Oxygen Transport Behavior Research Articles

The Effect of Liquid Saturation Transients on PEM Fuel Cell Impedance: Inductive Loop and Instability of Catalyst Layer Operation

We report a physics–based model for the electrochemical impedance of a PEM fuel cell cathode. The model takes into account the transient behavior of oxygen and proton transport in the cathode catalyst layer caused by a variation of the liquid saturation with cell current. Transients of the catalyst layer oxygen diffusivity result in a second capacitive arc in the Nyquist spectrum, while proton conductivity transients lead to the formation of an inductive loop. In the range of capillary pressures in which the liquid saturation in the catalyst layer is independent of the capillary pressures, the loop does not form. A stability analysis of a reduced system of equations reveals that the static limit of inductive loop is unstable with respect to spatial perturbations, implying that the post–oscillatory steady state is unattainable. Possible scenarios of instability development are discussed.

Boosting Bulk Oxygen Transport with Accessible Electrode Nanostructure in Low Pt Loading PEMFCs.

Despite the high potential for reducing carbon emissions and contributing to the future of energy utilization, polymer electrolyte membrane fuel cells (PEMFCs) face challenges such as high costs and sluggish oxygen transport in cathode catalyst layers (CCLs). In this study, the impact of pore size distribution on bulk oxygen transport behavior is exploredby introducing nano calcium carbonate of varying particle sizes for pore-forming. Physicochemical characterizationsfor are employed to examine the electrode structure, while in situ electrochemical measurements are used to scrutinize bulk oxygen transport resistance, effective oxygen diffusivity ( ) and fuel cell performance. Additionally, the CCLs are constructed with aid of Lattice Boltzmann method (LBM) simulations and for CCLs with different pore size distribution are calculated. The findings reveal that initially increases and then decreases as the most probable pore size increases. A "sphere-pipe" model is proposed to describe practical bulk oxygen transport in CCLs, highlighting the significant role of not only the pore size of secondary pores but also the number of primary pores in bulk oxygen transport.

Molecular dynamic simulations of Ti-6Al and Fe-12Cr alloys for their heat transfer and oxygen transport behaviors

The heat transfer and oxygen transport behaviors of Ti-6Al and Fe-12Cr alloys directly affect their aeronautical material application. In order to investigate the flame retardant mechanism in atomic scale, molecular dynamic (MD) simulations were performed to study the heat transfer and oxygen transport performances of Ti-6Al and Fe-12Cr alloys in the linear and uniform heating treatment. Next, the ignition performances of Ti-6Al and Fe-12Cr alloys were further verified by the frictional ignition tests. Therefore, this is a multi-scale research with a novel combination of MD simulations and ignition tests. Those obtained results show that the heat is more concentrated at the heating edge of Ti-6Al alloy while at the same heating rate. This leads to the intensification of atomic motion at the heating edge, and reduces the structural thermal stability of Ti-6Al alloy’s heating edge. Therefore, the heat transfer performance of Fe-12Cr alloy at the same state is better than that of Ti-6Al alloy. When there is an oxide layer on the surface of these two alloys, Fe-12Cr alloy can inhibit the oxygen transfer more effectively than Ti-6Al alloy, and further improve its flame retardant property. In addition, the frictional ignition tests with Ti alloy rotor under the same airflow environment show that the critical airflow velocity of the Fe-12Cr alloy stator is about 114[Formula: see text]m/s higher than that of Ti-6Al-4V alloy stator at 384∘. Generally, according to MD simulations and frictional ignition tests, it could be concluded that the flame retardancy of Fe-12Cr alloy is higher than Ti-6Al alloy.

