The transportation and storage of renewable energy remain two of the biggest challenges along of the energy transition. Here esmajor technologiesHydrogen-connected technologies offer promising solutions to tackle them. In this talk, we show how various electrochemical energy conversion and storage technologies can be integrated to an integrated physical network at megawatt scale. Hydrogen Terminal Braunschweig is a demonstration facility established by Steinbeis-Innovationszentrum (siz) energieplus and Technical Electrocatalysis Laboratory, Universität Hamburg and some institutes from the Technische Universität Braunschweig. The world's first commercially available 1-MW electrolyzer prototype with anion exchange membrane (AEM) technology is employed to produce hydrogen in larger scale [1]. The hydrogen is then stored and used for a heavy duty truck refilling station (350 bar) as well as transported to internal and external fuel cell test benches via pipeline. Parallel to the H 2 supply, one of the external consumption points is also fed with electrolysis waste heat. For this purpose, the waste heat from the 1 MW electrolyzer is collected, processed in a high-temperature heat pump and supplied via a local heating network. The waste heat distribution and total output of the electrolyzer are tested and optimized for various operating conditions (start-up behaviour, output ramps). Another focus is the interplay between electrolyzers, fuel cells, battery storage system (1.1 MWh storage capacity) and photovoltaic systems to stabilize the electrical grid, when conventional fossil fuel power plant capacity is no longer available. A medium-voltage switchgear enables off-grid island operation as well as partial load and full load scenarios of all connected electrical components via switch positions. This allows us to evaluate the behaviour of electrolysis plants in the area of grid dynamics, which includes the DC-side electrolysis process. The behavior of other electrolyzer technologies such as alkaline electrolysis and proton exchange membrane (PEM) are studied in this facility in terms of performance and long-term durability. In the field of H 2 logistics, alternative transport solutions for urban districts are explored and behaviors of different H 2 transport/storage materials are tested within this project. Altogether, the Hydrogen Terminal Braunschweig is one of largest German demonstration facility with the clear focus on sector coupling, research, education and consulting.

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H 2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4] In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrO x catalyst materials. References: [1] P. Mandal et al, J. Power Sources 2018, 397, 397-404. [2] C.Qin et al, Catalysts 2016, 6, 197. [3] M. Tovini et al, J. The Electrochem. Soc. 2021, 168, 06452. [4] R. Marić et al., J. The Electrochem. Soc. 2020, 124520.

Cell reversal events are based on the hydrogen starvation, that takes place during to fast load changes, blockage of flow field channels or catalyst layer pores by liquid water. During the hydrogen starvation, protons and electrons continue to be supplied to the cathode, which is why carbon oxidation reaction (COR) sets in at the anode.[1] To mitigate the carbon oxidation reaction (COR), various catalyst strategies have been reported in the literature. For instance, the addition of iridium-based co-catalysts such as IrOx promote the oxygen evolution reaction (OER) instead of the carbon oxidation reaction (COR). [1-5] Although iridium is very costly and scarce, its use can be further increased by atomically mixing it with platinum to form a Pt-Ir alloy.In this work, we have prepared atomically mixed Pt-Ir alloy catalysts that combine both functionalities (hydrogen oxidation reaction and OER) in one nanoparticle (NP) in a unique matter. A colloidal route was chosen to control the particle size and composition of Pt-Ir NPs. The adopted synthesis method is based on the “Co4Cat” concept in methanol. [6] Afterwards, the colloidal NPs with controlled size of 1 – 2 nm and atomic Pt:Ir ratio of 1:1 and 3:1 were deposited on Vulcan XC72 Carbon and characterized by TEM, XPS and XRF techniques.The electrochemical experiments were performed in a three-electrode arrangement using a thin film rotating disc electrode (TF-RDE) technique. 0.1 M HClO4 was used as electrolyte solution. The ECSA was determined by underpotential deposited hydrogen (Hupd). Linear sweep voltammetry (LSV) measurements were performed to establish the HOR and OER activity. Thereby, the electrolyte was saturated with H2 and Ar for HOR and OER measurements, respectively.The PtIr/V and Pt3Ir/V catalysts with 1 – 2 nm show values of electrochemically active surface area (ECSA) of 70 ± 2 m2 g-1 PtIr and 73 ± 3 m2 g-1 PtIr. The HOR kinetics on platinum – iridium surfaces is very fast in acidic media. Therefore, we could only compare the measured HOR polarization curves with the theoretical diffusion limiting current. Since these are always on top of each other, we can conclude that the Pt-Ir catalysts are very active for HOR. In addition, the OER polarization curves were analyzed and showed an Ir-based mass activity of 70 ± 6 A g-1 Ir for PtIr/V and 104 ± 6 A g-1 Ir for Pt3Ir/V at iR-corrected potential of 1.50 VRHE. As a comparison, commercial IrOx shows a mass activity of 47 ± 6 A g-1 Ir at 1.50 VRHE.To investigate the electrochemical reversibility of Pt-Ir alloy catalysts, we alternated between the LSV measurements in the region of HOR and OER at least five times. One cycle includes three LSV measurements under each HOR and OER conditions. The HOR and OER activities for PtIr/V and Pt3Ir/V continuously decrease within the 5 cycles between HOR and OER. In other words, after the 5th cycle the OER mass activity dropped to 28 ± 3 A g-1 Ir and 32 ± 4 A g-1 Ir for PtIr/V and Pt3Ir/V catalysts, respectively. However, the ECSA values mainly retain and are 68 ± 2 m2 g-1 PtIr for PtIr/V and 70 ± 2 m2 g-1 PtIr for Pt3Ir/V.We can sum up that the colloidal Pt-Ir catalysts show bifunctional properties towards HOR and OER and reversible behaviour, which can be helpful to improve the cell reversal tolerance during the H2 starvation. Literature: [1] R. Marić et al., Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells, Journal of Electrochemical Society (2020)167, 124520 DOI:10.1149/1945-7111/abad68, [2] E. Alizadeh et al., The experimental analysis of a dead-end H2 /O2 PEM fuel cell stack with cascade type design, International Journal of Hydrogen Energy 42 (2017)11662 -11672DOI: https./7doi.org/10.1016/j.ijhydene.2017.03.094[3]Wang et al., Ir-Pt/C composite with high metal loading as a high-performance anti-reversal anode catalyst for proton exchange membrane fuel cells, International journal of hydrogen energy 47 (2022) DOI:10.1016/j.ijhydene.2022.02.065 [4] Kim et al., Pt-IrO x catalysts immobilized on defective carbon for efficient reversal tolerant anode in proton exchange membrane fuel cell, Journal of Catalysis (2021)DOI:https://doi.org/10.1016/j.jcat.2021.01.028[5]Fang et al, Facile synthesis of Pt-decorated Ir black as bifunctional oxygen catalyst Nanoscale(2019)11,9091DOI:10.1039/c9nr00279k[6]Quinson et al., Surfactant-free synthesis of size controlled platinum nanoparticles: Insights from in situ studies;Applied Surface Science (2021)549,149263 DOI: 10.1016/j.apsusc.2021.149263

