Rapid Conversion of Co2+ to Co3+ by Introducing Oxygen Vacancies in Co3O4 Nanowire Anodes for Nitrogen Removal with Highly Efficient H2 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-center dot using oxygen-vacancy-rich Co3O4 nanowire (Ov-Co3O4) anodes and CuO nanowire cathodes. The Co2+/Co3+ cycle in Co3O4 activates Cl- in urine to Cl-center dot, 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 Co2+ to Co3+ is the key step for Cl-center dot 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, Co2+ loses electrons more efficiently to form Co3+. H-2 production in this system reaches 716 mu mol h(-1), which is 320% that of non-radical-mediated urine electrolysis. The utilization of O-v-Co3O4 further enhances H-2 generation, which is 490 and 210% those of noble Pt and RuO2, 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.

Automated summary

This research reports a novel system that decomposes urine into H-2 and N-2 under neutral conditions using Co3O4 nanowire anodes and CuO nanowire cathodes. The system effectively boosts electron transfer and overcomes kinetic limitations, resulting in higher H-2 production compared to conventional electrolysis methods. Additionally, the system successfully degrades urine and removes nitrogen with N-2 as the final product.