Simulation of OH– and oxygen transport in the air–cathode catalyst layer of microbial fuel cells

The mass transfer of OH– and oxygen within an air–cathode is critical for the performance of microbial fuel cells (MFCs). Improving the understanding of this complex transportation mechanism could help guide the design of air-cathodes to enhance the power density of MFCs. Herein, a 2D-agglomerate model is developed to study OH– and O2 transfer, and electrochemical performance within an air–cathode MFC. The effects of key variables (binder volume fraction, and Pt/carbon mass ratio) on OH– and oxygen transport behavior have been investigated. Simulation results reveal that the OH– and oxygen concentrations within the catalyst layer are closely related to the catalyst layer structure. A lower volume fraction of Nafion® binder is beneficial to OH– and oxygen transfer, while the Pt/carbon mass ratio has complex effects on OH– and oxygen transfer and reactions. This work aims to improve our understanding of OH– and oxygen mass transfer and offers an effective approach to constructing high-performance air–cathode MFCs.

Insight into Oxygen Transport in Solid and High-Surface-Area Carbon Supports of Proton Exchange Membrane Fuel Cells

Understanding the oxygen transport mechanism through an ionomer film that covered the catalyst surface is essential for reducing local oxygen transport resistance and improving the low Pt-loading proton exchange membrane fuel cell performance. Besides the ionomer material, the carbon supports, upon which ionomers and catalyst particles are dispersed, also play a crucial role in local oxygen transport. Increasing attention has been paid to the effects of carbon supports on local transport, but the detailed mechanism is still unclear. Herein, the local oxygen transports based on conventional solid carbon (SC) and high-surface-area carbon (HSC) supports are investigated by molecular dynamics simulations. It is found that oxygen diffuses through the ionomer film that covered the SC supports via "effective diffusion" and "ineffective diffusion". The former denotes the process by which oxygen diffuses directly from the ionomer surface to the Pt upper surface through small and concentrated regions. In contrast, ineffective diffusion suffers more restrictions by both carbon- and Pt-dense layers, and thus, the oxygen pathways are long and tortuous. The HSC supports exhibit larger transport resistance relative to SC supports due to the existence of micropores. Also, the major transport resistance originates from the carbon-dense layer as it inhibits oxygen from diffusing downward and migrating toward the pore opening, while the oxygen transport inside the pore is facile along the pore's inner surface, which leads to a specific and short diffusion pathway. This work provides insight into oxygen transport behavior with SC and HSC supports, which is the basis for the development of high-performance electrodes with low local transport resistance.

Performance of red mud oxygen carriers in chemical-looping hydrogen production using different components of plastic waste pyrolytic gas

This study proposed plastic waste-fueled Chemical-looping Hydrogen Production (CLHP) based on the concept of three-reactor chemical-looping process for the purposes of sustainable treatment of plastic wastes while producing high purity H2 and separating CO2. Oxygen carrier prepared from red mud wastes (Bauxite residues) was suggested to be circulating materials to improve combustion efficiency and H2 yield. The feasibility of using pelletized oxygen carrier prepared from red mud wastes was experimentally investigated with major components (H2, CH4 and C2H4) of plastics pyrolysis gases as fuels. The red mud oxygen carrier composed of around 38 wt% Fe2O3 and 50 wt% inert materials, and CuO-promoted oxygen carriers composed of 8.0 wt% CuO and 92 wt% red mud wastes were used. The two oxygen carriers were examined by parallel experiments, focusing on the aspects of oxygen transport, stability, hydrogen productivity and carbon deposition. Temperature and different components of plastic pyrolysis gases had significant impacts on oxygen transport behaviors; reduction tests using CH4 or C2H4 fuels suggested that the operation temperature of Fuel Reactor should be higher than 800 °C for deep reduction and high H2 productivity. CuO addition significantly promoted oxygen carrier's reactivity and oxygen transport capacity with various fuel components. The cyclic CLHP experiments, performed over 10 redox cycles with C2H4 as fuels, showed that there was only a limited degradation in oxygen carriers caused by carbon deposition and element migration. The developed oxygen carriers can meet the requirements of long-term operation for CLHP process. Carbon deposition on the oxygen carriers derived from hydrocarbon fuel cracking seemed to be inevitable, which experimentally determined in the range of 0.01–0.043 g g−1 oxygen carriers as C2H4 was used as fuels. However, the reactivity of these carbon deposits was extremely low; their initial steam-gasification temperatures were around 750 °C, much higher than the temperature used for water splitting reaction. This provides the potential opportunities for an industrial CLHP process to produce high purity H2 (>97%) despite of carbon deposits presents in Fuel Reactor.

Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

Exploration of the oxygen transport behavior in non-precious metal catalyst-based cathode catalyst layer for proton exchange membrane fuel cells

Modeling analysis of polymer electrolyte membrane fuel cell with regard to oxygen and charge transport under operating conditions and hydrophobic porous electrode designs

Increasing the power density of polymer electrolyte membrane fuel cells (PEMFCs) is vital for their commercial application but requires detailed knowledge of the charge, oxygen, and water transport mechanisms. In this study, an improved multi-phase non-isothermal PEMFC model coupled with a detailed catalyst-layer (CL) agglomerate model is developed to investigate the performance characteristics under different operating conditions and hydrophobic porous electrode designs. During the parametric analysis, the oxygen and charge transport behaviors on cell performance are analyzed, the contributions of bulk and local oxygen transport to the entire oxygen transport process are revealed, and the corresponding water retention, drainage, and transport are evaluated to clarify the internal mechanisms of oxygen transport and membrane hydration. It is found that an increase in temperature can accelerate the membrane water back diffusion and hence improve the sluggish charge transport. Increasing the relative humidity (RH) enhances the cell performance. The local oxygen and charge transport resistances decrease with an increase in the RH owing to the higher membrane hydration. The presence of microporous layer (MPL) improves the liquid-water retention capacity, deteriorating the bulk oxygen transport due to liquid-water blockage but leading to more rapid local oxygen transport and charge conduction. The optimum performance improvement obtained using an MPL occurs in the moderate cathode humidification scheme (50%). A low-hydrophobicity CL tends to induce a large bulk oxygen transport resistance due to severe water flooding. An optimum hydrophobic electrode design is recommended to realize a tradeoff of oxygen and charge transport, which consist of a super-hydrophobicity gas diffusion layer (contact angle 120°), low-hydrophobicity MPL (contact angle 105°), and middle-hydrophobicity CL (contact angle 95°). • Detailed CL model considering more complex physic and geometry is proposed. • Dominating role of local oxygen, bulk oxygen, and charge transport is revealed. • MPL improves cell performance significantly at middle cathode humidification. • An optimum matching design for hydrophobic porous electrodes is recommended.

New insight into the effect of Co2+ contamination on local oxygen transport in PEMFCs

Pt alloy electrocatalysts (e.g., Pt3Co) for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) have attracted a great deal of interest from worldwide researchers in past decades, due to the excellent ORR activity and cost-effective properties. However, the long period operation would yield sever dissolution of the non-precious metal which effects the ionomer microstructure, thus leading to significantly decreased ORR activity of catalyst and aggravated of the oxygen transport resistance in cathode catalyst layers (CCLs), especially the local oxygen transport resistance caused by the ultrathin ionomer film covering on catalyst surface. Herein, in this paper, the effects of Co2+ contamination on structure of ionomer films and the corresponding local oxygen transport behavior in CCLs are explored via physicochemical characterizations and molecular dynamics (MD) simulations, limiting current method, as well as fuel cell performance measurement. It is found that Co2+ contamination reduces water content and increases the modulus of the ultrathin ionomer film, while reducing the distance between the sulfonic acid groups and increasing the aggregation size of the ionomer, which is related to the volume of hydrophilic domains. Additionally, the electrochemical measurement results demonstrate that as the degree of Co2+ contamination increases from 0 to 85 %, the local oxygen transport resistance increases from 27.74 s cm−1 to 42.43 s cm−1, and the peak power density of fuel cell reduces from 510 mW cm−2 to 453 mW cm−2. The reason behind lies on that contaminated Co2+ tends to connect with sulfonate, then suppress the ionomer mobility and dislocate the local oxygen transport channels.

