Degradation Mechanisms in PEM Electrolyzers – Occurrence, Relevance and How We Can Measure Them

EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 1/9 B1004 Degradation Mechanisms in PEM Electrolyzers – Occurrence, Relevance and How We Can Measure Them Annik Bernhardt* (1,2), Katja Lange (1), Kerstin Witte-Bodnar (1,3), Klemens Ilse (1) (1) Fraunhofer IMWS, Halle (Saale)/Germany; (2) Martin-Luther-Universität, Halle (Saale)/Germany; (3) Hochschule Anhalt, University of Applied Science, Köthen/Germany; *Contact corresponding authors: www.EFCF.com/ContactRequest Abstract Polymer Electrolyte Membrane (PEM) electrolyzers are a promising technology for the production of green hydrogen especially for the use with variable renewable energy sources. One remaining challenge is the degradation of the electrolyzer during long-term operation. A multitude of degradation mechanisms can affect the different components of the electrolyzer, as can be seen in Figure 1. In addition, the interaction between different components and mechanisms leads to a high complexity. A lack of harmonized testing protocols impedes comparison between different studies. While membrane thinning and anode catalyst dissolution tend to be most discussed in literature, it remains unclear whether these results accurately reflect the mechanisms that operators find most concerning. For this reason, we conducted a survey among PEM electrolysis experts in both academia and industry, with almost 50 total participants. Based on this survey supplemented with literature analysis, we developed indicators of measurements independent from electrochemical analysis. These allow for the quantification of likely degradation mechanisms contributing to the loss of efficiency or failure of an electrolyzer, as well as mechanisms that occur less frequently but have a significant negative impact on the operability of the electrolyzer. Additional monitoring during operation and post-mortem analysis can contribute greatly towards the development of PEM electrolyzers with stable and efficient long-term operation. Figure 1: Degradations mechanisms present in PEM electrolyzers sorted by component. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 2/9 Introduction The production of hydrogen, especially green hydrogen created via water electrolysis, is a crucial puzzle piece in the renewable transformation of energy production and use. Polymer electrolyte membrane water electrolyzers (PEMWE) have garnered interest due to a high energy density and variability of operation [1]. Despite advances made to the lifetime of electrolyzers, degradation of PEMWE during the long-term operation remains a challenge. Recent reviews on this topic with varying focus have identified mechanisms, materials of interest, and mitigation strategies for degradation processes [2–6]. Nevertheless, the evaluation of which degradation mechanisms are the most impactful under realistic operation conditions, especially considering the fluctuating electricity profiles of renewable sources, remains a topic of discussion. For this reason, we have conducted a survey, enabling an overview of degradation mechanisms which are of highest interest. The focus was on the materials typically used in industrial applications, namely perfluorinated sulfonic acid polymer membranes as electrolyte; Ir or its oxides as anode catalyst; Pt/C as cathode catalyst; carbon gas diffusion layers (GDL); Ti porous transport layers (PTL); and Ti or steel bipolar plates (BPP). Another pertinent research question is how to diagnose and identify the cause of a performance drop. Particularly, whether it is due to a specific degradation mechanism, and how to differentiate it from other degradation processes. For this reason, literature analysis on measurement approaches for different degradation mechanisms was carried out. Through this analysis, quantifiable indicator measurements for PEMWE can be identified, which enable differentiation between mechanisms. Thus, measurement recommendations for PEMWE defect diagnostics can be given. 