Low Thermal Conductivity Of Thermoelectric Composite Materials Structure Regulation Research

The world’s huge demand for fossil energy has resulted in a serious energy crisis, environmental pollution and global climate change. One potential way to solve the problem is to convert waste heat into electricity by TE generators. In general, the efficiency of TE materials is given by the figure of merit, ZT, the ZT value depends on three transport parameters: the thermal conductivity κ, the Seebeck coefficient α, and the electrical conductivity σ. Increasing σ is usually accompanied with an increased κ and a decreased α, thus the strong interdependence of these three parameters impedes further enhancement of the ZT value in some potential TE materials.In this paper, the preparation of lightweight, low thermal conductivity of thermoelectric materials was discussed. We design three kinds of organic and inorganic composite materials.Hybridized conducting aerogels based on multi walled carbon nanotubes(MWCNTs) and carbonizedresorcinol-formaldehyde(RF) resin were prepared.It is demonstrated that the hybridized conducting aerogels show lower thermal conductivity, higher electrical conductivity and Seebeck coefficient than pure carbonized RF aerogel. Thus, the three thermoelectric parameters can be independently tuned in the unique structures of hybridized conducting aerogels, which overcomes the dilemma in bulk semiconductors that increasing electrical conductivity is generally accompanied with decreased Seebeck coefficient and increased thermal conductivity. As a result, we achieve an improvement of two orders of magnitude in the figure of merit(ZT) compared with that of pure carbonized RF aerogel. Thus, the hybridized conducting aerogels havethe potential to be applied as analternative category of thermal electric materials.New conducting aerogels based on carbon nanotube(CNT) and silver(Ag) nanocomposites have been systematically investigated. The CNT-Ag nanocomposite aerogels possess low thermal conductivity of only 0.06 to 0.095 W·m-1·k-1 with various Ag contents at room temperature, which are greatly lower than other reported CNT and Ag compositeswith non-porous structures. However, the electrical conductivity and Seebeck coefficient of the CNT-Ag nanocomposite aerogels can be simultaneously enhanced by increasing the Ag content in the unique structure, which overcomes the dilemma in bulk semiconductors that increasing electrical conductivity is generally accompanied with reduced Seebeck coefficient and enhanced thermal conductivity. As a result, this strategy promises a highest ZT value of 0.011, and the tenuous solid skeleton and highly open-cell foam structure of the CNT-Ag nanocomposite aerogels lead to a low apparent density(~130 kg·m-3). Our study in this work broadens the development of a facile and novel category of light weight TE material.Bismuth telluride based on calcium silicate were prepared through a low-cost and convenient preparation method. It is demonstrated that the composite materials have ultra-low thermal conductivity, and high electrical conductivity and Seebeck coefficient, which promises a high figure of merit(ZT) up to 0.72 at 473℃. The addition of calcium silicate materials makes thermal conductivity as low as 0.2 W·m-1·k-1, the value is much lower than other inorganic thermoelectric materials.