PEMFCs operating with reformate gases (a mixture of H2, CO2, and CO) are a promising alternative for CO2-neutral and environmentally friendly maritime transportation. [1] However, even trace amounts of CO in the hydrogen feed rapidly deactivate the platinum (Pt) electrocatalysts, leading to a high anode overpotential. [2] Pt-ruthenium (Ru) alloy nanoparticles (NPs) supported on carbon (PtRu/C) are among the most widely used anode electrocatalyst materials due to their high CO tolerance during the hydrogen oxidation reaction (HOR). [2, 3] Nevertheless, the PtRu/C anode catalysts suffer from the Ruz+ dissolution followed by crossover through the membrane and re-deposition onto the Pt/C cathode catalyst surface during the long-time PEMFC operation. [3] These phenomena are the main degradation processes in PEMFCs operated with reformate gas. Even at a Ru coverage of the Pt/C cathode catalyst surface of less than 20 %, there is an 8-fold decrease in the kinetics of the oxygen reduction reaction (ORR). [4, 5] Hence, the development of electrochemical regeneration procedures to mitigate or remove Ru-poisoning of the cathode catalyst surface on cell level is essential to extend the lifetime of PEMFCs, e.g. for maritime applications. [6] Based on our previous work in a three-electrode setup [6], we transferred a selective set of regeneration protocols for Ru-poisoned ORR catalysts using a fully automatic single-cell PEMFC test station. Therefore, catalyst coated membranes (CCMs) with a 12 cm2 geometric surface area were prepared by using two commercial Pt-Ru/C catalysts with different atomic ratios on the cathode side, maintaining the Pt loading of 0.2 - 0.3 mgPt cm-2 geo, while the anode electrode layer contained Pt/C with around 0.1 mgPt cm-2 geo. The anode side was exposed to successive H2/air fronts with different residence times as part of a regeneration strategy of the cathode electrode. The effect of the H2/air front and their residence time were investigated through electrochemical characterization methods, such as polarization curves, Tafel slope, ECSA, HFR, and impedance spectroscopy. Electrochemical performance results were correlated with PEMFC operating conditions (H2/air front, residence times) and structural data to evaluate changes in particle size, structure, and chemical composition of two different Pt-Ru/C catalysts using several techniques like cross-section scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and microscopic X-ray fluorescence spectroscopy (µ-XRF). Our work evaluated different electrochemical recovery protocols of Ru-poisoned ORR catalyst materials to identify the most promising set of parameters for their re-activation procedure and therefore improve the lifetime of PEMFCs. References [1] A.G. Elkafas. M. Rivarolo, E. Gadducci, L. Magistri, A.F. Massardo, Fuel Cell Systems for Maritime A Review of Research Development, Commercial Products, Applications, and Perspectives, Processes, 11, (2023), 97; https://doi.org/10.3390/pr11010097 [2] P.A. Henry, L. Guétaz, N. Pélisser, P.A. Jacques, S. Escribano, Structural and chemical analysis by transmission electron microscopy of Pt-Ru membrane precipitates in proton exchange membrane fuel cell aged under reformate, Journal of Power Sources, 275 (2015), 312; http://dx.doi.org/10.1016/j.jpowsour.2014.10.167 [3] E. Antolini, The problem of Ru dissolution from Pt–Ru catalysts during fuel cell operation: analysis and solutions, Journal of Solid-State Electrochemistry, 15 (2011) 455-472; https://doi.org/10.1007/s10008-010-1124-7 [4] L. Gancs, B.N. Hult, N. Hakim, S. Mukerjee, The Impact of Ru Contamination of a Pt∕C Electrocatalyst on Its Oxygen-Reducing Activity, Electrochemical and Solid-State Letters, 10 (2007) B150; https://doi.org/10.1149/1.2754382 [5] V. Berova, A.G. Manjón, M.V. Paredes, T. Schwarz, N.A. Rivas, K. Hengge, T. Jurzinsky, C. Scheu, Influence of the shell thickness on the degradation of Ru@Pt core-shell catalysts in PEM fuel cells, Journal of Power Sources, 554 (2023), 232327; https://doi.org/10.1016/j.jpowsour.2022.232327 [6] Q. Guo, F. Hasché, M. Oezaslan, Regeneration Strategies for Ruthenium-Poisoned ORR Catalysts in Reformate PEM Fuel Cells, ECS Transactions, 112 (2023), 389; https://doi.org/10.1149/11204.0389ecst

