Proton exchange membrane (PEM) water electrolysis is a highly efficient method for hydrogen production. Research cells typically consist of one proton exchange membrane, two catalyst layers, two porous transport layers, two flow-field plates, and two endplates. In commercial systems, the machined flow-field plates that are employed in research cells are typically replaced by stamped parts or open mesh material solutions to reduce manufacturing cost at scale. Nonetheless, the cell contains about eight total interfaces: bipolar plate/flow plate material/porous transport medium/electrode/membrane/electrode/porous transport medium/flow plate material/bipolar plate. All these materials and interfaces need to be optimized for maximum performance and efficiency. Reducing the number of interfaces by combining individual cell components directly benefits the fabrication cost (by reducing the parts count and the need for surface coatings) and the electrochemical performance (by reducing ohmic losses). We have designed a novel PEM electrolysis cell with a piece of channeled titanium felt functioning as both the anode flow-field and the PTL, referred to as the channeled diffusion layer (CDL). The pores of the felt facilitate both in-plane and through-plane diffusion, ensuring maximum catalyst utilization while also minimizing mass transport loss. The titanium felt can be mass manufactured with existing stamping and forming methods and is therefore a promising candidate to reduce the capital cost of PEM electrolyzers whilst improving hydrogen production efficiency. Experiments conducted with 3mg IrOx/cm 2 loading MEAs have shown a ~40% boost in peak current by implementing the CDL design. Low catalyst-loading MEAs are being tested in ongoing experiments and their results will be discussed and compared. This effort was sponsored by the U.S. Government under OTA W56HZV-24-9-C006 with the University of Delaware. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation herein. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the U.S. Government.

An XY segmented cell was developed for low temperature PEM water electrolysis (PEMWE). The system can assess the local performance by enabling in situ measurements of spatial currents and impedances. In this work, we show through experiments, as well as through modelling work, that the porous transport layer (PTL) must be segmented to eliminate crosstalk. Accurate measurements are only possible when crosstalk is fully eliminated. The XY segmented cell is applied to a case study characterizing the impact of a PTL platinum coating void on spatial performance. The localized performance impact of the coating void is found to be orientation specific: coating voids facing the catalyst layer reduce performance significantly more than coating voids facing the flow field. The results suggest that the tolerances for PTL coating uniformity can be lower at the side facing the flow field. The work showcases the feasibility of the XY segmented cell for impact assessment studies. The presented XY segmented cell enables the characterization of spatial phenomena in PEMWE devices and is envisioned to support modeling efforts and the investigation of manufacturing related tolerances for mass produced PEMWE devices. Electronic crosstalk between flow field segments can cause major measurement errorsShunt resistor choice directly impacts degree of crosstalk between segmentsCrosstalk between segments eliminated by segmenting the porous transport layerStandard electrolyzer configuration assessed using segmented cellVoids in porous transport layer coating affect performance depending on orientation

