Catalytic activity of OH functionalized N-doped graphene in oxygen reduction reaction for fuel cell applications: a DFT study

Catalytic behavior of metal-free hydroxyl group (OH) functionalized single nitrogen (N-Gra(OH)16) and triple nitrogen (N3-Gra(OH)16) doped graphene surface are investigated in the 4e− reduction pathway under oxygen reduction reaction (ORR) process. The thermodynamical parameters indicate that the reaction is highly exothermic and feasible with the N-Gra(OH)16 and N3-Gra(OH)16 as catalysts. However, N3-Gra(OH)16 exhibits better catalytic properties than N-Gra(OH)16. The chemisorption of all reactive species (*O2, *OOH, *O and *OH) via a covalent bond on the N3-Gra(OH)16 and the physisorption of the product H2O on the N3-Gra(OH)16 are essential for efficient reaction kinetics and the uninterrupted reaction cycle, respectively. Categorically, due to the presence of a large number of nitrogen atoms, the N3-Gra(OH)16 exhibits excellent catalytic activity which has resulted in lowered EHOMO–LUMO gap, concomitantly increasing the surface's reactivity. Besides the above, the barrier energies are comparable with platinum (Pt) catalysts. Our results show that the N3-Gra(OH)16 surface is the most suitable catalyst for ORR activity.