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

Urea electrolysis is a prospective technology for simultaneous H2 production and nitrogen suppression in the process of water being used for energy production. Its sustainability is currently founded on innocuous N2 products; however, we discovered that prevalent nickel‐based catalysts could generally over‐oxidize urea into NO2− products with ≈80 % Faradaic efficiencies, posing potential secondary hazards to the environment. Trace amounts of over‐oxidized NO3− and N2O were also detected. Using 15N isotopes and urea analogues, we derived a nitrogen‐fate network involving a NO2−‐formation pathway via OH−‐assisted C−N cleavage and two N2‐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 N2 production by a factor of two. These findings provide complementary insights into the nitrogen fate in water–energy nexus systems. A systematic investigation of the nitrogen network during the nickel‐catalyzed urea oxidation reaction was carefully performed. It revealed a dominant NO2− production rather than innocuous N2 present on various nickel‐based catalysts. Accordingly, polymer‐surface modification was put forward to increase the efficiency of harmless N2 products.