Structure of Graphene Oxide: Thermodynamics versus Kinetics

Graphene oxide (GO) is an important intermediate to prepare graphene, and it is also a versatile material with various applications. However, despite its importance, the detailed structure of GO is still unclear. For example, previous theoretical studies based on energetics have suggested that hydroxyl chain is an important structural motif of GO, which, however, is found to be contrary to nuclear magnetic resonance (NMR) experiments. In this study, by calculating vibrational frequencies, we find that hydroxyl chain structure is also inconsistent with infrared experiment. To resolve this controversy, we check both thermodynamic and kinetic aspects of GO structure. First-principles thermodynamics gives a free-energy based stability ordering similar to that solely based on inner energy, and the hydroxyl chain is indeed thermodynamically very favorable. Therefore, kinetics during GO synthesis is expected to have an important role in GO structure. Transition state calculations predict large energy barriers between local minima, which suggests that experimentally obtained GO samples have kinetically constrained structures.