, actinides, and dopant in a uranium dioxide matrix. The formulation of oxygen migration in the fuel is a function of the oxygen (and uranium) chemical potential gradient. The proposed formulation does not require the introduction of the Soret term and relies solely on the known mobilities of uranium and oxygen in the fuel. This coupling is applied to the simulation of a power ramp on a chromia-doped fuel rod using the PLEIADES/ALCYONE fuel performance code. The simulations successfully reproduce most of the available experimental observations on the fission products (Cs, Mo, Ru) and on the chromium dopant.

An inquiry into transport phenomena and artificial intelligence-based optimization of a novel bio-inspired flow field for proton exchange membrane fuel cells

Achieving an effective flow field configuration is requisite to ensure the optimal performance of a proton exchange membrane fuel cell (PEMFC). Herein, an unprecedented bio-inspired flow field is offered to improve species transport and enhance the power density of PEMFCs in order to provide a pathway for effective utilization of them. The flow field consists of two twin parts, resembling the lung structure, and a repeating converging-diverging pattern, so-called “converging-diverging lung-inspired serpentine (CDLIS).” Utilizing multiphase computational fluid dynamics, this study delves into the transport phenomena and evaluates the comprehensive efficacy of a three-dimensional PEMFC. The CDLIS flow field considerably enhances both crosswise and lengthwise mass transfer by inducing several favorable flow mixing phenomena and improving reactant's velocity distribution. The output power of CDLIS exhibits a substantial increase of 10.87%, 43.63%, 12.22%, 12.83%, 12.52%, and 13.8% compared with the simple serpentine, parallel, two-path serpentine, four-path serpentine, lung-inspired serpentine, and combined parallel-serpentine flow fields, respectively. Due to its highly efficient mass transfer capabilities, enhanced convective mass flow, and outstanding current density, CDLIS possesses the most effective water management and the lowermost flooding risk. To further improve the performance of the PEMFC, artificial intelligence codes based on the non-sorting genetic algorithm II (NSGA II) and a surrogate analytical model are developed to optimize the operating conditions of CDLIS at the limiting current density situation where concentration losses impede the mass transfer of reactants. The target parameters for optimization are current density, water saturation (WS), and oxygen transport resistance (OTR). Under optimum conditions, a remarkable current density of 6.35 A cm−2, a low WS of 0.043, and a reduced OTR of 5.06 s m−1 are obtained.

Mechanistic Insights and Genetic Approaches for Enhancing Submergence Tolerance in Rice

Rice, a pivotal staple crop, serves as a dietary foundation for approximately half of the global population. Its cultivation, traditionally reliant on submerged conditions, faces significant challenges due to sudden flooding events. The majority of rice varieties are highly sensitive to prolonged submersion beyond a mere seven days, resulting in substantial yield losses. As global climate patterns shift, the occurrence and intensity of flooding are predictable to increase, exacerbating this issue. Therefore, development of rice varieties having enhanced submergence tolerance is critical to sustaining productivity and ensuring food security in flood-prone regions. Understanding the physiological and biochemical mechanisms underlying submergence tolerance is crucial in this context. Key physiological mechanisms include the regulation of carbohydrate reserves for energy during low oxygen availability, ethylene-responsive factors, especially the Sub1A gene to, regulate growth and stress responses, curbing excessive elongation to conserve energy and enhance survival. Additionally, specialized tissues such as aerenchyma and adventitious roots improve oxygen transport and nutrient uptake under flooded conditions. Genetic approaches, including Marker-Assisted Selection (MAS), have been instrumental in the development of submergence-tolerant rice varieties. The integration of the Sub1 QTL, especially the Sub1A gene, into high-yielding rice varieties has led to significant advancements in breeding submergence-tolerant cultivars. These genetic improvements provide a promising solution to mitigate the detrimental effects of flooding on rice production, ensuring the stability and sustainability of this essential crop in the face of changing climate conditions. This review discusses various mechanisms adapted by rice and genetic advancements aimed at enhancing submergence tolerance in rice to secure food production for future generations.

