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

Abstract

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 Fe_<i>x</i>Ni_<i>y</i> 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.