Interfacial Engineering of Bimetallic Ni/Co-MOFs with H-Substituted Graphdiyne for Ammonia Electrosynthesis from Nitrate.

Abstract

The electrochemical synthesis of ammonia is highly dependent on the coupling reaction between nitrate and water, for which an electrocatalyst with a multifunctional interface is anticipated to promote the deoxygenation and hydrogenation of nitrate with water. Herein, by engineering the surface of bimetallic Ni/Co-MOFs (NiCoBDC) with hydrogen-substituted graphdiyne (HsGDY), a hybrid nanoarray of NiCoBDC@HsGDY with a multifunctional interface has been achieved toward scale-up of the nitrate-to-ammonia conversion. On the one hand, a partial electron transfers from Ni²⁺ to the coordinatively unsaturated Co²⁺ on the surface of NiCoBDC, which not only promotes the deoxygenation of *NO₃ on Co²⁺ but also activates the water-dissociation to *H on Ni²⁺. On the other hand, the conformal coated HsGDY facilitates both electrons and NO₃^- ions gathering on the interface between NiCoBDC and HsGDY, which moves forward the rate-determining step from the deoxygenation of *NO₃ to the hydrogenation of *N with both *H on Ni²⁺ and *H₂O on Co²⁺. As a result, such a NiCoBDC@HsGDY nanoarray delivers high NH₃ yield rates with Faradaic efficiency above 90% over both wide potential and pH windows. When assembled into a galvanic Zn-NO₃^- battery, a power density of 3.66 mW cm^-2 is achieved, suggesting its potential in the area of aqueous Zn-based batteries.