Fuel cells based on hydrogen are highly effective and energy-efficient. Because only water and electrical energy are created when hydrogen combines with oxygen, they don’t release any toxic emissions.
So, the technology has a lot of potential for supplying electric car power in the context of the suggested mobility transformation. Since hydrogen is the smallest of all molecules, the adhesives and sealants used for fuel cells must provide a very tight seal in order to prevent diffusion. The Duisburg-based hydrogen and fuel cell center ZBT has verified the low gas permeability of the silicones and polyurethanes WEVO-CHEMIE GmbH designed specifically for this use. Both the fuel cells themselves (referred to as “stacks”) and the surrounding system (referred to as “balance of plant”) can use the products.
Fuel cells are made up of numerous functional layers, each of which has a different working principle, materials, and componentry. Because of its applicability to the automotive industry, one of the most popular varieties is the so-called PEM fuel cell (Proton Exchange Membrane Fuel Cell), which is depicted in the image.
The bipolar plates manage the release of electrical energy while also ensuring a constant flow of hydrogen to the cells. Since hydrogen is combustible and can generate explosive combinations (“oxyhydrogen”) in oxygen-containing atmosphere, reliable sealing of the individual cells is necessary. In addition to being extremely impermeable to gas, the sealing materials must also be able to withstand adverse circumstances like prolonged high temperatures of up to 120 °C or low pH. Moreover, it may be necessary to correct for any manufacturing-related tolerations in the bipolar plates that result in unequal pressure distribution on the sealing materials, particularly while pressing the stacks.
Preformed inlay gaskets, for instance, have been utilized in this manner up until now. They are not ideal for automated large volume production, i.e. for the car industry in particular, because they must be manually inserted on both sides of each bipolar plate. Moreover, there is a chance that they could lose the bipolar plate during stacking, rendering the seal ineffective. Commercially available, addition-curing silicone liquid gaskets are available as alternatives, although they too have problems such generally high gas permeability and poor adherence to most surfaces. For use in proton exchange membrane (PEM) fuel cells, Wevo created specific, chemically resistant, two-component polymers based on polyurethane and silicone. They provide additional benefits for the production and use of fuel cell component parts and are used as liquid formed in-place gaskets.
Low gas-permeable Wevo materials
One of the top research institutions in Europe in this area, ZBT, the Duisburg hydrogen and fuel cell center, has confirmed the materials’ exceptionally low gas permeability. After 16 hours of measurement, one of the silicone-based products showed a very low hydrogen permeation coefficient of about 130 E-8 cm2/s (a number between 500 and 1000 E-8 cm2/s is normal for addition-curing silicones). Wevo also improved adherence to metal surfaces and decreased compression set.
Depending on the Shore hardness setting, Wevo’s polyurethane sealants, which resemble silicones in terms of their thermo-mechanical characteristics, offer even lower hydrogen permeability. After a 16-hour measuring period, their permeation coefficients range between around 30 and 70 E-8 cm2/s. Moreover, these materials attach to the various bipolar plate substrates far more well than silicones do. Loss of sealing effect is no longer a concern because this stops the seal from coming undone during the manufacturing process or while it is being stacked. Last but not least, compared to silicones, substantially faster curing is feasible, which is a significant advantage for automated high-volume production.
Stacks, BOP components and electrolysers adhesives
Due to their excellent adhesion qualities, Wevo’s polyurethane-based materials can also be utilized as adhesives for other purposes, including both inside the fuel cell stack and in the balance of plant (BOP), or the surrounding system. For example, utilizing tailored, soft and elastic Wevo polyurethanes, it is possible to unite and seal the two half-shells of the bipolar plates as well as bond the complete stack together. As an alternative to laser welding, this joining technique can be used to link metallic bipolar plates; however, for plates made of composites of graphite and polymer, strong bonding is required.
The components of the humidifier can also be sealed and bonded using Wevo products. Its excellent ion purity and low volatile component (VOC) content specifically rule out harm to the delicate, ion-selective polymer membranes and the resulting performance degradation. The unique composition of the customized goods also guarantees high hydrolysis resistance at temperatures as high as 100 °C.
Other potential BOP applications include the air compressor connected to the air circuit or the anode recirculation blower. Wevo’s epoxy resins and silicones enable potting of the stator for the drive motor in the latter scenario. The forces produced during rotation are adjusted appropriately, and the heat generated is evacuated specifically, by optimizing the thermal conductivity and crack resistance of the materials. Power electronic parts including DC/DC converters, on-board chargers, and control units employ specialized, thermally conductive polyurethane potting compounds and silicone gels for the power modules.
Wevo products for hydrogen production
Wevo’s specialized, durable polyurethane adhesives are ideal for various components used in the hydrogen generation process due to their low hydrogen permeability coefficient of only 3 to 4 E-8 cm2/s. For example, massive stacks for polymer membrane-based electrolysers required to make “green hydrogen” can be joined with the aid of.
Due to the fact that alkaline electrolysis plants use a type of electrolyser that uses aqueous potassium hydroxide solution (30–35% KOH) as its electrolyte and operates at temperatures between 90 and 95 °C, they require adhesive systems with even higher chemical resistance than polymer membrane technology can provide. Most organic glue and sealing methods can’t endure such circumstances over the long term. One of the few products now on the market that can satisfy these demands is a specifically optimized, highly cross-linked, and chemically resistant Wevo epoxy resin, which in its thixotropic state is appropriate for placing adhesive beads. In order to provide more solutions in this field in the future, Wevo is actively working with a number of academic institutions and industrial partners.