Segmented cells are a class of advanced diagnostic devices that enable the measurement of current distribution within the active area of an electrochemical cell, allowing for the evaluation of localized impacts from operating conditions, flow fields and component inhomogeneities 1–3 . Segmented cell devices have been applied to support R&D efforts for the advancement of polymer electrolyte membrane fuel cell technologies and more recently proton exchange membrane water electrolysis (PEMWE). Beyond current density distributions, segmented cells have been successfully deployed to collect the distribution of other relevant parameters such as high frequency resistance and electrode potentials 1,4,5 . Very recently, a promising impedance method has been reported for water electrolysis where a one-dimensional segmented cell is coupled to a multichannel potentiostat, to enable the measurement of local cell impedances, further expanding the diagnostic capabilities of the segmented cell 6 . In this study, we will present recent efforts to accurately measure local impedance characteristics for a PEMWE cell using a two-dimensional segmented cell device coupled with a multichannel potentiostat. The distribution of local resistances, i.e. high frequency, charge transfer, mass transport and catalyst layer, and iR-free overpotentials were successfully measured after eliminating sources of random and systematic error. We will discuss the application of this diagnostic on a cell containing a 1 cm 2 feature simulating an ionomer skin 7,8 . The results from these tests give insights into if such an irregularity needs to be classified as a defect and highlight the usefulness of coupling impedance spectroscopy with segmented cells for holistic spatial diagnostics of electrochemical devices. S. Cleghorn, C. Derouin, M. Wilson, and S. Gottesfeld, Journal of Applied Electrochemistry , 28 , 663–672 (1998). G. Bender, Proc. Vol. , 2002–31 , 212–219 (2002). W. Focke, Electrochimica Acta , 28 , 1137–1146 (1983). A. Roy, F. H. Roenning, D. S. Aaron, F.-Y. Zhang, and M. M. Mench, J. Electrochem. Soc. , 172 , 014509 (2025). S. Abbou, J. Dillet, G. Maranzana, S. Didierjean, and O. Lottin, Journal of Power Sources , 340 , 337–346 (2017). N. Hensle, S. Metz, A. Weber, and T. Smolinka, J. Electrochem. Soc. , 171 , 114510 (2024). E. Padgett et al., Journal of The Electrochemical Society , 170 , 084512 (2023). J. Xie, F. Garzon, T. Zawodzinski, and W. Smith, J. Electrochem. Soc. , 151 , A1084 (2004).

An empirical model is presented that describes anode-side losses related to porous transport layer (PTL) morphology in proton exchange membrane water electrolysis (PEMWE). The model is based on an advanced voltage breakdown analysis that links various overpotentials to PTL morphology. Custom Ti PTLs, spanning uncommonly low porosities (22 – 31%), were fabricated and analyzed with X-ray CT to obtain pore and particle size distributions. Particle size distributions were consistent across samples with an average particle diameter of 12.0 μm, whereas average pore diameters ranged from 6.0 to 7.0 μm. The PTLs were tested in standard PEMWE cell assemblies with anode catalyst loadings of 0.1 mgIr cm−2 to obtain polarization curves, electrochemical impedance spectra, and augmented Tafel analysis. The PTL-dependent anode side losses were deconvoluted and assigned to excess utilization, concentration, ion transport resistance, and electrical contact resistance overpotentials. The data and model reveal an optimal 20 – 28% PTL porosity region where utilization and contact resistance overpotentials are minimized without triggering concentration and ion transport losses related to water deprivation. The optimal PTL porosity depends on the operating current density and is demonstrated at realistic PEMWE water flow rates to establish PTL design guidance for operation at scale.

Titanium-based porous transport layers (PTLs) and iridium-based catalyst layers (CLs) are two main components of proton exchange membrane water electrolyzers (PEMWEs). PTLs are typically coated with platinum to minimize interfacial losses and to support long-term operation. Optimizing coatings and the PTL-CL interface requires comprehensive characterization. This study establishes time-of-flight secondary ion mass spectrometry (ToF-SIMS) as a valuable technique for PTL characterization, addressing capabilities and limitations related to PTL morphology. A methodology was developed that uses a Cs+ sputter beam for dynamic depth profiling, with data collected in both positive-ion (MCs+) and negative-ion modes to generate depth profiles, 2D ion maps, and 3D ion reconstructions. ToF-SIMS detected relative differences in platinum-layer thickness between samples; these trends were validated by cross-sectional scanning transmission electron microscope (STEM) measurements and flat-titanium substrate controls. Interfacial oxide layers are identified in both ion modes, with enhanced oxide sensitivity in negative mode. The technique's high sensitivity enables detection of nanometer-scale coatings and trace impurities within the bulk PTL structure. These results provide a methodological framework for analyzing Pt-coated PTLs, with the potential to extend to other components in PEMWEs and other electrolyzer systems.

