Characterization of thermoelectric properties of multifunctional multiscale composites and fiber-reinforced composites for thermal energy harvesting

We have fabricated two types of multifunctional composites, carbon nanotube (CNT)/glass fiber (GF)/epoxy composites and carbon fiber (CF)/epoxy composites, and evaluated thermoelectric properties of the composites for applications as n/p type thermoelectric materials as well as load carrying structural composites. Several test samples of CNT/GF/epoxy composites with various CNT concentrations were fabricated using a three-roll mill and hand-layup process on a hot plate, while CF/epoxy composite samples were manufactured using a hand-layup process. Experimental results demonstrated that the electrical resistivity of the CNT/GF/epoxy composite (multiscale composite) samples decreased as the CNT concentration increased. In-plane samples showed higher electrical and thermal conductivities due to partial alignment of CNTs in the multiscale composites and continuity of carbon fibers in CF/epoxy composites. Generally, CF/epoxy composites had better electrical and thermal conductivities than those of multiscale composites. In the Seebeck coefficient test, the multiscale composites showed n-type thermoelectric behavior, whereas the CF/epoxy composites showed p-type behavior. When temperature gradients were applied to closed circuits comprised of multiscale composites and CF/epoxy composites as n-type and p-type materials, respectively, an electric current was successfully generated.