A combined experimental and theoretical investigation approach has been applied to the electrochemical reduction of graphene oxide (GO) in order to unravel the corresponding reaction mechanism, so far scarcely addressed in the literature. Reduced graphene oxide (rGO) layers were prepared via electrochemical reduction of GO drop-casted onto hydrogenated Si(111) wafers in aqueous medium. A cyclic potential variation programme was applied at different scan rates, followed by an ex-situ characterization of the obtained rGO deposits by means of X-ray photoelectron spectroscopy (XPS). Elaboration of the cyclic voltammetric curves by deconvolution analysis put in evidence a 2:1 ratio between the reduction charges associated to the first and second reduction event, respectively. By means of density functional theory (DFT) based calculations, focused on the fate of epoxyl and carbonyl groups upon electrochemical reduction, an interpretation of the reduction path of the GO layers has been proposed, consistently with both XPS and CV results. Such interpretation is based on the sequential reduction of epoxyl and carbonyl moieties of GO through a two-electron and one-electron mechanism, respectively. (C) 2019 Elsevier Ltd. All rights reserved.