Unraveling the Crystal-Field-Mediated Cobalt Spin-State Evolution for Electrocatalytic Ethylene Glycol Oxidation by...

The electrocatalytic oxidation of polyethylene terephthalate (PET) derived ethylene glycol (EG) into valuable formate and hydrogen represents a sustainable waste valorization strategy. Although cobalt-based oxyhydroxides (CoOOH) have emerged as promising electrocatalysts for the ethylene glycol oxidation reaction (EGOR), achieving high product selectivity remains challenging due to incomplete understanding of reaction mechanisms. Herein, we developed a phosphorus-doped P-CoOOH catalyst, in which the heteroatom incorporation effectively triggers lattice distortion and electronic reconstruction. These synergistic effects collectively promote a spin-state transition of cobalt centers from a low-spin to a high-spin configuration. Such electronic reconfiguration creates synergistic electron-deficient Co and electron-rich P sites, with non-degenerate $e_g^{\ast }$ orbitals facilitating selective C─C bond cleavage during EGOR. The innovative application of in situ x-ray emission spectroscopy (XES) and x-ray absorption spectroscopy (XAS) dynamically captures spin-state evolution and suggests the structure-activity relationship between high-spin Co³⁺ electronic configuration and product selectivity. The optimized P-CoOOH/NF electrode achieves a low potential of 1.26 V versus RHE at 10 mA cm^-2 with a formate selectivity of 93.7%. Overall, this work highlights that spin-state engineering offers an effective strategy for steering polyol electrooxidation pathways.