A Fast Matrix Solver for Linear Boundary-Value Problem in the PEM Fuel Cell Impedance Model

A core physics-based model for PEM fuel cell impedance reduces to the numerical solution of a boundary value problem for two coupled, linear, complex–valued ordinary differential Eqs. with variable coefficients. We report a matrix formulation of a previously developed recurrent method for the fast numerical solution of this problem. This formulation does not require iterations and it utilizes only elementary functions and 4 × 4 matrix products, resulting in one to two orders of magnitude faster code compared to the standard Python boundary–value problem solver. This significantly improves the computational speed of the physics-based impedance model, making it competitive with the popular equivalent circuit modeling approach. The numerical calculation of cell impedance is demonstrated based on the model that includes proton transport in the catalyst layer and oxygen transport in the catalyst and gas-diffusion layers. Least–squares fitting of a real experimental spectrum shows that the matrix solver returns the cell transport parameters 50 times faster than the classic boundary–value problem solver.

Effect of Different Dietary Iron Contents on Liver Transcriptome Characteristics in Wujin Pigs.

Iron is an important trace element that affects the growth and development of animals and regulates oxygen transport, hematopoiesis, and hypoxia adaptations. Wujin pig has unique hypoxic adaptability and iron homeostasis; however, the specific regulatory mechanisms have rarely been reported. This study randomly divided 18 healthy Wujin piglets into three groups: the control group, supplemented with 100 mg/kg iron (as iron glycinate); the low-iron group, no iron supplementation; and the high-iron group, supplemented with 200 mg/kg iron (as iron glycinate). The pre-feeding period was 5 days, and the formal period was 30 days. Serum was collected from empty stomachs before slaughter and at slaughter to detect changes in the serum iron metabolism parameters. Gene expression in the liver was analyzed via transcriptome analysis to determine the effects of low- and high-iron diets on transcriptome levels. Correlation analysis was performed for apparent serum parameters, and transcriptome sequencing was performed using weighted gene co-expression network analysis to reveal the key pathways underlying hypoxia regulation and iron metabolism. The main results are as follows. (1) Except for the hypoxia-inducible factor 1 (HIF-1) content (between the low- and high-iron groups), significant differences were not observed among the serum iron metabolic parameters. The serum HIF-1 content of the low-iron group was significantly higher than that of the high-iron group (p < 0.05). (2) Sequencing analysis of the liver transcriptome revealed 155 differentially expressed genes (DEGs) between the low-iron and control groups, 229 DEGs between the high-iron and control groups, and 279 DEGs between the low- and high-iron groups. Bioinformatics analysis showed that the HIF-1 and transforming growth factor-beta (TGF-β) signaling pathways were the key pathways for hypoxia regulation and iron metabolism. Four genes were selected for qPCR validation, and the results were consistent with the transcriptome sequencing data. In summary, the serum iron metabolism parameter results showed that under the influence of low- and high-iron diets, Wujin piglets maintain a steady state of physiological and biochemical indices via complex metabolic regulation of the body, which reflects their stress resistance and adaptability. The transcriptome results revealed the effects of low-iron and high-iron diets on the gene expression level in the liver and showed that the HIF-1 and TGF-β signaling pathways were key for regulating hypoxia adaptability and iron metabolism homeostasis under low-iron and high-iron diets. Moreover, HIF-1α and HEPC were the key genes. The findings provide a theoretical foundation for exploring the regulatory pathways and characteristics of iron metabolism in Wujin pigs.

Comparison of the In Vitro Iron Bioavailability of Tempeh Made with Tenebrio molitor to Beef and Plant-Based Meat Alternatives.

