A Coral−Like Ni ₃ P/Ni ₃ Mo ₃ N Heterostructure With Built−In Electric Field for High−Current−Density Urea Electrooxidation Toward Energy−Saving Hydrogen Production and Battery Applications

The energy−efficient urea oxidation reaction (UOR), crucial for hydrogen production and environmental remediation, faces dual challenges of sluggish kinetics and competing oxygen evolution reaction (OER). To overcome these challenges, we construct a Ni 3 P/Ni 3 Mo 3 N heterostructure with a built−in electric field. Experimental and theoretical results collectively verify that pronounced electron transfer from Ni 3 P to Ni 3 Mo 3 N establishes a strong built−in electric field at the interface, creating distinct electron−deficient and electron‐rich regions. This field thus steers the oriented adsorption of urea molecules, with −NH 2 anchoring on Ni 3 P and C═O favoring Ni 3 Mo 3 N. This not only promotes urea activation and lowers the rate−determining step energy barrier but also enables efficient *COO desorption, ultimately overcoming the activity–stability compromise. Consequently, the catalyst delivers exceptional UOR performance, requiring only 1.46 V versus RHE to achieve 500 mA cm −2 , indicating superior UOR selectivity. In a urea−assisted water electrolyzer, the system operates at 1.72 V for 500 mA cm −2 , significantly outperforming conventional electrolysis (∼2.05 V), and exhibits robust stability over 450 h. Furthermore, the Zn−urea−air battery configuration demonstrates energy−efficient operation, excellent rechargeability, and electrochemical durability, highlighting its practical potential for energy storage. This work offers insights into built−in electric field−modulated UOR reaction pathways and provides a promising strategy for advanced energy‐saving catalysts.