Tuning the structure of borane-nitrogen derivatives towards high-performance carbon nanotubes-based n-type thermoelectric materials

Abstract

Recently, single-walled carbon nanotubes (SWCNTs)-based thermoelectric (TE) materials have received much interest owing to their advantages, such as high electrical conductivity and flexibility, as well as their ability to be easily tuned to exhibit p-type or n-type characteristics by the addition of redox reagents. Compared with the numerous p-type composites, less n-type agents have been reported. Borane-nitrogen derivatives (BNs) have been widely used as reducing agents; however, little attention has been paid on their TE performance. As the reducing ability of BNs can be tuned by the basicity and steric hindrance of the nitrogen containing derivatives, herein, pyridineborane (PYB), morpholineborane (MPB) and N,N-diethylanilineborane (DEANB) were investigated as n-type dopants of SWCNTs by simply dispersing each of them with SWCNTs in various solvents. The results suggested the structures of the borane complexes and their reducing ability affect the TE properties greatly. Among them, SWCNT/PYB displayed the best performance at all the investigated temperatures, with power factors ranging from 193.6 μW m−1 K−2 to 223.8 μW m−1 K−2, which are the highest PF values reported to date based on boron containing SWCNT composites. In addition, the TE devices containing five p-n junctions were also combined. SWCNT/PYB exhibited a higher open-circuit voltage (28.8 mV) and output power (1.15 μW) than SWCNT/NaBH4 (23.7 mV, 0.79 μW) at the same conditions. Our results suggest that organic boron compounds can be developed as good agents for boosting the performance of n-type TE materials.