During proton exchange membrane water electrolysis (PEMWE) device operation, gas generation results in the mixing of the liquid water streams with product gas, creating binary fluid mixtures with an increasing gas phase volume fraction along the flow path from cell inlet to cell outlet. Consequently, the local operating conditions of a PEMWE cell change as a function of channel length. Recently, it has been shown that the commonly observed low frequency (0.1Hz) feature in impedance spectra of proton exchange membrane water electrolysis (PEMWE) cells corresponds to heat accumulation phenomena at the membrane and thermal gradients along the flow path 1–3 . We will present recent efforts at our lab to spatially resolve the low frequency feature in a two-dimensional (XY) segmented cell to identify how gas build up and irregularities in cell components may drive the formation of thermal gradients (Figure 1). Results show that along the channel, the magnitude and time constant of the feature increase, indicating that the accumulation of gas and or waste heat has a noticeable impact on local thermal management. The influence that the thickness of the membrane and the morphology of the porous transport layer have on this observed phenomenon will be discussed. Figure 1. Schematic of XY segmented cell measurements of the low-frequency impedance feature at 4 A cm -2 . Total cell corresponds to the impedance that is observed for the device treated as a single cell. ○ 100 Hz △ 2 Hz □ 0.04 Hz. For visual clarity, high frequency resistance is subtracted. References: N. Hensle, S. Metz, A. Weber, and T. Smolinka, J. Electrochem. Soc. , 171 , 114510 (2024) https://iopscience.iop.org/article/10.1149/1945-7111/ad9064. N. Hensle, D. Brinker, S. Metz, T. Smolinka, and A. Weber, Electrochemistry Communications , 155 , 107585 (2023) https://linkinghub.elsevier.com/retrieve/pii/S1388248123001595. T. Franz, T. Miličić, G. Papakonstantinou, T. Vidaković-Koch, and K. Sundmacher, Journal of Power Sources , 655 , 237981 (2025) https://linkinghub.elsevier.com/retrieve/pii/S0378775325018178. Figure 1

Proton exchange membrane water electrolyzers rely on relatively expensive Ir-based catalysts for efficient and durable hydrogen production. To reduce system costs, Ir loadings can be reduced if performance and durability are maintained. Sputter deposition is a readily scalable method to synthesize uniform, low-loading catalyst layers with controlled composition. A catalyst applied directly to the porous transport layer can have advantages for performance, manufacturing simplicity, and catalyst recovery. Suitable porous transport layer porosity can minimize activity losses when reducing loadings. Here, methods are presented to deposit metallic Ir as well as amorphous and rutile Ir oxides. The activity and durability of these materials in the porous transport electrode architecture is evaluated. The metallic and amorphous forms have better initial activity, however, operation at 3 A cm-2 with 0.1 mg Ir cm-2 shows that only rutile IrO2 maintains performance beyond 100 h with a 50 mV improvement after 700 h. A >10x reduced dissolution rate is shown for rutile IrO2. With a low-porosity transport layer and 0.4 mg Ir cm-2, a steady-state voltage decay rate of 6 µV h-1 is achieved. The results demonstrate that sputter-deposited rutile IrO2 porous transport electrodes with low Ir loading can be operated at high current density to reduce hydrogen production costs.

Reducing Ir loadings in proton exchange membrane water electrolyzer anodes is critical for lowering capital expenses. Loading reduction could be achieved by improving the Ir activity via doping/alloying and/or the development of advanced microstructures. However, the anode porous transport layer (PTL) is a comparatively simple component whose properties also impact Ir utilization. Therefore, well-designed PTLs may also enable reduced Ir loadings. In this work, we survey eight PTLs from various manufacturers to observe their impact on cell performance at low (0.4 mgIr cm-2) and ultralow (0.1 mgIr cm-2) Ir loadings. The PTLs were characterized by their microstructural properties, including porosity, particle size distribution, and pore size distribution. Electrochemical cell performance was correlated to PTL morphology, and it was found that PTLs with lower porosities and smaller particle and pore radii enabled good performance even at ultralow Ir loadings. 1000-h durability testing indicated that using lower porosity PTLs can significantly improve durability behavior. A runaway voltage phenomenon was observed during durability testing of cells with ultralow Ir loadings, which was caused by increases in both anode and cathode overpotentials. Furthermore, we observed that the beginning of test performance of 0.1 mgIr cm-2 cells correlates to the 1000-h degradation rates of 0.4 mgIr cm-2 cells, suggesting that for the Ir catalyst used in this work, short-term testing at ultralow loadings can be used as an indicator of long-term degradation at higher loadings.

