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

2018 ◽  
Vol 11 (2) ◽  
pp. 365-382 ◽  
Author(s):  
Régis Chenitz ◽  
Ulrike I. Kramm ◽  
Michel Lefèvre ◽  
Vassili Glibin ◽  
Gaixia Zhang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Fuel Cells ◽  
Pem Fuel Cells ◽  
Initial Activity ◽  
Performance Loss ◽  
Highly Active ◽  
Catalytic Sites ◽  
Activity Loss

Micropores are largely responsible for Fe/N/C catalytic activity, but are also intrinsically responsible for the rapid initial performance loss in PEMFC.

scholarly journals Non-PGM Electrocatalysts for PEM Fuel Cells: A DFT Study on the Effects of Fluorination of FeNx-Doped and N-Doped Carbon Catalysts

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7370
Author(s):  
Mohamed Cherif ◽  
Jean-Pol Dodelet ◽  
Gaixia Zhang ◽  
Vassili P. Glibin ◽  
Shuhui Sun ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Fuel Cells ◽  
Density Functional ◽  
Realistic Model ◽  
Pem Fuel Cells ◽  
Reduction Reaction ◽  
Graphene Layers ◽  
Metal Free ◽  
Highly Active ◽  
Carbon Catalysts

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeNx-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeNx moiety of the Fe/N/C catalytic site, considerably reducing the activity of the resulting catalyst to that of carbon only doped with nitrogen. Using the density functional theory (DFT), we clarify in this work the mechanisms by which fluorine interacts with the catalyst. We studied 10 possible FeNx site configurations as well as 2 metal-free sites in the absence or presence of fluorine molecules and atoms. When the FeNx moiety is located on a single graphene layer accessible on both sides, we found that fluorine binds strongly to Fe but that two F atoms, one on each side of the FeNx plane, are necessary to completely inhibit the catalytic activity of the FeNx sites. When considering the more realistic model of a stack of graphene layers, only one F atom is needed to poison the FeNx moiety on the top layer since ORR hardly takes place between carbon layers. We also found that metal-free catalytic N-sites are immune to poisoning by fluorination, in accordance with our experiments. Finally, we explain how most of the catalytic activity can be recovered by heating to 900 °C after fluorination. This research helps to clarify the role of metallic sites compared to non-metallic ones upon the fluorination of FeNx-doped disorganized carbon catalysts.

scholarly journals Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells

2012 ◽  
Vol 14 (33) ◽  
pp. 11673 ◽  
Author(s):  
Ulrike I. Kramm ◽  
Juan Herranz ◽  
Nicholas Larouche ◽  
Thomas M. Arruda ◽  
Michel Lefèvre ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Pem Fuel Cells ◽  
O2 Reduction ◽  
Catalytic Sites

Reply to the ‘Comment on “Non-PGM electrocatalysts for PEM fuel cells: effect of fluorination on the activity and stability of a highly active NC_Ar + NH3 catalyst”’ by Xi Yin, Edward F. Holby and Piotr Zelenay, Energy Environ. Sci., 10.1039/D0EE02069A

2021 ◽  
Vol 14 (2) ◽  
pp. 1034-1041
Author(s):  
Jean-Pol Dodelet ◽  
Vassili Glibin ◽  
Gaixia Zhang ◽  
Ulrike I. Kramm ◽  
Régis Chenitz ◽  
...  
Keyword(s):  
Fuel Cells ◽  
High Performance ◽  
Pem Fuel Cells ◽  
Fast Decay ◽  
Highly Active ◽  
Energy Environ

The fast decay in PEM fuel cells of a highly active, high performance, but unstable Fe/N/C catalyst like our NC_Ar + NH3 follows a chemical, not an electrochemical, demetallation mechanism for its ORR active FeN4 sites in the catalyst micropores.

Non-PGM electrocatalysts for PEM fuel cells: effect of fluorination on the activity and stability of a highly active NC_Ar + NH3 catalyst

2019 ◽  
Vol 12 (10) ◽  
pp. 3015-3037 ◽  
Author(s):  
Gaixia Zhang ◽  
Xiaohua Yang ◽  
Marc Dubois ◽  
Michael Herraiz ◽  
Régis Chenitz ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Pem Fuel Cells ◽  
Highly Active

F2-Fluorination of Fe/N/C catalysts poisons FeN4, but not CNx sites. Main causes of instability in PEMFCs are either FeN4 demetalation for Fe/N/C or H2O2 when FeN4 sites are poisoned by fluorination or absent as in MOF_CNx_Ar + NH3.

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