Enhanced •Cl generation by introducing electrophilic Cu(II) in Co₃O₄ anode for efficient total nitrogen removal with...

Urine is a nitrogen-containing waste, but can be used as an attractive alternative substrate for H₂ recovery. However, conventional urea oxidation reaction is subject to complex six-electron transfer kinetics and requires alkaline conditions. Herein, an efficient method of enhancing •Cl generation by introducing electrophilic Cu(II) into Co₃O₄ nanowires anode was proposed, which realized the highly efficient TN removal and H₂ production in urine treatment under neutral conditions. The key mechanism is that the electrophilic effect of Cu(II) attracts electrons from the oxygen atom, which causes the oxygen atom to further attract electrons from Co(II), reducing the charge density of Co(II). Electrophilic Cu(II) accelerates the difficult conversion step of Co(II) to Co(III), which enhances the generation of •Cl. The generated •Cl efficiently converts urea to N₂, while the electron transport promotes H₂ production on the CuO@CF nanowires cathode. Results showed that the steady-state concentration of •Cl was increased to about 1.5 times by the Cu(II) introduction. TN removal and H₂ production reached 94.7% and 642.1 μmol after 50 min, which was 1.6 times and 1.5 times that of Co₃O₄ system, respectively. It was also 2.3 times and 2.1 times of RuO₂, and 3.3 times and 2.5 times of Pt, respectively. Moreover, TN removal was 11.0 times higher than that of without •Cl mediation, and H₂ production was 4.3 times higher. More importantly, excellent TN removal and H₂ production were also observed in the actual urine treatment. This work provides a practical possibility for efficient total nitrogen removal and hydrogen recovery in urine wastewater treatment.