PEM fuel cells, that are operated with a reformate gas (H2, CO2, CO), are of great interest in maritime applications. Despite its outstanding activity in the hydrogen oxidation reaction (HOR), platinum can be quickly poisoned by only very small amounts of CO. Therefore, high CO tolerant anode catalyst materials such as platinum (Pt)-ruthenium (Ru) alloy nanoparticles (NPs) supported on carbon (Pt-Ru/C) are used for PEMFCs supplied with reformate gas. (1) However, these Pt-Ru/C catalysts strongly suffer from the Ru dissolution followed by the crossover through the membrane to the cathode. At the cathode, the soluble Ruz+ species quickly re-deposit at the Pt/C catalyst, resulting in a dramatic loss of performance for the oxygen reduction reaction (ORR). For instance, the kinetics of the ORR decreases by a factor of 8, when the Ru coverage on the surface of Pt nanoparticles is in the range of 20 at.%. (2, 3) Very recently, we have reported different electrochemical regeneration strategies of Ru-poisoned cathode catalyst using rotating disc electrode (RDE) technique. (4) Although the poisoned catalyst could be mostly re-activated, the atomic processes during the regeneration are poorly understood to date. Therefore, operando and in-situ spectroscopic and microscopic techniques are needed. In this work, we combined the electrochemical regeneration protocols with in-situ XAS technique to better understand the re-dissolution processes of the RuOx species from the Pt-based catalyst particle surface. Our regeneration strategies can be categorized into dynamic and steady-state conditions. Each protocol involved an initial pre-activation process by holding the potential at 1.40 VRHE for 5 minutes in 0.1 M HClO4. The dynamic regeneration protocol was performed by potential pulsing between 1.40 VRHE and 1.60 VRHE in 10-second intervals using chronoamperometric method. Additionally, single pulse measurements at 1.60 VRHE with a duration time of 100 s and 300 s were applied for the steady-state regeneration protocol. The regeneration procedure plays an important role in the recovery of the Ru-poisoned ORR activity. The best results of a recovery procedure for PtRu2 and PtRu catalysts are obtained under steady-state condition at 1.60 VRHE for 100 s. The next step was to correlate the electrochemical regeneration experiments with in-situ XAS investigations on commercially available PtRu2 and PtRu catalysts. The Ru K edge and Pt L2/3 edges XAS measurements were carried out in a home-made electrochemical flow cell. Based on the in-situ XAS data, we were able to monitor the changes in the electronic structure and atomic environment of both elements in the alloy nanoparticles as a function of the recovery parameters (potential, holding time). In addition, ex-situ scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDX) investigations were carried out on Ru-poisoned catalysts after the regeneration protocol to collaborate with the results from XAS. In summary, XAS is a powerful technique to elucidate the electronic structure and atomic arrangement of Ru and Pt atoms and link them with the electrochemical parameters of the regeneration protocol. References [1] E. Antolini, The problem of Ru dissolution from Pt–Ru catalysts during fuel cell operation: analysis and solutions, Journal of Solid-State Electrochemistry, 15 (2011) 455-472; https://doi.org/10.1007/s10008-010-1124-7. [2] L. Gancs, B.N. Hult, N. Hakim, S. Mukerjee, The Impact of Ru Contamination of a Pt∕C Electrocatalyst on Its Oxygen-Reducing Activity, Electrochemical and Solid-State Letters, 10 (2007) B150; https://doi.org/10.1149/1.2754382 [3] T. Cheng, V. Colbow, S. Wessel, C. Chuy, and P. He, Impacts of Ru Dissolution and Crossover on Polymer Electrolyte Membrane Fuel Cell Performance and Anode Functionality, ECS Trans., 28(23), 243–251 (2010). https://doi.org/10.1149/1.3502355 [4] Q.Guo, F. Hasché and M. Oezaslan, Regeneration Strategies for Ruthenium-Poisoned ORR Catalysts in Reformate PEM Fuel Cells, ECS Transactions 112 389; https://doi.org/10.1149/11204.0389ecst

One of the main challenges to overcome for the wide implementation of PEMFCs is the improvement of their long-term durability. For instance, the blockage of the diffusion pathway by liquid water or rapid changes of load can lead to hydrogen starvation.[1] Due to the hydrogen starvation, the anode potential increases and accelerates the carbon oxidation reaction (COR) to further supply electrons and protons for the cathode ORR half-cell reaction, also referred to as cell reversal event.[2] Aggregation and particle detachment associated with the carbon corrosion occur, resulting in a drastic loss of the PEMFC performance.[3] Therefore, material innovation solutions are needed to overcome the cell reversal events. In this context, fast and simple accelerated stress tests and set-ups are needed. Currently, galvanostatic accelerated stress tests (G-AST) at single cell level are often used to evaluate the cell reversal tolerance (CRT) of catalyst materials, which is extremely time-consuming, costly and slow.[4] On the other hand, the rotating disc electrode (RDE) technique is widely used, simple, less expensive and fast for catalyst screening. However, the electrochemical measurements of activity and durability are usually carried out in the potentiostatic mode. The research question arises whether the RDE technique is capable of evaluating the CRT behaviour of novel catalyst materials using galvanostatic AST. This systematic work compared both galvanostatic and potentiostatic accelerated stress tests (G-AST and P-AST) protocols to evaluate the degradation behaviour of novel bifunctional Pt-Ir alloy catalyst materials for hydrogen starvation. The Pt-Ir alloy catalysts with 1:1 and 3:1 ratios were prepared by wet-impregnation route. Here, the PtIr and Pt3Ir catalysts supported on Vulcan XC72 show a mean particle size of 3-5 nm and total metal loading of 35-50 wt.%Pt+Ir obtained from TEM, TGA and EDX data. In a RDE set-up equipped with three-electrode configuration, all electrochemical measurements were performed in 0.1 M HClO4 and room temperature. At begin-of-life (BoL), the performance of the Pt-Ir catalysts was evaluated by measuring the ECSA via Hupd and CO stripping methods, HOR and OER polarization curves. It is noted that the HOR polarization curves were only fitted with the diffusion limiting current due to the fast kinetics of the HOR on platinum and iridium surfaces in acidic media. For the G-AST protocol, a current density of 0.5 mA/cm2 geo was held for 10h with a cut off at 2 VRHE. The time it takes to reach 2 VRHE is referred to as the fail time (FT) and signifies the loss of the protection mechanism of catalyst materials, namely the OER activity. Based on the results from the G-AST protocol, the same FT was used to perform the chronoamperometric measurements by holding the potential at 1.6 VRHE during the P-AST protocol. At the BoL, the Pt-Ir catalysts with 3-4 nm size show sufficient ECSA values (45-50 m2/gPt+Ir via Hupd) and improved OER activity (PtIr: 23±6 A/gPt+Ir and Pt3Ir: 8±1 A/gPt+Ir @1.5 VRHE) compared to the commercial Pt/V catalyst (79±4 m2/gPt via Hupd, 6±1 A/gPt @1.5 VRHE) and IrOx (47±6 A/gIr). During the G-AST, we observed that the FT increases with higher Ir content. In addition, the Pt3Ir/V catalyst shows a significant improvement of FT compared to the Pt/V. More precisely, during the G-AST protocol, the potential of 2 VRHE by applying a constant current density of 0.5 mA/cmgeo was already reached after 15min, while for the Pt3Ir/V catalyst this took at least 1 hour. Furthermore, our data shows that the G-AST protocol is more aggressive compared to the P-AST to evaluate the catalyst aging processes. Altogether, we showed the influence of galvanostatic and potentiostatic ASTs for rapid benchmarking of novel bifunctional cell reversal tolerant Pt-Ir alloy catalysts using the three-electrode RDE technique. This study can be helped to improve the electrochemical results obtained from the RDE to the catalyst coated membranes. [1] Marić, R. et al.Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration. J. Electrochem. Soc., 2020, 167, 124520. DOI: https://doi.org/10.1149/1945-7111/abad68 [2] Chen W. et al.: Thickness effects of anode catalyst layer on reversal tolerant performance in proton exchange membrane fuel cell. Int. J. Hydrog. Energy, 2021, 46, 8749. DOI: https://doi.org/10.1016/j.ijhydene.2020.12.041 [3] Zhou X. et al.: High-Repetitive Reversal Tolerant Performance of Proton-Exchange Membrane Fuel Cell by Designing a Suitable Anode. ACS OMEGA, 2020, 5, 10099. DOI: https://dx.doi.org/10.1021/acsomega.0c00638 [4] Peng Y. et al.: Pitfalls of a commonly used accelerated stress test for reversal tolerance testing of proton exchange membrane fuel cell anode layers. J. Power Sources, 2021, 500, 229986. DOI: https://doi.org/10.1016/j.jpowsour.2024.234087

