Conductivity and Wettability Changes of Ultrathin Nafion Films Subjected to Thermal Annealing and Liquid Water Exposure
Bibliographic record
Abstract
The ionomer in the catalyst layer of polymer electrolyte fuel cells exists as ultrathin films (4–10 nm) covering the aggregates of Pt/C catalyst and may experience elevated temperatures during hot-pressing step of the electrode fabrication process. In this study, we report the effect of thermal annealing on pertinent ionomer-film properties: proton transport and surface wettability. Self-assembled, 10 nm thin Nafion ionomer films on silica substrate were heat treated at different temperatures in the range 40–160 °C. It was found that both surface and bulk rearrangement/reorganization occur simultaneously upon annealing. Surface reorganization was evident by the dramatic change in free-surface wettability from super-hydrophilic to hydrophobic. On the other hand, bulk rearrangement was evident from significant depression in the proton conductivity with increasing treatment temperature. Extended exposure, up to 18 h, to water in vapor form at high humidity did not change the protonic conductivity. On the other hand, exposure to liquid water resulted in an interesting finding of simultaneous regeneration of the film surface and bulk properties. The latter has implications for in operando behavior of ionomer in PEFC cathode catalyst layers, where local water and heat generation may strongly influence its properties.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".