Development and modeling of electrically conductive resins for fuel cell bipolar plate applications

Fundamental and applied research is needed for the development of cost effective fuel cells for the transportation sector. Electrically conductive resins can be used for the bipolar plates, which are an essential component of the fuel cell. The current trend in the fuel cell bipolar plate technology is a thermosetting polymer as the matrix containing high concentrations of various types of electrically conductive carbon fillers.;A more efficient material design can benefit the time and cost of an optimized product. In order to fabricate an optimized bipolar plate, the use of an electrical conductivity model is helpful. The electrical conductivity can be utilized to predict the electrical conductivity behavior in the polymer composite. Within this investigation, several characterization experiment results indicated the electrical conductivity and filler concentration were not the only factors which influenced the electrical conductivity of a composite system. The use of accurate models can aid in the understanding of these mechanisms which control electrical conductivity.;In this investigation, a single filler evaluation was performed. Several carbon fillers were added to a liquid crystal polymer in increasing concentrations to result in a single filler composite system. These fillers were a carbon black, two synthetic graphites, a natural graphite, a calcined needle coke, and two carbon fibers. The single fillers which provided the most promising electrical conductivity results were used to formulate effective electrically conductive multiple filler systems. The 80 wt % Thermocarb TC-300 (synthetic graphite) single filler composite provided the highest electrical conductivity result of 12.4 S/cm. A 23 factorial design analysis was used to verify any synergistic effects present due to the combination of fillers. As in the single filler evaluation, in and through plane electrical conductivity tests were performed on the multiple filler injection molded samples. The most favorable electrical conductivity result of 6.51 S/cm for the multiple filler composites was the two filler 60 wt % Thermocarb TC-300 synthetic graphite and the 10 wt % Fortafil 243 carbon fiber. In addition optical microscopy and image analysis were also done to determine microstructure properties of the composite sample. The factorial design indicated there was a negative synergistic effect for electrical conductivity of the two filler composite system.;The single and multiple filler composite systems were also characterized by electrical conductivity models. The percolation based models used were the simplified additive, the simplified Mamunya, and the General Effective Media Equation. There were also four non percolation based models used. These were the linear, quadratic, exponential, and geometric. The electrical conductivity models used with the single filler composites all provided excellent agreement with the experimental data. The electrical conductivity model used for the multiple filler composite was able to be adapted for this system and also provided excellent agreement with the experimental data.