Food packaging and its oxygen transfer models in active multilayer structures: A theoretical review

Many food products are sensitive to oxygen which can promote rancidity, aerobic microorganism growth, browning, vitamin degradation, flavor loss, and other undesirable reactions. Active packaging concepts have been successfully applied to delay these deteriorative phenomena. In particular, oxygen scavengers help limit O2 ingress into packaging thus extending product shelf-life and thereby reducing food waste. Besides oxygen barrier polymers, other composite materials have been developed to reduce the overall O2 permeability into the package by adding oxygen scavengers or barrier fillers into the packaging structures. Typical thermoplastic food packaging barrier properties are summarized, including commercially available ones, and reported in the patent literature. Furthermore, various mathematical models have been developed to predict the oxygen transport behavior in active packaging to simulate oxygen transport in polymeric and composite materials. Such models are helpful to provide a better understanding of the mass transport fundamentals involved and shorten product development cycle time and cost. This review provides an overview of various oxygen absorber systems used in active food packaging. It also summarizes the mathematical models that simulate oxygen transport and absorption in different polymer films. Finally, these models can be adapted for other polymers and O2 scavengers to simulate O2 transfer on active polymeric materials. Simulation tools help the fundamental understanding of the O2 transport behavior and facilitate to developing novel active packaging systems that extend food shelf-life and enhance their safety.

Migration Kinetics of Surface Ions in Oxygen‐Deficient Perovskite During Topotactic Transitions (Small 51/2021)

Topotactic Transitions In article number 2104356, Lei Cao, Oleg Petracic, and co-workers report the first observation of a novel surface phase in La0.7Sr0.3MnO3-δ epitaxial thin films during the topotactic transition from perovskite to brownmillerite. Given the anisotropic vacancy channels found in the surface phase, the studies not only provide a deeper understanding of oxygen-transport behavior in oxides, but also offer optimal guidance to engineer coordination polyhedra towards desired properties.

(Invited) Investigating Preferential Pathways for Oxygen Removal through Porous Transport Layers of Polymer Electrolyte Water Electrolyzer Using Operando X-Ray CT

Polymer electrolyte water electrolyzer (PEWE) is one of the most appealing options to produce hydrogen and oxygen from renewable resources[1]. Understanding the relationships between porous transport layer (PTL) morphology and oxygen removal is essential to improve the cell performance of PEWE. In order to probe this more fully, operando x-ray computed tomography (CT)[2], machine learning, and LBM simulation[3] were performed on a model electrolyzer at different water flowrates and current densities to determine how these operating conditions alter oxygen transport in the PTLs. X-ray CT was employed to create 3D images (Figure 1A) and visualize oxygen content in the model electrolyzer (Figure 1C and 1D). Machine learning was used to quantify the oxygen content in the electrolyzer geometry, as well as any pathways or patterns the oxygen took as it exited the electrolyzer through the PTL. Computational fluid dynamics (CFD) was used to investigate the characteristics of oxygen transport in the PTL under different operating conditions.Our work has demonstrated new findings in oxygen transport behavior in the PTL. We report a direct observation of oxygen taking preferential pathways through the PTL regardless of the water flowrate or current density (1-4 A/cm2). The spatially periodic oxygen front has been observed in this study for the first time. Oxygen distribution in the PTL had a periodic behavior with period of 400 μm[4]. CFD model was used to predict oxygen distribution in the PTL showing periodic oxygen front. Observed oxygen distribution is due to low in-plane PTL tortuosity and high porosity enabling merging of oxygen bubbles in the middle of the PTL and also due to aerophobicity of the layer. A conceptual schematic showing transport of oxygen in the PTL is shown in Figure 1B. Once the transport pathway through the thickness of the PTL is established, oxygen bubbles will preferentially follow the pathway and no new pathways will be introduced within the current densities range studied here. These findings should be useful in improving mass transport and enhancing our understanding of processes in PEWE.

