The Stability of Nano-Structured-Thin-Film™ Supported Ir on Pt PEMFC Catalysts Under Rde Simulated Start-up and Shut-Down
Bibliographic record
Abstract
The instability of Pt oxygen reduction electro-catalysts is a principle cause of proton exchange membrane fuel cell (PEMFC) performance decline, and the main causes of this instability are load cycling and start-up shut-down (su/sd). The extent of Pt loss is primarily a function of 1) rate of potential change 2) upper potential limit.1 Work by 3M and partners on PEMFCs with Nano Structured Thin Film (NSTF) supported catalysts have shown minute amounts (2 – 10 µg cm2) of Ir added to Pt does not adversely affect Oxygen reduction reaction (ORR) activity and is effective in protecting Pt (loss < 10%) under simulated su/sd condition2 The rotating disk electrode (RDE) can also be used to study the behavior of NSTF supported catalysts.3 Many rotating disk electrode (RDE) durability studies subject candidate PEMFC electro-catalysts to triangular wave potential cycling. Stevens et al. have developed alternative electrochemical techniques to simulate the transient potentials associated with load cycling and su/sd.with the RDE.4Figure 1 shows the potential changes of one su/sd “pulse”, designed to simulate run, idle and rest potential with constant potential holds, and simulate start-up and shut-down with constant current holds. This unique approach allows the upper potential limit to change as the test progresses. Figure 2 shows how ORR activity changes under repeated su/sd “pulses” for various loadings of Ir on NSTF supported Pt (85 µg/cm2). Markers are also colored according to the final potential the constant current hold reaches prior to ORR characterization. The highest Ir loading of 19.1µg/cm2 reaches a stable state, where the ORR activity changes very little after 2500 su/sd pulses. For a lower Ir loading (10 µg/cm2) tested at the same current, the ORR activity continually declines. However for the same Ir loading of 10 µg/cm2 tested at 2/5th the current, ORR activity seems to achieve near stability. The results show an interesting relationship between the stability of Ir on Pt electro-catalysts, and the potential reached by the su/sd simulation current. When potential starts and stays below a threshold of approximately 1.5 VRHE, the Ir-Pt reaches a stable configuration where ORR and oxygen evolution reaction (OER) activity no longer decline. Achieving stability may be more dependant on the potential reached, or the charge delivered, than the Ir loading. Note that for pure Pt tested at a current an order of magnitude lower than the 19.2 µg/cm2 Ir sample, and started at a potential of 1.35 VRHE, ORR activity continued to decline, indicating that stability of the RDE-NSTF catalyst system requires both low (< 1.5 VRHE) potential and the presence of Ir. These results indicate a possibility of indefinitely stable Pt based PEMFC catalysts, and the important role the su/sd potential may play in determining stability of an Ir-Pt electro-catalyst. Work is ongoing to determine Ir loading thresholds for stability. 1. A. A. Topalov, I. Katsounaros, M. Auinger, S. Cherevko, J. C. Meier, S. O. Klemm, and K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 51, 12613–12615 (2012). 2. R. T. Atanasoski, D. A. Cullen, G. D. Vernstrom, G. M. Haugen, and L. L. Atanasoska, ECS Electrochem. Lett., 2, F25–F28 (2013). 3. G. C.-K. Liu, R. J. Sanderson, G. Vernstrom, D. A. Stevens, R. T. Atanasoski, M. K. Debe, and J. R. Dahn, J. Electrochem. Soc., 157, B207 (2010). 4. D. A. Stevens, J. Harlow, R. J. Sanderson, C. W. Watson, T. J. Crowtz, J. R. Dahn, G. D. Vernstrom, L. L. Atanasoska, G. M. Haugen, and R. T. Atanasoski, ECS Trans., 50, 1533–1538 (2013).
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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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".