Surface Oxidation of Pt(111) Studied By Surface X-Ray Diffraction and Grazing-Incidence Small-Angle X-Ray Scattering
Notice bibliographique
Résumé
Electrochemical growth of Pt oxide is important because of its role in the oxygen-reduction reaction (ORR) and in Pt dissolution, which affect the performance and durability of PEM fuel cell Pt electrocatalysts. It has been known for a long time that potential cycling leads to a restructuring of the surface, in which Pt atoms move away from their lattice sites. The details of this process have not been fully resolved, though early surface X-ray diffraction (SXRD) studies confirmed the key role of a "place exchange" in which Pt and O (or OH) species exchange places [1]. Reported here are in-situ SXRD and Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) studies of Pt(111) electrodes in 0.1 M HClO4 carried out at the European Synchrotron Radiation Facility [2-6]. The atoms are located by a crystal-truncation rod analysis, which shows that the place-exchanged Pt is located directly above its original lattice site. Simultaneous cyclic voltammograms of current and the intensity of the (1,1,1.5) reflection associate the initiation of the place exchange with the "oxide" peak at 1.05 V vs RHE. The voltammogram is unchanged by cycling to 1.15 V, as the place exchange is reversed on the reduction cycle, albeit with significant hysteresis. Cycling to higher potentials leads to irreversible changes to the surface, which were studied in detail with GISAXS. GISAXS probes the evolution of nanoscale features on the surface. Progressive surface roughening occurs with cycling, to an extent that is dependent on the upper reversal potential ( E up ). The average spacing of the islands ranges from 40-70 Å for E up from 1.4-1.6 V, with smaller spacing for higher potentials. The spacing increases slightly with cycle number but is mainly determined after the first cycle. The islands grow in height and become more prominent and homogeneous in size with the number of cycles. These changes are similar to the evolution of Pt surfaces in UHV undergoing deposition of Pt or surface erosion, showing that the underlying processes such as vacancy coalescence are common for the UHV and electrochemical cases. SXRD experiments in the presence of oxygen show no effect on the place exchange during cycling. The oxygen reduction current decreases at potentials more negative than the initiation of the place exchange, showing that it is limited by the adsorbed intermediate(s) in the ORR (likely OH) and not Pt oxide formation. The authors thank the European Synchrotron Radiation Facility, Deutsche Forschungsgemeinschaft, and the Natural Sciences and Engineering Research Council of Canada for support. [1] H. You, D.J. Zurawski, Z. Nagy, R.M. Yonco, J. Chem. Phys. , 100 , 4699 (1994). [2] J. Drnec, M. Ruge, F. Reikowski, B. Rahn, F. Carlà, R. Felici, J. Stettner, O.M. Magnussen, D.A. Harrington, Electrochim. Acta , 224 , 220 (2017). [3] M. Ruge, J. Drnec, B. Rahn, F. Reikowski, D.A. Harrington, F. Carlà, R. Felici, J. Stettner, O.M. Magnussen, J. Am. Chem. Soc. , 139 , 4532 (2017). [4] M. Ruge, J. Drnec, B. Rahn, F. Reikowski, D.A. Harrington, F. Carla, R. Felici, J. Stettner, O.M. Magnussen, J. Electrochem. Soc. , 164 , H608 (2017). [5] J. Drnec, M. Ruge, F. Reikowski, B. Rahn, F. Carlà, R. Felici, J. Stettner, O.M. Magnussen, D.A. Harrington, Pt oxide and oxygen reduction at Pt(111) studied by SXRD, Electrochem. Comm. , 84 , 50 (2017). [6] J. Drnec, D.A. Harrington, O.M. Magnussen, Current Opinion in Electrochemistry , (2017), doi:10.1016/j.coelec.2017.09.021
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 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 | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 tête enseignante, 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 ».