Considering the HOR activity of Pt/pN-C is much higher than Pt/C, we attribute the promotion of HOR kinetics to the O-down (H2O↓) conformation of interfacial water . The group of Jia proposed that water with such conformation acted as a catalyst to accelerate OH -transport via Grotthuss mechanism and reduced reorganization energy . To verify this attribution, we synthesized Pt nanoparticles first and then loaded onto the pN-C support (denoted as Pt NP/pN-C, which contains no SAs, see Methods). The intrinsic HOR activity of Pt NP/pN-C is similar to Pt/C, but much lower than Pt/pN-C (Supplementary Figure ). This result supports the essential role of Pt SAs in promoting the catalytic activity of Pt, likely by modulating the interfacial water structures as we proposed above .