Enriched and Sustained Oxygen Vacancies in Amorphous NiWO_x Enhance and Stabilize Urea Electrooxidation

Urea electrolysis is promising for energy-saving hydrogen production and effective treatment of urea-polluted water. However, the activity and stability of Ni-based electrocatalysts for the anodic urea oxidation reaction (UOR) are limited by the lack of active NiOOH and strong intermediates adsorption. Although oxygen vacancies (O_v) benefit for the UOR, continuous generation and stabilization of O_v remain challenges. Herein, we propose an "amorphous oxygen mechanism (AOM)" for urea electrooxidation in amorphous nickel tungsten oxide (NiWO_x) with tunable O_v concentrations. Systematic experimental and theoretical studies demonstrate that enriched O_v, not only facilitate the formation of active NiOOH species, but also significantly reduce the energy barrier of the rate-determining step. More importantly, the amorphous state allows more defects, which enables the in situ regeneration and sustainability of O_v during the UOR via a continuous oxygen escape in the amorphous catalyst. Notably, NiWO_x with the highest O_v achieves an ultralow potential of 1.34 V at 10 mA cm^-2 with incredible 400 h stability. Moreover, only 1.46 V is demanded for urea electrolysis with 100 mA cm^-2 in an anion-exchange membrane electrolyzer. The long-term stability is also impressive. This work highlights the significant role of amorphous structure, providing valuable insights into catalyst design in electrocatalysis.