| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Monday Sessions |
| Session TF+NM-MoE |
| Session: | Nanostructures, Graphene, and Magnetism |
| Presenter: | Akihide Ichikawa, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan |
| Authors: | A. Ichikawa, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan A. Akaishi, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan J. Nakamura, The University of Electro-Communications (UEC-Tokyo) and JST-CREST, Japan |
| Correspondent: | Click to Email |
Recently, several groups have reported high oxygen reduction reaction (ORR) activities in nitrogen-doped carbon nanomaterials which are candidates of metal-free catalysts for ORR [1]. Lee et al. have successfully fabricated nitrogen-doped graphene with the high ORR activity in acid media [2]. It has been confirmed that local atomic configurations of dopants in nitrogen-doped graphene are classified into three functional groups (pyrrole-like, pyridine-like, and graphite-like configurations) [3]. However, the mechanism of the ORR on the nitrogen-doped graphene has not fully understood.
In this work, we examine the ORR on the nitrogen-doped graphene containing the graphite-like N in a basal plane using first-principles calculations. In general, the ORR occurs mainly two pathways: The two-electron pathway (2e-) that is reduced to hydrogen peroxide (H2O2), and the direct four-electron pathway (4e-) that reduces to water (H2O). Thermodynamic electrode potentials of each process at standard conditions are about 0.68V (2e-) and 1.23V (4e-), respectively. In case of the associative mechanism for the two- and four- electron reduction pathways, the electrocatalytic activity is governed by the stability of reaction intermediates like OOH*, OH*, and O* (where “ * ” refers to a surface site). Free energies of the reaction intermediates have been calculated based on the computational hydrogen electrode model suggested by Norskov et al. [4]. We have taken account of effects of electrode potential, Ph of a solution, a local electric field in double layer, and water environment.
We have constructed energy diagrams at several electrode potentials on the basis of the first-principles calculations. It has been shown that the 2e- and 4e- reduction processes proceed at potentials up to about 0.5V and 0.8V, respectively. This means that we can control the reduction pathway for the nitrogen-doped graphene with the graphite-like N. Proton-electron transfer to OOH* (the 2e- pathway), and the formation of OOH* (the 4e- pathway) are confirmed to be the rate-limiting steps, respectively. The effects of electric field and water environment will also be discussed in the presentation.
Reference:
[1] J. Ozaki, N. Kimura, T. Anahara, A. Oya, Carbon 45, 1847 (2007).
[2] K. R. Lee, K. U. Lee, J. W. Lee et al., Electrochem. Commun. 12, 1052 (2010).
[3] H. Niwa, K. Horiba, M. Oshima et al., J. Power Sources 187, 93 (2009).
[4] J. K. Norskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J. Phys. Chem. B 108, 17886 (2004).