Bipolar Elements for PE Fuel Cell Stacks Based on the Mould to Size Process of Carbon/Polymer Mixtures

摘要

The bipolar plate is the main construction element of a fuel cell stack. Besides the performance of the electrochemical components, the characteristics of the bipolar plate determine the performance of the stack with respect to specific power and volume. Therefore, the bipolar plate needs to be optimized with respect to material, design, and manufacturing process. The main design requirements for the bipolar plate are low weight, low volume, and a low cost manufacturing process. The design of the bipolar plate should ensure optimal electrochemical performance by even distribution of gases to and removal of product water from the active area, allow heat removal, and include manifolds for fluids. Fulfillment of the material requirements is easiest with a graphite based material, because it is corrosion resistant. Graphite also has a low specific weight (≈ 2 g/cm~3). However, pure graphite is not easily shaped. Therefore, a graphite-polymer compound which can be shaped by pressure molding, was chosen as construction material. With a thermoplastic polymer compound the pressure molding process is able for an automatic manufacturing cycle with the necessity to cool the mould before releasing the part from the form. Half-plates were produced by SGL Carbon Group (D), and processed into complete bipolar plates at ETH and PSI. A complete bipolar plate has a thickness of 3.1 mm and a weight of approximately 125 g for 200 cm~2 active area. A 125 cell stack was completed for testing. The pitch of a repetitive unit is 3.2 mm. The specific power and volume of this stack at nominal (not maximum) power of 8.4 kW are 365 W/kg and 530 W/I, respectively.