Electrocatalytic cogeneration of reactive oxygen species for synergistic water treatment.

Graphical abstract Highlights • The in-situ cogeneration effects of OH and H 2 O 2 is examined for the first time using Sb-SnO 2 (SS) and CNT electrocatalysts. • An increase in the potential of SS enhances the OH generation yet decreases the current efficiency (CE) of OH (max. 30%). • The CE of H 2 O 2 with CNT is high at a less negative potential, reaching ∼80% with O 2 purging. • The SS/CNT pair exhibits similar OH generation kinetics and yet significantly enhanced H 2 O 2 generation kinetics. • The simultaneous evolution of O 2 microbubbles leads to a synergistic effect through the production of H 2 O 2. Abstract This study examines the co-generation effect of hydroxyl radicals (OH) via water oxidation and H 2 O 2 via O 2 reduction in electrocatalytic processes with Sb-doped SnO 2 (SS) anode and carbon nanotube (CNT) cathode pairs facing each other as a function of applied SS/CNT cell voltage and purging gas (O 2 vs. N 2). Prior to coupling the electrodes, both electrodes are examined for the generation kinetics and current efficiency of reactive oxygen species as well as the decomposition kinetics and total organic carbon (TOC) removal of phenol, as a function of applied half-potential (E SS or E CNT) and the purging gas. Regardless of the purging gas, a stepwise increase in E SS enhances the OH generation and phenol decomposition, yet inversely decreases the current efficiency of OH (max. ∼30%), owing to competitive O 2 evolution. Similar to this, the current efficiency of H 2 O 2 is high at a less negative E CNT , reaching ∼80% with O 2 purging. However, phenol decomposition with CNT is trivial, owing to the limited reactivity between H 2 O 2 and phenol. With N 2 purging, H 2 O 2 is not produced nor is phenol decomposed. Compared to the sum of the performance of the two half-electrodes, the SS/CNT pair exhibits similar OH generation kinetics regardless of the purging gas, yet significantly enhanced H 2 O 2 generation kinetics. The phenol decomposition and TOC removal with the pair are more than double their sums of the two half-electrodes at all E cell s with O 2 purging, whereas such a synergistic effect is found only at high E cell s when N 2 is purged. The simultaneous evolution of O 2 microbubbles appears to create an in situ oxic environment between the SS and CNT, leading to a synergistic effect through the production of H 2 O 2 , even under anoxic and anoxic-like conditions. [ABSTRACT FROM AUTHOR]