Reductant-Mediated Crystallinity Modulation of Nanoporous Nickel Metallic Aerogels for Nitrate Electroreduction

Nickel (Ni)-based materials are among the ideal candidates for nitrate reduction reaction (NO 3 RR) owing to their low cost and high reactivity. However, the mechanism by which the crystal structure of Ni-based materials influences catalytic performance, as well as the underlying structure–activity relationship, remains unclear. Here, by regulating the reduction intensity of the reducing agent, we successfully synthesized strong reductant-induced Ni metallic aerogels (sr-Ni MAs) and weak reductant-induced Ni MAs (wr-Ni MAs), both with a nanoporous structure, and systematically investigated the influence of their crystal structure on NO 3 RR performance. Among these, sr-Ni MAs exhibit a higher ammonia (NH 3 ) yield rate and Faradaic efficiency than wr-Ni MAs in both neutral and alkaline electrolytes. The NH 3 yield rate of sr-Ni MAs (15862.13 μg h –1 mg –1 cat. ) is 1.57 times that of wr-Ni MAs (10081.73 μg h –1 mg –1 cat. ) at −1.0 V RHE in a neutral electrolyte. Mechanistic studies confirm that the moderate d-band center closer to the Fermi level of sr-Ni MAs optimizes the adsorption–desorption equilibrium of intermediates and significantly reduces the energy barrier of the rate-determining step *NO → *NOH. This work clarifies the intrinsic relationship between crystallinity and electrocatalytic performance, providing insights into the structural design and mechanistic study of highly efficient Ni-based NO 3 RR catalysts.