Electrospinning has emerged as a promising approach to prepare porous cathode catalyst layers (CCLs) with low loading of platinum group metals (PGM) for PEM fuel cells. In particular, electrospun nanometer-sized fibers can be used as a backbone to increase the utilization and accessibility of catalytically active sites at low PGM loading as well as improve water management at high current density. [1, 2] Beside the low PGM loading, the absence of external humidifier is important for practical applications, because it can further decrease the parasitic power losses as well as complexity, weight, volume, and cost of the PEMFC system. [3] In this context, electrospun nanofiber CCLs show a pronounced humidity-dependent performance loss, which hinders their operation range compared to conventional CCLs prepared by decal transfer process. For example, Brodt et al. show a performance decrease for electrospun CCL of around 75 % at relative humidity (RH) of 40 % compared to 100 % RH. [4] In contrast, the electrosprayed CCL exhibits only a loss of around 30 % under the same conditions. [4] Therefore, the development of highly active and robust CCLs operating at high current density under low humidity remain a great challenge to date. In this work, we systematically investigated the effects of the humidity on the performance of the nanofiber-based CCLs. To prepare the CCLs with a geometric surface area of 50 cm2, a nozzle-free electrospinning machine by Elmarco S.R.O. (Liberec, Czech Republic) was employed. The ink containing Pt/C catalyst, ionomer, and polyacrylic acid (PAA) was mixed using a disperser. Thereby, several highly homogeneous CCLs deposited on a gas diffusion layer (GDL) with controlled platinum loading of up to 0.1 mg cm-2 geo were prepared and characterized using micro X-ray fluorescence spectroscopy (μXRF). The morphology and chemical distribution of the as-prepared CCLs were evaluated from the scanning electron microscope equipped with energy-dispersive X-ray spectroscopy (SEM-EDX). We then correlated the structural information (Pt and Nafion distribution, size of the nanofibers, etc.) of the CCLs with the electrochemical performance (U-I curve, ECSA, HFR, proton conductivity, etc.) at single cell level. Additionally, the impact of the humidity variations (20 – 100 % RH) for the nanofiber-based CCLs was compared to the conventional CCLs prepared by decal-transfer method. Moreover, high resolution (S)TEM-EDX was employed to uncover the distribution of the PFSA ionomer, Pt/C catalyst and PAA. These data are correlated with the ECSA and indicate the utilization and accessibility of Pt nanoparticles linked with the spatial distribution of PFSA ionomer. Altogether, we provide fundamental insights into the relationship between humidity and performance for nanofiber-based PEMFC CCLs prepared by electrospinning. New strategies will be presented to overcome the structure-humidity-sensitivity behavior of these novel three-dimensional nanofiber-based CCLs. [5] References [1] Brodt M, Wycisk R, Pintauro P N: Nanofiber Electrodes for High Power PEM Fuel Cells. J. Electrochem. Soc. 2013, 160 (8), F744-F749. DOI: https://doi.org/10.1149/2.008308jes. [2] Zhang W, Pintauro P N: High-Performance Nanofiber Fuel Cell Electrodes. ChemSusChem 2011, 4 (12), 1753-1757. DOI: https://doi.org/10.1002/cssc.201100245. [3] Ren G, Qu Z, Wang X et al.: Electrospun fabrication and experimental characterization of highly porous microporous layers for PEM fuel cells. International Journal of Hydrogen Energy 2024, 55, 455 - 463. DOI: https://doi.org/10.1016/j.ijhydene.2023.11.226. [4] Brodt M, Han T, Dale N et al.: Fabrication, In-Situ Performance, and Durability of Nanofiber Fuel Cell Electrodes. J Electrochem Soc 2015, 162, F84-F91. DOI: https://doi.org/10.1149/2.0651501jes. [5] Kallina V, Hasché F, Oezaslan M: Advanced Design of Electrospun Nanofiber Cathode Catalyst Layers for PEM Fuel Cells at Low Humidity. Current Opinion in Electrochemistry 2024, submitted.

Water management is critical for high performance of polymer electrolyte membrane water electrolysis (PEMWE). In this work, we investigated the water crossover for 5 cm 2 PEMWE single cell by varying the temperature (40–80 °C), current density (0–2 A cm −2 geo ), cathode pressure (ambient, 310 kPa gauge,inlet ), and nitrogen purge rate (50, 100 nccm). Using an advanced gravimetric method, the water crossover to the cathode could be established very accurately and also corrected by the water vapor fraction. Here, we pointed out that the cathode exhaust gas is saturated with water vapor, either from diffusion or by proton drag at low or high current densities, respectively. Very importantly, the water crossover at high current density is controlled by the proton drag and are used to extract the temperature-dependent proton drag coefficient at 1 A cm −2 geo . Our results reveal that the proton drag coefficient increases from 2.5 ± 0.2 at 40 °C to 3.2 ± 0.2 at 80 °C (+28%). Altogether, we have developed a sophisticated gravimetric method to accurately determine the water crossover under PEMWE operating conditions and proposed a model of the temperature-dependent proton drag coefficient. Unravelling the proton drag and diffusion is very important for modeling of water transport in PEMWE.

