Efficient oxidation of ammonium to nitrogen gas via accelerated ClO• generation at TiO2/Ru-IrO2 bifacial electrode in a UV-driven photoelectrochemical system

Photoelectrocatalysis is effective for the oxidation of ammonium (NH4+) due to the ability to produce oxidizing species such as •OH and Cl•. Compared to •OH and Cl•, ClO• is a more robust species capable of oxidizing NH4+, which can be produced by the combination of •OH and Cl• with free chlorine. However, the conventional photoelectrochemical (PEC) systems generally prefer to produce Cl• for NH4+ oxidation due to the lack of sufficient HOCl. Herein, a UV-driven PEC system consisting of TiO2/Ru-IrO2 bifacial electrode has been constructed for the enhanced ClO• generation for NH4+ oxidation. Large amounts of HOCl can be generated at the Ru-IrO2 interface, which can be further activated by UV irradiation to generate Cl• and •OH, and then rapidly react with HOCl to generate ClO•. The Cl• and •OH generated at the TiO2 interface could also react with HOCl, further accelerating the generation of ClO•. Under UV irradiation, the oxidation rate of TiO2/Ru-IrO2 was 6.7 times than TiO2, 1.5 times than Ru-IrO2, and even 1.24 times than the sum of individual TiO2 and Ru-IrO2. In addition, the bifacial electrode achieved highly efficient NH4+ oxidation for the treatment of actual wastewater, eliminating 81.0 mg L−1 of NH4+ in 120 min with a TN removal rate of 98.4%. The UV-driven PEC system with TiO2/Ru-IrO2 bifacial electrode is a promising potential technology for NH4+ oxidation due to its ability to rapidly produce ClO• and oxidize NH4+ to N2 without the addition of chemical reagents.