Issue 17, 2022

Mechanism insight into the oxygen reduction reaction on dual FeN2 embedded graphene for proton exchange membrane fuel cells

Abstract

The design of non-noble heteroatom-doped graphene electro-catalysts for the oxygen reduction reaction (ORR) is beneficial to the commercial application of fuel cells. Since a higher concentration of dispersed FeN2 moieties is more beneficial to the activity of the oxygen reduction reaction, the electronic properties and oxygen reduction performance of several possible dual FeN2 moieties embedded in graphene (Fe2N4/G) have been investigated by using density functional theory calculations (DFT) in this work. It is found that the series of dual FeN2 moiety embedded graphene is more stable than single FeN2 moiety embedded graphene, and the catalyst Fe2N4-1/G shows the most outstanding stability among these geometries. The magnetic moments for dual FeN2 catalysts are smaller than that of an isolated FeN2 catalyst, and the central symmetric geometry of dual FeN2 is beneficial to reducing the magnetism of Fe atoms. Moreover, the adsorption trend for these oxygen-containing intermediates adsorbed on these active centers is almost consistent with the increasing order of H2O < O2 < OOH < OH < O. The oxygen reduction reaction process on these active centers is thermally downhill except for Fe2N4-2/G and Fe2N4-3/G, all of which promote a single-site 4e ORR process on a pure FeN2 moiety through the reaction path O2 → O2* → OOH* → O* → OH* → H2O. It is found that these four reduction steps except for the second step of *OOH reduction could be the thermodynamic rate-determining step (RDS). The free energies of *O2, *OOH, *O and *OH on these active sites have an almost linear scaling relation with different slope values according to their adsorption properties, and the linear scaling relations of *O2vs. *OH, *O vs. *OH and *OOH vs. *OH have slope values close to 1, 2 and 1, respectively. The adsorption properties of OH have a strong relationship with the d-band center, the highest potential and Mulliken charge. Finally, the catalyst Fe2N4-1/G shows the most outstanding stability with a cohesive energy of −11.76 eV and activity with the highest potential of 0.73 V among these geometries.

Graphical abstract: Mechanism insight into the oxygen reduction reaction on dual FeN2 embedded graphene for proton exchange membrane fuel cells

Supplementary files

Article information

Article type
Paper
Submitted
24 Jun 2022
Accepted
27 Jul 2022
First published
27 Jul 2022

Sustainable Energy Fuels, 2022,6, 4024-4033

Mechanism insight into the oxygen reduction reaction on dual FeN2 embedded graphene for proton exchange membrane fuel cells

W. Qi, X. Zhang, J. Niu, Z. Zhang, J. Huang, S. Ge and Y. Zhang, Sustainable Energy Fuels, 2022, 6, 4024 DOI: 10.1039/D2SE00866A

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