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:

as well as our part­ners’ poly­mer-based solutions:

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

About Chris Perabo

Chris is an energetic and enthusiastic engineer and entrepreneur. He is always interested in taking highly technical subjects and distilling these to their essence so that even the layman can understand. He loves to get into the technical details of an issue and then understand how it can be useful for specific customers and applications. Chris is currently the Director of Business Development at CAPLINQ.

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