Analysis and outlook of mass transport in ultralow Pt loading proton exchange membrane fuel cells

<p indent=0mm>Proton exchange membrane fuel cells (PEMFCs) for automotive propulsions have been regarded as an ideal and the most promising alternative to replace fossil-fuel based internal combustion engines due to the high performance, high energy efficiency and zero-emission. However, the high cost has severely impeded the commercialization of PEMFCs, especially the high cost of Pt-based precious metal catalyst used for the cathode oxygen reduction reaction (ORR). It is critical to reducing the amount of Pt and thus decreasing the cost of fuel cell stacks, which would lead to numbers of new challenges. On the one hand, the reduction of Pt load could increase the oxygen transport resistance in cathode catalyst layers (CCLs). In fact, the oxygen transport resistance could be divided into several constituent parts, i.e., oxygen transport resistances in CCLs, gas diffusion layers (GDLs) and the flow channels, where the transport resistance in CCLs is much higher than other resistances. Further, CCLs are constructed as heterogeneous composites of ORR electrocatalysts, conductive polymer such as perfluorinated sulfonic acid (PFSA) ionomer as well as the pore space determined. Hence, the oxygen transport resistance in CCLs includes the bulk transport resistance caused by oxygen diffusion in the nanopore and the local transport resistance caused by oxygen permeation through the ultrathin ionomer film covering on the Pt surface. Local oxygen transport behavior could be divided into three processes: (1) Oxygen adsorption from gas phase into ionomer, (2) oxygen diffusion inside the ionomer, and (3) oxygen adsorption from the ionomer to Pt surfaces. As the Pt loading decreases, local oxygen transport resistance would increase significantly, thus leading to a dramatical performance degradation at high current density of fuel cells. In specific, the oxygen adsorption at gas/ionomer interface used to be considered as Henry’s adsorption. However, it is proved recently that this type of adsorption should be quasi-logarithmic, due to the finiteness of the adsorption site on ionomer surface. In addition, the bulk oxygen transport resistance depends on the porosity and pore size distribution inside the electrodes. We summarized plenty of experimental results of effective oxygen diffusivities reported by different research groups, and found that all the experimental values are obviously smaller than the calculated results based on the classical Bruggeman approximation. It is believed that the effective porosity plays a more important role relative to the geometrical porosity in the estimation of bulk oxygen transport resistance in PEMFCs. On the other hand, confining effect of the ultrathin ionomer film could weaken the separation of hydrophilic and hydrophobic phases and then cut down the pathway of proton migration. There are two proton conduction mechanisms in CCLs: Grotthuss hopping and vehicular mechanism. The proton conduction in CCLs could be affected by numerous factors, such as temperature, ionomer structure, thickness of ionomer film, as well as cation contaminants in the ionomer film. Both high oxygen transport resistance and low proton conduction in ultra-low Pt membrane electrode assemblies would damage the performance and the lifetime of PEMFCs. In this review, the bulk and local transport behavior, proton transport in CCLs, as well as the corresponding influence on fuel cell performance are systematically analyzed, and a series of coping strategies are presented.

Overlayer deposition-induced control of oxide ion concentration in SrFe0.5Co0.5O2.5 oxygen sponges.

Controlling the oxide ion (O2−) concentration in oxides is essential to develop advanced ionic devices, i.e. solid oxide fuel cells, smart windows, memory devices, energy storage devices, and so on. Among many oxides several transition metal (TM)-based perovskite oxides show high oxide ion conductivity, and their physical properties show high sensitivity to the change of the oxide ion concentration. Here, the change in the oxide ion concentration is shown through the overlayer deposition on the SrFe0.5Co0.5O2.5 (SFCO) oxygen sponge film. We grew SFCO films followed by the deposition of two kinds of complex oxide films under exactly the same growth conditions, and observed the changes in the crystal structure, valence states, and magnetic ground states. As the NSMO overlayer grows, strong evidence of oxidation at the O K edge is shown. In addition, the Fe4+ feature is revealed, and the electron valence state of Co increased from 3 to 3.25. The oxide ion concentration of SFCO changes during layer growth due to oxidation or reduction due to differences in chemical potential. The present results might be useful to develop advanced ionic devices using TM-based perovskite oxides.

