Fe-Doped Ni<sub>3</sub>S<sub>2</sub> Induces Self-Reconstruction\nfor Urea-Assisted Water Electrolysis Enhancement

Urea\noxidation reaction (UOR) is an attractive alternative anodic\nreaction to oxygen evolution reaction (OER) for its low thermodynamic\npotential (0.37 V vs RHE). A major challenge that prohibits its practical\napplication is the six-electron transfer process during UOR, demanding\nenhancements in the catalytic activity. Herein, a Fe-doped Ni<sub>3</sub>S<sub>2</sub> catalyst with a uniform flower-like structure\nis synthesized <i>in situ</i> on nickel foam via a simple\none-step hydrothermal method. The electrochemical properties of Fe-Ni<sub>3</sub>S<sub>2</sub> are significantly improved since a current density\nof 10 mA cm<sup>–2</sup> only requires a 1.33 V potential and\nremains stable for 60 h. The structural characterization demonstrates\na strong interaction between Fe and Ni<sub>3</sub>S<sub>2</sub>. After\nFe doping, the active site increases, which promotes the formation\nof NiOOH on the catalyst surface, thus speeding up the UOR process.\nThese changes are beneficial to charge transfer and optimize the adsorption\nenergy of the intermediates. <i>In situ</i> EIS further\nconfirms that Fe promotes electron transfer during the UOR process,\nreduces the interface resistance between the catalyst and the electrolyte,\nand lowers the driving voltage.