Water Mass Transport Research Articles

Thermal Imprints of Mesoscale Eddies in the Global Ocean

Abstract Mesoscale eddies have been widely documented for their significant role in regulating oceanic heat absorption and redistribution. However, our understanding of their thermal impacts on a global scale has been hampered by the scarcity of eddy-targeted observations. Here, we perform a comprehensive global analysis of over 2 million historical hydrographic profile measurements collocated with satellite-based eddy observations between 1993 and 2019, revealing rich geographical variability in the intensity, vertical extent, and asymmetry of the temperature anomalies induced by eddies. In tropical and subtropical oceans, temperature anomalies within eddies are dominated by eddy pumping and heavily influenced by near-surface vertical stratification, resulting in a relatively shallow extent of eddy effects (around 500 m) with subsurface maximum temperature anomalies occurring near 100 m. In midlatitude main current systems with sharp horizontal temperature gradients, the impact of eddy trapping becomes evident, leading to temperature anomalies extending to depths of 1000 m, with vertical peak values exceeding 4°C between 300 and 700 m, equivalent to perturbations in the local mean-state temperature of nearly 30%. This process also results in substantial temperature anomalies on isopycnal surfaces, indicating notable cross-frontal transport of heat and water mass with varying properties. The estimated meridional heat transport by eddy movement is on the order of O(1) MW, generally one order of magnitude smaller than previous estimates of the time-varying meridional heat transport (). However, this does not imply that they are unimportant, as this long-range cross-frontal heat transport may have significant consequences on regional temperature extremes and biogeochemical environments. Significance Statement Mesoscale eddies with a horizontal scale of O(100) km play a crucial role in modulating oceanic heat absorption and redistribution. However, their activities vary significantly across the global ocean, and our understanding of their thermal impacts remains incomplete. In this study, we conduct a global analysis of the influence of eddies on ocean temperature using over 2 million historical in situ temperature and salinity profile measurements combined with satellite-based eddy observations. Our analysis reveals substantial regional variability in the intensity, vertical extent, and asymmetry of temperature anomalies within eddies of different polarities and discusses the underlying mechanisms. Additionally, we estimate the meridional heat transport caused by eddy movement within each 2° × 2° grid, providing insights into the efficient pathways for eddy heat transport in western boundary currents and their extensions. These results enhance our understanding of the global-scale thermal impact of eddies and provide valuable references for assessing their biogeochemical and ecological consequences.

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

On the Layered Structure and Seasonal Variation of the Water Exchanges in the Sulawesi Sea Areas As Well As the Associated Dynamics

AbstractThe layered structure and seasonal variation of the water exchanges in the Sulawesi Sea areas, as well as the corresponding dynamics, are investigated using HYCOM data. A net inward water mass transport is identified in the upper and intermediate layers in the Sulawesi Sea and it is compensated by the net outward transport in the deep layer. As an important source of this net inward transport, the southward flow through the Sibutu Passage (denoted hereafter as Sibutu Flow) reaches 5.06 Sv in winter, accounting for ∼43% of the net inflow. However, it decreases substantially to 1.79 Sv in summer, accounting for only 12% of the inflow. Further analysis reveals that this Sibutu Flow modulates the seasonal variation of the corresponding outward flow at the Makassar Strait, the major exit of the water mass in the Sulawesi Sea. In winter, the enhancement of the Sibutu Flow associated with the greater intrusion of Kuroshio water into the Luzon Strait produces a stronger eastward pressure gradient force, suppressing the surface intrusion of the Mindanao Current. Conversely, this pressure gradient force weakens and shifts westward in summer, permitting a larger water intrusion from the eastern section. Given that the outward Makassar Flow is the main passage of the Indonesian Throughflow (ITF), our study highlights the essential role of the Sibutu Flow in modulating seasonal variabilities of the ITF via the Makassar Strait and, thus, the transfer of water masses and heat content between the Pacific and Indian Oceans.

