d–p Orbital Hybridization Modulation via Electronic Engineering: A Novel Strategy for Urea Removal beyond the Ni ³⁺ Driving Voltage Limit in Freshwater and Seawater

Based on the principles of electronic modulation engineering, this study successfully synthesized a nitrogen-doped carbon composite nickel catalyst (Ni@NC) via a one-step, high-temperature annealing method. The prepared catalyst demonstrates remarkable effectiveness in the removal of urea from both freshwater and seawater environments, operating at driving voltages lower than those required by conventional nickel-based catalysts in the urea oxidation reaction (UOR). By optimizing the proportion of urea as the nitrogen and carbon source, the as-prepared Ni@NC-5 catalyst achieved a current density of 10 mA cm^-2 at a low potential of 1.31 V (vs RHE) in an alkaline freshwater system, while maintaining stable operation for 30 h at 100 mA cm^-2. In seawater, it required only 1.36 V to reach the same current density target. Furthermore, through a combination of density functional theory (DFT) calculations and detailed characterization data, we elucidated the intricate interactions─cooperative yet competitive─among carbon, nitrogen, nickel, and urea during the catalytic process.