Iron is an essential mineral that supports biological functions like growth, oxygen transport, cellular function, and hormone synthesis. Insufficient dietary iron can lead to anemia and cause fatigue, cognitive impairment, and poor immune function. Animal-based foods provide heme iron, which is more bioavailable to humans, while plant-based foods typically contain less bioavailable non-heme iron. Edible insects vary in their iron content and may have heme or non-heme forms, depending on their diet. Edible insects have been proposed as a protein source that could address issues of food insecurity and malnutrition in low resource contexts; therefore, it is important to understand the bioavailability of iron from insect-based foods. In this study, we used Inductively Coupled Plasma and Mass Spectrometry (IPC-MS) and Caco-2 cell culture models to compare the soluble and bioavailable iron among five different lab-produced tempeh formulations featuring Tenebrio molitor (mealworm) with their non-fermented raw ingredient combinations. Finally, we compared the iron bioavailability of a mealworm tempeh with two sources of conventional beef (ground beef and sirloin steaks) and two commercially available plant-based meat alternatives. The results show that while plant-based meat alternatives had higher amounts of soluble iron, particularly in the Beyond Burger samples, the fermented mealworm-based tempeh had greater amounts of bioavailable iron than the other samples within the set. While all the samples presented varying degrees of iron bioavailability, all products within the sample set would be considered good sources of dietary iron.

Microscopic insights into the reaction mechanism of Fe-based oxygen carrier with CH4 in chemical-looping combustion

Fe-based oxygen carriers are regarded as a promising class of oxygen carriers in the field of chemical looping combustion. However, the elucidation of the detailed microscopic reaction mechanism of oxygen carriers remains a significant challenge. In this work, we combine in situ spectroscopy, density-functional theory (DFT) calculations, and micro-kinetic modelling to reveal the microscopic reaction mechanism of CH4 combustion on α-Fe2O3. The macroscopic reaction characterization of hematite with CH4 was carried out on a fixed bed, and gas chromatography (GC) was utilized to detect the combustion products (CO2, H2O and H2). Subsequently, in situ spectroscopy and DFT were combined to reveal the detailed pathways for the CH₄ oxidation process. The results indicated that the reaction intermediates evolve from methoxy (CH3O*) to the bridged bidentate formate (b-HCOO*) to the monodentate formate (m-HCOO*), which ultimately leads to the formation of CO2 through a combination of H transfer and lattice oxygen oxidation. A micro-kinetic model was developed which incorporates surface reaction with the oxygen transport. This revealed that CH3O* and CH3O* → CH2OO* are the key intermediates and radical reactions, respectively, for CO2 production. The elucidation of the reaction mechanism may prove beneficial for the future development of novel Fe-based oxygen carriers.

Optimizing oxygen transport properties in Al-substituted La0.5Sr0.5Co0.8Fe0.2-xAlxO3-δ (x = 0–0.20) perovskites

In recent years, there has been a surge in the investigation of perovskite-type complex oxides, with a particular focus on La1-xSrxCo1-yFeyO3, renowned for their exceptional mixed ionic-electronic conducting (MIEC) properties. La0.6Sr0.4Co1-yFeyO3 compositions have prominently emerged in this research domain. The hypothesis of enhancing redox stability and mitigating oxygen variations by incorporating trivalent aluminum (Al3+) into the B-site of perovskite structures has gained attention. In this study, single-phase La0.5Sr0.5Co0.8Fe0.2-xAlxO3-δ (x = 0–0.20) perovskite oxides were synthesized using the solution combustion technique. The physicochemical properties of the synthesized materials were thoroughly characterized, including their morphology, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) analysis, oxygen nonstoichiometry, and electrical transport properties. Results revealed lattice parameter variations associated with oxygen nonstoichiometry and B-site cation size, exhibiting a decline up to x = 0.10 followed by an increase. Al-substitution significantly influenced surface morphology, oxygen nonstoichiometry, and electrical conductivity. Notably, La0.5Sr0.5Co0.8Fe0.1Al0.1O3-δ displayed lower electrical conductivity (676 S cm−1 at 300 °C) among the studied oxides. Oxygen nonstoichiometry had a significant impact on oxygen transport parameters, with these perovskites demonstrating improved chemical diffusion coefficient, Dchem (5.5 × 10-5 cm2 s−1), and the oxygen surface exchange coefficient, Kchem (2.32 × 10-5 cm s−1) at 900 °C, suggesting its potential as an oxygen transport membrane. These findings underscore the promising role of Al-substituted perovskite oxides in various advanced applications.

