Reoriented Interfacial Water Structure Around Pd Enhances Oxygen Reduction Kinetics in Zn–Methanol–Air Batteries

The dynamics of interfacial water within the electrical double layer (EDL) play a pivotal role in governing charge transfer during electrocatalysis. While previous strategies primarily focused on modulating electrolyte compositions or pH to tune the EDL, tailoring the interfacial water structure through catalyst design remains underexplored. Herein, we report a composite catalyst comprising atomically dispersed cobalt sites (Co_SA) embedded in a N-doped carbon matrix and palladium nanoparticles (PdCo_NP@Co_SANC), which exhibits enhanced oxygen reduction reaction (ORR). In situ spectroscopy and density functional theory calculations reveal that Co_SA incorporation induces a negative shift in the potential of zero charge (E_PZC), causing more positively charged surface under working conditions compared to the Co-free analogue (Pd_NP@NC). This charge redistribution reorients interfacial water from H-down to O-down configuration, promoting *OH hydrogenation by strengthening electrostatic interaction with the OH_sol ^- product. Consequently, PdCo_NP@Co_SANC achieves an outstanding half-wave potential of 0.937 V and a mass activity of 2.58 A mg_Pd ^-1 for ORR, along with 6.15 A mg_Pd ^-1 for methanol oxidation reaction (MOR), outperforming Pd_NP@NC and commercial Pd/C. Leveraging its bifunctional ORR/MOR activity, we construct carbonate-free Zn-methanol-air battery with decent kinetics up to 100 mA cm^- ² and stable operation over 2500 h with an energy efficiency of 70%.