Pretreatment and purification of water is necessary to use it as a feed for the oxygen evolution reaction (OER) at the anode of PEM water electrolysis (PEMWE). Fresh water typically contains several multivalent cations such as Ca2+ and K+. In addition, iron cations may accumulate in PEMWE over a long period of time due to corrosion of system components and fittings of the PEMWE. The presence of these multivalent cations in the feed water causes higher ohmic resistance of the cell and higher iR-free voltages, resulting in a performance loss.[1] Furthermore, the cations can be transported by the water crossover stream from anode to cathode and by diffusion transport.[2] In other words, even traces of metal cations drastically influence the efficiency and durability of PEMWE stacks. Despite this knowledge, contamination with multivalent cations is one to the main reason for the breakdown of PEMWE stacks.[3] Very interestingly, simulations of cationic contamination for PEM fuel cells (PEMFCs)[4] have shown that the distribution of metal cations in the through-plane direction depends on the proton current through the membrane. The cation concentration profile indicates an accumulation of metal cations close to the cathode side and leads to an increase of the proton transport resistance. In addition, the simulations indicate that in case of a complete substitution of protons by metal cations, the proton transport resistance approaches infinity. Finally, the proton current cannot increase further and a limiting current is reached.[4] The transfer/adoption of these simulations from PEMFC to PEMWE allows to clarify the behavior of the limiting current in dependence of the nature of metal cations such as Ca2+ and K+ and their concentrations, which is still poorly understood to date. In this work, we investigated if the concept of limiting protonic current from simulations for the PEMFC can be (partially) transferred to PEMWE on a laboratory scale. For this purpose, we evaluated the effect of trace metal cations in the anode feed water on the performance of a PEMWE single cell and quantified the cation concentration in the membrane using spectroscopic techniques such as micro X-ray fluorescence (µ-XRF) and energy-dispersive X-ray (EDX). Electrochemical measurements were carried out in an in-house PEMWE test bench equipped with a single cell of 5 cm2 geometric electrode area and potentiostat with booster. Commercially available catalyst coated membranes with a loading of 0.3 mg cm-2 geo of Pt/C and 1 mg cm-2 geo of IrOx were used. The measurements were carried out at atmospheric pressure and a cell temperature of 80°C. First, a conditioning procedure was performed using highly purified feed water (>20 MΩ cm at room temperature) until a stable cell performance had been achieved. Cation contamination experiments were conducted by introducing various concentrations of metal sulfates (1-100 µmol L-1 cation concentration) into the anode feed water. Performance evaluation was carried out by measuring the polarization curves and electrochemical impedance spectroscopy (EIS) to determine the Tafel slope, overvoltage, and high frequency resistance (HFR). µ-XRF and EDX spectroscopy techniques were used to detect the cation concentration profile along the membrane. We observed a significant rise of the cell voltage by adding cations to the anode water feed within few hours. More precisely, a limiting current density of 1 A cm-2 geo after 16 hours of exposure to 100 µmol L-1 K+-ions in the anode feed water was determined using the Koutecký-Levich equation. This result is in line with our first simulations. The switch back to purified feed water allows us to monitor the dynamics of the performance recovery process obtained from EIS data. Additional measurements of the polarization curves and HFR were used to distinguish between reversible and irreversible degradation processes due to the cation contamination. Very interestingly, a partial reversibility was observed after the K+-contamination, as the limiting current increased from 1 to 2 A cm-2 geo after 16 hours recovery with purified water feed. Altogether, this study evaluated the transferability of limiting protonic current concept from simulations in PEMFC to PEMWE to uncover the impact of trace metal cations in the anode feed water on the performance of PEMWE. [1] C. Immerz, M. Singer, F. Hasché, B. Bensmann, M. Suermann, R. Hanke-Rauschenbach, M. Oezaslan, Meet. Abstr. 2020, MA2020-02, 2456. [2] M. Friedrichs-Schucht, F. Hasché, M. Oezaslan, ECS Trans. 2023, 111, 3. [3] N. Danilovic, K. E. Ayers, C. Capuano, J. N. Renner, L. Wiles, M. Pertoso, ECS Trans. 2016, 75, 395. [4] B. L. Kienitz, H. Baskaran, T. A. Zawodzinski, Electrochim. Acta 2009, 54, 1671.

Electrospinning has emerged as a very promising preparation method of PEMFC cathode catalyst layers (CCLs) with high performance in the mass transport region due to their unique network structure for water transport and O2 accessibility. We will present the recent improvement strategies and humidity effect for electrospun nanofiber CCLs. Additionally, we will discuss the possible causes of their humidity-dependent performance losses. Thereby, the ionomer – carrier polymer interactions and local ionomer distribution play a critical role on the proton conductivity and accessibility of active Pt nanoparticles. Despite the high current densities achieved so far, more demanding PEMFC operating strategies are required to maintain the performance of nanofiber CCLs in a wide range of humidity.

