Operando Identification of Ni dz² Orbital Descriptor Governing Urea Oxidation Electrocatalysis

Electrocatalytic urea oxidation reaction (UOR) offers a low-thermodynamic-potential alternative to the oxygen evolution reaction, yet the true reactive state of nickel and a quantitative electronic descriptor governing activity remain unresolved. Here, we construct a well-defined catalyst-support interaction platform that enables dynamic regulation of the Ni 3d electronic structure through π-π coupling between nickel phthalocyanine (NiPc) and carbon supports with tunable curvature. Crucially, operando x-ray absorption spectroscopy, Kβ x-ray emission spectroscopy, and high-energy-resolution fluorescence-detected XAS unambiguously demonstrate that enhanced UOR activity originates from dynamic redistribution of Ni 3d orbitals rather than oxidation-state evolution, thereby resolving a long-standing controversy in Ni-based catalysis. The operando results further confirm that Ni²⁺ remains the catalytically active state throughout the reaction and identify the occupancy of the 3dz² orbital as a quantitative electronic descriptor governing intrinsic activity. NiPc supported on 2 nm carbon nanotubes achieves a turnover frequency of 1.67 s^-1 at 1.45 V versus RHE, outperforming its planar and weakly interacting counterparts, in which strong interfacial interaction induces a high-spin Ni(II) configuration with a nearly half-filled 3dz² orbital. This study establishes operando-validated frontier orbital engineering via catalyst-support interactions as a rational strategy for advanced electrocatalyst design.