Built-In Positive Valence Space Shifting the Chemical Equilibrium Forward for Nitrate Reduction to Ammonia

The electrochemical conversion of nitrate pollutants into value-added ammonia (NH₃) is an appealing alternative synthetic route for sustainable NH₃ production. However, the development of the electrocatalytic nitrate-to-ammonia reduction reaction (NO₃RR) has been hampered by unruly reactants and products at the interface and the accompanied sluggish kinetic rate. In this work, a built-in positive valence space is successfully constructed over FeCu nanocrystals to rationally regulate interfacial component concentrations and positively shift the chemical equilibrium. With positive valence Cu optimizing the active surface, the space between the stern and shear layers becomes positive, which is able to continuously attract the negatively charged NO₃^- reactant and repulse the positively charged NH₄⁺ product even under high current density, thus significantly boosting the NO₃RR kinetics. The system with a built-in positive valence space affords an ampere-level NO₃RR performance with the highest NH₃ yield rate of 150.27 mg h^-1 mg^-1 at -1.3 V versus RHE with an outstanding NH₃ current density of 189.53 mA cm^-2, as well as a superior Faradaic efficiency (FE) of 97.26% at -1.2 V versus RHE. The strategy proposed here underscores the importance of interfacial concentration regulation and can find wider applicability in other electrochemical syntheses suffering from sluggish kinetics.