Internal Waves Force Elevated Turbulent Mixing at Barkley Canyon

AbstractSubmarine canyons are hot spots for topography‐internal wave interactions, with elevated mixing contributing to regional water mass transport and productivity. Two velocity time series compare and contrast internal waves deep inside Barkley Canyon to a nearby site on the shelf‐break slope of the Vancouver Island Continental Shelf. Elevation of internal wave energy occurs near topography, up to a factor of 10 above the slope and 100 in the canyon. All frequency bands display strong seasonal variability but weak interannual variability. Diurnal (K1) energy is sub‐inertial, trapped along topography, and forced locally through barotropic motions. Both sites have high near‐inertial (NI) energy linked to wind events, though fewer events are observed deep inside the canyon. At the slope site, near‐inertial energy is attenuated with depth, while in the canyon it is amplified near the bottom. Freely propagating semidiurnal (M2) energy appears focused near critical shelf‐break and canyon floor topography, due to local and remote baroclinic forcing. The high‐frequency internal wave continuum has enhanced near‐bottom energy at both sites (up to 7 × the Garrett‐Munk spectrum), and inferred dissipation rates, ɛ, reaching 10−7 W kg−1 near topography. Dissipation is most strongly correlated with semidiurnal energy variability at both sites, with secondary contributors that are site dependent. Forcing power law fits are on the slope, and NI0.2 in the canyon. There is also a build‐up of “shoulder” energy (PSh) near the buoyancy frequency, with a power law fit to dissipation of PSh ∼ ɛ0.3 at both sites.

Tracing Sediment‐Affected Water Masses From Coastal Areas to Offshore Oceans Using In Situ Sensing of Fluorescent Organic Matter

AbstractThe lateral transport of nutrient‐rich water masses from coastal areas to offshore areas is an important factor controlling the primary production of phytoplankton in offshore regions. If the coastal low‐salinity waters have high nutrient levels, lateral transport can be traced via salinity observations. However, if high level of nutrients in the waters are not coupled with low salinity, for example, input from coastal sediments, water transport cannot be traced via salinity observations. In this study, visible fluorescent organic matter (FOMvis) was monitored by an in situ sensor as a tracer for sediment‐affected water masses from coastal areas. The FOMvis distribution in the upper 500 m water layer in offshore Japan along the 143°E transect was generally controlled by the distributions of subtropical water (i.e., Kuroshio water and Tsugaru warm current water) and subarctic water (i.e., Oyashio water). However, anomalously high levels of FOMvis were observed at depths of 20–60 m at an observational station, which could not be explained by physical mixing. This likely originated from the lateral transport of water masses from coastal areas. In and around Sendai Bay, where observations were carried out as an example of the Japanese coast, high levels of FOMvis were observed, accompanied by negative N*, an indicator of denitrification, and phosphate and silicic acid inputs from anoxic sediments. These observational results imply that FOMvis observation via in situ sensors can be useful for tracing the input of nutrient‐rich sediment‐affected water masses from coastal areas to offshore oceans.

Variability of Indonesian Throughflow Transport in the Indonesian Seas during Triple-Dip La Niña

Abstract The Indonesian seas serve as an important conduit for the Indonesian Throughflow (ITF), a critical system of warm water and freshwater transport connecting the Pacific and Indian Oceans. El Niño-Southern Oscillation (ENSO) significantly impacts the regional variability in the Pacific and exerts a profound influence on water mass transport from the Pacific to the Indian Oceans. This study focuses on the influence of triple-dip La Niña events during two distinct periods (1998 – 2001 and 2020 – 2023) on the variability of ITF transport in key areas of the Indonesian seas, including the Makassar, Lombok, and Ombai Straits, Flores and Banda Seas, and Timor Passage. Using forecast and reanalysis data from the Copernicus Marine Environment Monitoring Service (CMEMS), transport calculations are conducted across cross-sectional profiles representing the study areas. The results reveal that the volume transport is significantly higher at depths ranging from ∼50 – 300 m. It also shows seasonal fluctuations in volume transport across all regions, with lower transport during winter (DJF) and higher transport during summer (JJA) and transition period (SON) in the Makassar and Lombok Straits. In the Flores and Banda Seas, Ombai Strait, and Timor Passage, the surface volume transport follows seasonal patterns, while at deeper depths (∼50 – 300 m and 300 – 800 m) exhibits distinct fluctuations compared to the surface. Triple-dip La Niña events lead to an overall increase in volume transport during both periods, with the 2019 – 2023 period showing larger values (∼19 Sv) compared to the 1997 – 2001 period (∼14 Sv). The strengthened ocean current during triple-dip La Niña events results in more significant variations in total transport, leading to larger differences between minimum and maximum transport during these periods. The volume transport in Makassar Strait is further analyzed using the Empirical Orthogonal Function (EOF) that identifies three dominant modes (86.4%), revealing the influence of semi-annual, interannual, and decadal factors on the observed variability.

