Engineering active sites on N, S co-doped carbon matrix-encapsulated Ni-modified Co₉S₈ nanoparticles enabling efficient urea electrooxidation

Interface engineering and electronic modulation enable precise tuning of the electronic structure, thereby maximizing the efficacy of active sites and significantly enhancing the activity and stability of the electrocatalyst. Herein, a hybrid material composed of Ni-modified Co₉S₈ nanoparticles ((Co, Ni)₉S₈) encapsulated within an N, S co-doped carbon matrix (SNC) and anchored onto S-doped carbonized wood fibers (SCWF) is synthesized using a straightforward simultaneous carbonization and sulfidation approach. Density functional theory (DFT) calculations reveal that the highly electronegative Ni element promotes electron cloud migration from Co to Ni, shifting the d-band center of Co closer to the Fermi level. This Ni modification induces a synergistic effect, optimizing the internal electronic structure of the central Co metal site and enhancing intermediate adsorption. Additionally, the N, S co-doped carbon encapsulation structure and the anchoring effect of SCWF protect (Co, Ni)₉S₈ nanoparticles from agglomeration during the catalytic process, resulting in excellent long-term operational stability. Consequently, an ultralow potential of 1.34 V (vs reversible hydrogen electrode, RHE) is sufficient to achieve a current density of 50 mA cm^-2 with remarkable stability. The (Co, Ni)₉S₈@SNC/SCWF material exhibits superior urea oxidation reaction (UOR) activity and long-term stability compared to recently reported electrocatalysts. For overall urea splitting, an electrolyzed utilizing UOR instead of oxygen evolution reaction (OER) requires only 1.47 V to reach 50 mA cm^-2 with excellent stability, which is 220 mV less than the HER||OER system. This research sets the foundation for developing highly efficient UOR electrocatalysts, offering significant potential for advancing energy-efficient hydrogen generation from renewable sources.