Structure of graphene oxide: thermodynamics versus kinetics

TL;DR

This study investigates the structure of graphene oxide by examining thermodynamic stability and kinetic constraints, revealing that kinetic factors during synthesis significantly influence its actual structure, which differs from thermodynamic predictions.

Contribution

It provides a combined thermodynamic and kinetic analysis of GO structure, highlighting the importance of kinetic constraints in determining its real structure.

Findings

Hydroxyl chain is thermodynamically favorable but inconsistent with infrared data.

High energy barriers suggest kinetically constrained GO structures.

Kinetics during synthesis influences GO structure more than thermodynamics.

Abstract

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) experiment. In this study, we check both thermodynamic and kinetic aspects missed previously. First principles thermodynamics gives a free energy based stability ordering similar to that based on energetics, and hydroxyl chain is thus thermodynamically still favorable. At the same time, by checking the calculated vibrational frequencies, we note that hydroxyl chain structure is also inconsistent with infrared experiment. Therefore, kinetics during GO synthesis is expected to make an important role in GO structure. Transition state calculations predict large energy barriers between local minima, which suggests that experimentally obtained GO has a kinetically constrained structure.