Effects of temperature and pressure on the limiting current density of PEM electrolysis cells based on a theoretical prediction model and experiments

Operation at high current density of polymer electrolyte membrane electrolysis cell (PEMEC) can reduce its electrode area and capital expense. The high current density operation is limited by the limiting current density (LCD), where electrolysis voltage abruptly increases. Effects of operating temperature and pressure on the LCD were evaluated in a lab-scale PEMEC within a range from 70 to 90 °C and from 0.1 to 0.3 MPa. Also, a theoretical model was developed to predict the LCD, and to clarify what determines LCD and how the operating conditions influence the LCD. The theoretical analysis suggests that when current density is close to the LCD, water mass transport at anode reaches a limitation, which indicates that water saturation reaches almost zero at anodic catalyst layer. The analysis also finds that lower operating temperature and higher operating pressure can reduce oxygen gas saturation and raise the water saturation in porous transport layer at anode, and finally enlarge the LCD.

Water management and mass transport of a fractal metal foam flow-field based polymer electrolyte fuel cell using operando neutron imaging

Metal foam flow-fields (MFFs) exhibit immense potential for enhancing the performance of polymer electrolyte fuel cells (PEFCs) owing to their advantageous pore connectivity and abundant gas pathways. Nevertheless, challenges remain with the conventional MFF concerning reactant homogeneity and water management. To address these concerns, this study incorporates a fractal manifold into the MFF design. By employing operando neutron imaging, device-level testing, and electrochemical impedance spectroscopy (EIS), a comprehensive understanding of mass transfer and water management characteristics across the fractal manifold MFF is obtained. This novel design delivers better cell performance and lower mass transport resistance compared to the conventional MFF under all experimental conditions investigated. Notably, neutron imaging reveals that the fractal manifold MFF consistently exhibits a reduced liquid water content and more uniformly distributed liquid water compared to the conventional MFF. These superior characteristics of the design contribute to a substantial ∼15% increase in maximum power density compared to the conventional MFF-based PEFC. The results indicate the potential for further performance improvement by optimizing manifold parameters.

Surface factors controlling the volume of accumulated Labrador Sea Water

Abstract. We explore historical variability in the volume of Labrador Sea Water (LSW) using ECCO, an ocean state estimate configuration of the Massachusetts Institute of Technology general circulation model (MITgcm). The model's adjoint, a linearization of the MITgcm, is set up to output the lagged sensitivity of the water mass volume to surface boundary conditions. This allows us to reconstruct the evolution of LSW volume over recent decades using historical surface wind stress, heat, and freshwater fluxes. Each of these boundary conditions contributes significantly to the LSW variability that we recover, but these impacts are associated with different geographical fingerprints and arise over a range of time lags. We show that the volume of LSW accumulated in the Labrador Sea exhibits a delayed response to surface wind stress and buoyancy forcing outside the convective interior of the Labrador Sea at important locations in the North Atlantic Ocean. In particular, patterns of wind and surface density anomalies can act as a “traffic controller” and regulate the North Atlantic Current's (NAC's) transport of warm and saline subtropical water masses that are precursors for the formation of LSW. This propensity for a delayed response of LSW to remote forcing allows us to predict a limited yet substantial and significant fraction of LSW variability at least 1 year into the future. Our analysis also enables us to attribute LSW variability to different boundary conditions and to gain insight into the major mechanisms that contribute to volume anomalies in this deep water mass. We point out the important role of key processes that promote the formation of LSW in both the Irminger and Labrador seas: buoyancy loss and preconditioning along the NAC pathway and in the Iceland Basin, the Irminger Sea, and the Nordic Seas.