In vitro osteogenesis of hMSCs on collagen membranes embedded within LEGO®-inspired 3D printed PCL constructs for mandibular bone repair

The field of bone tissue engineering aims to develop an effective and aesthetical bone graft substitute capable of repairing large mandibular defects. However, graft failure resulting from necrosis and insufficient integration with native tissue due to lack of oxygen and nutrient transportation remains a concern. To overcome these drawbacks, this study aims to develop a 3D printed polycaprolactone layered construct with a LEGO®-inspired interlocking mechanism enabling spatial distribution of biological components. To highlight itsin vitroosteogenic potential, human mesenchymal stromal cells are cultured onto Bio-Gide®Compressed collagen (Col) membranes, which are embedded within the layered construct for 28 d. The osteogenic response is assessed through the measurement of proliferation, relevant markers for osteogenesis including alkaline phosphatase (ALP) activity, expression of transcriptional genes (SP7, RUNX2/SOX9) as well matrix-related genes (COL1A1, ALPL IBSP, SPP1), osteoprotegerin secretion.In vitroosteogenic differentiation results showed increased levels of these osteogenic markers, indicating the layered construct's potential to support osteogenesis. In this study, a novel workflow of 3D printing a patient-specific LEGO®-inspired layered construct that can spatially deliver biological elements was successfully demonstrated. These layered constructs have the potential to be employed as a bone tissue engineering strategy, with particular focus on the repair of large mandibular defects.

Influence of Particle Size on Mass Transport during the Oxygen Reduction Reaction at Single Silver Particles Using Scanning Electrochemical Cell Microscopy.

Single entity electrochemical measurements enable insight into the electrocatalytic activity of individual particles based on composition, shape, and crystallographic orientation. In addition to structural effects, particle size can further influence electrocatalytic activity and reaction mechanisms through mass transport effects. In this work, electrodeposition was used to grow well-separated silver particles of varying sizes from 100 to 500 nm in radius. Using a multimicroscopy approach of scanning electrochemical cell microscopy combined with scanning electron microscopy, the electrocatalytic current of individual silver particles toward the oxygen reduction reaction was evaluated as a function of their size. It was found that the current density increased with decreasing particle radius, which was correlated to the mass transport of oxygen to the silver particle, demonstrating the importance of size dependent mass transport effects that can occur at the single particle level using scanning electrochemical cell microscopy and opening new opportunities for quantitative electrocatalysis measurements.

Agglomerate Engineering to Boost PEM Water Electrolyzer Performance

AbstractDensely packed IrOx‐ionomer agglomerates play a crucial role in the high mass transport resistance inside the anode catalyst layer (ACL), which in turn greatly affects the electrolysis performance at high current density. Therefore, agglomerate engineering for PEMWE is proposed in this work to enhance the oxygen transport process inside ACLs. Using self‐assembling nanotechnology, tightly packed primary aggregates are avoided and introduce the interconnected submicron pores and nanocavities into the catalyst‐ionomer agglomerate, confirmed by synchrotron radiation‐based nano‐CT, TEM, and BET. Such agglomerate engineering results in the enhancement of both dissolved oxygen and oxygen bubble transport inside the ACL confirmed by RDE tests and in‐situ bubble visualization. As a result, the mass transport overpotential is significantly reduced from 330 to 30 mV at 5 A cm−2 in PEMWE, optimized Ohmic resistance and catalyst utilization are also observed. Finally, high operating current density is achieved, i.e., 5 A cm−2 @2.04 V with Nafion 115 membrane and 7 A cm−2 @ 2.07 V with Nafion 212 membrane, under a low catalyst loading of 0.72 mgIr cm−2. This study proves the importance and feasibility of agglomerate engineering in further elevating the performance of PEMWE.

