Graphitized carbon papers as gas diffusion layers are a popular solution for fuel cell and electrolyzer applications since they can be manufactured at high volumes (scalability) and low thicknesses.
The main manufacturing steps are:
- Chopping fibers + Paper wet laying
- Resin impregnation + Graphitization
- MPL + PTFE treatment (if applicable)
1. Chopped carbon fibers are processed to a primary carbon fiber web using a papermaking (wet-laying) technology and subsequent thermo-bonding.
2. The raw paper is then impregnated with carbonizable resins (carbonizable resins with the optional addition of carbon fillers), cured, and recarbonized/ graphitized. This procedure serves to adjust the porosity and enhance electric and thermal conductivity.
3. Different GDL backings with different filler content could be the base for the final finishing processes, such as:
- Hydrophobic treatment with PTFE
- Coating with a microporous layer (MPL)
- Sintering (thermal annealing) to bond the substrate/MPL
Simple Carbon plate process goes through the following steps
Dispersion > Resin impregnation > Molding > Carbonization > Graphitization
These thicker products have higher thermal conductivity, high durability, low carbon corrosion and are typically used for Electrolyzers and distributed power generators. They are also known as Molded graphite papers or Carbon plates.
A carbon paper with MPL treatment will traditionally go through the following manufacturing steps:
- Dispersion
- Resin impregnation
- Low temperature carbonization
- High temperature graphitization
- Microporous Layer coating
- Resing impregnation
- Heat treatment (1600 or 2000°C)
These thinner carbon papers that usually (but not necessarily) come with an MPL coating are typically used for Fuel cells. These fuel cells are used in vehicles, forklifts, drones and residential applications. These vehicles tend to need higher power stacks with robust properties in thin assemblies with high gas permeability and porosity.
What is a PTFE treatment?
PTFE treatments on carbon papers are used to make them hydrophobic. Wettability affects water management and ultimately the overall cell performance. A hydrophobic agent such as PTFE or fluorinated ethylene propylene (FEP) could help to create a hydrophobic GDL, required in PEMFCs.
Advantages
- Removal of excess water
- Suitable for wet operating conditions at high relative humidity and low operating temperature
Disadvantages
- Porosity is reduced
- Change in pore size distribution
- Decreased air permeability
- Increase in thermal and electrical resistance
What is a Microporous layer?
To improve the water management in GDLs, a hydrophobic MPL (micro porous layer) is commonly applied to the GDL side next to the CL (catalyst later). MPL is commonly developed using carbon black and PTFE.
This overview should give you a good understanding of all the process steps that are necessary to manufacture a carbon paper with PTFE and a microporous layer such as LINQCELL GDP210-MPS. Other than the process complexity we want to focus on the multiple oven steps and the energy intensity of this process. This energy intensity is a huge part of the manufacturing cost and that’s why we want to optimize it for the maximum production yield with the minimum energy cost. For more details read this article where we discuss how we can collaborate to optimize your process and our manufacturing to reduce the total BOM cost of fuel cells and electrolyzers.
Contact us for more information and for a call with our product experts that can help you initiate or optimize your project.
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