Spatial variability of water mass transports in the Bransfield Strait based on direct current measurements

The Bransfield Strait connects the Bellingshausen and Weddell seas and is strongly affected by intense inflows of their water masses. In this work we analyzed Shipborne Acoustic Current Doppler Profiler (SADCP) measurements carried out in the Bransfield Strait from 2015 to 2022. The new dataset includes over 100 transects, crossing the main currents in the strait (namely, the Bransfield Current and the Transitional Weddell Water (TWW) flow). Based on these data, we studied spatial variability of water mass transports in the Bransfield Strait during austral summer season. As shown below in this research, the Bransfield Current was observed down to the 600 m depth. By considering deeper layers, we managed obtaining more precise assessments of mean water mass transports of the Bransfield Current. They were estimated at 1.4–2.1 Sv. We found that the transports of the Bransfield Current and TWW flow in the austral summer season (November–March) do not show significant variability. The water mass transport of the Bransfield Current and the TWW flow was stable within the central basin of the Bransfield Strait and differed in its western basin. We also found that in austral summer the heat transport into the Bransfield Strait varied between 0.2 and 0.4 Sv·°C and salinity transport was −0.07 to −0.06 Sv·psu, their sign reflecting a dominant northeastward flow of relatively warm and fresh water. In addition, we compared Lowered Acoustic Current Doppler Profiler (LADCP) and SADCP measurements and proved that the technical limitations of the SADCP do not significantly affect the estimates of the transports in this region.

Dissolved rare earth elements in the North Pacific Subtropical Gyre: Lithogenic sources and water mass mixing control

In the North Pacific Subtropical Gyre, which is one of the largest oligotrophic regions, there is a lack of information regarding the sources and transport of trace metals through water mass mixing. Rare earth elements (REEs) are essential for tracing lithogenic sources and water mass transport. In this study, we present dissolved REE concentrations and the factors controlling their distributions in the northwest Pacific during a GEOTRACES cruise (GP09). In the surface water along 11°N, we observed input signals from the Philippine and the Hawaiian Islands, characterized by positive Eu anomalies and slightly elevated REE concentrations. By incorporating our data and published REE data from the northwest Pacific to the southeast Pacific (40°N–40°S), we demonstrated that the REE concentrations and Yb/Nd ratios can distinguish North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW), and modified AAIW. By estimating the ratio of water mass mixing, we suggest that heavy REEs are predominantly contributed by water mass mixing (e.g., 93 % ± 4% for Yb) and can be used as semi-conservative tracers to quantify the mixing of NPIW and modified AAIW at the potential density of 27.2 kg/m3. At ∼800 m depth at stations K12, K13, and K14, weak negative Ce anomalies (>0.1) were observed, indicating the lateral transport of water masses imprinted with sediment signals from the Philippine Islands. In the deep waters (>1500 m) at the Luzon Strait (station K1), we propose that the weak Ce negative anomalies (>0.08) and low Yb/Nd ratios (<5), combined with the low beam transmission, are the result of particle resuspension and release. In deep water (>2000 m), combining high-resolution REE measurements with water mass analysis, our research reveals that dissolved REEs (except Ce) are dominantly controlled by water mass mixing (e.g., 80 %∼100 % for Yb and 70 %∼100 % for Nd). For the non-conservative behavior, which is not explained by water mass mixing, the residual fraction of heavy REEs (<20 % for Yb) originates from release of sinking particles (organic matter and siliceous particles), while the remaining concentrations of light REEs (<30 % for Nd) may be influenced by a combination of particle release and scavenging processes. These findings highlight valuable information about lithogenic sources and the proportions of REE distributions that are controlled by physical and biogeochemical processes. Moreover, it emphasizes the applicability of heavy REEs as effective tracers for understanding basin-scale water mass mixing in the northwest Pacific.