Lattice Boltzmann Model Investigation of Simultaneous Imbibition/Evaporation in PEMFC Cathodic Catalyst Layer Using Reconstructed 3D Image Data from Transmission Electron Microscopy

Proton Exchange Membrane Fuel Cells (PEMFCs) are widely used and significant attention is directed towards optimizing of the cathode catalyst layer. The critical focus revolves around refining the multi-phase boundary of the electrically conducting carbon support, the ion-conducting ionomer, the catalyst particles as well as the pore space that can be either occupied by oxygen (feedstock) or water (product). Challenges related to mass transport limitations of oxygen towards these multiple-phase boundaries, also denoted as active sites, persist, especially when liquid water increasingly saturates the pore space (Fig. 1). Furthermore, the evaporated water additionally hinders oxygen transport in the gas phase1,2. This study focuses on the investigation of pore-scale transport mechanisms inside of the cathodic catalyst layer, taking into account the counter-current diffusion of oxygen and water vapor in the gas phase as well as the generation of liquid water that increasingly saturates the void space. For this purpose, a multi-phase and multi-component pore scale Lattice Boltzmann model (LBM), coupled to two-phase reaction, was implemented. The LBM is tailored based on previous works3,4, including the localized generation of water at constant current densities, the imbibition of the pore structure with water counter-currently to the diffusion of oxygen, and the simultaneous evaporation of water. An actual 3D cathode catalyst layer from a commercial membrane electrode assembly, reconstructed from transmission electron microscopy (TEM) image data, was employed. It was imaged using a source voltage of 200kV and a current of 2 nA. The scanned sample had an approximate total volume of 500 × 500 × 100 nm3. From this, a 3D domain of 138 × 138 × 58 nm3 was reconstructed for this study. A 2D cross-section of the reconstructed image is exemplarily shown in Fig. 1. The in-silico study of water and oxygen transport through the catalyst layer elaborates the relationship between the rates of water invasion and evaporation in dependence of current density and catalyst layer structure. The critical conditions for water flooding are evaluated for different process conditions. Fig. 1 Schematic representation of the cathode catalyst layer: The ionomer is represented in white; the carbon for electron connectivity is represented in gray; pore space for oxygen and water transport in yellow; the black circles represent the active sites, i.e., Pt-particles located at the multi-phase boundary of ionomer, carbon and oxygen-filled pores; the red circles represent the inactive sites, that have no connection to ion and/or oxygen transport pathways. References A. Suzuki et al., Int. J. Hydrogen Energy, 36, 2221–2229 (2011) https://www.sciencedirect.com/science/article/pii/S0360319910022913.M. El Hannach, M. Prat, and J. Pauchet, Int. J. Hydrogen Energy, 37, 18996–19006 (2012) https://www.sciencedirect.com/science/article/pii/S0360319912022069.S. Bhaskaran et al., Dry. Technol., 40, 735–747 (2022) https://doi.org/10.1080/07373937.2021.1898417.S. Bhaskaran et al., Int. J. Hydrogen Energy, 47, 31551–31565 (2022) https://www.sciencedirect.com/science/article/pii/S0360319922030932. Figure 1

(Invited) Thermodynamics of Oxygen Transport in Resistive and Electrochemical Memory

Many neuromorphic computing architectures contain emerging memory devices that function through oxygen migration. Examples include resistive memory1 (ReRAM) and electrochemical memory2 (ECRAM), where tuning the distribution of oxygen vacancies enables analog information states. In this presentation, we discuss how oxygen transport in many metal oxides do not obey the drift-diffusion equation, which assumes ideal solution thermodynamics. Instead, the metal oxides undergo composition phase separation into oxygen-rich and oxygen-poor phases. This phase separation explains the long information retention time of ReRAM3. We further use this phase separation to improve the information retention time of oxygen-based ECRAM4,5 by at least ten orders of magnitude, yielding the highest temperature analog nonvolatile memory.