1. Scientific Approach In the survey carried out among the PEMWE community degradation mechanisms, which were identified from literature research, were ranked differentiating between severity and frequency of occurrence. The degradation mechanism with their corresponding short descriptions as they were used in the survey are given in Table 1. Additional literature evaluation on measurement techniques used for PEMWE was carried out with a focus on ex-situ techniques independent from electrochemical analysis. This narrowed focus was chosen since these techniques are most practical to differentiate and diagnose degradation mechanisms comprehensively in an applied context. In-situ methods are often not practical in industrial operation and tend to be specific to single mechanisms, thus necessitating further differentiation. Meanwhile, electrochemical measurements are well-suited to analyze the effect of degradation on performance in aggregate but have a limited ability to assign effects to specific mechanisms and their application to single cells in an operating stack is challenging. For each degradation mechanism, the quantifiable indicators that can be used to diagnose it are derived and corresponding established measurement techniques are given. From these evaluations and the survey, further conclusions were drawn, namely: which degradation mechanism should always/mostly/rarely be considered in defect diagnostics and which measurement methods are most suited to give a comprehensive picture of PEMWE degradation. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 3/9 Table 1: Identified degradation mechanisms and their description as given in the survey. Degradation Mechanism Description Anode Catalyst Dissolution Chemical dissolution of anode side catalyst such as Iridium Cathode Catalyst Dissolution Chemical dissolution of cathode side catalysts such as Platinum Cathode Catalyst Passivation Passivation of cathode side catalysts such as Platinum via reaction with oxygen or hydroxyl radicals Catalyst Particle Loss, Layer Detachment (Mechanical) Removal of catalyst as metallic particles Catalyst Particle Agglomeration Agglomeration of catalyst particles into bigger congregates with lower surface area Catalyst Migration Migration of catalyst ions through the membrane Cation-induced catalyst poisoning Degradation of catalysts due to cationic impurities, that accumulate and block active sites Ionomer Loss and Rearrangement Dissolution of ionomer, i.e. due to radical attack, and loss of contact to the catalyst layer due to rearrangement Membrane Mechanical Degradation Mechanical damage to the membrane by puncture, tearing, cracking, mechanical stresses and pressure Membrane Thinning via Radical Attack Decrease in membrane thickness due to attack of radical species, i.e. hydroxyl radicals Membrane Metal Poisoning Occupation of ion exchange sites in the membrane by foreign cations and precipitation of catalyst particles in the membrane Membrane Thermal Degradation Thinning of the membrane due to increased temperature and local hotspots Bipolar Plate: Hydrogen Embrittlement Mechanical Failure of Bipolar Plates from hydrogen gas absorption Bipolar Plate: Passivation Increasing contact resistance from the formation of a passivation layer on Bipolar Plates Bipolar Plate: Corrosion Corrosion of bipolar plates or coatings from i.e. fluoride ions causing an increase in contact resistance between BP and current collector. Bipolar Plate: Mechanical Degradation Mechanical degradation of BPPs, e.g. deformation, formation of cracks etc. PTL: Corrosion Degradation of the anode-side PTL from corrosion PTL: Passivation Degradation of the anode-side PTL from passivation PTL: Hydrogen Embrittlement Degradation of the anode-side PTL from hydrogen embrittlement PTL: Mechanical Degradation Mechanical degradation on anode-side PTL from high local pressures or temperatures GDL: Chemical Degradation Dissolution of cathode-side carbon GDL GDL: Mechanical Degradation Degradation of cathode-side carbon GDL due to high pressures and localized mechanical stress 2. Survey Design The survey on PEMWE degradation was circulated among PEM experts from academia and industry between April and October of 2024. This resulted in 49 total analyzable datasets. The survey was constructed as follows: EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 4/9 1. Page: Biographical Data (Sector, Length of PEMWE experience, Main Electrolyzer Component worked with) and Free Text Answers (Naming of up to three degradation mechanisms without prior biasing by the survey operators) 2. Page: Ranking of PEMWE components: Membrane, Anode Catalyst Layer, Cathode Catalyst Layer, PTL, GDL, BPP according to their susceptibility to degradation 3. Page: Assessment of highest ranked components degradation mechanisms (given by the survey operators) according to their frequency and severity. The two dimensions were evaluated separately from other. 