Investigating the Degradation of Porous Transport Layer (PTL) Materials in Proton Exchange Membrane Water Electrolyzer via in-Operando Distribution of Relaxation Times Approach
Bibliographic record
Abstract
Proton exchange membrane water electrolyzer (PEMWE) technology, while commercially mature and in high demand, faces degradation issues that lead to performance losses over time. These challenges reduce operational lifetime and increase regeneration and replacement costs. Components of the membrane electrode assembly (MEA), such as the ionomer, catalysts, membrane, porous transport layer (PTL), and bipolar plate (BPP), contribute to its degradation. Among these, PTL degradation is a significant contributor to performance loss. Therefore, understanding the PTL’s degradation mechanism is essential for improving the material's durability and optimizing the electrolyzer’s performance [1]. The PTL degradation not only causes mass transport losses due to inefficient reactant delivery and gas bubble removal but also negatively impacts the catalyst layer/PTL interface and increases contact resistances [2]. Isolating the degradation mechanism of the PTL from other components is challenging, even with advanced techniques like Electrochemical Impedance Spectroscopy (EIS), which often yields data that is complex to interpret. However, the Distribution of Relaxation Times (DRT) analysis presents a promising way of interpreting impedance data to differentiate and track distinct electrochemical phenomena within the complex system of PEM electrolyzers [3]. This work uses the DRT approach on in-operando EIS to interpret electrochemical loss mechanisms inside the cell while comparing the short-term performance of different PTL materials, such as carbon paper with a microporous layer (MPL), and uncoated and platinum-coated Ti felts. We present and compare the initial impedance and polarization results of these PTL materials, and analyze the corresponding DRT spectra at various applied current densities. Additionally, we utilized carbon PTL at the anode to investigate the durability of the PTL. The accelerated degradation profile involved applying a constant current of 1 A/cm² for 6 hours daily, followed by an overnight shutdown as a stressor. Figure 1(a) shows the preliminary DRT results of a PEMWE cell with carbon paper PTL, indicating an increase in diffusion impedance from 0.51 mΩ to 4.6 mΩ as the current density increases from 0.5 to 2 A/cm². This impedance increase can be attributed to the evolution of more oxygen bubbles at higher currents, which hinder water transport due to carbon paper's small pores size and low wettability [4]. At a current density of 1 A/cm2, the diffusion impedance on the carbon paper PTL was shown to be 9.2 times higher than Ti-felt PTL, as revealed by DRT analysis. This significant difference is likely due to the hydrophobic nature of the carbon PTL, which results in poor mass transport due to inadequate water interaction. Furthermore, the onset cell degradation test with the carbon paper PTL resulted in voltage overshoot after 160 hours, with the DRT analysis indicating increased diffusion and charge transfer resistances. Similarly, DRT analysis of Ti felt degradation showed increased ionic transport resistance and contact resistance over time, leading to passivation after short-term operation. In general, the online DRT analysis revealed that the interfacial properties of PTL materials strongly depend on the type of material used. Also, DRT analysis assists in identifying the root cause of degradation. References: [1] C. C. Weber, J. A. Wrubel, L. Gubler, G. Bender, S. De Angelis and F. N. Büchi, ACS Applied Materials & Interfaces, 15, 34750 (2023). [2] S. Duran, A. Grimaud, M. Faustini and J. Peron, Chemistry of Materials, 35, 8590 (2023). [3] J. K. Lee, F. Babbe, G. Wang, A. W. Tricker, R. Mukundan, A. Z. Weber and X. Peng, Joule, 8, 2357 (2024) [4] K. Bromberger, J. Ghinaiya, T. Lickert, A. Fallisch and T. Smolinka, International Journal of Hydrogen Energy, 43, 2556 (2018) Figure 1
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".