Large-scale hydrogen production by PEM water electrolysis (PEMWE) in the energy sector requires a deep understanding of the system behaviour in failure cases and possible recovery procedures. This includes the purification of the anolyte feed water because the contamination with ions can cause the PEMWE stack to breakdown. [1] For instance, the presence of iron trace cations or other metal cations in the feed water leads to a performance loss due to higher ohmic resistance of the cell and higher iR-free voltages. [2] [3] Moreover, cation contamination might influence the water transport in a PEMWE cell. In principle, the transfer of the water molecules to the cathode is proportional to the proton flux from the cathode to the anode. The proportionality factor is defined as water transport coefficient and is also temperature dependent. [4] In case of the mono- and multivalent cations as trace elements in the feed water, the water loading of the membrane, which is expressed by water molecules per sulfonic acid group of the membrane, λ, decreases over time and leads to successive increase in the ohmic resistance. [5] However, the influence of cation contamination on the water transport in PEMWE is poorly understood to date. In this work, we investigated the effect of cation contamination in the anode feed water on the water crossover for PEMWE. Cation contamination experiments were carried out at a constant current density by adding different concentrations such as K 2 SO 4 , Na 2 SO 4 , etc. to the anode feed water. All electrochemical measurements were carried out in an in-house test bench equipped with a single cell of 5 cm 2 geometric electrode area and potentiostat with booster. A commercially available catalyst coated perfluorosulfonic acid membranes (loading of 0.3 mg cm -2 geo Pt/C and 1 mgcm -2 geo IrO x ) was used. The anode and cathode compartments were kept at atmospheric pressure and cell temperature of 80°C. To determine the water crossover from anode to cathode at different current densities, the cathode exhaust was cooled in a heat exchanger and measured by a gravimetric method. [4] Firstly, a conditioning procedure was performed with purified feed water until steady cell performance was achieved. The cell performance was evaluated using polarization curves, electrochemical impedance spectroscopy (EIS) and water crossover measurements. The last two are of particular interest, because they provide information about membrane humidification. The Tafel slope and mass transport overvoltage were established from the polarization curves and high frequency resistance (HFR). We observed a significant rise of the cell voltage by adding cations to the anode water feed within few hours. The analysis of Tafel slope and EIS data also reveal an increase of ohmic and mass transport resistances. In these experiments, we were able to correlate the HFR results with the water crossover as a function of the nature of the cation and its concentrations. Our data shows that the specific water crossover per current density decreases as a consequence of cation contamination. The switch back to purified feed water allows us to monitor the dynamics of the performance recovery process obtained from EIS and water crossover measurements. Additional measurements of the polarization curves and HFR were used to distinguish between reversible and irreversible degradation processes due to the cation contamination. Altogether, we present the effect of cation contamination on the water transport processes and provide deeper insights into the mass transport and performance losses for PEMWE. References [1] N. Danilovic, K. E. Ayers, C. Capuano, J. N. Renner, L. Wiles, M. Pertoso, ECS Trans. 2016 , 75 , 395. [2] C. Immerz, M. Singer, F. Hasché, B. Bensmann, M. Suermann, R. Hanke-Rauschenbach, M. Oezaslan 2020 , MA2020-02 , 2456. [3] H. Becker, J. Murawski, D. V. Shinde, I. E. L. Stephens, G. Hinds, G. Smith, Sustainable Energy Fuels 2023 , 7 , 1565. [4] M. Friedrichs-Schucht, F. Hasché, M. Oezaslan, ECS Trans. 2023 , 111 , 3. [5] T. Okada, Y. Ayato, M. Yuasa, I. Sekine, J. Phys. Chem. B 1999 , 103 , 3315.

Two of the greatest challenges in the energy transition are still the transportation and storage of renewable energy. For a green hydrogen economy, electrochemistry will play a major role. This project will show a comprehensive integration of various hydrogen technologies to an integrated physical network at megawatt scale. Our demonstration facility, namely Hydrogen Terminal Braunschweig, is located in Lower Saxony, Germany and was established in Summer 2024 [1]. In the Hydrogen Terminal Braunschweig, the green hydrogen (H2) is generated by the world's first commercially available 1 MW electrolyzer prototype of anion exchange membrane (AEM) technology [2]. The produced H2 from the renewable energy will be stored and used for a heavy-duty truck refilling station (350 bar) as well as transported to internal and external fuel cell test benches via pipelines. In addition to the H2 supply, one of the external consumption points is also fed with electrolysis “waste” heat. The waste heat from the 1 MW electrolyzer is collected, processed in a high-temperature heat pump and supplied via a local heating network. Moreover, the technical interplay and conjunction between electrolyzers and fuel cells with a large battery storage system (1.1 MWh storage capacity) and photovoltaic systems to stabilize the electrical grid will be investigated in detail. Here, a medium-voltage switchgear enables off-grid island operation as well as partial load and full load scenarios of all connected electrical components via switch positions. Last but not least, we will develop an education and training program for various target groups in the field of hydrogen technologies and energy transition in the near future. References [1] https://magazin.tu-braunschweig.de/en/pi-post/opening-and-open-day-of-the-hydrogen-terminal-braunschweig/, press releases, 21. June 2024 [2] https://www.enapter.com/aem-electrolysers/aem-nexus/, Aug 2024

In this work, we investigated the temperature dependence on the water transport coefficient for proton exchange membrane water electrolysis (PEMWE). The experimental parameters varied between 40 and 80 °C at a current density of 1 A cm-2 geo and ambient pressure. The water crossover to the cathode was measured by cooling the exhaust and weighing the liquid fraction over 4 hours under steady conditions. The remaining water vapor from the gaseous fraction was taken into account by the temperature-dependent vapor pressure curve. The resulting data of the water crossover [mg cm-2 geo min-1] depends on the temperature, time and current density applied. The main driving force of the water crossover is the proton flux through the membrane and can be established by fitting the data of the relative changes in water mass over time with a linear function. For now, the water diffusion which has a minor contribution is not considered. Our results reveal that the water transport coefficient derived from the proton flux increases from 2.4 at 40 °C to 3.1 at 80 °C (growth of +29%). In summary, we have developed a method to more accurately determine the water transport coefficient, which is very useful in modeling the water crossover in PEMWE.

PEM fuel cells operating on reformate gases suffer from Ru crossover and its re-deposition in the cathode catalyst layer. Therefore, strategies for regeneration of Ru-poisoned ORR catalysts are needed. Here, we developed a regeneration protocol and tested this for commercial PtRu 2 /Vulcan, which represents a worst case scenario of Ru-poisoned ORR catalysts due to the high Ru content and good intermixture with Pt. Our protocol consists of two chronoamperometric cycles, namely at 1.4 V RHE for 5 minutes followed by 1.6 V RHE for 100 s. The Ru deletion as a function of the number of regeneration cycles was in-situ monitored by electrochemical CO stripping method. The mass and specific ORR activities of the recovered PtRu 2 /Vulcan increase by 6-times and 4.4-times, respectively. Very remarkably, our regeneration protocol aims to trigger the Ru dissolution by forming the RuO 4 during the OER without a negative impact on the catalytic ORR properties of Pt.

