Graphene materials have emerged as a promising alternative for electrodes in vanadium redox flow batteries due to their unique properties. However, its practical application in such large scale energy storage systems still needs further developments on low-cost and scalable processes for graphene production. The preparation of graphenes through the graphite oxide route, followed by thermal reduction, is an interesting option because it offers the possibility to obtain large quantities of solid products which can be directly used in the battery. Here we report on the advantages of applying the thermal reduction directly to the graphite oxide (which also produces exfoliation) instead of to the graphene oxide to produce graphenes suitable as positive electrodes in vanadium redox flow batteries. The results show that, apart from being a more simple procedure, the graphene thus obtained exhibits a better performance, mainly in terms of a lower overpotential and a faster electron transfer rate of the vanadium redox processes. These results are attributed to an enhanced restoration of the 2D graphitic structure in the platelets, leading to a higher electrical conductivity of the material, and also to the presence of a larger amount of reactive edges.