Graphitized Carbon Panels and Papers for GDL

Porous, compressible, graphitized resin bonded carbon fiber papers

Graphitized Carbon Papers for Electrochemical Devices

Graphitized Carbon Papers

LINQCELL™ Graphitized Carbon Fiber Panels, also called Graphitized Carbon Paper (GCP) are a type of carbon composite materials made by layering carbon fibers or particles with a conductive binder.  CAPLINQ's carbon fibers are made from petroleum pitch or polyacrylonitrile (PAN) which are then graphitized, by a process of heating the material to high temperatures in an inert atmosphere to convert it into graphite.  This process gives the carbon fibers or particles a high electrical conductivity and a high thermal stability.

Carbon Gas Diffusion Layers (GDL)

LINQCELL Graphitized Carbon Fiber Paper products are specifically developed to be used as Carbon Gas Diffusion Layer (GDL) sheets for use in range of Fuel Cells (DMFC & PAFC), Electrolyers (PEM & AEM), Humidifiers, Batteries, and other Electrochemical Devices.  These porous, graphitized, resin-bonded carbon fiber papers are optimized for electrical conductivity, mechanical strength, durability, gas & air permeability and water management.  These multi-ply panels provide a hydrophobic surface that prevents water from penetrating the GDL and reaching the catalyst, this is a commonly used alternative to PTFE in GDLs.

LINQCELL standard carbon panel sizes are either 20 x 20 cm or 40 x 40 cm.  Sheet thicknesses range from as low as 0.18mm (7mil) to as thick as 2.9mm (114mil). Densities of the panels range from as low as 0.5 g/cc to 0.8 g/cc. They can be coated, inked or loaded as Anode or Cathode catalyst layers for Membrane electrode assemblies. 

Custom sizes, machined discs, and other customer defined shapes, as well as machining, water proofing and surface grinding services are also available. Contact us with your inquiry.

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Product Selector Guide

Graphitized Carbon Fiber Papers and Plates
Product Thickness Thickness (mm) Density (g/cm3) Basis weight (g/m2) Through-Plane Resistance (mΩcm2) Through-Plane Resistivity (mΩcm) Voltage Loss (mV)
LINQCELL GDP 180 0.007" 0.18 50 7 - -
LINQCELL GDP 210 0.008" 0.21 - 51 10 - 14
LINQCELL GDP 240 0.009" 0.24 - 90 15 - -
LINQCELL GDP 340 0.013" 0.34 - 90 10 - -
LINQCELL GDL 1500 0.059" 1.5 0.60 858 13.32 90.6 24.3
LINQCELL GDL 1500B 0.059" 1.5 0.60 670 21 140 39
LINQCELL GDL 1850 0.072" 1.85 0.85 1562 13.18 70.5 25.5
LINQCELL GDL 2200 0.086" 2.2 0.6 1550 17 110 35
LINQCELL GDL 2900 0.011" 2.9 0.60 1734 24.57 87.7 27.6

All values are indicative and subject to tolerance


Frequently Asked Questions

Frequently asked questions about Graphitized Carbon Fiber Panels

What is Carbon GDL Wet proofing?


A very common technique that is applied on Carbon GDLs is Wet proofing. Wet proofing the panels improves the water transport, increasing the total power generation. Additionally, wet proofing can stop GDLs from shedding carbon particles which helps with GDL handling. 

Wet proofing Gas diffusion layers can be achieved by teflon dispersion or by applying hydrophobic treatments.

What is the GDL role in the assembly?


Gas diffusion layers structurally help the stack withstand the extension caused by the water absorbency. In addition to that, they aid with heat transfer, electrical surface conductivity, and the removal of excess water from the electrodes that is produced by redox reactions.

Finally, and most importantly, they clear the path for the Fuel and the Oxidizing agent towards the catalyst layers.

Can I just get an MPL treatment?


The carbon paper are not able to have a Microporous layer without PTFE. If you apply it on carbon paper without PTFE coating, the MPL will penetrate the back side of the carbon paper..

Do you have carbon papers in roll form?


Yes. Not every grade is flexible enough to be rolled without breaking or cracking but we do have sub-340um carbon papers that come in roll form. Higher than that it is usually difficult to roll without breaking so we can only provide standard 20 x 20cm, 40 x 40cm sheets, or custom dimensions if the quantities allow. Die cutting is also possible.

Do Carbon papers contain PFAS?

Since there are some talks about a PFAS ban in the European Union, starting from 2025, it is important to clarify where PFAS are present. Generally pure carbon paper doesn't contain any PFAS. Microporous layers and PTFE treatments are by nature susceptible to them. To outline:

    • Carbon papers without any special treatments do not contain any PFAS
    • Carbon papers with a Microporous layer contain PFAS
    • Carbon papers with a PTFE treatment contain PFAS

Read our blog article that explains more about where PFASs are used in Graphitized Carbon Paper.

What's the most common thickness for Carbon Paper?

Generally, thin (<1mm) sheets are used for fuel cell GDLs, while thicker panels (1.5 - 3.0 mm) are used for electrolyzers.  While CAPLINQ can custom-make specific thicknesses, these are what our customer most often ask us for.

Read our blog article that explains the most common thicknesses in GDLs for more info.

What type of binder resin is used for Carbon GDLs?


