4f-2p-3d Orbital Coupling in Ce-NiS Enhancing the Urea Oxidation Reaction.

The electrocatalytic urea oxidation reaction (UOR) provides a promising alternative to the oxygen evolution reaction (OER) for various renewable energy-related systems owing to its lower thermodynamic barriers. However, its optimization and commercial utilization were hampered due to a lack of mechanistic understanding. Here, we demonstrate a Ce-doped NiS catalyst supported on Ni foam (Ce-NiS/NF) with superior activity toward UOR. The resultant Ce-NiS/NF catalyst exhibits a lower Tafel slope of 20.3 mV dec, a higher current density of 100 mA cm at 1.39 V versus RHE, and better durability than those for NiS/NF. Based on in situ synchrotron radiation X-ray absorption spectroscopy, in situ Fourier transform infrared (FTIR), and in situ Raman spectroscopy, we observe the structural reconstruction of sulfide and identify the adsorbed intermediates during UOR. Density functional theory (DFT) calculations reveal that Ce can regulate the electronic structure of Ni through Ce(4f)-O(2p)-Ni(3d) orbital electronic coupling. The modulated Ni sites have weaker adsorption of carbonaceous intermediates, thus accelerating the UOR. This work provides a promising route for the design of high-activity UOR catalysts.