Drastic Enhancement of HO Electro-generation by Pulsed Current for Ibuprofen Degradation: Strategy Based on Decoupling Study on HO Decomposition Pathways.

Efficient HO electrogeneration from 2-electron oxygen reduction reaction (ORR) represents an important challenge for environmental remediation application. HO production is determined by 2-electron ORR as well as HO decomposition. In this work, a novel strategy based on the systematical investigation on HO decomposition pathways was reported, presenting a drastically improved bulk HO concentration. Results showed that bulk phase disproportion, cathodic reduction, and anodic oxidation all contributed to HO depletion. To decrease the extent of HO cathodic reduction, the pulsed current was applied and proved to be highly effective to lower the extent of HO electroreduction. A systematic study of various pulsed current parameters showed that HO concentration was significantly enhanced by 61.6% under pulsed current of "2s ON + 2s OFF" than constant current. A mechanism was proposed that under pulsed current, less HO molecules were electroreduced when they diffused from the porous cathode to the bulk electrolyte. Further results demonstrated that a proper pulse frequency was necessary to achieve a higher HO production. Finally, this strategy was applied to Electro-Fenton (EF) process with ibuprofen as model pollutant. 75.0% and 34.1% ibuprofen were removed under pulsed and constant current at 10 min, respectively. The result was in consistent with the higher HO and ·OH production in EF under pulsed current. This work poses a potential approach to drastically enhance HO production for improved EF performance on organic pollutants degradation without making any changes to the system except for power mode.