The binder resin component in the carbon paper papermaking process is Polyvinyl Alcohol; the binder in the carbon paper manufacturing process is Phenolic Resin. Both polyvinyl alcohol and phenolic resin do not contain PFAS

Additionally, after heat treatment in the manufacturing process, most of the resin is converted into carbon residue. Therefore, the main component of the finished carbon paper without MPL+PTFE is carbon.

Does CAPLINQ offer Spectracarb materials?


No. CAPLINQ no longer offers Spectracarb materials, but instead produces its own products under our LINQCELL brand name. Read here the history of CAPLINQ , Spectracarb, and LINQCELL.


Learn More

Carbon Gas diffusion layers (GDL)

Gas diffusion layers are mainly based on Carbon cloth, felt graphite or Carbon paper and they can be treated to acquire various properties. They ensure the uniform distribution of reactive gases on the surface of the electrodes, and they also aid the transport of electrons to or from the external electrical circuit.

Their two main roles are:

  1. Substrates for Electrodes / Catalyst layers
  2. Gas diffusion layers for 5 layer membrane assemblies

As an electrode we combine them with a catalyst ink to create the electrodes that go on either side of the ion exchange membranes.

For example they can be used as Cathode current collectors for PEM electrolyzers.

PEM water electrolysis uses electricity to split water into hydrogen and oxygen. A typical PEM eletrolyzer operates between 60°C and 90°C under pressures between 1 and 20 bars. An important part of the assembly is the porous current collector.

Main Functions of the current collector:

  • Current conduction BiP to electrodes
  • Medium to transport H2O and O2
  • Mechanical Support of MEA

Desired Properties of the collector are low Interfacial Contact Resistance, high electrical conductivity, structural stability and compressibility and finally Electrochemical corrosion and Hydrogen embrittlement resistance

Carbon Gas diffusion layers are used them for what they really are. In a MEA5 we have the following order (see image above):

  1. Gas diffusion layer
  2. Anode
  3. Ion exchange membrane
  4. Cathode
  5. Gas diffusion layer

Gas diffusion layers structurally help the stack withstand the extension caused by the water absorbency. In addition to that, they aid with heat transfer, electrical surface conductivity, and the removal of excess water from the electrodes that is produced by redox reactions. Finally, and most importantly, they clear the path for the Fuel and the Oxidizing agent towards the catalyst layers.

 

Microporous layers and PTFE

Gas diffusion layers can be treated with extra Microporous layers and PTFE.

The main properties of Carbon GDLs containing PTFE and MPL are that they improve water transport and management.

Because water retention reduces power generation, GDL treated with PTFE (Teflon) can make the material hydrophobic and improve water transport. Furthermore, the GDL with MPL treatment helps to reduce contact resistance between the GDL and catalyst layer, limit catalyst loss to the GDL interior, and improve water management by providing effective water transport.

These changes will result in higher through plane resistance so the density might need to be lowered to compensate for this increase. As an added note, thicker plates will see lower water management results from these treatments. They are more effective for thinner papers or plates.


Testing Methods

 

Resistance and Resistivity

Standard: Reference to ASTM C611-98

In house test method:We are Utilizing TSURUGA 3566 ( Battery Internal Resistance AC Tester) to make resistance measurements.  Additionally we are using our in house tools plus a small heat press facility.

Test piece size: Circular test piece with diameter of 5cm for which was cutted by mold.
Test pressure: 200 psi (14.1 kgf/cm2)
Hydraulic cylinder area:9.7 cm2

Test data:

  • bulk resistace = R:
  • Cutted piece area = A,
  • the thickness under tested pressure = t

    Calculation formula:   rt = (R x A)/t (Ωcm)  or Rt = R x A (Ωcm2)

 

 


Voltage Loss at 500mA/ cm² and 20N/ cm² is measured between a gold plated copper stamp and a gold plated base plate

Graphitized Carbon Panels

Graphitized carbon fiber plate applications

Graphitized carbon fiber papers have multiple uses but their main applications are typically gas diffusion layers or the base for the anode and cathode assembly sides. These are popular products for electrolyzers, PEM and AEM fuel cells, electrochemical devices and other specialty applications.

When used as Fuel cell electrodes they have very high strength, high conductivity and high durability. The GDLs have good air permeability and moisture transport and can be used for lab scale prototypes to mass commercial scale manufacturing.

PAFC (Phosphoric acid fuel cell) are mostly used for stationary power, PEM and AEM fuel cells for transportation power and eletrolyzers, well, they are electrolyzers. GDLs have been successfully used for fuel cells utilisation in the Asian markets and have powered the transportation grid for the Olympics and the World Expo.

 

GDL production process

There are multiple steps to ensure our Gas diffusion layers are meeting the expected application requirements.

Typical process looks like the following:

  1. Carbon handsheet production (wet laid process)
  2. Thermoset resin impregnation
  3. In process inspection/Molding Panel preparation
  4. Compression molding/Trim
  5. In process inspection - Testing/Furnace stack preparation
  6. Graphitization
  7. Final inspection/Evaluation 

Our technical expertise with materials development along with our established supply chain and engineering management is key to produce a consistent and high level graphitized carbon plate.

If quantity makes sense we are open to produce and provide alternative thicknesses and grades