PDT-50 ePTFE Reinforced Anion Exchange Membrane (AEM) is a ePTFE reinforced anion conducting membrane with a nominal thickness of ~50 microns.  This membrane product is manufactured from a proprietary polymer resin that is fully fluorinated for its backbone. It has good anion conductivity and excellent chemical and physical properties.  The main applications for this membrane are considered to be alkaline fuel cells and alkaline electrolyzers.  Other alkaline applications that can benefit from the usage of an intermediate thickness anion exchange membrane can also use this product.

This anion exchange membrane should not be exposed to alkaline electrolytes with concentrations greater than 1M. In terms of temperatures, it is recommended to use within the range of room temperature to 80 deg C.

Handling:

Keep membrane package closed / sealed when unused. Store, handle and process the membrane in a clean and dust-free area. Use only new and sharp knives or blades, when cutting down the membrane from a larger sheet. Always wear powder free gloves when handling the membrane. Puncturing, creasing, or scratching the membrane as a result of rough or improper handling may result in damages on the membrane and leaks. All surfaces in contact with the membrane during handling, inspection, storage and mounting should be smooth, free or oil and other contaminants and debris, and free of sharp projections.  Having the membrane surface being touched with bare fingers will leave finger print residuals that are usually oily in nature and loss of ionic conductivity at those sections.

Dry Form: The membrane can be stored dry for an unlimited amount of time. However, the membrane should be conditioned (activated (if needed), or washed and rinsed) prior to use.

Wet Form: Storage for short and long terms may be done in sealed containers in 0.1 to 0.5 Molar sodium chloride (NaCl) solution dissolved in 16-18 Megaohms deionized water or comparable neutral or near pH electrolytes (such as KCl, sodium carbonate, sodium bicarbonate, etc.). For storage over a longer time period, an airtight container is recommended using afore said electrolyte with a biocide (such as 5wt% sodium sulfite) to avoid biological fouling or prevent biofilm growth temporarily. Biocide addition should be implemented with neutral salts such as NaCl, KCl, etc. in order to prevent side reactions between the biocide agent and other components of the storage solutions. Use of biocides will not be a permanent solution for the wet storage and it is important to change the submersion solution with a fresh one once every 4-5 weeks.

In addition to these, 0.1-0.5 Molar alkaline solutions (such as NaOH or KOH) can also be used as the submersion electrolytes for the long term wet storage. Alkaline solutions may not need the addition of the biocide due to less likelihood of biofilm growth in such caustic media, though this would mean the end user to handle caustic solutions and use of storage containers that are chemically compatible with the electrolyte that will be used.

The membrane is delivered in proprietary non-hydroxyl form. Depending on application and cell design, assembling is possible in dry form (without pretreatment) or wet form. For optimum performance it is recommended to submerge the membrane in 0.1-0.5 Molar NaCl solution for up to 24 hr to remove any additive from the membrane and then follow with the proper activation step. Prior to submersion of the membrane into any liquid solutions for its pre-treatment and activation, it is recommended to place the membrane between two  porous meshes in order to avoid its curling (also known as mechanically securing the membrane). Ionically conducting membrane products will expand and contract based on water / electrolyte content of the submersion bath. With most aqueous submersion solutions containing <1 Molar salt solutions, it is normal to see the membrane sample expanding. As the concentrations of the salts is increased, there is a likelihood of the observing a small amount of shrinkage since salt species will compete for the freely available water molecules in the submersion media and force the membrane to lose its natural hydration.

