Proton exchange membrane fuel cells (PEMFCs) rely greatly on the key role of Catalyst-Coated Membranes (CMMs). Thanks to these membranes, electrochemical reactions that make electricity are possible. Since there is a growing emphasis on green and efficient energy, techniques for membrane production are developing too. Using the dry preparation method is now very popular, since it reduces waste, saves time, and can be used for mass production.
CMM by Dry Preparation Method
In this method, simply using a non-liquid substance, you prepare electrodes without adding any liquids. Unlike standard wet methods used before which need to mix, coat, dry and clean up solvents, these dry methods avoid drying altogether. As a result, the process is more effective from an environmental point of view.
There are only two methods when you use the dry technique:
- Dry spraying
- Transfer method
Both strategies are designed to add a catalyst layer onto a proton exchange membrane very precisely, strongly, and with as little resistance as possible.
Dry spraying technique
Overview
The powdered substance is shot directly over the proton exchange membrane (PEM) using the dry spraying process. The method was invented by German researchers and then enhanced for use in PEM fuel cells.
Step-by-Step Process
- Knife milling is used to evenly mix the main components: dry catalyst, Nafion or PTFE binder and any other additives.
- Next, the mixed powder is formed into very tiny particles with a nitrogen gas flow. This action results in an even distribution of the components.
- Atomized liquid is sent directly onto the surface of the proton exchange membrane using a spraying nozzle.
- In the process of calendering (roll finishing), a machine presses the sprayed coating onto the membrane to enhance its first bond.
- After that, the membrane is pressed with heat to form a strong link and decrease resistance in the electrical contacts.
Advantages
- No solvents : No need for drying or evaporation steps.
- Excellent uniformity : The catalyst layer is consistent across the membrane surface.
- Scalability : Easy to integrate into large-scale automated systems.
- High efficiency : Platinum loading can be reduced to as low as 0.08 mg/cm² , with layers as thin as 5μm .
- Gradient layers : Possible to create multi-composition layers by adjusting spray conditions.
Transfer Method
In the process of making PEMFCs, the transfer method is the most used type of dry preparation. A catalyst slurry is spread on a temporary material, the layer is dried and it is subsequently transferred by hot pressing to the PEM.
Step-by-Step Process
- A Temporary Medium is Prepared: Glass fiber-reinforced PTFE is carefully cleaned with solvents and is then treated using a release agent.
- A mixture of the catalyst, the ionomer and a solvent is poured onto the transfer medium during slurry coating.
- Here, the coated object is placed in an oven at 80°C to get rid of any solvents.
- The vacuum oven treatment is done by heating the medium in an oven at 100–150°C for 30–60 minutes to guarantee that drying and redistribution of the ionomer are complete.
- Hot Pressing Method: Two layers of coated transfer media are placed on each side of the membrane, the whole stack is heated and the catalyst links to the membrane.
- Once the transfer media are cooled, peel them gently so that the layer of catalyst stays attached to your PEM.
Benefits
Some benefits of the Transfer Method include.
- The bond between materials is strong because of hot pressing and preparation of the surfaces.
- Catalyst material spreads uniformly through all the areas of the PEM.
- If the resistance between the plate and other parts is low, it makes electron flow through the plate efficient.
- Loading of the platinum can be adjusted by modifying the number of coating steps.
Comparing the Two Methods
| Feature | Dry Spraying | Transfer Method |
| Solvent Use | None | Required during slurry preparation |
| Process Simplicity | High | Medium |
| Layer Thickness Control | Excellent | Good |
| Equipment Requirement | Moderate to High | Due to drying steps |
| Hot Pressing Needed | Yes | Yes |
| Uniformity | Excellent | Very Good |
| Scalability | Very High | Moderate |
Why Hot Pressing Matters
Both techniques finish with a last, vital step called hot pressing. It does not only bond structures or materials together. There are important reasons why it’s valuable to do virtual interviews.
Helps the catalyst layer adheres well to the PEM.
- It leads to lower contact resistance and hence better performance of the electrical system
- It ensures that the material wont start coming apart during use.
- Makes the fuel cell system stronger and lasts longer.
- Failing to execute the hot press stage thoroughly may cause the membrane to crack and greatly shorten the fuel cell’s useful life.
Industrial Significance
- There is a rising number of people who choose to prepare foods dry.
- An important benefit is cleaning products are often produced with less negative impact on the environment (for example, through dry spraying without solvents).
- Cost-effectiveness in mass production
- The ability to automate, so quality is always maintained at a large scale
With companies striving to use cleaner energy worldwide, interest in better and less costly fuel cells increases. Dry processes and mainly dry spraying, are on their way to being applied as industry standards in PEM fuel cell manufacturing.
Future Trends
- Mixing dry and wet techniques helps you achieve more flexibility.
- Improved ionomers and catalysts are being introduced in Advanced Materials.
- AI and robotics will enhance the organization of how food is made.
- Use materials that are good for the planet and follow zero-waste methods.
Conclusion
Dry spraying and liftoff methods in CMMs make the process easy, usable in several places and highly effective. By using these techniques, any complexities found in traditional wet coating go away, but the benefits such as good bonding are still achieved. As more green technologies appear, it will be vital to control these procedures for the future of clean energy.
FAQs
1. What makes dry spraying suitable for mass production?
Dry spraying eliminates the need for solvents and drying equipment, making the process cleaner, faster, and easily automatable for industrial-scale manufacturing.
2. Why is hot pressing necessary in both methods?
Hot pressing improves the bonding between the catalyst layer and the PEM, reducing contact resistance and enhancing the overall durability of the membrane.
3. Can dry preparation replace traditional wet methods?
Yes, especially in large-scale production, dry methods offer better control, reduced cost, and environmental benefits, making them strong contenders to replace wet methods.
4. What is the platinum loading achieved in dry spraying?
Platinum loading can be as low as 0.08 mg/cm² , which maintains high performance while reducing precious metal usage.
5. What materials are essential for the transfer method?
Key materials include glass fiber-reinforced PTFE membranes , catalyst slurry components (catalyst, ionomer, solvent), and release agents for easy separation post-transfer.
