Pore network model of the cathode catalyst layer of proton exchange membrane fuel cells: Analysis of water management and electrical performance

A pore network modeling approach is developed to study multiphase transport phenomena inside a porous structure representative of the Cathode Catalyst Layer (CCL) of Proton Exchange Membrane Fuel Cell. A full coupling between two-phase transport, charge transport and heat transport is considered. The liquid water evaporation is also taken into account. The current density profile and the liquid water distribution and production are investigated to understand the liquid production mechanism inside the CCL. The results suggest that the wettability and the pore size distribution have an important impact on the water management inside the cathode catalyst layer and thus on the performances of the proton exchange membrane fuel cell. Simulations show also that Bruggemann correlation used in classical models does not predict correctly gas diffusion

Long-term monitoring in Central Puget Sound: Are local climate anomalies impacting phytoplankton populations?

Puget Sound is a large and productive estuarine system at the southern end of the Salish Sea. King County’s comprehensive, long-term marine monitoring program tracks water quality in Puget Sound’s Central Basin through year-round collection of data for a suite of physical, chemical and biological parameters. Phytoplankton monitoring began with traditional microscopy methods in 2008, and expanded to include a particle imaging system in 2014. These data are critical to assess how changes from climate, physical conditions and other stressors linked to anthropogenic activity from the region’s growing population may impact the Sound’s biodiversity and trophic structure. Currently, twice-monthly surface water samples from 10 Central Basin locations (Point Wells to East Passage) are analyzed year round by FlowCAM, an imaging particle analyzer operating in the 10–300 µm particle range. Phytoplankton particle size, abundance and biovolume are quantified for sixty taxonomic categories. Additionally, zooplankton composition and abundance data are available at select stations. Given the considerable changes in physical conditions recorded for the Salish Sea in the last several years, such as higher than normal temperatures beginning in late 2014, data analysis has focused on key water column indicators (temperature, salinity, nutrients) and weather/climate patterns as drivers of phytoplankton abundance and community composition. Our data reveal important spatial differences within the Central Basin as well as inter-annual differences in seasonal succession patterns of phytoplankton species. These findings contribute to our understanding of the dynamics of Puget Sound phytoplankton communities in relation to environmental and biological drivers

Use of Flowcam Technology for Phytoplankton Monitoring in Central Puget Sound

The entire Puget Sound region faces challenges from a growing human population and a changing climate that will likely exacerbate already critical threats to the health of the Sound. Recent efforts to restore and protect Puget Sound highlight a need for essential information concerning biodiversity and the seasonal dynamics of its marine inhabitants. The King County Marine and Sediment Assessment Group manages a long-term marine monitoring program designed to assess water quality in the Central Puget Sound Basin. Since 1995, data are collected monthly for physical, chemical, and biological (chlorophyll a) parameters at various locations and depths throughout the Puget Sound Central Basin. The addition in 2008 of a long-term phytoplankton component to this program was deemed critical in order to predict how changes in climate and other regional stressors will impact the Sound’s trophic structure. With the recent acquisition of a FlowCAM system it will be possible to collect a more extensive and robust dataset for Puget Sound phytoplankton monitoring, as well as respond promptly when analysis of harmful algal bloom samples is needed. Emerging technologies, such as FlowCAM, allow for increased automation and standardization in phytoplankton analysis, thus representing a significant advancement over traditional microscopy methods. FlowCAM is an imaging particle analysis system that combines elements of flow cytometry, microscopy, fluorescence detection and sophisticated image analysis for the identification and classification of aquatic microorganisms. Efficient use of this technology for taxonomical work, however, requires a significant and sometimes lengthy development effort by the user, as the software needs to be “trained” to recognize and classify the particles of interest. We have developed a FlowCAM protocol that is able to identify and count approximately 25 Puget Sound phytoplankton taxa or groupings. Our protocol also yields data that are useful descriptors of assemblage composition, such as particle size distribution, total biovolume and the biovolume of chlorophyll-containing cells. We will present FlowCAM validation data and sample statistics obtained for three long-term stations in the Puget Sound central basin. While a light microscope is still necessary for accurate taxonomic identification, most samples can be adequately characterized using our FlowCAM protocol

Simulation et analyse des mécanismes de transfert diphasique dans les Couches Actives des Piles à Combustible PEMFC