Effect of Membrane Thickness and Operating Conditions on PEMFC Limiting Current Analysis

Hydrogen powered proton exchange membrane fuel cells (PEMFC) have great potentials to replace the traditional internal combustion engines due to its inherent advantages of zero greenhouse gas emissions, better fuel efficiency, quick startup, silent operation, less required maintenance, etc. In a PEMFC, oxygen transport is a critical performance limiting factor because of the sluggish oxygen reduction reaction kinetics. Limiting current method is a well-established in-situ diagnostic tool to measure the oxygen transport resistance in a PEMFC. To obtain accurate oxygen transport resistances, a few key assumptions need to be made including: (1) the effect of temperature gradient in the diffusion media is negligible, (2) no convective flow in the porous media, (3) oxygen is diluted in a gas mixture of nitrogen and water vapor, (4) the total oxygen transport resistance combines gas diffusion layer, microporous layer, and catalyst layer, (5) the effect of membrane thickness has negligible effect, and (6) the anode side does not affect the measurement results due to fast hydrogen oxidation reaction. In this study, we perform a systematic study of the effect of membrane thickness and operating conditions on obtaining robust and reliable limiting current measurement. Standard Nafion membranes of three different thicknesses (25, 50, and 85 µm) are tested with Toray 060 and Freudenberg H23C8 diffusion media. In addition, we further study the interaction between membrane thickness and asymmetric pressure and relative humidity and their effects on limiting current results. Our results show that membrane thickness and relative humidity are critical factors in obtaining reliable oxygen transport resistance due to their effect on overall water balance in the cell. Lastly, the experimental data are compared with the simulation results to establish fundamental understanding. Detailed experimental and analytical results will be presented at the conference.

Optimization of Transport Components and Electrode Interfaces for Low Iridium Oxide Loading PEM Electrolysis

Moving towards lower iridium oxide (IrOx) catalyst loadings for the anode side of polymer electrolyte membrane water electrolyzers (PEMWE) requires tuning of the catalyst layer-porous transport layer (PTL) interface. To see widespread deployment, PEMWE anodes need to lower the loadings from 1-2 mg/cm2 IrOx down to 0.1 mg/cm2 [1]. The catalyst layer can become less uniform and more disconnected at these lower loadings, so the addition and optimization of a microporous layer (MPL) onto the PTL to improve interfacial contact and in-plane connectivity is essential to move toward the more sustainable lower loadings [2]. First, a set of PTLs with MPLs are made such that morphological properties are varied between them. Then, the PTLs with MPLs are combined with anode catalyst layers with IrOx loadings of 0.7, 0.5, 0.3, and 0.1 mg/cm2 to create cells to record polarization curves, stability tests, and catalyst degradation rates. The morphology of the PTLs and MPLs is quantified using X-ray computed tomography (CT). The important morphological characteristics that can be varied and measured with X-ray CT include porosity, pore size distribution, tortuosity, and thickness for each the MPL and base PTL. Using operando X-ray CT and radiography, oxygen transport through the PTL and channel can be observed to provide further information to the performance of the novel PTLs and MPLs. By using a two-dimensional continuum PEMWE model, insights into the effects on the cell performance and the contact resistance present at the MPL-catalyst layer brought about from PTL and MPL morphology alterations can be extracted to help guide the optimization efforts. Through combining these results, an optimal set of manufacturing/morphological parameters can be found to tune PTL and MPL production for the low-loaded catalyst layers that are needed for the future of PEMWEs.

