Interfacial Water Structure Modulation on Unconventional Phase Non-Precious Metal Alloy Nanostructures for Efficient Nitrate Electroreduction to Ammonia in Neutral Media

Electrocatalytic nitrate reduction reaction (NO₃RR) has been recognized as a sustainable route for nitrate removal and value-added ammonia (NH₃) synthesis. Regulating the surface active hydrogen (*H) behavior is crucial but remains a formidable challenge, especially in neutral electrolytes, greatly limiting the highly selective NH₃ formation. Herein, we report the controlled synthesis of heterophase hcp/fcc non-precious CuNi alloy nanostructures for efficient NH₃ electrosynthesis in neutral media. Significantly, hcp/fcc Cu₁₀Ni₉₀ exhibits excellent performance with NH₃ Faradaic efficiency and yield rate of 98.1% and 57.4 mg h⁻¹ mg_cat⁻¹, respectively. In situ studies suggest that the high proportion of interfacial K⁺ ion hydrated water (K⁺–H₂O) on hcp/fcc Cu₁₀Ni₉₀ creates high *H coverage via boosting interfacial water dissociation, enabling the rapid hydrogenation kinetics for NH₃ synthesis. Theoretical calculations reveal that the superior NO₃RR performance of hcp/fcc Cu₁₀Ni₉₀ originates from both the existence of hcp phase to improve the electroactivity and the high Ni content to guarantee an efficient active hydrogen supply. The strong interaction between Ni and Cu also optimizes the electronic structures of Cu sites to realize fast intermediate conversions with low energy barriers. This work provides a novel strategy to optimize surface *H behavior via tuning interfacial water structure by crystal phase control.