Proton exchange membrane (PEM) water electrolysis is a promising technology to produce cost-efficient hydrogen. PEM electrolyzers offer a large current density range and the ability to operate at differential pressure which can be used to minimize both capital and operational expenditures. However, directly producing pressurized hydrogen at the cathode results in pushing the membrane against the anode porous transport layer (PTL). This can lead to detrimental effects, such as membrane deformation or ruptures, which depend on membrane properties as well as PTL material properties such as pore size, structure, and morphology. In this work, a range of sinter and felt-based commercial PTLs are evaluated for their contributions to the cell's electrochemical and H-2 crossover performance at cathode pressures up to 30 bar. X-ray tomography and post-operando optical microscopy are used to assess the morphology of the PTLs, and the PTL induced deformation experienced by the catalyst coated membrane (CCM), respectively. PTL samples with lower porosity were found to reduce both the cell voltage and the amount of H-2 permeating from the cathode to the anode exhaust, which was ascribed to improved catalyst layer contact and reduced membrane deformation, respectively. The best performing PTLs improved electrolyzer efficiency by similar to 1.5 kWh/kg(H2). Specifically, 1 kWh/kg(H2) was gained due to reducing membrane deformation and decreasing H-2 crossover. The remainder 0.5 kWh/kg(H2) were achieved by improving the electrical contact at the electrode/PTL interface which decreased cell voltage.

Hydrogen crossover poses critical safety and operational limitations for the use of high-pressure polymer electrolyte membrane (PEM) water electrolysis (WE) systems for green hydrogen production, and methods of in-situ electrochemical characterization of this important phenomenon are lacking in the literature. In this work, we proposed and investigated two in-situ methods of membrane hydrogen permeability extraction via electrochemical characterization. The first technique we investigated was a transient method capturing the open circuit potential decay under hydrogen crossover at pressure, coupled with a 1-D permeation model to extract and quantify the membrane’s hydrogen permeability. The second method consisted of a post-OCV decay linear sweep voltammetry method to capture the steady state flux of hydrogen through the membrane via a hydrogen oxidation current enabled by the iridium catalyst’s reduction to metallic iridium. The two methods were implemented at 10 and 20 bar differential pressure and yielded consistent membrane permeabilities between them and in agreement with published values from ex-situ membrane permeation studies.

This study investigates strategies to improve the quality of electrochemical impedance spectroscopy (EIS) measurements using reference electrodes (RE) in proton exchange membrane water electrolyzers (PEMWE). We demonstrate that adding a low impedance wire in parallel to the RE significantly enhances signal accuracy, especially at high frequencies. Additionally, we identify electrical pad heaters as a source of measurement noise. EIS measurements fulfilling Kramers–Kronig validity criteria were only achieved in their absence. These insights advance the diagnostic capabilities of REs in water electrolyzers and support more reliable, spatially resolved analysis of electrochemical losses within the cell.

The harmonization of testing protocols for proton exchange membrane (PEM) electrolyzers is essential for ensuring accurate and reliable performance assessments and accelerating the development of hydrogen production technologies. This protocol provides a structured approach to PEM electrolyzer setup and testing, incorporating key considerations for test station design and single-cell characterization techniques. Polarization curves and electrochemical impedance spectroscopy (EIS) are detailed, along with best practices from academic and industry research groups to enhance data accuracy and comparability. By addressing material variability and harmonizing testing methodologies, this framework enables more precise evaluations of membrane electrode assemblies and electrolyzer components. Harmonized protocols not only streamline development efforts but also foster collaboration across institutions, ultimately supporting the commercialization of hydrogen solutions through improved stack efficiency and durability.

