The ORR mechanism is much more complex than HOR and involves the formation of several intermediates. In acidic conditions, the protons in solution are the key medium to react with the adsorbed O2 to generate H2O. Namely, the electrochemical reduction of O2 can proceed via successive protonation steps. In general, two different pathways are identified for the ORR mechanism depending on whether the undesired hydrogen peroxide (H2O2) is formed or not: the two-electron H2O2 production and the direct four-electron reduction mechanism to H2O. Within the four-electron reduction mechanism, there are three possible pathways: associative (direct hydrogenation), O2 dissociative and OOH dissociative pathway. OOH* was found to dissociate spontaneously in all systems studied (vide infra), and for this reason, in this work, we decided to focus only on the OOH dissociation route. It should be mentioned that the electrochemical steps were approximated as concerted proton-electron transfer (CPET) reactions.