Effect of grain boundary interfaces on electrochemical and thermoelectric properties of a Bi2Te3/reduced graphene oxide composites

Abstract

The electrochemical and enhanced thermoelectric properties of pristine Bi2Te3 and Bi2Te3/reduced graphene oxide (Bi2Te3 + rGO) composites at 1%, 3% and 5% levels of rGO were synthesized via a simple ultrasonic method. The X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV–vis spectrometry (UV–vis) and their electrochemical and thermoelectric properties were measured. The ultrasonic method succeeded in producing rGO nanosheets composited with Bi2Te3 forming grain boundary interfaces of rGO with Bi2Te3. The resulting samples displayed a continuous network structure of rGO nanosheets in Bi2Te3 + rGO composites for electrons in the conduction band of the Bi2Te3 structure. Electrons were transferred to rGO nanosheets at the interface, contributing electron charge carriers in Bi2Te3 + rGO composites. This indicates band alignment between Bi2Te3 and rGO nanosheets. The Bi2Te3 + rGO composites exhibited an increasing storage charge mechanism of electrical double layer capacitors with greater rGO contents. The Bi2Te3 + rGO composites displayed negative a Seebeck coefficient for thermoelectric materials. The highest ZT value was 0.17 in the bulk 1% Bi2Te3 + rGO composite. Improved electrochemical and thermoelectric properties of the Bi2Te3 + rGO 1% composite resulted from the interaction of the grain boundary interfaces of rGO nanosheets with pristine Bi2Te3 following the model of band alignment between Bi2Te3 and rGO nanosheets.