Impacts of Annealing Temperature and Time on the Thermoelectric Performance of Recycled Carbon Fiber (RCF)/n-Bi₂Te₃ Heterostructure Thermoelectric Composites

Recycling carbon fibre waste is crucial for sustainability in the composites industry. Herein, we report the fabrication of a heterostructure composite using recycled carbon fiber (RCF) and n-type bismuth telluride (n-Bi₂Te₃) for thermoelectric applications. In the present study, we have comprehensively investigated the effects of annealing temperature and time on the thermoelectric, structural, charge carrier transport, morphological, and thermal stability properties of annealed RCF/n-Bi₂Te₃ composites. The optimum annealing temperature and time were at 350 °C and 2 h, respectively, which yielded a maximum power factor of 7.83 μWK⁻²m⁻¹. Annealing redistributed the bismuth and tellurium atomic percentage, decreased carrier concentration, improved carrier mobility, enhanced the crystallinity and increased the grain size of the bismuth telluride particles, subsequently improving the thermoelectric performance as well as the thermal stability of annealed RCF/n-Bi₂Te₃ composites. In addition, this study has explored the plausibility of a cross-plane configured Seebeck coefficient measurement utilizing recycled carbon fibre/n-type bismuth telluride heterostructure thermoelectric composite. Energy band diagram analysis indicated favorable heterojunction alignment between RCF and n-Bi₂Te₃, validating the viability of the thermoelectric composite in a cross-plane configuration. Our study provides a promising route for closing the recycling loop of carbon fiber waste and achieving sustainable thermoelectric materials.