Development of Air-Stable n-Type Doped Single-Walled Carbon Nanotube Sheet by Lewis Acids and Bases

When and Where

Dec 7, 2022
9:50pm - 9:55pm

NM02-virtual

Presenter

Naoki Tanaka

Aoi Hamasuna

Tsuyohiko Fujigaya

Co-Author(s)

Naoki Tanaka^1,2,Aoi Hamasuna¹,Tsuyohiko Fujigaya^1,2,3

Kyushu university¹,WPI-I2CNER²,Center for Molecular Systems³

Abstract

Naoki Tanaka^1,2,Aoi Hamasuna¹,Tsuyohiko Fujigaya^1,2,3

Kyushu university¹,WPI-I2CNER²,Center for Molecular Systems³

The chemical doping of single-walled carbon nanotubes (SWCNTs) using electron donor and acceptor molecules is a crucial step for controlling the frontier orbital energy gap of SWCNTs. This means that SWCNTs are promising materials for electronics applications such as thermoelectric conversion and thin-film transistors, due to their flexibility, stability, and light weight.1,2,3 For efficient thermoelectric generation, both p-type and n-type thermoelectric materials are required. However, SWCNTs act as p-type semiconductors owing to the hole doping by water and oxygen in air. Therefore, many efforts to develop n-type SWCNTs have been performed mainly by chemical doping using electron donors.4,5,6 Recently, our group reported that the boryl radical produced by cleavage of the boron-boron bond of bis(pinacolate)diboron (B2pin2) by coordinated pyridines to boron can serve as an electron dopant in SWCNTs.7 However, the n-doped SWCNTs did not show long-term air stability. In this study, we used tetrahydroxydiboron (B2(OH)4) in place of B2pin2 as the boron source and various pyridines to study the effect of the chemical structure of the boron to the n-doped air-stability. Electron doping of SWCNTs was performed by mixing SWCNT sheets (4 mm × 14 mm × 30 µm), B2(OH)4 (1.0 eq.), and pyridine derivatives (0.5 eq.) in THF solvent and shaking at 40 °C for 24 hours. Upon using 4-cyanopyridine (4-CNPy), 4-phenylpyridine (4-PhPy), and 4-carboxypyridine (4-COOHPy), the doped SWCNT sheets showed negative Seebeck coefficient values and higher electrical conductivity than pristine SWCNTs, indicating the electron-doping from the corresponding boryl radicals to SWCNT. Interestingly, the n-doped SWCNT sheets prepared with B2(OH)4/4-Phpy revealed n-type properties for more than 50 days in air. X-ray photoelectron spectroscopy of the n-doped SWCNTs with B2(OH)4/4-Phpy showed that the dopant coverage on SWCNTs was much higher than that of other dopants. In addition, the distance between the dopant cation and the SWCNT was shorter than when B2pin2/4Phpy was used as a dopant. Therefore, we consider that n-type stability is not only related to the amount of coverage, but also to the interaction between SWCNT and dopant. References- [1] E. Jouguelet, C. Mathis and P. Petit, Chem. Phys. Lett. 2000, 318, 561. [2] J. Kong and H. Dai, J. Phys. Chem. B 2001, 105, 2890. [3] L. Brownlie and J. Shapter, Carbon 2018, 126, 257. [4] M. Shim, A. Javey, N. W. S. Kam and H. Dai, J. Am. Chem. Soc. 2001, 123, 11512. [5] J.-Y. Choi and Y. H. Lee et al., J. Am. Chem. Soc. 2009, 131, 327. [6] Y. Nonoguchi and T. Kawai et al., Sci. Rep., 2013, 3. [7] N. Tanaka and T. Fujigaya et al., Chem. Commun. 2021, 57, 6019-6022.