In-Situ x-Ray Diffraction Study of Pt(111) Oxidation during Oxygen Reduction Reaction (ORR)
Notice bibliographique
Résumé
ORR is one of the most studied electrochemical reactions due to it’s tremendous fundamental and practical importance. Oxygen is common, readily accessible oxidizing agent and therefore Pt ORR cathode is part of many energy conversion devices, e.g., fuel cells. Unfortunately, slow kinetics of ORR negatively affects the performance and it is currently one of the main bottleneck in large scale fuel cells commercialization. It is partly caused by the presence of surface Pt oxides, which slow the reaction rate and trap reaction intermediates on the surface. The oxide formation and dissolution is also known to cause dissolution of Pt catalyst, which further degrades the performance. Even though the electrochemical formation of surface oxides on platinum surface has been extensively studied in the past, there are still many questions unanswered. Mainly about the detailed structure of the oxide and its growth mechanism [1 and references there-in]. Most of the studies were performed in the absence of O2, the fuel cell oxidant, and therefore they are less relevant to the fuel cell operation as gaseous O2 can modify the oxidation potentials and mechanism. Given the above, further fundamental understanding of Pt oxidation mechanism measured in-situ is clearly needed in order to determine the role of surface oxides in ORR and its effect on the fuel cell performance. Here we show the results of in-situ study of electrochemical oxide formation on Pt(111) and how it is influenced by presence of O2 during ORR. We find that oxide growth, and Pt-O site switching, is present as soon as 700 mV vs. Ag|AgCl reference electrode in 0.1M HClO4 and causes slow, irreversible roughening of the surface. When the potential is increased, the roughening is more severe and after several tens of cycles from -125 mV to 900 mV, the surface loses it’s order. This is seemingly in contradiction with widely accepted notion that cycling the Pt(111) up to 900 mV does not affect significantly surface structure. We show that the roughening is dependent on the initial state of the sample and it is an autocatalytic process. Adding oxygen into the electrolyte does not have any notable effect on the oxidation potentials or kinetics and it is in disagreement with previous results where negative shift of the oxidation onset was observed in O2 containing electrolyte [2]. This results points to the fact that OH- is dominated species during Pt electrooxidation and oxygen has only a side role. However, depending on the history of the sample, it is likely that PtO species are present on the surface and should be taken into the account in theoretical investigations. [1] Kongkanand and Ziegelbauer, Journal of Physical Chemistry C, 116 (2012) 3684-3693; [2] Matsumoto, Miyazaki, Imai, Phys. Chem. C, 115 (2011) 11163−11169.
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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».