Mechanistic Insight into the Spatial Scale of Nonuniform Oxidation of Micropollutants in Reactive Electrochemical Membranes for Water Purification

A reactive electrochemical membrane (REM) has been identified as an excellent platform in micropolluted water purification due to its rapid mass transfer capability. Unlike traditional flow-by systems, the convection-enhanced REM systems activate the REM's inner reaction sites, potentially imparting a spatially variable reactivity. Therefore, we explored the spatial scale of micropollutant oxidation in REM. Theoretical and experimental evidence demonstrated that an REM might feature nonuniform oxidation activity along its reaction depth (about hundreds of micrometers). That is, the zone generating •OH was located within a few micrometers beneath the REM surface, i.e., less than 1% of its reaction depth due to the rapid overpotential/potential drop in the REM. The nonuniform reactive character might render the REM of a strong direct electron transfer ability, enabling rapid removal of electron-rich micropollutants even at low potentials. However, unsatisfactory removal of electron-poor micropollutants has been observed, and a higher potential was required to prompt the generation of •OH. These results provide in-depth insight into the spatial scale of nonuniform oxidation of micropollutants in REM, contributing to the analysis of micropollutant oxidation mechanisms and the optimization of the design and operation of REM modules for cost-effective water purification.