Structure and stability of graphene edges in O2 and H2 environments from ab initio thermodynamics

Edges play a determining role in the electronic and transport properties of graphene, however, their actual morphology and configuration remain unknown. Using ab initio thermodynamics, we have systematically studied the stability and structure of armchair and zigzag edges of graphene in pure O2 and combined O2 and H2 environments. In total, 81 different nanostructures were investigated, however, only a few of them domain the phase diagram. Our calculations show that zigzag edges are less stable than armchair edges. Nonetheless, the former exhibit a much richer diversity in terms of structures. The oxygen-terminated edges occupy the largest regions in the phase stability diagram in comparison with hydrogen-oxygen-terminated edges, which correspond to carboxyl and alcohol functional groups.