May 23, 2014
Graphyne: a two-dimensional material with thermoelectric properties
The application of the thermoelectric effect to recycling waste heat from thermal engines could help alleviate dependence on fossil fuels. Despite its numerous properties, graphene is not an efficient thermoelectric material due to its ultra-high thermal conductivity. Reporting in Nanotechnology, researchers from RWTH Aachen University in Germany have systematically investigated the thermal and thermoelectric properties of graphyne (a new member of the graphene family). They reveal that this novel two-dimensional (2D) carbon allotrope may be a promising candidate for high-performance thermoelectric applications.
The thermoelectric effect converts a temperature gradient to electricity directly. The energy conversion efficiency of these materials are defined by the dimensionless figure of merit (ZT). The high thermal conductance of graphene and its related nanostructure derivatives means that they are not efficient thermoelectric materials and have a ZT of around 0.05. In order to overcome this, researchers have turned their attention to beta-graphyne (Β-graphyne), an allotrope of graphene. It has been suggested that the phonon contributed thermal conductance of graphyne is fundamentally lower than that of graphene which makes it an attractive thermoelectric material.
Unique thermal transport properties
Using a non-equilibrium Green’s function method, the researchers find that the thermal conductance of Β-graphyne nanoribbons (BGYNRs) is only 26% of that of their graphene counterparts. It also shows evident directional dependence. No matter what the kind of edge terminal is, the thermal conductance of armchair edged BGYNRs (A-BGYNRs) present abnormal stepwise width dependence.
Combined with the electronic transport calculation, the thermoelectric performance of BGYNRs is also investigated. The numerical simulation results reveal that, compared with the graphene counterparts (ZT ~0.05), Β-graphyne possesses a superior thermoelectric performance with a figure of merit (ZT) achieving 0.5 at room temperature.
Based on the samples of BGYNRs with a zigzag edge, the influence of edge and central geometric modulations on the thermoelectric efficiency are considered. Researchers find that the thermoelectric performance can be further enhanced dramatically (ZT can even exceed 1.5 at room temperature) and this strongly depends on the structure parameters.
More information about the research can be found in the journal Nanotechnology 25 245401.
Hybrid nanomaterial enhances performance of thermoelectric generator (Oct 2012)
Doped CNTs make better thermoelectrics (May 2014)
Could graphynes be better than graphene? (Mar 2012)
Thermoelectric nanodevices: Catering for global energy needs little by little (April 2014)
About the author
Tao Ouyang is currently a postdoctoral associate in Ming Hu’s group at the Institute of Mineral Engineering, Division of Materials Science and Engineering, RWTH Aachen University in Germany. The group’s current research focuses on nanoscale heat transfer with particular emphasis on nanotechnology energy applications, including the thermoelectric properties of low-dimensional materials.