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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