53 E-Mobility Engineering | January/February 2026 Fuel cell adhesives | Deep insight compensated and the heat generated is removed in a targeted way. Special thermally conductive, polyurethane potting compounds and silicone gels for the power modules are used for power electronic components such as DC– DC converters, onboard chargers and control units. Humidifiers The humidifiers used in PEM fuel cells need to withstand high levels of humidity as well as exposure to heat and chemicals. The materials used in these applications are therefore of key importance for their safe, reliable operation and efficient production. To meet the strict requirements, it is usual to use adhesives, sealants and potting compounds based on polyurethane, epoxy resin and silicone, which not only provide gas-tightness and hydrolysis resistance, but also need to have high ion purity and low content of volatile organic compounds (VOCs) to reliably protect the sensitive fuel cell membrane. The materials also need to have individually adaptable parameters for both semi- and fully automated manufacturing processes. In PEM fuel cells, humidifying the incoming air is crucial for maintaining the conductivity of the membrane – and thus, the efficiency of the entire system. This task is performed mainly by flatsheet membrane and hollow-fibre membrane humidifiers. Flat-sheet membrane humidifiers often consist of several hundred layers of membrane and spacer materials, which must be reliably and permanently bonded together to form a stack. In many cases, this stack is additionally glued into the housing of the humidifier or partially encapsulated to achieve a gas-tight seal. Hydrophobic adhesives and potting compounds meet these requirements. The water-repellent polymer backbone also makes them suitable for use as hydrolysis- and temperature-resistant sealants. The 2-component (2K) polyurethanes and silicones adhere very effectively to the substrates used most commonly as spacers, including polyolefins, polyphenylene sulphide (PPS) and fluorinated membrane materials – the bonding of which has been a challenge up until now. In humidifier applications, the high ion purity and low levels of VOCs rule out damage to the sensitive, ion-selective polymer membranes and the associated drop in performance. High hydrolysis resistance at temperatures up to 100 C is ensured by the special composition of the customised products. Another characteristic of the a measurement time of 16 hours, which compares favourably with the figure of 500–1000 E-8 cm²/s for addition-curing silicones. Moreover, the adhesion to metal surfaces also improves. Polyurethane sealants, which have similar thermo-mechanical properties to silicones, have even lower hydrogen permeability, depending on the Shore hardness setting. The permeation coefficient varies between about 30 and 70 E-8 cm²/s, also after a measurement period of 16 hours. These sealants adhere significantly better than silicones to the different substrates of bipolar plates. This prevents the seal from detaching either in the course of the manufacturing process or during stacking, so that loss of the sealing effect is no longer an issue. Much faster curing is also possible compared with silicones – a major asset when it comes to automated production of high volumes. Stacks The polyurethane-based products can also be used as adhesives for other applications, both within the fuel cell stack and in the balance of plant (BOP) that is the surrounding system, as a result of the good adhesion properties. As well as bonding the entire stack together, it is possible, for example, to simultaneously join and seal the two half-shells that form the bipolar plates using customised, soft and elastic polyurethanes. For metallic bipolar plates, this joining method can be employed as an alternative to laser welding; with plates based on graphite/polymer composites, durable bonding is key. The anode recirculation blower or the air compressor installed in the air circuit are other possible applications in the BOP. In the latter case, the epoxy resins and silicones enable potting of the stator for the drive motor. By optimising the thermal conductivity and crack resistance of the materials, the forces produced during rotation are Structure of a PEM fuel cell (Image: Wevo Chemie)
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