Potential‑Driven Tetragonal CuFe2O4 Phase Transition Enables Near‑Complete Nitrate‑to‑Ammonia Conversion with Minimal Nitrite Accumulation

The development of electrocatalyst for nearly complete electrocatalytic nitrate reduction without accumulating nitrites in the product feed is indispensable for sustainable nitrate contaminated wastewater treatment and carbon-neutral green ammonia production. In this study, CuFe 2 O 4 nanowires could mimic the bifunctional nature of nitrite reductase where Cu act as nitrate adsorption and deoxygenation center while Fe promoted adsorption of H* and the reduction of *NO to NH 2 . We demonstrate the involvement of a hydride‑transfer pathway supported by obtaining four‑electron transfer from rotating‑disk voltammetry and further corroborated by the mechanistic insights obtained from DFT analysis. The faradaic efficiency for ammonia exceeded 95% at all applied potentials, with an ammonia‑to‑nitrite yield‑rate ratio of 13 at −1.1 V vs. Reversible Hydrogen Electrode. The enhanced nitrite reduction was due to the potential dependent cubic to tetragonal phase transition at higher overpotential exposing undercoordinated iron sites promoting H* adsorption and hydrogenation of *NO. The tandem electrocatalysis mechanism led simultaneously to high NH 3 selectivity, suppressing hydrogen evolution reaction and resulting negligible nitrite accumulation. This work establishes a correlation between ammonia selectivity, surface structure and phase of spinel CuFe 2 O 4 and provides crucial mechanistic insights into reaction pathways of NO 3 - /NO 2 - electroreduction