Internal solitary waves observation and feature extraction based on wavelet transform by Sentinel-1A in Lombok Strait, Indonesia

Lombok Strait is an essential pathway in trans-oceanic water mass transport. Due to this water mass transport flowing over Indonesian waters, the current is known as Indonesian Throughflow (ITF), which plays a role in the transfer of warm water masses from the Pacific to the Indian Ocean annually. Lombok Strait has intensive characteristics of the internal waves (IWs) generation because of the strong current that passes through the complex bathymetry along the strait area. IWs with large amplitude and nonlinear properties are known as Internal Solitary Waves (ISW) that can be detected by Synthetic Aperture Radar (SAR) images. A Wavelet Transform method for ISW feature extraction was applied to SAR images by Sentinel-1A (C-band). ISW packet characteristics can be distinguished from other phenomena based on their geometrical structure and shape. ISW packet pattern consists of light and dark lines which decrease intensity from front to rear. SAR observation detected 5 parameters (phase speed, soliton numbers, wavelength, first crest length, and propagation direction). The arc-like ISW in the Lombok Strait propagated to the North of the sill with average phase speeds of about 2.13 m/s and was frequently detected during the northwest monsoon (NWM). The detected soliton number is less than 6 solitons per packet with a wavelength of about 1 – 4 km, and the first crest length varies from about 12.16 km to more than 100 km. ISW detected in Sentinel-1A images were located at the bathymetry about 800 meters around the Lombok Strait area.

Estimating daily semantic segmentation maps of classified ocean eddies using sea level anomaly data from along-track altimetry.

Mesoscale eddies, which are fast-moving rotating water bodies in the ocean with horizontal scales ranging from 10 km to 100 km and above, are considered to be the weather of the oceans. They are of interest to marine biologists, oceanographers, and geodesists for their impact on water mass, heat, and nutrient transport. Typically, gridded sea level anomaly maps processed from multiple radar altimetry missions are used to detect eddies. However, multi-mission sea level anomaly maps obtained by the operational processors have a lower effective spatiotemporal resolution than their grid spacing and temporal resolution, leading to inaccurate eddy detection. In this study, we investigate the use of higher-resolution along-track sea level anomaly data to infer daily two-dimensional segmentation maps of cyclonic, anticyclonic, or non-eddy areas with greater accuracy than using processed sea level anomaly grid map products. To tackle this challenge, we propose a deep neural network that uses spatiotemporal contextual information within the modality of along-track data. This network is capable of producing a two-dimensional segmentation map from data with varying sparsity. We have developed an architecture called Teddy, which uses a Transformer module to encode and process spatiotemporal information, and a sparsity invariant CNN to infer a two-dimensional segmentation map of classified eddies from the ground tracks of varying sparsity on the considered region. Our results show that Teddy creates two-dimensional maps of classified eddies from along-track data with higher accuracy and timeliness when compared to commonly used methods that work with less accurate preprocessed sea level anomaly grid maps. We train and test our method with a carefully curated and independent dataset, which can be made available upon request.

Altered Weddell Sea warm- and dense-water pathways in response to 21st-century climate change

Abstract. The transport of water masses with ocean circulation is a key component of the global climate system. In this context, the Filchner Trough in the southern Weddell Sea is critical, as it is a hotspot for the cross-shelf-break exchange of Dense Shelf Water and Warm Deep Water. We present results from Lagrangian particle tracking experiments in a global-ocean–sea-ice model (FESOM-1.4) which includes ice-shelf cavities and has eddy-permitting resolution on the southern Weddell Sea continental shelf. With backward and forward experiments, we assess changes between a present-day and a future (SSP5-8.5) time slice in the origin of waters reaching the Filchner Ice Shelf front and the fate of waters leaving it. We show that particles reaching the ice-shelf front from the open ocean originate from 173 % greater depths by 2100 (median; 776 m as compared to 284 m for the present day), while waters leaving the cavity towards the open ocean end up at 35 % shallower depths (550 m as compared to 850 m for the present day). Pathways of water leaving the continental shelf increasingly occur in the upper ocean, while the on-shelf flow of waters that might reach the ice-shelf cavity, i.e., at deeper layers, becomes more important by 2100. Simultaneously, median transit times between the Filchner Ice Shelf front and the continental shelf break decrease (increase) by 6 (9.5) months in the backward (forward) experiments. In conclusion, our study demonstrates the sensitivity of regional circulation patterns in the southern Weddell Sea to ongoing climate change, with direct implications for ice-shelf basal melt rates and local ecosystems.