Understanding How Porous Transport Layer Features Affect Proton Exchange Membrane Electrolyzer Performance

PEM Water electrolysis has emerged as a promising technology for the production of green hydrogen. A key component of PEM electrolyzer is the porous transport layer (PTL). The porous transport layer has numerous important roles in water electrolysis. In addition to enabling electrical conduction and water and gas transport, the PTL is necessary for maintaining excellent contact with the cell components. Cell performance is anticipated to be affected by PTL properties such as structure, composition, and thickness.This study delves into the critical contribution of porous transport layer properties to mass transport resistance, activation losses, catalyst layer resistance, and ohmic losses. I will present our experimental framework to deconvolute the impact of PTL properties such as thickness, porosity, and microporous layer on various overpotentials. Voltage loss breakdown analysis was conducted to determine kinetic, ohmic, mass transport, and catalyst layer losses. Theoretical calculations of thermodynamic voltage typically rely on standard reaction potentials adjusted for reactant and product concentrations, operating temperature, and pressure via Nernst corrections. Ohmic voltage, which accounts for contact resistances, bulk resistances, and ohmic losses from the membrane, was determined using high-frequency impedance spectroscopy measurements. To calculate losses from OER kinetics, a Tafel fit is subsequently implemented on the HFR-free voltage. Typically, this process tends to result in residual voltage at elevated current densities, including losses arising from mass transport of water and oxygen, resistance within the catalyst layer, and impacts stemming from ionic impurities. Ionic contamination is omitted from our analysis as a result of the short duration of the experiment.Our detailed analysis reveals that the properties of PTL can have a substantial impact on the performance of the water electrolyzer, which is crucial for enhancing the performance and durability of PEMWE. This study presents a novel framework for forecasting the performance of diverse PTL materials, which may be effectively used to drive the development and optimization of PTL for water electrolyzers. Figure 1

Machine Learning Accelerated Identification of Bifunctional Active Sites in Metal-Organic Framework Derived Metal Oxide Heterostructures for High-Performance Zinc-Air Batteries

The demand for electrochemical energy storage (ESS) systems and their market size has drastically increased in many applications ranging from portable devices through electric vehicles to large-scale grid systems over the past decades. Yet, a more advanced ESS is required due to the safety issues and limited energy density of currently commercialized lithium-ion batteries (LIBs) for wide and matured applications. As a solution to this challenge, zinc-air batteries (ZABs) have gained tremendous attention due to their high energy density, low cost, environmental friendliness, and much lower fire risk characteristics. ZABs utilize oxygen from the atmosphere at their cathode during discharge, where the atmospheric oxygen is reduced to hydroxide via an oxygen reduction reaction (ORR). On the other hand, hydroxide is released as oxygen via oxygen evolution reaction (OER) during charge. The fact that oxygen is drawn directly from the air enables high gravimetric and volumetric energy densities of ZABs compared to those of commercial LIBs. However, the sluggish kinetics of the four-electron transfer steps in ORR and the mass transport of oxygen in OER remain major challenges for the practical application of ZABs. Meanwhile, precious metal-based catalysts such as Pt/C and RuO2 are known to have good catalytic activity towards ORR and OER. However, the integration of different catalysts into the same cathode is very difficult. Additionally, the high cost and natural scarcity of novel metals limit their usage for practical applications.We synthesized a bifunctional CoO/Mn3O4 heterostructure (CMH) OER/ORR electrocatalyst which was derived from metal-organic framework (MOF) for excellent activities in ZABs. The CMH cathode exhibited high ORR and OER performances, as demonstrated by the higher ORR current density than that of the Pt/C catalyst as well as the low OER overpotential exceeding those of the RuO2 catalyst. Remarkably, atomic structures of the CMH were elucidated using global optimization of genetic algorithm integrated with the machine learning force field. By adopting first-principles electronic structure calculations, we further revealed the charge transfer and active sites for both reactions in the identified heterojunction. Furthermore, assembling CMH cathode and Zn metal anode into a ZAB full-cell configuration achieves a ~5.5-fold higher energy density of 879 Wh kg-1 exceeding those of commercial lithium-ion batteries (LIBs), a high-discharge outstanding power density that is 1.39 times higher than novel metal catalysts, and robust cycle stability with negligible voltage decay which is far superior to that of benchmark Pt/C+RuO2 electrocatalysts.