# Visualizing Enhanced Microfluidic Electromembrane Desalination Using Nafion-Coated Heterogeneous Ion-Exchange Membranes

## TL;DR

This study shows how coating membranes with Nafion improves desalination efficiency by enhancing electro-hydrodynamic behavior and reducing unwanted reactions.

## Contribution

The study visually confirms that hydrophilic Nafion coatings amplify electro-convection and suppress water-splitting in desalination membranes.

## Key findings

- Nafion coating amplifies electro-convection vortices by acting as an electrical nozzle.
- The coating suppresses parasitic water-splitting reactions by sealing catalytic sites.
- Coated membranes show 32% higher current efficiency and 18% higher salt removal in desalination.

## Abstract

Heterogeneous ion-exchange membranes (IEMs) are cost-effective but suffer from low electrochemical efficiency due to surface inhomogeneities. While surface coating with homogeneous ionomers is a known modification strategy, its direct impact on electro-hydrodynamic behavior and desalination performance has rarely been visually verified. In this study, we employed a microfluidic platform to visualize and quantify the performance enhancement of Nafion-coated heterogeneous cation exchange membranes (CEMs). Contrary to conventional theories linking electro-convection (EC) to surface hydrophobicity, our results show that the hydrophilic Nafion coating significantly amplifies EC vortices. Direct visualization revealed that the coating layer acts as an electrical nozzle, inducing intense electric field focusing that triggers macroscopic vortex growth. Furthermore, we visually confirmed that the coating layer physically seals catalytic sites, effectively suppressing parasitic water-splitting reactions. In continuous desalination experiments, this hydrodynamic synergy led to a 32% increase in current efficiency (CE: 1.23) and an 18% increase in salt removal ratio (SRR: 79.4%) compared to bare membranes in the over-limiting regime. These findings demonstrate that inducing controlled hydrodynamic instability via surface modification is a dominant factor for high-efficiency desalination.