These results differ from those obtained on Ru(0001) electrodes mainly in the following features. First, the CVs for Ru(pc) in H 2 SO 4 electrolyte do not show the pronounced inhibition of the ORR by *HSO 4 in the potential range between 0.0 and 0.25 V. Second, the complete inhibition of the ORR in the positive-going scan in the same electrolyte at potentials > 0.25 V is missing as well. These differences are also reflected in the H 2 O 2 formation. On the other hand, also on Ru(pc), the currents are lower in H 2 SO 4 than in HClO 4 electrolyte, suggesting that the presence of (bi)sulfate species reduces the effective overall activity of the electrode.