The Regenesys fuel cell stack is assembled from up to 250 identical bipole components. Each bipole consists of a conducting electrode welded into a surrounding polyethylene frame. The frames are clamped together in the stack between steel core end plates, so that they form an integral container for the electrolytes and support the electrodes. The contact between the frames is engineered to form a seal, whose integrity must be maintained throughout the life of the stack. The clamping force depends on the mechanical properties of the stack, which is governed by the mechanical and thermal properties of the frame materials and the mechanics of their interfaces.
The behaviour of the polymer frame stack cannot be reliably predicted without understanding the deformation of the interfaces. The stiffness of the interface and how it changes is key to the integrity of the stack. There are two important considerations; firstly how the bulk frame geometry contacts with its neighbour, and secondly how contact at an asperity level takes place and the effect this has on sealing. These considerations underlie both the pressures that are brought to bear on the seals, and the sealing mechanism itself.
The processes under investigation are:
- The bulk local mechanical response of the internal seal / frame region
- The asperity level response of the seal
- The bulk mechanical response of the frame / frame contact
- The asperity level mechanical response of the frame / frame contact
In the course of stack compression and preparation for service, several different processes can be identified. The internal seals make first contact, and are rapidly brought to a high stress and deformation level. A wider area of the frame then comes into contact, and is then more slowly brought to a lower stress, which is then sustained for a long time.
The purpose of this project is to obtain a fundamental understanding of the behaviour of the frames in contact. The goals are to define the surface conditions, geometries and stress levels required for a reliable seal, and to define the methods for assuring their maintenance in long term service. These methods will apply directly to existing stacks and provide a resource for the design of new and improved stacks.
We are grateful to Regenesys Technologies for their sponsorship of this work.