PFAS (per- and polyfluoroalkyl substances) are a group of man-made chemicals that have been used in a wide range of industrial and consumer products since the 1950s. They are characterized by a unique chemical structure that includes a carbon-fluorine bond, which makes them highly stable and resistant to degradation.
PTFE (polytetrafluoroethylene) is a synthetic fluoropolymer that is made by polymerizing tetrafluoroethylene, it does not contain PFAS by itself. However, PTFE is produced by a process that uses a precursor called PFOA (Perfluorooctanoic acid) which is a PFAS.
The use of PFAS in GDLs for fuel cells and electrolyzers
It should be no surprise that PTFE (and thus PFAS) has been useful for the manufacturing of carbon-based Gas Diffusion Layers (GDLs). Due to its hydrophobic nature, PTFE has been used as a microporous layer in the production of graphitized carbon paper for fuel cells. This layer acts as a barrier, effectively preventing water from penetrating the gas diffusion layer and reaching the catalyst, which is necessary for the proper functioning of the fuel cell.
GDL’s come in various thicknesses, however, and unlike fuel cells, electrolyzers tend to use much thicker GDLs. Where fuel cells often use GDL’s that are less than 400 micron thick, electrolyzers more often use carbon panels that are thicker than 1.5mm (1500 micron).
Thick gas diffusion layers (GDLs) do not typically require a microporous layer (MPL) because they are able to effectively prevent water from reaching the catalyst on their own. This is due to their greater porosity, which allows water to be effectively wicked away from the catalyst, and their greater thickness, which provides a more effective barrier to water penetration.
Furthermore, contrary to what some people think, neither PTFE nor any PFAS-based substance is used as the binding resin in the manufacture of carbon paper for GDLs.
PFAS are considered a hazard and are at risk of being banned
PFAS are considered to be potentially harmful to human health and the environment. They have been found to be persistent in the environment and can be found in water, soil, and even in human blood. They have also been linked to a range of health effects including cancer, developmental and reproductive issues, and other health concerns. Because of these risks and hazards, many countries are taking steps to phase out the use of PFAS.
In 2019, the European Chemicals Agency (ECHA) proposed to include several PFAS in the REACH regulation candidate list of Substances of Very High Concern (SVHC). This means that these PFAS would be subject to authorization for certain uses, with the aim of eventually phasing them out.
In 2020, the European Union also adopted a new regulation on the use of certain PFAS in food contact materials, which will put a ban on certain PFASs that are considered to be harmful to human health from being used in food packaging, such as PFOS and PFOA.
In 2021, the European Union adopted a new regulation to restrict the use of PFAS in articles and mixtures, which will put a ban on certain PFASs that are considered to be harmful to human health and the environment in various articles and mixtures.
On January 13, 2023, the Netherlands, Germany, Denmark, Norway and Sweden took the first steps to ban PFAS’s entirely from the European Union.
Alternatives to PFAS in the manufacture of Gas Diffusion Layers
Alternative materials are being developed to replace PFAS in gas diffusion layers. Though CAPLINQ continues to offer PTFE as a hydrophobic coating in some of its thinner graphitized carbon paper for fuel cells, we are actively evaluating alternatives for future generations of these same GDL’s.
There are several alternative PFAS-free hydrophobic coatings that can be used as a replacement for PTFE in applications where a water-repellent surface is desired. Some examples include:
- Polyolefin coatings are thermoplastics made from polyethylene or polypropylene
- Silicone coatings are made from a synthetic polymer that can provide a hydrophobic surface that is resistant to high temperatures and chemicals.
- Non-PFAS yet fluorinated polymers, such as polyvinylidene fluoride (PVDF) are non-PFAS alternatives that can provide hydrophobic properties similar to PTFE.
- Wax-based coatings are made from natural waxes, such as beeswax or carnauba wax, and can provide a hydrophobic surface.
- Hydrophobic nanoparticles, such as silica nanoparticles coated with hydrophobic surfactants, can be incorporated into a coating to provide hydrophobic properties.
Furthermore, companies that produce PTFE have implemented measures to minimize and phase out the use of PFOA during the production of PTFE. One of the methods is called “fluorine-free PTFE” which uses a different process that doesn’t require the use of PFOA, this method is not yet widely used but it’s a promising alternative that could produce PTFE without the use of PFAS.
It’s worth noting that these alternatives may not provide the same performance as PTFE in all cases, so it is important that CAPLINQ carefully evaluates their suitability to be used as a Microporous Layer before making a switch. Be sure to follow updates on our newest materials for PFAS-free GDL’s for fuel cells.
- Graphitized carbon paper & panels
- Carbon cloths and activated carbon fabrics &
- Electrically conductive plastics
as well as our partners’ polymer-based solutions:
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