Electroconvective circulating flows by asymmetric Coulombic force distribution in multiscale porous membrane

Abstract

Electroconvection (EC) near an ion-selective membrane has attracted significant attention in concentration polarization platform and been generally accepted as a cause of the overlimiting current. Especially, the heterogeneous structures of the ion-selective membrane have been extensively studied for enhancing perm-selective mass transportations in an EC-dominant regime. However, there is lack of studies considering EC on a multiscale porous membrane, which has been often utilized in desalination and fuel cell platform. In this work, we developed a modeled micro/nanofluidic device consisted of an array of ion-selective patches so that micropores were formed between the patches. Rigorous theoretical and experimental analysis on EC near the membrane demonstrated that asymmetric Coulombic force distribution among the micropores induced electroconvective circulating flows, leading to significant enhancement of ion transport and lowering resistivity of the entire system. Furthermore, we verified that the appearance of the circulating flow critically depended on the configuration of micropores so that one can maximize the ion transportation by tweaking the configuration. Therefore, the new finding of the circulating flows would advance the fundamental understanding of electrokinetics in concentration polarization platforms which have been extensively applied for environmental and energy applications.