The Cation Exchange Membrane (CEM)

The CEM Property

The cation exchange membrane (CEM) is a selective polymer barrier in electrochemical processes with fixed negative charges, Its primary job is to allow positive ions (cations like protons, H+) to pass through while blocking negative ions (anions) and neutral molecules. These essential components act as separators in electrochemical systems like fuel cells, electrolyzers, and electrodialysis for water treatment, enabling the selective transport of ions for energy conversion, water purification, and material recovery, with common materials
The cation exchange membrane (CEM) can be think of as a "security gate" that only lets specific people through based on the "charge" they carry.

Operational Principles

The secret to a CEMs selectivity lies in its chemical structure. The membrane is made of a polymer matrix (like a plastic) that has negatively charged functional groups (such as sulfonic acid or carboxylic acid, permanently attached to it.
The Attraction: Because the membrane is "lined" with negative charges, it attracts positive ions (cations) like Na+, H+. These ions can "hop" from one negative site to the next to move across the membrane.
The Repulsion: Negative ions (anions) like Cl- or SO4 are pushed away by the fixed negative charges in the membrane.12 This is known as Donnan Exclusion.
Selective Permeability: Permits cations (such as H+, Na+) to move but restricts anions (such as OH-, Cl-) due to electrostatic repulsion (Donnan effect).
Structure: Made from crosslinked polymers with covalently bound acidic groups like sulfonic or carboxylic groups, creating a fixed negative charge.
Function: Serves as a solid electrolyte, separator, and charge carrier in electrochemical devices

Performance Metrics

Ion Exchange Capacity (IEC): The amount of exchangeable groups per unit weight, influencing conductivity.
Water Uptake: Affects the formation of ionic channels but can reduce mechanical stability if excessive.
Permselectivity: The ability to differentiate between oppositely charged ions, vital for efficiency.
Monovalent/Divalent Selectivity: Advanced CEMs are designed to separate specific cations (e.g.,Li+ from (Mg2+) for resource extraction.

Primary Applications

CEMs are critical components in several modern green technologies:
Electrodialysis: For desalination, removing salts from water, and concentrating valuable ionsfrom wastewater, work with BPM to produce the base and acid.
Water Desalination (Electrodialysis): CEMs work with Anion Exchange Membranes (AEMs) to pull salt ions out of brackish water or seawater.
Metal Recovery: Selectively separating metal ions from contaminated water.
Fuel Cells (PEMFC): Often called Proton Exchange Membranes (PEM) in this context, as Proton Exchange Membranes (PEMs) to conduct protons (H+), they allow H+ protons to move from the anode to the cathode to create electricity.
Chlor-Alkali Industry: Used to produce chlorine gas and caustic soda (sodium hydroxide) by separating the products of brine electrolysis.
Redox Flow Batteries: They act as a separator that allows charge-balancing ions to pass while preventing the two liquid electrolytes from mixing, separating reactive electrolytes in large-capacity rechargeable batteries.

Membrane size

40*20cm per piece
80*40cm per piece
110*55cm per piece
120*60cm per piece
other size