Are PFASs used in the manufacture of carbon paper for GDL?

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.

CAPLINQ is an inno­v­a­tive man­u­fac­tur­er and devel­op­er of key com­po­nents for elec­trolyz­ers and fuel cells includ­ing our car­bon-based products:

• Graphi­tized car­bon paper & panels
• Car­bon cloths and acti­vat­ed car­bon fab­rics &
• Elec­tri­cal­ly con­duc­tive plastics

as well as our part­ners’ poly­mer-based solutions:

• Ion-exchange mem­branes
• Ion-exchange poly­mers

Please vis­it our web­site and feel free to con­tact us if you have any ques­tions about any of the prod­ucts we offer.