Electroconvective instability at the surface of one-dimensionally patterned ion exchange membranes

Abstract

The development of an electroconvective vortex explains the induction of overlimiting current in high voltage applications. However, an in-depth understanding of the dynamics remains challenging because the electrohydrodynamic behavior is unstable. Here, we show how the vortex develops and actively control this using a one-dimensional (1D) grid-patterned ion exchange membrane (IEM). We employed ultraviolet nanosecond laser ablation to fabricate micro-scale (100 μm) non-conductive 1D grid patterns on a commercial IEM. Vortex growth and the electrical responses were simultaneously monitored to derive correlations between the vortex dynamics and ion transport. The rate of electric potential fall increased rapidly during vortex development but decreased more gradually on transverse merging of the vortices. When shear flow was present, the modified scaling law was redefined via dimensionless number analysis of the electroconvective flow by the length of the impermeable 1D grid pattern and the applied voltage. The overlimiting currents and the desalination performances of 1D grid-patterned IEMs were successfully demonstrated. Based on these insights into the electroconvective vortex, we show that the electrical heterogeneity of the IEM actively controls the vortex and enhances desalination performance.