Efficient electrochemical generation of active chlorine to mediate urea and ammonia oxidation in a hierarchically porous-Ru/RuO2-based flow reactor

• Published in: Journal of hazardous materials Vol. 444; p. 130327
• Main Authors: Zhang, Kai, Duan, Yuanxiao, Graham, Nigel, Yu, Wenzheng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2023
• Subjects: Circular flow reactor; Electrocatalysis; Electrochemical chlorination of urea; Hierarchically porous channels; Ru/RuO2 electrode; Ru/RuO2 electrode; Hierarchically porous channels; Electrochemical chlorination of urea; Electrocatalysis; Circular flow reactor
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2022.130327

The electrochemical chlorination of urea to CO2 and N2 end-products, via active-chlorine-mediated oxidation under nearly neutral conditions, is an effective treatment for medium-concentrated urea-containing wastewater. Herein, we design a novel flow reactor integrated with three-dimensional hierarchically porous Ru/RuO2 architectures anchored on a Ti mesh. The hierarchically macroporous electrode can create sufficient exposure of catalytically active sites and facilitate the microscopic mass transport and diffusion inside the active layer, thereby contributing to the increased removal efficiency of urea-N and ammonia-N. The combined results of electrochemical measurements, UV–visible spectrometry and in situ Raman spectrometry, show that the OCl- species produced by chlorine evolution reaction (CER) are the main active constituents for removing urea-N. Theoretical calculations reveal thLTWAat the Ru/RuO2 possesses a moderate Cl binding strength, lower theoretical overpotentials of CER and a higher conductivity, compared with pure RuO2. On this basis, we assemble a circular flow reactor with the hierarchically porous electrodes in a two-electrode system to obtain an enhanced microfluidic process, which during 9 days of uninterrupted operation, at a high electrolysis current of 500 mA, achieve a total nitrogen removal of 92.6% and an energy consumption of 7.94 kWh kg−1 N, demonstrating the promising application of the novel process. [Display omitted] •A novel flow reactor with 3D hierarchically porous Ru/RuO2 architectures was designed.•The OCl- species produced by CER are the main active constituents for removing urea-N.•Ru/RuO2 possesses moderate Cl binding strength, low overpotentials and high conductivity.•The assembled circular flow reactor presents excellent performance and durability.