Rapid Conversion of Co 2+ to Co 3+ by Introducing Oxygen Vacancies in Co 3 O 4 Nanowire Anodes for Nitrogen Removal with Highly Efficient H 2 Recovery in Urine Treatment.

Urine is a nitrogenous waste biomass but can be used as an appealing alternative substrate for H 2 recovery. However, urine electrolysis suffers from sluggish kinetics and requires alkaline condition. Herein, we report a novel system to decompose urine to H 2 and N 2 under neutral conditions mediated by Cl • using oxygen-vacancy-rich Co 3 O 4 nanowire (O v -Co 3 O 4 ) anodes and CuO nanowire cathodes. The Co 2+ /Co 3+ cycle in Co 3 O 4 activates Cl - in urine to Cl • , which rapidly and selectively converts urea into N 2 . Thus, electron transfer is boosted for H 2 production, eliminating the kinetic limitations. The shuttle of Co 2+ to Co 3+ is the key step for Cl • yield, which is accelerated due to the introduction of O v . Electrochemical analysis shows that O v induces positive charge on the Co center; therefore, Co 2+ loses electrons more efficiently to form Co 3+ . H 2 production in this system reaches 716 μmol h -1 , which is 320% that of non-radical-mediated urine electrolysis. The utilization of O v -Co 3 O 4 further enhances H 2 generation, which is 490 and 210% those of noble Pt and RuO 2 , respectively. Moreover, urine is effectively degraded in 90 min with the total nitrogen removal of 95.4%, and N 2 is the final product. This work provides new insights for efficient and low-cost recovery of H 2 and urine remediation.