For standard alkaline fuel cell / alkaline electrolysis applications, the membrane should be converted into OH- (hydroxyl anion or hydroxide) form by treating it with 0.5 – 1.0 M NaOH or KOH solution since the main ion of interest in these two applications is the hydroxide anions and the membrane will be transferring hydroxide anions after its assembly in the electrochemical cell or stacks.  Most of the commercial AEMs would come either in the halogenated anion (such as Br-) or carbonated anion from (such as (CO3)2- or (HCO3)-) and submerging these forms into NaOH or KOH would usually require extremely long activation times and frequent exchange of the stated alkaline electrolyte.  Converting the AEMs into Cl- first and then converting it into OH- found to shorten the processing time.  Put the Cl- form of the anion exchange membrane in an aqueous solution of 0.5 – 1.0 M NaOH or KOH for 3-4 h at 20°C – 30°C and repeat this process 2-3 times. Then, rinse the hydroxyl form of the AEM with deionized water and it will be ready to use. Prolonged exposure of the hydroxyl form of any kind of AEMs would result in the conversion of these into carbonate or bicarbonate as a result of interaction with the CO2 existing in the ambient air.  It is recommended to do the hydroxide conversion under CO2 free atmosphere such as dry box (and there is no need to use glovebox) that is purged with N2, Ar, or zero air that has <3 ppm CO2.  This is needed to keep the anion exchange membrane in its hydroxide form. 

Assembly of the membrane into the alkaline cells (especially for alkaline fuel cell application) also should be done under CO2-free conditions.  Since alkaline fuel cells will be using carbon based gas diffusion layer (that may have PTFE as a part of the GDL), after the fuel cell assembly with GDEs or GDLs, it will be difficult to activate the membrane and catalyst layers because of superhydrophobic PTFE limiting the diffusion of the alkaline electrolyte from the back side of the GDLs to the catalyst layer and to the membrane surface.

Alkaline electrolyzer cells would typically use porous electrodes that are easily wetted with the alkaline electrolytes and even if the hydroxide form of the membrane gets partially or fully converted to carbonate or bicarbonate form, the membrane can easily be converted back to hydroxide form by simply doing the flushing step where the anode or cathode side is flooded with a desired alkaline electrolyte and recirculated with the help of a pump.

For electrochemical CO₂ reduction applications, the membrane should be converted into carbonate or bicarbonate form if it is not already in that form from the manufacturer since the main ion of interest for this application would be either carbonate or bicarbonate.  To achieve full carbonate or bicarbonate conversion for the AEM, it is suggested that the membrane to be initially treated with 0.1 to 0.5 M NaCl or KCl solution, then with 0.1 to 0.5 M KOH or NaOH solution and finally with 0.1 to 0.5 M water soluble carbonate or bicarbonate salt solutions (such as potassium carbonate or potassium bicarbonate that is dissolved in de-ionized water or distilled water).  Put the anion exchange membrane in an aqueous solution of 0.5 – 1.0 M NaCl or KCl for 3-4 h at 20°C – 30°C and then rinse it with distilled water. Then, submerge the Cl- form of the AEM into 0.5 – 1.0 M NaOH or KOH for 3-4 h at 20°C – 30°C and repeat this process 2-3 times. Then, rinse the hydroxyl form of the AEM with deionized water. Finally, place the membrane in 0.5-1.0 Molar sodium carbonate, sodium bicarbonate or any other desired carbonate or bicarbonate submersion bath for 3-4 h at 20°C – 30°C and repeat this process 2-3 times and then rinse it with distilled water.  After this step, the AEM should be in the desired anionic form for the electrochemical CO2 reduction application.

For other electrochemical (electrodialysis, desalination, electro-electrodialysis, reverse electrodialysis, acid recovery, salt splitting, etc.) and non-electrochemical applications, the membrane should be converted into the anionic form that is relevant for the intended application.  For example, if the application is requiring the Cl- anions to be transferred through the membrane, then this anion exchange membrane needs to be converted into the Cl- form.  In order to convert this membrane into Cl- form, it needs to be submerged into a 0.5-1.0 M salt solution of NaCl or KCl (dissolved in deionized water) for a period of 24-72 hours and then rinsed with deionized water to remove the excess salt from the membrane surface.  Or if the intended application is requiring to transfer sulfate anions, then this anion exchange membrane needs to be converted into the sulfate form prior to its assembly into the cell.  A neutral salt solution of Na₂SO₄ or K₂SO₄ would usually be sufficient to achieve the full conversion of membrane into the sulfate form after fully submerging the membrane into the salt solution for 24-72 hours at room temperature.  

If you have any concerns about storage, chemical stability, pre-treatment or before proceeding, please feel free to contact us for further information.

Please note that a current lead time of 1-2 weeks to be expected.

PDT-50 ePTFE Reinforced Anion Exchange Membrane Technical Specification Sheet