The electrochemical reduction of GO was investigated in aqueous, at both acid and basic pH, and organicmedia, to identify the possible role of protons (Hþ) in the reduction mechanism of this material. Theobtained rGOfilms were characterized by FTIR, electrochemical methods, Raman and XPS spectroscopy.Data showed that the reduction was more efficient in acid and basic media due to the presence ofprotons and the capacity of water that works as a proton donor, resulting in C/O ratios of 3.8 and 7.8,respectively. Mostly hydroxyl, epoxide and carbonyl moieties were removed. In a proton-free organicelectrolyte, a C/O ratio of 1.8 was obtained for most of the samples; nevertheless, the graphitic carbon sp2domains were restored to a large extent in the absence of Hþ. The characterization of the materialshowed that the presence of protons, during the electrochemical reduction, caused hydrogenation re-actions, which targeted the graphitic domains in rGO and resulted in the loss of sp2hybridization. Thepresence of such defects modified the electrochemical properties of the rGOfilms, where, despite ofexhibiting higher C/O ratio, thefilms reduced in aqueous electrolytes displayed lower electron transfer(e.g. ferrocyanide redox-probe) than those reduced in organic electrolyte