Enhanced •Cl generation by introducing electrophilic Cu(II) in CoO anode for efficient total nitrogen removal with hydrogen recovery in urine treatment.

Urine is a nitrogen-containing waste, but can be used as an attractive alternative substrate for H 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 CoO nanowires anode was proposed, which realized the highly efficient TN removal and H 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 N, while the electron transport promotes H 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 H production reached 94.7% and 642.1 μmol after 50 min, which was 1.6 times and 1.5 times that of CoO system, respectively. It was also 2.3 times and 2.1 times of RuO, 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 H production was 4.3 times higher. More importantly, excellent TN removal and H 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.