Synergistic optimization of thermoelectric performance in cementitious composites by lithium carbonate and carbon nanotubes
Jian Wei, Mengjie Zhang, Yuan Wang, Li Ma, Hao Zhang, Xueting Li
Abstract
Thermoelectric cement-based composite materials can convert the temperature difference between indoor and outdoor into electrical energy in summer. And the energy can be reversed to remove ice and snow on the pavement in winter. However, how to improve its thermoelectric conversion efficiency is the primary technical problem currently facing. Carbon nanotubes are often used as a container for their unique tubular structure. In this study, lithium acetate was filled in carbon nanotubes to obtain lithium carbonate modified carbon nanotubes (after heat treatment) by utilizing its capillary force. XRD, SEM, and TEM were used to characterize the morphology and crystal structure of lithium carbonate-modified carbon nanotubes. ST2722-SZ semiconductor powder resistivity tester was used to characterize the change of electrical conductivity before and after modification of carbon nanotubes (48.22 S/cm reduced to 3.43 S/cm, ∅11.28 mm, 30 MPa). The thermoelectric power factor of lithium carbonate modified carbon nanotubes reinforced cement-based composites reaches 0.039 μW m−1 k−2. The Fermi level calculated by the Mott formula fluctuates between 0.116 and 0.256 eV. And the order of magnitude of the carrier concentration is stable at 1020 cm−3.The composite material not only exhibits superior thermoelectric properties but also reduces the carbon nanotube content to achieve a more cost-effective purpose.