We further analyzed the interfacial water structures of Pt/C and Pt/pN-C. Shown in Fig. , Pt/pN-C has a large water peak centered at ~3250 cm -1 , while for Pt/C, the major peak centered at ~3480 cm -1 . We attribute the peak shift to the presence of Pt-SA in Pt/pN-C, as it is the sole structural difference between Pt/pN-C and Pt/C. The H2O at ~3250 cm -1 is known to have an Odown (H2O↓) conformation and we reason that the SAs prefer such structure because their positive charge and empty d orbitals can interact with the lone pairs of the oxygen atoms of H2O. In order to confirm our assignment, we tested the 0.1%-Pt/pN-C sample, which indeed exhibits only a single peak at ~3250 cm -1 due to the presence of only Pt SAs (Supplementary Figure ). Moreover, the relative fraction of the ~3250 cm -1 peak is much higher in Pt/pN-C than in Ru/pN-C, consistent with our previous observation that the population of Pt SAs are higher than Ru SAs on pN-C (Fig. ).