Delicate Control of the Shell Structure of N‐Doped Carbon‐Coated Fe ₂ P/Ni ₂ P Hollow Spheres for Efficient Urea‐Assisted Hydrogen Evolution

Abstract Hollow multishelled structures (HoMSs) have garnered considerable attention in electrocatalysis owing to their unique hierarchical architecture and highly tunable chemical composition. Although delicate multiscale structural control exhibits potential for enhancing performance, HoMSs synthesis is challenging. Herein, triple‐shelled NiFe 2 O 4 (3s‐NiFe 2 O 4 HoMSs) structures are synthesized using metallurgical solid waste (steel rolling sludge, SRS). A subsequent low‐temperature phosphorization transforms the dense solid shells into a bubble‐like morphology, yielding sextuple‐shelled structures (6s‐FeNiP HoMSs) enriched with phosphorus vacancies. Finally, the 6s‐FeNiP HoMSs are integrated with carbon nitride to construct 7s‐FeNiP@NC HoMSs, which retain the morphology and structure of the 6s‐FeNiP HoMSs and exhibit enhanced electrical conductivity and stability. Electrochemical activity analyses demonstrate that the 7s‐FeNiP@NC HoMSs exhibit an excellent performance in the urea oxidation reaction (UOR), requiring only 1.38 and 1.41 V to achieve 100 mA cm −2 in urea (UOR||HER) and urine (UROR||HER) electrolyzers, respectively. Moreover, the 7s‐FeNiP@NC HoMSs maintain an almost constant voltage during continuous operation for 100 h at industrial‐level current densities (200 mA cm −2 ). This study provides a comprehensive strategy for the resource utilization of metallurgical solid waste, precise engineering of HoMSs, and efficient electrocatalysis of urea‐containing wastewater.