Deciphering and Suppressing Over‐Oxidized Nitrogen in Nickel‐Catalyzed Urea Electrolysis

Abstract Urea electrolysis is a prospective technology for simultaneous H 2 production and nitrogen suppression in the process of water being used for energy production. Its sustainability is currently founded on innocuous N 2 products; however, we discovered that prevalent nickel‐based catalysts could generally over‐oxidize urea into NO 2 − products with ≈80 % Faradaic efficiencies, posing potential secondary hazards to the environment. Trace amounts of over‐oxidized NO 3 − and N 2 O were also detected. Using 15 N isotopes and urea analogues, we derived a nitrogen‐fate network involving a NO 2 − ‐formation pathway via OH − ‐assisted C−N cleavage and two N 2 ‐formation pathways via intra‐ and intermolecular coupling. DFT calculations confirmed that C−N cleavage is energetically more favorable. Inspired by the mechanism, a polyaniline‐coating strategy was developed to locally enrich urea for increasing N 2 production by a factor of two. These findings provide complementary insights into the nitrogen fate in water–energy nexus systems.