| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Poster Session II |
| Presenter: | Haruyuki Matsuyama, The University of Electro-Communications (UEC-Tokyo), Japan |
| Authors: | H. Matsuyama, The University of Electro-Communications (UEC-Tokyo), Japan S. Gomi, The University of Electro-Communications (UEC-Tokyo), Japan J. Nakamura, The University of Electro-Communications (UEC-Tokyo), Japan |
| Correspondent: | Click to Email |
Recently, much attention has been devoted to the oxygen reduction reaction (ORR) on nitrogen(N)-doped graphene [1]. It has been theoretically revealed that N atoms prefer to be located near the edge of graphene [2,3]. The structure of graphene edge can be mainly classified into two types, armchair and zigzag edges. However, the effect of edge structures on ORR activity has not been fully understood.
We investigated the ORR activity for the N-doped graphene nanoribbons with armchair (N-ACGNRs) and zigzag (N-ZZGNRs) edges using first-principles calculations within the density functional theory. We used the computational hydrogen electrode model [3] to evaluate the maximum electrode potential (Umax). ORR mainly proceeds in two pathways: For the two-electron (2e-) pathway, O2 molecule is reduced to H2O2, and for the direct four-electron (4e-) pathway, the final product is H2O. H2O2 for the 2e- pathway might corrode a carbon based electrocatalyst itself, leading to low durability. We also examined the selectivity with respect to these two pathways.
The calculation models are the N-ACGNRs and the N-ZZGNRs, in which a C atom is substituted by a N atom for each doping site from edge to in-plane. The reaction sites are set to C atoms adjacent to the N atom. We calculated the values of Umax for each doping site and reaction site for the N-ACGNRs and the N-ZZGNRs. The Umax for N-ACGNR becomes positive for each doping and reaction site. On the other hand, the Umax for N-ZGNR has a parity dependence with regard to the nitrogen doping site in the vicinity of the zigzag edges. For the even-numbered doping sites from the edge, the values of Umax are larger than 0 V, while for the odd-numbered ones, the values of Umax become negative. The reaction selectivity for the 4e- pathway appears only in the vicinity of armchair and zigzag edges. For the models showing the reaction selectivity, the sp2 configuration of GNR is maintained, even if reaction intermediates are adsorbed on GNR. On the other hand, reaction intermediates adsorb on GNR with sp3-like configuration for the other models. The mechanism for appearance of the selectivity will be discussed in the presentation.
[1] K. R. Lee et al., Electrochem. Commun. 12, 1052 (2010)
[2] S. F. Huang et al., Phys. Rev. B 80, 235410 (2009)
[3] Y. Uchida, S. Gomi, H. Matsuyama, A. Akaishi, and J. Nakamura, J. Appl. Phys. 120, 214301 (2016)
[4] J. K. Nørskov et al., J. Phys. Chem. B 108, 17886 (2004)