Transport and dispersion of PFOA and PFOS in the Black Sea

A 3-D transport and dispersion model was applied to study the recent past and future dynamics of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) concentrations in the Black Sea for the 2016–2030 period. The modelled surface concentrations show a distinct seasonal behaviour, shaped by winter to spring convective mixing. A significant increasing long-term trend in PFOS concentrations is established, with concentrations in water layers 200 m below the surface increasing at 4–8% per year. Driving mechanisms for PFOA and PFOS transport and accumulation in the subsurface and deeper layers are the cooling of the surface water in winter and the transport of water masses from the North Western Shelf (NWS) of the Black Sea. A simulated 50% phase-out of PFOA and PFOS from 2020 to 2030 shows a 21% reduction in PFOA, while PFOS continues to increase.

Experimental investigation into the effects of strong winds on the transport of overtopping water mass over a vertical seawall

ABSTRACT Hydraulic experiments using a wave flume with a wind tunnel at a scale of 1/40 were carried out to investigate the effect of wind on wave overtopping of a vertical seawall. To ascertain the possible effects of wave breaking, incident waves with various wave steepness (0.0102 to 0.0371) and three kinds of wind forcing (0 m/s, 6.84 m/s, 10.04 m/s) were used. The authors found that winds significantly increased the overtopping rate in general, and that there is a clear relationship between the overtopping rate and the wave steepness. Velocity fields obtained from PIV analysis revealed that the onshore winds directly enhanced the transport of overtopping water mass. The influence of the wind on the wave hydrodynamic processes that indirectly have an effect on the overtopping rate (such as the formation of a partially standing wave, breaker location, and breaker type) is also discussed. The perspective of treating wave overtopping as a transport of water mass could provide a novel understanding of complex fluid behavior, which would help to formulate countermeasures against future disasters influenced by intensive wind forcing.

Effect of Operating Temperature and Pressure on the Limiting Current Density of PEM Electrolysis Cell Based on Theoretical Prediction Model and Experiments

