The chlor-alkali membrane is an ion exchange membrane used in the chlor-alkali process to produce chlorine, hydrogen and sodium hydroxide (caustic soda). Made from perfluorinated sulfonic acid polymers such as Nafion, these ion exchange membranes allow the passage of ions while blocking the passage of gases and larger molecules. This selective movement of ions enables efficient separation of the products of the electrolysis process. Its molecular structure consists of a perfluorinated main chain and side chains containing sulfonic acid groups (SO₃H). The perfluorinated structure can provide excellent mechanical, chemical and thermal stability. This sulfonic acid group allows ions to pass through the membrane. ion exchange sites.
Its simplified molecular structure can be expressed as:

-CF₂-CF₂-SO₂-F
         |
     -O-SO₃H
where -CF₂-CF₂- is the perfluorinated main chain, and -OSO₃H is the sulfonic acid side chain.

What are the main characteristics of chlor-alkali membrane?
1. Ion selectivity, the membrane allows cations (such as sodium ions) to pass through while blocking anions (such as chloride ions) and larger molecules. This selectivity is critical for the efficient separation of products in the chlor-alkali process.
2. Chemical stability, the perfluorinated structure of the membrane makes it resistant to chemical degradation, including the highly corrosive environment encountered in the chlor-alkali process.
3. Mechanical and thermal stability, the perfluorinated structure also provides excellent mechanical and thermal stability, enabling the membrane to withstand the harsh conditions of the chlor-alkali process.
4. Low resistance, the membrane has low resistance, which helps to minimize the energy consumption during the electrolysis process.

The chlor-alkali membrane process has a variety of applications in the battery industry, including the production of certain types of batteries and the recycling of used batteries.
1. Chlor-alkali membrane In the production process of alkaline batteries, the electrolyte solution is usually a mixture of potassium hydroxide (KOH) and zinc oxide (ZnO). KOH is produced by the electrolysis of potassium chloride (KCl) solution in a chlor-alkali membrane process, while ZnO is produced in a separate process. The resulting KOH solution is then mixed with ZnO to form the electrolyte solution used in batteries.
2. Chlor-alkali membranes are also used in the recycling of certain types of batteries, such as nickel-cadmium (NiCd) batteries. In these batteries, the electrolyte solution is usually a mixture of potassium hydroxide (KOH) and cadmium hydroxide (Cd(OH)2). During the recycling process, spent batteries are shredded and the metals and electrolyte solutions are separated. Cadmium hydroxide is then treated with hydrochloric acid (HCl) to generate cadmium chloride (CdCl2), which can be used as a raw material for the production of chlorine and sodium hydroxide by the chlor-alkali membrane method. The potassium hydroxide solution can also be reused in the production of new batteries.
3. In addition to being applied to the production and recycling of batteries, the chlor-alkali membrane process can also be used to produce hydrogen, which is a clean and renewable energy source. During electrolysis, the cathode produces hydrogen gas and sodium hydroxide. This hydrogen can then be harvested and used as a fuel source for various industrial applications, including power generation in fuel cells.

As far as the application in the battery industry is concerned, the application advantages of chlor-alkali membranes are unmatched by other membranes.
It has high cost-effectiveness, and adopts chlor-alkali membrane process in the battery industry, which is environmentally friendly. Its properties make it a valuable source of raw materials for a wide range of uses, including recycling and providing clean energy.

Citation
1.Zhang, Y., & Chen, G. (2019). Electrolytes for alkaline zinc batteries: a review. Journal of Materials Chemistry A, 7(33), 19325-19339. doi: 10.1039/C9TA04454C
2.Duan, J., Zhang, Y., Xiang, W., Chen, G., & Wang, L. (2019). Recycling of spent nickel-cadmium batteries through chlor-alkali process for the recovery of cadmium. Journal of Power Sources, 417, 142-148. doi: 10.1016/j.jpowsour.2019.01.073
3.Liu, X., & Xie, K. (2015). Electrolyte solutions for nickel-metal hydride batteries. Journal of Power Sources, 274, 909-921. doi: 10.1016/j.jpowsour.2014.10.176
4.Singh, P., & Singh, R. (2020). Membrane technology for hydrogen production from chlor-alkali process: A review. Journal of Cleaner Production, 255, 120299. doi: 10.1016/j.jclepro.2020.120299