Corrosion Susceptibility of Mesoporous Carbons: Evidential Understanding of the Effects of Quasi-Passive Oxide Formation
Bibliographic record
Abstract
Carbon is an essential component of catalyst layers in Proton Exchange Membrane Fuel Cells (PEMFCs), especially in cathodes, serving as a support material to disperse electrocatalysts. However, one of the challenges in the use of carbon in electrochemical applications is its propensity towards corrosion due to electrochemical oxidation at positive potentials, a crucial factor limiting device lifetime and thus large-scale commercialization. While most prior studies of carbon corrosion have focussed on microporous carbon powders, such as carbon black (e.g., Vulcan powder (VC)), CNTs, and graphite), there is a growing recognition of the need for larger pores in order to access the full internal surface area of carbon, especially at high currents. Here, we provide evidence from our own testing protocols focussed on sucrose-derived ordered mesoporous carbons (OMC-S) and other analogous carbons, that an oxide film with pseudo-passivating characteristics, forms on carbon surfaces once the potential is above that for oxygen evolution (E 0 =1.23 V) in deaerated 0.5 M H 2 SO 4 . The conclusion builds on the observation of a never previously reported electrochemical feature in the first full cathodic scan after oxidation at higher potentials, with a cathodic plateau current that commences at 0.8 V, having a charge that is threefold higher than that of pseudocapacitive oxides, and is independent of sweep rate and solution agitation. Its steady current response upon reduction and other properties will be shown to be similar to what is seen for the reduction of a passive oxide film, as it is clearly shown to protect carbon at least partly from corrosion. We refer to this as a 'quasi-passive oxide' film, due to its electrochemical characteristics and its ability to prevent further carbon roughening. This oxide shares commonality with passive oxides commonly formed anodically on metals as well. We also show that due to its partially protective nature, more aggressive corrosion of the OMC-S occurs when this quasi-passive oxide is removed from the surface, presumably as fresh carbon surfaces are then available for corrosion. While more quasi-passive oxide can be reduced at potentials negative of 0 V vs RHE, the hydrogen evolution reaction is an interferent. We also discuss the effects of various electrochemical conditions, such as the upper potential used (E+) and the time of holding at E+ on quasi-passive oxide formation and its role in carbon corrosion susceptibility. While the formation of quinone-type passive oxide films has been evidenced based on carbon corrosion studies carried out by others, there have been no in-depth electrochemical studies that clearly distinguish the formation of various types of surface oxides or of CO 2 , or that correlate oxide formation with corrosion susceptibility, Therefore, our approach in this study presents significant insights that differentiate the carbon oxidation products, most importantly the irreversible oxidation of C to CO 2 from the likely more harmless formation of a surface oxide. All analogous mesoporous carbons we investigated in this study are also found to form the quasi-passive oxide film at high potentials in acidic media, showing that this type of quasi-passive oxide film formation is a general phenomenon for carbons when subjected to at high potentials, albeit at varying rates due to surface area and porosity effects.
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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 | 0.001 |
| 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".