Cross-dimensional model of the oxygen transport behavior in low-Pt proton exchange membrane fuel cells

Engineering low-Pt membrane electrode assembly without sacrificing performance is essential to accelerate the commercialization of proton exchange membrane fuel cells (PEMFCs). The increased oxygen transport resistance, however, limits the performance improvement in the low-Pt fuel cell. Herein, a cross-dimensional agglomerate model (1-2D model) focusing on oxygen transport behaviors is proposed and developed by coupling a 1-D oxygen transport sub-model with a 2-D two-phase multicomponent PEMFC sub-model. The oxygen dissolution, adsorption and diffusion from gas pore to active sites in cathode catalyst layer (CCL) are considered in the 1-D sub-model. With the aid of the developed 1-2D model, the oxygen transport characteristics under different structural parameters and operation conditions are analyzed. It is found that the oxygen transport resistance in cathode backing layer (CBL-OTR) is larger than the OTR in cathode microporous layer (CMPL-OTR), and both are much higher than the OTR in the gas pores of the CCL (bulk OTR). When changing the structural parameters and operation conditions, the CBL-OTR, CMPL-OTR, and the bulk OTR remain almost unchanged. While, the OTR in the CCL that is caused by the oxygen transport penetrating through ionomer film from water film to active sites (local OTR) is markedly varied. The local OTR possesses a largest contribution to the total OTR, which is more than 50%. When Pt loading goes to 0.1 mg cm−2, the ratios of the CBL-OTR, the CMPL-OTR, the bulk OTR, and the local OTR are respectively 20%, 18%, 7%, and 55%. If reducing Pt loading to 0.05 mg cm−2, the local OTR takes over 72% of the total OTR. Moreover, based on the understanding of oxygen transport behaviors, the PEMFC with an optimized CCL shows a high peak power density, even better than that with a 1.2 mgPt cm−2 original CCL, saving the 91% Pt loading. This work provides a deep insight into oxygen transport behaviors and offers an effective way to construct a high-performance ultra-low-Pt fuel cell.

A-site cation deficiency tuned oxygen transport dynamics of perovskite Pr0.5Ba0.25-xCa0.25CoO3-δ oxide for intermediate temperature solid oxide fuel cells

Abstract Perovskite oxides with ionic and electronic conductivity are the key cathode materials of solid oxide fuel cells. Most of these materials, however, exhibit large cathodic polarization resistance which is mainly determined by their tardy oxygen transport kinetics. Herein, Pr 0.5 Ba 0.25-x Ca 0.25 CoO 3-δ is studied to understand the roles of Ba-deficiency in tuning oxygen transport and electrochemical behaviors in the system. Our findings indicate that Ba-deficiency can significantly accelerate oxygen surface exchange process and bring ∼77% reduction of polarization resistance in this process. It is interesting to note that Ba-deficiency can slightly slow oxygen ion bulk diffusion rate and induce a minor increase of polarization resistance in the corresponding process, which associates with the inhibited oxygen vacancy mobility caused by the interactions between negatively charged Ba vacancy and positively charged oxygen vacancy. These new findings pave a new path for solid oxide fuel cell design and chemical sensor developments.

