The influence of surface functionalization on the thermoelectric properties of carbon nanotube/Bi₂Te₃ composites

Carbon nanotube-dispersed Bi₂Te₃ matrix (CNT/Bi₂Te₃) composites were fabricated using chemical routes followed by spark plasma sintering (SPS) and their thermoelectric properties were compared in terms of the surface functionalization of CNTs. It was revealed that the electrical resistivity of pure Bi₂Te₃ was increased by an addition of CNTs and was further increased by strongly functionalized CNTs (fCNTs). A maximum Seebeck coefficient of -132 μV/K was obtained from an fCNT/Bi₂Te₃ composite at 423 K. The total thermal conductivity of the fCNT/Bi₂Te₃ composite shows an extremely low value of approximately 0.65 W/mK, although there are no major differences in the power factors compared to a CNT/Bi₂Te₃ composite. Due to these thermoelectric properties, the fCNT/Bi₂Te₃ composite exhibits the highest dimensionless figure-of-merit values in the measured temperature range. These results indicate that the surface modification of CNTs to vary the amount of interfacial oxygen atoms simultaneously causes a decrease in the electrical and thermal conductivity.