Swelling and related mechanical and physical properties of carbon nanofiber filled mesophase pitch for use as a bipolar plate material

Mesophase pitch was investigated as a melt processable precursor to a compression or injection moldable all carbon bipolar plate. After shaping, carbonization to 1000 °C or greater is required to achieve the desired electrical and mechanical properties, but gases evolved during this step lead to swelling. Carbon nanofiber was added to suppress swelling during carbonization and bypass the typical oxidation steps used when processing mesophase pitch. The addition of carbon nanofiber decreased swelling by increasing the viscosity of the melt. Carbonized materials with carbon nanofibers can show strengths (30–50 MPa) and conductivities (20–80 S cm−1) consistent with composite bipolar plate materials. The materials show conductivities below Department of Energy target values at the current carbonization temperatures, which were limited to 1000 °C. The use of glass fibers as a secondary filler led to reduced gas permeability in porous samples.