Tiara Ni Clusters for Electrocatalytic Nitrate Reduction to Ammonia with 97% Faradaic Efficiency.

The electroreduction of nitrate (NO) for sustainable ammonia (NH) production has recently emerged as a green process to solve water contamination and produce valuable chemicals. In this study, we developed Ni@CuFe-LDH composites comprising tiara Ni(SCHCOOH) (Ni) clusters anchored on the edges of 2D CuFe-LDH (LDH: layered double hydroxides) nanosheets via electrostatic interactions. The Ni@CuFe-LDH catalyst exhibits high electrochemical performance in nitrate reduction reaction (NORR). Specifically, the Ni@CuFe-LDH gives rise to an excellent faradaic efficiency of ∼97%, significantly surpassing the ∼73% FE of the pristine CuFe-LDH, with the NH productivity (0.91 mmol mg h) being similar to that of the CuFe-LDH. Mechanistic studies reveal that the superior electrocatalysis of Ni-based catalysts is primarily due to the synergistic interaction between Ni clusters and CuFe-LDH, which alters the rate-determining step (RDS) of the desorption of *NH species (for CuFe-LDH) to the *NO → *NO step (for Ni@CuFe-LDH); this is corroborated by the control experiments of NORR, in situ Raman and infrared spectroscopies, and computational approaches. In all, these efforts push forward the NORR research to study the structure-property relationships from the micro/nano-level to the precise atomic-level.