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The superlative strength-to-weight ratio of carbon fibers (CFs) can substantially reduce vehicle weight and improve energy efficiency. However, most CFs are derived from costly polyacrylonitrile (PAN), which limits their widespread adoption in the automotive industry. Extensive efforts to produce CFs from low cost, alternative precursor materials have failed to yield a commercially viable product. Here, we revisit PAN to study its conversion chemistry and microstructure evolution, which might provide clues for the design of low-cost CFs. We demonstrate that a small amount of graphene can minimize porosity/defects and reinforce PAN-based CFs. Our experimental results show that 0.075 weight % graphene-reinforced PAN/graphene composite CFs exhibits 225% increase in strength and 184% enhancement in Young’s modulus compared to PAN CFs. Atomistic ReaxFF and large-scale molecular dynamics simulations jointly elucidate the ability of graphene to modify the microstructure by promoting favorable edge chemistry and polymer chain alignment.

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Carbon/carbon-composite bipolar plates for proton exchange membrane fuel cells (PEMFC) have been fabricated by slurry molding a chopped-fiber preform followed by sealing with chemically vapor-infiltrated carbon. The resulting component is hermetic with respect to through-thickness leakage and has a high electronic conductivity (200-300 S/cm) as a result of the deposited graphitic carbon. The material has a low density (0.96 g/cm 3 ) due to retained porosity resulting in a low-weight component. Biaxial flexure strength was measured to be 175 Ϯ 26 MPa. Cell testing of a 100 cm 2 active area, single-sided plate indicated very low cell resistance and high efficiency, but with a somewhat steep drop-off in voltage with current at high values. Corrosion testing indicated minimal corrosion in fuel cell environments.