Oxygen transport behavior and characteristics of nonmetallic inclusions during vacuum electroslag remelting

The oxygen transport behavior and characteristics of nonmetallic inclusions during electroslag remelting (ESR) under vacuum condition were investigated by comparison with ESR under argon atmosphere. The improvement of VSR on oxygen control and refinement of inclusions was further understood. The results show that oxygen content increases from 13 ppm to 24 ppm and 18 ppm after ESR process under argon atmosphere (101325 Pa) and vacuum condition (10000 Pa), respectively. The carbon deoxidization contributes to the smaller oxygen increase when vacuum condition was applied. The complex inclusions with two-layer structure are found after ESR process, and less oxide inclusions are observed in the ingot under vacuum condition. The inclusion amount per mm2 increases after ESR process, but the maximum equivalent diameter of inclusions decreases. Due to the lower oxygen content and faster solidification rate in ESR under vacuum condition, the total area of inclusions per mm2 in the ingot are smallest and the inclusions is much finer and more uniform. The results confirm that ESR under vacuum condition is more beneficial to improve steel cleanliness.

Insight into the Effect of Pore-forming on Oxygen Transport Behavior in Ultra-Low Pt PEMFCs

Although a continuous reduction of Pt loading further lowers the cost of polymer electrolyte membrane fuel cells (PEMFCs), it increases the oxygen transport resistance within cathode catalyst layers (CCLs) and in turn undesirably sacrifices the cell performance. Tailoring the structure of CCLs via pore-forming has been frequently utilized to enhance oxygen transport, however, the mechanism of enhanced oxygen transport has yet not been fully understood. In this work, magnesium oxide is employed to modify the structure of CCLs, and then the local and bulk resistances as well as the oxygen effective diffusivity () are experimentally measured using a dual-layer CCL design. It is found that after pore-forming, the bulk resistance significantly decreases. Since the experimentally tested is two orders of magnitude lower than the calculated value from classical Bruggeman approximation, a modificatory expression of is thus given by defining an effective porosity (εeff). The extremely low εeff (2.14%–3.22%) implies that a highly efficient strategy for ultra-low Pt PEMFCs lies in the design of appropriate electrode structures rather than increasing the porosity blindly.

Tuning MPL Intrusion to Increase Oxygen Transport in Dry and Partially Saturated Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers

Pore network modelling was utilized to simulate oxygen transport behavior and water saturation within stochastically generated gas diffusion layers (GDLs) at various liquid water inlet coverages of the GDL/catalyst layer interface. This study demonstrates that when the GDL is invaded by liquid water through cracks in the microporous layer (MPL), a deeply intruded MPL leads to lower breakthrough saturation for all liquid water inlet coverages ranging from 7% to 80%. Furthermore, a deeply intruded MPL shifts the peak liquid water saturation away from the catalyst layer, reduces the in-plane coverage of water, and reduces the tortuosity of the liquid water pathways. Under dry conditions, the oxygen diffusion coefficient was found to linearly decrease as a function of the MPL intrusion depth into the GDL. Under partially saturated conditions, increasing MPL intrusion depth has a beneficial effect on oxygen transport. The beneficial impact of increasing MPL intrusion depth on oxygen transport increases at higher inlet coverages.

Electronic Origin of Oxygen Transport Behavior in La-Based Perovskites: A Density Functional Theory Study

Understanding the oxygen transport behavior in perovskites is of central importance for tailoring their physical and chemical properties to various practical applications. In this contribution, periodic DFT+U calculations have been performed to unravel the electronic origin of the oxygen mobility difference in La-based perovskites involving 3d-block transition metals from Sc through Cu. Calculated results indicate that the perovskites generally exhibit an increased reducibility on going from LaScO3 to LaCuO3, and the exceptionally high oxygen vacancy formation energy in LaFeO3 is due to the significant lowering of the electron exchange stabilization upon reduction. The oxygen migration barrier in the first four perovskites varies from 1.2 to 2.1 eV while that for the later five materials is much lower and lies between 0.4 and 0.9 eV. Electronic structure analysis indicates this abrupt change in the migration barrier can be attributed to the different degrees of charge redistribution on the central transit...