Cu-Doped Iron Oxide for the Efficient Electrocatalytic Nitrate Reduction Reaction

The electrochemical nitrate reduction reaction (NO₃RR) is a promising alternative synthetic route for sustainable ammonia (NH₃) production, because it not only eliminates nitrate (NO₃^-) from water but also produces NH₃ under mild operating conditions. However, owing to the complicated eight-electron reaction and the competition from the hydrogen evolution reaction, developing catalysts with high activities and Faradaic efficiencies (FEs) is highly imperative to improve the reaction performance. In this study, Cu-doped Fe₃O₄ flakes are fabricated and demonstrated to be excellent catalysts for electrochemical conversion of NO₃^- to NH₃, with a maximum FE of ∼100% and an NH₃ yield of 179.55 ± 16.37 mg h^-1 mg_cat^-1 at -0.6 V vs RHE. Theoretical calculations reveal that doping the catalyst surface with Cu results in a more thermodynamically facile reaction. These results highlight the feasibility of promoting the NO₃RR activity using heteroatom doping strategies.