Thickness and Tolerance of Graphitized Carbon Paper & Panels for GDLs

As our LINQCELL Graphi­tized Car­bon Paper and Pan­els grow in pop­u­lar­i­ty for use as cur­rent col­lec­tors and gas dif­fu­sion lay­ers in both fuel cells and elec­trolyz­ers, we are get­ting more and more ques­tions about the phys­i­cal prop­er­ties of the prod­ucts after manufacturing.

One of the inquiries we get most often relates to the thick­ness of the car­bon paper or car­bon pan­els we man­u­fac­ture. In a pre­vi­ous arti­cle, I tried to explain what the most com­mon thick­ness­es were for car­bon pan­els. In this arti­cle, I will try to pro­vide as much detail as I can about the thick­ness itself, including:

• What thick­ness­es are pos­si­ble in the man­u­fac­ture of car­bon paper
• What is the min­i­mum and max­i­mum thick­ness pos­si­ble when mak­ing car­bon-based GDL’s?
• How does CAPLINQ mea­sure the thick­ness of car­bon panels?
• What is the tol­er­ance of the thick­ness of the car­bon-pro­duced GDLs?
• Can CAPLINQ improve the cur­rent tol­er­ance of its car­bon paper & panels?

Before get­ting into the var­i­ous thick­ness­es, let’s start by under­stand­ing the process by which car­bon-paper type GDL’s are made. CAPLINQ makes car­bon paper-type gas dif­fu­sion lay­ers using the wet lay­ing of chopped PAN-based car­bon fibers. The advan­tage of such a method (as it con­cerns thick­ness) is that by using very thin car­bon fibers, we are able to pro­duce both very thin GDL paper and by lay­er­ing, we can also pro­duce much thick­er GDL panels.

As a side-note, we can use the terms “paper” and “pan­els” inter­change­ably, but the very thin sheets we typ­i­cal­ly refer to as paper, and the thick­er sheets we refer to as pan­els. CAPLIN­Q’s nomen­cla­ture reflects this also, with thin sheets less than 1 mil­lime­ter bear the name “GDP” where­as the thick­er sheets greater than 1 mil­lime­ter bear the name “GDL”.

What thicknesses are possible in the manufacture of carbon paper?

As can be under­stood from the man­u­fac­tur­ing process, the car­bon fiber thick­ness ulti­mate­ly deter­mines the min­i­mum thick­ness of the GDL paper. It is also impor­tant to real­ize that the goal of the GDL is to cre­ate a porous struc­ture for GDL. This is what allows for effi­cient trans­port of gas in a fuel cell.

As such, a sin­gle lay­er — though it may be pos­si­ble — is not desir­able, as there is then no poros­i­ty built into the GDL. So right away, we talk about mul­ti­ple lay­ers of fibers, which in turn of course will affect the thickness.

Com­mer­cial-grade car­bon fibers are avail­able as thin as 5 — 10 microns (and this excludes nanofibers which are also com­mer­cial­ly avail­able). Lay­er­ing such thin fibers might allow us to make sheets as thin as 15 microns using this process. More com­mon­ly, how­ev­er, we dis­cuss min­i­mum thick­ness­es as low as 25 microns. Even though this is pos­si­ble, our cus­tomers do not often request such think paper — opt­ing more often for paper in the 75-micron range. Our thinnest pop­u­lar prod­uct is LINQCELL GDP 180 at 180 microns.

On the oppo­site extreme, this process of lay­er­ing is very repeat­able and scal­able and as such allows CAPLINQ to pro­duce car­bon sheets much thick­er. Though it is tech­ni­cal­ly pos­si­ble to pro­duce car­bon paper as thick as 10mm (or more!) cus­tomers often request thick car­bon pan­els in the 2.2 to 2.9 mm range. Our thick­est com­mer­cial­ly avail­able prod­uct as of this writ­ing is LINQCELL GDL 2900 at 2.9mm.

What is the minimum and maximum thickness possible when making carbon-based GDL’s?

The pre­vi­ous ques­tion most­ly answers this ques­tion, but let’s just sum­ma­rize by say­ing that the thinnest pos­si­ble LINQCELL GDP we can pro­duce today is 15 micron and the thick­est pos­si­ble LINQCELL GDL we can pro­duce today is 10mm. 

If you want any­thing thick­er or thin­ner, let us know and we’ll talk.

How does CAPLINQ measure the thickness of carbon panels?

CAPLIN­Q’s test method for the thick­ness is done using the through Mitu­toyo 543–691 under a 50 Kpa press. Cus­tomers may use oth­er instru­ments to test, but the Mitu­toyo absolute Digi­mat­ic indi­ca­tor has a range of 0.5in or 12.7mm. Unlike the con­ven­tion­al Digi­mat­ic indi­ca­tors that sim­ply dis­play a spin­dle dis­place­ment, this cal­cu­la­tion-type Digi­mat­ic indi­ca­tor incor­po­rates an inter­nal cal­cu­la­tion func­tion in place of spin­dle dis­place­ment. This indi­ca­tor comes with fix­tures that facil­i­tate easy mea­sure­ments of a feel­er, inside diam­e­ter and radius of cur­va­ture mea­sure­ment with­out the has­sle of con­ver­sion tables of equivalents. 

This test method (and the mea­sure­ment tool) is report­ed on each of our Cer­tifi­cates of Analy­sis (CoA) after manufacturing.

What is the tolerance of the thickness of the carbon-produced GDLs?

This ques­tion depends on a num­ber of fac­tors. The thin­ner the paper, the more dif­fi­cult it is to get an absolute­ly tighter tol­er­ance. Also, the tol­er­ance of the thick­ness will also depend on the num­ber of post-man­u­fac­tur­ing han­dling steps. For exam­ple, we can pro­vide loos­er tol­er­ances with min­i­mal addi­tion­al steps, but if tighter tol­er­ances are required, these might be pos­si­ble, but might incur addi­tion­al steps which in turn might incur addi­tion­al costs.

The sec­ond option is to “bin” the thick­ness­es of our mate­ri­als togeth­er, which basi­cal­ly entails a selec­tion process of the accept­able thick­ness­es while rejec­tion oth­er thick­ness­es that do not fall with­in that tol­er­ance. Again, this method involves waste while increas­ing costs.

With­out avoid­ing the ques­tion, we can say that as of this writ­ing, the tol­er­ances we can pro­vide with min­i­mal extra expen­di­tures is +/-0.2mm. This said, we are work­ing to reduce this tol­er­ance to 0.1mm with min­i­mum extra costs.

If you absolute­ly need tighter tol­er­ances, ask us and we will see what is pos­si­ble and can agree on a man­u­fac­tur­ing spec­i­fi­ca­tion for your exact product.

Can CAPLINQ improve the current tolerance of its carbon paper & panels?

In a word, “YES!”. We are con­stant­ly chal­leng­ing our cur­rent process­es and push­ing for improve­ments and tighter tol­er­ances with min­i­mal adverse cost effects. Through con­tin­u­ous improve­ment, I am con­fi­dent we will improve — and I’ll be hap­py to update this arti­cle once we make these improvements.

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.