4. Further Optional Pages: Same ranking as page 3 for components which were ranked lower than the first spot on Page 2. For component identification, participants were provided with an image similar to Figure 1. The ranking of components was achieved by sorting them from most to least susceptible to degradation. Subsequent assessment of mechanisms was on a scale from 1 (least severe/frequent) to 5 (most severe/frequent). The full list of mechanisms for each component as used in the survey including the short definition given there is shown in Table 1. Since assessment of components that were not ranked on the highest spot in Page 2 was optional, the number of answers for each component may vary and is lower than the total number of 49 participants. Figure 1: Components of PEMWE cells. 3. Results 3.1. Ranking of Mechanisms A ranking of degradation mechanisms according to a combined evaluation of severity and frequency can be seen in Figure 2. It is calculated by multiplying the average rank of frequency and average rank of severity for each mechanism with each other, leading to a value between 1 and 25. In order to visualize if severity or frequency have a higher impact the contribution of both measures to the product is calculated with the following formula, where Rav denotes the average rank: 𝐶𝑜𝑛𝑡𝑟𝑖𝑏𝑢𝑡𝑖𝑜𝑛(𝑥)= 𝑅𝑎𝑣(𝑥)𝑅𝑎𝑣(𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦)+𝑅𝑎𝑣(𝑆𝑒𝑣𝑒𝑟𝑖𝑡𝑦) ⁄ ∙(𝑅𝑎𝑣(𝐹𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦)∙𝑅𝑎𝑣(𝑆𝑒𝑣𝑒𝑟𝑖𝑡𝑦)) Generally, severity values tend to be higher than frequency values, but no strong disbalances between the two measures emerge. The overall ranking gives an indication on which degradation mechanism the hydrogen community evaluates to be the most important for PEM electrolysis. As the top degradation mechanism the following emerge: EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 5/9 • PTL Passivation • Anode Catalyst Dissolution • Membrane Thinning by Radical Attack • Catalyst Particle Loss/Layer Detachment • Membrane Mechanical Degradation • BPP Corrosion • Cathode Catalyst Dissolution • Membrane Metal Poisoning This allows for a judgement for which degradation mechanisms should always be considered to explain performance drops and which are only necessary when needing to differentiate confounding mechanisms or when other indication for this mechanism exists. It is obvious that the membrane and catalyst layer degradation mechanisms dominate the evaluations, with PTL passivation and BPP corrosion being the only mechanism outside of these components. This is congruent with the initial evaluation on which components are most susceptible to degradation carried out on the second page of the survey. Figure 2: Product of average rank of severity and frequency for all degradation mechanisms with the relative contribution of severity and frequency. 3.2. Measurement of Mechanisms From literature research on the observable effects of degradation mechanisms, quantifiable indicators and the most commonly used methods to measure them were derived. The results of this can be seen listed in Table 2. Highlighted red and bolded are degradation mechanisms that should always be evaluated (as ranked from the survey). Highlighted orange and italicized are mechanisms that should be evaluated in order to differentiate confounding mechanisms or those with reasonable suspicion. Namely, these are: • Catalyst Migration • Electrode Cationic Poisoning • PTL Corrosion • BPP Passivation EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 6/9 These mechanisms are both of medium concern as derived from the survey and literature analysis and either influence the higher-ranked degradation mechanisms or cause observations that need to be differentiated from them. Highlighted blue are the mechanisms that are of low concern for these considerations and only rarely need to be evaluated, i.e. when an experimental parameter was changed with the goal of accelerating these specific mechanisms or the degradation cannot be fully explained from the evaluation of higherranked mechanism. Overall it is clear that most important degradation mechanisms within the catalyst-coated membrane can be diagnosed and quantified using comprehensive scanning electron microscopy with energy-dispersive x-ray analysis (SEM-EDX) [7–11], monitoring of effluent water (i.e. via Inductively coupled plasma mass spectrometry (ICP-MS) [12–21]), gas crossover testing [22–27] and either titration or a bond analysis technique (such Fouriertransformed infrared (FT-IR) spectroscopy) for further membrane ion exchange capacity (IEC) analysis [28–30]. First indications of catalyst loss mechanisms and poisoning can quickly be implemented using x-ray fluorescence (XRF) [31–33], although further analysis is needed for differentiation of mechanisms. For PTL passivation and BPP corrosion analysis, conductivity measurements [34–38] present