Affordable and clean energy is one of the 17 sustainable development goals proposed by the United Nations in 2015. [1] In this context, polymer electrolyte membrane fuel cells (PEMFCs) are a promising renewable and clean energy conversion technology. The large implementation of PEMFCs, however, is hindered by high loading of very costly and scarce platinum group metals (PGM) and insufficient long-term durability. Most of the cathode catalysts are suffering from hydrogen/air start-up/shut-down (SUSD) conditions. [2, 3] Generally, the performance of the PEMFC is controlled by the utilization of the catalytically active sites and the mass transport properties within the porous catalyst layers (CL) in particular operating at high current density. New strategies in the design of functional porous catalyst layers are needed to overcome these challenges. As a very promising strategy, nanometer-sized fibers prepared by electrospinning can be used as a backbone to improve the utilization and accessibility of catalytically active sites by maintaining the PGM loading. [4, 5] In this work, a nozzle-free electrospinning machine by Elmarco S.R.O. (Liberec, Czech Republic) was employed to design and nano-engineer advanced catalyst layers with improved catalytic as well as mass transport properties. Thereby, several highly homogeneous catalyst layers deposited on gas diffusion layer with controlled platinum loading of up to 0.1 mg/cm 2 were prepared and characterized by scanning electron microscope (SEM) and micro X-ray fluorescence spectroscopy (μ-XRF). The structural information such as morphology and chemical distribution was correlated with the electrochemical data obtained from the single cell measurements in a fuel cell test station. Additionally, the durability of the as-prepared nanofiber-based catalyst layers was studied under real hydrogen/air SUSD conditions. Our results show the impact of different nanostructured catalyst layers prepared by electrospinning process on the long-term performance of the PEMFC. Here, we will present the great advantages of the electrospun catalyst layers over the classical catalyst layers prepared by decal transfer process. References [1] https://sdgs.un.org/goals/goal7 (date 26 March 2023). [2] Mittermeier et al., J. Electrochem. Soc. 2017, 164 (2) F127-F137. DOI: https://doi.org/10.1149/2.1061702jes [3] Mittermeier et al., J. Electrochem. Soc. 2018, 165 (16) F1349-F1357. DOI: https://doi.org/10.1149/2.0931816jes [4] M. Brodt et al., J. Electrochem. Soc. 2013, 160 (8), F744-F749. DOI: https://doi.org/10.1149/2.008308jes [5] W. Zhang et al., ChemSusChem 2011, 4 (12), 1753-1757. DOI: https://doi.org/10.1002/cssc.201100245

For several decades, proton exchange membrane fuel cells (PEMFCs) have been a topic of zero-emission energy conversion technology research, spanning from material development to system control. Most of the PEMFC research is focused on the cost reduction of catalyst and membrane as well as the improvement of the long-term durability. Harsh and dynamic operating conditions such as rapid load changes, cold start temperatures, insufficient gas supply or flooding of the anode with water lead to a fatal damage of the very thin anode catalyst layer. [1-2] During the hydrogen starvation, the carbon corrosion occurs to supply further protons and electrons to the cathode, resulting in an increase of the anode potential. This event is well-known as cell reserval and results in a decrease of the overall PEMFC performance. In this study, we evaluated a new catalyst concept by combining both functionalities (hydrogen oxidation reaction (HOR) and oxygen evolution reaction (OER)) in single nanoparticles. The potential of this bifunctional catalyst concept will be compared with the mostly used catalyst system prepared by a physical mixture of Pt/C and IrOx as co-catalyst. Controlling the chemical composition and structure of the bifunctional nanoparticle catalyst system allows to improve the cell reversal tolerance. References [1] Moore, C. E., Eastcott, J., Cimenti, M., Kremliakova, N., & Gyenge, E. L. (2019). Novel methodology for ex situ characterization of iridium oxide catalysts in voltage reversal tolerant proton exchange membrane fuel cell anodes. Journal of Power Sources, 417, 53-60. DOI: https://doi.org/10.1016/j.jpowsour.2019.02.006 [2] Marić, R., Gebauer, C., Nesselberger, M., Hasché, F., & Strasser, P. (2020). Towards a Harmonized Accelerated Stress Test Protocol for Fuel Starvation Induced Cell Reversal Events in PEM Fuel Cells: The Effect of Pulse Duration. Journal of The Electrochemical Society, 167(12), 124520. DOI: https://doi.org/10.1149/1945-7111/abad68

The importance of hydrogen production by proton exchange membrane water electrolysis (PEMWE) in the energy sector makes it worthwhile to understand the system behaviour in failure cases and possible recovery procedures. In particular, insufficient feed water supply to the anode can be caused by inhomogeneous distribution in the stack, pump failure or erroneous operation strategy. For the PEMWE, a distinct turnover point has been reported if feed water supply is reduced in isothermal conditions.[1] Further reduction of the water supply results in higher ohmic resistance due to gradual membrane dehydration and increased mass transport losses.[2] Here, we will use the term “ water starvation ” to describe this event. The drainage of water from the anode can be explained by oxygen evolution reaction (OER), humidification of oxygen gas and water crossover to the cathode. The last one was measured for well hydrated membranes at atmospheric pressure [3] or below typical operating temperatures [4]. In the first part of this work, we present the water crossover in a PEMWE on single cell level to understand their dependence on the operating parameters such as temperature and pressure. Media were supplied and conditioned to a 5 cm 2 single cell by using an in-house test bench and a potentiostate with booster. The electrochemical measurements were performed with a commercially available catalyst coated perfluorosulfonic acid membranes (loading of 0.3 mg/cm 2 geo Pt/C on cathode and 1 mg/ cm 2 geo Ir-Oxide on anode). The anode was kept at atmospheric pressure, whereas the cathode pressure was varied from atmospheric to 400 kPa abs at various current densities and cell temperatures of 40 – 80 °C. To determine the water crossover under several operating conditions, the water vapour was condensed to liquid phase in a heat exchanger and measured by a gravimetric method. Furthermore, the measured water crossover is used to force a water starvation in the second part of this work. After cell assembly, a conditioning procedure was performed until steady cell performance was achieved. Cell performance was evaluated using polarization curve, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and water crossover. The last two are of particular interest, because they provide information about membrane humidification. The Tafel slope and mass transport overvoltage were evaluated from the polarization curves and high frequency resistance (HFR). Water starvation experiments were then carried out at a constant cell voltage by reducing the feed water supply, resulting in a dramatic decay of the current density. The analysis of Tafel slope and EIS data reveals an increase of ohmic and mass transport resistances. Furthermore, the HFR measurements were correlated with water crossover as a function of membrane hydration. We observed that the specific water crossover per current density decreases as a consequence of membrane dehydration. After this step, feed water supply was increased to an unrestricting level for membrane rehydration and performance recovery. For this recovery procedure, different operation modes were employed by varying the current densities. At constant current density, membrane hydration is influenced by the ionic current from the cathode to the anode via proton drag. EIS and water crossover measurements allow us to determine the influence of operation on the dynamics of the membrane rehydration process. Together with the polarization curves, cyclic voltammetry and HFR data, reversible and irreversible degradation processes caused by the water starvation can be identified. Altogether, we present a deeper understanding of water crossover for a wide operating parameter range and provide a guideline for recovery of the performance for PEMWE. [1] Christoph Immerz et al 2020 Meet. Abstr. MA2020-02 2456 [2] C. Immerz, B. Bensmann, P. Trinke, M. Suermann, R. Hanke-Rauschenbach, J. Electrochem. Soc. 2018, 165, F1292-F1299. [3] K. Onda, T. Murakami, T. Hikosaka, M. Kobayashi, R. Notu, K. Ito, J. Electrochem. Soc. 2002, 149, A1069. [4] P. Medina, M. Santarelli, International Journal of Hydrogen Energy 2010, 35, 5173.

