Non-negligible effects of reinforcing structures inside ion exchange membrane on stabilization of electroconvective vortices

Concentration polarization (CP) phenomena near ion-exchange membranes have been utilized not only in micro/ nanofluidic platforms but also in macro-scale systems such as electro-desalination and battery, etc. Such systems are highly demanded to have high energy efficiency and stability so that the stabilizing unstable electroconvection as a major nuisance of CP system has been widely studied. However, the methods for controlling electroconvection were mainly limited to structural modifications outside a membrane such as microstructures in a bulk and heterogeneous membrane surfaces, despite ions should flow through inside a membrane. Thus, the internal structures of the membrane may have a significant effect on ion transportation. One example of the structure is dielectric reinforcing structures that mechanically hold the membrane. Therefore, in this work, we investigate the non-negligible effect of the reinforcing structures on an electric field near the membrane for the alignment of electroconvection. The alignment was demonstrated that it depends on the geometry of the reinforcements through numerical simulations and experiments. Moreover, the stabilization of electroconvection with the reinforcements in chaotic regime was demonstrated through the visualization of ion depletion zone and electrical measurements. While the stabilization of electroconvection was validated in a micro/nanofluidic platform in this work, it is easy to expand for designing macro scale CP system due to the high scalability of micro/nanofluidic platform. Thus, the presenting results would be strongly useful for a highly energy-efficient and stable CP system.

Automated summary

In this study, the effect of reinforcing structures on electroconvection near a membrane was investigated. Numerical simulations and experiments were conducted to demonstrate that the geometry of the reinforcements determines the alignment of electroconvection. The stabilization of electroconvection in a chaotic regime was also demonstrated through visualization and electrical measurements. The findings of this study are highly valuable for the design of energy-efficient and stable concentration polarization systems.