Carbon-Based Thermoelectrics

Carbon nanotubes and organic polymers can be combined to form composite materials with useful thermoelectric properties, according to researchers at Texas A&M University (ACS Nano, DOI: 10.1021/nn202868a). Thermoelectric materials used in commercial solid-state cooling applications and in conversion of waste heat to electric power tend to be inorganic semiconductors such as bismuth telluride and related alloys containing lead and antimony (C&EN, June 20, page 33). Carbon-based materials, as a result of their low weight and cost, high flexibility, and nontoxic nature, would make ideal substitutes for the brittle inorganic materials used for these applications. But the organic materials studied until now have exhibited poor thermoelectric properties. Texas A&M’s Choongho Yu and coworkers prepared various composites of single-walled carbon nanotubes coated with poly(3,4-ethylenedioxythiophene), poly(styrenesulfonate), and poly(vinyl acetate). Samples with nanotubes 35 to 60% by weight exhibited electrical conductivities measuring 10⁴ to 10⁵ siemens per meter, which are orders of magnitude greater than those of typical nanotube-polymer composites. Owing to vibrational characteristics of the nanotube-polymer junctions in those samples, the best electrical conductors turned out to be poor thermal conductors—a combination of properties well suited to thermoelectric applications.