The Abnormally Excellent Figure of Merit of 14,14,18-Graphyne at Room Temperature: A Study on the Thermoelectric Characteristic of Graphyne

Abstract

The application of carbon-based nanomaterials in the field of thermoelectric is enormously restricted for its high thermal conductivity. Graphyne, as the allotrope of graphene, expresses low thermal conductivity; therefore, it can be expected to break the limitation of carbon-based materials in thermoelectric field. By using the first-principles calculation combined with the Boltzmann theory, the thermoelectric properties of types of graphynes, i.e., 6,6,6-, 6,6,12-, 14,14,18-, and 18,18,18-graphyne, are systematically investigated. It is interesting to find that 14,14,18-graphyne presents excellent thermoelectric properties, whose maximum value of ZT can reach 1.6 at room temperature; therefore, it can be seen as an excellent carbon-based thermoelectric material. More importantly, its ZT at low temperature is abnormally higher than that at high temperature, which breaks the traditional view that the higher ZT exists in a high temperature range. Furthermore, it can also be noticed that the other three types of graphynes exhibit unexpected special thermoelectric properties: (1) 6,6,6-graphyne shows the highest Seebeck coefficient; however, its ZT value is the lowest. Moreover, its ZT value for n-type doping is twice as that for p-type doping. (2) The ZT of 6,6,12-graphyne expresses enormous anisotropy, whose value along the zigzag direction is even 1–2 orders of magnitude higher than that along the armchair direction. (3) The ZT of 18,18,18-graphyne shows completely opposite anisotropy compared with the other three types of graphynes, and its ZT value along the armchair direction is higher. Our research provides some meaningful results for enhancing the thermoelectric performance of carbon-based nanomaterials, especially for the development of high-performance thermoelectric materials at room temperature.

Design, synthesis, and application of some two-dimensional materials

“… 160 Due to the low efficiency of thermoelectric conversion, the application of traditional organic solid materials in flexible thermoelectric devices is greatly limited. 161 Recent studies have shown that low-dimensional materials can have higher thermoelectric conversion efficiency due to quantum confinement effects. 162 Therefore, the study of the thermoelectric properties of 2D materials has become an attractive research spot, which can not only provide powerful theoretical support for alleviating the energy and environmental crisis faced by current society but also provide theoretical models for obtaining higher-performance thermoelectric materials.…”

Biaxial negative thermal expansion in carbon nets – graphyne and derivatives

“…15 Qi and co-workers showed higher ZT (Figure of merit) for 14,14,18-graphyne than most of the other graphynes and it can be used as a very good thermoelectric material. 16 Mortazavi et al performed detailed first-principle calculations on various substituted graphyne and graphdiyne systems (N, B, P, Al, As, Ga) for their mechanical, optical and electronic properties. 17…”

“…15 Qi and co-workers showed higher ZT (Figure of merit) for 14,14,18-graphyne than most of the other graphynes and it can be used as a very good thermoelectric material. 16 Mortazavi et al performed detailed firstprinciple calculations on various substituted graphyne and graphdiyne systems (N, B, P, Al, As, Ga) for their mechanical, optical and electronic properties. 17 Unlike pure sp 2 -sp 2 hybridization on graphene, an sp-sp 2 network in graphyne introduces voids in the system and makes it extremely attractive for storage and controlled electron-transport along C-C triple bonds.…”