We utilize periodic density functional theory to study singly and triply N- and B-substituted graphene. We examine their doping mechanisms and effects on Pt atom adsorption and migration on graphene. We find a seemingly contradictory behavior between dopant type (n- vs p-type) and charge accumulation on the dopant atoms: the N atoms in both n-type singly N-doped graphene (NG) and p-type triply N-doped graphene (3NG) gain electron density while the B atoms in both singly (BG) and triply (3BG) B-doped graphene are p-type and lose electron density. This behavior arises from unequal charge sharing within C-B and C-N sp2 σ bonds and the requirement that the pz orbitals of N and B are singly occupied in order to maintain graphene's aromaticity. NG's N atom stabilizes Pt atom adsorption up to -0.39 eV (Eads = -1.86 eV) and by -0.13 eV even at distances 12.3 Å away from the N dopant. The Pt atom hopping energy barrier is lowered in graphene rings containing an NG N atom relative to undoped graphene, but the migration of a Pt atom over the N atom is unlikely due to a 1.0 eV barrier. 3NG's most stable Pt adsorption site (Eads= -2.86 eV) is the vacant C site at the center of 3NG's three N atoms and arises because of the formation of covalent bonds between Pt's d orbitals and the N atoms' three in-plane dangling sp2 orbitals. When a Pt atom adsorbs at a ring containing a pyridinic N, the strong N-Pt bonds trap the Pt atom, limiting its diffusion over the graphene sheet. The BG and 3BG structures bind Pt with a maximum adsorption energy of Eads= -2.16 eV and -5.30 eV, respectively. BG's high-lying B-C bonding orbitals allow the Pt atom to form strong σ bonds directly to the graphene sheet, while 3BG's B atoms donate electron density to the Pt atom creating an ionic bond between the negative Pt atom and the positive B atoms. These bonding mechanisms result in only short-range Pt stabilization and the B atoms having little influence on Pt atom migration outside B containing C rings; however, the depth and short-range nature of these energy wells funnel Pt atoms toward the B atoms and trap them there.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films