Spontaneous Demetallation of Mn<sup>(II)</sup>N<sub><i>x</i></sub> Catalytic Sites in Proton Exchange Membrane Fuel Cell Conditions
Bibliographic record
Abstract
The present work is about a thermodynamic assessment of the stability behavior of several Mn (II) N x - and Mn (III) N x /C active sites in Mn/N/C catalysts at 298 and 353 K (80 °C) in the acidic environment of proton exchange membrane (PEM) fuel cells. The calculated Gibbs free energies for the manganese ion leaching reaction indicate that all Mn (II) N x active sites considered in this work are unstable in these conditions. However, the opposite is observed when a three-valent state is adopted for the Mn ion. The transition of manganese from the divalent to the trivalent state is accompanied by the addition of an axial ligand (particularly, by an O 2 molecule). The adsorption of an O 2 molecule to the metal ion of the sites to obtain O 2 ···Mn (III) N 4 /C, O 2 ···Mn (III) N (2+2) /C, or O 2 ···Mn (III) N (4+2) /C leads to highly resisting sites to acid leaching at 298 and 353 K. The thermodynamic stability toward acid leaching is also analyzed for the de-oxygenated Mn (III) N 4 /C, Mn (III) N (2+2) /C, and Mn (III) N (4+2) /C sites. Such sites are also rather stable toward demetallation. In addition, the importance of other aspects (Fenton reaction, electrochemical functionalization/corrosion) affecting the stability of Mn/N/C and Fe/N/C catalysts is also discussed. From this discussion, it is concluded that, contrary to demetallation and also to electro-functionalization/oxidation, Fenton reaction is not an important cause of instability either for Mn/N/C or for Fe/N/C cathode catalysts in fuel cells.
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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 | 0.000 |
| 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) | 0.001 | 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".