Mn Enhanced Dynamic Catalysis on NiCoMnS/NF in Urea Electrooxidation: Insights into Mn²⁺/Mn⁴⁺ Redox Cycle

Organic electrocatalytic mechanisms are crucial for advancing efficient energy conversion technologies. Recent research has increasingly focused on transition metal catalysts to deepen the understanding of these mechanisms. This work fabricates NiCoMnS/NF for urea oxidation coupled water electrolysis for efficient hydrogen production. It is demonstrated that Mn doping significantly enhances the dynamic catalysis performance. Through X-ray photoelectron spectroscopy, in situ Raman and ultraviolet photoelectron spectroscopy (UPS), it is revealed that urea in the electrolyte spontaneously reduces Mn⁴⁺ to Mn²⁺ without applied potential, thereby promoting the Mn²⁺/Mn⁴⁺ redox cycle. Electrochemical characterization further confirms that Mn doping significantly boosts catalytic activity, exhibiting a volcano-shaped trend that likely arises from d-orbital filling-induced electronic structure modulation. Moreover, UPS analysis indicates that the Fermi level of the catalyst shifts away from the vacuum level, which enhances the electron transfer efficiency between urea and the catalyst surface, thus accelerating the oxidative decomposition of urea. Remarkably, NiCoMnS/NF achieves a current density of 100 mA cm⁻² at a potential of only 1.34 V versus RHE. Additionally, it demonstrates exceptional long-term stability, maintaining its performance over 1000 h in a UOR//HER flow electrolyzer.