Modulating Intermediate Adsorption and Interfacial Water Structure to Unlock the Potential of Nickel for Ammonia...

Metallic Ni stands out to be a promising electrocatalyst for nitrate reduction reaction (NO₃RR) to ammonia (NH₃), yet is bottlenecked by limited water dissociation kinetics for active hydrogen (*H) supply particularly at low potentials and insufficient adsorption/activation capability toward NO₃ ^-. We unveil for the first time that NO₃RR performance of Ni can be activated by synergistic unconventional phase design and alloying engineering. Specifically, anomalous hcp Ni with Cu alloying (NiCu-hcp) is readily engineered via a facile metal-organic frameworks mediated route. Impressively, the NiCu-hcp can deliver prominent NO₃RR performance with record NH₃ yield rate of 2.24 mmol h^{- 1} cm^{- 2} and Faradaic efficiency of 98.3% at -0.4 V versus RHE, favorably rivaling the state-of-the-art ones. Moreover, integrating NiCu-hcp into Zn-NO₃ ^- battery delivers eminently high power density of 23.9 mW cm^{- 2}. From experimental and theoretical studies, unusual hcp phase together with Cu alloying engineering over Ni can regulate interfacial water structure for facilitated dissociation to generate *H, and meanwhile, manipulate electronic state, thereby promoting NO₃ ^- affinity/activation and lowering Gibbs free energy barrier of the rate-determining step (*NO→*NOH). This contribution presents a new paradigm to unlock the potential of Ni for NO₃RR via elegant unusual phase design synergistic with alloying engineering.