Contamination of polymer electrolyte membrane (PEM) water electrolysis (WE) systems is one of the critical technical hurdles hindering mass adoption of PEM technology for green hydrogen production and has led to stringent water quality requirements and expensive water purification equipment to enable high efficiency operation and reach durability targets. The sources of contamination to the water supply to the electrolysis stack are numerous, and in the scope of this work, include leached metallic ions from balance-of-plant and stack components that are in direct contact with the de-ionized feedwater to the membrane electrode assembly (MEA) but downstream of the filtration system. These leachates are of critical interest, due to their extremely low concentration and detectability limitations, as well as their ability to accumulate over time to achieve significant uptakes in the MEA and cause significant performance loss and contribute to membrane aging/thinning. However, few published studies have investigated the effects of leached metal ions in PEM WE. In this investigation, we sought to characterize and understand the behavior of metallic contaminants in the MEA system, once absorbed, by adding the cations directly to the membrane prior to the deposition of the catalyst layers. This approach yields good control of the contamination level and the ability to study performance effects at low occupation fractions without requiring significant operational periods with which to accumulate the ions. We selected iron (Fe), aluminum (Al), and copper (Cu) as the metal ions of interest, given their prevalence in water systems and their unique expected behaviors in the acidic media of a PEM WE MEA. The results show clearly that the Fe and Al ions behave solely as mobile contaminants that accumulate in/near the cathode, while Cu shows the additional complexity of plating behavior in the cathode catalyst layer. Further, our results indicate the sensitivity of the performance and impedance signals to low-level contamination, indicating the possibility of early detection and mitigation prior to cell failure.

To reach cost targets that accelerate the widespread deployment of renewable hydrogen production by electrolysis, research and development efforts must be rapid, efficient, and highly collaborative. To facilitate efforts, the H2NEW consortium has developed a benchmarking protocol as the basis for accurate comparison of PEM electrolyzer research results. Herein, three U.S. National Laboratories harmonize and validate this protocol to establish minimum requirements for test stations, cell hardware, cell test procedure, and the fabrication of a baseline material set, while maintaining maximum agreement of test results. The baseline membrane electrode assembly (MEA) features significantly lower loadings than commercially available and is referred to as the "Future Generation MEA (FuGeMEA)". It consists of commercially available materials and is used as a baseline material set for research and development across the consortium. Using this material set, a phased harmonization approach is applied to isolate and address sources of variation associated with the test stations, cell hardware, and FuGeMEA fabrication procedure. Troubleshooting experiments are conducted within each phase, yielding a set of Lessons Learned (LL) that we present and discuss. In the final phase, the participating laboratories separately fabricate the FuGeMEA, assemble the cell, and conduct the harmonized test protocol to obtain cell performance results with a maximum standard deviation of 18 mV at 4 A cm-2. This work thus establishes the FuGeMEA performance benchmark and test protocol as a baseline system for broad use in test equipment validation and comparison of performance results across the research community.

A critical aspect of water electrolysis is the mass transport of water into the system and the efficient removal of gaseous products from the catalyst layer. In an electrolyzer stack, flow fields contribute to the control of these multiphase fluid dynamics. This presentation discusses the use of expanded metal sheets as flow fields, compared to engineered bipolar plates. Three dimensional single-phase and multiphase computational fluid dynamics (CFD) studies are conducted to predict key hydrodynamic properties, including pressure drop and velocity field. Figure 1 displays an example pressure distribution output from a single-phase model analysis. Additionally, these models describe how various rates of hydrogen and oxygen production affect these features. This digital model is validated using an experimental setup for pressure drop measurements and an operando view of mass transport. Expanded metals are shown to be an economical alternative to highly engineered bipolar plate designs, highlighting the utility of CFD in material selection Figure 1

