Embedded Fe-Cu Pairs Enable Tandem Nitrate-to-Ammonia Electroreduction.

Abstract

Electrochemical nitrate reduction (e-NO₃RR) to ammonia (NH₃) represents a transformative technology that seamlessly integrates environmental remediation with resource regeneration. This approach is crucial for restoring equilibrium in the global nitrogen cycling, advancing green chemistry, and accelerating the transition toward a sustainable circular economy. However, under pH-neutral conditions, the simultaneous occurrence of two competing reactions (Hydrogen Evolution Reaction and NO₃RR) at the same active sites results in considerable interference, significantly limiting the catalytic efficiency and selectivity. Here a Fe-Cu pair (Cu-N₃/Fe₃-N₈) electrocatalyst is meticulously designed, achieving a NH₃ production rate of 18.83 mg∙h^‒1∙mg_cat ^‒1 at -0.65 V versus the reversible hydrogen electrode (RHE), accompanied with a Faradaic efficiency of 97.1%. This as-prepared Fe-Cu pair overcomes the limitations of conventional bimetallic catalysts, which typically rely on direct atomic coupling. The electron-deficient region formed by Cu-N₃ enhances the adsorption of nitrate, while the electron-rich domain generated by the Fe₃-N₈ cluster facilitates the adsorption of nitrite and promotes water activation. The spatially separated charge gradient optimizes the adsorption energies of multi-step reaction intermediates, thereby establishing a relay mechanism. The work provides valuable insights into the design of multi-active-site electrocatalysts and offers a promising approach to addressing critical challenges in nitrogen resource conversion.