Humidifiers in proton exchange membrane (PEM) fuel cells need to withstand high levels of humidity as well as exposure to heat and chemicals. This fact requires materials with characteristics that allow for their safe, reliable operation and efficient production. To meet these requirements, WEVO-CHEMIE GmbH has developed certain adhesives, sealants, and potting compounds based on polyurethane, epoxy resin, and silicone. These products provide gas-tightness and hydrolysis resistance and feature ion purity and low VOC content, which are essential for reliably protecting the sensitive fuel cell membrane. The two-component (2K) systems are highly durable and offer individually adaptable parameters for both semi-automated 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 mainly performed by flat-sheet membrane and hollow fiber membrane humidifiers.

Precise Bonding and Gas-tight Sealing

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 developed by Wevo meet these requirements. Their water-repellent polymer backbone also makes them suitable for use as hydrolysis- and temperature-resistant sealants. The 2K polyurethanes and silicones adhere very effectively to the substrates most commonly used as spacers, including polyolefins, polyphenylene sulphide (PPS), and fluorinated membrane materials — the bonding of which has been a challenge up to now.

Another characteristic of these formulations is their low glass transition temperature, which ensures high tear resistance, long-lasting elasticity, and resistance to temperature changes — essential when cold-starting fuel cell systems.

Controlled Reaction Heat and Wetting

In hollow-fiber membrane humidifiers, bundles of tubular membranes are potted into a support tube at both ends — a principle familiar from water filtration. The resins must penetrate between the hollow fibers and ensure sufficient wetting of the bundle without clogging the individual fibers.

For this reason, potting compounds need to be designed for optimal exothermicity. The heat generated during the reaction between the resin and hardener is therefore controlled, effectively preventing oxidative damage to the sensitive membrane tubes. At the same time, the 2K polyurethane systems are hydrophobic to prevent a reaction with the moisture contained in the membrane material and the resulting bubble formation.

Efficient Production

For more efficient production, materials can be applied by standard mixing and dosing systems and integrated into both semi- and fully automated production lines. Processing properties such as viscosity and pot life can be customized to meet individual requirements on request. Curing usually takes place at room temperature. However, to accelerate manufacturing cycles, it is also possible to use thermal curing in a convection oven or via infrared radiators.

These 2K systems can also be used for other applications in humidifiers, such as for sealing and bonding housings, for seals on water inlets and outlets, for sealing and bonding bypass valves, and for creating internally sealed zones.

Solutions for Fuel-cell Technology

Wevo develops special formulations for fuel cells, electrolysers, and BOP components in close collaboration with manufacturers and research institutes. If required, materials based on polyurethane, epoxy resin, and silicone can be adapted to suit individual needs by incorporating specified properties — in addition to the parameters relevant for processing. Among other things, viscosity, gas permeability (e.g. hydrogen and water vapor permeability) and adhesive properties can be precisely adjusted.

Learn more about Wevo Chemie at www.wevo-chemie.de.

By experts at Wevo Chemie