Preparation Technology of PEM Fuel Cell Membrane Electrode

Membrane electrode is the site of heterogeneous material transport and electrochemical reaction, which determines the performance, life and cost of proton exchange membrane fuel cells. The membrane electrode and the bipolar plates on both sides constitute the basic unit of the fuel cell—the fuel cell. In practical applications, multiple single cells can be combined into a fuel cell stack according to design requirements to meet the needs of different power outputs.

MEA structure design and optimization, material selection and preparation process optimization have always been the key technology of PEMFC research. In the development process of PEMFC, membrane electrode technology has undergone several generations of innovations, which can be roughly divided into three types: hot pressing method, CCM method and ordered membrane electrode. The following will analyze the advantages and disadvantages of the three types of MEA and the latest research progress.

1. GDE hot pressing membrane electrode

The first-generation MEA preparation technology is to use the hot pressing method to press the cathode and anode GDL coated with CL on both sides of the PEM to obtain an MEA. This MEA is called a “GDE” structure.

The preparation process of GDE-type MEA is relatively simple. Since the catalyst is coated on the GDL, it is beneficial to the formation of pores in the MEA, and at the same time, it can protect the PEM from deformation. However, in the preparation process of GDE-type MEA, the amount of catalyst coated on the GDL is not easy to control, and the catalyst slurry is easy to penetrate into the GDL, causing part of the catalyst to not fully function, and its utilization rate is even lower than 20%, which increases the MEA the cost of. In addition, due to the difference in the expansion system between the catalyst-coated GDL and the PEM, it is easy to cause local peeling of the interface between the two during the long-term operation of the fuel cell, resulting in an increase in the internal contact resistance of the fuel cell, and the comprehensive performance of the MEA is not enough. ideal. At present, the preparation process of GDE structure MEA has been rarely used and basically eliminated.

2. CCM three-in-one membrane electrode

The slurry composed of catalyst, Nafion and appropriate dispersant is directly coated on both sides of the proton exchange membrane by roll-to-roll direct coating, screen printing, spray coating and other methods to obtain MEA.

Compared with the GDE-type MEA preparation method, the CCM type is better, less prone to peeling, and at the same time reduces the transfer resistance between the catalyst layer and the PEM, which is conducive to improving the diffusion and movement of protons in the catalyst layer, thereby promoting the catalytic layer and PEM. The contact and transfer of protons between them reduces the resistance of proton transfer, so that the performance of MEA has been greatly improved, and the research on MEA has shifted from GDE type to CCM type. In addition, the overall cost of the MEA is reduced due to the lower Pt loading of the CCM-type MEA and the greatly improved utilization. The disadvantage of CCM-type MEA is that it is prone to “water flooding” during the operation of the fuel cell. The main reason is that there is no hydrophobic agent in the catalytic layer of the MEA, there are relatively few gas channels, and the gas and water transmission resistance is relatively large. Therefore, in order to reduce the gas and water transmission resistance, the thickness of the catalyst layer generally does not exceed 10 μm.

Due to the good comprehensive performance of the CCM type MEA, it has been commercialized in the field of vehicle fuel cells.

3. Ordered membrane electrodes

The catalytic layers of GDE-type MEA and CCM-type MEA are both mixed with catalyst and electrolyte solution to form a catalyst slurry and then coated. The transport channels of protons, electrons, gases, water and other substances in the prepared MEA are in a disordered state, resulting in material transport. The efficiency is very low, and there is a large polarization phenomenon, which is not conducive to the large current discharge of the MEA. In addition, the platinum loading in MEA is relatively high. The development of high-performance, long-life, and low-cost MEA has become the focus of attention. The Pt utilization rate of the ordered MEA is very high, which effectively reduces the cost of the MEA, and at the same time realizes the efficient transportation of protons, electrons, gases, water and other substances, thereby improving the comprehensive performance of the PEMFC.

Ordered membrane electrodes include ordered membrane electrodes based on carbon nanotubes, ordered membrane electrodes based on catalyst thin films and ordered membrane electrodes based on proton conductors.

Ordered Membrane Electrode Based on Carbon Nanotubes

The graphitic lattice properties of carbon nanotubes are durable to high potentials, and their interaction with Pt particles and their elasticity improve the catalytic activity of Pt particles. In the past ten years, people have developed films based on vertically aligned carbon nanotubes (VACNTs) electrode. The vertically aligned mechanism enhances the gas diffusion layer, drainage capacity, and utilization of Pt.

VACNTs can be divided into two types: one is VACNTs composed of curved and sparse carbon nanotubes; the other is VACNTs composed of straight and dense carbon nanotubes.

Ordered Membrane Electrode Based on Catalyst Thin Film

Catalyst film ordering mainly refers to Pt nano-ordered structures such as Pt nanotubes and Pt nanowires. Among them, the representative of the catalyst-ordered membrane electrode is the commercial product NSTF of 3M Company. Compared with traditional Pt/C catalysts, NSTF has four main features: the catalyst support is an ordered organic whisker; the catalyst forms a Pt-based alloy film on the whisker-like organism; there is no carbon support in the catalytic layer; NSTF catalyst The thickness of the layer is below 1um.

4. Conclusion

Ordered membrane electrodes are undoubtedly the main direction of next-generation membrane electrode preparation technology. While reducing the loading of platinum group elements, five aspects need to be further considered: ordered membrane electrodes are very sensitive to impurities; through material optimization, Characterization and modeling to broaden the operating range of membrane electrodes; introduction of fast proton conductor nanostructures in the catalytic layer; low-cost mass production process development; in-depth study of the relationship between the proton exchange membrane, electrocatalyst and gas diffusion layer of membrane electrodes and synergy.

Cheersonic’s fuel cell catalyst coating systems are uniquely suited for these challenging applications by creating highly uniform, repeatable, and durable coatings. Using the company’s patented ultrasonic spray head technology, it can spray uniformly and efficiently on proton exchange membranes and gas diffusion layers. Uniform catalyst coatings are deposited onto PEM fuel cells, GDLs, electrodes, various electrolyte membranes, and solid oxide fuel cells with suspensions containing carbon black inks, PTFE binder, ceramic slurries, platinum and other precious metals. Other metal alloys, including Platinum, Nickel, Ir, and Ru-based fuel cell catalyst coatings of metal oxide suspensions can be sprayed using ultrasonics for manufacturing PEM fuel cells, polymer electrolyte membrane (PEM) electrolyzer, DMFCs (Direct Methanol Fuel Cells) and SOFCs (Solid Oxide Fuel Cells) to create maximum load and high cell efficiency.

The advantages of Cheersonic’s ultrasonic equipment include：

1.Very high Platinum utilization proven in MEA fabrication; as high as 90%.
2.Non-clogging
3.Low-flow spray reduces spillage and air pollution.
4.Continuous or intermittent operation possible
5.Highly porous coatings are extremely durable, preventing cracking or peeling of catalyst layer.
6.No moving parts to wear out
7.Minimal maintenance and downtime.
8.Robust design and materials resist corrosion.
9.Ultrasonic energy disperses the agglomerated particles, producing a homogeneous coating.

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