Global fuel starvation is an undesired event during fuel cell operation that results in serious degradations at the anode catalyst layer caused by the concomitant reversal of the cell potentials. Several groups have therefore intensified their research efforts towards the implementation of suitable diagnostic tools and accelerated stress test (AST) protocols that mimic cell reversal events. However, the current number of different test protocols requires consolidation and harmonization to define durability targets towards cell reversal tolerance and to benchmark newly developed materials. To create a basis for harmonization, this study examines the difference between pulsed and quasi-continuous AST protocols at the catalyst-coated membrane level. Utilizing a single-cell setup combined with an on-line mass spectrometer, a 2.5-fold increase in the carbon corrosion rates were found for short-pulsed compared to long-lasting cell reversal events. The enhanced corrosion was associated with a 2.2-fold higher loss of electrochemically active surface area and a 15% higher reduction in anode catalyst layer thickness. By contrast, the overall cell performance decreased additionally by 40–50 mV for samples under long-lasting cell reversal events. The decay is mainly driven by an increased ohmic resistance, presumably originating from a more pronounced surface oxide formation on the carbon support.

A broad scientific consensus exists that anthropogenic emissions are major factors fueling global warming and its potential impacts on the earth’s ecosystem. On the way to a sustainable and decarbonized energy supply, "green" hydrogen is an emission-free alternative to conventional energy carriers. In this context, proton exchange membrane fuel cells (PEMFCs) offer promising properties for the electromobility by a simple scalability of the performance through the modular design of fuel cell stacks, a refueling time and range comparable with conventional combustion engines and zero emissions if "green" hydrogen is used. Despite all scientific work on this field – performance, cost and durability issues still hamper the wide commercialization of PEMFCs. Concerning the durability, global fuel starvation causes destructive and irreversible degradation at the anode catalyst. A lack of fuel supply leads to the anode potential being raised to levels where the oxygen evolution reaction (OER) and carbon oxidation reaction (COR) take place instead of the hydrogen oxidation reaction (HOR). Thus, the overall cell voltage reverses compared to normal operation. In consequence, the widely employed carbon-supported anode catalyst corrodes and the overall cell performance is reduced if appropriate mitigation strategies are absent [1]. Among other remedies, incorporating a second catalyst component with an enhanced OER activity, such as IrO2 [2], is a promising material-specific strategy. Within this study we present a technical approach on single cell level (50 cm2 geo) to investigate and evaluate the impact of short-pulsed versus long-lasting fuel starvation events on the degradation of a reversal-tolerant anode catalyst layer comprising Pt/C and IrO2 [3]. By utilizing an on-line mass spectrometer, the anode exhaust gas stream is examined in terms of O2- and CO2-amounts to reveal the origin of the degrading effect. References: [1] T. Ioroi and K. Yasuda, J. Power Sources, 450, 227656 (2020). [2] K. H. Lim, W. H. Lee, Y. Jeong, and H. Kim, J. Electrochem. Soc., 164, F1580 (2017). [3] R. Marić, C. Gebauer, M. Nesselberger, F. Hasché, and P. Strasser, to be submitted.

Proton exchange membrane water electrolysis (PEMWE) will play a major role in the clean and versatile energy conversion in the near future.[1] Offering scalable solutions of PEMWE are of high industrial interest and have to provide a sufficient durability and reliability.[2] To achieve this, a better understanding of the impact of contamination on the PEMWE performance is very crucial. In this context, the membrane electrode assembly (MEA) is susceptible to several degradation processes like metallic cations (Fe3+/2+ stemmed from tubing). In particular, soluble and reduced iron species forming by Fenton reaction might attack via radicals the MEA.[3,4] Hence, analyzing impurities and their resulting impacts on e.g. the proton transport resistance and degradation mechanisms at different length scales and local distributions are of large interest. In this work, the influence of spatially resolved iron contamination in MEAs on the cell performance has been investigated using a 50 cm single-channel PEMWE cell equipped with local current density measurement setup.[5] Adding defined amounts of FeSO4 via the anode inlet feed, the changes on the three main regimes of overpotentials, i.e. kinetic, ohmic and mass transport, is correlated with the current density mapping as well as local and global electrochemical impedance spectroscopy (EIS) measurements. Ex-situ scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to detect the distribution and agglomeration of iron species within the MEA. With this combined approach of electrochemical and ex-situ physical methods, the contamination pathways and their effects of (spatially resolved) iron contamination on the overall performance of MEA are investigated as a function of degree of contamination and operating conditions. Especially, the (spatially resolved) overpotential-specific degradation processes along the 0.5 m channel, which mimic a technically relevant stack size, allow us to conclude on the optimum design of MEA, targeting use of mitigation strategies and development of accelerated stress test protocols. [1] M.A. Pellow, C.J.M. Emmott, C.J. Barnhart, S.M. Benson, Energy Environ. Sci. 8 (2015) 1938-1952. [2] P.K. Shen, C.-Y. Wang, S.P. Jiang, X. Sun, J. Zhang, Electrochemical Energy: Advanced Materials and Technologies, CRC Press, 2015. [3] X. Wang, L. Zhang, G. Li, G. Zhang, Z.-G. Shao, B. Yi, Electrochim. Acta 158 (2015) 253-257. [4] C. Rozain, P. Millet, Electrochim. Acta 131 (2014) 160e167. [5] C. Immerz, B. Bensmann, P. Trinke, M. Suermann, R. Hanke-Rauschenbach, JECS 165 (16) (2018)