Introduction The PEM electrolysis cell (PEMEC) exhibits great potential to produce hydrogen gas. However, the high cost associated with cell components, such as the iridium oxide catalyst and titanium porous transport layer, poses a challenge to the commercialization of PEMEC. So, continued research is needed to improve the cost-effectiveness of PEMEC. Operation at high current densities can minimize the electrode area and reduce capital expenses. However, high current density operation is limited by limiting current density (LCD), which causes a sharp increase in electrolysis voltage. At high current densities, the generation of oxygen gas bubbles creates additional flow restrictions to the water supply and increase overvoltage. Although previous studies have achieved relatively high current densities [1-2], the limit of operating current density and its mechanism still remain unknown.In this study, it reveals the impact of operating temperature and pressure on LCD of a lab-scale PEMEC. The experiments are conducted over a range of temperatures from 80 to 90 ℃ and pressures from 0.1 to 0.3 MPa. In conjunction with experiments, a mathematical model is developed to analyze the mechanism of LCD. The model includes mass and momentum equations for liquid water and oxygen gas through the porous transport layer. And the model also involves electrochemical equations to study overvoltages associated with mass transport. By combining experimental and theoretical analysis, this study provides valuable insights into the factors affecting LCD of PEMECs and facilitates the optimization of high-performance operation. Experimental apparatus The specifications of crucial components such as membrane (PEM), catalyst layer (CL), porous transport layer (PTL) is listed in Table.1 . Nafion NR212 is used as PEM, and the thickness is 51 μm. The catalyst is contained on CL, and its loading amount are 1.5 mg/cm2 IrO2 on anode and 0.5 mg/cm2 Pt on cathode, respectively. The anodic PTL is a Titanium mesh plated by Pt (Nikko Techno, NKT-1803-03), and the carbon paper (SGL 38BA) is used as cathodic GDL. For separators, the anode separator is fabricated from titanium, and the cathode separator is carbon. The anodic and cathodic flow pattern is designed as single-serpentine channels, and the channel depth, channel width, and rib width are 1 mm ×1 mm ×1 mm, respectively. Results and discussions Fig.1 shows the theoretical and experimental I-V curves. In Fig.1, the electrolysis voltage in both experiment and simulation raises abruptly, which is corresponding to LCD. The experimental LCD is 11.6 A/cm2 as indicated by the black circle, and the predicted LCD is 10.1 A/cm2. Although the prediction of LCD is qualitative, simulation could follow the IV characteristics obtained by experiment before LCD.Fig.2 and Fig.3 shows the effect of operating temperature and pressure on LCD. The electrolysis voltage “E” is experimentally determined, while the gas saturation at interface of PTL-CH “Sg” is obtained through simulation. As shown in Fig.2, the lower operation temperature enlarges the LCD, the experimental LCD increases 8% from 90 ℃ to 80 ℃. Theoretically, high operating temperature increases oxygen bubbles and then rises the gas saturation S g at the anode CL. So, the water supply flowing to CL is insufficient, and the electrochemical performance also decrease. Therefore, the overvoltages caused by mass transport becomes larger in higher operating temperature. As shown in Fig.3, higher operating pressure shrinks the volume of oxygen gas and enhance the water supply from CH to CL, leading to a larger LCD. Under 80 ℃, the experimental LCD rises by 17 % from 0.1 MPa to 0.3 MPa.Although the theoretical analysis reproduced the experimental results in a qualitative manner, the theoretical analysis suggests that, when electrolysis current density is quite close to the LCD, water mass transport at anode reaches a limitation, indicating that water saturation drops to zero at anodic catalyst layer. References Lee J K, et al. Cell Reports Physical Science, 2020:100147.A Zinser, et al. International Journal of Hydrogen Energy, 2019, 44(52): 28077-28087. Figure 1

Modelling of the Water Mass Transport through the Membrane of Direct Toluene Electro-Hydrogenation Electrolyzers

The organic hydride toluene/methylcyclohexane (MCH) is an attractive carrier for the bulk and long-distance transport of green hydrogen. On the other hand, the direct toluene electro-hydrogenation in a proton exchange membrane electrolyzer exhibits advantages concerning the conventional two-step toluene hydrogenation process, such as the lower theoretical voltage by avoiding thermal losses [1]. Figure 1 (a) shows the internal structure and illustrates the basic working principle of this electrochemical device.However, the effective toluene supply to the cathode catalyst is a central issue. It is assumed that the accumulation of water dragged from the anode side inhibits the toluene mass transport to the reaction site [2]. Therefore, in practice, a fraction of the toluene stream entering the cathode fails to convert to MCH; instead, hydrogen bubbles are generated. According to the theoretical approach illustrated in Fig. 1 (a), protons transported across the membrane and can be the carrier of associated water. Nevertheless, the water transfer mechanism inside a cell is complex, diverse, and unclear (e.g., as mist, small droplet) [3].According to most conventional modelling approaches, electro-osmosis and back diffusion mainly govern the total water flux through electrolytic membranes. The open literature dealing with PEM fuel cells agrees that the water content of the membrane (correlated with the water activity by earlier studies) is a central factor concerning not only these mass transport mechanisms inside the membrane, but also concerning the mass transfer resistance on its surface. Indeed, to calculate both the electro-osmotic drag and the diffusion coefficients, authors have developed numerous correlations based on a relationship with the membrane water content. However, the experimental data available in the open literature dealing with PEM fuel cells devices largely disagree. Complex factors such as the Schroeder’s Paradox in Nafion® membranes [4] can explain those discrepancies. This leads into a huge uncertainty in the parametrization of those parameters involved in the numerical modelling and simulation of the water transport in electrochemical devices based on PEM technology [5].The objective of this work is to qualitatively study, through numerical simulation, the influence of the main parameters involved in the transport of water through the electrolytic membrane of a direct toluene electro-hydrogenation electrolyzer. To accomplish this aim, a sensitivity analysis was conducted, and the probability distributions set for each modelling parameter (i.e., potential variation range) are consistent with the state-of-the-art. The anode reactants considered were pure water and also diluted solutions of sulfuric acid with concentrations between 0.1-1.5 L/mol. Figure 1 (b) shows the preliminary results obtained when supplying pure water as anode reactant and under the assumption of null water mass transport by back diffusion mechanism. The experimental data gathered from the monitoring of an in-house toluene electro-hydrogenation cell are used as reference to discuss the results obtained from the simulations and to tighten the modelling parameters. Acknowledgements Antonio Atienza-Márquez acknowledges the Ministerio de Universidades of Spain and the Recovery, Transformation and Resilience Plan for financially supporting the postdoctoral contract 2021URV-MS-01.

