In the context of Electrodialysis (ED), Anion Exchange Membranes (AEM) are designed to selectively allow anions (like Cl-, SO4^{2-}) to pass through while blocking cations and water. Choosing between homogeneous and heterogeneous AEMs is a critical decision that balances energy efficiency against physical durability.

In a homogeneous AEM, the fixed quaternary ammonium groups (positive charges) are chemically bonded directly to the polymer backbone. The entire membrane is a single, uniform phase. (1) Structure: A continuous polymer matrix where the functional groups are evenly distributed at the molecular level. (2) Performance: Low Resistance: Because the path for ions is unobstructed by non-conductive binders, these membranes have very low Area Specific Resistance (ASR). High Permselectivity: The dense, uniform structure provides a superior "sieve" effect, often exceeding 95% selectivity. Energy Efficiency: Lower resistance means less voltage is required to move ions, significantly reducing kWh per ton of product. It is suitable for high-value separations, battery applications (like AEMFC or Redox Flow Batteries), and high-concentration salt recovery.

Heterogeneous AEMs are produced by taking finely ground ion-exchange resin beads and mixing them with a thermoplastic binder (like Polyethylene). This mixture is then rolled or extruded into a film. (1) Structure: It is a "composite" that is mixed by ion-exchange resin powder with polymer binder. (2) Performance: Physical Ruggedness: These are much thicker and tougher than homogeneous membranes. They can withstand higher pressure differentials and rougher handling. Higher Resistance: The binder is an insulator. Ions must "hop" from one resin particle to the next, which increases electrical resistance and heat generation. Cost-Effective: The manufacturing process is much cheaper, making them ideal for large-scale, low-margin water treatment. It is suitable for basic wastewater desalination, pre-treatment of brackish water, and environments where frequent mechanical cleaning is required.

Reference: 

1. M.C. Martí-Calatayud, et al., Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions, J. Membrane Sci., 2014, 466, 45-57.
2. N.D. Pismenskaya, et al., Can the electrochemical performance of heterogeneous ion-exchange membranes be better than that of homogeneous membranes?, J. Membrane Sci., 2018, 566, 54-68.