Anisotropic Electrical Conductivity and Isotropic Seebeck Coefficient Feature Induced High Thermoelectric Power Factor >1800 µW m⁻¹ K⁻² in MWCNT Films

Abstract

Lightweight and low-cost flexible thermoelectric (TE) materials improve the heat-to-electricity conversion efficiency compared to rigid materials by minimizing the heat loss between TE devices and heat sources in waste heat recovery. Multi-walled carbon nanotube (MWCNT) has excellent mechanical and electrical properties. However, the TE power factor (PF) of MWCNTs is much lower than single/double-walled carbon nanotube (S/DWCNT), which is often lower than 40 µW m −1 -K −2 . Herein an effective way to achieve high PFs of ≈1800 µW m −1 -K −2 for p-type and ≈1000 µW m −1 -K −2 for n-type in flexible MWCNT films is reported. The high power factor is achieved by taking advantage of the anisotropic electrical conductivity and isotropic Seebeck coefficient feature of 1D CNTs as well as the following doping and cold-pressing to improve the electrical conductivity of MWCNT films. The PF values are comparable to that of state-of-the-art S/DWCNT films and most inorganic TE materials. A Lego-like TE generator (TEG) with an assembling structure is fabricated to show the heat-to-electricity ability of the materials, which exhibits the highest areal output power of ≈27 W m −2 among CNT-based flexible TEGs. This method may be extended to other 1D-material based composites to boost the development of high PF flexible TE materials.

Construction of Flexible, Self-Supporting, and In-Plane Anisotropic PEDOT:PSS Thermoelectric Films via the Wet-Winding Approach

“…It is noticed that although evident anisotropy can be observed in the structure and σ of the A-PEDOT:PSS film, its anisotropy in S is relatively inferior. These results are consistent with those reported for an anisotropic carbon nanotube film and can be understood by Mott’s hopping theory . σ and S are represented by eqs and , respectively, as shown below. where f is the Fermi distribution function, k is the Boltzmann constant, and e is the elemental charge.…”

“…As the fiber loading increases, S almost remains in the range of 15.0–17.5 μV K –1 . Similar phenomena have also been observed in carbon nanotube-based anisotropic films by Wang et al , Details for this mechanism will be discussed later. Nevertheless, in comparison with the I-PEDOT:PSS counterpart, S in A-PEDOT:PSS films is constantly higher.…”

“…These results are consistent with those reported for an anisotropic carbon nanotube film and can be understood by Mott's hopping theory. 40 σ and S are represented by eqs 3 and 4, respectively, as shown below.…”

N-type silver ammonia-polyethyleneimine/single-walled carbon nanotube composite films with enhanced thermoelectric properties

“…Thermoelectric (TE) materials are a new type of eco-friendly energy materials, which can directly convert thermal energy into electrical power and vice versa. [1][2][3] The thermoelectric conversion efficiency of TE materials was assessed by figure-of-merit (ZT = S 2 sT/k, where S, s, T, and k are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively) and power factor (PF = S 2 s). [4][5][6][7] Carbon nanotubes (CNTs) and their composite thermoelectric materials, which have the advantages of easy preparation, high electrical conductivity, and good flexibility, have been widely studied and have shown potential applications in supplying power to flexible electronics.…”

Green biopolymer-CNT films exhibit high thermoelectric power factor and electrical conductivity for low temperature heat energy harvesting

“…11,12 Our group also reported a high power factor of >1800 mW m −1 K −2 with high electrical conductivity of organic molecule-doped multi-walled carbon nanotube lms. 13 It is about time to explore green and sustainable materials with high performance for future green energy harvesting in thermoelectrics. However, biopolymerbased TE materials oen showed poor thermoelectric power factors since biopolymers and their composites oen had low electrical conductivities although a high concentration CNT of >90 wt% was induced in the biopolymer matrix.…”