the easier to implement diagnostic method. Nevertheless, transmission electron microscopy (TEM) [34–37, 39–42] analysis is recommended for full differentiation from other mechanisms affecting the PTL and if necessary, the BPP. Many of the degradation mechanisms highlighted orange can also be evaluated and differentiated using the aforementioned measurement techniques. PEMWE experiments that are expected to cause certain degradation mechanisms, e.g. tests using contaminated feed water or tests with higher pressure differentials, may necessitate a different prioritization of measurements. One challenge that is not addressed through this evaluation is the inhomogeneity of electrolysis cells. Choosing a single sample location, e.g. for electron microscopy, might lead to incomplete conclusions. This necessitates either an initial region of interest evaluation or a high number of measurements at different locations. Table 2: Quantifiable indicator of each degradation mechanism and how to measure them. Red and bold: Evaluate always; Yellow and italicized: Evaluate for differentiation or with reasonable suspicion; Blue: Evaluate Rarely; Grey: Excluded Abbreviations: Catalyst (Cat.), Membrane (M.), Computer Tomography (CT), Nuclear Magnetic Resonance Spectroscopy (NMR), Atomic Force Microscopy (AFM), Brunauer– Emmett–Teller Measurements (BET) Mechanism Quantifiable Indicator Measurement Anode Cat. Dissolution Amount in water ICP-MS Amount in membrane SEM-EDX Amount in layer XRF Cathode Cat. Dissolution Amount in water ICP-MS Amount in membrane SEM-EDX Amount in layer XRF Cathode Cat. Passivation Pt oxide thickness TEM Loss of conductivity Conductivity measurements Cat. Particle Loss/ Detachment % of delaminated area SEM-EDX, CT Amount in layer XRF Cat. Particle Agglomeration Mean particle/crystallite size TEM, XRD Cat. Migration Metal/ionomer or membrane ratio SEM-EDX, XRF EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 7/9 Area covered by metal layer SEM-EDX Electrode Cationic Poisoning IEC Titration, FT-IR, NMR Metal/ionomer ratio SEM-EDX, XRF Area covered by metal layer SEM-EDX Ionomer Loss/ Rearrangement Ionomer/catalyst ratio SEM-EDX FRR and SRR in water ICP-MS, Ion-Selective Electrodes Mean size of ionomer regions AFM M. Mechanical Degradation Size and number of pinholes Gas crossover testing Variability of thickness Light microscopy, SEM M. Thinning via Radical Attack FRR and SRR in water ICP-MS, Ion-Selective Electrodes Membrane thickness Light microscopy, SEM IEC Titration, FT-IR, NMR M. Metal Poisoning IEC Titration, FT-IR, NMR Metal/membrane ratio SEM-EDX, XRF Area covered by metal layer SEM-EDX Membrane Thermal Degradation IEC Titration, FT-IR, NMR Number of crosslinks formed FT-IR, NMR PTL Passivation Contact resistance Conductivity measurements Thickness of Passivation Layer TEM-EDX PTL Hydrogen Embrittlement H2 uptake Mass measurements Stress until breakage Mechanical testing PTL Corrosion Contact resistance Conductivity measurements Amount of Ti SEM-EDX, XRF Stress until break Mechanical testing GDL Chemical Degradation CO2 release CO2-Sensors Changes to Carbon-Bonds Raman Spectroscopy GDL Mechanical Degradation Stress until break Mechanical testing Porosity Porosity measurements (SEM, BET) Conductivity Conductivity measurements PTL Mechanical Degradation Stress until break Mechanical testing BPP Hydrogen Embrittlement H2 uptake Mass measurements Stress until break Mechanical testing BPP Passivation Contact resistance Conductivity measurements Thickness of passivation Layer TEM-EDX BPP Corrosion Contact resistance Conductivity measurements Amount of Ti SEM-EDX, XRF Stress until break Mechanical testing EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476286 B1004 Page 8/9 BPP Mechanical Degradation Stress until break Mechanical testing 5. Conclusion In conclusion, the degradation mechanisms PTL passivation, anode catalyst dissolution, membrane thinning by radical attack, catalyst particle loss/layer detachment, membrane mechanical degradation, cathode catalyst dissolution, BPP corrosion and membrane metal poisoning were identified as most relevant for PEMWE operation. Their initial diagnosis and comparative quantification are possible using a combination of SEM-EDX, effluent water monitoring, gas crossover testing, IEC determination and conductivity measurements. Especially SEM-EDX is a very localized method, which necessitates supporting measurements by more large-scale methods or a high number of measurement locations. For further differentiation, additional measurements may also become necessary. 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