Chenitz, Régis ; Kramm, Ulrike I. ; Lefèvre, Michel ; Glibin, Vassili ; Zhang, Gaixia ; Sun, Shuhui ; Dodelet, Jean-Pol (2018)
A specific demetalation of Fe–N4 catalytic sites in the micropores of NC_Ar + NH3 is at the origin of the initial activity loss of the highly active Fe/N/C catalyst used for the reduction of oxygen in PEM fuel cells.
In: Energy & Environmental Science, 11 (2)
doi: 10.1039/c7ee02302b
Artikel, Bibliographie
Kurzbeschreibung (Abstract)
In this study, we explored the behavior of NC_Ar + NH3, an initially highly active catalyst for oxygen electroreduction, in H2/air fuel cells from 0.8 to 0.2 V at 80 °C and 25 °C, in order to find the causes of its instability. We discovered that the decay of the current density always involves the superposition of fast and slow first order kinetics, for which half-lives were obtained. The half-life of the fast decay was practically the same at all potentials and temperatures with a value of around 138 ± 55 min, while the half-life of the slow decay greatly varied from a minimum of ≈2400 min (40 h) to infinity. From the adsorption–desorption isotherm of NC_Ar + NH3, it was deduced that the Fe/N/C carbonaceous catalyst is characterized by interconnected open-end slit-shaped micropores, in which water (with dissolved H+ and O2) quickly flows in the fuel cells if their width is ≥0.7 nm as it has no interaction with the hydrophobic walls of the micropores. The driving force of this quick water flow is the humidified air streaming through the working cathode. Fe–N4-like active sites are thermodynamically stable in stagnant acidic conditions, but according to the Le Chatelier principle, they demetalate in the flux of water running into the micropores. This specific demetalation is the cause of the initial loss of ORR activity of NC_Ar + NH3 catalysts assigned to the fast current decay in fuel cells.
| Typ des Eintrags: | Artikel |
|---|---|
| Erschienen: | 2018 |
| Autor(en): | Chenitz, Régis ; Kramm, Ulrike I. ; Lefèvre, Michel ; Glibin, Vassili ; Zhang, Gaixia ; Sun, Shuhui ; Dodelet, Jean-Pol |
| Art des Eintrags: | Bibliographie |
| Titel: | A specific demetalation of Fe–N4 catalytic sites in the micropores of NC_Ar + NH3 is at the origin of the initial activity loss of the highly active Fe/N/C catalyst used for the reduction of oxygen in PEM fuel cells |
| Sprache: | Englisch |
| Publikationsjahr: | 1 Februar 2018 |
| Verlag: | Royal Socity of Chemistry |
| Titel der Zeitschrift, Zeitung oder Schriftenreihe: | Energy & Environmental Science |
| Jahrgang/Volume einer Zeitschrift: | 11 |
| (Heft-)Nummer: | 2 |
| DOI: | 10.1039/c7ee02302b |
| URL / URN: | https://doi.org/10.1039/c7ee02302b |
| Kurzbeschreibung (Abstract): | In this study, we explored the behavior of NC_Ar + NH3, an initially highly active catalyst for oxygen electroreduction, in H2/air fuel cells from 0.8 to 0.2 V at 80 °C and 25 °C, in order to find the causes of its instability. We discovered that the decay of the current density always involves the superposition of fast and slow first order kinetics, for which half-lives were obtained. The half-life of the fast decay was practically the same at all potentials and temperatures with a value of around 138 ± 55 min, while the half-life of the slow decay greatly varied from a minimum of ≈2400 min (40 h) to infinity. From the adsorption–desorption isotherm of NC_Ar + NH3, it was deduced that the Fe/N/C carbonaceous catalyst is characterized by interconnected open-end slit-shaped micropores, in which water (with dissolved H+ and O2) quickly flows in the fuel cells if their width is ≥0.7 nm as it has no interaction with the hydrophobic walls of the micropores. The driving force of this quick water flow is the humidified air streaming through the working cathode. Fe–N4-like active sites are thermodynamically stable in stagnant acidic conditions, but according to the Le Chatelier principle, they demetalate in the flux of water running into the micropores. This specific demetalation is the cause of the initial loss of ORR activity of NC_Ar + NH3 catalysts assigned to the fast current decay in fuel cells. |
| Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 07 Fachbereich Chemie > Eduard Zintl-Institut > Fachgebiet Anorganische Chemie > Fachgruppe Katalysatoren und Elektrokatalysatoren 07 Fachbereich Chemie 07 Fachbereich Chemie > Eduard Zintl-Institut > Fachgebiet Anorganische Chemie |
| Hinterlegungsdatum: | 06 Jul 2018 12:07 |
| Letzte Änderung: | 18 Aug 2021 08:17 |
| PPN: | |
| Sponsoren: | R. C., M. L., G. Z., and J. P. D. acknowledge the financial support from MESRST-Gouvernement du Que ́bec, Ministe´re de l’E ́conomie, de l’Innovation et des Exportations., R. C., M. L., G. Z., S. S, and J. P. D. also acknowledge the financial support from Innovation Fund Denmark, contract number 4106-00012B., Financial support by the graduate school of excellence energy science and engineering (GSC1070) is gratefully acknowledged by U. I. K. |
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