Asymmetric Ni-O-Co Active Sites Induce Spin-State Transitions to Break Performance Trade-Offs in Urea Electrolysis

Urea-assisted water electrolysis represents a sustainable paradigm for concurrent hydrogen production and wastewater remediation; however, its efficiency is fundamentally limited by the Sabatier trade-off between urea activation and CO₂ product desorption. Here, we report an asymmetric electronic structure engineering strategy to overcome this bottleneck by incorporating atomically dispersed Ni into Co₃O₄ cubic hollow nanoboxes. The construction of asymmetric Ni-O-Co sites triggers a critical spin-state transition of octahedral Co³⁺ from low-spin to intermediate-spin through lattice distortion and polarization. This electronic reconfiguration effectively strengthens urea binding while simultaneously weakening the adsorption of poisonous *CO₂ intermediates. Synergized by a superhydrophilic and superaerophobic surface that facilitates rapid bubble release, the Ni_SAC-Co₃O₄ catalyst achieves an exceptionally low potential of 1.32 V for urea oxidation. In a full-cell configuration, the system delivers a current density of 10 mA·cm^-2 at only 1.34 V, doubling the hydrogen output compared to traditional water splitting while achieving a 96.7% urea degradation efficiency. Life cycle assessment further validates the environmental superiority of this system. Our work provides a versatile design principle for tailoring spin states in asymmetric architectures to break linear scaling relationships in complex multi-electron electrocatalysis.