Binary Metal-Oxide Active Sites Derived from Cu-Doped MIL-88 with Enhanced Electroactivity for Nitrate Reduction

Nitrate-to-ammonia electrochemical conversion is important for decreasing water pollution and increasing the production of valuable ammonia. However, achieving high ammonium production without undesirable byproducts is difficult. Cu-doped MIL-88-derived bimetallic oxide catalysts with electrocatalytically active Fe-O-Cu bridges, which have high NO₃^- adsorption energy and facilitate N-intermediate hydrogenation, are developed for NH₄⁺ production. Cu doping promotes hybridization between the O 2p of NO₃^- and Fe-Cu 3d, facilitating the adsorption and reduction of NO₃^- with a low Tafel slope (62.1 mV dec^-1) and high ammonia yield (1698.8 μg·h^-1·cm^-2). The cathode efficiency is stable for seven cycles. Cu adjacent to Fe sites inhibits hydrogen evolution, promotes NO₃^- adsorption, and decreases the intermediate adsorption energy barrier. This study provides new opportunities for fabricating diverse binary metal oxides with new interfaces as efficient cathode materials for selective electroreduction.