A technoeconomic analysis is performed to evaluate the economic benefits of implementing cell-level switches in a PEM electrolyzer stack used for hydrogen production. Cell-level switches coupled with in-situ monitoring have the potential to disconnect individual cells from the stack by shunting the stack current around the specific cell. Cell state parameters such as voltage, impedance etc coupled with insights into cell health or failure status are used to determine whether cell switches are turned on. Potential cost savings can be realized by switching off inefficient cells with higher degradation rates or cells with failures such as pinholes that would cause a stack failure and consequently a stack replacement. Models are developed in Python to compare electrolyzers including switches with conventional electrolyzers. A techno-economic model is built to capture the economic impacts of switches on hydrogen production costs as well as the net present value of stack replacement costs. Two scenarios are designed to study the economic impacts of potential benefits of electrically switching cells on and off. Scenario One is designed to capture the impact of switches on managing random stack failures by utilizing a cell failure model coupled to the electrolyzer model. Scenario Two is designed to isolate the impact of switches on managing cell degradation by using cell degradation models informed by lab-scale studies. The results of Scenario One are presented in Figure 1 in the attached image file. Up to 400,000$ (present value) in stack replacement costs can be saved (equivalent to 160% of uninstalled stack costs of $250k for a 1 MW stack in the simulation) over a 40-year operating period. Replacement costs are assumed to be 15% of the total system capital cost. Additional savings are realized with higher single cell failure rates as, more stack replacements are prevented over a fixed time period with increasing cell failures. There is a high likelihood that operational expenses can be reduced by operating electrolyzers with switches to address random stack failures under the assumptions and parameters considered in this study. The results of Scenario Two are presented in Figure 2 in the attached image where stack replacement costs are abbreviated as rep. There is an economic benefit to implementing switches across almost all simulations performed. The replacement cost savings range from the worst-case scenario where the switch costs are not recouped up to replacement cost savings of $250k to $3000k (present value) depending on the stack operating/performance assumptions and stack cost assumptions. This is equivalent to 100% to 1200% of uninstalled stack costs where uninstalled stack costs are $250k for a 1 MW stack. The results of the techno-economic analyses identify a clear parameter space where there is likely an economic benefit to implement switches that can turn off individual cells electrically in a stack. The economic impact of cell failures and degradation can be partially mitigated by implementing switches in a stack. Degradation and cell failure rates may be significantly reduced with innovation in the PEM electrolyzer space but, there are still a multitude of other benefits of switching electrolyzers that have not yet been quantified in this analysis. Stack failures, operational reliability, reduced downtime, and improved safety can all be realized in reduced operating capital costs. Thus under the assumptions and parameter spaces considered in this study show, there are potentially economic benefits from introducing cell-level switches within an electrolyzer stack. Figure 1

Achieving high stack durability, lifetime, and reliability are key requirements to enable low-cost hydrogen production through water electrolysis. However, failures in individual electrolyzer cells can significantly impact stack performance and lead to costly downtime or failures. Effective state-of-health monitoring of electrolyzer cells remains a critical unmet need. Electrochemical Impedance Spectroscopy (EIS) provides valuable diagnostic insights, but existing sensing solutions do not offer a clear, automated method for identifying anomalous cells. In this talk, we will present the first demonstration of automated anomaly detection in polymer electrolyte membrane water electrolyzer (PEMWE) cells using machine-learning techniques applied to EIS data. We leverage a dataset collected in collaboration with the National Renewable Energy Laboratory (NREL), consisting of EIS measurements from 14 baseline cells and 46 anomalous cells with 4 different kinds of defects, yielding 125 baseline and 378 anomalous EIS sweeps. Our approach formulates the anomaly detection problem as a classification task, where we distinguish between baseline (healthy) and anomalous (defective) cells based on EIS sweep data. We evaluate three algorithmic approaches: (1) thresholding of extracted EIS features, (2) random forest classification, and (3) hypothesis testing with Gaussian mixture models. The random forest model achieves a true positive rate (TPR) of ~80% and a true negative rate (TNR) of ~80%, demonstrating promising performance in identifying defective cells. The decision threshold can be further tuned to achieve the user’s preferences for False Positive Rate (FPR) vs. False Negative Rate (FNR). Further analysis reveals that defect type and DC current influence classification accuracy, with some defects being algorithmically detectable despite lacking visually discernible signatures in Nyquist plots. This study represents a significant step toward scalable, real-time electrolyzer health monitoring. By enabling automated detection of cell anomalies, our approach can facilitate condition-based maintenance, improve system reliability, and reduce operational costs. Future work will focus on refining model accuracy through hyperparameter tuning, exploring algorithm failure modes, and integrating stack-level monitoring capabilities.

