​​​In the laboratory, in collaboration with LCBM team, ​we synthesize graphene using a chemical exfoliation method of graphite. Graphene oxide (GO) is produced during the first oxidation/exfoliation step, and it must be reduced to obtain partially reduced graphene oxide (rGO). Hydrazine hydrate is the most commonly used GO reducing agent, but it is toxic and explosive. Therefore, many other reducers are tested in the literature. Vitamin C (or L-ascorbic acid) is among the less hazardous and more eco-friendly reducers. Numerous examples of its use exist, and we aimed to rationalize the operating conditions to compare the reduction degrees of different rGO samples.

In this study, we were surprised to find that longer reaction times led to a less reduced graphene oxide than that obtained from shorter reaction time​s (Figure – right). This phenomenon is even more pronounced when the vitamin C concentration is higher. This observation suggests that, under these reaction conditions, both the reduction of the initial graphene oxide and its re-oxidation occur simultaneously. The proposed explanation is that, at high temperatures and vitamin C concentrations, vitamin C undergoes auto-oxidation, leading to graphene re-oxidation. Mechanistic studies could confirm the involvement of reactive species, such as H₂O₂ or radicals from its degradation, in this process.

By rationalizing the reduction conditions with vitamin C, we identified those leading to the production of highly reduced rGO, an important result for the design of efficient supercapacitor electrodes.​