Development of fuel cell bipolar plates from graphite filled wet-lay thermoplastic composite materials

A method with the potential to produce economical bipolar plates with high electrical conductivity and mechanical properties is described. Thermoplastic composite materials consisting of graphite particles, thermoplastic fibers and glass or carbon fibers are generated by means of a wet-lay (paper-making) process to yield highly formable sheets. The sheets are then stacked and compression molded to form bipolar plates with gas flow channels. Poly(phenylene sulfide) (PPS) based wet-lay composite plates have in-plane conductivity of 200-300 S cm−1, tensile strength of 57 MPa, flexural strength of 96 MPa and impact strength (unnotched) of 81 J m−1 (1.5 ft-lb in.−1). These values well exceed industrial as well as Department of Energy requirements or targets and have never been reached before for composite bipolar plates. The use of wet-lay sheets also makes it possible to choose different components including polymer, graphite particle and reinforcement for the core and outer layers of the plate, respectively, to optimize the properties and/or reduce the cost of the plate. The through-plane conductivity (around 20 S cm−1) and half-cell resistance of the bipolar plate indicate that the through-plane conductivity of the material needs some improvement.