The advancement of low temperature water electrolyzers at scale requires reduction of precious metal loadings, which are used as protective coatings and catalyst material within the device. In this talk, our progress in developing porous transport electrode (PTE) anodes for proton exchange membrane (PEM) water electrolysis will be discussed. The PTEs are based on Ti porous transport layer (PTL) substrates first coated with a Pt interlayer and subsequently coated with an Ir-based catalyst layer using readily scalable sputter deposition methods. Investigations toward reducing the total Pt and Ir loading without compromising performance lend understanding to the influences of 1) different PTL types, 2) the Pt interlayer, and 3) the form of IrO x in the catalyst layer. Physical characterization of the developed PTE architectures by XRF, XPS, RBS, XRD, SEM-EDS, and STEM will be presented and discussed. Beginning-of-life (BOL) performance characterization and analysis include polarization curve, electrochemical impedance spectroscopy, and cyclic voltammetry measurements. Durability testing conducted at 3 A/cm 2 for 1000 h will be presented. Results suggest that Ir loading may be reduced, without compromising performance, from 0.4 to 0.1 mg/cm 2 depending on the PTE architecture and fabrication methodology. Conclusions of this work support the potential for physical vapor deposition methods to deliver scalable, low-Ir loading, and durable PTE anodes for PEM water electrolysis.

Proton exchange membrane water electrolysis (PEMWE) is a promising route to produce cost-effective H 2 . However, thinner membranes and high cathode differential pressure are required to maximise its efficiency, and minimize cost. [1] Under such conditions, hydrogen crossover leads to undesired efficiency losses and safety hazards. Efforts to mitigate the effects of H2 crossover include the development of membranes which include a Pt recombination catalyst that consumes the H 2 and thus improves the turn down ratio of the electrolyzer. Methods to quantify the rate of recombination at the different components and interfaces in PEMWE cells are necessary to assess the effectiveness of the recombination catalyst. In this contribution, we quantify the total amount of H 2 harvested at the cathode, consumed in the cell, and leaving the anode compartment. By measuring the rates of hydrogen leaving both anode and cathode and comparing to Faraday’s law, we can quantify the total amount of H 2 being consumed in the cell. Figure 1 shows a schematic of the different processes occurring across a cell’s cross-section, as well as the newly developed technique to quantify H 2 exiting the cathode. The anode stream is measured using our previous method for analyzing the anode exhaust. [2] In this talk we will discuss results that verify the technique using a benchmark system at different cathode pressures, and apply it to membranes with and without recombination catalysts. References [1] A. Badgett, M. Ruth, and B. Pivovar, Electrochemical Power Sources: Fundamentals, Systems, and Applications Hydrogen Production by Water Electrolysis , Elsevier, 2021, pp. 327–364. doi: 10.1016/B978-0-12-819424-9.00005-7. [2] J. A. Wrubel, C. Milleville, E. Klein, J. Zack, A. M. Park, and G. Bender, Int J Hydrogen Energy , vol. 47, no. 66, pp. 28244–28253, Aug. 2022, doi: 10.1016/j.ijhydene.2022.06.155. Figure 1