New Computational Insights to Describe the Oxygen Reduction Reaction on Graphene Containing Multiple Nitrogen Functional Groups

The development of new cathodes for low temperature fuel cells has spurred the research of low cost and durable materials, particularly non-noble materials displaying a similar performance as Platinum [1]. To this concern, metal-free nitrogen doped graphene containing various nitrogen functional groups (quaternary, pyrollic, and pyridinic species) have been found to facilitate the electrocatalysis of Oxygen Reduction Reaction (ORR) as in traditional Pt-based catalysts [2]. Atomistic simulations have been conducted to describe the ORR mechanism on different carbonaceous materials. However, these analysis have mostly been dedicated to Platinum (Pt)-based catalysts, and single nitrogen groups on Carbon nanotubes (CNTs) [3]. Thus, this study is oriented to account for the quantum mechanics interactions arising during the ORR on N-doped graphene structures containing pyridinic, pyrollic and quaternary species. Density functional theory is utilized to compute the Gibbs energy of the adsorbed intermediates and chemical species (e.g. H, OOH, H₂O₂, OH, O, and O₂) formed during the course of the ORR mechanism. The calculations evaluate the scale-up of the cluster in order to screen out local effects due to dimensions, and the reactivity of the aforementioned species on all possible catalytic sites (refer to positions a,b,c, adjacent to C1, C2, PR, PD in figure 1a). It was found that H, OOH, OH, O, and O₂ preferentially chemisorb or physorb on the quaternary site C1-a, whereas H₂O₂ species reacts favorably on C2-b. 

Keywords: ORR, DFT, Pyridinic, Pyrollic, and Quaternary Species.

[1] Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L., Science 2009, 323, 760.

[2] Biddinger, E.; Deak, D. v.; Ozkan, U., Top. Catal. 2009, 52, 1566.

[3] Hyman, M. P.; Medlin, J. W., J. Phys. Chem. B 2006, 110, 15338–15344.