High thermoelectric performance of graphite nanofibers

TL;DR

This paper demonstrates that graphite nanofibers, especially in platelet form, exhibit exceptional thermoelectric properties with high ZT values, which can be further enhanced by isotope doping and phonon effects.

Contribution

The study reveals the potential of graphite nanofibers for thermoelectric applications, highlighting their high ZT values and the effects of doping and phonon mean-free path.

Findings

ZT reaches 3.55 in 0.5 nm fibers

ZT can be enhanced to over 5 with isotope doping

ZT exceeds 8 considering phonon mean-free path effects

Abstract

Graphite nanofibers (GNFs) have been demonstrated to be a promising material for hydrogen storage and heat management in electronic devices. Here, by means of first-principles and transport simulations, we show that GNFs can also be an excellent material for thermoelectric applications thanks to the interlayer weak van der Waals interaction that induces low thermal conductance and a step-like shape in the electronic transmission with mini-gaps, which are necessary ingredients to achieve high thermoelectric performance. This study unveils that the platelet form of GNFs in which graphite layers are perpendicular to the fiber axis can exhibit outstanding thermoelectric properties with a figure of merit ZT reaching 3.55 in a 0.5 nm diameter fiber and 1.1 for a 1.1 nm diameter one. Interestingly, by introducing 14C isotope doping, ZT can even be enhanced up to more than 5, and more than 8 if we include the effect of finite phonon mean-free path, which demonstrates the amazing thermoelectric potential of GNFs.