The fuel cell is a promising alternative energy source of the future for vehicles. In contrast to competing technologies such as batteries, fuel cells are more competitive and environmentally friendly — increasingly so if successful in boosting efficiency and service life while simultaneously reducing the price. For developing solutions for the technical requirements and to reach the cost goals, the core components of the fuel cell — thereby the gas diffusion layer (GDL) in particular — play a significant role.

The following developmental themes were addressed within the »OptiGAA« project:

  • Develop a comprehensive understanding of materials and the impact on the GDL in terms of performance, together with corresponding simulation and characterisation methods
  • Development of GDL surfaces that do not damage even thin membranes and guarantee a long service life for the fuel cell
  • Adjustment of the mass transfer properties to the prevailing operational conditions in the vehicle application according to the developed specification
  • Optimisation of the mechanical characteristics to minimise
  • › intrusion of the GDL into the gas channels of the flow field, as well as
  • › contact resistance of the GDL to the catalyst layer for more effective use of the catalyser.
  • »OptiGAA« is a joint project of Freudenberg FCCT SE & Co. KG and Daimler AG.

Daimler provided the design requirements, operating conditions of the PEMFC, developed the requisite specification and characterisation know-how and clarified the necessary requirements for the GDL to improve operating characteristics and cost effectiveness. The developmental products from Freudenberg where evaluated by Daimler both in and ex situ. The results were subsequently compared with the calculations arising from simulations.

Freudenberg could reduce the GDL’s potential to damage membranes by 80 % due to the improved GDL manufacturing process that was developed. The result is a significant increase in fuel cell service life.

Through the deployment of new raw materials to impregnate and coat the GDL, both the mass transfer properties and contact resistance could be improved and performance was enhanced by up to 30 %, while simultaneously achieving more robust operation.

The GDL mechanical characteristics were improved due to the use of new raw fibres and an adjusted production process, resulting in the reinforced GDLs delivering improved cell performance by up to 20 % — especially in wide gas channels.

The developments were both very cost-intensive and time-consuming as they were required to be conducted on continuous production plants. It was also shown that the new impregnation and coating materials make an adjustment of the current production process necessary. A finding made in the project was that the GDL microstructure has a great influence on the transfer properties for the reactant gases and water. Through an improved understanding of the relationships between the structure and function of the GDL materials, further GDL optimisation is achievable.

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