Maximizing Available Active Hydrogen on FeNi Substitutional Solid-Solution Alloy to Boost Electrosynthesis of Ammonia from Nitrate

Electrochemical nitrate reduction reaction (NO3RR) stands out as a promising route for sustainable ammonia synthesis, in which active hydrogen (*H) plays a crucial role in both the deoxygenation and hydrogenation steps. However, the regulation of surface *H is still overlooked, and without intervention, the competing hydrogen evolution reaction is kinetically more favored over the NO3RR, leaving the current system as far from satisfactory. Herein, based on reverse utilization of the Sabatier principle, a series of FexNiy substitutional solid-solution alloys (SSAs) are synthesized to manipulate *H behavior for enhanced NO3RR. Upon precise optimization of the alloy composition, the d-band center of HER-active Ni shifts toward the Fermi level, endowing the catalyst with strong interaction to *H and greatly prolonging its lifetime, which enables abundant supply to facilitate the NO3RR. As expected, a maximum NH3 yield rate of 31.46 mmol h-1 mg-1 is delivered over the optimized Fe3Ni1-SSA, which is considerably higher than most of the extensively reported works. Several in situ characterizations are combined to gain in-depth insight. Especially, in situ Fourier transform infrared spectroscopy in internal reflection mode directly observes *H enrichment on the catalyst surface, while the accompanied facilitation of the NO3RR process is verified by external reflection mode.