indicate that the 4e -ORR on Au(100) is unlikely to be blocked by the suspension of O-O* bond cleavage. Furthermore, if it was the RDS, there would be an accumulation of O2* on Au(100) above 0.9 V (RHE). But in a recent surface enhanced Raman study, the signal for O-O* actually disappears in that potential region. By exclusion, it leaves the first step, O2 adsorption, as the RDS, which has been suggested before, based on the well-known low adsorption probability of O2 on Au surfaces, and studied in details by Schmickler and co-workers using a combination of theoretical modelling, DFT and classical MD calculations. Our calculation results lend further supports to this suggestion. As discussed earlier, an O2 molecule in its triplet ground state could hardly adsorb on Au surfaces at room temperature. The presence of water molecules in the electrode interfacial region does not facilitate the transformation of triplet O2 into the more reactive singlet state. The more likely adsorption route is for an electron to be transferred to the outer sphere,