Trends in Buckled and Planar Halogen-Doped Graphene for ORR Activity: A DFT Study

Abstract

Owing to the sluggish oxygen reduction reaction (ORR), high-performance catalysts like Pt-based alloys are widely used to render the reaction practically useful in systems like fuel cells. Nonetheless, high costs and technical complications associated with such catalysts have encouraged the exploration of alternative ORR catalysts like heteroatom-doped carbon nanomaterials. To improve the catalytic activity of carbon, earlier studies used boron, nitrogen, phosphorus, sulfur, and selenium as dopants. In this paper, we perform density functional theory (DFT) calculations to explore the potential of halogens (X = F, Cl, Br, I) substituted within the two-dimensional structure of graphene. We also validate some of the results of previous experimental and theoretical studies on halogen-doped graphene. For example, we compare halogen adsorption and band structures of the resulting halogen-doped materials, as well as the possible influence of atomic size and atomic interactions (e.g., Br2/Br interactions, polyiodide formation) on their experimentally observed properties. Based on the resulting electronic and structural information, we then identify which among the buckled and planar forms of halogen-substituted graphene show the most promise for ORR activity. Finally, we compare this method of doping with previously studied methods like adsorption and edge-halogenation to provide additional insight on halogen doping.