Main processes in the production of membrane electrodes for fuel cells
Main processes in the production of membrane electrodes for fuel cells – Cheersonic
At present, many domestic membrane electrode manufacturers have started mass production of membrane electrodes, and more and more equipment manufacturers have also entered the fuel cell industry.
As the core component of the fuel cell, the membrane electrode is composed of a proton exchange membrane, a catalyst layer, a frame and a diffusion layer, so how does it change from a raw material to a finished product? The two main process links are film preparation and catalyst. coating.
Film Preparation
A fuel cell membrane must have relatively high proton conductivity, provide an adequate barrier to fuel and oxidizing gases, and remain chemically and mechanically stable in the fuel cell operating environment. Usually the membrane of PEM fuel cell is composed of perfluorosulfonic acid (PSA) ionic polymer, which is essentially a copolymer of tetrafluoroethylene (TFE) and different perfluorosulfonic acid monomers.
How to turn the membrane material into a polymer film that meets the needs?
There are two main types of polymer film production methods in the industry—calendering and extrusion. Among them, extrusion is divided into extrusion blow molding, extrusion stretching and extrusion casting.
Since its appearance, film material forming technology has been developing continuously, both in terms of technical equipment and in theory, and now a series of static casting processes such as gel casting molding process, UV-initiated polymer molding process, casting and so on have been derived. New molding processes such as pressure composite molding process make the development of film material molding process more and more perfect.
For proton exchange membranes to generate electricity, catalysts must be coated on both sides of the membrane. The coating process must ensure that the thickness of the catalytic layer is uniform, and defects such as cracks, particles, bubble opening, edge effects, and sawtooth cannot appear. At present, the coating processes of mass production mainly include blade type, roll coating transfer type and slit extrusion type.
1. Doctor blade coating
The working principle is shown in the figure below. The film substrate passes through the coating roller and is in direct contact with the slurry tank. The excess slurry is coated on the film substrate. When the substrate passes between the coating roller and the scraper, the scraper and the substrate The gap between them determines the thickness of the coating, while scraping off excess slurry to reflow, thereby forming a uniform coating on the surface of the substrate. Scraper Type Main comma scraper. The comma scraper is one of the key components in the coating head. Generally, a comma-like edge is formed along the busbar on the surface of the round roll. This scraper has high strength and hardness, and is easy to control the coating amount and coating accuracy. It is suitable for High solids and high viscosity slurries.
2. Roller transfer coating
The rotation of the coating roller drives the slurry, and the amount of slurry transfer is adjusted through the comma scraper gap, and the rotation of the back roller and the coating roller is used to transfer the slurry to the substrate. The process is shown in the figure below. Roll transfer coating involves two basic processes:
(1) The rotation of the coating roller drives the slurry to pass through the gap between the metering rollers to form a slurry layer of a certain thickness;
(2) The slurry layer of a certain thickness transfers the slurry to the film material through the rotation of the opposite coating roll and the back roll to form a coating.
3. Slot extrusion coating
As a precise wet coating technology, the working principle is that the coating liquid is extruded and sprayed along the gap of the coating die under a certain pressure and a certain flow rate and transferred to the substrate. Compared with other coating methods, it has many advantages, such as fast coating speed, high precision, and uniform wet thickness; the coating system is closed, which can prevent the entry of pollutants during the coating process, and has high slurry utilization rate and can maintain the slurry. The properties are stable and multi-layer coating can be carried out at the same time. And it can adapt to different slurry viscosity and solid content range, and has stronger adaptability compared with transfer coating process.
In order to form a stable and uniform coating, the coating process needs to meet the following conditions at the same time:
(1) The properties of the slurry are stable, no sedimentation occurs, and the viscosity and solid content do not change.
(2) The slurry feeding supply is stable, and a uniform and stable flow state is formed inside the die.
(3) The coating process forms a stable flow field between the die and the coating roll within the coating window.
(4) The film is stably running, and there is no slippage, serious jitter and wrinkles.
In actual mass production, the process has a great impact on the quality of the product. Fuel cells can learn from the development of lithium batteries more than ten years ago. The large-scale production of lithium-ion power batteries has gone through a stage of rapid growth. With the continuous improvement of lithium-ion batteries, the energy density and safety of lithium-ion batteries have also been continuously improved. The progress and maturity of the technology have continuously improved the performance of market products.
Ultrasonic spray fuel cell catalyst coating system can produce highly uniform, repeatable and durable coatings. Our ultrasonic spraying can well control coating properties, significantly reduce material usage, and reduce maintenance and downtime.
Our company’s ultrasonic spraying equipment can be sprayed on a variety of different metal alloys, including the preparation of platinum, nickel, iridium and ruthenium-based fuel cell catalyst coatings, as well as PEMs, GDLs, DMFCs (direct methanol fuel cells) and SOFCs (solid Oxide fuel cell) manufacturing. The battery manufactured by this technology has the characteristics of high battery load and high battery efficiency.
The optional ultrasonic dispersion system can uniformly disperse the catalyst solution without blocking the ultrasonic nozzle, thereby providing a uniform and homogeneous fuel cell catalyst coating, and has a controlled droplet size from ultra-low flow to production-scale flow.