Afin de pouvoir utiliser les piles à combustible du type PEMFC dans une application automobile, leur coût doit être diminué et leur durée de vie doit être augmentée. De nombreux résultats montrent que la gestion de l'eau dans les piles PEMFC est essentielle sur ces aspects et qu’une meilleure maitrise contribuera a développer des piles plus performantes. La couche active cathodique (CCL, Cathode Catalyst Layer) est le lieu de production de l'eau ce qui en rend l'optimisation importante pour assurer une bonne gestion de l'eau. Dans ce travail, la méthode réseau de pores a été adaptée pour modéliser le transport diphasique dans la structure poreuse de la CCL. Dans l'état de l'art actuel, le modèle développé est le seul permettant d’analyser l'effet des proprietes locales de la CCL (structure, mouillabilite…) sur les mecanismes de transport diphasique. Cet outil de compréhension constitue également une base pour proposer des améliorations de la CCL afin d'améliorer les performances des piles. Les algorithmes d'invasion développés ont été analysés d'une façon détaillée. Le transport fluidique (gaz et liquide) est couplé avec le transport des charges (électrons et protons) par un modèle de réaction électrochimique. Les mécanismes de capillarité, de diffusion gazeuse et d’evaporation sont integres au modele afin d'avoir une représentation la plus complète possible du fonctionnement de la CCL. La description de la structure poreuse par un réseau de pore régulier, l'algorithme d'invasion de l'eau liquide et le modèle de la diffusion des gaz ont été validés par des comparaisons avec des résultats expérimentaux de la littérature ou spécifiques de ce travail. Le modèle est ensuite exploité pour analyser l'effet des paramètres de la CCL tels que la mouillabilité et la taille des pores sur les performances de la couche active. Les résultats permettent d’analyser de premieres idees de modifications de la CCL pour ameliorer la gestion de l’eau et les performances des PEMFC. ABSTRACT : In order to use PEM fuel cells in an automotive application, their cost must be reduced and their lifetime must be increased. Many results show that water management is a critical issue in PEMFC optimization. The water is produced in the cathode active layer (CCL) which makes the optimization of this component very important to ensure a better water management in the PEMFC. In this work, the pore network method has been adapted to model the two-phase transport in the porous structure of the CCL. Considering the state of the art, this is the only model developed to analyze the effect of local properties of the CCL (structure, wetting ...) on the two-phase transport mechanisms. This model is proposed as a scientific tool to help understanding the fundamentals behind the transport phenomena inside the CCL and also to help in the conception of the future CCL. The liquid invasion algorithms developed in this work were analyzed in details. The fluids transport (gas and liquid) is coupled with the charges transport (electrons and protons) using an electrochemical reaction model. The capillary driven liquid transport, the gas phase diffusion and the evaporation process are all integrated into the model in order to have the most possible complete description of the CCL. The description of the porous structure by a regular network, the liquid invasion algorithm and the gas diffusion model all have been validated by comparisons with experimental results from literature or specific work . The model is then exploited to analyze the effect of parameters such as the CCL wettability and pore size distribution on the performance. The results allow analysis of initial ideas that can help in the conception of the CCL in order to improve the water management and the performances of the PEMFC

Characterization of pore network structure in catalyst layers of polymer electrolyte fuel cells

We model and validate the effect of ionomer content and Pt nanoparticles on nanoporous structure of catalyst layers in polymer electrolyte fuel cells. By employing Pore network modeling technique and analytical solutions, we analyze and reproduce experimental N2-adsorption isotherms of carbon, Pt/ carbon and catalyst layers with various ionomer contents. The porous catalyst layer structures comprise of Ketjen Black carbon, Pt and Nafion ionomer. The experimental pore size distributions obtained by N2- adsorption are used as an input to generate porous media using the pore network approach. Subsequently, the simulated porous structures are used to produce simulated N2-adsorption isotherms, which are then compared to the experimentally measured isotherms. The results show a good agreement in the prediction of the effect of the ionomer content on the microstructure of catalyst layers. Moreover, the analysis of the isotherms confirms the hypothesis of ionomer distribution on the surface of agglomerates as well as the existence of different sorption regimes in primary and secondary pores of fuel cell catalyst layers

