Modulating the Reorientation of Interfacial Water to Promote Electrochemical NO Reduction to NH₃ on Palladium–Copper Catalysts

In neutral or alkaline conditions, the active hydrogen species (H*) required for the electrocatalytic nitric oxide reduction reaction (NORR) originates from the splitting of H2O, a process significantly influenced by the orientation of H2O molecules. Therefore, investigating the reorientation behavior of H2O at the catalyst–electrolyte interface is crucial for optimizing the NORR process. Herein, Pd nanoparticles (Pd NPs) were loaded onto the oxide-derived Cu surface to modulate the localized electric field, enabling the investigation of the impact of interfacial water reorientation behavior on the NORR. In situ spectroscopy studies revealed that the Pd NP loading enhanced the sensitivity of H2O to the localized electric field, prompting interfacial water molecules to reorient into an “H-down” configuration, which shortened the M–H bond length (where M represents the metal active site), facilitated the conversion of 4-hydrogen-bond coordinated water and 2-hydrogen-bond coordinated water into Na+ ion-hydrated water, and thereby promoted H2O dissociation. Theoretical calculations combined with electron paramagnetic resonance spectroscopy confirmed that the incorporation of Pd NPs facilitated H* generation and migration, enhancing the stability of the *NOH intermediate and thereby favoring NH3 production during the NORR process. This work profoundly reveals the impact of localized electric field-induced reorientation of interfacial water molecules on the effective execution of NORR, offering valuable insights for the design of high-performance NORR electrocatalysts.