Graphitized Carbon Paper & Panels Thickness & tolerance

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:

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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