Computational Studies of the Structural, Electronic and Catalytic Properties of Hetero-atom Doped Graphene

Abstract

Graphene’s physical, chemical, and high electrical properties makes it an excellent material for electronics, and
energy conversion devices in particular low temperature fuel cells that experience sluggish reactions at the cathode where
oxygen is reduced. However, the chemical inertness of pristine graphene has been a hindrance to its widespread use. In this work, computational studies based on first principles density functional theory (DFT) calculations are conducted to investigate the structural, electronic, and catalytic activities of graphene upon hetero-atom doping. The dopants explored include: Boron (B), nitrogen (N), aluminium (Al) and sulfur (S) as single atom types. The DFT calculations are also performed on graphene co-doped with Al and S atoms. Compared with pristine graphene, the incorporation of dopants alters the bond lengths within the graphene structure with B and N only causing minimal alterations in the lattice due to their covalent radii being very close to that of carbon (C) atom. Aluminium and S on the other hand causes noticeable alteration to graphene unit cell. The calculated electronic density of states (DOS) and band structures results show the zero-gap behavior of pristine graphene with the conduction and valence bands touching at the K-point. However, upon doping with B atom a band-gap opening of 0.1922 eV is observed. Being electron deficient, the B dopant causes the Fermi level to shift downwards inducing p-type doping. When graphene is doped with N atom, a band-gap of 0.1909 eV is realized and the DOS results indicate that the N dopant induces n-type doping. On the other hand, the incorporation of S and Al dopants in graphene induces a band-gap of 0.2436 eV and 0.3944 eV respectively. It is observed that co-doping graphene with Al and S further opens the energy gap with a band-gap of 1.059 eV resulting. These results shows that by doping graphene, the electronic properties are enhanced and such can be utilized in electronics and energy devices applications. The catalytic activity of Al-S was also investigated through the DFT calculations of the adsorption energy and oxygen reduction reaction (ORR) mechanism of the intermediate states and the obtained results show that Al-S co-doped graphene could be a potential electro-catalyst for low-temperature fuel cells.