However, it should be thermodynamically impossible for O2 molecules to be formed so early and desorb only from around 1500 mVRHE since this process cannot be potential-dependent because it neither requires electron transfer nor involves a charged species. Hence, the reasonable conclusion is that during the OCP period, O2 is dissociatively adsorbed according to Eq. 3, and *O and O-upd denote the same kind of oxygen species on the platinum surface. Then, the O-upd reduction corresponds to Eq. 4a-b, combining to a complete path of the reduction of O2 to water via the dissociative mechanism.