Distribution and Abundance of MAAs in 33 Species of Microalgae across 13 Classes

We provide a direct comparison of the distribution and abundance of mycosporine-like amino acids (MAAs) in a diverse range of microalgal cultures (33 species across 13 classes) grown without supplementary ultraviolet radiation (UV). We compare the MAAs in cultures with those present in characterised natural phytoplankton populations from the English Channel. We detected 25 UV absorbing compounds including at least two with multiple absorption maxima. We used LC-MS to provide chemical characterisation of the six most commonly occurring MAAs, namely, palythene, palythine, mycosporine-glycine, palythenic acid, porphyra-334 and shinorine. MAAs were abundant (up to 7 pg MAA cell−1) in 10 species, with more minor and often unknown MAAs in a further 11 cultures. Shinorine was the most frequently occurring and abundant MAA (up to 6.5 pg cell−1) and was present in all but two of the MAA-containing species. The study provides further insight into the diversity and abundance of MAAs important from an ecological perspective and as potential source of natural alternatives to synthetic sunscreens

Anti-photoaging and Photoprotective Compounds Derived from Marine Organisms

Marine organisms form a prominent component of the oceanic population, which significantly contribute in the production of cosmeceutical and pharmaceutical molecules with biologically efficient moieties. In addition to the molecules of various biological activities like anti-bacterial, anti-cancerous, anti-inflammatory and anti-oxidative etc., these organisms also produce potential photoprotective or anti-photoaging agents, which are attracting present day researchers. Continuous exposure to UV irradiation (both UV-A and UV-B) leads to the skin cancer and other photoaging complications, which are typically mediated by the reactive oxygen species (ROS), generated in the oxidative pathways. Many of the anti-oxidative and anti-photoaging compounds have been identified previously, which work efficiently against photodamage of the skin. Recently, marine originated photoprotective or anti-photoaging behavior was observed in the methanol extracts of Corallina pilulifera (CPM). These extracts were found to exert potent antioxidant activity and protective effect on UV-A-induced oxidative stress in human dermal fibroblast (HDF) cells by protecting DNA and also by inhibiting matrix metalloproteinases (MMPs), a key component in photoaging of the skin due to exposure to UV-A. The present review depicts various other photoprotective compounds from algae and other marine sources for further elaborative research and their probable use in cosmeceutical and pharmaceutical industries

Differentiation of haploid and diploid fertilities in Gracilaria chilensis affect ploidy ratio

Background Algal isomorphic biphasic life cycles alternate between free-living diploid (tetrasporophytes) and haploid (dioicious gametophytes) phases and the hypotheses explaining their maintenance are still debated. Classic models state that conditional differentiation between phases is required for the evolutionary stability of biphasic life cycles while other authors proposed that the uneven ploidy abundances observed in the field are explained by their cytological differences in spore production. Results We monitored the state and fate of individuals of the red seaweed Gracilaria chilensis periodically for 3 years in five intertidal pools from two sites with distinct conditions. We tested for differentiation in fecundity and spore survival among the gametophyte males and females (haploids) and the tetrasporophytes (diploids). We tested for the influence of fecundity and spore survival on the observed uneven ploidy abundances in recruits. The probability of a frond becoming fecund was size-dependent, highest for the haploid males and lowest for the haploid females, with the diploids displaying intermediate probabilities. Fecund diploids released more tetraspores than carpospores released by the haploid females. Spore survival depended on ploidy and on the local density of co-habiting adult fronds. An advantage of diploid over haploid germlings was observed at very low and very high adult fronds densities. Conclusions Neither spore production nor spore survival determined the highly variable ploidy ratio within G. chilensis recruits. This result invalidates the hypothesis of natural cytological differences in spore production as the only driver of uneven field ploidy abundances in this species. Diploid spores (carpospores) survived better than haploid spores (tetraspores), especially in locations and time periods that were associated with the occurrence of strong biotic and abiotic stressors. We hypothesise that carpospore survival is higher due to support by their haploid female progenitors passing-on nutrients and chemical compounds improving survival under stressful conditions.AHE was supported by fellowships SFRH/BPD/63703/2009, SFRH/BPD/ 107878/2015 and UID/Multi/04326/2016 of the National Science Foundation FCT of Portugal.info:eu-repo/semantics/publishedVersio