Common preparation processes for membrane electrode catalyst layers: thermal transfer, direct coating

Membrane electrode (MEA) is the core component of hydrogen fuel cells and PEM hydrogen production electrolyzers, and is a key component of electrochemical reactions. Its structural components mainly include proton exchange membrane, catalyst layer, gas diffusion layer, frame membrane, etc.

Common preparation processes for membrane electrode catalyst layer: thermal transfer, direct coating

The current common membrane electrode production process mainly involves catalyst slurry preparation, coating proton membrane to form CCM, hot pressing gas diffusion layer, and laminating frame membrane.

Among them, there are many coating processes for membrane electrode catalyst layer, the most common ones are thermal transfer, direct coating, etc.

1. Thermal transfer

The thermal transfer process involves pre-coating or printing the catalyst ink or powder onto a transferable substrate (usually a film that is stable at high temperature), and then transferring the catalyst from the transfer membrane to the proton exchange membrane or gas diffusion layer through a hot pressing process.

Preparation steps:

1. Preparation of catalyst ink: First, mix the catalyst powder with an appropriate solvent and adhesive to prepare a catalyst ink. This step is similar to the preparation of catalyst solution in other coating methods.

2. Catalyst coating: Coat or print the catalyst ink onto a transfer membrane with good thermal stability. This transfer membrane needs to remain intact during the subsequent hot pressing process and be able to release the catalyst at an appropriate temperature.

3. Hot pressing transfer: The transfer membrane containing the catalyst is stacked with the proton exchange membrane or gas diffusion layer and heated and pressed in a hot press. In this process, the catalyst is transferred from the transfer membrane to the target substrate.

4. Removal of the transfer membrane: After the catalyst transfer is completed and cooled, the transfer membrane is removed, leaving the catalyst layer tightly attached to the PEM or GDL.

Advantages and disadvantages of thermal transfer:

1. The shape and size of the catalyst can be precisely controlled: through digital design, catalysts of different shapes and sizes can be finely customized and completely transferred to the electrode surface, which is conducive to improving the efficiency and selectivity of the electrochemical reaction;

2. The preparation process is more precise: by transferring the catalyst to the electrode surface, an extremely thin and highly consistent catalyst layer can be formed in a smaller area. The reaction surface and morphology at the microscopic scale are more controlled;

3. Multi-layer catalyst stacking can be achieved: multiple catalysts can be sequentially transferred to the electrode surface to improve the efficiency of composite catalysis; it can also reduce external interference, such as the influence of factors such as temperature, and can also be conveniently removed selectively to avoid environmental pollution and other problems.

However, the thermal transfer method has the problem of further improving efficiency in mass production.

2. Direct coating

The direct coating process, as the name suggests, is to directly coat the catalyst slurry on the proton exchange membrane. At present, membrane electrode manufacturers with high production capacity all use double-sided roll-to-roll direct coating process. Some manufacturers will use one side of thermal transfer and one side of direct coating to avoid the problem of direct coating swelling and improve efficiency at the same time.

Common preparation processes for membrane electrode catalyst layer: thermal transfer, direct coating

Cathode CCM coating process

Anode CCM coating process

Roll-to-roll CCM coating process

Production steps:

1. Preparation of catalyst slurry:

First, prepare a slurry containing a catalyst (such as platinum), an ion exchange resin, a solvent, and other additives. This slurry must have good rheological properties for easy coating.

2. Selection of proton exchange membrane:

Select a suitable proton exchange membrane that is required to provide good chemical stability and conductivity under fuel cell operating conditions.

3. Coating process:

The catalyst slurry is directly coated on the membrane using direct coating technology. The coating method can be brushing, spraying, blade coating, or other suitable coating techniques.

After coating, the membrane electrode is dried and heat treated under specific conditions to remove the solvent and ensure good bonding between the catalyst layer and the membrane.

4. Drying and heat treatment:

During the drying process, the solvent evaporates, leaving behind the solid catalyst and ion exchange resin. Heat treatment further improves the structure of the catalyst layer and strengthens its bonding with the membrane.

5. Lamination process:

The treated membrane electrode is laminated together with the gas diffusion layer (GDL) to form a complete membrane electrode assembly (MEA).