Square-Pyramidal Fe-N4 with Defect-Modulated O-Coordination: Two-Tier Electronic Structure Fine-Tuning for Enhanced Oxygen Reduction
Notice bibliographique
Résumé
Engineering the structure of molecularly dispersed 3d-transition metal phthalocyanines is emerging as an effective avenue for developing low-cost and efficient atomically dispersed catalysts (ADC). The strategy of using axial coordination to adjust the electronic structure of the M-N4 active site is effective for improving the performance of the catalysts, but the question to be asked is how to go beyond that. In this study, we propose and demonstrate a two-tier electronic modulation strategy, for the first time using carbon defects to regulate the tuning power of O-coordination, which in turn provides a more desirable electronic modulation on the Fe center of FePc, as compared to that of bare O-coordination. Such FePc-O-defect ADC was achieved using a one-step wet-ball-milling process with ethylene glycol as liquid media. The mechanochemically constructed active site is a square-pyramidal Fe-N4, with the Fe atom located out of the N4-plane towards an axially coordinated O that is singly bonded to graphene at vacancy defects. The resulting FePc-O-defect ADC with defect-modulated O-coordination exhibits excellent ORR activity in alkaline media, in terms of E1/2 and mass-specific activity. Compared to the baseline with bare O-coordination whose performance is already among the best reported nonprecious metal electrocatalysts, the defect-modulated O-coordination further enhanced the halfwave potential and doubled the kinetic current density. Combining with theoretical investigations, we elucidate how defect-modulated O-coordination would adjust the electronic and geometric structures of the Fe center and thus affect the electrocatalytic ORR. Also, resolving the structural configuration of bilayer catalysts with axial coordination is very challenging. The existed literature on bilayer catalyst, which either relies on 2D FT-EXAFS fitting analysis or simply assumes a bilayer configuration to work on, is in our opinion far from unambiguous structural determination. In this study, we differentiate our work from the existed literature, through a systematic structural determination process by comparing the experimental XANES with the simulated ones, based on various structural models predicted by DFT calculations. Such analysis is especially necessary for catalysts with a 3D atomistic arrangement, but only a handful of studies have used this step of analysis (e.g., Nature Catalysis 1, 63-72 (2018)). We believe that our study presents significant advances regarding the atomistic structure of bilayer catalysts with complex axial coordination. Overall, this work demonstrates a conceptually advanced two-tier electronic modulation strategy, through defect-modulated O-coordination, to further optimize the electronic structure of the Fe center in FePc toward ORR. The concept can be extended to modulate the electrocatalytic properties of molecular catalysts toward other electrochemical processes. Moreover, our catalysts were prepared at room temperature using an industrially available ball milling process. Such a facile pyrolysis-free synthetic approach is ready for scaleup with potentially 100 % usage of the FePc and graphene precursors.
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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 | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 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 ».