Combination of nanoparticles and carbon nanotubes for organic hybrid thermoelectrics

Carbon nanotubes (CNTs) are usually very expensive, but inexpensive CNTs have been massproduced by a super-growth (SG) method. The SG-CNTs, however, have many defects resulting in a low conductivity, which is a disadvantage of the SG-CNTs. We discovered that even the defective SG-CNTs can provide a good thermoelectric performance by forming ternary hybrid films made of the SG-CNTs, nanoparticles (NPs) of a conducting polymer complex, poly(nickel 1,1,2,2-ethenetetrathiolate) (PETT) and poly (vinyl chloride) (PVC). The good thermoelectric performance of the ternary film (PETT-NP/SG-CNT/PVC) was possibly attributed to the defect repair effect in addition to the bridging effect of the PETT-NPs among the CNTs. In order to confirm this new concept, we attempted the deposition of metal NPs at the defects of the SG-CNTs. Weinitially made a physical mixture of palladium (Pd) NPs and the SG-CNTs in dispersions to cover the SG-CNT defects with the Pd-NPs. The obtained films showed only a slight improvement in electrical conductivity. Chemical reduction of the Pd ions in the dispersion of the SG-CNTs, on the other hand, provided hybrids with an enhanced electrical conductivity, thus, use as thermoelectric materials. The thermoelectric figure-of-merit was estimated to be similar to 0.3, which is a relatively high value for organic hybrid materials.