Parameterization and Validation of a 2-Dimensional, Transient, Two-Phase MEA Model Capable of Simulating Electrochemical Impedance Spectra

Proton exchange membrane fuel cells (PEMFC) are promising energy converters, offering both sustainability and efficiency. Achieving optimal performance, however, requires a deep understanding of the underlying cause-effect relationships within the functional layers. One effective approach for validating models that capture the complex physics of PEMFC is through differential cells, which reduce computational effort by allowing along-the-channel-effects to be discarded [1,2].In this study, we present a 2-dimensional, transient, non-isothermal PEMFC model that enables the disentanglement of loss contributions, facilitating effective material screening. Our model accounts for multiphase transport to provide insights into water management and mass transport. To ensure robust parameterization, we conducted a multitude of both ex-situ and in-situ experiments, reducing our reliance on often-contradictory literature data [3].We fitted our model to a wide range of polarization curves obtained under operating conditions spanning temperatures of 50-80 °C and relative humidities of 40-100 %. Notably, our model is able to simulate impedance spectra, which enables the disentanglement of processes with different time constants [4]. This approach provides a unique opportunity to study the electrochemical behavior and offers a more profound understanding of PEMFC performance limitations. The thorough parameterization process and validation against a broad range of operating conditions and impedance spectra render our model reliable and effective for industry professionals and researchers. We also highlight shortcomings and physics aspects that require further research to deepen insights and enable faster industrialization cycles.

Investigation of Gas Diffusion Layer Degradation in Polymer Electrolyte Fuel Cell Via Chemical Oxidation

The gas diffusion layer (GDL) is a key part of the membrane electrolyte assembly and is critical for the transport of fuel, oxygen and water. The GDL is made up of two layers: macroporous substrate (MPS) and microporous layer (MPL) (1). To achieve the hydrophobicity required for water management, the two layers are typically treated with polytetrafluoroethylene (PTFE) (2). In many long-term experiments, it has been observed that GDL degradation, such as carbon corrosion and PTFE loss, leads to a deterioration of water management, conductivity and mass transport (3).To solve this durability problem, a thorough and in-depth understanding of the GDL degradation mechanism is required. In this study, GDLs are subjected to an accelerated stress test to investigate degradation by chemical oxidation. GDLs are soaked in Fenton's reagent for 24 hours. The hydrophobic properties of pristine and soaked GDLs are compared based on contact angle measurements, thermogravimetry and scanning electron microscopy. In addition, the chemical composition of the solutions before and after the immersion test is analyzed using a total organic carbon analyzer and an ion chromatograph. The results show that the hydrophobicity of GDL exposed to Fenton reagent is decreased by 5 and 4 degrees for the MPL and the MPS respectively. Fig 1. depicts a decrease in surface contact angle, which is associated with surface oxidation and PTFE deterioration.AcknowledgementThis research work is performed under the project AlpeDHues (AlpeDHues / FFG 889328) which is supported by the Austrian Research Promotion Agency (FFG).References C. Csoklich, R. Steim, F. Marone, T. Schmidt and F. Büchi, ACS Applied Materials & Interfaces, 13, 9908–9918 (2021).A. Ozden, S. Shahgaldi, X. Li and F. Hamdullahpur, Progress in Energy and Combustion Science, 74, 50–102 (2019).Y. Yang, X. Zhou, B. Li and C. Zhang, Applied Energy, 303, 117688 (2021). Figure 1